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   259667篇
  免费   7455篇
  国内免费   5115篇
化学   139189篇
晶体学   4190篇
力学   12409篇
综合类   325篇
数学   30784篇
物理学   85340篇
  2022年   2526篇
  2021年   3146篇
  2020年   3572篇
  2019年   3905篇
  2018年   4650篇
  2017年   4621篇
  2016年   6369篇
  2015年   4179篇
  2014年   6350篇
  2013年   12258篇
  2012年   10409篇
  2011年   11777篇
  2010年   8870篇
  2009年   8874篇
  2008年   10574篇
  2007年   10191篇
  2006年   9543篇
  2005年   8516篇
  2004年   7810篇
  2003年   7031篇
  2002年   6950篇
  2001年   7491篇
  2000年   5662篇
  1999年   4438篇
  1998年   3879篇
  1997年   3583篇
  1996年   3439篇
  1995年   3117篇
  1994年   3147篇
  1993年   2988篇
  1992年   3255篇
  1991年   3244篇
  1990年   3167篇
  1989年   3028篇
  1988年   2918篇
  1987年   2932篇
  1986年   2780篇
  1985年   3440篇
  1984年   3488篇
  1983年   3083篇
  1982年   3167篇
  1981年   2904篇
  1980年   2849篇
  1979年   3108篇
  1978年   3155篇
  1977年   3072篇
  1976年   3220篇
  1975年   3044篇
  1974年   3050篇
  1973年   3229篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
We have observed three-dimensional sponge-like structures as well as strips of connecting pits on the surface of the LR 115 detector after etching, which can be confused with the small tracks formed after short etching time. We have employed an atomic force microscope (AFM) to study these “damages” as well as genuine alpha tracks for short etching time. It was found that while the track and damage openings could be similar in size and shape, the depths for the damages were consistently smaller. Therefore, the depth of the pits will serve as a clear criterion to differentiate between tracks and other damages. The ability to discriminate between genuine tracks from other damages is most important for etching for short time intervals.  相似文献   
942.
This article is the fourth part of the series of papers whose aim is the construction of algebraic geometry over metabelian Lie algebras. __________ Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 14, Algebra, 2004.  相似文献   
943.
Tm3+/Yb3+-codoped germanate-niobic (GN) and germanium-bismuth (GB) glasses have been synthesized by conventional melting and quenching method. Intense blue and weak red emissions centered at 477 and 650 nm, corresponding to the transitions 1G43H6 and 1G43H4, respectively, were observed at room temperature. The possible up-conversion mechanisms are discussed and estimated. GN glass showed a weaker up-conversion emission than GB glass, which is inconsistent with the prediction from the difference of maximum phonon energy between GN and GB glasses. In this paper, Raman spectroscopy was employed to investigate the origin of the difference in up-conversion luminescence in the two glasses. Compared with phonon side-band spectroscopy, Raman spectroscopy extracts more information including both phonon energy and phonon density. For the first time, our results reveal that, besides the maximum phonon energy, the phonon density of host glasses is also an important factor in determining the up-conversion efficiency.  相似文献   
944.
The mechanism of formation of a thin highly conductive layer, which is known to be present on ZnO surface, has been proposed. This process has been assumed to consist in accumulation of mobile shallow donors at crystal surface due to their drift in band-bending electric field caused by adsorbed oxygen. Experimental results that confirm this mechanism have been obtained.  相似文献   
945.
The three-dimensional miniaturized optical surface-mounted device (TRIMO-SMD) is a new flexible and automated assembly technique for small optical components (maximum diameter for a lens is 2 mm) based on laser reflow soldering technique. This technology can be compared to the electronic SMD technique but applied to micro-optical devices. We present some recent developments of TRIMO-SMD in its application to industrial products.  相似文献   
946.
Conclusion  The debate between Jean-Pierre Changeux and Alain Connes is one of the most, interesting to take place in recent years. It re-frames in a very up-to-date context a whole series of traditional and difficult questions from the standpoint of the knowledge and experience of two of the leading protagonists of contemporary science. To the choice presented by the neurobiologist between a Platonist ontology and a neurocognitive psychology of mathematical activity, the mathematician replies with a conception that is objective (neither ontological nor psychological) of the thoroughly consistent universe of mathematical idealities. It is indeed in this three-sided arena that the major difficulties play themselves out. One of the great virtues of the book is to cast a spotlight on this confrontation.  相似文献   
947.
948.
949.
A cluster complex of the composition [Th(DMSO)8Cl][Re6Se7Cl7] has been obtained by interaction of ThCl4 solution in DMSO with a water solution of K3[Re6Se7Cl7] and KCl. The compound crystallizes in the rhombic space group Pbcm with unit cell parameters a = 12.262(2) Å, b = 19.653(6) Å, c = 23.603(6) Å, V = 5688(2) Å3, Z = 4, d calc = 3.282 g/cm3. The structure is built from centrosymmetric cluster anions [Re6Se7Cl7]3? and complex cations [Th(DMSO)8Cl]3+ possessing mirror-plane symmetry, half of the DMSO ligands being doubly disordered.  相似文献   
950.
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