全文获取类型
收费全文 | 19169篇 |
免费 | 2196篇 |
国内免费 | 1678篇 |
专业分类
化学 | 4075篇 |
晶体学 | 98篇 |
力学 | 1347篇 |
综合类 | 417篇 |
数学 | 10908篇 |
物理学 | 6198篇 |
出版年
2024年 | 22篇 |
2023年 | 143篇 |
2022年 | 399篇 |
2021年 | 466篇 |
2020年 | 402篇 |
2019年 | 407篇 |
2018年 | 411篇 |
2017年 | 569篇 |
2016年 | 599篇 |
2015年 | 471篇 |
2014年 | 953篇 |
2013年 | 1383篇 |
2012年 | 976篇 |
2011年 | 1158篇 |
2010年 | 987篇 |
2009年 | 1165篇 |
2008年 | 1290篇 |
2007年 | 1320篇 |
2006年 | 1118篇 |
2005年 | 1037篇 |
2004年 | 882篇 |
2003年 | 841篇 |
2002年 | 802篇 |
2001年 | 606篇 |
2000年 | 603篇 |
1999年 | 542篇 |
1998年 | 533篇 |
1997年 | 442篇 |
1996年 | 364篇 |
1995年 | 292篇 |
1994年 | 279篇 |
1993年 | 182篇 |
1992年 | 170篇 |
1991年 | 147篇 |
1990年 | 114篇 |
1989年 | 111篇 |
1988年 | 102篇 |
1987年 | 91篇 |
1986年 | 65篇 |
1985年 | 99篇 |
1984年 | 69篇 |
1983年 | 67篇 |
1982年 | 71篇 |
1981年 | 51篇 |
1980年 | 46篇 |
1979年 | 46篇 |
1978年 | 45篇 |
1977年 | 22篇 |
1976年 | 21篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
BEM for simulation of a 2D elastic body with randomly distributed circular inclusions 总被引:7,自引:0,他引:7
Based on our 2D BEM software THBEM2 which can be applied to the simulation of an elastic body with randomly distributed identical
circular holes, a scheme of BEM for the simulation of elastic bodies with randomly distributed circular inclusions is proposed.
The numerical examples given show that the boundary element method is more accurate and more effective than the finite element
method for such a problem. The scheme presented can also be successfully used to estimate the effective elastic properties
of composite materials.
Project supported by the National Natural Science Foundation of China (No. 19772025). 相似文献
72.
73.
Jiyong Park 《Entropy (Basel, Switzerland)》2022,24(2)
We derive the lower bounds for a non-Gaussianity measure based on quantum relative entropy (QRE). Our approach draws on the observation that the QRE-based non-Gaussianity measure of a single-mode quantum state is lower bounded by a function of the negentropies for quadrature distributions with maximum and minimum variances. We demonstrate that the lower bound can outperform the previously proposed bound by the negentropy of a quadrature distribution. Furthermore, we extend our method to establish lower bounds for the QRE-based non-Gaussianity measure of a multimode quantum state that can be measured by homodyne detection, with or without leveraging a Gaussian unitary operation. Finally, we explore how our lower bound finds application in non-Gaussian entanglement detection. 相似文献
74.
Free-space quantum key distribution (QKD) has attracted considerable attention due to its lower channel loss and link flexibility. It allows two participants share theoretical unconditional secure keys, and can potentially be applied to air-to-ground quantum communication to establish a global quantum network. Free-space QKD using modulating retro-reflectors (MRR-QKD) significantly reduces the pointing requirement and simplifies the structure of the mobile terminal, therefore making it suitable for lightweight aircraft such as unmanned aerial vehicle and Cubesat, etc. Based on intensity modulation of two non-orthogonal states and the B92 protocol, we proposed a scheme to improve the previous work (Optics Express 2018, 26, 11331). Our scheme simplifies the optical structure and shows more robustness in equipment imperfection. The analysis and simulation show that the number of multiple quantum well modulators needed in our scheme decreases from eight to three with similar performance. Additionally, while the previous scheme cannot work due to low modulator extinction ratio or high optical misalignment, our scheme can still operate. 相似文献
75.
A random vector (X1, …, Xn), with positive components, has a Liouville distribution if its joint probability density function is of the formf(x1 + … + xn)x1a1.1 … xnan.1 with theai all positive. Examples of these are the Dirichlet and inverted Dirichlet distributions. In this paper, a comprehensive treatment of the Liouville distributions is provided. The results pertain to stochastic representations, transformation properties, complete neutrality, marginal and conditional distributions, regression functions, and total positivity and reverse rule properties. Further, these topics are utilized in various characterizations of the Dirichlet and inverted Dirichlet distributions. Matrix analogs of the Liouville distributions are also treated, and many of the results obtained in the vector setting are extended appropriately. 相似文献
76.
77.
Photoelectron angular distribution (PAD) in the laboratory frame for randomly oriented molecules is typically described by a single anisotropy parameter, the so-called asymmetry parameter. However, especially from a theoretical perspective, it is more natural to consider molecular photoionization by using a molecular frame. The molecular frame PADs (MFPADs) may be used to extract information about the electronic structure of the system studied. In the last decade, significant experimental efforts have been directed to MFPAD measurements. MFPADs are highly characterizing signatures of the final ionic states. In particular, they are very sensitive to the nature of the final state, which is embodied in the corresponding Dyson orbital. In our previous work on acetylacetone, a prototype system for studying intra-molecular hydrogen bond interactions, we followed the dynamics of the excited states involved in the photoexcitation–deexcitation process of this molecule. It remains to be explored the possibility of discriminating between different excited states through the MFPAD profiles. The calculation of MFPADs to differentiate excited states can pave the way to the possibility of a clear discrimination for all the cases where the recognition of excited states is otherwise intricate. 相似文献
78.
79.
N. Villedieu T. Quintino M. Ricchiuto H. Deconinck 《Journal of computational physics》2011,230(11):4301-4315
We construct a third order multidimensional upwind residual distribution scheme for the system of the Navier–Stokes equations. The underlying approximation is obtained using standard P2 Lagrange finite elements. To discretise the inviscid component of the equations, each element is divided in sub-elements over which we compute a high order residual defined as the integral of the inviscid fluxes on the boundary of the sub-element. The residuals are distributed to the nodes of each sub-element in a multi-dimensional upwind way. To obtain a discretisation of the viscous terms consistent with this multi-dimensional upwind approach, we make use of a Petrov–Galerkin analogy. The analogy allows to find a family of test functions which can be used to obtain a weak approximation of the viscous terms. The performance of this high-order method is tested on flows with high and low Reynolds number. 相似文献
80.
液氘在高压下有丰富的电学光学性质。利用反射率和相对介电函数关系并从广义极化角度出发初步建立了计算低Z材料电导率的简易模型;在神光-Ⅱ装置上利用第九路激光冲击加载液氘材料并测量了其在强激光冲击下的高压状态参数和反射率。结合上述理论模型和实验,研究了高压下液氘的电离度和电导率。结果表明,液氘在约70 GPa时的电导率约为2.87105 (Wm)-1,已呈现出较为明显的金属电导特性。显然,冲击加载下液氘从绝缘分子态开始电离并向金属氘转变发生在更低的压强。 相似文献