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   1707篇
  免费   250篇
  2021年   17篇
  2019年   26篇
  2018年   41篇
  2017年   25篇
  2016年   35篇
  2015年   55篇
  2014年   51篇
  2013年   79篇
  2012年   78篇
  2011年   72篇
  2010年   57篇
  2009年   50篇
  2008年   60篇
  2007年   62篇
  2006年   60篇
  2005年   63篇
  2004年   74篇
  2003年   65篇
  2002年   50篇
  2001年   63篇
  2000年   49篇
  1999年   49篇
  1998年   27篇
  1997年   30篇
  1996年   23篇
  1995年   14篇
  1994年   21篇
  1993年   21篇
  1992年   45篇
  1991年   32篇
  1990年   29篇
  1989年   36篇
  1988年   28篇
  1987年   31篇
  1986年   30篇
  1985年   34篇
  1984年   22篇
  1983年   20篇
  1982年   17篇
  1981年   16篇
  1980年   18篇
  1979年   28篇
  1978年   20篇
  1977年   22篇
  1976年   18篇
  1974年   14篇
  1973年   13篇
  1972年   12篇
  1968年   15篇
  1967年   14篇
排序方式: 共有1957条查询结果,搜索用时 15 毫秒
91.
92.
Putrescine and other amines are known to rapidly reduce or prevent increases in ornithine decarboxylase activity in a number of systems. We have confirmed reports of a nondialyzable inhibitor of the enzyme in serum-starved H-35 hepatoma cells exposed to serum and putrescine. In contrast, we detected little if any nondialyzable inhibitor in serum-limited Swiss 3T3 cells treated similarly. Also, evidence of a dissociable enzyme-inhibitor complex was found in H-35 cells but not in 3T3 cells. These results suggest that assimilated putrescine can reduce ornithine decarboxylase activity by mechanisms not involving a macromolecular inhibitor.  相似文献   
93.
94.
To evaluate the effects of freezing and thawing on Ca2+ transport and permeability, inside-out red cell membrane vesicles (IORCMV) are examined. Exposure to the cryoprotectant Me2SO as well as different cooling regimes on unprotected and cryoprotected vesicles do not affect the membrane Ca2+ transport. However, freezing and thawing increase the membrane permeability to sucrose.  相似文献   
95.
North Carolina, USA, is the southernmost extent of the American black duck's (Anas rubripes) breeding range; however, little is known about their nesting ecology in this region. We located and monitored 140 nesting black ducks over 2 years (2017–2018) to quantify preferred nesting habitat and assess nesting productivity within coastal North Carolina. We located nests in brackish marshes (75%) and man-made dredge spoil islands (25%) at a density of 1 nest/22 ha. Black ducks selected high marsh and nested an average of 21.81 m from open water at a mean elevation of 1.36 m. In preferred nesting habitat, visual obstruction readings were 0.50 m with a maximum mean vegetation height of 0.81 m and land cover consisted largely of grasses (84.6%). Apparent nest success rates varied from 31% (2017) to 63% (2018) across years. The majority (72.2%) of variability in nest success was best predicted by nest location (mainland marsh, natural island, or spoil island), vegetation density, maximum vegetation height, and year. Management for breeding black ducks in coastal North Carolina should focus on promoting selected nesting habitat and reducing nest predators. Prescribed burns, used to set back succession on spoil islands and in brackish marshes should be conducted in the winter or in the early growing season not to exceed the twenty-fifth quantile date of black duck nest initiation (2 Apr). © 2021 The Wildlife Society.  相似文献   
96.
97.
As nonhuman animals age, geriatric individuals require additional care and veterinary support to ensure their well being. The focus on lifelong care is a relatively newer approach when providing good welfare, and few studies have examined how veterinary care impacts behavior at different ages or how best to accommodate geriatric individuals in zoos. The objectives of this study were to (a) assess both the immediate and long-term (one year later) behavioral impacts of cataract removal for macaroni (Eudyptes chrysolophus) and southern rockhopper (Eudyptes chrysocome) penguins; (b) compare the behavior of penguins following cataract surgery to that of other conspecifics in the same habitat; and (c) monitor the impacts of cataract surgery on swimming behavior using time-depth recorders. Individual responses to cataract removal differed in direction and magnitude, and these mixed results highlight that welfare is experienced and thus measured at the individual level. Positive responses included increased habitat use, increased time spent swimming, and increased rates of affiliative interactions. This study highlights the importance of assessing welfare impacts of veterinary interventions on geriatric individuals.  相似文献   
98.
The third Heidelberg Unseminars in Bioinformatics (HUB) was held on 18th October 2012, at Heidelberg University, Germany. HUB brought together around 40 bioinformaticians from academia and industry to discuss the ‘Biggest Challenges in Bioinformatics’ in a ‘World Café’ style event.  相似文献   
99.
Abstract

7-Chloro- and 7- Iodo-7-Deaza-2′-Deoxyguanosine-5′-Triphosphates were employed as substrates replacing dGTP, dITP, or 7-Deaza-2′-Deoxyguanosine-5′-Triphosphate in sequencing reactions with Thermo SequenaseTM. Analysis of the reaction products by denaturing gel electrophoresis indicates DNA containing these halogenated analogs can form strong secondary structures.  相似文献   
100.
Abstract

The use of Cyanine dye (CyTM 5 and Cy5.5) labeled dideoxy terminators with Thermo SequenaseTM DNA polymerase in DNA sequencing provides uniform band intensity, improved sequence read-length, and accuracy. It also greatly improves the ability to detect single base heterozygotes with dye-terminator sequencing method.  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