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   6713篇
  免费   589篇
  国内免费   32篇
耳鼻咽喉   52篇
儿科学   103篇
妇产科学   66篇
基础医学   1280篇
口腔科学   45篇
临床医学   831篇
内科学   1821篇
皮肤病学   91篇
神经病学   579篇
特种医学   234篇
外科学   860篇
综合类   21篇
预防医学   571篇
眼科学   46篇
药学   368篇
中国医学   9篇
肿瘤学   357篇
  2023年   31篇
  2022年   44篇
  2021年   174篇
  2020年   89篇
  2019年   175篇
  2018年   184篇
  2017年   109篇
  2016年   122篇
  2015年   189篇
  2014年   265篇
  2013年   322篇
  2012年   511篇
  2011年   489篇
  2010年   286篇
  2009年   265篇
  2008年   447篇
  2007年   452篇
  2006年   430篇
  2005年   459篇
  2004年   424篇
  2003年   422篇
  2002年   405篇
  2001年   104篇
  2000年   86篇
  1999年   108篇
  1998年   94篇
  1997年   75篇
  1996年   60篇
  1995年   59篇
  1994年   51篇
  1993年   29篇
  1992年   50篇
  1991年   33篇
  1990年   42篇
  1989年   41篇
  1988年   31篇
  1987年   27篇
  1986年   27篇
  1985年   23篇
  1984年   20篇
  1983年   11篇
  1982年   10篇
  1981年   4篇
  1979年   7篇
  1978年   4篇
  1975年   4篇
  1973年   8篇
  1972年   3篇
  1971年   6篇
  1966年   3篇
排序方式: 共有7334条查询结果,搜索用时 10 毫秒
81.
82.
BACKGROUND/AIMS: Liver failure is a life threatening condition currently treated by palliative measures and, when applicable, organ transplantation. The use of a bioartificial organ capable of fulfilling the main functions of the liver would represent an attractive alternative. However, the shortage of suitable donor cells, and their limited growth ability have impeded the development of this strategy. We investigated whether lentiviral vectors allow for conditional immortalization of human hepatocytes and whether these immortalized hepatocytes could reverse lethal acute liver failure. METHODS: We exposed primary human hepatocytes to Cre-excisable lentiviral vectors coding for SV40T Antigen, telomerase, and/or Bmi-1 and tested the functionality of the resulting cell lines. Therapeutic potential of immortalized hepatocytes were tested in a murine model of acetaminophen-induced hepatic injury. RESULTS: The immortalized hepatocytes grew continuously yet were non-tumorigenic, stopped proliferating when exposed to Cre recombinase, and conserved defining properties of primary hepatocytes, including the ability to secrete liver-specific proteins and to detoxify drugs. The implantation of encapsulated immortalized human hepatocytes rescued mice from lethal doses of acetaminophen. CONCLUSIONS: Lentiviral vectors represent tools of choice for immortalization of non-dividing primary cells, and lentivirally immortalized human hepatocytes are promising reagents for cell-based therapy of acute liver failure.  相似文献   
83.

Background

Seaweed polysaccharides are highly active natural substances having valuable applications. The present study was conducted to characterize the physico-chemical properties of sulphated polysaccharides from three Mediterranean brown seaweeds (Cystoseira sedoides, Cystoseira compressa and Cystoseira crinita) and to evaluate their anti-radical, anti-inflammatory and gastroprotective activities.

Methods

The different rates of neutral sugars, uronic acids, L-fucose and sulphate content were determined by colorimetric techniques. The different macromolecular characteristics of isolated fucoidans were identified by size exclusion chromatography equipped with a triple detection: multiangle light scattering, viscometer and differential refractive index detectors, (SEC/MALS/VD/DRI). Anti-inflammatory activity was evaluated, using the carrageenan-induced rat paw edema test in comparison to the references drugs Acetylsalicylate of Lysine and Diclofenac. The gastroprotective activity was determined using HCl/EtOH induced gastric ulcers in rats and to examine the antioxidant effect of fucoidans in the three species, the free radical scavenging activity was determined using 1,1-diphenyl-2-picrylhydrazyl.

Results

The pharmacological evaluation of the isolated fucoidans for their anti-inflammatory, and their gastroprotective effect established that these products from C. sedoides, C. compressa and C. crinita exhibited a significant anti-inflammatory activity at a dose of 50 mg/kg, i.p; the percentages of inhibition of the oedema were 51%, 57% and 58% respectively. And, at the same dose, these fucoidans from C. sedoides and C. compressa showed a significant decrease of the intensity of gastric mucosal damages compared to a control group by 68%, whereas, the fucoidan from C. crinita produced a less gastroprotective effect. Furthermore, the isolated fucoidans exhibited a radical scavenging activity.

Conclusion

The comparative study of fucoidans isolated from three species of the genus Cystoseira showed that they have similar chemicals properties and relatives anti-radical, anti-inflammatory and gastroprotective activities which are found to be promising.  相似文献   
84.
Transvenous (transjugular) liver biopsy consists in taking a liver specimen through a needle introduced into the liver parenchyma from the lumen of a hepatic vein. This procedure was attempted 104 times in 98 patients in whom percutaneous needle liver biopsy was contraindicated because of massive ascites and/or bleeding tendency. A liver specimen was obtained in 100 out of these 104 attempts; the tissue specimens were unfragmented and large enough to allow correct evaluation of liver architecture in 57 biopsies. The procedure was followed by no or only minor complications in all our patients except one who suffered a fatal intraperitoneal hemorrhage in relation to perforation of liver capsule; perforation was due to an excessive front rotation applied to the needle, a maneuver which therefore must be avoided. It is concluded that transvenous liver biopsy is a workable, efficient, and acceptably safe procedure for obtaining liver specimens in patients with massive ascites and/or bleeding tendency.  相似文献   
85.
86.
Among protease inhibitors, atazanavir has not been associated with urolithiasis in clinical studies. We describe 11 cases of atazanavir-associated urolithiasis in patients with human immunodeficiency virus (HIV) infection. Patients with low water intake, high urinary pH, and a prior history of urinary stones may have a higher risk of atazanavir-associated urine crystallization.  相似文献   
87.
88.
89.
The role of catecholamines in the genesis of ventricular arrhythmias during the reperfusion period following coronary occlusion remains incompletely understood. An isolated rat heart preparation, free from the influence of autonomic innervation or of circulating catecholamines, was used to assess the effects of beta-adrenoceptor blockade. The hearts were prelabeled with tritiated norepinephrine ( NE3H ), and the total radioactivity and that in NE3H were measured in the effluent coronary flow. The left main coronary artery was ligated for 10 minutes after which reperfusion followed. The liberation of NE3H and the development of ventricular tachycardia and fibrillation were monitored throughout. The cardioselective beta-antagonist agent, acebutolol, in a high concentration (1.1 X 10(-4)M), had good beta-antagonist effect in response to the added isoproterenol (10(-6)M); this concentration of acebutolol also suppressed sustained reperfusion ventricular arrhythmias but unexpectedly increased the release of NE3H . Atenolol, another cardioselective agent, did not prevent reperfusion ventricular arrhythmias even in a high concentration of 40 mg/L (1.5 X 10(-4)M). The d-isomer of propranolol, with poorer beta-antagonist properties than the l-isomer, prevented such ventricular arrhythmias in a concentration of 1.3 X 10(-5)M, which was low when compared to that of atenolol. It is proposed that the beta-antagonist activity of the compounds tested could not explain the inhibition of reperfusion ventricular arrhythmias and that another quality such as membrane-stabilizing activity may be involved.  相似文献   
90.
Ca2+ ions passing through a single or a cluster of Ca2+-permeable channels create microscopic, short-lived Ca2+ gradients that constitute the building blocks of cellular Ca2+ signaling. Over the last decade, imaging microdomain Ca2+ in muscle cells has unveiled the exquisite spatial and temporal architecture of intracellular Ca2+ dynamics and has reshaped our understanding of Ca2+ signaling mechanisms. Major advances include the visualization of "Ca2+ sparks" as the elementary events of Ca2+ release from the sarcoplasmic reticulum (SR), "Ca2+ sparklets" produced by openings of single Ca2+-permeable channels, miniature Ca2+ transients in single mitochondria ("marks"), and SR luminal Ca2+ depletion transients ("scraps"). As a model system, a cardiac myocyte contains a 3-dimensional grid of 104 spark ignition sites, stochastic activation of which summates into global Ca2+ transients. Tracking intermolecular coupling between single L-type Ca2+ channels and Ca2+ sparks has provided direct evidence validating the local control theory of Ca2+-induced Ca2+ release in the heart. In vascular smooth muscle myocytes, Ca2+ can paradoxically signal both vessel constriction (by global Ca2+ transients) and relaxation (by subsurface Ca2+ sparks). These findings shed new light on the origin of Ca2+ signaling efficiency, specificity, and versatility. In addition, microdomain Ca2+ imaging offers a novel modality that complements electrophysiological approaches in characterizing Ca2+ channels in intact cells.  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