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   1006篇
  免费   2篇
  国内免费   2篇
系统科学   13篇
理论与方法论   5篇
现状及发展   259篇
研究方法   100篇
综合类   567篇
自然研究   66篇
  2018年   4篇
  2016年   4篇
  2014年   3篇
  2013年   8篇
  2012年   31篇
  2011年   98篇
  2010年   6篇
  2008年   39篇
  2007年   37篇
  2006年   36篇
  2005年   37篇
  2004年   34篇
  2003年   31篇
  2002年   34篇
  2001年   20篇
  2000年   44篇
  1999年   16篇
  1994年   2篇
  1993年   3篇
  1992年   18篇
  1991年   10篇
  1990年   19篇
  1989年   15篇
  1988年   12篇
  1987年   14篇
  1986年   19篇
  1985年   12篇
  1984年   13篇
  1983年   12篇
  1982年   6篇
  1981年   9篇
  1980年   10篇
  1979年   16篇
  1978年   19篇
  1977年   20篇
  1976年   15篇
  1975年   20篇
  1974年   23篇
  1973年   17篇
  1972年   20篇
  1971年   31篇
  1970年   44篇
  1969年   15篇
  1968年   27篇
  1967年   26篇
  1966年   22篇
  1965年   10篇
  1964年   8篇
  1963年   2篇
  1961年   2篇
排序方式: 共有1010条查询结果,搜索用时 15 毫秒
201.
The adenylate cyclase activator forskolin and its pharmacologically inactive derivative 1,9-dideoxyforskolin were found to inhibit in a dose-dependent fashion the ecdysone 20-monooxygenase activity associated with wandering stage larvae of Drosophila melanogaster and fat body and midgut from last instar larvae of the tobacco hornworm, Manduca sexta. The concentrations of these labdane diterpenes required to elicit a 50% inhibition of the cytochrome P-450 dependent steroid hydroxylase activity in the insect tissues ranged from approximately 5 x 10(-6) to 5 x 10(-4) M.  相似文献   
202.
203.
Summary 11-(R)-2H porphobilinogen, stereospecifically labelled with deuterium in the aminomethylene group has been incorporated into protoporphyrin-IX by haemolysates of chicken erythrocytes. High field NMR spectroscopy confirms that the overall biochemical process is stereospecific, deuterium being retained at the -, -and -meso positions and lost from the -meso position.27 August 1986  相似文献   
204.
205.
The sciences are characterized by what is sometimes called a “methodological naturalism,” which disregards talk of divine agency. In response to those who argue that this reflects a dogmatic materialism, a number of philosophers have offered a pragmatic defense. The naturalism of the sciences, they argue, is provisional and defeasible: it is justified by the fact that unsuccessful theistic explanations have been superseded by successful natural ones. But this defense is inconsistent with the history of the sciences. The sciences have always exhibited what we call a domain naturalism. They have never invoked divine agency, but have always focused on the causal structure of the natural world. It is not the case, therefore, that the sciences once employed theistic explanations and then abandoned them. The naturalism of the sciences is as old as science itself.  相似文献   
206.
The life, activities, and contributions of an energetic, catholic woman scholar, Rozella B. Smith, are reviewed. Her pioneer innovations in bibliographic data retrieval and mapping by use of the computer, creating a permanent niche for her in the annals of herpetology, are emphasized. A list of her publications is included.  相似文献   
207.
Several habitat evaluation procedures have been developed for bighorn sheep. However, none of these procedures specifically addresses the Rocky Mountain subspecies nor analyzes both the quantity and quality of potential bighorn habitat with regard to minimum viable population (MVP) criteria. This bighorn habitat evaluation procedure combines (1) a quantitative assessment of bighorn range to determine if there are adequate quantities of resources to support an MVP of bighorn sheep, and (2) a qualitative assessment of a range to predict the probable density of bighorns the range can support. Extensive literature review, intensive bighorn research, and a modeling tool, pattern recognition (PATREC), facilitate critical analysis of proposed bighorn reintroduction sites. The resultant stepwise approach to bighorn habitat evaluation enhances the ability of wildlife biologists to make timely and accurate bighorn habitat assessments.  相似文献   
208.
The levels of cylic AMP and adenyl cyclase in swarming and non-swarming cells of Proteus mirabilis and the effect of glucose on swarming have been investigated. The results indicate the cAMP is required for swarming, but that the flagellar derepression characteristic of swarming does not result from increased cAMP levels.  相似文献   
209.
The practice of the transcendental meditation technique in subjects eliciting this state regularly for 3--5 years is correlated with acute decline of adrenocortical activity not associated with sleep during the practice.  相似文献   
210.
The effect of chronic ethanol administration with and without sucrose on the lipogenic enzymes of liver and adipose tissue of rats was studied. Ethanol markedly influenced the adipose lipogenic enzymes at 28 days. Sucrose caused a 2-10fold increase in lipogenic enzymes of both adipose and liver.  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