全文获取类型
收费全文 | 70015篇 |
免费 | 5225篇 |
国内免费 | 6527篇 |
专业分类
化学 | 27871篇 |
晶体学 | 324篇 |
力学 | 6268篇 |
综合类 | 1237篇 |
数学 | 24989篇 |
物理学 | 21078篇 |
出版年
2023年 | 536篇 |
2022年 | 1035篇 |
2021年 | 1193篇 |
2020年 | 1333篇 |
2019年 | 1570篇 |
2018年 | 1295篇 |
2017年 | 1544篇 |
2016年 | 1794篇 |
2015年 | 1639篇 |
2014年 | 2333篇 |
2013年 | 4496篇 |
2012年 | 2736篇 |
2011年 | 3100篇 |
2010年 | 2671篇 |
2009年 | 3821篇 |
2008年 | 4255篇 |
2007年 | 4467篇 |
2006年 | 4221篇 |
2005年 | 3552篇 |
2004年 | 3288篇 |
2003年 | 3343篇 |
2002年 | 3046篇 |
2001年 | 2552篇 |
2000年 | 2507篇 |
1999年 | 2258篇 |
1998年 | 2110篇 |
1997年 | 1725篇 |
1996年 | 1537篇 |
1995年 | 1409篇 |
1994年 | 1291篇 |
1993年 | 1108篇 |
1992年 | 1080篇 |
1991年 | 824篇 |
1990年 | 687篇 |
1989年 | 595篇 |
1988年 | 548篇 |
1987年 | 433篇 |
1986年 | 367篇 |
1985年 | 432篇 |
1984年 | 424篇 |
1983年 | 207篇 |
1982年 | 341篇 |
1981年 | 399篇 |
1980年 | 302篇 |
1979年 | 292篇 |
1978年 | 221篇 |
1977年 | 206篇 |
1976年 | 154篇 |
1974年 | 109篇 |
1973年 | 104篇 |
排序方式: 共有10000条查询结果,搜索用时 335 毫秒
981.
本文分析了传统的网络可靠性优化设计方法所存在的问题 ,给出了网络的通信通路数的定义 ,并基于网络的通信通路数给出了更能反映网络运行的实际情况的网络可靠性的定量模型 ,从而解决了传统网络可靠性优化设计方法所存在的问题 . 相似文献
982.
T. González-Lezana G. Delgado-Barrio P. Villarreal F.X. Gadéa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):227-232
The stabilization method is applied to the case of interacting resonances in the photo-dissociation of van der Waals clusters
composed by a rare gas atom bound to a dihalogen molecule. The study of an illustrative two-dimensional model consisting in
a T-shaped NeI2 molecule shows the adequacy of the method whenever the projection of the stabilization wave functions on the assumed prepared
initial state is accounted for. The agreement of the fragmentation cross-sections with some previous results using the effective
resolvent method and accurate close-coupling calculations is excellent. The method reveals its utility as a complementary
tool since allows, through the analysis of the stabilization wave function in terms of zero-order levels, a precise characterization
of the resonant states involved.
Received 5 April 2002 / Received in final form 24 May 2002 Published online 19 July 2002 相似文献
983.
该文给出了Logistic分布纪录值序列部分和的中心极限定理;对于Pareto分布纪录值序列的部分和T_n,获得了lnT_n的中心极限定理.这一工作不仅具有概率论的极限理论方面的研究价值,而且在金融、保险等领域也具有相当重要的应用前景. 相似文献
984.
The constants of binding dye molecules with the micelles of sodium dodecyl sulfate are determined using quenching of delayed fluorescence of acridine dyes by sodium iodide in aqueous–micellar solutions. Kinetic equations have been composed that describe the processes of deactivation of the excited states of dyes. By solving these equations at the concentration of the quencher sodium iodide corresponding to the minimum lifetime of triplet states and at the concentration of micelles corresponding to the least value of the delayed fluorescence quenching rate constants, we obtained the constants of binding dyes with micelles equal to 1.3·107, 2.9·107, and 3.1·107 M–1 for trypaflavine, acridine orange, and acridine yellow, respectively. We calculated the rate constants of quenching of the triplet states of the molecules of dyes by iodide ions (I
–) that decreased in transition from trypaflavine to acridine orange and acridine yellow. 相似文献
985.
N. B. Brusnikina A. V. Lotov 《Computational Mathematics and Mathematical Physics》2007,47(11):1779-1787
A method is proposed for approximating the reachable set of a dynamic system with a state space dimension no higher than six-eight considered on a finite time interval. The system is governed by linear differential equations with piecewise constant coefficients and impulse actions specified at prescribed times. The method is based on guaranteed-accuracy polyhedral approximations of reachable sets at researcher-specified times. Every approximation is constructed using the preceding one. A procedure is described for choosing parameters of the method that ensure the required accuracy with close-to-minimal time costs. 相似文献
986.
讨论具有无穷时滞中立型泛函微分方程$ \frac{\rm d}{{\rm d}t}\left(x(t)-\int_{-\infty}^{0}g(s,x(t+s)){\rm d}s\right) =A(t,x(t))x(t)+f(t,x_t)$的周期解问题,利用重合度理论中的延拓定理得到了周期解的存在性和唯一性条件;特别地,当$g(s,x)\equiv 0, A(t,x)=A(t)$时, 给出了存在唯一稳定周期解的条件. 相似文献
987.
988.
A simple and rapid method is developed to determine the high acidity and the basicity of solutions by chronopotentiometry with a platinum working electrode. The acidity range from 5.0 mol/l H+ to 1.0 mol/l OH− can be measured by the adjustment of deposition potential and time. The response mechanism to acidity and basicity has been explored. The transition potential plateau in chronopotentiograms is caused from the oxidation of hydrogen adsorbed on electrode surface. 相似文献
989.
傅里叶变换红外光谱固体制样技术 总被引:2,自引:1,他引:1
通过对溴化钾与纳米固体超强酸样品的比例进行了探讨 ,得出制样时溴化钾与样品比例范围为1∶ 0 .0 0 1— 1∶ 0 .0 2 9,其最佳比例范围为 1∶ 0 .0 0 98— 1∶ 0 .0 1 5 ,并且应用于其他固体样品的测定 ,结果基本一致。同时得出 ,固体样品的最少检测量为 2 .0× 1 0 -5g 相似文献
990.
A. Meister 《Mathematical Methods of Statistics》2007,16(1):63-76
This paper addresses the statistical problem of density deconvolution under the condition that the density to be estimated
has compact support. We introduce a new estimation procedure, which establishes faster rates of convergence for smooth densities
as compared to the optimal rates for smooth densities with unbounded support. This framework also allows us to relax the usual
condition of known error density with non-vanishing Fourier transform, so that a nonparametric class of densities is valid;
therefore, even the shape of the noise density need not be assumed. These results can also be generalized for fast decaying
densities with unbounded support. We prove optimality of the rates in the underlying experiment and study the practical performance
of our estimator by numerical simulations.
相似文献