全文获取类型
收费全文 | 124814篇 |
免费 | 1529篇 |
国内免费 | 456篇 |
专业分类
化学 | 68461篇 |
晶体学 | 2035篇 |
力学 | 4955篇 |
综合类 | 5篇 |
数学 | 12104篇 |
物理学 | 39239篇 |
出版年
2016年 | 1272篇 |
2015年 | 982篇 |
2014年 | 1319篇 |
2013年 | 4775篇 |
2012年 | 3376篇 |
2011年 | 4383篇 |
2010年 | 2733篇 |
2009年 | 2513篇 |
2008年 | 3922篇 |
2007年 | 3977篇 |
2006年 | 4036篇 |
2005年 | 3962篇 |
2004年 | 3453篇 |
2003年 | 3150篇 |
2002年 | 3053篇 |
2001年 | 3570篇 |
2000年 | 2674篇 |
1999年 | 2196篇 |
1998年 | 1884篇 |
1997年 | 1872篇 |
1996年 | 1802篇 |
1995年 | 1772篇 |
1994年 | 1545篇 |
1993年 | 1533篇 |
1992年 | 1753篇 |
1991年 | 1745篇 |
1990年 | 1677篇 |
1989年 | 1683篇 |
1988年 | 1684篇 |
1987年 | 1674篇 |
1986年 | 1587篇 |
1985年 | 2135篇 |
1984年 | 2262篇 |
1983年 | 1887篇 |
1982年 | 2212篇 |
1981年 | 2027篇 |
1980年 | 2073篇 |
1979年 | 2058篇 |
1978年 | 2186篇 |
1977年 | 2090篇 |
1976年 | 2115篇 |
1975年 | 2053篇 |
1974年 | 1895篇 |
1973年 | 2102篇 |
1972年 | 1282篇 |
1971年 | 975篇 |
1970年 | 912篇 |
1969年 | 923篇 |
1968年 | 1050篇 |
1967年 | 1101篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
We provide a detailed investigation of limits of N–soliton solutions of the Toda lattice as N tends to infinity. Our principal results yield new classes of Toda solutions including, in particular, new kinds of soliton–like
(i.e., reflectionless) solutions. As a byproduct we solve an inverse spectral problem for one–dimensional Jacobi operators
and explicitly construct tri–diagonal matrices that yield a purely absolutely continuous spectrum in (-1,1) and give rise
to an eigenvalue spectrum that includes any prescribed countable and bounded subset of .
Received: 16 October 1995/Accepted: 23 July 1996 相似文献
182.
Merck W.F.H. Zatelepin V.N. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1997,25(5):947-953
The aim of this paper is to extend our knowledge about the gas-dynamic processes in arcs during immobility time. For this purpose, the conservation equations in a magnetohydrodynamic approximation were coupled with the thermochemical and Maxwell equations. Special features arc the introduction of dissociation and ionization of nitrogen and oxygen, and the simultaneous calculation of the distributions of current density and magnetic induction in the arc. Numerical calculations were performed with a reduced two-dimensional (2-D) time-dependent model. Results of the calculations were compared with measurements. The development in time of the measured and calculated are voltage and arc chamber pressure show very good agreement. The pumping effect of the double vortex in the arc region was confirmed by optical measurements. It is concluded that the three-layer model is a good representation for the main physical features during the immobility time, and that the presence of highly conducting gas in the downstream region of the arc is essential for its downstream movement 相似文献
183.
A. Hoffknecht O. Uwira A. Frank S. Schennach W. Spies M. Wagner S. Schippers A. Müller R. Becker M. Kleinod N. Angert P.H. Mokler 《Hyperfine Interactions》1998,114(1-4):257-261
The origin of the widely observed enhancement of rates for electron-ion recombination at very low energies is still unknown.
We investigated the recombination of Au25+ with free electrons in a merged-beams experiment at the UNILAC accelerator of the GSI in Darmstadt. At E
rel= 0 eV we found an enormous enhancement factor of 365 compared to the theory of radiative recombination. An increase of the
electron density by a factor of 10 had not much influence on the measured rate coefficient.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
184.
185.
186.
Studies that focus on the decision making process can be classified in (at least) two ways: by psychological content and by contextual content. The first describes the degree to which the analysis focuses on the mental processes associated with decision making and the second deals with the degree to which the analysis is dependent upon the study's context. Several studies are examined in terms of where they fall in this two-dimensional taxonomy. Two analyses of maritime command and control conducted by the authors are examined more fully within this taxonomy. Both are context full, but are at opposite ends of the psychological content spectrum. These categorizations are useful in focusing future research aimed at developing models of decision making. 相似文献
187.
188.
189.
In the nineteenth century, field theory brilliantly resolveda number of questions that had taxed mathematicians for centuries;for example, The circle cannot be squared by straightedge and compass, and solving polynomial equations by radicalsis not always possible. These successes have continued to beheld up as superb examples of the power of mathematical thought,and are demonstrated at an undergraduate level. The purposeof this article is to provide another such natural example whichleads to a concrete realisation of the free group on 2 generators. 相似文献
190.
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