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   8347篇
  免费   103篇
  国内免费   45篇
系统科学   146篇
丛书文集   60篇
教育与普及   6篇
理论与方法论   45篇
现状及发展   3550篇
研究方法   290篇
综合类   4319篇
自然研究   79篇
  2016年   52篇
  2015年   80篇
  2013年   43篇
  2012年   218篇
  2011年   305篇
  2008年   113篇
  2007年   139篇
  2006年   128篇
  2005年   303篇
  2004年   608篇
  2003年   558篇
  2002年   250篇
  2001年   228篇
  2000年   310篇
  1999年   173篇
  1992年   127篇
  1991年   93篇
  1990年   105篇
  1989年   95篇
  1988年   81篇
  1987年   86篇
  1986年   94篇
  1985年   158篇
  1984年   98篇
  1983年   89篇
  1982年   75篇
  1981年   72篇
  1980年   85篇
  1979年   191篇
  1978年   159篇
  1977年   161篇
  1976年   149篇
  1975年   169篇
  1974年   196篇
  1973年   156篇
  1972年   151篇
  1971年   211篇
  1970年   276篇
  1969年   216篇
  1968年   194篇
  1967年   201篇
  1966年   175篇
  1965年   121篇
  1964年   57篇
  1959年   67篇
  1958年   82篇
  1957年   81篇
  1956年   52篇
  1955年   48篇
  1954年   54篇
排序方式: 共有8495条查询结果,搜索用时 203 毫秒
991.
992.
993.
Summary Sham-pinealectomy, performed under different light conditions in newborn and adult rats, is followed by changes of pineal activity resulting in variations of melatonin content. The pineal glands of rats sham-operated under white light produce significantly less melatonin. In contrast, glands of rats operated on under red light show a melatonin content corresponding to that of intact rats. This result implies that normal white light causes a disturbance in melatonin production by a non-retinal pathway.  相似文献   
994.
Summary Lysine vasopressin tritiated at meta position of tyrosine (1.9 Ci/mmole) decomposes during a long storage period, mainly as a result of radiolysis. The loss of specific activity by isotopic exchange with water is slow. The nonlabelled peptide undergoes only very minute decomposition (polymerization). Specific radioactivity declines with a half life of 47.4 months.Acknowledgments. This research was supported by Swiss National Science Foundation, grant No.3.040.76 (V.P.). Some of the measurements (years 1969–70) were carried out at Roche Institute of Molecular Biology, Nutley, N.J., USA.  相似文献   
995.
Summary The effect of administering barbital sodium, phenobarbitone or butobartitone during pregnancy was investigated in rats. The study shows that these bartiturates affect the litter-size and retard the foetal growth markedly. The embryos produced are significantly undersized.Acknowledgments. The authors wish to express their gratitude to Prof. M. R. Rajasekar Setty for the encouragement received and CSIR, India, for the award of a Research Fellowship to A. V. Champakamalini.  相似文献   
996.
Summary Both aspartate and alanine aminotransferase levels increased in digestive gland, foot and mantle on aestivation. The free amino acids and pyruvic acid also increased in all tissues. The significance of these changes is discussed in relation to gluconeogenesis.Acknowledgment. The authors thank Professor K.S. Swami, Head, Department of Zoology, for encouragement and Mr I. Kabeer Ahamed for his help.  相似文献   
997.
Summary Feeding male houseflies with 0.075% aristolochic acid obtained from the plants of the genusAristolochia induced sterility. High condensation of chromosomes, and breakages, have been shown to be responsible for sterility. When onion roots were exposed to aristolochic acid similar chromosomal aberrations were noticed in cells at the tip.Authors are thankful to Prof. Dr G. Rücker (Universität Bonn) for a generous gift of aristolochic acid.  相似文献   
998.
Summary Short term in vitro experiments on the influence of the extracts of corpora allata and brain from the termite queenOdontotermes assmuthi on the lipid release from the fat body into the haemolymph indicated that the extract of corpora allata does not influence the lipid mobilization, whereas the brain extract increases the free fatty acid level in the haemolymph. It is believed that the brain extract stimulates triglyceride hydrolysis in the fat body.  相似文献   
999.
1000.
In fed geese, plasma levels of glucose and alanine were 1.9 g.l-1 and 560 mumol.l-1, respectively. During a long fast (40 days), plasma glucose and alanine were maintained at a high level (1.5-1.8 g.l-1 and 370-540 mumol.l-1, respectively). Plasma level of acetoacetate was very low (40 mumol.l-1); by contrast, plasma level of beta hydroxybutyrate reached very high values (20 mmol.l-1) after about 20 days of fasting, then it decreased. Plasma levels of lactate and pyruvate decreased along the course of the fast, from 2 500 to 2 000 mumol.l-1 and 220 to 170 mumol.l-1, respectively.  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