全文获取类型
收费全文 | 134578篇 |
免费 | 1278篇 |
国内免费 | 400篇 |
专业分类
化学 | 67970篇 |
晶体学 | 2242篇 |
力学 | 6439篇 |
综合类 | 9篇 |
数学 | 12417篇 |
物理学 | 47179篇 |
出版年
2022年 | 1133篇 |
2021年 | 1326篇 |
2020年 | 1383篇 |
2019年 | 1502篇 |
2018年 | 2148篇 |
2017年 | 2165篇 |
2016年 | 3011篇 |
2015年 | 1637篇 |
2014年 | 2682篇 |
2013年 | 5693篇 |
2012年 | 5130篇 |
2011年 | 6168篇 |
2010年 | 4687篇 |
2009年 | 4729篇 |
2008年 | 5600篇 |
2007年 | 5336篇 |
2006年 | 5108篇 |
2005年 | 4485篇 |
2004年 | 4143篇 |
2003年 | 3752篇 |
2002年 | 3710篇 |
2001年 | 5109篇 |
2000年 | 3697篇 |
1999年 | 2755篇 |
1998年 | 2173篇 |
1997年 | 2052篇 |
1996年 | 1750篇 |
1995年 | 1590篇 |
1994年 | 1494篇 |
1993年 | 1415篇 |
1992年 | 1794篇 |
1991年 | 1861篇 |
1990年 | 1701篇 |
1989年 | 1638篇 |
1988年 | 1532篇 |
1987年 | 1545篇 |
1986年 | 1379篇 |
1985年 | 1726篇 |
1984年 | 1774篇 |
1983年 | 1371篇 |
1982年 | 1387篇 |
1981年 | 1279篇 |
1980年 | 1195篇 |
1979年 | 1376篇 |
1978年 | 1532篇 |
1977年 | 1568篇 |
1976年 | 1372篇 |
1975年 | 1251篇 |
1974年 | 1305篇 |
1973年 | 1209篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
Using the DFT/B3LYP method with a 6-31G(d) basis set, the structure, normal vibration frequencies, and the absolute band intensities in the IR spectra of the chlorin molecule and its four symmetric isotopomers have been calculated. Scaling of the force field by the Pulay method in independent and natural coordinates has been carried out. A method for obtaining effective force fields without using experimental data on the fundamental vibration frequencies is proposed. By comparing the vibration modes and constructing special matrices, complete assignment of the fundamental frequencies of porphin and chlorin has been carried out. It has been shown that the majority of porphin macroring vibrations upon pyrrolenine ring hydrogenation are frequency-characteristic and only 12 vibrations change considerably. A frequency correlation with regard for the mode transition between chlorin and all its isotopomers under consideration has been established. Comparative analysis of the force fields of porphin and chlorin in dependent natural coordinates has revealed the unique nonlocal character of the change in force constants of the macroring upon hydrogenation of one pyrrolenine ring. Modeling of the IR spectra of chlorin and its isotopomers has been performed. Assignment and interpretation of the normal vibrations of the molecules under consideration have been carried out. 相似文献
95.
96.
C Guéret N Jussien O Lhomme C Pavageau C Prins 《The Journal of the Operational Research Society》2003,54(5):458-465
In this paper, we describe an aircraft loading problem submitted by the French military agency (DGA) as part of a more general military airlift planning problem. It can be viewed as a kind of bi-dimensional bin-packing problem, with heterogeneous bins and several additional constraints. We introduce two-phase methods for solving this NP-hard problem. The first phase consists in building good initial solutions, thanks to two fast algorithms: a list-based heuristic and a loading pattern generation method. Both algorithms call a constraint-based subroutine, able to determine quickly if the items already loaded can be reshuffled to accommodate a new object. The second phase improves these preliminary solutions using local search techniques. Results obtained on real data sets are presented. 相似文献
97.
O. A. Mulyar 《Journal of Mathematical Sciences》2005,130(3):4735-4746
In the paper we describe automorphisms and derivations of simple Lie algebras of family R. The Lie algebra of the automorphism group is found. Bibliography: 11 titles.__________Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 305, 2003, pp. 165–186. 相似文献
98.
It is shown that the three-dimensional Navier-Stokes equation for incompressible fluid can be represented as an equation including
only quaternions as co-ordinate operators and variables. Only the quaternion operations such as a quaternion product and a
quaternion conjugation over these variables are used. 相似文献
99.
Data on methods for the production of isatin and indole aldoximes, ketoximes, and amidoximes and their reactions are reviewed. Individual syntheses of new heterocycles from indole and isatin oximes are discussed. The principal results from investigation of the biological activity of derivatives of the oximes are also presented. 相似文献
100.
The influence of ultrasonic shock treatment on variation in the pearlite structure and properties is studied in the surface layer of carburized steel. It is shown that plastic deformation results in carbon redistribution and formation of new phases. 相似文献