全文获取类型
收费全文 | 615431篇 |
免费 | 5386篇 |
国内免费 | 1444篇 |
专业分类
化学 | 308326篇 |
晶体学 | 8981篇 |
力学 | 30840篇 |
综合类 | 20篇 |
数学 | 84996篇 |
物理学 | 189098篇 |
出版年
2021年 | 4873篇 |
2020年 | 5323篇 |
2019年 | 5944篇 |
2018年 | 13127篇 |
2017年 | 13529篇 |
2016年 | 13912篇 |
2015年 | 7190篇 |
2014年 | 10916篇 |
2013年 | 24873篇 |
2012年 | 21859篇 |
2011年 | 31020篇 |
2010年 | 21465篇 |
2009年 | 21606篇 |
2008年 | 28324篇 |
2007年 | 30358篇 |
2006年 | 20042篇 |
2005年 | 21589篇 |
2004年 | 18533篇 |
2003年 | 16899篇 |
2002年 | 15680篇 |
2001年 | 16756篇 |
2000年 | 12755篇 |
1999年 | 9848篇 |
1998年 | 8330篇 |
1997年 | 7967篇 |
1996年 | 7755篇 |
1995年 | 6977篇 |
1994年 | 6886篇 |
1993年 | 6710篇 |
1992年 | 7261篇 |
1991年 | 7612篇 |
1990年 | 7252篇 |
1989年 | 7150篇 |
1988年 | 7053篇 |
1987年 | 6943篇 |
1986年 | 6587篇 |
1985年 | 8492篇 |
1984年 | 8596篇 |
1983年 | 6954篇 |
1982年 | 7101篇 |
1981年 | 6989篇 |
1980年 | 6476篇 |
1979年 | 7089篇 |
1978年 | 7321篇 |
1977年 | 7248篇 |
1976年 | 7294篇 |
1975年 | 6712篇 |
1974年 | 6683篇 |
1973年 | 6842篇 |
1972年 | 4979篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
181.
William F. Bowlin 《The Journal of the Operational Research Society》1987,38(2):127-135
The objective of this research is to evaluate a new methodology, data envelopment analysis (DEA), as a tool for measuring and evaluating the operational efficiency of US Air Force organizations. This study involves the application of DEA to locate possible inefficiencies in the performance of US Air Force real-property maintenance activities. Dynamic behaviour, as exhibited via window analyses, is reviewed along with static counterparts. The testing was done in close coordination with Air Force officials, who reviewed the results for accuracy, validity and relevance. We conclude that this type of efficiency analysis does have value for the Air Force, where it can serve as a guide to auditors, budget programmers, managers and others in measuring, evaluating and enhancing operational efficiency. 相似文献
182.
183.
We study matter-wave solitons in Bose-Einstein condensates of ultracold gaseous atoms with spin degrees of freedom and present a class of exact solutions based on the inverse scattering method. The one-soliton solutions are classified with respect to the spin states. We analyze collisional effects between solitons in the same or different spin state(s), which reveals a very interesting possibility: we can manipulate the spin dynamics by controlling the parameters of colliding solitons. 相似文献
184.
185.
The acoustic field inside a shell excited by a spatially inhomogeneous harmonic pressure field is studied. The shell is assumed
to have a finite length, a set of orthogonal stiffening ribs, two ends bounding the acoustic volume, and a sound-insulating
structure, which includes layers of sound-insulating material, resonant elements, and an interior panel. The shell is considered
to be orthotropic with boundary conditions corresponding to a free support. For the acoustic field in the closed volume, analytical
expressions are derived with allowance for the elastoacoustic interaction of the shell with the sound-insulating layers and
with the medium both inside the shell (with arbitrary impedance values at the ends) and outside it. These expressions are
used to investigate the effect of different types of resonant systems on the sound field inside the shell. 相似文献
186.
An efficient synthesis of isothiazolidines in good yields is described. 相似文献
187.
188.
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
189.
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
190.
V. I. Korobov 《Few-Body Systems》2002,31(2-4):133-138
In this contribution we consider a phenomenon of metastable states in antiprotonic helium atoms, precise spectroscopy of
these states and a present-day study of the electromagnetic properties of antiprotons.
Received October 16, 2001; accepted for publication November 13, 2001 相似文献