全文获取类型
收费全文 | 419313篇 |
免费 | 3123篇 |
国内免费 | 975篇 |
专业分类
化学 | 201537篇 |
晶体学 | 6022篇 |
力学 | 22719篇 |
综合类 | 12篇 |
数学 | 59820篇 |
物理学 | 133301篇 |
出版年
2020年 | 2900篇 |
2019年 | 3368篇 |
2018年 | 11524篇 |
2017年 | 12278篇 |
2016年 | 9677篇 |
2015年 | 4333篇 |
2014年 | 6060篇 |
2013年 | 14468篇 |
2012年 | 14927篇 |
2011年 | 24128篇 |
2010年 | 15883篇 |
2009年 | 16244篇 |
2008年 | 21692篇 |
2007年 | 24627篇 |
2006年 | 12308篇 |
2005年 | 16282篇 |
2004年 | 12925篇 |
2003年 | 11867篇 |
2002年 | 10322篇 |
2001年 | 10659篇 |
2000年 | 8185篇 |
1999年 | 6075篇 |
1998年 | 5081篇 |
1997年 | 4923篇 |
1996年 | 4829篇 |
1995年 | 4284篇 |
1994年 | 4120篇 |
1993年 | 4033篇 |
1992年 | 4358篇 |
1991年 | 4618篇 |
1990年 | 4310篇 |
1989年 | 4364篇 |
1988年 | 4271篇 |
1987年 | 4240篇 |
1986年 | 3984篇 |
1985年 | 5374篇 |
1984年 | 5389篇 |
1983年 | 4512篇 |
1982年 | 4721篇 |
1981年 | 4535篇 |
1980年 | 4290篇 |
1979年 | 4577篇 |
1978年 | 4785篇 |
1977年 | 4775篇 |
1976年 | 4819篇 |
1975年 | 4614篇 |
1974年 | 4469篇 |
1973年 | 4742篇 |
1972年 | 3332篇 |
1971年 | 2803篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
Curtis T. Mcmullen 《Acta Mathematica》2003,191(2):191-223
952.
A. Henderson 《Mathematische Zeitschrift》2003,243(1):127-143
We prove that the local intersection cohomology of nilpotent orbit closures of cyclic quivers is trivial when the two orbits
involved correspond to partitions with at most two rows. This gives a geometric proof of a result of Graham and Lehrer, which
states that standard modules of the affine Hecke algebra of GLd corresponding to nilpotents with at most two Jordan blocks are multiplicity-free.
Received: 7 February 2002 / Published online: 8 November 2002 相似文献
953.
It is proved that every finite group for which the degrees of its nonmonomial characters are primes is solvable. The proof uses the classification of the finite simple groups. 相似文献
954.
955.
The form of the probability density derived from the evolution in time of a previously truncated frequency distribution of animal Liveweights is of interest in animal husbandry. Truncated frequency distributions arise when the heavier animals are sold for slaughter and the lighter animals retained. The demands of modern quality assurance schemes require that, given information on animal growth, the farmer is able to estimate the number of animals that would meet the specifications at some time in the future after truncation. Assuming that animal growth can be described by a linear stochastic differential equation, we derive an explicit expression for the probability density of animal Liveweights at any time after the truncation of an initial Gaussian density. It is shown that this probability density converges rapidly to a Gaussian density, so that after about 20 days of typical growth rates for lambs, the resulting density is practically indistinguishable from Gaussian. 相似文献
956.
O. A. Alekseeva N. I. Sorokina I. A. Verin T. Yu. Losevskaya V. I. Voronkova V. K. Yanovskii V. I. Simonov 《Crystallography Reports》2003,48(2):205-211
This study is a continuation of research into the atomic structure and physical properties of niobium-doped potassium titanyl phosphate crystals, KTiOPO4 (KTP: Nb). Crystals containing 7 and 11 at. % of niobium were grown and studied. With an increase in niobium content, the number of vacancies and additional potassium positions in the structure also increase. This fact accounts for an increase in both the intensities of relaxation peaks and the conductivity of KTP: Nb crystals. 相似文献
957.
I. P. Kuranova K. M. Polyakov E. A. Smirnova W. E. Höhne V. S. Lamzin R. Meijer 《Crystallography Reports》2003,48(6):953-958
Crystals of Saccharomyces cerevisiae inorganic pyrophosphatase suitable for X-ray diffraction study were grown by cocrystallization of the enzyme with cobalt chloride and imidodiphosphate. Saccharomyces cerevisiae is a metal-dependent enzyme which catalyzes hydrolysis of inorganic pyrophosphate to orthophosphate. The three-dimensional structure of this enzyme was solved by the molecular-replacement method and refined at 1.8 Å resolution to an R factor of 19.5%. Cobalt and phosphate ions were revealed in the active centers of both identical subunits (A and B) of the pyrophosphatase molecule. In subunit B, a water molecule was found between two cobalt ions. It is believed that this water molecule acts as an attacking nucleophile in the enzymatic cleavage of the pyrophosphate bond. It was demonstrated that cobalt ions and a phosphate group occupy only part of the potential binding sites (two chemically identical and crystallographically independent subunits have different binding sites). The arrangement of ligands and the structure of the nucleophile-binding site are discussed in relation to the mechanism of action of the enzyme and the nature of the metal activator. 相似文献
958.
Until recently, simple and reliable high repetition-rate laser sources with nanosecond pulses much shorter than from conventional A-O Q-switch lasers were not available. However over the past 2 years we have developed such lasers based on proprietary fast E-O switching technology, which allows designs delivering 1 ns pulses and subnanosecond jitter for good synchronisation. The technology provides pulses with multi-kW peak power and repetition-rates to >100 kHz.Most recently, the performance of these short pulse lasers has been developed further by implementing oscillator/amplifier (master oscillator and power amplifier, MOPA) technology which increases the output to >1 W average power. Here we report on a simple model that has been used to predict the performance of the CW pumped Nd:YVO4 amplifier used in the MOPA laser. The model is based on the well-known expressions for the saturated gain applying to laser pulses, but more usually applied to pulse-excited amplifiers. The model is shown to allow a good interpretation of the amplifier behaviour for kHz pulses and to be a useful tool for predicting the performance of the MOPA laser. 相似文献
959.
V. I. Tsoy 《Optics and Spectroscopy》2003,94(4):607-612
In the framework of the matrix formulation of the coupled plane wave approach, a method is proposed for increasing the stability of the numerical analysis of vector electromagnetic fields in periodic structures, including dielectric and metallic anisotropic layers and relief boundaries. 相似文献
960.
C.H. Chen 《Journal of sound and vibration》2003,263(4):797-813
A neural-network-based method is offered to determine the flutter derivatives of section models under smooth and turbulent flows. The approach uses the observed dynamic responses to train an appropriate neural network. Subsequently, the modal parameters of the model for different mean velocities of wind flow are directly estimated using weight matrices in the neural network. The flutter derivatives can then be determined accurately. The validity of the present method is verified through numerical studies. Finally, the procedure is employed to process experimental data from an inverted-U-type section model, obtained from wind tunnel tests. 相似文献