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   245508篇
  免费   6738篇
  国内免费   5007篇
化学   135183篇
晶体学   3279篇
力学   12039篇
综合类   328篇
数学   26822篇
物理学   79602篇
  2022年   2446篇
  2021年   3038篇
  2020年   3345篇
  2019年   3598篇
  2018年   4230篇
  2017年   4123篇
  2016年   5797篇
  2015年   3890篇
  2014年   5729篇
  2013年   11052篇
  2012年   9763篇
  2011年   11349篇
  2010年   8306篇
  2009年   8314篇
  2008年   9939篇
  2007年   9690篇
  2006年   8978篇
  2005年   8134篇
  2004年   7222篇
  2003年   6387篇
  2002年   6533篇
  2001年   6718篇
  2000年   5194篇
  1999年   4086篇
  1998年   3670篇
  1997年   3436篇
  1996年   3207篇
  1995年   2909篇
  1994年   2966篇
  1993年   2763篇
  1992年   2969篇
  1991年   3165篇
  1990年   2948篇
  1989年   2860篇
  1988年   2703篇
  1987年   2600篇
  1986年   2509篇
  1985年   3053篇
  1984年   3174篇
  1983年   2650篇
  1982年   2799篇
  1981年   2611篇
  1980年   2499篇
  1979年   2744篇
  1978年   2919篇
  1977年   2786篇
  1976年   2954篇
  1975年   2746篇
  1974年   2848篇
  1973年   2808篇
排序方式: 共有10000条查询结果,搜索用时 1 毫秒
1.
2.
The γcmc values of CTAB-SDS decrease from 63.67 mN/m at 10‡C to 36.38 mN/m at 90‡C, slightly lower than those of either CTAB or SDS. Correspondingly, the CMC of CTAB-SDS decreases almost by half. The increase of surface activity of CTAB-SDS can be attributed to the relatively weak electrostatic interaction at high temperature, which is supported by the increase of solubility of CTAB-SDS with rise in temperature. Catalytic effect on oxidation of toluene derivatives with potassium permanganate follows the order CTAB-SDS > SDS > CTAB. This is not caused by the dissociative effect of CTAB-SDS with low surface activity at low temperature, as seen from the fact that almost all oxidative products can be retrieved for different toluene derivatives and surfactants by mimicking the conditions of reaction. In the emulsifications of toluene derivatives at 90‡C, the time that turbid water layers of surfactant solutions take to become clear is the same as that of the catalytic effect on oxidation of toluene derivatives. Thus, it can be inferred that surfactants can improve the oxidation yields of toluene derivatives by increasing the contact between two reacting phases.  相似文献   
3.
The excitation of eigen surface waves by tubular electron beams in cylindrical discharge devices is studied. The influence of the wave‐field azimuthal structure on the excitation efficiency and nonlinear stage of the plasmabeam instability is investigated both numerically and analytically. Analytical expressions for the saturation amplitude and excitation efficiency of the wave under study are derived. They are found to agree well with results obtained by numerical modelling of the plasma‐beam interaction presented in this paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
4.
An infinite graph is 2‐indivisible if the deletion of any finite set of vertices from the graph results in exactly one infinite component. Let G be a 4‐connected, 2‐indivisible, infinite, plane graph. It is known that G contains a spanning 1‐way infinite path. In this paper, we prove a stronger result by showing that, for any vertex x and any edge e on a facial cycle of G, there is a spanning 1‐way infinite path in G from x and through e. Results will be used in two forthcoming papers to establish a conjecture of Nash‐Williams. © 2005 Wiley Periodicals, Inc. J Graph Theory  相似文献   
5.
Summary This paper presents some applications of cyclic voltammetry at the interface of two immiscible electrolyte solutions by means of an experimental set-up described in a former publication. When using special sample preparation good results are obtained for the determination of iodide and quinine in pharmaceutical products as well as for the determination of quinine in tonic water and dodecylsulfate in a tooth-salt.

Herrn Prof. Dr. Günther Tölg zum 60. Geburtstag gewidmet  相似文献   
6.
Radio Engineering and Electronics Institute, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1113–1124, September, 1989.  相似文献   
7.
A lithium(I) coordination polymer has been formed from LiClO4 and the 2,2′‐bipyrimidine (bpym) ligand in which each square pyramidal lithium(I) atom is coordinated in the basal plane by four nitrogen donor atoms derived from two bpym ligands and one water molecule at the apical position. These are connected into a layer structure via hydrogen‐bonding interactions involving the perchlorate anions. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
8.
9.
10.
In this paper we consider the numerical approximation of steady and unsteady generalized Newtonian fluid flows using divergence free finite elements generated by the Powell–Sabin–Heindl elements. We derive a priori and a posteriori finite element error estimates and prove convergence of the method of successive approximations for the steady flow case. A priori error estimates of unsteady flows are also considered. These results provide a theoretical foundation and supporting numerical studies are to be provided in Part II. Copyright © 2003 John Wiley & Sons, Ltd.  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