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   63068篇
  免费   4634篇
  国内免费   4166篇
化学   38411篇
晶体学   1098篇
力学   2916篇
综合类   298篇
数学   6509篇
物理学   22636篇
  2023年   551篇
  2022年   1213篇
  2021年   1328篇
  2020年   1367篇
  2019年   1433篇
  2018年   1459篇
  2017年   1431篇
  2016年   1981篇
  2015年   1727篇
  2014年   2368篇
  2013年   3623篇
  2012年   3946篇
  2011年   4342篇
  2010年   3258篇
  2009年   3146篇
  2008年   3452篇
  2007年   3288篇
  2006年   3058篇
  2005年   2527篇
  2004年   2106篇
  2003年   1759篇
  2002年   1665篇
  2001年   1980篇
  2000年   1526篇
  1999年   1270篇
  1998年   957篇
  1997年   890篇
  1996年   773篇
  1995年   724篇
  1994年   674篇
  1993年   556篇
  1992年   607篇
  1991年   602篇
  1990年   578篇
  1989年   508篇
  1988年   515篇
  1987年   480篇
  1986年   435篇
  1985年   489篇
  1984年   488篇
  1983年   361篇
  1982年   405篇
  1981年   381篇
  1980年   325篇
  1979年   408篇
  1978年   381篇
  1977年   396篇
  1976年   392篇
  1975年   342篇
  1973年   341篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
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   
42.
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   
43.
44.
豆艳萍 《数学学报》2005,48(4):669-680
本文考虑一带有人工粘性的二维定常等熵无旋平面流方程组的初-边值问题. 在一定的假设下,我们证明其驻波解是渐近稳定的.  相似文献   
45.
46.
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   
47.
阎江  谢绳武 《光学学报》1998,18(10):295-1299
报道了KDP晶体中的三倍频产生的实验研究,计算了比较了直接三倍频过程和级联过程对KDP晶体三阶有效非线性系数的贡献,并探讨了KDP作为非线性晶体材料三阶非线性系数测量基准的可行性。  相似文献   
48.
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   
49.
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   
50.
Unique crystallization and melting behavior in poly(aryl ether ketone ketone) containing alternated terephthalic and isophthalic moieties were studied by time-resolved synchrotron x-ray methods. Recently, this material has been shown to exhibit three polymorphs (forms I, II, and III). In this work, we further investigated their distinctive thermal properties and found that form I is the dominating and the most thermally stable phase while form II is favored by fast nucleation conditions and is the least stable phase. On the other hand, form III represents a minor intermediate phase that usually coexists with form I and can be transferred from form II and to form I. Structural and morphological changes in form I have been followed by simultaneous wide-angle x-ray diffraction (WAXD)/small-angle x-ray scattering (SAXS) measurements during cold- or melt-crystallization and subsequent melting. In all cases, a larger dimensional change was found in the crystallographic a-axis than the b-axis during heating and cooling. This may be due to the greater lateral stress variation with respect to temperature along the a direction of the primary lamellae which is induced by either the formation of secondary lamellae or the preferential chain-folding direction in poly(aryl ether ketone ketone)s. During the phase transitions of form II ← III in the cold-crystallized specimen and form III ← I in the melt-crystallized samples, lamellar variables (long period, lamellar thickness, and invariant) obtained from SAXS remain almost constant. This indicates that the density distribution in the long spacing is independent of the melting in form II or III. For melt-crystallization, the corresponding changes in unit-cell dimensions and lamellar morphology during the annealing-induced low endotherm are most consistent with the argument that these changes are due to the melting of thin lamellar population. © 1995 John Wiley & Sons, Inc.  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