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   3088篇
  免费   203篇
  国内免费   4篇
耳鼻咽喉   15篇
儿科学   92篇
妇产科学   106篇
基础医学   366篇
口腔科学   44篇
临床医学   655篇
内科学   381篇
皮肤病学   23篇
神经病学   294篇
特种医学   44篇
外科学   272篇
综合类   38篇
一般理论   2篇
预防医学   454篇
眼科学   33篇
药学   182篇
中国医学   3篇
肿瘤学   291篇
  2023年   21篇
  2022年   20篇
  2021年   64篇
  2020年   47篇
  2019年   63篇
  2018年   79篇
  2017年   74篇
  2016年   84篇
  2015年   73篇
  2014年   87篇
  2013年   162篇
  2012年   241篇
  2011年   251篇
  2010年   140篇
  2009年   125篇
  2008年   245篇
  2007年   220篇
  2006年   240篇
  2005年   201篇
  2004年   194篇
  2003年   188篇
  2002年   162篇
  2001年   24篇
  2000年   11篇
  1999年   30篇
  1998年   36篇
  1997年   19篇
  1996年   15篇
  1995年   20篇
  1994年   19篇
  1993年   14篇
  1992年   15篇
  1991年   10篇
  1990年   11篇
  1989年   8篇
  1988年   7篇
  1987年   3篇
  1986年   5篇
  1985年   9篇
  1984年   13篇
  1983年   9篇
  1982年   9篇
  1981年   10篇
  1980年   5篇
  1979年   2篇
  1976年   3篇
  1975年   1篇
  1974年   1篇
  1971年   1篇
  1964年   1篇
排序方式: 共有3295条查询结果,搜索用时 250 毫秒
21.
Organization and expression of human telomere repeat binding factor genes   总被引:1,自引:0,他引:1  
The ends of mammalian chromosomes terminate in structures called telomeres. Recently a human telomere repeat binding factor (TRF1) that binds the vertebrate TTAGGG telomeric repeat in situ was isolated by Chong et al. (1). TRF1 regulates telomere length (2), which is often altered in cancer cells. To understand their genetic organization, TRF1 genes were localized to human chromosomes 13 cen, 21cen, and Xq13 by analysis of human monochromosomal hybrids, and by fluorescent in situ hybridization. We also confirmed the recent localization of a human TRF1 gene to chromosome 8, and provide evidence that this locus is alternatively spliced. In contrast to the TRF1 genes on chromosomes 8 and X, the chromosomes 13 and 21 TRF1 genes contained a 60 bp deletion in the coding region. The results suggest that two distinct forms of TRF1 are expressed and that the TRF1 gene family includes at least three pseudogenes whose dispersal in the human genome may have occurred via cDNA intermediates.  相似文献   
22.
BACKGROUND: Meta-analysis and randomized clinical trial results reported in June 1998 indicated a significant reduction in perinatal HIV transmission rates among mothers undergoing a cesarean section (C-section). OBJECTIVE: The objective of this study was to examine recent trends in and factors associated with C-section deliveries among HIV-infected women in the United States. DESIGN: A multisite pediatric medical record review of a cohort of HIV-exposed and HIV-infected infants in the Pediatric Spectrum of HIV Disease (PSD) Cohort study (n = 6467) and the national Pediatric HIV/AIDS Reporting System (HARS) (n = 8,306) was conducted. SETTING/PATIENTS: All infants born between 1994 and 2000 to HIV-positive mothers referred to the PSD study or to a Pediatric HARS hospital or clinic site were enrolled. RESULTS: The proportion of deliveries by C-section was steady at about 20% from 1994 through June 1998. From July 1998 through December 2000, this proportion increased to 44% in the PSD study and to nearly 50% in the Pediatric HARS. On analysis by multiple logistic regression, delivery of infants by C-section was associated with the release of study results (OR = 2.83), delivery in four PSD sites in reference to Texas (OR: 2.02-1.43), having private medical care reimbursement (OR = 1.62), and having maternal prenatal care (OR = 1.43). CONCLUSIONS: The PSD and Pediatric HARS data demonstrate a sharp increase in C-section rates mainly among HIV-infected women in the United States after the release of the meta-analysis and randomized clinical trial results in 1998. This finding highlights the rapid impact of study results on obstetric practice. It underscores the critical role of prenatal care in offering perinatal interventions such as scheduled C-section when indicated to reduce the likelihood of HIV transmission.  相似文献   
23.
Two FDA-approved agents, ferumoxides (Feridex), a suspension of superparamagnetic iron oxide (SPIO) nanoparticles and protamine sulfate, a drug used to reverse heparin anticoagulation, can be complexed and used to label cells magnetically ex vivo. Labeling stem cells with ferumoxides-protamine sulfate (FePro) complexes allows for non-invasive monitoring by MRI. However, in order for stem cell trials or therapies to be effective, this labeling technique must not inhibit the ability of cells to differentiate. In this study, we examined the effect of FePro labeling on stem cell differentiation. Viability, phenotypic expression and differential capacity of FePro labeled CD34 + hematopoietic stem cells (HSC) and mesenchymal stem cells (MSC) were compared with unlabeled control cells. Colony-forming unit (CFU) assays showed that the capacity to differentiate was equivalent for labeled and unlabeled HSC. Furthermore, labeling did not alter expression of surface phenotypic markers (CD34, CD31, CXCR4, CD20, CD3 and CD14) on HSC, as measured by flow cytometry. SDF-1-induced HSC migration and HSC differentiation to dendritic cells were also unaffected by FePro labeling. Both FePro-labeled and unlabeled MSC were cultured in chondrogenesis-inducing conditions. Alcian blue staining for proteoglycans revealed similar chondrogenic differentiation for both FePro-labeled and unlabeled cells. Furthermore, collagen X proteins, indicators of cartilage formation, were detected at similar levels in both labeled and unlabeled cell pellets. Prussian blue staining confirmed that cells in labeled pellets contained iron oxide, whereas cells in unlabeled pellets did not. It is concluded that FePro labeling does not alter the function or differentiation capacity of HSC and MSC. These data increase confidence that MRI studies of FePro-labeled HSC or MSC will provide an accurate representation of in vivo trafficking of unlabeled cells.  相似文献   
24.
Cytomegalovirus reactivation and infection post-allogeneic hematopoietic stem cell transplant continue to cause morbidity and mortality. Current pharmacologic therapies are limited by side effects. Adoptive transfer of ex vivo generated cytomegalovirus-specific T cells has the potential to restore immunity, prevent cytomegalovirus, and circumvent the need for pharmacologic therapies. We have generated donor-derived cytomegalovirus-specific cytotoxic T cells using dendritic cells pulsed with the HLA-A2 restricted nonapeptide NLVPMVATV (NLV) derived from the cytomegalovirus-pp65 protein. These cytotoxic T cells have been given prophylactically to 9 recipients aged 4 to 65 years on or after day 28 post-allogeneic hematopoietic stem cell transplant. Only 2 of 9 recipients received T cell depletion in vivo or in vitro. There were no immediate adverse reactions to the infusions. During 97-798 days of follow-up, 2 recipients developed cytomegalovirus reactivation; neither developed cytomegalovirus disease or required pharmacotherapy. Three recipients developed acute graft versus host disease after infusion. Two recipients died, 1 from thrombotic thrombocytopenia purpura secondary to cyclosporine, 1 from complications of graft versus host disease. A transient increase in numbers of cytomegalovirus-specific T cells demonstrated by NLV-tetramer binding was seen in 6 recipients. Prophylactic adoptive transfer of NLV-specific T cells is safe and may be effective in preventing cytomegalovirus reactivation.  相似文献   
25.

To examine the health status of Hispanic agricultural workers in Florida and Georgia. Health data from agricultural workers in the Farm Worker Family Health Program (June 2019) and research studies in Florida (May 2015 and May 2019) were examined. Data from 728 agricultural workers were collected through sociodemographic questionnaire and clinical data. In the Florida sample, 83% were overweight or obese, 70% elevated blood pressure, 60% met the definition of prediabetes. In Georgia, 64% were overweight or obese and 67% had elevated blood pressure. Weak correlations were observed between BMI and systolic blood pressure (unadjusted r?=?0.20), diastolic blood pressure (unadjusted r?=?0.19), and glucose (unadjusted r?=?0.14). Adjusting for age and gender did not show statistically significant correlation between BMI and systolic and diastolic blood pressure or glucose. While BMI has been shown to be strongly associated with high blood pressure and impaired glucose, we found a weak correlation among agricultural workers. Given the common and high use of pesticides and elevated rates of hypertension, impaired glucose, and adiposity in agricultural workers, the public health impact of this relationship may require and lead to occupational reform that protects the health of agricultural workers. Future studies should assess occupational and environmental factors and lifestyle differences between agricultural workers and the general population to better understand these discrepancies in health status.

  相似文献   
26.
检测孕妇血浆中的urocortin   总被引:2,自引:0,他引:2  
目的:研究urocortin(促肾上腺皮质激素释放激素肽类家族新成员)是否存在于孕妇血循环中及其含量,以证实urocortin是否能在妊娠中产生并由此调节子宫-胎盘的血管张力。方法:用放射免疫测定法从受孕16周起检测孕妇血浆中是否含有urocortin,并用凝胶层析法检测从孕妇血浆中提取的urocortin是否与人工合成的urocortin标准品一致。结果:从受孕16周起孕妇的血浆中即可测得uro  相似文献   
27.
This study explores three issues: thoughts and feelings of individuals with and without physical disabilities concerning encounters in different situations, ways of grouping self-statements into valenced categories, and use of states-of-mind (SOM) ratios as an alternative to positive and negative thought frequencies. Data from 127 able-bodied and 46 physically disabled college students indicate that, in everyday social encounters, nondisabled individuals' thoughts and feelings were more negative, while those of disabled individuals were more negative when helping was involved and when encounters centered on the impairment. Thus, problematic encounters between people with and without disabilities may be due to the reactions of individuals with disabilities in situations which involve help, and to reactions of able-bodied persons in everyday contexts. The data also confirm the utility of SOM ratios as an alternative to valenced frequencies in cognitive assessment: SOM scores discriminated groups when situational demands were manipulated and scores were linearly related to criterion measures. However, SOM ratios differed dramatically, depending on the attentional focus of thoughts. The findings illustrate types of thoughts which occur during interaction between people with and without disabilities, demonstrate a simple technique for grouping thoughts into valenced categories on an empirical basis, and highlight the relative contribution of cognitive and affective elements to overall valenced scores. Implications for research on assessment of self-statements are discussed and recommendations are made concerning programming to facilitate the social integration of people with disabilities.This research was supported by grants to the first author from the Social Sciences and Humanities Research Council of Canada and from Fonds F.C.A.R. pour l'aide et le soutien à la recherche. Thanks are due to Meribah Aikens, Maria Barile, Leo Bissonette, Bosco Daude, Jim Dubois, Lillian Fox, Evelyn Gold, Naomi Goodz, Darlene Judd, André Leblanc, John Martos, Sue McKenzie, Irwin Slopak, and Joan Wolforth for their assistance with various stages of this investigation.  相似文献   
28.
OBJECTIVE: Although most methods for selecting the sex of offspring by sorting spermatozoa are ineffective at shifting the ratio of Y- to X-containing cells, some commercial sources continue to offer such services. Our objective was to evaluate commercially “sorted” samples with use of dual-color fluorescence in situ hybridization and to identify variations in assessment by comparing motile and total sperm populations, donors, observers, and fluorescence in situ hybridization probes.STUDY DESIGN: Cryopreserved sperm from seven anonymous donors were processed as for insemination. Sperm cells from each total sample or motile subfraction were prepared for fluorescence in situ hybridization by incubation with disulfide-reducing agents to expand sperm nuclei. Two sets of X and Y chromosome–specific, fluorophore-labeled deoxyribonucleic acid probes were used. At least 400 nuclei from each preparation were classified independently by three blinded observers. Hybridization efficiency, aneuploidy, and sex chromosome content were evaluated in subsets of five unsorted, five female-oriented, and five male-oriented samples. Total and motile subfractions were compared with eight samples. Fluorescence in situ hybridization probes were compared in five paired unsorted samples.RESULTS: No differences were detected between washed samples and paired motile subfractions. No differences in hybridization and aneuploidy were detected between groups of sorted samples. The Y/X ratio was significantly different between the sorted groups. However, male-oriented samples had a lower Y/X ratio than female-oriented samples did. Observer and probe choice accounted for small but significant variations that did not alter conclusions about the Y/X ratio for sorted samples.CONCLUSION: In a series of 10 sorted samples from one commercial source, dual-color fluorescence in situ hybridization demonstrated a small but significant shift in the sex chromosome ratios among samples. However, this shift was opposite to that expected by the orientation of the sorted samples. (Am J Obstet Gynecol 1997;176:1172-80.)  相似文献   
29.
The National Notifiable Disease Surveillance System (NNDSS) received 982 tuberculosis (TB) notifications in 2003, of which 947 were new cases, 33 were relapses and two were cases with unknown history. The incidence of TB in Australia has remained at a stable rate since 1985 and was 4.9 cases per 100,000 population in 2003. The high-incidence groups remain people born overseas and Indigenous Australians at 19.9 and 8.7 cases per 100,000 population, respectively. By contrast the incidence in non-Indigenous Australians was 0.9 per 100,000. Comparison of the 2003 TB notification data against the performance indicators set by National Tuberculosis Advisory Committee highlights that enhanced TB control measures should be considered among these high-risk groups.  相似文献   
30.
The estrogen receptor ?? (ER??) splicing variant with an in-frame deletion of exon 3 (ER??3) is frequently expressed in the normal breast, but its influence on tumorigenesis has not been explored. In vitro, ER??3 has dominant negative activity, suggesting it may suppress estrogen stimulation in the breast. ER??3 may inhibit classical signaling on estrogen response element (ERE)-regulated genes as well as activate non-classical pathways at Sp1 and AP-1 sites. Transgenic mice were developed that express mouse ER??3 in all tissues examined, including the mammary gland. To investigate if ER??3 expression affects tumorigenesis, ER??3 mice were crossbred with MMTV-Neu mice. Mammary tumor onset was significantly delayed in ER??3/Neu versus MMTV-Neu females and metastatic incidence and burden was significantly reduced. Consequently, ER??3 expression suppressed tumor development and metastasis in this aggressive model of HER2/Neu-positive breast cancer. To determine if ER ligands with anticancer activity may augment ER??3 protection, the bitransgenic mice were treated with tamoxifen and soy isoflavones starting at age 2?months. Soy protein with isoflavones (181?mg/1,800?kcal) did not affect tumor development in MMTV-Neu or ER??3/Neu mice; however, metastatic progression was not inhibited in soy-treated ER??3/Neu mice, as it was in untreated ER??3/Neu mice. In contrast, tamoxifen (20?mg/1,800?kcal) significantly enhanced tumor prevention in ER??3/Neu versus MMTV-Neu mice (98?% vs. 81?% tumor free). The results in ER??3/Neu mice demonstrate that ER??3 influences estrogen-dependent mammary carcinogenesis and, thus, may be protective in women expressing ER??3 in the breast. However, exposure to different estrogens may augment or block its beneficial effects.  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