全文获取类型
收费全文 | 26254篇 |
免费 | 2156篇 |
国内免费 | 1403篇 |
专业分类
化学 | 1936篇 |
晶体学 | 34篇 |
力学 | 2891篇 |
综合类 | 223篇 |
数学 | 20004篇 |
物理学 | 4725篇 |
出版年
2024年 | 44篇 |
2023年 | 248篇 |
2022年 | 223篇 |
2021年 | 382篇 |
2020年 | 694篇 |
2019年 | 727篇 |
2018年 | 680篇 |
2017年 | 684篇 |
2016年 | 720篇 |
2015年 | 626篇 |
2014年 | 1172篇 |
2013年 | 2737篇 |
2012年 | 1146篇 |
2011年 | 1481篇 |
2010年 | 1288篇 |
2009年 | 1709篇 |
2008年 | 1660篇 |
2007年 | 1675篇 |
2006年 | 1461篇 |
2005年 | 1115篇 |
2004年 | 1046篇 |
2003年 | 989篇 |
2002年 | 980篇 |
2001年 | 775篇 |
2000年 | 793篇 |
1999年 | 719篇 |
1998年 | 608篇 |
1997年 | 560篇 |
1996年 | 425篇 |
1995年 | 302篇 |
1994年 | 281篇 |
1993年 | 211篇 |
1992年 | 190篇 |
1991年 | 146篇 |
1990年 | 140篇 |
1989年 | 95篇 |
1988年 | 82篇 |
1987年 | 75篇 |
1986年 | 67篇 |
1985年 | 94篇 |
1984年 | 131篇 |
1983年 | 61篇 |
1982年 | 95篇 |
1981年 | 96篇 |
1980年 | 87篇 |
1979年 | 75篇 |
1978年 | 69篇 |
1977年 | 54篇 |
1976年 | 41篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 219 毫秒
71.
甲基对硫磷的快速测定及电化学性质 总被引:3,自引:2,他引:1
研究了杀虫剂甲基对硫磷的电化学性质。在pH10.38的Bdtton—Robinson缓冲溶液中,采用微分脉冲溶出伏安法在悬汞电极上得到一个还原峰,峰电位为-0.5V(vs.Ag/AgCl),本工作对实验条件进行了深入的研究,结合线性扫描伏安法等手段。研究了体系的电化学行为。实验表明,甲基对硫磷在汞电极上具有吸附性,电极反应具有不可逆性。该法用于水果及水样中甲基对硫磷残余量的测定,结果满意。 相似文献
72.
A tomographic reconstruction method based on Monte Carlo random searching guided by the information contained in the projections
of radiographed objects is presented. In order to solve the optimization problem, a multiscale algorithm is proposed to reduce
computation. The reconstruction is performed in a coarse-to-fine multigrid scale that initializes each resolution level with
the reconstruction of the previous coarser level, which substantially improves the performance. The method was applied to
a real case reconstructing the internal structure of a small metallic object with internal components, showing excellent results. 相似文献
73.
V. I. Sakharov 《Fluid Dynamics》2007,42(6):1007-1016
The results of numerical simulation are presented for thermally and chemically nonequilibrium air plasma flows in a plasmatron discharge channel and underexpanded dissociated and partially ionized air jets flowing past a cylindrical model with a blunt leading edge and cooled copper surface under the experimental conditions realized in a VGU-4 100 kW induction plasmatron (Institute for Problems in Mechanics of the Russian Academy of Sciences) (see, for example, [1, 2]). The nonequilibrium excitation of the vibrational degrees of freedom of the molecules in the modal approximation and the difference between the electron and translational heavy-particle temperatures are taken into account in the calculations. The calculated data on the heat transfer and pressure at the stagnation point are compared with the results obtained within the framework of the thermally equilibrium model. Comparison with the experimental data obtained in the Institute for Problem in Mechanics of the Russian Academy of Sciences (Laboratory for interaction between plasma and radiation and materials) and kindly provided for comparison purposes gives satisfactory agreement. 相似文献
74.
A new stochastic method of reconstructing porous media 总被引:1,自引:0,他引:1
We present a new stochastic method of reconstructing porous medium from limited morphological information obtained from two-dimensional
micro- images of real porous medium. The method is similar to simulated annealing method in the capability of reconstructing
both isotropic and anisotropic structures of multi-phase but differs from the latter in that voxels for exchange are not selected
completely randomly as their neighborhood will also be checked and this new method is much simpler to implement and program.
We applied it to reconstruct real sandstone utilizing morphological information contained in porosity, two-point probability
function and linear-path function. Good agreement of those references verifies our developed method’s powerful capability.
The existing isolated regions of both pore phase and matrix phase do quite minor harm to their good connectivity. The lattice
Boltzmann method (LBM) is used to compute the permeability of the reconstructed system and the results show its good isotropy
and conductivity. However, due to the disadvantage of this method that the connectivity of the reconstructed system’s pore
space will decrease when porosity becomes small, we suggest the porosity of the system to be reconstructed be no less than
0.2 to ensure its connectivity and conductivity. 相似文献
75.
76.
一类非线性微分方程的脉冲镇定 总被引:5,自引:0,他引:5
针对一般形式的常微分系统提出了脉冲指数镇定的概念,具体研究了一类分离变量型非线性常微分方程的脉冲镇定问题,得到了该方程可脉冲指数镇定的充分判据,全文的概念及结论突出了脉冲在方程稳定性方面的控制效果。 相似文献
77.
Frank Jochmann 《Journal of Differential Equations》2004,203(2):232-254
In this paper, Maxwell's equations involving generally nonlinear polarization and field-dependent currents are studied. The main objective is the asymptotic behavior of the solution for t→∞ if no damping term occurs in the equation governing the polarization field. 相似文献
78.
Svitlana P. Rogovchenko 《Journal of Mathematical Analysis and Applications》2003,279(1):121-134
In this paper, we are concerned with a class of nonlinear second-order differential equations with a nonlinear damping term. Passage to more general class of equations allows us to remove a restrictive condition usually imposed on the nonlinearity, and, as a consequence, our results apply to wider classes of nonlinear differential equations. Two illustrative examples are considered. 相似文献
79.
Oleg Palumbíny 《Czechoslovak Mathematical Journal》2003,53(2):467-477
The paper deals with oscillation criteria of fourth order linear differential equations with quasi-derivatives. 相似文献
80.
A stochastic approximation algorithm for estimating multichannel coefficients is proposed, and the estimate is proved to converge to the true parameters a.s. up-to a constant scaling factor. The estimate is updated after receiving each new observation, so the output data need not be collected in advance. The input signal is allowed to be dependent and the observation is allowed to be corrupted by noise, but no noise statistics are used in the estimation algorithm. 相似文献