全文获取类型
收费全文 | 3857篇 |
免费 | 619篇 |
国内免费 | 386篇 |
专业分类
化学 | 820篇 |
晶体学 | 35篇 |
力学 | 322篇 |
综合类 | 55篇 |
数学 | 1713篇 |
物理学 | 1917篇 |
出版年
2024年 | 9篇 |
2023年 | 46篇 |
2022年 | 78篇 |
2021年 | 97篇 |
2020年 | 108篇 |
2019年 | 115篇 |
2018年 | 123篇 |
2017年 | 145篇 |
2016年 | 161篇 |
2015年 | 109篇 |
2014年 | 199篇 |
2013年 | 373篇 |
2012年 | 187篇 |
2011年 | 179篇 |
2010年 | 188篇 |
2009年 | 204篇 |
2008年 | 244篇 |
2007年 | 239篇 |
2006年 | 221篇 |
2005年 | 232篇 |
2004年 | 200篇 |
2003年 | 181篇 |
2002年 | 175篇 |
2001年 | 139篇 |
2000年 | 132篇 |
1999年 | 120篇 |
1998年 | 113篇 |
1997年 | 82篇 |
1996年 | 89篇 |
1995年 | 65篇 |
1994年 | 58篇 |
1993年 | 33篇 |
1992年 | 37篇 |
1991年 | 21篇 |
1990年 | 21篇 |
1989年 | 27篇 |
1988年 | 21篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1971年 | 2篇 |
排序方式: 共有4862条查询结果,搜索用时 15 毫秒
991.
992.
Patrick Das Gupta 《Pramana》2004,63(4):845-850
After a short review of gamma ray bursts (GRBs), we discuss the physical implications of strong statistical correlations seen
among some of the parameters of short duration bursts (T
90 < 2 s). Finally, we conclude with a brief sketch of a new unified model for long and short GRBs. 相似文献
993.
994.
Fluctuation properties of the regular and irregular energy levels for the Hénon-Heiles Hamiltonian are examined. The spacing
distributions and the calculated values of the Δ3-statistic show that there is no difference in the short range correlation properties of these spectra. Remarkably, the Δ3 values agree with the results of random matrix theory.
on leave of absence from P.R.L., Ahmedabad 相似文献
995.
Summary For a simple class of Lagrangians and variational integrators, derived by time discretization of the action functional, we
establish (i) the Γ-convergence of the discrete action sum to the action functional; (ii) the relation between Γ-convergence
and weak* convergence of the discrete trajectories in {itW{su1,℞}}({ofR};{ofr{sun}; and (iii) the relation between Γ-convergence
and the convergence of the Fourier transform of the discrete trajectories as measured in the flat norm. 相似文献
996.
Large‐eddy simulation with complex 2‐D geometries using a parallel finite‐element/spectral algorithm
A parallel stabilized finite‐element/spectral formulation is presented for incompressible large‐eddy simulation with complex 2‐D geometries. A unique discretization scheme is developed consisting of a streamline‐upwind Petrov–Galerkin/Pressure‐Stabilized Petrov–Galerkin (SUPG/PSPG) finite‐element discretization in the 2‐D plane with a collocated spectral/pseudospectral discretization in the out‐of‐plane direction. This formulation provides an efficient approach for solving 3‐D flows over arbitrary 2‐D geometries. Utilizing this discretization and through explicit temporal treatment of the non‐linear terms, the system of equations for each Fourier mode is decoupled within each time step. A novel parallelization approach is then taken, where the computational work is partitioned in Fourier space. A validation of the algorithm is presented via comparison of results for flow past a circular cylinder with published values for Re=195, 300, and 3900. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
997.
This paper deals with the spectrum of the almost periodically correlated (APC) processes defined on
. It is established that the covariance kernel of such a process admits a Fourier series decomposition, K(s+t, s)
, whose coefficient functions b are the Fourier transforms of complex measures m,
, which are absolutely continuous with respect to the measure mo. Considering the APC strongly harmonizable processes, the spectral covariance of the process can be expressed in terms of these complex measures m.
The usual estimators for the second order situation can be modified to provide consistent estimators of the coefficient functions b from a sample of the process. Whenever the measures m are absolutely continuous with respect to the Lebesgue measure, so m(dλ)=f(λ) dλ, the estimation of the corresponding density functions f is considered. Under hypotheses on the covariance kernel K and on the coefficient functions b, we establish rates of convergence in quadratic mean and almost everywhere of these estimators. 相似文献
998.
999.
1 INTRODUCTION The aconitum plants produce various diterpene and norditerpene alkaloids[1, 2]. Up to now more than 450 diterpenoid and norditerpenoid alkaloids have been isolated from the roots of this genus[3]. Sub- sequent studies on the flower of the same subspecies were directed to the other secondary metabolites such as flavonoids[4, 5]. The flavonoidic composi- tions of several oriental species of A. plants have been reported[6~8]. A. sungpanense hand. Mazz., a very highly poi- s… 相似文献
1000.
The purpose of this study is to investigate non-Darcian mixed convection flow, heat and mass transfer in a non-Newtonian power-law fluid over a flat plate embedded in porous medium with suction and viscous dissipation and also is to demonstrate the application and utility of a recently developed multi-domain bivariate spectral quasi-linearisation method (MD-BSQLM) in finding the solutions of highly nonlinear differential equations. The flow is subject to, among other source terms, internal heat generation, thermal radiation and partial velocity slip. The coupled system of nonlinear partial differential equations are solved using a MD-BSQLM to find the fluid properties, the skin friction, as well as the heat and mass coefficients. We have presented selected results that give the significance of some system parameters on the fluid properties. This MD-BSQLM has not been used before in the literature to find the nature of the solutions of power-law fluids. Indeed, validation of this numerical method for general fluid flows, heat and mass transfer problems has not yet been done. This study presents the first opportunity to evaluate the accuracy and robustness of the MD-BSQLM in finding solutions of non-Newtonian fluids. 相似文献