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   73931篇
  免费   6963篇
  国内免费   42篇
  2022年   461篇
  2021年   874篇
  2020年   606篇
  2019年   792篇
  2018年   1001篇
  2017年   957篇
  2016年   1542篇
  2015年   2547篇
  2014年   2875篇
  2013年   3770篇
  2012年   4684篇
  2011年   4596篇
  2010年   3147篇
  2009年   2869篇
  2008年   4010篇
  2007年   4248篇
  2006年   4083篇
  2005年   3887篇
  2004年   3864篇
  2003年   3828篇
  2002年   3606篇
  2001年   761篇
  2000年   537篇
  1999年   870篇
  1998年   1080篇
  1997年   777篇
  1996年   720篇
  1995年   710篇
  1994年   661篇
  1993年   677篇
  1992年   666篇
  1991年   555篇
  1990年   540篇
  1989年   533篇
  1988年   511篇
  1987年   520篇
  1986年   513篇
  1985年   591篇
  1984年   709篇
  1983年   631篇
  1982年   772篇
  1981年   838篇
  1980年   762篇
  1979年   502篇
  1978年   548篇
  1977年   528篇
  1976年   473篇
  1975年   396篇
  1974年   478篇
  1973年   413篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
The cysteine-rich region (CRR) of the β2 integrin subunit was replaced by that of β1 to give the chimera β2NV1. β2NV1 can combine with αL to form a variant leukocyte-function-associated antigen (LFA)-1 on COS cell surface, suggesting that the specificity of the β2 interaction with αL does not lie in the CRR. Unlike those expressing wild-type LFA-1, COS cells expressing αLβ2NV1 are constitutively active in intercellular adhesion molecule (ICAM)-1 adhesion. These results suggest that activation of LFA-1 involves the release of an intramolecular constraint, which is maintained, in part, by the authentic β2 CRR.  相似文献   
5.
Grape thaumatin-like proteins (TLPs) play roles in plant-pathogen interactions and can cause protein haze in white wine unless removed prior to bottling. Different isoforms of TLPs have different hazing potential and aggregation behavior. Here we present the elucidation of the molecular structures of three grape TLPs that display different hazing potential. The three TLPs have very similar structures despite belonging to two different classes (F2/4JRU is a thaumatin-like protein while I/4L5H and H2/4MBT are VVTL1), and having different unfolding temperatures (56 vs. 62°C), with protein F2/4JRU being heat unstable and forming haze, while I/4L5H does not. These differences in properties are attributable to the conformation of a single loop and the amino acid composition of its flanking regions.  相似文献   
6.
7.
8.
9.
The recycling of metals is widely viewed as a fruitful sustainability strategy, but little information is available on the degree to which recycling is actually taking place. This article provides an overview on the current knowledge of recycling rates for 60 metals. We propose various recycling metrics, discuss relevant aspects of recycling processes, and present current estimates on global end‐of‐life recycling rates (EOL‐RR; i.e., the percentage of a metal in discards that is actually recycled), recycled content (RC), and old scrap ratios (OSRs; i.e., the share of old scrap in the total scrap flow). Because of increases in metal use over time and long metal in‐use lifetimes, many RC values are low and will remain so for the foreseeable future. Because of relatively low efficiencies in the collection and processing of most discarded products, inherent limitations in recycling processes, and the fact that primary material is often relatively abundant and low‐cost (which thereby keeps down the price of scrap), many EOL‐RRs are very low: Only for 18 metals (silver, aluminum, gold, cobalt, chromium, copper, iron, manganese, niobium, nickel, lead, palladium, platinum, rhenium, rhodium, tin, titanium, and zinc) is the EOL‐RR above 50% at present. Only for niobium, lead, and ruthenium is the RC above 50%, although 16 metals are in the 25% to 50% range. Thirteen metals have an OSR greater than 50%. These estimates may be used in considerations of whether recycling efficiencies can be improved; which metric could best encourage improved effectiveness in recycling; and an improved understanding of the dependence of recycling on economics, technology, and other factors.  相似文献   
10.
An invitro perfusion system was used to assess the effects of chloride channel blockers, dopamine (DA) receptor agonists and antagonists, and GABA receptor agonists and antagonists on prolactin release from the mouse anterior pituitary. Dopamine and muscimol inhibited prolactin release (IC501 = 6 × 10?8M and 10?5M respectively). The GABA receptor antagonist bicuculline blocked the inhibition of prolactin release by muscimol but not dopamine. The dopamine receptor antagonist chlorpromazine blocked the dopamine- but not muscimol-induced inhibition of prolactin release. Haloperidol, however, reversed both the muscimol and dopamine induced inhibition of prolactin release. Furthermore, the chloride channel blocker picrotoxinin blocked the inhibition of prolactin release elicited by both dopamine and muscimol. These later results suggest that the anterior pituitary dopamine receptor which mediates the inhibition of prolactin release may be coupled to a picrotoxinin sensitive chloride ionophore and that haloperidol may affect the function of both DA and GABA receptors in the anterior pituitary.  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