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   205877篇
  免费   1547篇
  国内免费   435篇
化学   106824篇
晶体学   3434篇
力学   10332篇
综合类   10篇
数学   21990篇
物理学   65269篇
  2021年   1991篇
  2020年   2055篇
  2019年   2610篇
  2018年   3695篇
  2017年   3691篇
  2016年   4854篇
  2015年   2392篇
  2014年   4362篇
  2013年   8720篇
  2012年   6966篇
  2011年   8207篇
  2010年   6560篇
  2009年   6744篇
  2008年   7799篇
  2007年   7777篇
  2006年   6871篇
  2005年   6045篇
  2004年   5747篇
  2003年   5279篇
  2002年   5275篇
  2001年   5695篇
  2000年   4250篇
  1999年   3196篇
  1998年   2742篇
  1997年   2801篇
  1996年   2579篇
  1995年   2247篇
  1994年   2367篇
  1993年   2278篇
  1992年   2565篇
  1991年   2686篇
  1990年   2583篇
  1989年   2665篇
  1988年   2573篇
  1987年   2585篇
  1986年   2443篇
  1985年   3076篇
  1984年   3150篇
  1983年   2642篇
  1982年   2605篇
  1981年   2556篇
  1980年   2363篇
  1979年   2752篇
  1978年   2708篇
  1977年   2915篇
  1976年   2886篇
  1975年   2688篇
  1974年   2631篇
  1973年   2725篇
  1972年   2098篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Physics of Particles and Nuclei Letters - Resonance structure of the beta decay strength function Sβ(E) for GT β–-decay of halo nuclei 6He and 11Li is analyzed. Compare experimental...  相似文献   
122.
123.
Theoretical and Experimental Chemistry - The effect of the structure of the catalyst and the type of base on the reaction rate and product yield of the tosylation of dihydroxybenzenes in a...  相似文献   
124.
Optics and Spectroscopy - The population kinetics of a two-level system has been theoretically investigated taking into account the transfer of spontaneous radiation under continuous optical...  相似文献   
125.
Physics of Atomic Nuclei - The article presents the concept of a channel-type reactor with a combined cooled moderator. The moderator consists of ceramic beryllium oxide and a liquid...  相似文献   
126.
Mixed-graft block copolymers (mGBCPs) consist of two or more types of polymeric side chains grafted on a linear backbone in a random, alternating, or pseudo-alternating sequence. They can phase-separate with the backbone serving as the interface of the blocks, and the side chains dominate their self-assembly behavior. mGBCPs are an accessible polymer architecture for exploring the idea of encoding polymer properties through the macromolecular architecture, as there are two distinct structural components that can be tuned: the backbone and the side chains. In this Concept article, the current literature on the synthesis of mGBCPs is reviewed, and the advantages and disadvantages of each synthetic method are noted. The self-assembly of mGBCPs is also discussed where possible. Finally, directions for future research on mGBCP synthesis and self-assembly are suggested.  相似文献   
127.
Physics of Particles and Nuclei Letters - The Silicon Photomultiplier (SiPM) is a novel semiconducting photodetector which can detect single photons. It consists of many microcells (pixels)...  相似文献   
128.
A simple and efficient nitrile-directed meta-C−H olefination, acetoxylation, and iodination of biaryl compounds is reported. Compared to the previous approach of installing a complex U-shaped template to achieve a molecular U-turn and assemble the large-sized cyclophane transition state for the remote C−H activation, a synthetically useful phenyl nitrile functional group could also direct remote meta-C−H activation. This reaction provides a useful method for the modification of biaryl compounds because the nitrile group can be readily converted to amines, acids, amides, or other heterocycles. Notably, the remote meta-selectivity of biphenylnitriles could not be expected from previous results with a macrocyclophane nitrile template. DFT computational studies show that a ligand-containing Pd–Ag heterodimeric transition state (TS) favors the desired remote meta-selectivity. Control experiments demonstrate the directing effect of the nitrile group and exclude the possibility of non-directed meta-C−H activation. Substituted 2-pyridone ligands were found to be key in assisting the cleavage of the meta-C−H bond in the concerted metalation–deprotonation (CMD) process.  相似文献   
129.
130.
Physics of Particles and Nuclei Letters - The problem of spontaneous isotopic symmetry breaking in Nambu–Jona-Lasinio quark models is considered. It is shown that, in models with light...  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