全文获取类型
收费全文 | 146937篇 |
免费 | 1293篇 |
国内免费 | 397篇 |
专业分类
化学 | 80140篇 |
晶体学 | 2387篇 |
力学 | 6063篇 |
综合类 | 3篇 |
数学 | 13566篇 |
物理学 | 46468篇 |
出版年
2021年 | 1031篇 |
2020年 | 1181篇 |
2019年 | 1249篇 |
2018年 | 1638篇 |
2017年 | 1689篇 |
2016年 | 2540篇 |
2015年 | 1559篇 |
2014年 | 2348篇 |
2013年 | 6031篇 |
2012年 | 4840篇 |
2011年 | 5931篇 |
2010年 | 4180篇 |
2009年 | 4206篇 |
2008年 | 5722篇 |
2007年 | 5504篇 |
2006年 | 5377篇 |
2005年 | 4941篇 |
2004年 | 4445篇 |
2003年 | 4114篇 |
2002年 | 4005篇 |
2001年 | 5541篇 |
2000年 | 3970篇 |
1999年 | 3072篇 |
1998年 | 2109篇 |
1997年 | 2207篇 |
1996年 | 2069篇 |
1995年 | 1915篇 |
1994年 | 1912篇 |
1993年 | 1725篇 |
1992年 | 2213篇 |
1991年 | 2298篇 |
1990年 | 2134篇 |
1989年 | 2099篇 |
1988年 | 2076篇 |
1987年 | 2085篇 |
1986年 | 1909篇 |
1985年 | 2370篇 |
1984年 | 2391篇 |
1983年 | 1909篇 |
1982年 | 1913篇 |
1981年 | 1751篇 |
1980年 | 1737篇 |
1979年 | 2026篇 |
1978年 | 2100篇 |
1977年 | 2046篇 |
1976年 | 1975篇 |
1975年 | 1859篇 |
1974年 | 1842篇 |
1973年 | 1874篇 |
1972年 | 1235篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
T. A. Beu 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,27(3):263-266
New analytical formulas for the torsionL-tensor are reported, which are used in molecular normal mode analysis calculations for the nonlinear transformation of the force constants from internal coordinates to normal coordinates. The proposed formalism exhibits a relative simplicity as compared to previous reported results. Sample calculations for methanol and hydrazine are presented. 相似文献
12.
13.
Summary The main purpose of this paper is to introduce the concepts of η-sets, ηζ-sets,η-continuity and ηζ-continuity and to obtain
a decomposition of continuity. 相似文献
14.
The paper mentioned above is a contribution of the authors to Volume 18 (2002) of this journal, see . Recently, J. Domsta pointed out to us that the proof of Theorem 4.2 in that paper contains an error. The purpose of this
addendum is to present a correct argument for it. 相似文献
15.
Zarubitskii O. G. Budnik V. G. Omel'chuk A. A. Melekhin V. T. Opanasyuk V. P. Zakharchenko N. F. 《Russian Journal of Applied Chemistry》2002,75(4):558-561
Electrochemical separation of lead-silver alloys into the constituents by thin-layer electrolysis in molten electrolytes, with bismuth as metal separator, is studied. It is proposed to determine the extent of component recovery by potentiometry. 相似文献
16.
Data Envelopment Analysis (DEA) offers a piece-wise linear approximation of the production frontier. The approximation tends to be poor if the true frontier is not concave, eg in case of economies of scale or of specialisation. To improve the flexibility of the DEA frontier and to gain in empirical fit, we propose to extend DEA towards a more general piece-wise quadratic approximation, called Quadratic Data Envelopment Analysis (QDEA). We show that QDEA gives statistically consistent estimates for all production frontiers with bounded Hessian eigenvalues. Our Monte-Carlo simulations suggest that QDEA can substantially improve efficiency estimation in finite samples relative to standard DEA models. 相似文献
17.
A numerical procedure, with an exact strain-displacement relationship of twisted and curved cylindrical panels having variable thickness derived by considering the Green strain tensor on general shell theory, is presented using the principle of virtual work and the Rayleigh-Ritz method with algebraic polynomials as in-plane and transverse displacement functions. The accuracy and applicability of the procedure are verified by comparing the present results with previous experimental and theoretical results for several panels. The effects of variation ratio of thickness in chordwise and lengthwise directions, twist, and curvature both in two directions aforementioned on vibrations of cylindrical panels are studied in detail, and typical vibration mode shapes are plotted to demonstrate the effects. 相似文献
18.
19.
K Kawasaki T Tsuji K Hirase M Miyano Y Imoto M Iwamoto 《Chemical & pharmaceutical bulletin》1991,39(3):584-589
N-Terminal tripeptide analogs of fibrin alpha-chain were synthesized and their inhibitory effect on fibrinogen/thrombin clotting was examined. A new water-soluble active ester, 3-pyridinium ester, was used for the synthesis. Among the synthetic peptides, H-Gly-Pro-Arg-hexamethyleneimine exhibited the highest inhibitory effect on fibrinogen-thrombin clotting. 相似文献
20.
The structural properties of polycrystalline silicon films, prepared by plasma enhanced chemical vapor deposition system, with different flow rates of SiH4/SiF4 mixtures at 300 °C were investigated. This study indicates that the low hydrogen coverage on the growing surface, under optimum fluorine radicals, will be leaded to an improvement of crystallized area as compared with case of high hydrogen coverage surface. Moreover, the studies of the role of SiH4 and SiF4 radicals show that the SiH4 radicals are important in the nucleation and growth of grains. However, SiF4 radicals are effective in the structural change of grain boundaries regions and by this way, in the present system, establish the growth of grains under the dominant 〈1 1 0〉 direction. The stress investigation indicates that addition of high flow rate of SiF4 in amorphous film, results in the nearly stress free films. Finally, we found that the changes in g-value reflect the changes in the intrinsic compressive and tensile stress in the both polycrystalline and amorphous silicon films. 相似文献