全文获取类型
收费全文 | 407609篇 |
免费 | 3450篇 |
国内免费 | 949篇 |
专业分类
化学 | 189662篇 |
晶体学 | 6450篇 |
力学 | 21390篇 |
综合类 | 7篇 |
数学 | 59849篇 |
物理学 | 134650篇 |
出版年
2021年 | 3117篇 |
2020年 | 3329篇 |
2019年 | 3762篇 |
2018年 | 11918篇 |
2017年 | 12617篇 |
2016年 | 10500篇 |
2015年 | 4817篇 |
2014年 | 7122篇 |
2013年 | 16002篇 |
2012年 | 15760篇 |
2011年 | 24768篇 |
2010年 | 16808篇 |
2009年 | 16792篇 |
2008年 | 21812篇 |
2007年 | 24596篇 |
2006年 | 12304篇 |
2005年 | 15892篇 |
2004年 | 12517篇 |
2003年 | 11452篇 |
2002年 | 9859篇 |
2001年 | 10518篇 |
2000年 | 7932篇 |
1999年 | 5998篇 |
1998年 | 5002篇 |
1997年 | 4823篇 |
1996年 | 4645篇 |
1995年 | 3958篇 |
1994年 | 3904篇 |
1993年 | 3777篇 |
1992年 | 4159篇 |
1991年 | 4374篇 |
1990年 | 4167篇 |
1989年 | 4083篇 |
1988年 | 3862篇 |
1987年 | 3994篇 |
1986年 | 3756篇 |
1985年 | 4713篇 |
1984年 | 4777篇 |
1983年 | 3975篇 |
1982年 | 4055篇 |
1981年 | 3781篇 |
1980年 | 3734篇 |
1979年 | 4015篇 |
1978年 | 4016篇 |
1977年 | 3931篇 |
1976年 | 3940篇 |
1975年 | 3722篇 |
1974年 | 3663篇 |
1973年 | 3723篇 |
1972年 | 2638篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
971.
972.
We review data on methods for synthesis, chemical and pharmacological properties of pyrido[1,2-a)pyrimidines.Scientific-Research Institute of Pharmacology of the Russian Academy of Medical Sciences, All-Union Science Center for Biologically Active Substances, Staraya Kupavna, 124432. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 579–596, May, 1994. Original article submitted March 3, 1994. 相似文献
973.
The interactions of Cu(II) in Cu(II)-exchanged K-L gallosilicate with adsorbates containing coordinative nitrogens in ammonia, pyridine, aniline, acetonitrile and hydrazine, and with the adsorbates carbon monoxide, benzene, propanol and dimethyl sulfoxide are investigated by electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies. These results are compared with those in Cu(II)-exchanged K-L aluminosilicate and the differences are discussed. Adsorption of ammonia produces a complex containing four molecules of ammonia based on resolved nitrogen superhyperfine interaction. Upon equilibrium with pyridine, Cu(II) forms a complex containing four molecules of pyridine in CuK-L gallosilicate and a complex containing only three molecules of pyridine in CuK-L aluminosilicate based on resolved nitrogen superhyperfine. Upon adsorption of aniline and acetonitrile, Cu(II) forms complexes containing two molecules of each in CuK-L gallosilicate based on resolved nitrogen superhyperfine. However, no resolved nitrogen superhyperfine between hydrazine and Cu(II) is seen. Adsorption of carbon monoxide, benzene, propanol and dimethyl sulfoxide causes changes in the ESR spectrum of Cu(II), indicating migration of Cu(II) into cation positions in the main channels where adsorbate coordination can occur. Cu(II) forms complexes with one molecule of benzene and two molecules of propanol based on ESEM data in both K-L gallosilicate and K-L aluminosilicate. However, Cu(II) interacts directly with one dimethyl sulfoxide in K-L aluminosilicate but only indirectly at a longer distance with one dimethyl sulfoxide in K-L gallosilicate based on ESEM data. 相似文献
974.
A. A. Bormisov E. S. Gudkova F. Kh. Mukminov 《Theoretical and Mathematical Physics》1997,113(2):1418-1430
We consider equations of the form Uxy = U * Ux, where U(x, y) is a function taking values in an arbitrary finite-dimensional algebra T over the field ℂ. We show that every
such equation can be naturally associated with two characteristic Lie algebras, Lx and Ly. We define the notion of a ℤ-graded Lie algebraB corresponding to a given equation. We prove that for every equation under consideration, the corresponding algebraB can be taken as a direct sum of the vector spaces Lx and Ly if we define the commutators of the elements from Lx and Ly by means of the zero-curvature relations. Assuming that the algebra T has no left ideals, we classify the equations of the
specified type associated with the finite-dimensional characteristic Lie algebras Lx and Ly. All of these equations are Darboux-integrable.
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 113, No. 2, pp. 261–275, November, 1997. 相似文献
975.
S. K. Godovikov 《JETP Letters》1998,68(8):629-633
In research on the production of beams of coherent γ rays (γ-ray lasers), conditions under which a substantial change Δλ/λ=?(0.114 ±0.027) in the radioactive decay constant λ (the isomeric level 89.53 keV 119m Sn, T 1/2=293 days) can occur have been found experimentally for the first time. This is made possible by coherent Mo ssbauer (23.87 keV) backscattering from a resonant screen located nearby. An interpretation of the effect observed is proposed on the basis of the idea of dynamic synchronization of oscillations between a nuclear level and a standing wave of Mössbauer radiation. Possibilities for further increasing Δλ/λ up to 0.5 are found. 相似文献
976.
The dependence of the type of magnetic ordering in multilayer structures on the magnitude of the exchange interaction between
the magnetic layers and on the degree of roughness of the interfaces between the layers is investigated. In the case of a
three-layer system the regions of existence of the domain structure, of noncollinear ordering of the homogeneous magnetic
layers, and of the collinear ferromagnetic phase and collinear antiferromagnetic phase are found.
Fiz. Tverd. Tela (St. Petersburg) 39, 1244–1247 (July 1997) 相似文献
977.
978.
E. S. Sinaiskii 《Ukrainian Mathematical Journal》1997,49(11):1768-1776
We consider an integral equation describing the contagion phenomenon, in particular, the equation of the state of a hereditarily
elastic body, and interpret this equation as a stochastic model in which the Rabotnov exponent of fractional order plays the
role of density of probability of random delay time. We invesgigate the approximation of the distribution for sums of values
with a given density to the stable distribution law and establish the principal characteristics of the corresponding renewal
process.
Ukrainian Mining Academy, Dnepropetrovsk. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 49, No. 11, pp. 1572–1579,
November, 1997. 相似文献
979.
V. D. Dyachenko S. G. Krivokolysko Yu. A. Sharanin V. P. Litvinov 《Chemistry of Heterocyclic Compounds》1997,33(7):793-798
Ammonium 6-amino-4-aryl-3,5-dicyano-1,4-dihydropyridine-2-thiolates were synthesized by recyclization of 4-aryl-2,6-diamino-3,5-dicyano-4H-thiopyranes in the presence of organic bases. On acidification of the products, the corresponding substituted 3,4-dihydropyridine-2(1H)-thiones were obtained which were used in the synthesis of 2-alkylthio-1,4-dihydropyridines, bis-(pyridyl-2)disulfides and thieno[2,3-b]pyridines.Deceased.T. G. Shevchenko Lugansk State Pedagogical Institute, Lugansk 348011. N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 909–914, July, 1997. 相似文献
980.