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   117773篇
  免费   7273篇
  国内免费   230篇
  2023年   672篇
  2021年   1574篇
  2020年   1334篇
  2019年   1406篇
  2018年   3105篇
  2017年   2726篇
  2016年   3725篇
  2015年   5038篇
  2014年   5145篇
  2013年   6822篇
  2012年   7932篇
  2011年   7059篇
  2010年   4620篇
  2009年   3579篇
  2008年   5646篇
  2007年   5366篇
  2006年   5300篇
  2005年   4441篇
  2004年   4488篇
  2003年   4021篇
  2002年   3699篇
  2001年   3082篇
  2000年   2919篇
  1999年   2283篇
  1998年   1009篇
  1997年   739篇
  1996年   767篇
  1995年   741篇
  1994年   656篇
  1992年   1421篇
  1991年   1321篇
  1990年   1205篇
  1989年   1291篇
  1988年   1105篇
  1987年   1114篇
  1986年   998篇
  1985年   1079篇
  1984年   893篇
  1983年   778篇
  1979年   921篇
  1978年   667篇
  1977年   651篇
  1975年   745篇
  1974年   805篇
  1973年   769篇
  1972年   703篇
  1971年   646篇
  1970年   697篇
  1969年   756篇
  1968年   698篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
31.
32.
An apparently novel human plasma and urinary protein of low molecular weight was isolated from several highly purified preparations of protein HC by gel chromatography and high voltage electrophoresis with a yield of about 8 mg/g. The protein has a molecular weight of about 20,000, neutral electrophoretic mobility at pH 6.5 and a high content of half-cystine. It is associated with a yellow-brown chromophore like protein HC and could be demonstrated in all investigated preparations of isolated human, rabbit and guinea-pig protein HC and alpha 1-microglobulin.  相似文献   
33.
34.
V jarovisovaných a nejarovisovaných obilkách jedné ozimé a jedné jarní odr?dy p?enice byly chromatograficky stanoveny látky typu auxin? a giberelin?. Chromatogramy byly vyhodnoceny pomocí biologických test?. U ozimé odr?dy jsme nena?li rozdíly v rozlo?ení r?stových látek mezi jarovisovanou a nejarovisovanou variantou. U jarní odr?dy jsme rozdíly na?li. Na základě výsledk? soudíme, ?e rozdíly mezi oběma variantami jarní odr?dy byly zp?sobeny nespecifickým p?sobením nízké teploty a ?e proces jarovisace není kausálně spjat se změnami hladiny r?stových látek.  相似文献   
35.
36.
37.
In male Wistar rats, the inhalation exposure to acrylonitrile (AN), 271 mg X m-3, 8 hours a day, 5 days a week, did not affect protein sulfhydryl concentration in liver and blood and decreased glutathione concentration in the liver, but not in the brain at the end of the fifth exposure. The urinary excretion of the main AN metabolites, thioethers (AN-mercapturic acids) and thiocyanate was proportional to the inhaled AN concentration (57, 125, 271 mg X m-3, respectively) in a single exposure for 12 hours, and their mutual ratio was greatly different from that after injection of AN. The results revealed that the urinary excretion of thioethers is a very sensitive and dose-related indicator of exposure to AN and extrapolation of the results indicates that the exposure to AN concentration below 10 mg X m-3 could thus be demonstrated.  相似文献   
38.
In recent years, Staphylococcus epidermidis has become a major nosocomial pathogen and the most common cause of intravascular catheter-related bacteremia, which can increase morbidity and mortality and significantly affect patient recovery. We report a draft genome sequence of Staphylococcus epidermidis AU12-03, isolated from an intravascular catheter tip.  相似文献   
39.
Cord-forming fungi form extensive networks that continuously adapt to maintain an efficient transport system. As osmotically driven water uptake is often distal from the tips, and aqueous fluids are incompressible, we propose that growth induces mass flows across the mycelium, whether or not there are intrahyphal concentration gradients. We imaged the temporal evolution of networks formed by Phanerochaete velutina, and at each stage calculated the unique set of currents that account for the observed changes in cord volume, while minimizing the work required to overcome viscous drag. Predicted speeds were in reasonable agreement with experimental data, and the pressure gradients needed to produce these flows are small. Furthermore, cords that were predicted to carry fast-moving or large currents were significantly more likely to increase in size than cords with slow-moving or small currents. The incompressibility of the fluids within fungi means there is a rapid global response to local fluid movements. Hence velocity of fluid flow is a local signal that conveys quasi-global information about the role of a cord within the mycelium. We suggest that fluid incompressibility and the coupling of growth and mass flow are critical physical features that enable the development of efficient, adaptive biological transport networks.  相似文献   
40.
1. In rat kidney cortex, outer and inner medulla the development of activities of seven enzymes was investigated during postnatal ontogeny (10, 20, 30, 60 and 90 days of age). The enzymes were selected in such a manner, as to characterize most of the main metabolic pathways of energy supplying metabolism: hexokinase (glucose phosphorylation, HK), glycerol-3-phosphate dehydrogenase (glycerolphosphate metabolism or shunt, GPDH), triose phosphate dehydrogenase (glycolytic carbohydrate breakdown, TPDH), lactate dehydrogenase (lactate metabolism, LDH), citrate synthase (tricarboxylic acid cycle, aerobic metabolism, CS), malate NAD dehydrogenase (tricarboxylic acid cycle, intra-extra mitochondrial hydrogen transport, MDH) and 3-hydroxyacyl-CoA-dehydrogenase (fatty acid catabolism, HOADH). 2. The renal cortex already differs metabolically from the medullar structures on the 10th day of life. It displays a high activity of aerobic breakdown of both fatty acids and carbohydrates. Its metabolic capacity further increases up to the 30th day of life. 3. The outer medullar structure is not grossly different from the inner medulla on the 10th day of life. Further it differentiates into a highly aerobic tissue mainly able to utilize carbohydrates. It can, however, to some extent, also utilize fatty acids aerobically and produce lactate from carbohydrates anaerobically. 4. The inner medullar structure is best equipped to utilize carbohydrates by anaerobic glycolysis, forming lactate. This feature is already pronounced on the 10th day of life, its capacity increases to some extent during postnatal development, being highest between the 10th and the 60th day of life.  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