全文获取类型
收费全文 | 261777篇 |
免费 | 1773篇 |
国内免费 | 538篇 |
专业分类
化学 | 134666篇 |
晶体学 | 4246篇 |
力学 | 13067篇 |
综合类 | 11篇 |
数学 | 29007篇 |
物理学 | 83091篇 |
出版年
2021年 | 2561篇 |
2020年 | 2684篇 |
2019年 | 3284篇 |
2018年 | 4719篇 |
2017年 | 4758篇 |
2016年 | 6282篇 |
2015年 | 3093篇 |
2014年 | 5529篇 |
2013年 | 11072篇 |
2012年 | 9007篇 |
2011年 | 10506篇 |
2010年 | 8363篇 |
2009年 | 8562篇 |
2008年 | 9882篇 |
2007年 | 9739篇 |
2006年 | 8785篇 |
2005年 | 7723篇 |
2004年 | 7325篇 |
2003年 | 6725篇 |
2002年 | 6713篇 |
2001年 | 7281篇 |
2000年 | 5396篇 |
1999年 | 4127篇 |
1998年 | 3621篇 |
1997年 | 3583篇 |
1996年 | 3267篇 |
1995年 | 2863篇 |
1994年 | 2941篇 |
1993年 | 2872篇 |
1992年 | 3182篇 |
1991年 | 3354篇 |
1990年 | 3190篇 |
1989年 | 3323篇 |
1988年 | 3149篇 |
1987年 | 3108篇 |
1986年 | 2977篇 |
1985年 | 3696篇 |
1984年 | 3858篇 |
1983年 | 3230篇 |
1982年 | 3248篇 |
1981年 | 3117篇 |
1980年 | 2903篇 |
1979年 | 3291篇 |
1978年 | 3404篇 |
1977年 | 3585篇 |
1976年 | 3486篇 |
1975年 | 3239篇 |
1974年 | 3219篇 |
1973年 | 3306篇 |
1972年 | 2512篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
Photoisomerization of provitamin D 3 (7-dehydrocholesterol) in a nematic liquid crystal (ZLI-1695, Merck) is investigated in detail by UV absorption spectroscopy. It is found that dissolution of chiral molecules of provitamin D 3 induces the cholesteric phase in a nematic. The spectral kinetics of photoisomerization in this phase changes significantly from that in an ethanol solution. A sharp nonmonotonic dependence of the increase in accumulation of trans isomer tachysterol in a liquid crystal matrix with a decrease in the induced cholesteric pitch from 2200 to 25 μm is revealed. 相似文献
93.
Evstafyeva I. T. Bozhenkov G. V. Aizina Ya. A. Rozenzveig I. B. Ermakova T. G. Levkovskaya G. G. Mirskova A. N. 《Russian Journal of Organic Chemistry》2002,38(8):1178-1182
1H-Pyrazoles, triazoles, and imidazoles in reaction with ethoxycarbonylimine and arylsulfonylimines of chloral yield addition products, corresponding 1-(1-amidotrichloroethyl)azoles. Derivatives of 1-alkylpyrazoles and pyrazolones react with chloral 4-chlorophenylsulfonylimine to furnish products of C-amidotrichloroethylation into position 4 of the azole ring. 相似文献
94.
The effect of hydrogen on the photoluminescence and planar conductivity of GaAs/InGaAs quantum-well heterostructures with an island Pd layer at the anodically oxidized surface was studied. Unlike continuous deposited Pd layers, island layers do not cause the formation of defects in the GaAs surface region and yet the Pd layer maintains high catalytic activity with respect to hydrogen. It is found that the thermal treatment of such a structure in a hydrogen atmosphere causes atomic-hydrogen passivation of the defects in quantum wells. Studies of the characteristics of planar photoresistors with an island Pd layer acting as hydrogen sensors show that their hydrogen detectivity is approximately two orders of magnitude higher than that of diode structures with continuous Pd layers. 相似文献
95.
96.
O. Ya. Savchenko 《Optics and Spectroscopy》2006,101(2):179-182
The efficiency with which a magnetic field acts on sublevels of the first and second doublets of a hydrogen-like atom is shown to vary because of relativistic effects by a factor of 1 ? 2γ(l + 1)/(2l + 3) and 1 ? 2γl/(2l ? 1), respectively, where γ is the ratio of the electron binding energy to the rest energy and l is the quantum number of the orbital angular momentum. 相似文献
97.
S. K. Godunov V. T. Zhukov O. B. Feodoritova 《Computational Mathematics and Mathematical Physics》2006,46(6):971-982
An algorithm is constructed for calculating invariant subspaces of symmetric hyperbolic systems arising in electromagnetic, acoustic, and elasticity problems. Discrete approximations are calculated for subspaces that correspond to minimal eigenvalues and smooth eigenfunctions. Difficulties related to the presence of an infinite-dimensional kernel in the differential operator are successfully handled. The efficiency of the algorithm is demonstrated using acoustics equations. 相似文献
98.
Kurenkov V. F. Zaitseva O. A. Kirdyashova G. N. 《Russian Journal of Applied Chemistry》2002,75(4):641-644
The kinetics of radical copolymerization of acrylamide with lithium, sodium, and potassium 2-acrylamido-2-methylpropanesulfonates in concentrated aqueous solutions in the presence of potassium persulfate as initiating agent at pH 9 and 50°C was studied by dilatometry. 相似文献
99.
Bairamov R. K. Ermakov A. I. Vedernikova N. R. 《Russian Journal of Applied Chemistry》2002,75(3):408-410
The influence exerted by the nature and concentration of a number of organic and mineral acids on the composition of products formed in electric-spark dispersion of aluminum was studied. 相似文献
100.
Shunin D. G. Filippova A. G. Okhotina N. A. Liakumovich A. G. Samuilov Ya. D. 《Russian Journal of Applied Chemistry》2002,75(6):1020-1023
Procedures are discussed for production of rubber-bitumen compounds based on spent rubber items. A possibility of using these binders for paving is studied experimentally. 相似文献