全文获取类型
收费全文 | 309552篇 |
免费 | 10618篇 |
国内免费 | 2248篇 |
专业分类
化学 | 182271篇 |
晶体学 | 4479篇 |
力学 | 12587篇 |
综合类 | 1篇 |
数学 | 34578篇 |
物理学 | 88502篇 |
出版年
2021年 | 2297篇 |
2020年 | 3617篇 |
2019年 | 5137篇 |
2018年 | 4547篇 |
2017年 | 3968篇 |
2016年 | 8278篇 |
2015年 | 6721篇 |
2014年 | 8249篇 |
2013年 | 16235篇 |
2012年 | 13190篇 |
2011年 | 14556篇 |
2010年 | 11104篇 |
2009年 | 10674篇 |
2008年 | 13550篇 |
2007年 | 13022篇 |
2006年 | 11970篇 |
2005年 | 11286篇 |
2004年 | 10192篇 |
2003年 | 8885篇 |
2002年 | 9286篇 |
2001年 | 9016篇 |
2000年 | 7125篇 |
1999年 | 4987篇 |
1998年 | 3926篇 |
1997年 | 3802篇 |
1996年 | 3734篇 |
1995年 | 3298篇 |
1994年 | 3272篇 |
1993年 | 3370篇 |
1992年 | 3486篇 |
1991年 | 3620篇 |
1990年 | 3348篇 |
1989年 | 3293篇 |
1988年 | 3287篇 |
1987年 | 3167篇 |
1986年 | 2984篇 |
1985年 | 4123篇 |
1984年 | 4292篇 |
1983年 | 3390篇 |
1982年 | 3692篇 |
1981年 | 3579篇 |
1980年 | 3442篇 |
1979年 | 3541篇 |
1978年 | 3628篇 |
1977年 | 3521篇 |
1976年 | 3666篇 |
1975年 | 3315篇 |
1974年 | 3345篇 |
1973年 | 3382篇 |
1972年 | 2319篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
A. J. Maroulis P. D. Akrivos C. P. Hadjiantoniou-Maroulis 《Journal of heterocyclic chemistry》1993,30(4):913-916
Oxidation of the title compounds yields, besides the reported isoimides 3 and/or the amides 4 , also the imides 5 . The observed product dichotomy is considered as the result of an intramolecular nucleophilic attack on the aroyl group, of the pressumed zwitterionic intermediate 2 , by O or N present in the ambident N-aroylimine site of 2 . The results of AM1 calculations agree with the product studies and both permit the formulation of a set of rules correlating structure and selectivity. 相似文献
32.
33.
34.
In this paper, the authors studied certain properties of the estimate of Liang and Krishnaiah (1985, J. Multivariate Anal. 16, 162–172) for multivariate binary density. An alternative shrinkage estimate is also obtained. The above results are generalized to general orthonormal systems. 相似文献
35.
36.
We consider the growth of a spherical crystal in a supersaturatedsolution. In the first part, existence and uniqueness resultsfor radially symmetric growth are obtained, provided that thesupersaturation is not too large; conversely, when the far-fieldsupersaturation exceeds a critical value, it is shown that theradially symmetric solution ceases to exist in finite time.In the second part, we examine the linear stability of a radiallysymmetric similarity solution (in which the radius grows ast?) to shape perturbations. The results are compared with previousquasi-static analyses, and, in particular, the critical radiusat which the crystal becomes unstable is found to be largerfor small supersaturations, but smaller for large supersaturations,than those predicted by the quasi-static analysis 相似文献
37.
38.
J. Maul I. Strachnov S. Karpuk P. Bernhard A. Oelsner G. Schönhense G. Huber 《Applied Physics A: Materials Science & Processing》2006,82(1):43-47
We report morphologic changes of metallic surfaces at the onset of ablation, starting from gentle ablation to the emergence of ablation craters. The evolution of both observed melting zones and of ablation craters therein are investigated in dependence of the ablation laser fluence for nanosecond ultraviolet laser pulses. Further, consequences of crater formation for cluster synthesis within the released atomic vapor are pointed out. PACS 52.38.Mf; 79.20.Ds; 65.40.De 相似文献
39.
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
40.
J. C. Fabris S. V. B. Gonçalves P. E. de Souza 《General Relativity and Gravitation》2002,34(12):2111-2126
The mass power spectrum for a Universe dominated by the Chaplygin gas is evaluated numerically from scales of the order of the Hubble horizon to 100 Mpc. The results are compared with a pure baryonic Universe and a cosmological constant model. In all three cases, the spectrum increases with k, the wavenumber of the perturbations. The slope of the spectrum is higher for the baryonic model and smaller for the cosmological constant model, the Chaplygin gas interpolating these two models. The results are analyzed in terms of the sound velocity of the Chaplygin gas and the moment the Universe begins to accelerate. 相似文献