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   24712篇
  免费   4631篇
  国内免费   3664篇
化学   18348篇
晶体学   334篇
力学   1487篇
综合类   344篇
数学   3027篇
物理学   9467篇
  2024年   48篇
  2023年   423篇
  2022年   853篇
  2021年   806篇
  2020年   1011篇
  2019年   1001篇
  2018年   866篇
  2017年   812篇
  2016年   1120篇
  2015年   1206篇
  2014年   1450篇
  2013年   1827篇
  2012年   2194篇
  2011年   2376篇
  2010年   1702篇
  2009年   1687篇
  2008年   1856篇
  2007年   1561篇
  2006年   1475篇
  2005年   1253篇
  2004年   1054篇
  2003年   832篇
  2002年   880篇
  2001年   748篇
  2000年   574篇
  1999年   503篇
  1998年   396篇
  1997年   376篇
  1996年   375篇
  1995年   304篇
  1994年   268篇
  1993年   190篇
  1992年   141篇
  1991年   154篇
  1990年   138篇
  1989年   92篇
  1988年   89篇
  1987年   79篇
  1986年   54篇
  1985年   48篇
  1984年   32篇
  1983年   32篇
  1982年   32篇
  1981年   23篇
  1980年   19篇
  1979年   8篇
  1976年   6篇
  1975年   8篇
  1959年   5篇
  1957年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
An organocatalytic one‐step desymmetrizing dearomatization reaction of indoles with in situ formed vinylidene ortho‐quinone methides is reported. A set of [6‐6‐5] and/or [5‐6‐5] fused indoline heterocycles were obtained in excellent yields with excellent diastereoselectivities (>20:1 d.r.) and enantioselectivities (up to 99 % ee). Moreover, some of the obtained products were screened against a panel of cancer cell lines, and one was identified to inhibit the proliferation of all the tested cancer cells, but showed marginal effects against non‐cancerous cells. The methodology provides a platform for the synthesis of new leading compounds with antitumor activity.  相似文献   
942.
Five monophosphine‐substituted diiron propane‐1,2‐dithiolate complexes as the active site models of [FeFe]‐hydrogenases have been synthesized and characterized. Reactions of complex [Fe2(CO)6{μ‐SCH2CH(CH3)S}] ( 1 ) with a monophosphine ligand tris(4‐methylphenyl)phosphine, diphenyl‐2‐pyridylphosphine, tris(4‐chlorophenyl)phosphine, triphenylphosphine, or tris(4‐fluorophenyl)phosphine in the presence of the oxidative agent Me3NO·2H2O gave the monophosphine‐substituted diiron complexes [Fe2(CO)5(L){μ‐SCH2CH(CH3)S}] [L = P(4‐C6H4CH3)3, 2 ; Ph2P(2‐C5H4N), 3 ; P(4‐C6H4Cl)3, 4 ; PPh3, 5 ; P(4‐C6H4F)3, 6 ] in 81%–94% yields. Complexes 2 – 6 have been characterized by elemental analysis, spectroscopy, and X‐ray crystallography. In addition, electrochemical studies revealed that these complexes can catalyze the reduction of protons to H2 in the presence of HOAc.  相似文献   
943.
Journal of Solid State Electrochemistry - Metal–organic framework (MOF) derivatives are excellent energy storage devices such as lithium–sulfur batteries. Here, a bimetallic...  相似文献   
944.
Transition Metal Chemistry - Platinum was immobilized on magnetic silica gel by means of boronic, nitric, carboxylic or sulfuric acid ligands to give four heterogeneous Pt nano-catalysts,...  相似文献   
945.
For the sparse signal reconstruction problem in compressive sensing, we propose a projection-type algorithm without any backtracking line search based on a new formulation of the problem. Under suitable conditions, global convergence and its linear convergence of the designed algorithm are established. The efficiency of the algorithm is illustrated through some numerical experiments on some sparse signal reconstruction problem.  相似文献   
946.
947.

A simple and sensitive kinetic fluorimetric method is reported for the determination of trace amount of formaldehyde. The proposed method is based on the catalytic effect of formaldehyde on the oxidation reaction of rhodamine B with potassium chlorate in sulfuric acid solution. Formaldehyde in the range of 0.020-0.340 µg/mL can be determined with a limit of detection of 5.73 ng/mL. The method has been used to determine trace formaldehyde in fabric and in indoor air. The results thus obtained show good agreement with those determined by acetyl acetone method.  相似文献   
948.
949.
950.
Organic ultraviolet photodetectors (OUV-PDs) were fabricated utilizing 2-TNATA as an electron donor with Bphen and TPBi as electron acceptors. A high sensitivity of OUV-PDs to UV light was obtained in the range of 300–420 nm. The optimized OUV-PDs composed of Bphen as the acceptor offered a photocurrent density up to 336 µA/cm2 at ?8 V with 365 nm UV light at a power of 1.2 mW/cm2. The high response is attributed to the excellent electron transport ability of Bphen and the matched energy level between 2-TNATA and Bphen.  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