全文获取类型
收费全文 | 12935篇 |
免费 | 1612篇 |
国内免费 | 1090篇 |
专业分类
化学 | 3068篇 |
晶体学 | 69篇 |
力学 | 1002篇 |
综合类 | 289篇 |
数学 | 6294篇 |
物理学 | 4915篇 |
出版年
2024年 | 14篇 |
2023年 | 99篇 |
2022年 | 262篇 |
2021年 | 310篇 |
2020年 | 274篇 |
2019年 | 260篇 |
2018年 | 286篇 |
2017年 | 370篇 |
2016年 | 404篇 |
2015年 | 325篇 |
2014年 | 653篇 |
2013年 | 946篇 |
2012年 | 645篇 |
2011年 | 770篇 |
2010年 | 662篇 |
2009年 | 790篇 |
2008年 | 905篇 |
2007年 | 873篇 |
2006年 | 761篇 |
2005年 | 703篇 |
2004年 | 583篇 |
2003年 | 549篇 |
2002年 | 553篇 |
2001年 | 398篇 |
2000年 | 392篇 |
1999年 | 378篇 |
1998年 | 351篇 |
1997年 | 285篇 |
1996年 | 233篇 |
1995年 | 220篇 |
1994年 | 214篇 |
1993年 | 131篇 |
1992年 | 138篇 |
1991年 | 104篇 |
1990年 | 81篇 |
1989年 | 86篇 |
1988年 | 82篇 |
1987年 | 68篇 |
1986年 | 50篇 |
1985年 | 77篇 |
1984年 | 52篇 |
1983年 | 38篇 |
1982年 | 50篇 |
1981年 | 28篇 |
1980年 | 27篇 |
1979年 | 29篇 |
1978年 | 33篇 |
1977年 | 23篇 |
1976年 | 21篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
In this paper, we derive non-exponential asymptotic forms for solutions of defective renewal equations. These include as special
cases asymptotics for compound geometric distribution and the convolution of a compound geometric distribution with a distribution
function. As applications of these results, we study the Gerber-Shiu discounted penalty function in the classical risk model
and the reliability of a two-unit cold standby system in reliability theory.
相似文献
993.
Mass distribution principle is one of important tools in studying Hausdorff dimension and Hausdorff measure.In this paper we will give a numerical approximate method of upper bound and lower bound of mass distribution function f(x)(it is a monotone increasing fractal function)and its some applications. 相似文献
994.
S. Ramasubramanian 《Proceedings Mathematical Sciences》2008,118(2):161-182
2007 Abel prize has been awarded to S R S Varadhan for creating a unified theory of large deviations. We attempt to give a
flavour of this branch of probability theory, highlighting the role of Varadhan. 相似文献
995.
This work employed numerical experiments simulating colloid and solute transport in single parallel-plate fractures, using the random walk particle tracking method, to demonstrate that (1) there exists an aspect ratio of the colloid radius to half the fracture aperture, δo, where the average velocities of colloids and solutes are similar. When δ > δo, the velocity distribution assumption is satisfied, and the fact that the ratio of the colloid transport velocity to the solute transport velocity, τp, decreases as δ increases is well documented in the literature. However, when δ < δo, the velocity distribution assumption is violated, and τp increases as δ increases and (2) the Taylor dispersion coefficient and its extension by James and Chrysikopoulos [S.C. James, C. V. Chrysikopoulos, J. Colloid Interface Sci. 263 (2003) 288] will overestimate the colloid dispersion coefficient significantly. Additionally, numerical experiments simulating colloid and solute transport in variable-aperture fractures demonstrated that τp and DL,coll/DL,solute decrease with increasing CoV, and the anisotropy ratio only plays a minor role compared to the CoV. These observations have important implications towards the interpretation of colloid transport in both porous and fractured media. 相似文献
996.
997.
风沙两相流跃移层中沙粒相的速度分布 总被引:6,自引:1,他引:5
从单个跃移沙粒在气流中的运动方程出发导出了风沙两相流中沙粒相速度分布函数的Boltzmann方程,对风沙流研究中几种不同的分布函数及其相应的统计平均值等基本概念给出了严密的数学定义,指出了不同分布函数之间的区别和联系,在略去铅垂方向空气阻力的情况下,给出了沙粒相速度分布函数沿铅垂方向的边缘分布,作为风沙流中跃移理论的主要基础之一。利用结果对前人在风沙流研究中发现的某些重要规律和现象进行了解释。 相似文献
998.
Sheng Jiang E. David Sudol Victoria L. Dimonie Mohamed S. El‐Aasser 《Journal of polymer science. Part A, Polymer chemistry》2008,46(11):3638-3647
The effect of the medium composition (monomer and solvent) on the kinetics of dispersion polymerization of methyl methacrylate (MMA) was studied via reaction calorimetry. It was found that increasing the monomer concentration increased the reaction rate; the exponent of the dependency of the initial reaction rate on the MMA concentration was found to be 0.93. Narrow particle size distributions were achieved at the lower monomer concentrations (0.24–0.81 mol/L) and a minimum size (2.45 μm) was found at an intermediate concentration (0.44 mol/L). The average molecular weight of the PMMA increased and the molecular weight distribution broadened with increasing monomer concentration. During a dispersion polymerization, the MMA concentration was found to decrease linearly with conversion in both phases, whereas the ratio of concentrations in the particles and continuous phase ([M]p/[M]c) remained constant (0.47) with partitioning favoring the continuous phase. The average number of free radicals per particle in MMA dispersion polymerization was estimated to be high from the nucleation stage onward (>5000). The increasing rate during the first ~ 40% conversion was primarily caused by the increasing volume of the polymer particle phase. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3638–3647, 2008 相似文献
999.
导出了具有正定对称核的积分方程最小特征值的一个下界估计式,为此为基础,获得了相应特征值的一种算法。 相似文献
1000.
K. D. Kirchberg 《Journal of Geometry and Physics》1990,7(4):449-468
If M2m is a closed Kähler spin manifold of positive scalar curvature R, then each eigenvalue λ of type r (r {1, …, [(m + 1)/2]}) of the Dirac operator D satisfies the inequality λ2 ≥ rR0/4r − 2, where R0 is the minimum of R on M2m. Hence, if the complex dimension m is odd (even) we have the estimation for the first eigenvalue of D. In the paper is also considered the limiting case of the given inequalities. In the limiting case with m = 2r − 1 the manifold M2m must be Einstein. The manifolds S2, S2 × S2, S2 × T2, P3(
), F(
), P3(
) × T2 and F(
3) × T2, where F(
3) denotes the flag manifold and T2 the 2-dimensional flat torus, are examples for which the first eigenvalue of the Dirac operator realizes the limiting case of the corresponding inequality. In general, if M2m is an example of odd complex dimension m, then M2m × T2 is an example of even complex dimension m + 1. The limiting case is characterized by the fact that here appear eigenspinors of D2 which are Kählerian twistor-spinors. 相似文献