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   29911篇
  免费   2362篇
  国内免费   53篇
耳鼻咽喉   281篇
儿科学   1006篇
妇产科学   766篇
基础医学   4022篇
口腔科学   404篇
临床医学   4118篇
内科学   5568篇
皮肤病学   411篇
神经病学   2790篇
特种医学   731篇
外科学   3454篇
综合类   379篇
一般理论   53篇
预防医学   3661篇
眼科学   419篇
药学   1932篇
  1篇
中国医学   47篇
肿瘤学   2283篇
  2023年   324篇
  2022年   430篇
  2021年   962篇
  2020年   616篇
  2019年   959篇
  2018年   1051篇
  2017年   766篇
  2016年   799篇
  2015年   900篇
  2014年   1170篇
  2013年   1624篇
  2012年   2335篇
  2011年   2340篇
  2010年   1267篇
  2009年   1049篇
  2008年   1793篇
  2007年   1897篇
  2006年   1715篇
  2005年   1641篇
  2004年   1462篇
  2003年   1275篇
  2002年   1182篇
  2001年   369篇
  2000年   325篇
  1999年   276篇
  1998年   250篇
  1997年   195篇
  1996年   175篇
  1995年   119篇
  1994年   113篇
  1993年   128篇
  1992年   178篇
  1991年   183篇
  1990年   164篇
  1989年   173篇
  1988年   161篇
  1987年   205篇
  1986年   158篇
  1985年   156篇
  1984年   133篇
  1983年   111篇
  1981年   63篇
  1980年   61篇
  1979年   76篇
  1978年   74篇
  1976年   63篇
  1974年   73篇
  1973年   80篇
  1972年   66篇
  1971年   66篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Rabbits given goat anti-rabbit angiotensin-converting enzyme antibodies or derived antibody fragments develop rapidly fatal pulmonary edema. Endothelial cell injury is manifested by bleb formation and the disintegration of cell membranes. Platelets are found along the injured endothelium and leukocytes block capillary lumens. The pathologic features are similar when immune IgG, F(ab')2, or Fab are given. In vitro studies of complement activation show that solubilized, purified angiotensin-converting enzyme alone activates C1, with consumption of C4 and C3. Addition of immune IgG plus converting enzyme enhances this activation. F(ab')2 plus enzyme enhances only C3 consumption, while Fab with enzyme produces no additional complement utilization. Thus, while complement activation may be involved in the pathogenesis of injury induced by IgG or F(ab')2, the mechanism of Fab-induced endothelial injury remains unclear.  相似文献   
142.
BACKGROUND: Monocytic cells and alveolar macrophages (AMs) are activated in patients with asthma, producing inflammatory cytokines. This occurs despite a TH2 environment that consists of the cytokines interleukin (IL) 4, IL-10, and IL-13. The mechanism by which this occurs may involve cross-linking of the low-alphaffinity IgE receptor CD23. OBJECTIVE: To determine the effect of the TH2 environment with interferon-gamma (IFN-gamma) and heat shock protein 70 (HSP 70) on CD23 receptor expression and tumor necrosis factor alpha (TNF-alpha) production. METHODS: We examined the effect of IL-4 and IL-13 in culture with IFN-gamma and HSP 70 on CD23 expression in both THP-1 cells and AMs from healthy controls via flow cytometry. AMs from mild asthmatic patients and THP-1 cells were evaluated for TNF-alpha production after cross-linking CD23 with immune complexes. RESULTS: Asthmatic AMs stimulated with anti-IgE exhibited a 5.7- +/- 1.9-fold increase in TNF-alpha protein. AMs from healthy controls increased the geometric mean +/- SD of CD23 2.00- +/- 0.50-fold in IL-4 and 2.14- +/- 0.50-fold in IL-13. THP-1 cells cultured with IL-4 and IL-13 then stimulated with IFN-gamma or HSP 70 increased CD23 expression above baseline as follows: IL-4, 2.16- +/- 0.31-fold; IL-13, 2.66- +/- 0.43-fold; IFN-gamma, 2.03- +/- 0.34-fold; IL-4/IFN-gamma, 9.14- to 4.02-fold; IL-13/IFN-gamma, 11.51- +/- 5.51-fold; IL-4/HSP, 5.20- +/- 0.61-fold; and IL-13/HSP, 5.60- +/- 0.79-fold. Stimulating the CD23 receptor with immune complexes significantly increased TNF-alpha production by THP-1 cells stimulated with IFN-gamma, IL-4, IL-13, or a combination of these. CONCLUSIONS: Both IFN-gamma and HSP 70, in the TH2 environment, up-regulate CD23 expression and thus may play an important role in maintaining the chronic inflammatory state in asthma.  相似文献   
143.
Thirty patients have been described with cytogenetically visible deletion of the short arm of chromosome 6. However, subtelomeric 6p deletion detected by subtelomeric specific probes has been reported only twice. We report two new patients with terminal 6p deletion detected by subtelomeric screening using fluorescence in situ hybridization (FISH). The two patients exhibited mental retardation, ocular abnormalities, hearing loss, and a characteristic facial appearance. Detailed FISH analyses with probes covering the distal 6p25 region estimated the size of the terminal deletions to approximately 5.5 Mb and approximately 4.8 Mb. Array-based comparative genomic hybridization (array CGH) was used to confirm the cryptic deletions. Most patients with subtelomeric defects lack a characteristic phenotype. However, some of the subtelomeric deletions result in a specific phenotype, which can direct the clinician towards the diagnosis. Submicroscopic 6p deletion appears to be a recognizable clinical phenotype, and this region should be thoroughly investigated with FISH probes, including at least a subtelomeric 6p probe and a probe covering FOXC1, for patients presenting with a characteristic facial appearance, ocular abnormalities, predominantly anterior-chamber eye defects, hearing loss, and mental retardation.  相似文献   
144.
Biparental Phodopus campbelli and uniparental P. sungorus juvenile litters (2 males, 2 females) both consumed amniotic fluid and placenta during the birth of younger siblings. Three days later, P. campbelli juveniles were most responsive to a displaced younger sibling. Thus, P. campbelli are responsive to pups as juvenile alloparents and as new parents; however, at intervening ages, infanticidal attack (bite) was seen. At 5, 7, 9, 11, or 13 weeks of age, male and female P. campbelli were given a 5-min test with an unrelated, 3-day-old, anesthetized pup. Females attacked more often than males, yet pup-retrieval rates did not differ. Female aggression increased with age and was replaced by retrieval behavior 3 days after parturition. Male attack ceased after a birth, but parental behavior did not increase, remaining below the rate for new fathers tested with their own awake pup. Over repeated testing, behavior in one test did not predict behavior in another. Transitions from caregiving alloparent to infanticidal adult and back to parental care were clear in females, but less discrete with this stimulus paradigm in these highly paternal males.  相似文献   
145.
The National Breast Cancer Coalition (NBCC) is a grassroots organization that represents breast cancer advocates and is committed to eradicating breast cancer. NBCC defines a breast cancer advocate as someone who has been personally affected by the disease (e.g., a breast cancer survivor, family member, or friend), represents a constituency, and is motivated to join the fight against the disease. One of the organization's goals is to ensure that breast cancer advocates have a seat at the table when decisions are made about breast cancer research and policy. To accomplish this goal, NBCC educates advocates so that they can participate in and make meaningful contributions to legislative, scientific, and regulatory decision-making bodies. In addition to creating educational opportunities for advocates, NBCC has spearheaded several initiatives designed to directly increase the quality and quantity of breast cancer research. NBCC has also played a major role in making funding available to breast cancer researchers. Two of NBCC's most notable programs include Project LEAD, an intensive science-training course for breast cancer advocates, and the Environmental Initiative, a collection of activities designed to improve research into the relationship between breast cancer and the environment. Breast cancer advocates trained by NBCC have partnered with the scientific community and individual scientists to improve the peer review, design, and implementation of breast cancer research.  相似文献   
146.
Fischer F344 rats were given a cyclical diet of 0.06% 2-acetylaminofluorene (AAF), which progressively induced oval cell proliferation, cirrhosis and hyperplastic (or neoplastic) nodules. Primary liver tumours developed from 7 months after ceasing the diet. Liver samples taken during and after AAF administration and specimens of primary tumours were processed into frozen sections and examined microscopically for morphological changes in cell populations, stained histochemically for gamma-glutamyl transpeptidase (GGTase) and four phosphatases, and stained by the immunoperoxidase technique for the presence of antigens detected by seven anti-liver cell monoclonal antibodies and monoclonal antibodies to six oncoproteins. During and after AAF treatment several of the anti-liver antibodies revealed foci of aberrantly or heterogeneously-stained cells, although anti-oncoprotein antibodies showed no consistent changes. Foci of cells positive for GGTase and heterogeneous for adenosine triphosphatase (ATPase) were also seen. Nodules invariably showed heterogeneous antigenicity, raised GGTase and abnormal ATPase expression. Primary tumours exhibited varying degrees of positivity, negativity and heterogeneity with the anti-liver monoclonal antibodies, and all were positive for GGTase. Comparison between various parameters and different lesions showed the greatest concordance between nodules and tumours, suggesting that nodules are probably the precursors of malignant tumours in this system.  相似文献   
147.
Summary To study the host-dependent genetic variations in murine hepatitis virus type 3 (MHV 3) induced diseases, we localized the sites of MHV 3 (Mill Hill strain) expression within liver and brain by immunohistochemistry or hybridization in situ. Two strains of mice were studied: BALB/c mice, which develop an acute and lethal hepatitis and C3H mice which develop a chronic brain infection. In BALB/c mice, viral RNA and antigens appeared during the first 24 h post infection (p.i.) in liver, whereas viral RNA was barely detectable in brain, up until death at day 3 p.i. In C3H mice, viral RNA and antigens were detected simultaneously in liver and brain only at day 2 p.i. In brain, the virus was detected in meningeal and ependymal cells and in perivascular cortical areas (days 5 and 7 p.i.). After day 49, the virus was no longer detected in brain parenchyma, but persisted in meningeal cells. Two host-dependent genetic differences in viral processing were observed in the liver: (1) the virus was first detected in Kupffer cells in BALB/c mice and mostly in hepatocytes in C3H mice; (2) in BALB/c mice, the 180 kDa S viral glycoprotein appeared more frequently cleaved in 90 kDa form than in C3H mice.  相似文献   
148.
Quality control in cervical cytology   总被引:2,自引:1,他引:2       下载免费PDF全文
From surveys conducted by the authors it is concluded that the best and most acceptable quality control methods in cytology are those from within the laboratory. Most of these have results which can be reported centrally. Where the overall control and codes of practice are high, there the results are the most reliable, as sources of error from whatever cause are quickly brought to light. These conclusions are illustrated by data from the five centres and correlated in the tables.  相似文献   
149.
A fastidious gram-negative bacterium was isolated from the blood of a 37-year-old man who had insidious endocarditis with a sudden rupture of a cerebral aneurysm. Characterization of the organism through phylogenetic and phenotypic analyses revealed a novel species of Cardiobacterium, for which the name Cardiobacterium valvarum sp. nov. is proposed. C. valvarum will supplement the current sole species Cardiobacterium hominis, a known cause of endocarditis. Surgeries and antibiotic treatment cured the patient's infection and associated complications. During cardiac surgery, a congenital bicuspid aortic valve was found to be the predisposing factor for his endocarditis.  相似文献   
150.
Polyphasic taxonomic methods were employed to characterize a new species of slowly growing, nonpigmented mycobacteria. We propose the name Mycobacterium triplex sp. nov. for this new taxon. Conventional identification testing demonstrated a group of similar organisms that were geographically widespread in the United States. Commercially available nucleic-acid probes specific for the Mycobacterium avium complex were unreactive for these strains. High-performance liquid chromatography analysis of the mycolic acids revealed mycolate profiles that closely resembled Mycobacterium simiae. Comparative 16S rRNA sequence data confirmed the phylogenetic relationship of the strains with the slowly growing mycobacteria. Representative-type strains have been deposited in the American Type Culture Collection as strain ATCC 700071 [corrected].  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