全文获取类型
收费全文 | 825篇 |
免费 | 13篇 |
国内免费 | 7篇 |
专业分类
化学 | 522篇 |
晶体学 | 7篇 |
力学 | 19篇 |
数学 | 156篇 |
物理学 | 141篇 |
出版年
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 13篇 |
2017年 | 5篇 |
2016年 | 14篇 |
2015年 | 8篇 |
2014年 | 10篇 |
2013年 | 47篇 |
2012年 | 36篇 |
2011年 | 64篇 |
2010年 | 23篇 |
2009年 | 26篇 |
2008年 | 59篇 |
2007年 | 60篇 |
2006年 | 53篇 |
2005年 | 36篇 |
2004年 | 36篇 |
2003年 | 38篇 |
2002年 | 23篇 |
2001年 | 10篇 |
2000年 | 17篇 |
1999年 | 8篇 |
1998年 | 16篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 20篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 17篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 16篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1970年 | 3篇 |
1966年 | 2篇 |
1942年 | 2篇 |
排序方式: 共有845条查询结果,搜索用时 3 毫秒
1.
2.
在空间电荷主导电子束研究中,纵向聚焦非常重要,在输运过程中由于强空间电荷力的影响,束团将很快变长并崩溃,马里兰大学的电子环设计用于方形束团和抛物线形束团的研究,环中需要用三个感应腔对束团进行纵向聚焦.文中首先介绍了方形束团和抛物线形束团的纵向束流动力学,推导了两种束团纵向聚焦所需要的5MHz重复率高压脉冲波形,并给出了实现纵向聚焦的感应腔设计及其特殊要求. 相似文献
3.
A Network Simulation of High-congestion Road-traffic Flows in Cities with Marine Container Terminals
James A. Pope Terry R. Rakes Loren Paul Rees Ingrid W. M. Crouch 《The Journal of the Operational Research Society》1995,46(9):1090-1101
Port cities where marine cargo terminals are located are generally near urban areas characterized by high-congestion road traffic. Changes in cargo traffic volumes into a marine terminal, or in the surrounding traffic arteries, which carry this traffic, can significantly affect the terminal's operations. Conversely, activity at the terminal can have an impact on the traffic levels and congestion for a considerable distance from the terminal. This paper demonstrates a methodology useful for studying the impact of road traffic flows on marine container terminals located in highly congested areas. This model was developed at the request of the Virginia Center for World Trade and was used to answer three planning questions in the port of Hampton Roads, Virginia, USA-what would be the impact of: opening a new section of interstate highway, a projected doubling of container traffic at one terminal, and a daily unit train in the vicinity of another terminal. The problem was made more challenging by limited data-collection funds. None the less, the model was deemed valid by a panel of traffic experts and officials from several major state and private agencies involved in marine traffic management. The model results were subsequently a factor in two major decisions related to terminal management. 相似文献
4.
5.
6.
7.
KL Britton HF Rogers Y Asano T Dairi Y Kato TJ Stillman DW Rice 《Acta crystallographica. Section D, Biological crystallography》1998,53(4):124-126
The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres. 相似文献
8.
9.
Jonathan A. Yoffe Gerald M. Maggiora A.Terry Amos 《Theoretical chemistry accounts》1981,58(2):137-144
Stieltjes conditions and the ratio test provide necessary but not sufficient conditions onS(-2k) dipole sums. If the dipole sums are accurate the associated [n, n –1] Padé approximant provides a better representation of (), the frequency-dependent dipole polarizability, than a truncated series expression and, in addition, should bound () below. It is shown how constraints on the dipole sums effect the form of the [2,1] Padé approximant and an additional constraint is derived that ensures the analyticity of the approximant on 0 < 1. There then follows a discussion of the reliability of available literature dipole sum values for small molecules containing H, C, N and O. 相似文献
10.
A parallel version of the popular molecular mechanics package AMBER suitable for execution on workstation clusters has been developed. Computer-intensive portions of molecular dynamics or free-energy perturbation computations, such as nonbonded pair list generation or calculation of nonbonded energies and forces, are distributed across a collection of Unix workstations linked by Ethernet or FDDI connections. This parallel implementation utilizes the message-passing software PVM (Parallel Virtual Machine) from Oak Ridge National Laboratory to coordinate data exchange and processor synchronization. Test simulations performed for solvated peptide, protein, and lipid bilayer systems indicate that reasonable parallel efficiency (70–90%) and computational speedup (2–5 × serial computer runtimes) can be achieved with small workstation clusters (typically six to eight machines) for typical biomolecular simulation problems. PVM-AMBER is also easily and rapidly portable to different hardware platforms due to the availability of PVM for numerous computers. The current version of PVM-AMBER has been tested successfully on Silicon Graphics, IBM RS6000, DEC ALPHA, and HP 735 workstation clusters and heterogeneous clusters of these machines, as well as on CRAY T3D and Kendall Square KSR2 parallel supercomputers. Thus, PVM-AMBER provides a simple and cost-effective mechanism for parallel molecular dynamics simulations on readily available hardware platforms. Factors that affect the efficiency of this approach are discussed. © 1995 by John Wiley & Sons, Inc. 相似文献