全文获取类型
收费全文 | 409487篇 |
免费 | 3506篇 |
国内免费 | 1226篇 |
专业分类
化学 | 205577篇 |
晶体学 | 6123篇 |
力学 | 20566篇 |
综合类 | 17篇 |
数学 | 64115篇 |
物理学 | 117821篇 |
出版年
2020年 | 2709篇 |
2019年 | 2953篇 |
2018年 | 13511篇 |
2017年 | 13404篇 |
2016年 | 11484篇 |
2015年 | 4353篇 |
2014年 | 5963篇 |
2013年 | 15008篇 |
2012年 | 14311篇 |
2011年 | 23277篇 |
2010年 | 14716篇 |
2009年 | 15172篇 |
2008年 | 18308篇 |
2007年 | 20349篇 |
2006年 | 11561篇 |
2005年 | 11580篇 |
2004年 | 10747篇 |
2003年 | 10297篇 |
2002年 | 9152篇 |
2001年 | 10018篇 |
2000年 | 7735篇 |
1999年 | 5888篇 |
1998年 | 4906篇 |
1997年 | 4755篇 |
1996年 | 4546篇 |
1995年 | 4235篇 |
1994年 | 4071篇 |
1993年 | 3781篇 |
1992年 | 4594篇 |
1991年 | 4621篇 |
1990年 | 4391篇 |
1989年 | 4435篇 |
1988年 | 4407篇 |
1987年 | 4303篇 |
1986年 | 4095篇 |
1985年 | 5276篇 |
1984年 | 5416篇 |
1983年 | 4322篇 |
1982年 | 4582篇 |
1981年 | 4493篇 |
1980年 | 4236篇 |
1979年 | 4674篇 |
1978年 | 4827篇 |
1977年 | 4811篇 |
1976年 | 4674篇 |
1975年 | 4373篇 |
1974年 | 4372篇 |
1973年 | 4326篇 |
1972年 | 2957篇 |
1968年 | 2677篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
202.
O. Perru F. Ibrahim O. Bajeat C. Bourgeois F. Clapier E. Cottereau C. Donzaud M. Ducourtieux S. Galès D. Guillemaud-Mueller C. Lau H. Lefort F. Le Blanc A. C. Mueller J. Obert N. Pauwels J. C. Potier F. Pougheon J. Proust B. Roussière J. Sauvage O. Sorlin D. Verney 《Physics of Atomic Nuclei》2003,66(8):1421-1427
The PARRNe facility has been used to produce neutron-rich isotopes 83,84Gaby the ISOL method. Their decay has been studied, and β-γ coincidence and γ-γ coincidence data were collected as a function of time. The first two excited levels in 83Ge and the first excited level in 84Ge have been measured for the first time. 相似文献
203.
B. F. Svaiter 《Proceedings of the American Mathematical Society》2003,131(12):3851-3859
Any maximal monotone operator can be characterized by a convex function. The family of such convex functions is invariant under a transformation connected with the Fenchel-Legendre conjugation. We prove that there exists a convex representation of the operator which is a fixed point of this conjugation.
204.
We examine several interesting relationships and expressions involving Fourier-Feynman transform, convolution product and
first variation for functionals in the Fresnel class F(B) of an abstract Wiener space B. We also prove a translation theorem and Parseval's identity for the analytic Feynman integral.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
205.
206.
The concept and application of phase-space reconstructions are reviewed. Fractional derivatives are then proposed for the purpose of reconstructing dynamics from a single observed time history. A procedure is presented in which the fractional derivatives of time series data are obtained in the frequency domain. The method is applied to the Lorenz system. The ability of the method to unfold the data is assessed by the method of global false nearest neighbors. The reconstructed data is used to compute recurrences and correlation dimensions. The reconstruction is compared to the commonly used method of delays in order to assess the choice of reconstruction parameters, and also the quality of results. 相似文献
207.
208.
A preconditioning approach based on the artificial compressibility formulation is extended to solve the governing equations for unsteady turbulent reactive flows with heat release, at low Mach numbers, on an unstructured hybrid grid context. Premixed reactants are considered and a flamelet approach for combustion modelling is adopted using a continuous quenched mean reaction rate. An overlapped cell‐vertex finite volume method is adopted as a discretisation scheme. Artificial dissipation terms for hybrid grids are explicitly added to ensure a stable, discretised set of equations. A second‐order, explicit, hybrid Runge–Kutta scheme is applied for the time marching in pseudo‐time. A time derivative of the dependent variable is added to recover the time accuracy of the preconditioned set of equations. This derivative is discretised by an implicit, second‐order scheme. The resulting scheme is applied to the calculation of an infinite planar (one‐dimensional) turbulent premixed flame propagating freely in reactants whose turbulence is supposed to be frozen, homogeneous and isotropic. The accuracy of the results obtained with the proposed method proves to be excellent when compared to the data available in the literature. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
209.
Large eddy simulations of two basic configurations (decay of isotropic turbulence, and the academic plane channel flow) with heat transfer have been performed comparing several convection numerical schemes, in order to discuss their ability to evaluate temperature fluctuations properly. Results are compared with the available incompressible heat transfer direct numerical simulation data. It is shown that the use of regularizing schemes (such as high order upwind type schemes) for the temperature transport equation in combination with centered schemes for momentum transport equation gives better results than the use of centred schemes for both equations. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
210.
We carried out detailed calculations for photorefractive wave-mixing switches based on one of three crystals with high electro-optic coefficients, namely, BaTiO3, Strontium Barium Niobate (SBN (0.75)), and Potasium Sodium Strontium Barium Niobate (KNSBN). A comparison of results for the three crystals shows that a 0_-cut BaTiO3 crystal is suitable for a longitudinal switch and requires a voltage of about 80 for a 2-mm-thick crystal to induce sufficient phase mismatch. The electrodes must be transparent for the incident and diffracted beams. A 45_-cut SBN (0.75) crystal, however, is suitable for a lateral switch and requires a voltage of about 150 for a 1-mm-wide crystal. The electrodes do not need to be transparent. 相似文献