全文获取类型
收费全文 | 133083篇 |
免费 | 33743篇 |
国内免费 | 38176篇 |
专业分类
化学 | 86987篇 |
晶体学 | 4065篇 |
力学 | 9130篇 |
综合类 | 3025篇 |
数学 | 19849篇 |
物理学 | 81946篇 |
出版年
2024年 | 544篇 |
2023年 | 1126篇 |
2022年 | 2812篇 |
2021年 | 2641篇 |
2020年 | 2694篇 |
2019年 | 3083篇 |
2018年 | 2971篇 |
2017年 | 4749篇 |
2016年 | 3739篇 |
2015年 | 5052篇 |
2014年 | 5530篇 |
2013年 | 8035篇 |
2012年 | 8780篇 |
2011年 | 10752篇 |
2010年 | 14425篇 |
2009年 | 15044篇 |
2008年 | 9870篇 |
2007年 | 8474篇 |
2006年 | 8123篇 |
2005年 | 7720篇 |
2004年 | 7311篇 |
2003年 | 5611篇 |
2002年 | 5415篇 |
2001年 | 5818篇 |
2000年 | 5282篇 |
1999年 | 4063篇 |
1998年 | 2897篇 |
1997年 | 2537篇 |
1996年 | 2809篇 |
1995年 | 3254篇 |
1994年 | 3276篇 |
1993年 | 3342篇 |
1992年 | 2874篇 |
1991年 | 2415篇 |
1990年 | 2070篇 |
1989年 | 2180篇 |
1988年 | 2122篇 |
1987年 | 1369篇 |
1986年 | 1398篇 |
1985年 | 966篇 |
1984年 | 1107篇 |
1983年 | 515篇 |
1982年 | 997篇 |
1981年 | 819篇 |
1980年 | 830篇 |
1979年 | 602篇 |
1978年 | 560篇 |
1977年 | 642篇 |
1976年 | 1053篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
针对智能化柔性制造过程存在的再制造过程,对中小型设备生产车间及其仓储转运的模型构建、分析方法、以及参量相关性提出了新的解决思路.为了最大限度的减少建设周期、合理化投资成本、以及优化生产流程,建立了考虑非结构性的多级生产流程的数学模型,以完成度、完工时间和调度频次为目标函数分析生产要素间的相关性.实验结果表明,融合再加工过程的智能化柔性制造单元中,生产要素为非线性相关,个别要素具备对称性,为实际工况中的生产改进及优化提供了一定理论基础. 相似文献
12.
13.
15.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface. 相似文献
16.
Summary Carbon deposits on the surface ofRu/Fe2O3 catalysts used in the water-gas shift reaction have been investigated by Auger Electron Spectrometry. A correlation has been
found between the thickness of the carbon deposit and the catalytic activity in WGSR. The carbon deposit covers the metallic
active centers and blocks their contact with reagents. The dotting of the iron oxide support with sodium has been found to
reduce the amount of carbon deposit. . 相似文献
17.
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
18.
Ji-Dong Lou Chun-Ling Gao Li Li Zhi-Gang Fang 《Monatshefte für Chemie / Chemical Monthly》2006,41(10):1071-1074
A new procedure for the selective oxidation of alcohols to the corresponding aldehydes and ketones with potassium permanganate
supported on aluminum silicate at room temperature under solvent-free conditions and shaking is reported. 相似文献
19.
The possibility of realizing SASE Free Election Laser in x-ray waveband with EM-wave wiggler is studied in this paper. SASE effect including saturation length, saturation power and nonlinear process is explored through a 3-D simulation code. A utilization of seed light from laser plasma x-ray is also analyzed, which demonstrates the feature of shortening the interaction length for saturation. The results show that sizeable output power of x-ray laser would be generated with a middle energy electron beam. 相似文献
20.