全文获取类型
收费全文 | 17748篇 |
免费 | 1852篇 |
国内免费 | 1994篇 |
专业分类
化学 | 5765篇 |
晶体学 | 107篇 |
力学 | 2466篇 |
综合类 | 245篇 |
数学 | 9861篇 |
物理学 | 3150篇 |
出版年
2024年 | 47篇 |
2023年 | 202篇 |
2022年 | 314篇 |
2021年 | 445篇 |
2020年 | 582篇 |
2019年 | 527篇 |
2018年 | 523篇 |
2017年 | 591篇 |
2016年 | 677篇 |
2015年 | 455篇 |
2014年 | 793篇 |
2013年 | 1638篇 |
2012年 | 901篇 |
2011年 | 927篇 |
2010年 | 836篇 |
2009年 | 1083篇 |
2008年 | 1162篇 |
2007年 | 1154篇 |
2006年 | 960篇 |
2005年 | 883篇 |
2004年 | 793篇 |
2003年 | 720篇 |
2002年 | 710篇 |
2001年 | 566篇 |
2000年 | 544篇 |
1999年 | 547篇 |
1998年 | 432篇 |
1997年 | 386篇 |
1996年 | 322篇 |
1995年 | 282篇 |
1994年 | 249篇 |
1993年 | 194篇 |
1992年 | 156篇 |
1991年 | 172篇 |
1990年 | 111篇 |
1989年 | 84篇 |
1988年 | 73篇 |
1987年 | 82篇 |
1986年 | 61篇 |
1985年 | 70篇 |
1984年 | 59篇 |
1983年 | 40篇 |
1982年 | 43篇 |
1981年 | 35篇 |
1980年 | 34篇 |
1979年 | 34篇 |
1978年 | 19篇 |
1977年 | 26篇 |
1976年 | 12篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
本文考虑生存函数为${\ol{F}(x_{1},x_{2})}=\exp\{-[(x_{1}^{1/\alpha}/\theta_{1})^{1/\delta}+(x_{2}^{1/\alpha}/\theta_{2})^{1/\delta}]^{\delta}\},\;x_{i}>0,\;\alpha>0$, $1\geq\delta>0,\;\theta_{i}>0\;(i=1,2)$的二元威布尔分布的两种可靠性问题, 提出可靠度$\pr$的估计并讨论了它们的渐近性, 最后还作了模拟计算. 相似文献
102.
Simon R. Blackburn 《Journal of Combinatorial Theory, Series A》2006,113(7):1572-1581
The paper contains proofs of the following results. For all sufficiently large odd integers n, there exists a set of 2n−1 permutations that pairwise generate the symmetric group Sn. There is no set of 2n−1+1 permutations having this property. For all sufficiently large integers n with n≡2mod4, there exists a set of 2n−2 even permutations that pairwise generate the alternating group An. There is no set of 2n−2+1 permutations having this property. 相似文献
103.
分析由若干段等截面或者变截面构件组成的压杆平面内稳定问题.从由三段等截面构件组成的压杆平面内稳定问题出发,对两端为变截面、中间为等截面构件组成的压杆的平面内稳定问题进行了分析,得出和两端为等截面构件情况类似的屈曲荷载计算公式.并对两端固接的情况进行了研究分析. 相似文献
104.
105.
In this paper, the Leslie predator-prey system with two delays is studied. The stability of the positive equilibrium is discussed by analyzing the associated characteristic transcendental equation. The direction and stability of the bifurcating periodic solutions are determined by applying the center manifold theorem and normal form theory. The conditions to guarantee the global existence of periodic solutions are given. 相似文献
106.
李明融 《数学物理学报(B辑英文版)》2007,27(4):703-734
In this article the author works with the ordinary differential equation u" = |u|^p for some p 〉 0 and obtains some interesting phenomena concerning blow-up, blow-up rate, life-span, stability, instability, zeros and critical points of solutions to this equation. 相似文献
107.
The aim of this paper is to introduce a new functional in thestudy of swelling porous elastic soils saturated by a fluid.This new functional is a useful tool; it allows us to provethe existence of solutions in the case of a compressible fluid.We also prove the stability of solutions and the exponentialdecay in the case of an incompressible fluid. We study as wellthe continuous dependence with respect to the initial time. 相似文献
108.
The effect of the cation concentration, hydrolysis temperature, and composition in the CeO2–ZrO2 system on the direct precipitation of ceria–zirconia solid solutions and the structure of the precipitates from acidic aqueous solutions of (NH4)2Ce(NO3)6 and ZrOCl2 by hydrolysis under hydrothermal conditions were investigated. Nanometer-sized (8–10 nm) ceria–zirconia solid solution particles in a composition range of 0 to 60 mol% ZrO2 were directly precipitated from the solutions with total metal cation concentration less than 0.2 mol/dm3 by simultaneous thermal hydrolysis at 150–240°C. The crystalline phase of the precipitates gradually changed from cubic and/or tetragonal to monoclinic with increasing the cation concentration of the solution from 0.2 to 0.8 mol/dm3 at the starting composition of 50 mol% ZrO2 under hydrolysis condition of 150°C for 48 h, which was attributed to decrease in the supply of hydrolyzed Ce component caused by decrease in the hydrolysis ratio of (NH4)2Ce(NO3)6. Ceria–zirconia solid solutions containing large amount of ZrO2 maintained high specific surface area and small-sized crystallite after heat-treatment at 900–1000°C for 1 h. 相似文献
109.
简要叙述了稠密等离子体聚焦装置作为中子发生器的工作原理,对影响稠密等离子体聚焦装置放电出中子产额及其稳定性的一些因素和改进措施进行了简单讨论.通过使用不同电极形状的场畸变开关很好地提高了焦点装置的运行,使装置输出中子的起伏得到明显的改善.通过对腔内电极的清洁,在不更换气体的条件下,聚焦装置放电出中子产额稳定.The principle of dense plasma focus(DPF) as neutron generator has been investigated in this paper. We have stated briefly some factors that mainly influnce the DPF s neutron yield and some methods improving the stability of neutron yields on the dense plasma focus. It is showed that the fluctuation of DPF output neutron becomes smaller by using different types of field-distortion elements. Over 100 consecutive shots without purging the test gas the neutron yields has no obvious change. 相似文献
110.
We consider the problem of determining the dielectric permittivity for a nonconducting and nonmagnetic medium. As information we take the traces of the tangential components of the electromagnetic field on the lateral surface of a cylindrical domain. These traces correspond to a solution to some direct problem for the Maxwell system. The impulse source of the current flux lies outside the domain in which the coefficient is sought. The main result of the article is a stability estimate for a solution to the inverse problem in question. 相似文献