全文获取类型
收费全文 | 9978篇 |
免费 | 1590篇 |
国内免费 | 678篇 |
专业分类
化学 | 3012篇 |
晶体学 | 42篇 |
力学 | 827篇 |
综合类 | 309篇 |
数学 | 3995篇 |
物理学 | 4061篇 |
出版年
2024年 | 31篇 |
2023年 | 152篇 |
2022年 | 472篇 |
2021年 | 468篇 |
2020年 | 324篇 |
2019年 | 267篇 |
2018年 | 213篇 |
2017年 | 378篇 |
2016年 | 432篇 |
2015年 | 350篇 |
2014年 | 599篇 |
2013年 | 819篇 |
2012年 | 617篇 |
2011年 | 588篇 |
2010年 | 556篇 |
2009年 | 647篇 |
2008年 | 635篇 |
2007年 | 636篇 |
2006年 | 538篇 |
2005年 | 466篇 |
2004年 | 377篇 |
2003年 | 390篇 |
2002年 | 344篇 |
2001年 | 275篇 |
2000年 | 292篇 |
1999年 | 225篇 |
1998年 | 219篇 |
1997年 | 184篇 |
1996年 | 150篇 |
1995年 | 92篇 |
1994年 | 86篇 |
1993年 | 92篇 |
1992年 | 45篇 |
1991年 | 41篇 |
1990年 | 41篇 |
1989年 | 23篇 |
1988年 | 21篇 |
1987年 | 16篇 |
1986年 | 30篇 |
1985年 | 21篇 |
1984年 | 24篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 12篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1959年 | 4篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
A. V. Balakrishnan 《Applied Mathematics and Optimization》1995,31(2):177-187
In this paper we generalize the Kalman-Yakubovic lemma to infinite dimensions—or, more precisely, to semigroups of operators over a Hilbert space. The proof differs substantially from the finite-dimensional version and is based on the Paley-Wiener-Helson-Lowdenslager factorization theorem. 相似文献
932.
After establishing hemi-Parkinsonian rat models, the relationships between neuron death and the expression of several proteins, such as c-Fos, GFAP, GDNF, NF-κB and some cytokines were determined. Therapeutics experiments with notoginsenoside-Rg1 were carried out. The research results show that the expressions of GFAP, NF-κB and c-Fos will obviously increase in the lesion side of the striatum and the expression of GDNF will decrease, which implies that the signal transduction pathway may participate in the apoptosis in neurons. The levels of some cytokines such as TNF-α, IL-1β in the striatum of PD rat models increased compared to those of normal rats. The results of the therapeutics experiments show that notoginsenoside-Rg1 may repress the immune inflammation response and regulate the immune function through the neuro-immune molecular network. Therefore, notoginsenoside-Rg1 can be used as an effective drug for anti-oxidation and anti-inflammation, and can be used in the therapy of Parkinson's disease(PD). 相似文献
933.
A class of service stage Petri net models whose equilibrium probabilities satisfy local balance equations is presented. Examples of their applicability include bus oriented multiprocessor interconnections, the classical dining philosophers problem and the alternating bit protocol. The natural topological space for embedding the state transition lattice for this class of SSPN is shown to be a multidimensional toroidal manifold. 相似文献
934.
G. A. Kohring 《Journal of statistical physics》1990,59(3-4):1077-1086
Using a multi-spin coding algorithm, the Hopfield model is studied for network sizes up toN=33,968. Thermodynamically stable states are found in a region where the replica-symmetric solution predicts none should exist, but where a one-step replica symmetry-breaking calculation predicts some should exist. Furthermore, the order parameter in this region is found to take on two distinct values, one of which is not predicted by any theory. 相似文献
935.
The prolapse-free relativistic adapted Gaussian basis sets (RAGBSs), developed by our research group on the basis of the four-component approach, are used for the first time in Douglas–Kroll–Hess 2nd order scalar relativistic calculations (DKH2) of simple diatomic molecules containing Hydrogen and the halogens from Fluorine up to Iodine: HX and X2, where X = F, Cl, Br, and I. To this end, the RAGBSs were contracted with the general contraction scheme to triple-, quadruple-, and quintuple-zeta sets. Polarization functions were also added to the basis sets by optimization with the configuration interaction method including single and double excitations into the DKH2 environment, DKH2-CISD. The molecular properties were then calculated with the coupled cluster electronic correlation treatment and the DKH2 scalar relativistic method, DKH2-CCSD(T), and indicated that our RAGBSs should be contracted as quadruple-zeta basis sets. The results achieved with the DKH2-CCSD(T) calculations and the selected quadruple-zeta RAGBSs are able to reproduce the experimental data of equilibrium distances, dissociation energies, and harmonic vibrational frequencies with root-mean-square (rms) errors of 0.015 Å, 3.6 kcal mol−1, and 21.7 cm−1, respectively. 相似文献
936.
B. T. Bilalov 《Siberian Mathematical Journal》2006,47(1):18-27
We consider power systems with complex-valued coeficients. We establish a necessary and suficient condition for completeness and minimality and also a necessary condition for the basis property of these systems in Lebesgue spaces. 相似文献
937.
基于神经网络中小城市空气污染指数预估器的设计 总被引:5,自引:0,他引:5
针对大气环境参数预测精确性和可靠性的要求提出一种基于 BP神经网络快速收敛算法 ,经仿真表明提出的这一算法切实可行 . 相似文献
938.
A nonnormable ?-space possessing an unconditional basis is not necessarily isomorphic to a generalized Köthe space. 相似文献
939.
有限域上互反本原正规元的存在性 总被引:1,自引:0,他引:1
设q是素数方幂,n是正整数,Fqn是qn个元素的有限域.本文证明了:当正整数n≥32时,对任意的素数方幂q,存在Fqn中的本原元ξ满足ξ和ξ-1都是Fqn 在Fq上的正规元,也即{ξ,ξq,…,ξqn-1}和{ξ-1,ξ-q,…,ξ-qn-1)都构成Fqn在Fq 上的本原正规基. 相似文献
940.
遗传算法BP神经网络的预报研究和应用 总被引:26,自引:1,他引:25
针对目前 BP神经网络在实际气象预报应用中 ,网络结构难以确定以及网络极易陷入局部解问题 ,用遗传算法优化神经网络的连接权和网络结构 ,并在遗传进化过程中采取保留最佳个体的方法 ,建立基于遗传算法的 BP网络模型 ,并以广西的月降水量进行实例分析 ,计算结果表明 ,该方法预报精度高、而且稳定 . 相似文献