全文获取类型
收费全文 | 10822篇 |
免费 | 2380篇 |
国内免费 | 1855篇 |
专业分类
化学 | 5470篇 |
晶体学 | 115篇 |
力学 | 624篇 |
综合类 | 127篇 |
数学 | 1249篇 |
物理学 | 7472篇 |
出版年
2024年 | 20篇 |
2023年 | 106篇 |
2022年 | 236篇 |
2021年 | 272篇 |
2020年 | 342篇 |
2019年 | 251篇 |
2018年 | 248篇 |
2017年 | 310篇 |
2016年 | 359篇 |
2015年 | 437篇 |
2014年 | 593篇 |
2013年 | 869篇 |
2012年 | 668篇 |
2011年 | 782篇 |
2010年 | 707篇 |
2009年 | 801篇 |
2008年 | 865篇 |
2007年 | 873篇 |
2006年 | 786篇 |
2005年 | 720篇 |
2004年 | 532篇 |
2003年 | 599篇 |
2002年 | 511篇 |
2001年 | 428篇 |
2000年 | 416篇 |
1999年 | 384篇 |
1998年 | 306篇 |
1997年 | 259篇 |
1996年 | 228篇 |
1995年 | 166篇 |
1994年 | 168篇 |
1993年 | 128篇 |
1992年 | 123篇 |
1991年 | 108篇 |
1990年 | 51篇 |
1989年 | 73篇 |
1988年 | 49篇 |
1987年 | 44篇 |
1986年 | 22篇 |
1985年 | 49篇 |
1984年 | 26篇 |
1983年 | 15篇 |
1982年 | 34篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1975年 | 5篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
How can the basic compatibility of theory and observations be investigated for nonlinear processes without requiring stochastic characterizations for residual error terms? The present paper proposes a flexible least-cost approach. For each possible estimatex for the sequence of process states, letc D (x) andx M(x) denote the costs incurred for deviations away from the prior dynamic specifications and prior measurement specifications, respectively. Define the cost-efficiency frontier to be the greatest lower bound for the set of all possible cost pairs [c D (x),c M(x)], conditional on the given observations. State sequence estimatesx that attain the cost-efficiency frontier indicate the possible ways that the actual process could have developed over time in a manner minimally incompatible with the prior dynamic and measurement specifications. An algorithm is developed for the exact sequential updating of the cost-efficient state sequence estimates as the duration of the process increases and additional observations are obtained. 相似文献
72.
使用“对称性匹配簇-组态相互作用”方法,对Li2分子三重态的第一激发态、LiH分子的基态、单重态的第一和第二激发态的几何构型与谐振频率进行了优化计算.利用“群操作求和”方法分别对这4个态进行单点能扫描计算,并拟合出了相应各态的Murrell-Sorbie势能函数.使用多种方法对Li2H分子的基态结构进行优化,并用优选出的密度泛函(B3P86)方法对该分子进行了进一步的频率计算.结果发现Li2H分子的基态稳态结构为C2v构型,在此基础上用多体项展式理论导出了它的解析势能函数,其等值势能图准确再现了Li2H分子的结构特征和离解能.首次报导了该分子对称伸缩振动等值势能图中存在的两个对称鞍点,对应于反应LiH Li→Li2H,活化能大约为18.7×4.184 KJ/mol. 相似文献
73.
非对称三态叠加多模泛函叠加态光场的高次压缩——广义电场分量的不等幂次和压缩效应研究 总被引:2,自引:0,他引:2
多模真空态|{0j}〉q与两个空间强度分布特征不同的多模复共轭泛函相干态|{f(j a)*(x,y,z)}〉q和|{f(j b)*(x,y,z)}〉q的线性叠加组成的三态叠加多模泛函叠加态光场|ψ(f3)〉q,利用多模压缩态理论,研究了态|ψ(f3)〉q中广义电场分量的不等幂次高次和(H)压缩特性.结果表明:在一定的条件下,态|ψ(f3)〉q的广义电场分量可呈现出周期性变化的任意奇数次和任意偶数次的不等幂次高次H压缩效应;光场的经典振幅和经典初始相位的任意非对称空间分布特征对其压缩程度和压缩深度等压缩特性将产生直接的影响. 相似文献
74.
Chemical techniques were employed to synthesize CdS nanoparticles embedded in polymer (PEG 300) and sol-gel silica matrices. Systematic growth of particles (radius 3–9 nm) was obtained by adjusting post-deposition annealing temperature and time to examine the dependence of surface-state–related luminescence on particle size. Photoluminescence (PL) peak energy showed a linear dependence with a gentle slope in the weak confinement region and a steep slope in the strong confinement region, the divergence being observed near the excitonic Bohr radius for CdS. The empirical relation proposed for the weak confinement region could be used for estimating chemically prepared CdS nanoparticle size with a high degree of reliability from PL peak energy. 相似文献
75.
Let { X n} be a Markov chain that is either f -mixing or satisfies the Poisson equation.In this note we obtain the convergence rate under L 1 -criterion for bounded functions of the X k 's. And in the hidden Markov model setup { (X n ,Y n ) }we study the kernel estimate of the density of the observed variables { Y n }when a 'stable' status is reached. 相似文献
77.
The convergent iterative procedure for solving the groundstate Schr?dinger
equation is extended to derive the excitation energy and the wavefunction of the
low-lying excited states. The method is applied to the one-dimensional quartic
potential problem. The results show that the iterative solution converges rapidly
when the coupling g is not too small. 相似文献
78.
Howel Tong 《应用数学学报(英文版)》2002,18(2):177-184
Abstract I reflect upon the development of nonlinear time series analysis since 1990 by focusing on five majorareas of development. These areas include the interface between nonlinear time series analysis and chaos,thenonparametric/semiparametric approach,nonlinear state space modelling,financial time series and nonlinearmodelling of panels of time series. 相似文献
79.
Recent joint theoretical and experimental investigations of Auger core-core-valence spectra of alkali adatoms on simple metals have revealed that such technique is capable to ascertain contributions from different adsorption environments in the signal [M.I. Trioni, S. Caravati, G.P. Brivio, L. Floreano, F. Bruno, A. Morgante, Phys. Rev. Lett. 93 (2004) 206802]. Consequently, to verify if such an effect is present also for other chemical species, we study theoretically the KLV transition of oxygen either as a bulk impurity or as an adsorbate in/on Al and Ag (jellium-like). We make use of the Fermi golden rule in which the matrix elements of the interaction are calculated within DFT. We verify that the relevant physical quantity of this phenomenon is the excited local density of states (LDOS), calculated within a region centered on the core ionized atom. The Auger rate for oxygen in Ag bulk displays a single asymmetric peak, while for adsorbed oxygen a second smaller feature at lower energies, and very close to the first one, appears. This unexpected result follows from the removal of the degeneracy of the m quantum number of the 2p states of oxygen at the surface. It is only displayed on the electronically less dense metal (Ag), but not on Al. 相似文献
80.