首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1992篇
  免费   158篇
  国内免费   4篇
耳鼻咽喉   9篇
儿科学   84篇
妇产科学   56篇
基础医学   267篇
口腔科学   24篇
临床医学   207篇
内科学   318篇
皮肤病学   17篇
神经病学   213篇
特种医学   206篇
外科学   223篇
综合类   67篇
预防医学   263篇
眼科学   22篇
药学   111篇
中国医学   2篇
肿瘤学   65篇
  2021年   15篇
  2020年   14篇
  2019年   17篇
  2018年   24篇
  2017年   19篇
  2016年   15篇
  2015年   28篇
  2014年   31篇
  2013年   62篇
  2012年   58篇
  2011年   76篇
  2010年   45篇
  2009年   47篇
  2008年   65篇
  2007年   67篇
  2006年   56篇
  2005年   73篇
  2004年   60篇
  2003年   66篇
  2002年   60篇
  2001年   61篇
  2000年   67篇
  1999年   60篇
  1998年   35篇
  1997年   55篇
  1996年   46篇
  1995年   36篇
  1994年   26篇
  1993年   23篇
  1992年   36篇
  1991年   53篇
  1990年   46篇
  1989年   49篇
  1988年   50篇
  1987年   48篇
  1986年   58篇
  1985年   47篇
  1984年   33篇
  1983年   29篇
  1982年   35篇
  1981年   26篇
  1980年   29篇
  1979年   26篇
  1978年   23篇
  1977年   19篇
  1976年   15篇
  1974年   17篇
  1973年   23篇
  1972年   18篇
  1971年   12篇
排序方式: 共有2154条查询结果,搜索用时 31 毫秒
61.
This study analyses the influence of female and male patient age and human menopausal gonadotrophin (HMG) requirements on clinical pregnancy rates and live birth rates with ovulation stimulation using HMG in combination with intrauterine insemination (IUI). In this study, 363 consecutive HMG/IUI treatment cycles in 184 patients carried out at a university fertility centre were analysed in a retrospective fashion. The main outcomes measured were clinical pregnancy rates and live birth rates. Increased female partner age (> or = 35) and male partner age (> or = 40) were found to negatively influence pregnancy rates with HMG/ IUI therapy. In addition, this study demonstrated a critical threshold of HMG requirements beyond which pregnancy did not occur. No pregnancies occurred in treatment cycles requiring > 25 ampoules (1875 IU) of menotrophins to achieve follicular maturity, irrespective of patient age. In conclusion, female partner age, male partner age, and HMG requirements all significantly influence pregnancy rates with HMG/IUI therapy.   相似文献   
62.
We examined if rat myometrial cells in culture generate nitric oxide (NO) and express various isoforms of NO synthase (NOS). Myometrial cells isolated from rats on day 18 of gestation were incubated with various stimulators and inhibitors of NOS for 24 and 48 h, and NO production was evaluated by measuring nitrites in the media and NOS proteins in the cell lysates. NO was produced by myometrial cells and its production inhibited by N(G)-methyl-L-arginine (L-NMMA). This inhibition was reversed by L-arginine (3 mM). Interleukin-1beta (IL- 1beta) significantly stimulated NO production, in a dose-dependent manner. The IL-1beta-stimulated NO production was inhibited by the NOS inhibitor, L-NMMA, whose effects were reversed by L-arginine. Abundant NOS III protein was detectable in freshly isolated myometrial cells, and this was maintained in culture in the presence of fetal bovine serum (FBS; 10%). In the absence of FBS, NOS III levels decreased significantly (by 90%) within 24 h. In contrast, NOS I and NOS II proteins were undetectable in freshly isolated muscle cells and in cells cultured without IL-1beta. However, NOS II protein in these cells was induced by IL-1beta. Thus, NO is produced by myometrial cells through the NOS III isoform, and the myometrial NO may be important in maintaining uterine quiescence during pregnancy.   相似文献   
63.
A collection of 1,308 clinical Mycobacterium tuberculosis isolates from Ontario, Canada, was genotyped by IS6110 restriction fragment length polymorphism (RFLP) and mycobacterial interspersed repetitive-unit-variable-number tandem-repeat (MIRU-VNTR) analysis. RFLP or >12 MIRU-VNTR loci were necessary for resolution of Indo-Oceanic strains. The low clustering rate and high strain diversity indicate that, in Ontario, most tuberculosis results from reactivation of latent infections.Tuberculosis (TB), which is caused by pathogens of the Mycobacterium tuberculosis complex (MTBC), remains a global scourge (19). In Canada, the average incidence rate is 5.0 cases/100,000 people, but the burden of disease varies across the country. In 2007, the four Atlantic provinces accounted for only ∼1% of TB cases, whereas ∼42% of new cases occurred in the province of Ontario (11). The Public Health Laboratories (PHL) of the Ontario Agency for Health Protection and Promotion provide diagnostic testing for TB in Ontario. The TB and Mycobacteriology Laboratory at PHL-Toronto is the largest facility of its kind in Canada, processing 50,000 patient samples plus 2,000 referred acid-fast positive cultures, with 600 to 650 new cases of TB detected annually (8, 11). Historically, the PHL has employed IS6110 restriction fragment length polymorphism (RFLP) for genotyping. Despite its utility, IS6110 RFLP is labor-intensive and only performed upon request. The current turnaround time of 21 days also makes the method incompatible with the PHL goal of universal, real-time MTBC genotyping. More recently, mycobacterial interspersed repetitive-unit-variable-number tandem-repeat (MIRU-VNTR) typing has been introduced (6, 7, 9, 15). The current PHL strategy relies upon agarose gel electrophoresis for comparison of PCR products. This method is low throughput, and gel-to-gel variability confounds comparison of samples processed at different times. Here, we describe implementation and validation of an improved MIRU-VNTR strategy and its utility for analysis of a large clinical strain collection.The semiautomated MIRU-VNTR strategy was derived from the 12-loci method of Cowan et al. (6, 7). Briefly, multiplex PCR was performed with dye-labeled primers in 96-well plates. For each reaction, 5 ng of template DNA was combined with 11 μl of a master mix (Red Taq; Sigma-Aldrich, Oakville, Canada) containing three primer pairs. PCR conditions were 95°C for 10 min and 34 cycles of 94°C for 30 s, 62°C for 30 s, and 72°C for 60 s, with a final extension at 72°C for 7 min. PCR amplification was confirmed by electrophoresis on 1% Tris-borate-EDTA agarose gels. Samples were diluted 1:20 in sequence loading solution (Beckman Coulter, Mississauga, Canada) containing a 600-bp sequencing standard (Beckman Coulter) and then subjected to fragment analysis on a CEQ8800 genetic analysis system (Beckman Coulter). To reduce the manual labor and potential for human error associated with extensive pipetting, a Biomek NX Span-8 automation workstation (Beckman Coulter) was programmed to set up the initial PCRs and dilute PCR products for fragment analysis.To validate the method, a blinded set of 99 DNA samples was provided by the Public Health Research Institute (NJ). Strain identities and MIRU-VNTR patterns were unblinded only after complete 12-digit patterns were generated for all 99 DNA samples. Concordance between PHL and Public Health Research Institute results was 100%.To evaluate the utility of MIRU-VNTR in Ontario, typing was performed on 1,308 clinical samples from the PHL strain collection for which IS6110 RFLP profiles were also available. Strains were identified as MTBC by using DNA probes (AccuProbe; Gen-Probe, San Diego, CA) and were originally isolated during 1999 to 2001. Strains identified as Mycobacterium bovis or M. bovis BCG and samples containing multiple Mycobacterium species were excluded from analysis. For cases with multiple cultures, only the first isolate was used. Genomic DNA was extracted according to standard protocols (17) in a dedicated biosafety containment facility.MIRU-VNTR and IS6110 RFLP data were analyzed with BioNumerics 5.0 (Applied Maths, St-Martin Latem, Belgium). RFLP patterns were compared using band-based Dice statistics with 1% position tolerance such that clustered strains exhibited bands of identical number and position. Strains clustered by MIRU-VNTR were identical at all 12 loci. Analysis by MIRU-VNTR plus IS6110 RFLP employed the unweighted-pair group method with arithmetic mean. MTBC lineages were assigned by comparison to the MIRU-VNTR reference strain database (1).Independently, both methods revealed a large number of unique profiles and some clustered isolates (Table (Table1).1). Maximum strain resolution was achieved when both methods were combined. In general, RFLP was superior for multiband IS6110 strains, whereas resolution of single-band IS6110 isolates required MIRU-VNTR. Initial typing at 12 MIRU-VNTR loci generated two large “pseudoclusters.” One contained East Asian lineage strains (pattern 223325173533; n = 110), which are known to be poorly resolved by these 12 loci (12, 16). The second was comprised of strains from the Indo-Oceanic lineage (pattern 254326223432; n = 80). This group was typed at 12 additional loci (15). Even though four of the new loci were invariant, extended typing generated 47 new patterns (Fig. (Fig.1).1). Thirty-five Indo-Oceanic strains had unique profiles, whereas the remaining isolates formed 12 MIRU-VNTR-defined clusters (6 clusters with 2 isolates in each cluster, 3 with 3 each, 1 with 4, and 2 with 10 each). However, 11 of these could be resolved further by RFLP.Open in a separate windowFIG. 1.Improved typing of the Indo-Oceanic pseudocluster. Whereas all strains (n = 80) shared the same, original 12-loci pattern (254326223432), typing at 12 additional loci produced 47 distinct patterns, including 35 unique profiles. The remaining strains formed 12 clusters (6× n = 2; 3× n = 3; 1× n = 4; 2× n = 10), most of which could be further resolved by RFLP. However, one pair (cluster A) was identical by both methods, and two (clusters D and G) exhibited single band shifts. Conversely, one RFLP-defined pair (cluster M) exhibited differences at two loci upon extended MIRU-VNTR typing. For each strain, IS6110 RFLP profiles and repeat values at the extended MIRU-VNTR loci are shown. Relationships between strains are indicated by the phylogenetic (unweighted-pair group method with arithmetic mean) tree, and strains in MIRU-VNTR-defined clusters are labeled (clusters A to L).

TABLE 1.

Clustering results from MIRU-VNTR and IS6110 RFLP genotyping
MethodTotal no. of patternsNo. of unique patternsNo. of clustersNo. of isolates in largest clusterClustering ratea
MIRU-VNTR only6534931601100.623
IS6110 RFLP only1,06798582650.247
MIRU-VNTR + RFLP1,1851,1087790.153
Open in a separate windowaThe clustering rate is based on the number of isolates in all clusters divided by the total number of isolates.Previous genotyping studies have suggested that there is extensive local transmission of TB in Canada. A single MTBC strain is responsible for ∼25% of all cases in the province of Manitoba (2, 3). In Quebec, a pyrazinamide-resistant strain and its drug-sensitive ancestor are endemic (10). In contrast, 84.7% (1,108/1,308) of strains in the present study displayed unique genotypes. The remaining 200 strains formed 77 clusters (Fig. (Fig.2).2). The largest cluster, 12 strains associated with an outbreak in a homeless shelter in the urban metropolis of Toronto, accounts for <1% of all provincial cases (20). Although identical by MIRU-VNTR, RFLP distinguished two groups within this “Toronto” cluster: nine strains of one pattern and three with an extra IS6110 band.Open in a separate windowFIG. 2.Minimum spanning tree of 77 strain clusters. Each circle represents a cluster of strains (2 to 12 isolates) identical by 12-loci MIRU-VNTR typing. Circle sizes are proportional to the number of isolates. Divisions within circles represent sets of clusters that have identical MIRU-VNTR patterns but different IS6110 RFLP profiles. Connected clusters differ at one (thick line), two (thin line), three (dotted line), or four (dashed line) MIRU-VNTR loci. Lineage names were assigned by comparison of MIRU-VNTR patterns to the MIRU-VNTRplus reference strain database (1). The Toronto cluster is endemic to our population.The genotypic diversity of MTBC strains found in this study is likely due to the ethnic diversity of the provincial population. Many Ontarians (3.4 million/12.1 million people) are foreign-born (14). Since 1996, ∼687,000 immigrants have arrived from the 22 nations identified as high-burden countries by the World Health Organization (13, 19). Reactivation disease is common among recent immigrants to both the United States and Canada (4, 18). The proportion of total TB cases (∼85%) attributed to foreign-born Ontarians is similar to trends in Minnesota (85.3%) and New York (71.1%) but much higher than levels in other Great Lakes states (e.g., Illinois, 58.9%; Wisconsin, 54.3%; Pennsylvania, 51.4; Ohio, 45.6%; Indiana, 43.0; Michigan, 37.6%) (5, 11).This study, the first to evaluate the utility of MIRU-VNTR in Ontario, Canada, indicates that the method is an effective first-line genotyping tool. However, the 12-loci strategy can generate pseudoclusters. Resolution of some strains, especially those from the East Asian and Indo-Oceanic lineages, require second-line testing with IS6110 RFLP, additional loci, or spoligotyping. Genotyping revealed MTBC isolates from diverse global lineages, which is consistent with the multicultural origins of Ontario''s population. Despite the predominance of reactivation disease, 77 clusters, comprising 200 isolates, were identified. Rapid detection of such clusters, especially those involving unrelated individuals, is essential for effective TB control. Due to its speed and high throughput, MIRU-VNTR will be an important component of the universal, real-time genotyping strategy in Ontario, Canada.  相似文献   
64.
Abstract: The utility of the MLC assay as a test of HLA-D region matching and predictor of graft-versus-host disease (GvHD) was evaluated in 435 patients receiving marrow grafts from unrelated donors. Donors and recipients were phenotyped for HLA-A, B and DR antigens by serology, tested in MLC, and retrospectively genotyped for DRB1, B3, B4, B5, DQB1 and DPB1 alleles by PCR/SSOP. Of the 244 HLA-A, B, DR-identical donor-recipient pairs with evaluable MLC and DRB1 typing results available, 208 were matched for HLA-A, B and DRB1, while 36 were matched for HLA-A and B and mismatched for a DRB1 allele. Donor anti-recipient relative responses (RR) in MLC, corresponding to the GvHD vector in marrow transplantation, ranged from 7.2 to 100%, with a median of 4.0%. A comparison of reactivity in MLC between pairs matched versus mismatched for DRB1 alleles showed a significant overlap in the distribution of RRs. Using optimally-defined RR cutoffs of 4 and 16%, no correlation between MLC results and risk of developing clinically significant grades III-IV GvHD (p=0.6 and 0.5, respectively) was found when the contribution of DRB1 mismatch was accounted for. Matching for DRB1 alleles, in contrast, was a better predictor of clinically significant GvHD, with DRB1-matched transplant recipients less likely to develop grades III-IV GvHD than DRB1-mismatched recipients (p=0.14). Among the 208 patients and donors matched for DRB1 alleles, the MLC, although reactive (RR > 4.0%) in 45% of cases, did not predict GvHD. Overall, these results underscore the limitations in using the MLC to predict DRB1 matching or risk of clinically significant GvHD among patients receiving unrelated marrow grafts. The availability of DRB1 allele matching by sequence-specific oligonucleotide probes (SSOP) or by direct sequencing provides a method for donor matching that is rapid, precise and superior to the MLC for predicting clinically relevant outcome.  相似文献   
65.
We have sequenced DNA from six new DR52-associated DRB1 alleles initially detected by PCR/SSOP analysis. Three DR8 associated alleles differed from previously known alleles by single nucleotide substitutions. DRB1*0807 and DRB1*0811 both vary from DRB1*08021 at codon 57 resulting in two different amino acids at this residue. DRB1 *0807 was identified in samples of Brazilian origin while *0811 was identified among samples from the Tlingit Native American population of Southeast Alaska. DRB1*0814, identified in a family of Chinese origin, differed from DRB1*08032 at codon 12 at both the nucleotide and the amino acid level. In addition, two alleles of DR11, DRB1*1113 and *1119, were each detected in Caucasian individuals. DRB1*1113 differs from other DR11 alleles at codons 37, 67, 70 and 74, while DRB1*1119 differs from *1101 by a single nucleotide substitution at codon 67. Finally, DRB1*1418 was detected in a sample from an Asian or Pacific Islander and shares sequences with several other DR52-associated DRB 1 alleles. These six DRB 1 alleles appear to have been generated by either gene conversion events, DRB1*1113 and * 1418, or by point mutations, DRB1*0814, *0807, *0811 and *1119, although the single nucleotide substitutions found in the latter three alleles are also present in at least one other DRB1 allele and, therefore, could have been the product of gene conversions.  相似文献   
66.
Urinary pathology requiring urinary diversion, partial or full bladder replacement, is a significant clinical problem affecting ~14,000 individuals annually in the United States alone. The use of gastrointestinal tissue for urinary diversion or bladder reconstruction/replacement surgeries is frequently associated with complications. To try and alleviate or reduce the frequency of these complications, tissue engineering and regenerative medicine strategies have been developed using bio-absorbable materials seeded with cells derived from the bladder. However, bladder-sourced cells may not always be suitable for such applications, especially in patients with bladder cancer. In this study, we describe the isolation and characterization of smooth muscle cells (SMCs) from porcine adipose and peripheral blood that are phenotypically and functionally indistinguishable from bladder-derived SMCs. In a preclinical Good Laboratory Practice study, we demonstrate that autologous adipose- and peripheral blood-derived SMCs may be used to seed synthetic, biodegradable tubular scaffold structures and that implantation of these seeded scaffolds into a porcine cystectomy model leads to successful de novo regeneration of a tubular neo-organ composed of urinary-like neo-tissue that is histologically identical to native bladder. The ability to create urologic structures de novo from scaffolds seeded by autologous adipose- or peripheral blood-derived SMCs will greatly facilitate the translation of urologic tissue engineering technologies into clinical practice.  相似文献   
67.
Multiple studies have shown bilateral improvement in motor symptoms in Parkinson disease (PD) following unilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) and internal segment of the globus pallidus, yet the mechanism(s) underlying this phenomenon are poorly understood. We hypothesized that STN neuronal activity is altered by contralateral STN DBS. This hypothesis was tested intraoperatively in humans with advanced PD using microelectrode recordings of the STN during contralateral STN DBS. We demonstrate alterations in the discharge pattern of STN neurons in response to contralateral STN DBS including short latency, temporally precise, stimulation frequency-independent responses consistent with antidromic activation. Furthermore, the total discharge frequency during contralateral high frequency stimulation (160 Hz) was greater than during low frequency stimulation (30 Hz) and the resting state. These findings demonstrate complex responses to DBS and imply that output activation throughout the basal ganglia-thalamic-cortical network rather than local inhibition is a therapeutic mechanism of DBS.  相似文献   
68.
69.
This study tested the proposal that negative appraisals represent a risk factor for developing posttraumatic stress disorder (PTSD) after trauma. Trainee firefighters (N = 68) were assessed during training (before trauma exposure) for PTSD, history of traumatic events, and tendency to engage in negative appraisals. Firefighters were reassessed 4 years later (N = 52), after commencing firefighter duty (after trauma exposure), for PTSD and depression using the Posttraumatic Stress Disorder Scale (E. B. Foa, L. Cashman, L. Jaycox, & K. Perry, 1997) and the Beck Depression Inventory (Version 2; A. T. Beck, R. A. Steer, & G. K. Brown, 1996). At follow-up, 12% met criteria for PTSD. Pretrauma negative appraisals about oneself accounted for 20% of variance in PTSD severity at follow-up. These data provide the first evidence that preexisting negative appraisals are a risk factor for PTSD.  相似文献   
70.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号