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   13308篇
  免费   847篇
  国内免费   77篇
耳鼻咽喉   126篇
儿科学   366篇
妇产科学   239篇
基础医学   1478篇
口腔科学   567篇
临床医学   1139篇
内科学   3068篇
皮肤病学   230篇
神经病学   764篇
特种医学   397篇
外国民族医学   4篇
外科学   2019篇
综合类   594篇
一般理论   10篇
预防医学   870篇
眼科学   400篇
药学   1117篇
  1篇
中国医学   88篇
肿瘤学   755篇
  2024年   13篇
  2023年   204篇
  2022年   617篇
  2021年   857篇
  2020年   446篇
  2019年   545篇
  2018年   657篇
  2017年   367篇
  2016年   447篇
  2015年   446篇
  2014年   582篇
  2013年   731篇
  2012年   1054篇
  2011年   1041篇
  2010年   537篇
  2009年   447篇
  2008年   680篇
  2007年   673篇
  2006年   606篇
  2005年   601篇
  2004年   606篇
  2003年   465篇
  2002年   463篇
  2001年   114篇
  2000年   97篇
  1999年   84篇
  1998年   98篇
  1997年   55篇
  1996年   51篇
  1995年   61篇
  1994年   43篇
  1993年   31篇
  1992年   28篇
  1991年   42篇
  1990年   38篇
  1989年   35篇
  1988年   30篇
  1987年   31篇
  1986年   39篇
  1985年   28篇
  1984年   27篇
  1983年   23篇
  1982年   17篇
  1981年   24篇
  1980年   22篇
  1979年   19篇
  1978年   16篇
  1977年   11篇
  1975年   11篇
  1974年   13篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
61.
The aim of this study was to determine the relationships between bone mineral density (BMD) and blood pressure in 214 men, age 20–76. BMD measurements were done by dual X‐ray absorptiometry using a Lunar DPXMD densitometer at the lumbar spine (L2–L4) and different femoral regions. Systolic (SBP) and diastolic (DBP) blood pressure were measured using an MPC‐350 sphygmomanometer. Physicians gathered demographic data and participants' dietary intake of calcium were determined by using food frequency questionnaires. After adjusting for age, body mass index, dietary calcium, and exercise history, multiple linear regression models showed that DBP was negatively related to femoral neck BMD (β = ?0.145, P = 0.032) and just shy of significant association with femoral neck BMC (β = ?0.114, P = 0.079). SBP was correlated with femoral neck (r = ?0.171, P = 0.012) and Ward's (r = ?0.186, P = 0.006) BMD but not after adjusting for possible confounders. Further studies are needed to determine whether elevated blood pressure is causally related to the development of low bone mass. Am. J. Hum. Biol. 16:168–171, 2004. © 2004 Wiley‐Liss, Inc.  相似文献   
62.
High-level antiseptic resistance of Staphylococcus aureus is mediated by multidrug efflux pumps encoded by qacA and qacB genes. We investigated distribution and genomic diversity of these antiseptic resistance genes in a total of 522 clinical strains of S. aureus isolated recently in a Japanese hospital. The qacA/B gene was detected in 32.6% of methicillin-resistant S. aureus (MRSA) and 7.5% of methicillin-susceptible S. aureus (MSSA), whereas the low-level resistance gene smr, which was examined simultaneously, was detected at lower frequencies in both MRSA (3.3%) and MSSA (5.9%). Epidemiologic typing of S. aureus isolates suggested that higher prevalence of qacA/B in MRSA may be due to spread of a single predominant MRSA strain carrying qacA/B in the hospital. Restriction fragment length polymorphism (RFLP) analysis indicated higher prevalence of the qacB-type gene (59.3%) than the qacA-type gene (40.7%) among the qacA/B genes detected. Nucleotide sequencing analysis revealed the presence of two genetic variants in qacA (V1 and V2) and four variants in qacB (V1-V4) that differ from the qacA prototype in pSK1 by 1-5 nucleotides and 7-9 nucleotides, respectively. Although most strains with qacA-V1, qacA-V2, qacB-V3, and qacB-V4 showed high-level resistance to ethidium bromide (EB)(MIC > 100 microg/ml), all of the S. aureus isolates carrying qacB-V1 and qacB-V2 showed lower MICs of EB and some monovalent cationic antiseptic substances. By analysis of the genomic organization of the qacA/B downstream region, divergent forms of this region rearranged with an insertion of IS256 or IS257 were found primarily for qacB. The downstream region of qacA-V1 was suggested to be an evolutionary origin for other divergent forms. These findings indicated that both qacA and qacB are prevalent in recent clinical isolates, especially in MRSA, and these genes consist of variable genetic variants that may be responsible for different resistance levels against antiseptic substances.  相似文献   
63.
Genetic linkage analysis has been instrumental in mapping thegene for X-linked agammaglobulinemia (XLA) to the proximal longarm of the human X chromosome, to Xq22. Due to the relativerarity of this disease the localization of the gene within Xq22has remained imprecise. We have investigated twenty-nine familiesaffected by XLA and have found no recombinants with the DXS178locus in over 30 informative meioses. DXS178 is now the mostreliable and informative locus for use in pre-natal diagnosisand carrier detection of XLA. In addition, we have identifiednew closely linked proximal and distal flanking markers forXLA, DXS442 and DXS101, respectively. These loci are separatedby 2cM, considerably reducing the extent of DNA within whichthe XLA locus can be contained. This will open up the way formore directed positional cloning efforts for the isolation ofthe XLA gene.  相似文献   
64.
Clinical specimens from 317 patients suspected of cytomeglovirus infection were examined by immunofluorescence (IF) using monoclonal antibodies and by a biotinylated DNA probe kit after cell culture isolation. Of the 317 samples, 68 were positive by culture isolation. Of these 67 were IF positive when the cytopathic effect (CPE) was 1+ or less, whereas 56 gave positive results with DNA probes when the CPE was 2+. A further 83 specimens were examined directly by immunoperoxidase histopathology (IHP), IF and the DNA probe kit: 26 of these were positive by IHP examination, 25 by IF and only 6 by DNA probes. The sensitivity of the DNA probe kit was not satisfactory when the clinical tissue specimens were directly examined. However, the sensitivity improved considerably to 82% if the specimens were propagated first in cell culture. The IF method detected the virus before and after cell culture isolation equally well (96%–98.5%). Compared to the IF method, the DNA probe kit is costly and requires more labor and time.This paper was presented in part at the 88th annual meeting of the American Society for Microbiology, Miami Beach, FL, USA, 1988  相似文献   
65.
66.
Chronic distal spinal muscular atrophy (Chronic DSMA, MIM (*)607088) is a rare autosomal recessive disorder characterized by a progressive motor weakness and muscular atrophy, predominating in the distal parts of the limbs. A form of Chronic DSMA gene has been previously mapped to chromosome 11q13 in the 10.3 cM interval defined by loci D11S1889 and D11S1321. By linkage analysis in 12 European Chronic DSMA families, we showed that a disease gene maps to chromosome 11q13.3 (Z(max)=6.66 at theta=0.00 at the DSM4 locus) and suggested that this condition is genetically homogeneous. Recombination events allowed us to reduce the genetic interval to a 2.6 cM region, telomeric to the IGHMBP2 gene, excluding this gene as the disease causing gene in Chronic DSMA. Moreover, partial linkage disequilibrium was found between three rare alleles at loci D11S1369, DSM4 and D11S4184 and the mutant chromosome in European patients. Analysis of the markers at these loci strongly suggests that most Chronic DSMA chromosomes are derived from a single ancestor. Refinement of the Chronic DSMA locus will hopefully allow to test candidate genes and lead to identification of the disease-causing mutations.  相似文献   
67.
IFN-alpha and IFN-beta: a link between immune memory and chronic inflammation   总被引:11,自引:0,他引:11  
The majority of expanded T cells generated during an immune response are cleared by apoptosis. Prevention of death in some activated T cells enables the persistence of a memory T-cell pool. Here, observations that IFN-alpha and IFN-beta inhibit activated T-cell apoptosis are described. Although this enables memory T cells to persist without antigen, excessive IFN-alpha or IFN-gamma secretion might lead to chronic inflammation.  相似文献   
68.
BACKGROUND: The aim of this study was to examine the role of apoptosis and reactive oxygen species (ROS) in inducing DNA damage in ejaculated spermatozoa. METHODS: We examined ejaculated spermatozoa from 31 patients examined for infertility and 19 healthy donors for apoptosis, production of ROS and DNA damage using annexin V binding, chemiluminescence assay and sperm chromatin structure assay. RESULTS: The percentage of spermatozoa that underwent apoptosis in the whole ejaculate and mature fraction was higher in the patients than in the donors (P<0.001 and P=0.009, respectively). Levels of ROS in the whole ejaculate and immature fraction were higher in the patients than in the donors (P=0.002 and P=0.009). Apoptosis was significantly correlated with ROS within patients in the whole ejaculate [r (95% confidence interval)=0.53 (0.19-0.86)] and in the mature [0.71 (0.39-1.00)] and immature spermatozoa [0.75 (0.45-1.00)]. Only apoptosis and the DNA fragmentation index (DFI) were significantly correlated within patients in the whole ejaculate [0.57 (0.18-0.97)]. CONCLUSIONS: DNA damage may be induced by oxidative assault. Apoptosis may not contribute significantly to the DNA damage.  相似文献   
69.
In the case of water soluble polymers, the use of size exclusion chromatography (SEC) for the determination of the molecular weight involves numerous difficulties. In order to analyse and determine the molecular weight of acrylic acid telomers we have first tried to obtain a satisfactory and reproducible separation. In this particular case, low-molecular-weight standards are not commercially available. Therefore, we decided to prepare standards based on acrylic acid, either by telomerization with a fluorinated telogen or by polymerization with an initiator bearing a fluorinated group. A calibration curve was obtained from the standards. Telomers of acrylic acid with thioglycolic acid were analysed. This is a general method for determination of DP n by SEC when there is no standard for the polymers. It can be used in a wide range of DP n from 1 to 700.  相似文献   
70.
Fine-needle aspiration biopsy findings in three cases of chromophobe cell carcinoma are described and correlated with histologic and ultrastructural observations. In addition, comparisons are made with three cases each of oncocytoma and granular cell carcinoma. The cells in aspiration smears from chromophobe cell carcinoma closely correlated with histologic pattern of three cell types which were not present in oncocytomas and granular cell carcinomas. These cells had prominent cell borders, and their cytoplasm was either opaque and granular (type I) or variably translucent and reticular (type II and III). Ultrastructurally, the translucent areas within the cytoplasm contained large numbers of microvesicles which were unique to chromophobe cell carcinoma and were not seen in other neoplasms. Fine-needle aspiration may be used to diagnose chromophobe cell carcinoma and distinguish it from other related renal neoplasms. © 1995 Wiley-Liss, Inc.  相似文献   
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