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   467439篇
  免费   297800篇
  国内免费   47174篇
耳鼻咽喉   4692篇
儿科学   7678篇
妇产科学   3605篇
基础医学   103407篇
口腔科学   6784篇
临床医学   84834篇
内科学   113082篇
皮肤病学   7372篇
神经病学   27328篇
特种医学   17362篇
外国民族医学   28篇
外科学   60130篇
综合类   112829篇
现状与发展   56篇
一般理论   8篇
预防医学   67146篇
眼科学   21196篇
药学   83673篇
  390篇
中国医学   65625篇
肿瘤学   25188篇
  2023年   5820篇
  2022年   11625篇
  2021年   14182篇
  2020年   15047篇
  2019年   17315篇
  2018年   17960篇
  2017年   20159篇
  2016年   17395篇
  2015年   21739篇
  2014年   24126篇
  2013年   26159篇
  2012年   32753篇
  2011年   35390篇
  2010年   35451篇
  2009年   41296篇
  2008年   30089篇
  2007年   25264篇
  2006年   22568篇
  2005年   19262篇
  2004年   17566篇
  2003年   15157篇
  2002年   13965篇
  2001年   15601篇
  2000年   10195篇
  1999年   13521篇
  1998年   14064篇
  1997年   13955篇
  1996年   14977篇
  1995年   15135篇
  1994年   14871篇
  1993年   13575篇
  1992年   12794篇
  1991年   12191篇
  1990年   11148篇
  1989年   10998篇
  1988年   10532篇
  1987年   9897篇
  1986年   9415篇
  1985年   8475篇
  1984年   6541篇
  1983年   6550篇
  1982年   7606篇
  1981年   7144篇
  1980年   6813篇
  1979年   6643篇
  1978年   5820篇
  1977年   6124篇
  1976年   5747篇
  1975年   5485篇
  1974年   5036篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The virD locus of Agrobacterium tumefaciens Ti plasmid encodes functions necessary for endonucleolytic cleavage of transferred DNA (T-DNA) prior to its transfer to plant cells. For the overproduction of the VIRD proteins in Escherichia coli a tac-virD operon fusion was constructed. A significant increase in the accumulation of VIRD proteins was observed in a lon protease-deficient E. coli host. The presence of an overlapping open reading frame (ORF) upstream of the VIRD1 coding sequence had a negative effect on VIRD1 production. A preparation containing VIRD proteins catalyzes the conversion of supercoiled (form I) DNA to relaxed (form IV) DNA. This activity is similar to that of a DNA topoisomerase. The relaxation activity lacks DNA sequence specificity, requires magnesium ion, and has no requirement for an energy source. Studies with plasmids that had lost defined DNA segments encompassing various virD coding regions showed that VIRD1 is the DNA-relaxing enzyme. In a density gradient centrifugation experiment, the DNA-relaxing activity sedimented as a 21-kDa polypeptide. Earlier studies of Jayaswal et al. [Jayaswal, R., Veluthambi, K., Gelvin, S. & Slightom, J. (1987) (J. Bacteriol. 169, 5035-5045] have shown that in E. coli VIRD2 alone is not sufficient for endonucleolytic cleavage of T-DNA and requires VIRD1 for its activity.  相似文献   
92.
Synovial fluid phospholipase A2s and inflammation.   总被引:1,自引:1,他引:0       下载免费PDF全文
The activation of phospholipase A2 is believed to have an important role in the inflammatory process owing to its induction of eicosanoids, platelet activating factor, and other mediators. Soluble phospholipase A2 has been associated with exudates in different inflammatory conditions. In this review the general physiology and control of this enzyme and, in particular, the most recent findings on human synovial fluid phospholipase A2s are discussed.  相似文献   
93.
Forty elderly patients with basicervical and pertrochanteric fractures were managed with uniplanar AO external fixator under regional anaesthetic block of the femoral nerve and lateral cutaneous nerve of the thigh from April 2003 to March 2006. The mean age of the patients was 67.9 ± 5.5 years. External fixator application was performed under radiological control after closed reduction had been obtained. Comorbid factors, duration of surgery, duration of hospitalisation, complications, walking ability, time to union and mortality rate were recorded. Patients were followed up for a mean period of 12 ± 4.5 months. Superficial pin tract infection occurred in 13 patients, healing in varus >10° and with shortening >2 cm occurred in six patients, and one patient suffered a spontaneous ipsilateral femoral neck fracture after removal of the fixator. The mean time for union was 10.4 ± 1.2 weeks. Rapid union rate and minor complications obtained in the present study are comparable to those obtained with standard internal fixation techniques. Minimal intraoperative blood loss, short operative time and early patient mobilisation are advantages signifying uniplanar external fixator application under regional anaesthetic block to be a viable option in treatment of basicervical and pertrochanteric fractures in high-risk elderly patients.  相似文献   
94.
During much of the past century, the microbe itself stood at the heart of microbial pathogenesis. Little thought was devoted to the host per se, though it was granted that differences in susceptibility to certain infections did exist between individuals, and between different ethnic groups. During the past 20 years, extraordinary strides in our grasp of mammalian genetics have made the host side of the equation far more approachable. A restricted collection of genes now presents itself as the likely repository for genetic differences that foretell susceptibility to infectious disease. The Toll-like receptors, of which 10 are presently known to exist in humans, offer an excellent example of this genetic reductionism, in that they embody the afferent component of the innate immune system, and strongly influence the containment of an infection from its earliest stages. The Toll-like receptors were identified as the culmination of a long and relentless inquiry into the yet-unsolved clinical problem of sepsis.  相似文献   
95.
96.
Summary: Fifty-seven isolates of Basidiobolus from reptiles and amphibians, and 7 other obtained from the American Type Culture Collection (ATCC) in Maryland were studied for their extracellular enzyme activities on solid media. The Conidiobolus isolates studied included 4 recovered from Nigerian soil and additional 4 obtained from the ATCC All these isolates produced active extracellular lipase and protease and failed to exhibit amylase, deoxyribonuclease and ribonuclease activities. The significance of the findings is discussed.
Zusammenfassung: Fünfundsiebzig Basidiobolus-Isolate aus Reptilien und Amphibien und sieben weitere aus der American Type Culture Collection (ATCC) in Maryland wurden auf Aktivtäten extrazellulärer Enzyme auf festen Medien untersucht Die untersuchten Conidiobolus-Isolate schlossen vier aus nigerianischen Böden und vier weitere aus der ATCC ein. Alle Isolate zeigten extrazellulär Lipase- und Proteaseaktivität Amylase-, Desoxyribonuclease- und Ribonucleaseaktivität war jedoch nicht nachzuweisen. Die Bedeutung dieser Befunde wird diskutiert.  相似文献   
97.
98.
Pseudomonas aeruginosa isolates from environmental sources and bacteremic patients were compared for their levels of elastolytic activity. No significant differences were found. The incidence of production of toxin A, phospholipase C, alkaline protease, and elastase among the environmental strains was also as high as that previously reported for clinical isolates.  相似文献   
99.
100.
Eleven white male right handed violin players complained of transient muscular deficit of the extensor compartment of the left forearm during and after prolonged playing. This was associated with paraesthesiae and pain. Relief was achieved keeping the wrist and the elbow flexed, with the supinated forearm held by the contralateral hand. An anatomical study showed changes of the relationship of the posterior interosseous nerve with its surrounding structures with pronation and supination of the forearm. On the basis of the clinical features, the anatomical studies and the response to a simple physiotherapeutic regime, it is suggested that prolonged pronation of the forearm may cause transient entrapment of the nerve.  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