全文获取类型
收费全文 | 429120篇 |
免费 | 4654篇 |
国内免费 | 1391篇 |
专业分类
化学 | 224516篇 |
晶体学 | 5756篇 |
力学 | 19261篇 |
综合类 | 3篇 |
数学 | 49804篇 |
物理学 | 135825篇 |
出版年
2020年 | 3263篇 |
2019年 | 3827篇 |
2018年 | 4802篇 |
2017年 | 4642篇 |
2016年 | 7118篇 |
2015年 | 4589篇 |
2014年 | 7249篇 |
2013年 | 19524篇 |
2012年 | 14162篇 |
2011年 | 17493篇 |
2010年 | 12056篇 |
2009年 | 11879篇 |
2008年 | 15976篇 |
2007年 | 16079篇 |
2006年 | 15080篇 |
2005年 | 13733篇 |
2004年 | 12535篇 |
2003年 | 11143篇 |
2002年 | 10999篇 |
2001年 | 12582篇 |
2000年 | 9609篇 |
1999年 | 7558篇 |
1998年 | 6435篇 |
1997年 | 6398篇 |
1996年 | 6010篇 |
1995年 | 5546篇 |
1994年 | 5332篇 |
1993年 | 5444篇 |
1992年 | 5822篇 |
1991年 | 6000篇 |
1990年 | 5623篇 |
1989年 | 5404篇 |
1988年 | 5474篇 |
1987年 | 5272篇 |
1986年 | 5017篇 |
1985年 | 6907篇 |
1984年 | 7239篇 |
1983年 | 5863篇 |
1982年 | 6373篇 |
1981年 | 6171篇 |
1980年 | 6031篇 |
1979年 | 6195篇 |
1978年 | 6501篇 |
1977年 | 6259篇 |
1976年 | 6521篇 |
1975年 | 5900篇 |
1974年 | 6022篇 |
1973年 | 6346篇 |
1972年 | 4189篇 |
1971年 | 3386篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Published in Teoreticheskaya i Matematicheskaya Fizika, Vol. 95, No. 2, pp. 183–186, May, 1993. 相似文献
902.
We present a systematic comparison of the correlation contribution at the level of the second-order polarization propagator approximation (SOPPA ) and MP 2 to the static dipole polarizability of (1) Be, BeH?, BH, CH+, MgH?, AIH, SiH+, and GeH+; (2) BH3, CH4, NH3, H2O, HF, BF, and F2; and (3) N2, CO, CN?, HCN, C2H2, and HCHO . Fairly extended basis sets were used in the calculations. We find that the agreement with experimental values is improved in SOPPA and MP .2 over the results at the SCF level. The signs and magnitudes of the correlation contribution in SOPPA are similar to those obtained in analytical derivative MP 2 calculations. However, it is not possible to say, in general, which method gives the largest correlation contribution or the best agreement with experiment, nor is it possible to make a priori prediction of the sign of the correlation contribution. For the first group of molecules, which have a quasi-degenerate ground state, additional CCDPPA and CCSDPPA calculations were performed and compared with polarizabilities obtained as analytical/numerical derivatives of the CCD and CCSD energies. The CCSDPPA results were found to be in better agreement with other calculations than were the SOPPA results, demonstrating the necessity of using methods based on infinite-order perturbation theory for these systems. © 1994 John Wiley & Sons, Inc. 相似文献
903.
Modeling and numerical simulations of the convective flows induced by the vibration of the monocrystal during crystal growth have been performed for two configurations simulating the Cz and FZ methods. This permitted to emphasize the role of different vibrational mechanisms in the formation of the average flows. It is shown that an appropriate combination of these mechanisms can be used to counteract the usual convective flows (buoyancy- and/or thermocapillary-driven) inherent to crystal growth processes from the liquid phase. While vibrational convection is rather complex due to these identified mechanisms, the new modeling used in the present paper opens up very promising perspectives to efficiently control heat and mass transfer during real industrial applications of crystal growth from the liquid phase. 相似文献
904.
905.
906.
JOSEF MÁLEK JINDŘICH NEČAS K. R. RAJAGOPAL 《Archive for Rational Mechanics and Analysis》2002,165(3):243-269
To describe the flows of fluids over a wide range of pressures, it is necessary to take into account the fact that the viscosity
of the fluid depends on the pressure. That the viscosity depends on the pressure has been verified by numerous careful experiments.
While the existence of solutions local-in-time to the equations governing the flows of such fluids are available for small,
special data and rather unrealistic dependence of the viscosity on the pressure, no global existence results are in place.
Our interest here is to establish the existence of weak solutions for spatially periodic three-dimensional flows that are
global in time, for a large class of physically meaningful viscosity-pressure relationships.
(Accepted May 1, 2002) Published online November 15, 2002
Communicated by S. S. ANTMAN 相似文献
907.
Yu. V. Belovitskaya I. V. Pekov E. R. Gobechiya N. A. Yamnova Yu. K. Kabalov N. V. Chukanov J. Schneider 《Crystallography Reports》2002,47(2):223-228
The crystal structures of two ancylite specimens from Khibiny massif (the Kola Peninsula, Russia)—ancylite-(Ce) from alkali hydrothermalites (Sr1.01Ca0.02Ba0.01)Σ1.04(Ce0.52La0.28Nd0.11Pr0.04 Sm0.01)Σ0.96(CO3)2(OH0.83F0.13)Σ0.96 · 0.9H2O and ancylite-(Ce) from carbonatites—have (Sr0.80Ca0.05Ba0.01)Σ0.86(Ce0.62La0.40Nd0.09Pr0.03) Σ1.14(CO3)2(OH0.99F0.15)Σ1.14 · 1.0H2O been refined by the Rietveld method. A focusing STOE-STADIP diffractometer with a bent Ge(111) primary monochromator was used (λ MoK α 1 radiation, 2.16° < 2θ < 54.98°; reflection number 237–437). All the computations for ancylite from alkali hydrothermalites were performed within the sp. gr. Pmc21, a = 5.0634(1) Å, b = 8.5898(1) Å, c = 7.2781(1) Å, V = 316.55(1) Å3, R wp = 1.90; the computations for ancylite from carbonatites were performed within the sp. gr. Pmcn, a = 5.0577(1) Å, b = 8.5665(2) Å, c = 7.3151(2) Å, V = 316.94(1) Å3, R wp = 2.38 in the anisotropic approximation of thermal vibrations of cations and oxygen atoms. 相似文献
908.
The results of Monte Carlo simulations of the beta dose rate to enamel are presented. The dose rates are the most comprehensive to date, incorporating the beta spectrum from 21 different radionuclides, all internal conversion and Auger electrons, the majority of the bremsstrahlung radiation, effects due to radon loss in the uranium series, and variations in the moisture content of the sediment. Applications to a new dating technique in archaeology using electron spin resonance and beta-gradient isochrons are discussed. 相似文献
909.
K. Venkatakrishnan B.K.A. Ngoi P. Stanley L.E.N. Lim B. Tan N.R. Sivakumar 《Applied Physics A: Materials Science & Processing》2002,75(4):493-496
Photomasks are the backbone of microfabrication industries. Currently they are fabricated by a lithographic process, which
is very expensive and time consuming since it is a multi-step process. These issues can be addressed by fabricating photomasks
by direct femtosecond laser writing, which is a single-step process and comparatively cheaper and faster than lithography.
In this paper we discuss our investigations on the effect of two types of laser writing techniques, namely front- and rear-side
laser writing, with regard to the feature size and the edge quality of a feature. It is proved conclusively that for the patterning
of masks, front-side laser writing is a better technique than rear-side laser writing with regard to smaller feature size
and better edge quality. Moreover the energy required for front-side laser writing is considerably lower than that for rear-side
laser writing.
Received: 22 May 2001 / Accepted: 14 September 2001 / Published online: 17 October 2001 相似文献
910.