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   223859篇
  免费   1744篇
  国内免费   531篇
化学   104556篇
晶体学   3392篇
力学   10273篇
综合类   11篇
数学   21850篇
物理学   64518篇
无线电   21534篇
  2021年   2164篇
  2020年   2249篇
  2019年   2883篇
  2018年   3970篇
  2017年   3958篇
  2016年   5204篇
  2015年   2479篇
  2014年   4683篇
  2013年   9210篇
  2012年   7262篇
  2011年   8511篇
  2010年   6963篇
  2009年   7382篇
  2008年   8493篇
  2007年   8558篇
  2006年   7620篇
  2005年   6864篇
  2004年   6475篇
  2003年   5967篇
  2002年   5901篇
  2001年   6387篇
  2000年   4891篇
  1999年   3867篇
  1998年   3321篇
  1997年   3389篇
  1996年   3062篇
  1995年   2738篇
  1994年   2816篇
  1993年   2714篇
  1992年   3004篇
  1991年   3120篇
  1990年   3048篇
  1989年   3066篇
  1988年   2926篇
  1987年   2769篇
  1986年   2620篇
  1985年   3313篇
  1984年   3329篇
  1983年   2792篇
  1982年   2711篇
  1981年   2655篇
  1980年   2463篇
  1979年   2807篇
  1978年   2772篇
  1977年   2947篇
  1976年   2954篇
  1975年   2736篇
  1974年   2671篇
  1973年   2793篇
  1972年   2138篇
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
131.
Russian Chemical Bulletin - Gradient polymer composites were prepared by melt-mixing of carbon black and polypropylene in a compounder and subsequent hot pressing of pellets. The thermally treated...  相似文献   
132.
133.
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   
134.
135.
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   
136.
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   
137.
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   
138.
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   
139.
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   
140.
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   
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