全文获取类型
收费全文 | 113942篇 |
免费 | 32873篇 |
国内免费 | 26924篇 |
专业分类
化学 | 47794篇 |
晶体学 | 941篇 |
力学 | 5292篇 |
综合类 | 202篇 |
数学 | 10263篇 |
物理学 | 53514篇 |
综合类 | 55733篇 |
出版年
2024年 | 545篇 |
2023年 | 886篇 |
2022年 | 901篇 |
2021年 | 977篇 |
2020年 | 1836篇 |
2019年 | 4900篇 |
2018年 | 4977篇 |
2017年 | 5843篇 |
2016年 | 6120篇 |
2015年 | 6088篇 |
2014年 | 6005篇 |
2013年 | 7089篇 |
2012年 | 6783篇 |
2011年 | 9766篇 |
2010年 | 12387篇 |
2009年 | 12386篇 |
2008年 | 4699篇 |
2007年 | 4171篇 |
2006年 | 3397篇 |
2005年 | 3948篇 |
2004年 | 6291篇 |
2003年 | 4681篇 |
2002年 | 4053篇 |
2001年 | 3904篇 |
2000年 | 2855篇 |
1999年 | 3218篇 |
1998年 | 2802篇 |
1997年 | 2576篇 |
1996年 | 2601篇 |
1995年 | 3042篇 |
1994年 | 3137篇 |
1993年 | 3560篇 |
1992年 | 3062篇 |
1991年 | 2741篇 |
1990年 | 2211篇 |
1989年 | 2248篇 |
1988年 | 2256篇 |
1987年 | 1308篇 |
1986年 | 1401篇 |
1985年 | 941篇 |
1984年 | 1025篇 |
1982年 | 904篇 |
1981年 | 731篇 |
1980年 | 769篇 |
1979年 | 526篇 |
1978年 | 530篇 |
1977年 | 633篇 |
1976年 | 1041篇 |
1973年 | 436篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
21.
用正交试验法优化手性镍催化二乙基锌对α,β不饱和酮的不对称麦克尔加成反应条件,优化后的不对称麦克尔加成反应的一般条件为:低温(近反应溶剂冰点),常压,非质子非极性溶剂(环己烷). 相似文献
22.
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
23.
In this paper,the new development of three basic theories of Extenics,incluing basic-element theory,extension set theory and extension logic theory ,has been introduced.And the new theoretical frame of Extenics has also been set forth. 相似文献
24.
The use of supercritical fluid carbon dioxide (SF-CO_2) in extraction of lanolin and its alcohol issuperior to the conventional solvent extractionmethod. Its distinctive advantages include highextractive ratio, nontoxic and nonflammablesolvents, and minimal by-product pollution. The 相似文献
25.
The tracing evaluation index system was designed to be used in virtual enterprise and established neural network trace evaluation model. As a result, it was more simple and nicer than the traditional method, so it had wider application foreground. 相似文献
26.
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
27.
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
28.
自主机器人人工进化方法研究 总被引:1,自引:0,他引:1
在介绍人工进化研究状况的基础上 ,着重阐述了进化机器人学的关键问题 :基本概念、进化技术、进化计算和实验研究方法等 ,探索了进化机器人学未来的研究趋势及所面临的挑战 . 相似文献
29.
A face recognition system based on Support Vector Machine(SVM) and Hidden Markov Model (HMM) has been proposed. The powerful discriminative ability of SVM is combined with the temporal modeling ability of HMM. The output of SVM is moderated to be probability output, which replaces the Mixture of Gauss (MOG) in HMM. Wavelet transformation is used to extract observation vector, which reduces the data dimension and improves the robustness.The hybrid system is compared with pure HMM face recognition method based on ORL face database and Yale face database. Experiments results show that the hybrid method has better performance. 相似文献
30.
The shrink proofing on wool with treatment of protease named Argaenzyme STL was studied. The various pretreating auxiliaries, different parameters for protease treating process and the effect of stabilizer were discussed in detail. The varieties of some properties before and after protease treatment were also investigated. 相似文献