全文获取类型
收费全文 | 405214篇 |
免费 | 20513篇 |
国内免费 | 11181篇 |
专业分类
化学 | 207425篇 |
晶体学 | 5808篇 |
力学 | 23527篇 |
综合类 | 534篇 |
数学 | 67334篇 |
物理学 | 132280篇 |
出版年
2022年 | 4770篇 |
2021年 | 5410篇 |
2020年 | 5991篇 |
2019年 | 6140篇 |
2018年 | 15421篇 |
2017年 | 14964篇 |
2016年 | 14445篇 |
2015年 | 8025篇 |
2014年 | 10191篇 |
2013年 | 18017篇 |
2012年 | 20130篇 |
2011年 | 28352篇 |
2010年 | 18017篇 |
2009年 | 18124篇 |
2008年 | 21048篇 |
2007年 | 22525篇 |
2006年 | 13728篇 |
2005年 | 13092篇 |
2004年 | 11541篇 |
2003年 | 10488篇 |
2002年 | 9308篇 |
2001年 | 9146篇 |
2000年 | 7316篇 |
1999年 | 6372篇 |
1998年 | 5525篇 |
1997年 | 5268篇 |
1996年 | 5343篇 |
1995年 | 4600篇 |
1994年 | 4454篇 |
1993年 | 4251篇 |
1992年 | 4236篇 |
1991年 | 4359篇 |
1990年 | 3898篇 |
1989年 | 3627篇 |
1988年 | 3570篇 |
1987年 | 3380篇 |
1986年 | 3221篇 |
1985年 | 4158篇 |
1984年 | 4281篇 |
1983年 | 3378篇 |
1982年 | 3583篇 |
1981年 | 3478篇 |
1980年 | 3344篇 |
1979年 | 3416篇 |
1978年 | 3483篇 |
1977年 | 3396篇 |
1976年 | 3493篇 |
1975年 | 3184篇 |
1974年 | 3201篇 |
1973年 | 3247篇 |
排序方式: 共有10000条查询结果,搜索用时 43 毫秒
851.
852.
T. Engel M. Würtz S. Borneis St. Becker I. Klaft A. Kohl T. Kühl F. Laeri D. Marx K. Meier R. Neumann F. Schmitt P. Seelig L. Völker 《Hyperfine Interactions》1997,108(1-3):251-258
Laser spectroscopy at storage rings often suffers from a limited resolution due to Doppler-broadened resonances. Broadening
is caused by the velocity spread of the ions stored in the beam. In the following, the present status of our work on laser
systems specialized on the specific needs of laser spectroscopy at storage rings is reported.
Two pulsed laser systems were developed. One is a dye laser whose spectral bandwidth can be switched by inserting different
Littrow-prisms into the resonator. An increase in bandwidth up to a factor of 45 was achieved. This laser was used for fast
qualitative scans and high resolution measurements. The other laser system is a Nd : YAG laser pumped optical parametric oscillator.
It is a tunable laser system covering the spectral range from 410 to 4000 nm. Furthermore, a continuous wave laser with a
frequency shifted feedback cavity is described. It shows broadband emission with an adjustable bandwidth of up to 4.5 GHz.
This laser can be advantageous for laser cooling of ion beams.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
853.
L.-Q. Han S.-Y. Zhao Y.-D. Zhou P.-L. Zhang 《Applied physics. B, Lasers and optics》1997,65(3):399-402
Received: 18 June 1996/Revised version: 3 January 1997 相似文献
854.
Operational Research groups were established in private and public sector organizations following on from their success supporting the military in the Second World War. In the early years their numbers grew rapidly but by the mid-1970s evidence started to accumulate that they were being viewed less favourably. Many organizations chose not to set up OR groups. Established groups were closed down or dispersed to operating units in organizations, particularly during the recessionary periods. In 1993 following on the closures of some major OR groups in the UK, the Operational Research Society decided to fund research to examine those factors influencing a group's success and survival. This review, which forms part of the research, first examines the history of OR groups in the UK and North America, arguing that in practice they were one of a number of internal organizational consultancies. As such they were judged by their competitive performance. Despite the intent of the founding fathers of OR many groups found their scope was limited to mainly tactical problems using analytical model based approaches although there were exceptions that were successful in making major contributions at the strategic level also. Within their chosen fields of activity however many groups flourished whilst some failed. This review presents a comprehensive list of influences on success and survival. They include changes in the external environment, together with shifts in managerial style and culture, organizational factors, and the OR group itself. The review concludes that, while OR groups can do much to protect themselves from closure, organizational changes within a hostile managerial culture demand a creative response that acknowledges new requirements. Areas where an OR group has greatest influence over its effectiveness include its leadership and personnel, project balance and management. In addition, to be successful OR groups need to positively develop and market their services in an increasingly competitive managerial climate. 相似文献
855.
A free-piston driver that employs entropy-raising shock processes with diaphragm rupture has been constructed, which promises
significant theoretical advantages over isentropic compression. Results from a range of conditions with helium and argon driver
gases are reported. Significant performance gains were achieved in some test cases. Heat losses are shown to have a strong
effect on driver processes. Measurements compare well with predictions from a quasi-one-dimensional numerical code.
Received 7 September 1996 / Accepted 5 October 1996 相似文献
856.
857.
讨论了浅海中波导的声波散射问题,我们将该问题归结为一个第一类边界积分方程,利用正同化方法求解,并证明了该方法的收敛性,数值例子表明了该方法的简单与有效性。 相似文献
858.
A complete study of the spectrum of a finite-dimensional Bose operator is carried out in the paper. The cases in which the
spectrum is discrete or continuous are studied.
Translated fromMatematicheskie Zametki, Vol. 61, No. 6, pp. 835–854, June, 1997.
Translated by A. M. Chebotarev 相似文献
859.
基于无穷维空间中的生存定理,我们研究了集值映象的不动点,得到了一个新的不动点定理,推广和改进了[1]和[5]中的相应结果。 相似文献
860.
L.-H. Tang P. Smilauer D.D. Vvedensky 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):409-412
Two types of mechanisms are proposed for mound coarsening during unstable epitaxial growth: stochastic, due to deposition
noise, and deterministic, due to mass currents driven by surface energy differences. Both yield the relation H=(RWL)2 between the typical mound height W, mound size L, and the film thickness H. An analysis of simulations and experimental data shows that the parameter R saturates to a value which discriminates sharply between stochastic () and deterministic () coarsening. We derive a scaling relation between the coarsening exponent 1/z and the mound-height exponent which, for a saturated mound slope, yields .
Received: 11 November 1997 / Revised in final form: 28 November 1997 /
Accepted: 28 November 1997 相似文献