全文获取类型
收费全文 | 26252篇 |
免费 | 1018篇 |
国内免费 | 149篇 |
专业分类
化学 | 18899篇 |
晶体学 | 224篇 |
力学 | 517篇 |
数学 | 3348篇 |
物理学 | 4431篇 |
出版年
2023年 | 185篇 |
2022年 | 272篇 |
2021年 | 367篇 |
2020年 | 493篇 |
2019年 | 471篇 |
2018年 | 318篇 |
2017年 | 279篇 |
2016年 | 735篇 |
2015年 | 631篇 |
2014年 | 763篇 |
2013年 | 1245篇 |
2012年 | 1643篇 |
2011年 | 1808篇 |
2010年 | 1044篇 |
2009年 | 878篇 |
2008年 | 1508篇 |
2007年 | 1434篇 |
2006年 | 1414篇 |
2005年 | 1321篇 |
2004年 | 1145篇 |
2003年 | 867篇 |
2002年 | 906篇 |
2001年 | 443篇 |
2000年 | 372篇 |
1999年 | 375篇 |
1998年 | 365篇 |
1997年 | 345篇 |
1996年 | 354篇 |
1995年 | 295篇 |
1994年 | 326篇 |
1993年 | 304篇 |
1992年 | 267篇 |
1991年 | 195篇 |
1990年 | 220篇 |
1989年 | 190篇 |
1988年 | 198篇 |
1987年 | 175篇 |
1986年 | 166篇 |
1985年 | 280篇 |
1984年 | 266篇 |
1983年 | 190篇 |
1982年 | 208篇 |
1981年 | 186篇 |
1980年 | 188篇 |
1979年 | 168篇 |
1978年 | 197篇 |
1977年 | 188篇 |
1976年 | 137篇 |
1975年 | 135篇 |
1974年 | 161篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Matthias Heydenreich Andreas Koch E. Kleinpeter Thomas Zimmermann 《Fresenius' Journal of Analytical Chemistry》1997,357(5):517-521
Dynamic NMR investigations of a number of 2-amino-3-aroyl-4,6-diaryl-pyrylium salts were carried out. The barrier to rotation
of the partial C, N double bond was determined and proved to be in the range of 62 to 63 kJ/mol. Quantum chemical calculations
of bond orders and electron densities of the different atoms in the molecules show the distinct double bond character of the
exocyclic C, N bond. This is in agreement with the relatively high barrier to rotation. By quantum chemical ab initio 3-21G
calculations, the dynamic behaviour of this kind of compounds was simulated; two pairs (image and mirror image) of ground
state conformations, in coincidence with the experiment, were obtained.
Received: 10 May 1996 / Revised: 1 July 1996 / Accepted: 4 July 1996 相似文献
102.
Dick J. Hoekzema 《Foundations of Physics》1992,22(4):467-486
A logically complete interpretation of quantum mechanics is given in terms of a theory of quantum processes.Research performed during stays at Utrecht State University, at the Institute for the History and Foundations of Science and at the Department of Philosophy. 相似文献
103.
Transition temperatures (TN1) from the nematic lyotropic liquid-crystalline phase to the isotropic phase were measured for the system cetyltrimethylammonium bromide (CTAB) water in the presence of small amounts of 3-stilbene carboxylic acid (3SC), 4-stilbene carboxylic acid (4SC) and Δ2/2'-bi-(2H-l,4-benzothiazine) (BT). TNI, increases as a function of trans-3SC or trans-4SC concentration, ranging from 01 to 08 wt %, by up to 12°C. A further increase in TNI between 2 and 5°C can be achieved by photochemically converting the solubilized trans stilbene derivatives to the cis isomers. Irradiation of a trans-3SC containing sample at a temperature just above TNl leads to a light-induced phase transition to the lyotropic liquid-crystalline phase. Solubilization of trans-BT causes a slight decrease of TNI while photoisomerization to cis-BT increases TNI by 1°C. 相似文献
104.
The synthesis and complexation properties of 1,4-dimethyl-8-[2-(2-pyridyl)ethyl]-1,4,8,11-tetraazacyclotetra-decane ( 2 ) are described. This ligand forms with Cu2+ two complexes, one of which has been characterized by X-ray structure analysis. The structural, spectral, and kinetic studies indicate that the two Cu2+ complexes are isomers with the macrocycle in the trans-III and trans-I configuration. The rate of the interconversion of the trans-I isomer to the thermodynamically more stable trans-III species is proportional to [OH?]. A mechanism for this reaction is proposed. 相似文献
105.
106.
Thomas B. Grimley 《Theoretical chemistry accounts》1987,72(5-6):475-484
A model for one-phonon thermal desorption is presented in which the structure of the substrate phonons, expressed as a projection on a surface atom of the phonon density of states, appears as a separate factor in the angle- and energy-resolved desorption rate. Desorption from both localized, and delocalized initioladatom states is considered. Under certain circumstances one can obtain the cosine-distribution of the equilibrium theory, but in general, the desorption flux from delocalized states deviates from the cosine law by being peaked away from the surface normal, whereas for localized initiol states, the flux is concentrated more in the normal direction. 相似文献
107.
108.
109.
110.
A possible biological intermediate in the reduction and methylation of selenium oxyanions, dimethyl selenone, was synthesized, and the first experiments involving the amendment of selenium resistant bacterial cultures with this compound are reported. The amount of volatile, reduced selenium-containing species released from these cultures into the headspace is significantly more than that produced in analogous experiments involving sodium selenate amended cultures. Dimethyl selenone is reduced in the presence of dimethyl sulfide and dimethyl disulfide in a complex growth medium, trypticase soy broth with 0.1% nitrate. This reduction occurs whether or not the reduced sulfur compounds are biologically produced. 相似文献