全文获取类型
收费全文 | 21743篇 |
免费 | 1681篇 |
国内免费 | 961篇 |
专业分类
化学 | 6368篇 |
晶体学 | 36篇 |
力学 | 1472篇 |
综合类 | 90篇 |
数学 | 6535篇 |
物理学 | 3021篇 |
综合类 | 6863篇 |
出版年
2024年 | 38篇 |
2023年 | 226篇 |
2022年 | 295篇 |
2021年 | 380篇 |
2020年 | 554篇 |
2019年 | 480篇 |
2018年 | 430篇 |
2017年 | 477篇 |
2016年 | 707篇 |
2015年 | 735篇 |
2014年 | 1041篇 |
2013年 | 1440篇 |
2012年 | 1255篇 |
2011年 | 1271篇 |
2010年 | 912篇 |
2009年 | 1351篇 |
2008年 | 1261篇 |
2007年 | 1385篇 |
2006年 | 1231篇 |
2005年 | 957篇 |
2004年 | 894篇 |
2003年 | 839篇 |
2002年 | 768篇 |
2001年 | 670篇 |
2000年 | 618篇 |
1999年 | 508篇 |
1998年 | 499篇 |
1997年 | 409篇 |
1996年 | 424篇 |
1995年 | 353篇 |
1994年 | 272篇 |
1993年 | 277篇 |
1992年 | 189篇 |
1991年 | 170篇 |
1990年 | 164篇 |
1989年 | 155篇 |
1988年 | 122篇 |
1987年 | 88篇 |
1986年 | 87篇 |
1985年 | 52篇 |
1984年 | 59篇 |
1983年 | 21篇 |
1982年 | 34篇 |
1981年 | 33篇 |
1980年 | 25篇 |
1979年 | 29篇 |
1978年 | 43篇 |
1977年 | 46篇 |
1976年 | 42篇 |
1975年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Guillemette Chapuisat 《Journal of Differential Equations》2007,236(1):237-279
This paper deals with the existence of curved front solution of a partial differential equation coming from a mathematical model of stroke. The equation is of reaction-diffusion type in a cylinder of radius R and of diffusion and absorption type outside of the cylinder. We prove the nonexistence of a travelling front when R is small enough and the existence if R is large enough using a recent energy method. We construct the travelling front as the limit in time of a solution with a well-chosen initial condition, in a travelling referential. 相似文献
32.
In this paper, we study the consistency of a variant of fractionalstep Runge–Kutta methods. These methods are designed tointegrate efficiently semi-linear multidimensional parabolicproblems by means of linearly implicit time integration processes.Such time discretization procedures are also related to a splittingof the space differential operator (or the spatial discretizationof it) as a sum of simpler linear differentialoperators and a nonlinear term. 相似文献
33.
The major goal of this paper is to examine the hypothesis that stock returns and return volatility are asymmetric, threshold nonlinear, functions of change in trading volume. A minor goal is to examine whether return spillover effects also display such asymmetry. Employing a double-threshold GARCH model with trading volume as a threshold variable, we find strong evidence supporting this hypothesis in five international market return series. Asymmetric causality tests lend further support to our trading volume threshold model and conclusions. Specifically, an increase in volume is positively associated, while decreasing volume is negatively associated, with the major price index in four of the five markets. The volatility of each series also displays an asymmetric reaction, four of the markets display higher volatility following increases in trading volume. Using posterior odds ratio, the proposed threshold model is strongly favored in three of the five markets, compared to a US news double threshold GARCH model and a symmetric GARCH model. We also find significant nonlinear asymmetric return spillover effects from the US market. 相似文献
34.
Nis Halland Tore Hansen Karl Anker Jrgensen 《Angewandte Chemie (International ed. in English)》2003,42(40):4837-4837
35.
In this paper, we formulate the l
p
-norm optimization problem as a conic optimization problem, derive its duality properties (weak duality, zero duality gap, and primal attainment) using standard conic duality and show how it can be solved in polynomial time applying the framework of interior-point algorithms based on self-concordant barriers. 相似文献
36.
Some previous works show that symmetric fixed- and variable-stepsize linear multistep methods for second-order systems which do not have any parasitic root in their first characteristic polynomial give rise to a slow error growth with time when integrating reversible systems. In this paper, we give a technique to construct variable-stepsize symmetric methods from their fixed-stepsize counterparts, in such a way that the former have the same order as the latter. The order and symmetry of the integrators obtained is proved independently of the order of the underlying fixed-stepsize integrators. As this technique looks for efficiency, we concentrate on explicit linear multistep methods, which just make one function evaluation per step, and we offer some numerical comparisons with other one-step adaptive methods which also show a good long-term behaviour.
37.
Jean-Pierre Dedieu Gregorio Malajovich Mike Shub 《Foundations of Computational Mathematics》2005,5(2):145-171
We prove a linear bound on the average total curvature of the
central path of linear programming theory in terms of the number
of independent variables of the primal problem, and independent of
the number of constraints. 相似文献
38.
Numerical schemes for systems with multiple spatio-temporal scales are investigated. The multiscale schemes use asymptotic results for this type of systems which guarantee the existence of an effective dynamics for some suitably defined modes varying slowly on the largest scales. The multiscale schemes are analyzed in general, then illustrated on a specific example of a moderately large deterministic system displaying chaotic behavior due to Lorenz. Issues like consistency, accuracy, and efficiency are discussed in detail. The role of possible hidden slow variables as well as additional effects arising on the diffusive time-scale are also investigated. As a byproduct we obtain a rather complete characterization of the effective dynamics in Lorenz model. 相似文献
39.
LabVIEW在曲线拟合中的应用研究 总被引:1,自引:0,他引:1
李继容 《五邑大学学报(自然科学版)》2004,18(3):57-63
介绍了LabVIEW中用于曲线拟合的子模块,对各子模块的曲线拟合理论作了介绍,重点介绍了非线性Lev-Mar拟合理论,并以例子辅助说明. 相似文献
40.
培养体育专业学生的创新精神和创造能力的关键在于教师,因此体育教师的创新思维至关重要.运用调查法、逻辑分析法建构了体育专业教师创新思维的途径. 相似文献