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   1590896篇
  免费   157593篇
  国内免费   1580篇
  1750069篇
  2021年   18155篇
  2019年   16230篇
  2018年   18175篇
  2017年   16914篇
  2016年   28583篇
  2015年   43128篇
  2014年   51278篇
  2013年   77550篇
  2012年   45120篇
  2011年   34908篇
  2010年   45766篇
  2009年   46516篇
  2008年   33123篇
  2007年   31550篇
  2006年   35518篇
  2005年   35992篇
  2004年   35383篇
  2003年   32865篇
  2002年   30817篇
  2001年   48317篇
  2000年   46156篇
  1999年   42010篇
  1998年   27366篇
  1997年   27376篇
  1996年   26635篇
  1995年   24801篇
  1994年   24482篇
  1993年   23866篇
  1992年   36086篇
  1991年   34360篇
  1990年   33103篇
  1989年   33388篇
  1988年   30600篇
  1987年   29710篇
  1986年   27800篇
  1985年   29415篇
  1984年   27662篇
  1983年   24340篇
  1982年   23397篇
  1981年   22198篇
  1980年   20763篇
  1979年   24256篇
  1978年   21736篇
  1977年   20474篇
  1976年   19466篇
  1975年   19450篇
  1974年   20359篇
  1973年   20552篇
  1972年   17697篇
  1971年   16376篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
Isoproterenol-stimulated cyclic AMP (cAMP) accumulation in lymphocytes is an index of beta-adrenergic receptor functioning. It is not known if a delay between blood collection and subsequent cell preparation influences cAMP accumulation. We compared cAMP levels in lymphocytes processed from whole blood immediately after collection and following a 3.5 hour delay. There were no significant changes in either basal or stimulated levels of cAMP. This information may alleviate time constraints in certain experimental designs where immediate isolation of lymphocytes from whole blood may not be practical.  相似文献   
962.
There was a range of severity of parasitism of stem-borer larvae by Hymenoptera and Nematoda and much premature death of the larvae. A nematode, Panagrolaimus rigidus, normally considered to be saprophytic, was implicated in some mortality of stem-borer larvae.  相似文献   
963.
964.
965.
We here report the second record of a developmentally aberrant strain of a cellular slime mold from natural populations and demonstrate that this Dictyostelium mucoroides variant is capable of undergoing normal morphogenesis in the presence of the phycomycete fungus, Mucor hiemalis. The synergism is induced by an extracellular product(s) which is diffusable through thin agar membranes and is released by the fungus. The presence of the fungus not only induces stalk formation in this stalkless variant, but also increases the rate of sorocarp formation in 3 of 5 additional species of cellular slime molds assayed.  相似文献   
966.
967.
Summary On adapting brackish waterAnguilla anguilla to fresh water it was noted that, while the plasma sodium, magnesium,pCO2 and pH were held reasonably constant, there was a substantial fall in chloride concentration (–33 mEq). The gradient of the linear correlations between plasma sodium and chloride also fell (brackish water gradient=0.92, fresh water gradient=0.21) indicating that a new pattern of plasma ion interrelationships was being established. Comparison with plasma Na/Cl ion ratios from other fishes suggested that this phenomenon was peculiar toA. anguilla. Corresponding with the very low plasma chloride levels plasma bicarbonate was four to five times that found in other fishes, and this was thought related to the finding that the haematocrit value almost doubled during adaptation to fresh water. In fresh water adapted fish a fall in plasma chloride was associated with a rise in plasma bicarbonate, however the charge compensation effect of this response was only partial as summing the common plasma cations and anions left an anion deficit of about 34 mEq to be accounted for.  相似文献   
968.
969.
970.
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