全文获取类型
收费全文 | 246031篇 |
免费 | 7117篇 |
国内免费 | 3888篇 |
专业分类
化学 | 139569篇 |
晶体学 | 3613篇 |
力学 | 10139篇 |
综合类 | 142篇 |
数学 | 26273篇 |
物理学 | 77300篇 |
出版年
2022年 | 2418篇 |
2021年 | 3071篇 |
2020年 | 3343篇 |
2019年 | 3626篇 |
2018年 | 4366篇 |
2017年 | 4158篇 |
2016年 | 5848篇 |
2015年 | 3876篇 |
2014年 | 5749篇 |
2013年 | 11631篇 |
2012年 | 9722篇 |
2011年 | 11280篇 |
2010年 | 7921篇 |
2009年 | 7689篇 |
2008年 | 10096篇 |
2007年 | 9921篇 |
2006年 | 9233篇 |
2005年 | 8183篇 |
2004年 | 7117篇 |
2003年 | 6394篇 |
2002年 | 6242篇 |
2001年 | 6506篇 |
2000年 | 5137篇 |
1999年 | 4055篇 |
1998年 | 3513篇 |
1997年 | 3525篇 |
1996年 | 3311篇 |
1995年 | 2744篇 |
1994年 | 2759篇 |
1993年 | 2726篇 |
1992年 | 2872篇 |
1991年 | 2875篇 |
1990年 | 2754篇 |
1989年 | 2680篇 |
1988年 | 2553篇 |
1987年 | 2512篇 |
1986年 | 2460篇 |
1985年 | 3110篇 |
1984年 | 3228篇 |
1983年 | 2603篇 |
1982年 | 2854篇 |
1981年 | 2725篇 |
1980年 | 2510篇 |
1979年 | 2722篇 |
1978年 | 2833篇 |
1977年 | 2856篇 |
1976年 | 2833篇 |
1975年 | 2688篇 |
1974年 | 2665篇 |
1973年 | 2810篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
G. I. Malofeeva O. M. Petrukhin B. Ya. Spivakov E. V. Poteshkina 《Journal of Analytical Chemistry》2003,58(3):211-216
Conditions of the liquid–liquid and solid-phase extraction of metal chelates are compared. The analogy and differences in the behavior of chelates and the effect of stability and partition constants on the completeness of the extraction of metals are discussed. 相似文献
992.
993.
994.
995.
In the present paper, the Bol loops and related groups are studied. We suggest a universal way to construct a Bol loop and find criteria for simplicity and finiteness of such loops. 相似文献
996.
J. Salgado E. Martinho I. F. Gonçalves 《Journal of Radioanalytical and Nuclear Chemistry》2004,260(2):317-320
The resonance neutron self-shielding factor, G
res, is required in neutron metrology and activation data analysis. In a previous paper, the authors have shown that a dimensionless
variable can be introduced which converts the dependence of G
res on the physical and nuclear properties of the material samples into an universal curve, valid for the isolated resonances
of any nuclide. This work presents a methodology based on the universal curve, which enables to calculate G
res for a group of isolated resonances by weighting its individual contributions. A good agreement was reached with results calculated
by the MCNP code and with experimental values for Mo foils and wires.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
997.
Absorption of cnoidal electromagnetic waves, which are the most general periodic solution to the sine-Gordon equation, by electrons of a one-dimensional quantum semiconductor superlattice in the process of impurity ionization is studied in terms of the semiclassical approximation. The dependence of the absorption coefficient on the electric field of an electromagnetic wave is found to be nonmonotone with a pronounced peak. 相似文献
998.
E. A. Bogdanov A. A. Kudryavtsev L. D. Tsendin R. R. Arslanbekov V. I. Kolobov V. V. Kudryavtsev 《Technical Physics》2003,48(8):983-994
Results from kinetic and fluid simulations of the positive column plasma of a dc oxygen discharge are compared using commercial
CFDRC software (), which enables one to perform numerical simulations in an arbitrary 3D geometry with the use of both the fluid equations
for all the components (fluid model) and the kinetic equation for the electron energy distribution function (kinetic model).
It is shown that, for both the local and nonlocal regimes of the formation of the electron energy distribution function (EEDF),
the non-Maxwellian EEDF can satisfactorily be approximated by two groups of electrons. This allows one to take into account
kinetic effects within the conventional fluid model in the simplest way by using the proposed two-temperature approximation
of the nonequilibrium and nonlocal EEDF (2T fluid model). 相似文献
999.
G. Palfinger B. Bitnar H. Sigg E. Müller S. Stutz D. Grützmacher 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):481
In order to obtain a low band gap photocell based on the widely spread silicon technology, e.g. for thermophotovoltaics, SiGe nanostructures can be introduced into a monocrystalline silicon photocell. Beforehand, it is necessary to know the absorption coefficient of the SiGe quantum wells. On a silicon (1 0 0) substrate multiple Si/SiGe quantum well structures were grown by UHV-CVD. The Ge concentration and the well width were used as growth parameters. To obtain significant absorption, the experiment was set up to allow for 200 internal reflections.The total reflection of the light results in a standing electromagnetic wave. The absorption coefficient was obtained from the experimental data taking the geometry and the electric field distribution in the absorbing layer into account. The influence of well width and germanium content on the absorption was investigated with the goal of maximizing the absorption for photons with energies below the band gap energy of silicon. The measurement results are compared with a theoretical model, which takes the band structure of strained SiGe including confinement effects into account. 相似文献
1000.
Mechanics of Composite Materials - A three-dimensional ply-level modeling of multiple matrix cracking near an open hole in a quasi-isotropic composite laminate was performed. A mesh-independent... 相似文献