全文获取类型
收费全文 | 284706篇 |
免费 | 4502篇 |
国内免费 | 574篇 |
专业分类
化学 | 161095篇 |
晶体学 | 4050篇 |
力学 | 10200篇 |
综合类 | 12篇 |
数学 | 34055篇 |
物理学 | 80370篇 |
出版年
2021年 | 2261篇 |
2020年 | 2861篇 |
2019年 | 2988篇 |
2018年 | 3928篇 |
2017年 | 3806篇 |
2016年 | 6279篇 |
2015年 | 4568篇 |
2014年 | 5915篇 |
2013年 | 14334篇 |
2012年 | 11899篇 |
2011年 | 13339篇 |
2010年 | 9033篇 |
2009年 | 8422篇 |
2008年 | 11733篇 |
2007年 | 11527篇 |
2006年 | 10649篇 |
2005年 | 9905篇 |
2004年 | 8856篇 |
2003年 | 7807篇 |
2002年 | 7243篇 |
2001年 | 7682篇 |
2000年 | 6065篇 |
1999年 | 4541篇 |
1998年 | 3549篇 |
1997年 | 3393篇 |
1996年 | 3495篇 |
1995年 | 3062篇 |
1994年 | 3064篇 |
1993年 | 2877篇 |
1992年 | 3562篇 |
1991年 | 3331篇 |
1990年 | 3295篇 |
1989年 | 3249篇 |
1988年 | 3233篇 |
1987年 | 3214篇 |
1986年 | 3041篇 |
1985年 | 4025篇 |
1984年 | 3960篇 |
1983年 | 3092篇 |
1982年 | 3268篇 |
1981年 | 3330篇 |
1980年 | 3025篇 |
1979年 | 3358篇 |
1978年 | 3322篇 |
1977年 | 3382篇 |
1976年 | 3289篇 |
1975年 | 2971篇 |
1974年 | 2961篇 |
1973年 | 2896篇 |
1972年 | 1923篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
S. K. Godovikov 《JETP Letters》1998,68(8):629-633
In research on the production of beams of coherent γ rays (γ-ray lasers), conditions under which a substantial change Δλ/λ=?(0.114 ±0.027) in the radioactive decay constant λ (the isomeric level 89.53 keV 119m Sn, T 1/2=293 days) can occur have been found experimentally for the first time. This is made possible by coherent Mo ssbauer (23.87 keV) backscattering from a resonant screen located nearby. An interpretation of the effect observed is proposed on the basis of the idea of dynamic synchronization of oscillations between a nuclear level and a standing wave of Mössbauer radiation. Possibilities for further increasing Δλ/λ up to 0.5 are found. 相似文献
142.
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
143.
The characterisation of iron-containing species in Chinkombe ilmenite and its reduction products was undertaken using Mössbauer Spectroscopic techniques. The ore was reduced by graphite in an inert atmosphere. The effects of such variables as quantity of reductant, temperature and preoxidation were investigated. The ore was completely reduced to alpha-iron and titanium dioxide with 20% carbon for a period of one hour at 1373 K. Chemical mechanisms are proposed for the reduction and oxidation of Chinkombe ilmenite. In the processing of ilmenite to obtain synthetic rutile, the ultimate desire is to separate the Fe phase from the TiO2. Mössbauer Spectroscopy has unambiguously confirmed the desired transformation of the iron phase according to thermodynamic predictions. The information gained would be used to choose the conditions of the reduction process. The alpha-iron could be separated physically or chemically from the completely reduced product mass to obtain synthetic titanium dioxide suitable for the paint industry. 相似文献
144.
A. Sánchez-Lavega A. Salazar A. Ocariz L. Pottier E. Gomez L.M. Villar E. Macho 《Applied Physics A: Materials Science & Processing》1997,65(1):15-22
Received: 16 September 1996/Accepted: 6 January 1997 相似文献
145.
E. Hatta H. Hosoi H. Akiyama T. Ishii K. Mukasa 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):347-349
We have observed a remarkable two-armed spiral in the collapse process of a floating monolayer at the air-water interface
by phase contrast microscopy. This demonstrates that the floating monolayer as a form of soft condensed matter reorganizes
itself due to a certain kind of macroscopic or collective behavior of molecules as it collapses. This pattern formation is
caused by the breakdown of a critical dynamical balance between the deformation of solid domain and the applied surface pressure.
The fragility as well as the flexibility of the floating monolayer can be associated with the observed pattern growth. There
are also observed interesting, periodically arranged collections of molecules in numerous collapsed regions.
Received: 8 July 1997 / Accepted: 4 November 1997 相似文献
146.
A new scheme for controlling photodissociation through preparation of a variationally optimized linear superposition of field free vibrational eigenstates is applied for selective control of IBr and HI dissociation. The dependence of photodissociation on various field parameters and initial conditions is examined to investigate the mechanistic basis of selective control. The parametric equations of motion approach for determining vibrational dynamics as a function of field parameters without having to solve the time dependent Schrödinger equation explicitly for each field parameter separately is outlined and its use to identify field characteristics which will provide the requisite population mix represented by the optimal linear superposition of vibrational states is advocated. 相似文献
147.
148.
We prove that in some reasonable sense, every possible physical law can be reformulated in terms of symmetries. This result explains the well-known success of the group-theoretic approach in physics. 相似文献
149.
An effective residual interaction between particles and holes for shell model calculations around 208Pb, derived from the interaction between free nucleons, is compared with the measured properties of proton-hole neutron states
in 208Tl and the interaction between proton holes is adjusted to newly measured level energies in 206Hg. These interaction elements are particularly relevant for neutron-rich nuclei. The adjustment of two mixing elements reproduces
the known γ-decay data in 208Tl.
Received: 2 April 2002 / Accepted: 2 May 2002 相似文献
150.
K. Weibert J. Main G. Wunner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(3):379-388
In the periodic orbit quantization of physical systems, usually only the leading-order ? contribution to the density of states is considered. Therefore, by construction, the eigenvalues following from semiclassical
trace formulae generally agree with the exact quantum ones only to lowest order of ?. In different theoretical work the trace formulae have been extended to higher orders of ?. The problem remains, however, how to actually calculate eigenvalues from the extended trace formulae since, even with ? corrections included, the periodic orbit sums still do not converge in the physical domain. For lowest-order semiclassical trace formulae the convergence problem can be elegantly, and universally, circumvented by application of the
technique of harmonic inversion. In this paper we show how, for general scaling chaotic systems, also higher-order
? corrections to the Gutzwiller formula can be included in the harmonic inversion scheme, and demonstrate that corrected semiclassical
eigenvalues can be calculated despite the convergence problem. The method is applied to the open three-disk scattering system,
as a prototype of a chaotic system.
Received 10 September 2001 and Received in final form 3 January 2002 相似文献