全文获取类型
收费全文 | 1344624篇 |
免费 | 29717篇 |
国内免费 | 7707篇 |
专业分类
化学 | 674501篇 |
晶体学 | 20250篇 |
力学 | 74657篇 |
综合类 | 108篇 |
数学 | 241185篇 |
物理学 | 371347篇 |
出版年
2021年 | 13527篇 |
2020年 | 15948篇 |
2019年 | 16073篇 |
2016年 | 27679篇 |
2015年 | 20731篇 |
2014年 | 30422篇 |
2013年 | 74438篇 |
2012年 | 38078篇 |
2011年 | 34818篇 |
2010年 | 36850篇 |
2009年 | 39187篇 |
2008年 | 34165篇 |
2007年 | 29641篇 |
2006年 | 36435篇 |
2005年 | 28242篇 |
2004年 | 29733篇 |
2003年 | 28265篇 |
2002年 | 29383篇 |
2001年 | 29776篇 |
2000年 | 25526篇 |
1999年 | 22909篇 |
1998年 | 21176篇 |
1997年 | 21243篇 |
1996年 | 21146篇 |
1995年 | 19227篇 |
1994年 | 18655篇 |
1993年 | 18187篇 |
1992年 | 18387篇 |
1991年 | 18685篇 |
1990年 | 17919篇 |
1989年 | 17959篇 |
1988年 | 17521篇 |
1987年 | 17492篇 |
1986年 | 16412篇 |
1985年 | 22771篇 |
1984年 | 23971篇 |
1983年 | 20079篇 |
1982年 | 21706篇 |
1981年 | 20919篇 |
1980年 | 20266篇 |
1979年 | 20592篇 |
1978年 | 21789篇 |
1977年 | 21454篇 |
1976年 | 21208篇 |
1975年 | 19851篇 |
1974年 | 19582篇 |
1973年 | 20009篇 |
1972年 | 14483篇 |
1968年 | 12339篇 |
1967年 | 12686篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
J. E. Fischer E. Werwa P. A. Heiney 《Applied Physics A: Materials Science & Processing》1993,56(3):193-196
We have used both reflection-geometry and grazing-incidence-geometry X-ray scattering to study thin films of C60 evaporated onto mica substrates via a hot-wall technique. The growth mode yields close-packed C60 planes, which are parallel to the substrate surface and which exhibit out-of-plane correlation lengths of 850 Å. In the film plane the C60 is at best pseudo-epitaxial, with a 0.9° distribution of crystallite orientations, a 450 Å in-plane correlation length, and a 3.7% lattice mismatch, better than obtained by other thin film techniques but far from the accepted definition of single crystal thin film epitaxy. 相似文献
882.
A simple method is proposed for increasing the accuracy of computation of the eigenvalues of elliptic operators, which does not require high-order accurate schemes.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 63, pp. 63–68, 1987. 相似文献
883.
Summary Consider the solution of one-dimensional linear initial-boundary value problems by a finite element method of lines using a piecewiseP
th
-degree polynomial basis. A posteriori estimates of the discretization error are obtained as the solutions of either local parabolic or local elliptic finite element problems using piecewise polynomial corrections of degreep+1 that vanish at element ends. Error estimates computed in this manner are shown to converge in energy under mesh refinement to the exact finite element discretization error. Computational results indicate that the error estimates are robust over a wide range of mesh spacings and polynomial degrees and are, furthermore, applicable in situations that are not supported by the analysis.This research was partially supported by the U.S. Air Force Office of Scientific Research, Air Force Systems Command, USAF, under Grant Number AFOSR 90-0194; by the U.S. Army Research Office under Contract Number DAAL03-91-G-0215; and by the National Science Foundation under Institutional Infrastructure Grant Number CDA-8805910 相似文献
884.
V. M. Shopa B. N. Polevoi I. I. Popadyuk V. I. Tusevich 《Journal of Mathematical Sciences》1993,63(3):398-401
We propose a method of determining the contact pressures between the shells in a packet under the influence of nonlinear internal and constant external pressure. Using the equations of the general moment theory of shells we determine the stress-deformed state of a packet of finite cylindrical shells taking account of frictional forces on the contacting surfaces. One table. Bibliography: 10 titles.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 30, 1989, pp. 94–98. 相似文献
885.
I. V. Ukrainets S. G. Taran O. V. Gorokhova P. A. Bezuglyi A. V. Turov 《Chemistry of Heterocyclic Compounds》1994,30(2):204-207
In a solution of DMF, 2-carbethoxymethyl-4H-3,1-benzoxazin-4-one reacts with primarily aromatic amines basically with the formation of the corresponding 2-carbethoxymetlzyl-3-arylquinazolin-4(3H)-ones. Possible mechanisms of these chemical transformations are reported and discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 225–228, February, 1994. Original article submitted June 28, 1993. 相似文献
886.
I. M. Karnaukh A. S. Moskovkin G. V. Ponomarev 《Chemistry of Heterocyclic Compounds》1994,30(1):20-25
The mass spectral behavior of 1, 2-di (mesoetioporphyr inyl-1)- and 1, 2-di (mesooctaethylporphyrlnyl) ethanes and ethylenes, their Cu and Ni complexes, as well as Ni Schiff bases of 1, 2-di (mesooctaethylporphyrinyl)ethane complexes, under ionization by electron impact and bombardment by accelerated atoms, was studied. Peaks of molecular ions, for which the basic decomposition pathways were established on the basis of an analysis of the parent and daughter ions, were observed in the electron impact mass spectra of all these compounds.For Communication 29, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 24–29, January, 1994. 相似文献
887.
Translated from Khimiya Geterotsiklicheskikh Soedinenii. Vol. 30. No. 3, pp. 424–425, March, 1994. 相似文献
888.
V. A. Samsonov L. B. Volodarskii V. L. Korolev G. Kh. Khisamutdinov 《Chemistry of Heterocyclic Compounds》1994,30(10):1243-1249
The reaction of 4-aminobenzofurazan with aryldiazonium salts leads to the formation of 4-amino-5-aryl-azobenzofurazans and 5-amino-2-aryl-4-nitroso-2H-benzotriazoles, products of the rearrangement of the initially formed 4-amino-7-(arylazo)benzofurazans. Oxidation of the benzofurazan as well as of the triazole derivatives gives 7-aryl-1,2,3-triazol[4,5-e]benzofurazans. The chemical properties of some of the compounds obtained have been investigated.Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1432–1438, October, 1994. Original article submitted July 25, 1994. 相似文献
889.
Molecular n-v complexes of quinoline N-oxides with BF3 have been studied by electronic and IR spectroscopy. In most case the donor centre is the oxygen atom of the N-oxide group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1087–1092, August, 1994. 相似文献
890.
A. V. Anisimov A. A. Grishkyan Kh. A. Gaisina E. A. Viktorova 《Chemistry of Heterocyclic Compounds》1994,30(4):420-421
1-Allyloxy-2-allylthio-4-methylbenzene rearranges in NN-diethylaniline at 215°C with migration of allyloxy and allylthio groups to form 2,4-dimethyl-6-allyl-7-hydroxy-2,3dihydrobenzothiophene.M. V. Lomonosov State University, Moscow 119899. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 480–482, 1994. Original article submitted March 5, 1994. 相似文献