全文获取类型
收费全文 | 407750篇 |
免费 | 3450篇 |
国内免费 | 951篇 |
专业分类
化学 | 189776篇 |
晶体学 | 6450篇 |
力学 | 21390篇 |
综合类 | 7篇 |
数学 | 59856篇 |
物理学 | 134672篇 |
出版年
2021年 | 3128篇 |
2020年 | 3330篇 |
2019年 | 3762篇 |
2018年 | 11918篇 |
2017年 | 12618篇 |
2016年 | 10500篇 |
2015年 | 4818篇 |
2014年 | 7122篇 |
2013年 | 16002篇 |
2012年 | 15763篇 |
2011年 | 24769篇 |
2010年 | 16808篇 |
2009年 | 16793篇 |
2008年 | 21812篇 |
2007年 | 24600篇 |
2006年 | 12306篇 |
2005年 | 15895篇 |
2004年 | 12518篇 |
2003年 | 11453篇 |
2002年 | 9860篇 |
2001年 | 10519篇 |
2000年 | 7935篇 |
1999年 | 5998篇 |
1998年 | 5002篇 |
1997年 | 4823篇 |
1996年 | 4646篇 |
1995年 | 3958篇 |
1994年 | 3904篇 |
1993年 | 3778篇 |
1992年 | 4160篇 |
1991年 | 4376篇 |
1990年 | 4167篇 |
1989年 | 4083篇 |
1988年 | 3862篇 |
1987年 | 3994篇 |
1986年 | 3756篇 |
1985年 | 4714篇 |
1984年 | 4781篇 |
1983年 | 3976篇 |
1982年 | 4057篇 |
1981年 | 3783篇 |
1980年 | 3736篇 |
1979年 | 4017篇 |
1978年 | 4016篇 |
1977年 | 3933篇 |
1976年 | 3942篇 |
1975年 | 3724篇 |
1974年 | 3664篇 |
1973年 | 3724篇 |
1972年 | 2638篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
991.
S. Zschocke G. Plunien G. Soff 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(2):147-156
The renormalization method of Bogoljubov-Parasiuk-Hepp-Zimmermann (BPHZ) is used in order to derive the renormalized energy
shift due to the gauge invariant K?llén-Sabry diagram of the two-photon vacuum polarization (VPVP) as well as the self energy
vacuum polarization S(VP)E beyond the Uehling approximation. It is outlined, that no outer renormalization is required for
the two-photon vacuum polarization and that only the inner renormalization has to be accomplished. It is shown that the so-called
nongauge invariant spurious term is absent for a wide class of vacuum polarization (VP) diagrams if one applies the widely
used spherical expansion of bound and free-electron propagator. This simplifies significantly calculations in bound state
quantum electrodynamics. As one result of our paper the use of the BPHZ-approach in bound state QED is established.
Received 28 September 2001 相似文献
992.
Atomic-force microscopy was used to study the surface topography of SiGe structures grown by epitaxial deposition of Ge on profiled Si(111) substrates under electromigration conditions. Systems of highly ordered germanium nanosized islands with dimensions of 10–20 nm and a density of 6×1010 cm?2 were obtained. It is shown that the geometrical parameters of self-organizing nanoislands can be controlled by a proper choice of the growth and postgrowth annealing conditions for these structures. 相似文献
993.
We discuss some variant superfield representations which can arise by the replacement of some of the usual fields in a multiplet with p-form gauge fields. 相似文献
994.
It was found that a beta-fructofuranosidase produced by Microbacterium sp. H-1 has potent trans-beta-fructofuranosylation activity from sucrose (donor). By means of this enzyme system, rebaudioside A (RA), the second major sweet steviol glycoside of the leaves of Stevia rebaudiana, was subjected to transfructosylation, affording a mono-beta-fructofuranosylated product (RA-F) in a high yield. The structure of RA-F was elucidated as beta-D-fructofuranosyl-(2----6)-beta-D-glucopyranosyl ester of steviol-13-O-[beta-D-glucopyranosyl-(1----2)]- [beta-D-glucopyranosyl-(1----3)]-beta-D-glucopyranoside. Some improvement in the quality of sweetness was observed for RA-F. 相似文献
995.
N. S. Smirnova 《Journal of Mathematical Sciences》1991,55(3):1741-1746
We consider theoretical seismographs of a wave field passing through an elastic layer with high propagation velocity. We note the presence of a low-frequency part of the seismogram for longitudinal waves. It is shown that the propagation time of low-frequency vibrations is equal to that of longitudinal disturbances screened by the layer.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova, AN SSSR, Vol. 173, pp. 134–141, 1988. 相似文献
996.
S. M. Novoselova 《Journal of Mathematical Sciences》1991,57(3):3147-3153
The transversally inhomogeneous cross-section of the model is constructed from the data obtained by Retzius, Hardesty, Wever, and Miller. On the basis of a three-dimensional linear mechanical WKB model of a cochlea without negative friction we obtain high frequency selectivity and a phase shift in the domain of the peak of the amplitude function comparable with the measurements taken by Sellick and Robles.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova, Vol. 179, pp. 128–138, 1989. 相似文献
997.
998.
S. A. Salem 《Journal of Applied Mathematics and Computing》2006,21(1-2):331-355
We study a model procedure to solve the incompressible Navier-Stokes equations on the flow inside contraction geometry. The governing equations are expressed in the primitive variable formulation. A rectangular computational plane is arises by elliptic grid generation technique. The numerical solution is based on a technique of automatic numerical generation of a curvilinear coordinate system. By transformed the governing equation into computational plane. The time dependent momentum equations are solved explicitly for the velocity field using the explicit marching procedure, the continuity equation is applied at each grid point in the solution of pressure equation, while the successive over relaxation (SOR) method is used for the Neumann problem for pressure. We will apply the technique on several irregular-shape. 相似文献
999.
Y. Qu J.X. Zhang A. Uddin C.Y. Liu S. Yuan M.C.Y. Chan B. Bo G. Liu H. Jiang 《Applied Physics A: Materials Science & Processing》2006,82(2):305-308
Ridge-waveguide InGaAsN triple-quantum-well strain-compensated lasers grown by metal organic chemical vapor deposition were fabricated with pulsed anodic oxidation. The laser’s output power reached 145 mW in continuous-wave mode at room temperature for a 4-?m -stripe-width laser. Continuous-wave single longitudinal mode operation was maintained at a high injection current level with a wavelength of 1287.3 nm at room temperature. Single longitudinal mode operation at 1317.2 nm was achieved at twice the threshold current at 100 °C. The band gap of InGaAsN in the quantum wells at different temperatures was calculated and compared to the measured temperature-dependent laser wavelength. 相似文献
1000.
S. P. Popov 《Computational Mathematics and Mathematical Physics》2006,46(6):983-994
Numerical solutions to three systems of integrable evolutionary equations from the Toda lattice hierarchy are analyzed. These are the classical Toda lattice, the second local dispersive flow, and the second extended dispersive flow. Special attention is given to the properties of soliton solutions. For the equations of the second local flow, two types of solitons interacting in a special manner are found. Solutions corresponding to various initial data are qualitatively outlined. 相似文献