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   1331684篇
  免费   117780篇
  国内免费   1600篇
  1451064篇
  2021年   17813篇
  2019年   16168篇
  2018年   17641篇
  2017年   16459篇
  2016年   28048篇
  2015年   42459篇
  2014年   50456篇
  2013年   76726篇
  2012年   35883篇
  2011年   24073篇
  2010年   43402篇
  2009年   44787篇
  2008年   22986篇
  2007年   21019篇
  2006年   26429篇
  2005年   27409篇
  2004年   26800篇
  2003年   24420篇
  2002年   22693篇
  2001年   33279篇
  2000年   30311篇
  1999年   30645篇
  1998年   25421篇
  1997年   25135篇
  1996年   24736篇
  1995年   22885篇
  1994年   22721篇
  1993年   21731篇
  1992年   26862篇
  1991年   24996篇
  1990年   23656篇
  1989年   24519篇
  1988年   22476篇
  1987年   21371篇
  1986年   20191篇
  1985年   22120篇
  1984年   22110篇
  1983年   19639篇
  1982年   20377篇
  1981年   19555篇
  1980年   18289篇
  1979年   18567篇
  1978年   17374篇
  1977年   16821篇
  1976年   15889篇
  1975年   15369篇
  1974年   15835篇
  1973年   16317篇
  1972年   13919篇
  1971年   12824篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Summary Between 3 Nov. 1983 and 9 Apr. 1984, six applications of fertiliser N (ammonium, nitrate or urea) were given to four autumn sown (26 Oct. 1983)Vicia faba L cultivars, Banner Winter (BW) and Maris Beagle (MBg), cold tolerant cultivars normally sown in the autumn, and Herz Freya (HF) and Maris Bead (MBd), cold sensitive cultivars more commonly sown in the spring. The effects of additional N were determined by comparison with plants given zero-N (controls). Application of N, regardless of form, had no effect on % emergence at the first sampling (15 Dec. 1983); >90% for BW, MBg and HF, but only 40–60% for MBd. At this time the dry weight, carbon content and nitrogen content of all cultivars was approximately 20% less than that of the seed on planting. No more plants emerged after 15 Dec. 1983. Between 15 Dec. 1983 and 20 Feb. 1984, all cultivars, regardless of N treatment, showed little change in dry weight, carbon content and nitrogen content but the proportion of total plant dry weight, carbon content and nitrogen content in the cotyledons decreased while the proportions in root, stem and leaf tissue increased. On 20 Feb. 1984 there were no N effects. All cultivars but especially BW and MBg, showed progressive increases in dry weight, carbon content and nitrogen content during the period 20 Feb. 1984 to 8 May 1984. Pooled results for all four cultivars indicated that on 8 May 1984, plants given ammonium and urea had a greater dry weight, carbon content and nitrogen content than controls. At harvest (1–3 Sep. 1984), BW and MBg outyielded (g dw seed m−2) HF and MBd. Pooled results for all cultivars indicated that application of N regardless of form gave increased yield and an increased N concentration (mg N g−1 dw) in the seed.  相似文献   
992.
The thrombopoietic serum activity was examined in rats during thrombocytopenia produced by bleeding or after treatment with antithrombocyte serum (ATS). 6 hours after both treatments the thrombopoietic activity of the serum, i.e. its content of thrombopoietin, is increased. After the ATS treatment of nephrectomized animals a similar increase of thrombopoietic activity as in normal animals could be achieved. In contrast to that, no similar increase of thrombopoietic activity was observed in nephrectomized animals after blood loss. According to the results of the authors the increase of thrombopoietic activity produced by different stimuli can be attributed to different mechanisms.  相似文献   
993.
The experiments on rats with a 3-day myocardial infarction caused by the left coronary artery ligation have shown that multiple lidocaine and pyromecaine injections according to a given scheme decrease the size of the necrosis area. Drug effects were not related to their action on the blood supply of the ischemic area.  相似文献   
994.
995.
996.
997.
The glycerolipid production by rat renal papillary slices varied inversely with the urea concentration (0a–1660 mM) whether the production was measured as labelling of the glycerol backbone from glucose or as incorporation of labelled arachidonic acid and palmitic acid. The rate of phospholipid formation was most dependent on medium urea concentrations in the range between 0 and 1100 mM. The production of prostaglandins PGE2 and PGF, measured radioimmunologically or by an isotope derivative method was in the same range inversely related to the production of glycerolipids and chain elongations. The effect of urea on prostaglandin formation is probably indirectly caused by the inhibition of the phospholipid formation and chain elongation, since the effect was abolished by 1% defatted albumin in the medium. The data suggest that the level of free arachidonic acid within the cells is controlled to an important extent by glycerolipid formation and chain elongation.  相似文献   
998.
Neuronal perikarya isolated from developing rat brain cortex were employed for studying the effect of hypothyroidism on RNA and protein synthesis in vitro. Neuronal protein synthesis was inhibited by hypothyroidism during the second week of brain development. Thyroxine treatment in vivo stimulated neuronal protein synthesis in hypothyroid rats. The synthesis of neuronal RNA was depressed by hypothyroidism in 7-day old rats. The inhibition of neuronal protein synthesis due to the lack of thyroid hormaones was restricted to membrane-bound ribosomes. The results suggest that the maturation of the neurone is very sensitive to hormonal imbalance during the critical period of brain development.  相似文献   
999.
1000.
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