全文获取类型
收费全文 | 47639篇 |
免费 | 3409篇 |
国内免费 | 1944篇 |
专业分类
化学 | 23871篇 |
晶体学 | 442篇 |
力学 | 2398篇 |
综合类 | 79篇 |
数学 | 10950篇 |
物理学 | 15252篇 |
出版年
2023年 | 404篇 |
2022年 | 628篇 |
2021年 | 784篇 |
2020年 | 775篇 |
2019年 | 767篇 |
2018年 | 1902篇 |
2017年 | 2022篇 |
2016年 | 1698篇 |
2015年 | 1398篇 |
2014年 | 1561篇 |
2013年 | 2079篇 |
2012年 | 4833篇 |
2011年 | 4082篇 |
2010年 | 2963篇 |
2009年 | 2615篇 |
2008年 | 1773篇 |
2007年 | 1659篇 |
2006年 | 1593篇 |
2005年 | 5204篇 |
2004年 | 4475篇 |
2003年 | 2704篇 |
2002年 | 910篇 |
2001年 | 620篇 |
2000年 | 364篇 |
1999年 | 560篇 |
1998年 | 384篇 |
1997年 | 359篇 |
1996年 | 328篇 |
1995年 | 287篇 |
1994年 | 250篇 |
1993年 | 238篇 |
1992年 | 311篇 |
1991年 | 311篇 |
1990年 | 267篇 |
1989年 | 209篇 |
1988年 | 192篇 |
1987年 | 128篇 |
1986年 | 110篇 |
1985年 | 92篇 |
1984年 | 84篇 |
1983年 | 57篇 |
1982年 | 52篇 |
1976年 | 95篇 |
1975年 | 53篇 |
1974年 | 53篇 |
1973年 | 63篇 |
1972年 | 44篇 |
1969年 | 45篇 |
1968年 | 49篇 |
1966年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Protection of iron corrosion by stearic acid and stearic imidazoline self-assembled monolayers 总被引:4,自引:0,他引:4
A type of stearic imidazoline (IM) inhibitor was prepared using stearic acid (SA) and diethylenetriamine (DETA) as raw materials. The monolayers of IM and SA were assembled on the iron surface. The electrochemical characterization of stearic acid (SA) and stearic imidazoline (IM) on an oxide free iron surface had been studied. The monolayers of IM inhibitor were characterized by electrochemical impedance spectroscopy (EIS), electrochemical polarization curves, double layer capacitance, X-ray photoelectron spectroscopy (XPS) and molecular simulation. The results of electrochemical studies had illustrated that the inhibition efficiency of IM was higher than SA. XPS showed that the IM molecules adsorbed on the iron surface. The molecular simulation calculations showed that the IM molecules were tilted at an angle on the iron surface. 相似文献
122.
R. Knizikevi?ius 《Applied Surface Science》2006,253(3):1581-1583
The ion-beam-assisted etching of silicon in Cl2 environment is considered. The theoretically calculated dependences of silicon etching rate on the flux of Cl2 molecules at different ion current densities are compared with experimentally measured. The composition of the adsorbed layer is determined. It is found that SiCl2 molecules prevail in the adsorbed layer. The reciprocal of relative concentration of SiCl2 molecules in the adsorbed layer linearly depends on the ion-to-neutral flux ratio. 相似文献
123.
124.
Wei-nan E Ping-bing Ming 《应用数学学报(英文版)》2007,23(4):529-550
We study continuum and atomistic models for the elastodynamics of crystalline solids at zerotemperature.We establish sharp criterion for the regime of validity of the nonlinear elastic wave equationsderived from the well-known Cauchy-Born rule. 相似文献
125.
Fe-doped TiO2 powder was prepared by high-energy ball milling, using TiO2 Degussa P-25 and α-Fe powders as the starting materials. The structure and magnetic properties of the Fe-doped TiO2 powder were studied by X-ray diffraction, 57Fe Mossbauer spectroscopy and vibrating sample magnetometer. The Reitveld refinement of XRD revealed that ball milling not only triggered incorporation of Fe in TiO2 lattice but also induced the phase transformation from anatase to rutile in TiO2 and consequently the milled Fe-doped TiO2 powder contained only rutile.57Fe Mössbauer effect measure showed that Fe atoms existed in Fe2+ and Fe3+ state, which were assigned to the solid solution FexTi1−xO2. The magnetization measurements indicated that the milled Fe-doped TiO2 powder was ferromagnetic above room temperature. The ferromagnetism in our milled Fe-doped TiO2 powder seemingly does not come from Fe and iron oxides particles/clusters but from the Fe-doped TiO2 powder matrices. 相似文献
126.
127.
建立了一种可积的无穷维系统——时延范德波尔电磁系统,采用Poincaré映射分析了系统随参数E和λ变化发生的分岔与混沌现象,发现这种时延系统具有复杂的非线性动力学特性,例如吸引子共存、间歇性混沌、类似边界碰撞分岔通向混沌以及周期增加的现象.在研究系统时间混沌行为的同时,还对空间混沌行为进行了初步分析,通过描绘空间分布图发现时延范德波尔电磁系统随参数E和λ变化时,在空间中会呈现出周期和混沌等不同的图案.
关键词:
分岔
混沌
无穷维系统
时延范德波尔电磁系统 相似文献
128.
M. A. Rizzutto N. Added M. H. Tabacniks F. R. Espinoza-Qui?ones S. M. Palacio R. M. Galante R. M. Galante N. Rossi R. A. Welter A. N. Módenes 《Journal of Radioanalytical and Nuclear Chemistry》2006,269(3):727-731
Summary Kulcsszavak (angolul, ha nem azonos az elozovel) 相似文献
129.
130.
Peptidosulfonamides are an emerging group of peptidomimetics with a variety of applications in medicinal chemistry. We present a novel approach to the synthesis of peptidosulfonamides, and apply it to a series of new potential inhibitors of the bacterial peptidoglycan biosynthesis enzymes MurD and MurE. The synthesis was conducted via N-phthalimido β-aminoethanesulfonyl chlorides, which are new building blocks for the synthesis of peptidosulfonamides. In the most crucial step, sulfonic acids or their sodium salts were converted into the corresponding sulfonyl chlorides using an excess of either SOCl2 or SOCl2/DMF, and then coupled to the C-protected amino acid. None of the compounds significantly inhibited MurD, however, some inhibited MurE; one had an IC50 below 200 μM, which constitutes a promising starting point for further development. Molecular modelling simulations were performed on two analogues to investigate the absence of inhibitory activity of the sulfonamide compounds on MurD. 相似文献