全文获取类型
收费全文 | 365篇 |
免费 | 18篇 |
国内免费 | 30篇 |
专业分类
化学 | 53篇 |
晶体学 | 1篇 |
力学 | 106篇 |
综合类 | 17篇 |
数学 | 128篇 |
物理学 | 108篇 |
出版年
2023年 | 9篇 |
2022年 | 14篇 |
2021年 | 11篇 |
2020年 | 10篇 |
2019年 | 9篇 |
2018年 | 11篇 |
2017年 | 12篇 |
2016年 | 14篇 |
2015年 | 10篇 |
2014年 | 21篇 |
2013年 | 20篇 |
2012年 | 23篇 |
2011年 | 12篇 |
2010年 | 16篇 |
2009年 | 17篇 |
2008年 | 20篇 |
2007年 | 23篇 |
2006年 | 21篇 |
2005年 | 13篇 |
2004年 | 18篇 |
2003年 | 8篇 |
2002年 | 16篇 |
2001年 | 15篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 10篇 |
1992年 | 2篇 |
1990年 | 4篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有413条查询结果,搜索用时 15 毫秒
51.
Victor García Jesús Sánchez-Márquez Estefanía Torres David Zorrilla Manuel Fernández 《International journal of quantum chemistry》2020,120(6):e26129
As part of previous studies, we introduced a new type of basis function named Simplified Box Orbitals (SBOs) that belong to a class of spatially restricted functions which allow the zero differential overlap (ZDO) approximation to be applied with complete accuracy. The original SBOs and their Gaussian expansions SBO-3G form a minimal basis set, which was compared to the standard Slater-type orbital basis set (STO-3G). In the present paper, we have developed the SBO basis functions at double-zeta (DZ) level, and we have assessed the option of expanding the SBO-DZ as a combination of Gaussian functions. Finally, we have determined the quality of the new basis set by comparing the molecular properties calculated with SBO-nG with those achieved with some standard basis sets. 相似文献
52.
Let be a distance-regular graph of diameter d and valency k > 2. Suppose there exists an integer s with d 2s such that c
i
= b
d-i
for all 1 i s. Then is an antipodal double cover. 相似文献
53.
Venera Khoromskaia Boris N. Khoromskij 《Numerical Linear Algebra with Applications》2016,23(2):249-271
In this paper, we present a method for fast summation of long‐range potentials on 3D lattices with multiple defects and having non‐rectangular geometries, based on rank‐structured tensor representations. This is a significant generalization of our recent technique for the grid‐based summation of electrostatic potentials on the rectangular L × L × L lattices by using the canonical tensor decompositions and yielding the O(L) computational complexity instead of O(L3) by traditional approaches. The resulting lattice sum is calculated as a Tucker or canonical representation whose directional vectors are assembled by the 1D summation of the generating vectors for the shifted reference tensor, once precomputed on large N × N × N representation grid in a 3D bounding box. The tensor numerical treatment of defects is performed in an algebraic way by simple summation of tensors in the canonical or Tucker formats. To diminish the considerable increase in the tensor rank of the resulting potential sum, the ?‐rank reduction procedure is applied based on the generalized reduced higher‐order SVD scheme. For the reduced higher‐order SVD approximation to a sum of canonical/Tucker tensors, we prove the stable error bounds in the relative norm in terms of discarded singular values of the side matrices. The required storage scales linearly in the 1D grid‐size, O(N), while the numerical cost is estimated by O(NL). The approach applies to a general class of kernel functions including those for the Newton, Slater, Yukawa, Lennard‐Jones, and dipole‐dipole interactions. Numerical tests confirm the efficiency of the presented tensor summation method; we demonstrate that a sum of millions of Newton kernels on a 3D lattice with defects/impurities can be computed in seconds in Matlab implementation. The tensor approach is advantageous in further functional calculus with the lattice potential sums represented on a 3D grid, like integration or differentiation, using tensor arithmetics of 1D complexity. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
54.
以优化特大型桥梁防撞钢套箱防撞效果为目标,对防撞钢套箱的设计构造、尺寸、钢板厚度等进行参数分析,探讨了钢套箱构造及钢板厚度等对防撞效果的影响规律,并对钢套箱与船舶碰撞过程进行推理.结果表明:合理地选取钢套箱的结构形式及尺寸,并使其刚度与碰撞船艏相匹配,可有效地减少对基础的局部破坏,使防撞钢套箱发挥更大的防撞效果. 相似文献
55.
对箱梁各翼板(顶板、悬臂板、底板)分设不同剪力滞广义纵向位移,其横向分布均取二次抛物线形式,并引入载荷横向位置参数η,以分析载荷横向变位对剪力滞效应的影响.运用能量变分原理,建立剪力滞控制微分方程,求解了简支梁和悬臂梁在均布载荷作用下的控制微分方程的解.算例分析表明:载荷横向变位改变直接承受载荷的翼板的正负剪力滞特性,对非直接承载翼板只改变其应力幅度;箱梁横向框架效应对直接承载翼板纵向应力的贡献远远大于剪切变形.与块体有限元分析结果较吻合,表明该算法能较准确分析载荷横向变位作用下箱梁剪力滞的变化规律. 相似文献
56.
57.
58.
根据神光Ⅲ激光器的运作方式和靶室结构,配套建设的X射线条纹相机在结构和性能上同以往有很大不同,建成后不仅应用于高时间分辨的实验诊断,也将用于神光Ⅲ主机各束激光同步性能的检验.设计的X射线条纹相机将全部采用模块化组件,拥有优于10 ps的时间分辨、15 lp/mm以上的空间分辨以及100 eV-10 keY能区的光阴极响应.相机在结构方面采用了非常独特的密闭气室结构,变像管、CCD,所有的电气控制设备都寄宿在气室内并保持常温和一个大气压的工作状态.整个相机系统内嵌了计算机工控设备,通过一根以太网线获得相机所有功能的远程控制.相机其它的特性还包括拥有完善的安全互锁系统以确保相机远程控制的安全;满足严格的EMI/EMP屏蔽要求以避免神光Ⅲ主机高能量激光发射带来的电磁干扰,并可采用光纤引入紫外时标光建立信号的绝对时间基准. 相似文献
59.
60.
The three dimensional structure of Ferric uptake regulation protein dimer from E. coli, determined by molecular modeling, was docked on a DNA fragment (iron box) and Zn2+ ions were added in two steps. The first step involved the binding of one Zn2+ ion to what is known as the zinc site which consists of the residues Cys 92, Cys 95, Asp 137, Asp141, Arg139, Glu 140, His
145 and His 143 with an average metal-Nitrogen distance of 2.5 Å and metal-oxygen distance of 3.1–3.2 Å. The second Zn2+ ion is bound to the iron activating site formed from the residues Ile 50, His 71, Asn 72, Gly 97, Asp 105 and Ala 109. The
binding of the second Zn2+ ion strengthened the binding of the first ion as indicated by the shortening of the zinc-residue distances. Fe2+, when added to the complex consisting of 2Zn2+/Fur dimer/DNA, replaced the Zn2+ ion in the zinc site and when a second Fe2+ was added, it replaced the second zinc ion in the iron activating site. The binding of both zinc and iron ions induced a
similar change in Fur conformations, but shifted residues closer to DNA in a different manner. This is discussed along with
a possible role for the Zn2+ ion in the Fur dimer binding of DNA in its repressor activity.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献