全文获取类型
收费全文 | 849872篇 |
免费 | 12851篇 |
国内免费 | 5820篇 |
专业分类
化学 | 432595篇 |
晶体学 | 11597篇 |
力学 | 43471篇 |
综合类 | 159篇 |
数学 | 129626篇 |
物理学 | 251095篇 |
出版年
2021年 | 7614篇 |
2020年 | 8245篇 |
2019年 | 8979篇 |
2018年 | 20131篇 |
2017年 | 19881篇 |
2016年 | 21236篇 |
2015年 | 10790篇 |
2014年 | 15820篇 |
2013年 | 36270篇 |
2012年 | 31721篇 |
2011年 | 42907篇 |
2010年 | 28875篇 |
2009年 | 28999篇 |
2008年 | 36644篇 |
2007年 | 38240篇 |
2006年 | 28774篇 |
2005年 | 26514篇 |
2004年 | 24563篇 |
2003年 | 22487篇 |
2002年 | 21427篇 |
2001年 | 21989篇 |
2000年 | 17104篇 |
1999年 | 13583篇 |
1998年 | 11577篇 |
1997年 | 11281篇 |
1996年 | 10969篇 |
1995年 | 9861篇 |
1994年 | 9537篇 |
1993年 | 9177篇 |
1992年 | 9857篇 |
1991年 | 10189篇 |
1990年 | 9666篇 |
1989年 | 9432篇 |
1988年 | 9415篇 |
1987年 | 9012篇 |
1986年 | 8653篇 |
1985年 | 11377篇 |
1984年 | 11734篇 |
1983年 | 9830篇 |
1982年 | 10432篇 |
1981年 | 9987篇 |
1980年 | 9514篇 |
1979年 | 10095篇 |
1978年 | 10344篇 |
1977年 | 10234篇 |
1976年 | 10148篇 |
1975年 | 9718篇 |
1974年 | 9474篇 |
1973年 | 9906篇 |
1972年 | 6754篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
N.-K. Lee T.A. Vilgis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):451-465
We study the elastic properties of single A/B random copolymer chains, with a specific sequence and use them as theoretical
model for so called HP proteins. HP proteins carry hydrophilic (P) and hydrophobic (H) monomers. We predict a rich structure
in the force-extension relations which can be attributed to the information in the sequence. The variational method is used
to probe local minima on the path of stretching and releasing for the chain molecules. At a given force, we find multiple
configurations which are separated by energy barriers. A collapsed globular configuration consists of several domains which
unravel cooperatively. Upon stretching, the unfolding path shows a stepwise pattern corresponding to the unfolding of each
domain. While releasing, several cores can be created simultaneously in the middle of the chain, resulting in a different
path of collapse. The long-range interactions and stiffness of the chain simplify the potential landscape given by the disorder
in sequence.
Received 5 March 2002 / Received in final form 16 May 2002 Published online 13 August 2002 相似文献
992.
Ying Zhang Gang Hu Shigang Chen H.A. Cerdeira 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):381-384
A method of controlling global stochasticity in Hamiltonian systems by applying nonlinear perturbation is proposed. With the
well-known standard map we demonstrate that this control method can convert global stochasticity into regular motion in a
wide chaotic region for arbitrary initial condition, in which the control signal remains very weak after a few kicks. The
system in which chaos has been controlled approximates to the original Hamiltonian system, and this approach appears robust
against small external noise. The mechanism underlying this high control efficiency is intuitively explained.
Received 15 January 2002 Published online 6 June 2002 相似文献
993.
R. Adhikari A. Sil A. Raychaudhuri 《The European Physical Journal C - Particles and Fields》2002,25(1):125-130
We present a solution of the solar neutrino deficit using three flavors of neutrinos and R-parity non-conserving supersymmetry. In this model, in vacuum, the is massless and unmixed, mass and mixing being restricted to the - sector only, which we choose in consistency with the requirements of the atmospheric neutrino anomaly. The flavor changing
and flavor diagonal neutral currents present in the model and the three-flavor picture together produce an energy dependent
resonance-induced - mixing in the sun. This mixing plays a key role in the new solution to the solar neutrino problem. The best fit to the solar
neutrino rates and spectrum (1258-day SK and 241-day SNO data) requires a mass square difference of eV2 in vacuum between the two lightest neutrinos. This solution cannot accommodate a significant day-night effect for solar neutrinos
nor CP violation in terrestrial neutrino experiments.
Received: 26 December 2001 / Revised version: 16 February 2002 / Published online: 26 July 2002 相似文献
994.
The Constraint Molecular Dynamics approach is illustrated together with calculation on different heavy ion collisions. In particular the charge-mass distribution produced in the collision 124Sn + 64Ni and 112Sn + 58Ni at 35 MeV/nucleon is discussed. By comparing the Y = (N ? Z)/A distributions for fragments produced in central collisions it results that this observable can be sensitive to the dynamic effects induced on the two systems by the different charge/mass ratio. 相似文献
995.
The maximum likely and optimal (Bayesian) algorithms for detecting an arbitrary-shaped signal observed against the background of Gaussian white noise and for measuring the duration are synthesized. Exact expressions for the characteristics of the maximum likely algorithms are found. The characteristics of the Bayesian algorithms are obtained using computer simulations. 相似文献
996.
In this paper, we review and unify some classes of generalized convex functions introduced by different authors to prove minimax results in infinite-dimensional spaces and show the relations between these classes. We list also for the most general class already introduced by Jeyakumar (Ref. 1) an elementary proof of a minimax result. The proof of this result uses only a finite-dimensional separa- tion theorem; although this minimax result was already presented by Neumann (Ref. 2) and independently by Jeyakumar (Ref. 1), we believe that the present proof is shorter and more transparent. 相似文献
997.
Atomic-force microscopy was used to study the surface topography of SiGe structures grown by epitaxial deposition of Ge on profiled Si(111) substrates under electromigration conditions. Systems of highly ordered germanium nanosized islands with dimensions of 10–20 nm and a density of 6×1010 cm?2 were obtained. It is shown that the geometrical parameters of self-organizing nanoislands can be controlled by a proper choice of the growth and postgrowth annealing conditions for these structures. 相似文献
998.
The stationary and the time-dependent homogeneous ordered states in convection may both become unstable against localized perturbations. Defects are then created and they may contribute to the disorganization of the homogeneous state. We present an experimental study of defects in some homogeneous stationary structures as well as in the traveling-wave states of convection of a nematic liquid crystal. We show that the core of the defects is a germ of the unstable state and it can become unstable under the external stress. Then, either fully homogeneous states with the symmetry of the core, or complex disordered states can develop from the local instability of defects in processes quite similar to displacive transitions in solids. Some of the main features are qualitatively similar to numerical simulations of an appropriate Landau-Ginzburg equation. 相似文献
999.
The pulsed positron beam at the Helsinki University of Technology is designed for the end energy of 3-30 keV and grounded target. This is achieved with a constant voltage acceleration followed by an adjustable deceleration. In the design of this accelerator-decelerator the possibility for electrical breakdowns and partial discharges must be eliminated.For designing the electrode and insulator structures for accelerator-decelerator configuration electric field simulations were carried out with the finite element analysis program. In this paper we present the design of the accelerator-decelerator and the results of the electric field simulations. The results of high voltage tests will also be presented and compared with the simulations. 相似文献
1000.
V. A. Kulbachinskiĭ A. Yu. Kaminskiĭ P. M. Tarasov P. Lostak 《Physics of the Solid State》2006,48(5):833-840
The Fermi surface anisotropy of (Bi1?x Sbx)2Te3 single crystals (0.25 ≤ x ≤ 1) was studied by analyzing the angular dependence of the frequency of Shubnikov-de Haas oscillations and the effect of tin and silver doping on the thermoelectric power in these crystals in the temperature range 77 ≤ T ≤ 300 K. It was shown that silver doping of (Bi1?x Sbx)2Te3 mixed crystals produces acceptors, while silver in Bi2Te3 acts as a donor. Tin also exhibits acceptor properties. Both tin and silver doping of p-(Bi1?x Sbx)2Te3 mixed crystals decrease the thermoelectric power due to an increase in the hole concentration. 相似文献