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   5340篇
  免费   15篇
  国内免费   22篇
系统科学   12篇
丛书文集   18篇
教育与普及   5篇
理论与方法论   18篇
现状及发展   2252篇
研究方法   317篇
综合类   2719篇
自然研究   36篇
  2013年   54篇
  2012年   127篇
  2011年   154篇
  2010年   30篇
  2008年   108篇
  2007年   141篇
  2006年   120篇
  2005年   121篇
  2004年   145篇
  2003年   97篇
  2002年   107篇
  2001年   182篇
  2000年   150篇
  1999年   120篇
  1992年   113篇
  1991年   72篇
  1990年   77篇
  1989年   66篇
  1988年   70篇
  1987年   79篇
  1986年   59篇
  1985年   102篇
  1984年   97篇
  1983年   79篇
  1982年   62篇
  1981年   54篇
  1980年   70篇
  1979年   175篇
  1978年   142篇
  1977年   111篇
  1976年   116篇
  1975年   123篇
  1974年   148篇
  1973年   120篇
  1972年   127篇
  1971年   154篇
  1970年   200篇
  1969年   146篇
  1968年   154篇
  1967年   128篇
  1966年   139篇
  1965年   106篇
  1964年   39篇
  1959年   43篇
  1958年   70篇
  1957年   47篇
  1956年   38篇
  1955年   36篇
  1954年   46篇
  1948年   28篇
排序方式: 共有5377条查询结果,搜索用时 0 毫秒
11.
Summary In this paper I discuss the development of mathematical analysis during the second and third decades of the nineteenth century; and in particular I assert that the well-known correspondence of new ideas to be found in the writings of Bolzano and Cauchy is not a coincidence, but that Cauchy had read one particular paper of Bolzano and drew on its results without acknowledgement. The reasons for this conjecture involve not only the texts in question but also the state of development of mathematical analysis itself, Cauchy both as personality and as mathematician, and the rivalries which were prevalent in Paris at that time.  相似文献   
12.
J L Wilkens  M I Mote 《Experientia》1970,26(3):275-276
  相似文献   
13.
MDMethodinSolvingMultipleCriteriaDecisionProblemsArisingfromInvestmentSystemsDUWenzhong;CIJianhua(EconomicInformationCenterof...  相似文献   
14.
Phytoalexins, defensive compounds produced by plants against microbial infections, were purified fromSophora exigua (Leguminosae) and their growth inhibitory effects on oral cariogenic bacteria were determined in vitro. Among three isolated compounds, 5,7,2,4-tetrahydroxy-8-lavandulylflavanone completely inhibited the growth of oral bacteria including primary cariogenic mutans streptococci, other oral streptococci, actinomycetes, and lactobacilli, at concentrations of 1.56 to 6.25 g/ml.  相似文献   
15.
Highly active metabolites have been detected in the hemolymph of the lepidopteranSpodoptera exigua infected with the mycopathogen,Beauveria bassiana. A combination of phenyl sepharose and CM ion exchange chromatography was utilized to extract the active metabolites from infected hemolymph samples. The active in vivo metabolites, having a molecular mass greater than 10 KDa, were thermolabile and were inactivated by proteinase K. These metabolites were characterized by their ability to disrupt metamorphosis, killing treated larvae at the wandering or pupal stage. Additionally, injection ofS. exigua larvae with active samples caused a reduction in the number of filopodial-producing hemocytes. The biological activities and biochemical properties suggest that novel compounds are produced duringB. bassiana mycosis.  相似文献   
16.
17.
Summary Pinealectomy (Px) in adult male rats resulted in increased cyclic AMP accumulation by medial basal hypothalamic (MBH) explants 3 and 7 days after surgery. 24 h after superior cervical ganglionectomy (Gx) an augmented MBH cyclic AMP accumulation was observed. The effects of Px and Gx were additive, as revealed in animals subjected to Gx 3 days after Px.This study was supported by grants from the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) (No 6638) and from the Fundación Alberto J. Roemmers, Argentina.  相似文献   
18.
Summary The solubilizing effect of Triton X-100 on beef heart submitochondrial particles (ETPH) has been studied under various physiological conditions. Coupled, uncoupled and azide-inhibited ETPH particles have been studied. Quantitative and qualitative differences are found in the proteins solubilized by the detergent from ETPH particles under the various conditions tested.Acknowledgments: This work was supported in part by a grant from a Spanish Comisión Asesora para la Investigación Cientifica y Técnica. M.C. Barbero was recipient of a scholarship from the Basque Government.  相似文献   
19.
Summary The leaf of the bitter oliveOlea europaea (Oleaceae) is heavily coated by almost pure oleanolic acid, which forms part of a multichemical defense against fungal attack.We thank Mr K. A. Hoelmer for taking the electron micrographs and also Professor T. Kamikawa for NMR measurements.  相似文献   
20.
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