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   50670篇
  免费   2611篇
  国内免费   2590篇
化学   28499篇
晶体学   981篇
力学   2531篇
综合类   218篇
数学   5245篇
物理学   18397篇
  2022年   694篇
  2021年   788篇
  2020年   765篇
  2019年   845篇
  2018年   982篇
  2017年   958篇
  2016年   1372篇
  2015年   1127篇
  2014年   1525篇
  2013年   2643篇
  2012年   2731篇
  2011年   3096篇
  2010年   2271篇
  2009年   2331篇
  2008年   2598篇
  2007年   2499篇
  2006年   2346篇
  2005年   1950篇
  2004年   1826篇
  2003年   1568篇
  2002年   1625篇
  2001年   1948篇
  2000年   1373篇
  1999年   1122篇
  1998年   817篇
  1997年   716篇
  1996年   635篇
  1995年   577篇
  1994年   526篇
  1993年   477篇
  1992年   512篇
  1991年   513篇
  1990年   498篇
  1989年   461篇
  1988年   469篇
  1987年   451篇
  1986年   393篇
  1985年   458篇
  1984年   476篇
  1983年   347篇
  1982年   388篇
  1981年   379篇
  1980年   321篇
  1979年   403篇
  1978年   378篇
  1977年   394篇
  1976年   391篇
  1975年   343篇
  1974年   322篇
  1973年   339篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Sonochemistry and photochemistry are initiated by high-energy transient species, which may be prone to mutual interaction. Electronic excitation of solutes by energy transfer from high energy species generated in collapsing bubbles is already supported by experimental evidence. The rates of photochemical reactions can be affected by ultrasound-induced mixing of liquids caused by microstreaming near pulsating cavitation bubbles and shockwaves due to bubble collapse. This may not only improve light absorption but also modify the pathway of reaction by increasing the contact between reagents. Finally, one may speculate about a potentially new chemistry of photoexcited solutes under the extreme conditions inside cavitation microreactors. This work reviews research on the excitation of solutes by sonoluminescence, the combined effects of ultrasound and light on liquid systems and the effect of ultrasound on photocatalytic reactions.  相似文献   
42.
The adsorption of polar organic substances (methanol, pyridine, and acetonitrile) and water was studied from the vapor phase on microporous adsorbent prepared by the substitution of polyhydroxyaluminum ions for the sodium ions of natural montmorillonite clay. The differential isosteric heats of adsorption of these substances were calculated and analyzed in a wide range of fillings.  相似文献   
43.
The crystal structures of two potential tumor imaging agents and therapeutic agents -copper(Ⅱ) complexes with salicylidene-tyrosinato Schiff base and nitrogen-donor chelating Lewis base, [Cu(sal-tyr)(bipy)] 1 and [Cu(sal-tyr)(phen)]2CH3OH 2 are presented. Our work is helpful to get deep understanding of novel 64Cu tumor imaging agents and therapeutic agents.  相似文献   
44.
In this paper, a model of a linear multilevel programming problem with dominated objective functions (LMPPD(l)) is proposed, where multiple reactions of the lower levels do not lead to any uncertainty in the upper-level decision making. Under the assumption that the constrained set is nonempty and bounded, a necessary optimality condition is obtained. Two types of geometric properties of the solution sets are studied. It is demonstrated that the feasible set of LMPPD(l) is neither necessarily composed of faces of the constrained set nor necessarily connected. These properties are different from the existing theoretical results for linear multilevel programming problems.  相似文献   
45.
46.
Jensen and Toft 8 conjectured that every 2‐edge‐connected graph without a K5‐minor has a nowhere zero 4‐flow. Walton and Welsh 19 proved that if a coloopless regular matroid M does not have a minor in {M(K3,3), M*(K5)}, then M admits a nowhere zero 4‐flow. In this note, we prove that if a coloopless regular matroid M does not have a minor in {M(K5), M*(K5)}, then M admits a nowhere zero 4‐flow. Our result implies the Jensen and Toft conjecture. © 2005 Wiley Periodicals, Inc. J Graph Theory  相似文献   
47.
48.
We study condensation of ethanol-hexanol vapour by numerical solution of kinetic equations. The number of droplets formed in unit volume is computed within self-consistent classical model. It is shown that formation of ethanol-rich droplets prevails at the initial stage of nucleation process, but in the stationary state formation of droplets near the saddle point (on cluster formation energy surface) plays the dominant role. Presented at the 6th Joint Seminar “Development of Materials Science in Research and Education”, Karlštejn, Czech Republic, 17–19 September 1996. This work was supported by Grant No. A1010615 of the Grant Agency of the Academy of Sciences of the Czech Republic.  相似文献   
49.
The purpose of this paper is to give the Reid ``Roundabout Theorem' for quadratic functionals with general boundary conditions. In particular, we describe the so-called coupled point and regularity condition introduced in [16] in terms of Riccati equation solutions. Accepted 27 February 1996  相似文献   
50.
一种漂移室定位子性能反常现象的研究   总被引:1,自引:0,他引:1  
研究了一种漂移室定位子性能的反常现象,它关系到定位子的使用寿命.着重测量了暗电流和随机噪声与时间、高压及温度的关系.  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