全文获取类型
收费全文 | 276837篇 |
免费 | 2276篇 |
国内免费 | 729篇 |
专业分类
化学 | 150305篇 |
晶体学 | 4155篇 |
力学 | 11279篇 |
综合类 | 7篇 |
数学 | 30549篇 |
物理学 | 83547篇 |
出版年
2021年 | 2398篇 |
2020年 | 2673篇 |
2019年 | 3078篇 |
2018年 | 4328篇 |
2017年 | 4304篇 |
2016年 | 5841篇 |
2015年 | 3148篇 |
2014年 | 5155篇 |
2013年 | 11877篇 |
2012年 | 9159篇 |
2011年 | 10908篇 |
2010年 | 8092篇 |
2009年 | 7929篇 |
2008年 | 10505篇 |
2007年 | 10431篇 |
2006年 | 9777篇 |
2005年 | 8779篇 |
2004年 | 7934篇 |
2003年 | 7273篇 |
2002年 | 7190篇 |
2001年 | 7734篇 |
2000年 | 5997篇 |
1999年 | 4503篇 |
1998年 | 3935篇 |
1997年 | 3882篇 |
1996年 | 3564篇 |
1995年 | 3030篇 |
1994年 | 3117篇 |
1993年 | 3145篇 |
1992年 | 3336篇 |
1991年 | 3441篇 |
1990年 | 3267篇 |
1989年 | 3289篇 |
1988年 | 3146篇 |
1987年 | 3066篇 |
1986年 | 2942篇 |
1985年 | 3776篇 |
1984年 | 3998篇 |
1983年 | 3244篇 |
1982年 | 3551篇 |
1981年 | 3326篇 |
1980年 | 3089篇 |
1979年 | 3349篇 |
1978年 | 3593篇 |
1977年 | 3626篇 |
1976年 | 3523篇 |
1975年 | 3357篇 |
1974年 | 3345篇 |
1973年 | 3457篇 |
1972年 | 2364篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
Sufficient conditions are presented for the stabilizability and global controllability of certain natural Lagrangian systems with a non-negative potential energy when there are ideal unilateral constraints. In the general case, the number of controls is less than the number of degrees of freedom and the controls are bounded by preassigned quantities. Examples of globally controlled systems with two degrees of freedom are considered in which the action of the unilateral constraints is modelled within the framework of classical collision theory. 相似文献
982.
S. S. Banerjee S. Goldberg Y. Myasoedov M. Rappaport E. Zeldov A. Soibel F. de la Cruz J. van der Beek M. Konczykowski T. Tamegai V. Vinokur 《Pramana》2006,66(1):43-54
Disorder and porosity are parameters that strongly influence the physical behavior of materials, including their mechanical,
electrical, magnetic and optical properties. Vortices in superconductors can provide important insight into the effects of
disorder because their size is comparable to characteristic sizes of nanofabricated structures. Here we present experimental
evidence for a novel form of vortex matter that consists of inter-connected nanodroplets of vortex liquid caged in the pores
of a solid vortex structure, like a liquid permeated into a nanoporous solid skeleton. Our nanoporous skeleton is formed by
vortices pinned by correlated disorder created by high-energy heavy ion irradiation. By sweeping the applied magnetic field,
the number of vortices in the nanodroplets is varied continuously from a few to several hundred. Upon cooling, the caged nanodroplets
freeze into ordered nanocrystals through either a first-order or a continuous transition, whereas at high temperatures a uniform
liquid phase is formed upon delocalization-induced melting of the solid skeleton. This new vortex nanoliquid displays unique
properties and symmetries that are distinct from both solid and liquid phases. 相似文献
983.
984.
985.
O. A. Veliev 《Mathematical Notes》2007,81(3-4):440-448
We obtain asymptotic formulas for non-self-adjoint operators generated by the Sturm-Liouville system and quasiperiodic boundary conditions. Using these asymptotic formulas, we obtain conditions on the potential for which the system of root vectors of the operator under consideration forms a Riesz basis. 相似文献
986.
In this investigation, the crystalline structure of a nanometric CoSi2 layer, formed in heat treated Co/WxTa(1−x)/Si(1 0 0) systems, has been studied by XRD analysis. Careful measurements of the diffraction intensities revealed that temporary formation of a metastable diamond cubic structure of CoSi2 phase, rather than its usual CaF2 structure, was occurred. It has been shown that formation of this metastable structure depends on the kind of the applied interlayer in addition to the annealing temperature. Among the studied systems with x = 0, 0.25, 0.5, 0.75 and 1, the second and the last systems resulted in growing a (1 0 0) single-texture CoSi2 layer with the preferred usual CaF2 structure, a strained lattice parameter, and the best thermal stability (900-1000 °C). 相似文献
987.
G.M. Bilmes D.J.O. Orzi O.E. Martínez A. Lencina 《Applied physics. B, Lasers and optics》2006,82(4):643-648
The measurement of surface cleanliness is a significant problem in many industrial and technological processes. Existing methods are based on laboratory procedures, that are not performed in real time, can not be automated, and usually are restricted to a small portion of the sample. In this study we describe a new method for real time measurement of the amount of surface dirt or contamination deposited on a surface. It relies on the ablation of the surface dirt film by means of a short laser pulse, and the subsequent measurement of the emitted sound. The intensity of the sound is proportional to the amount of surface dirt and provides a direct measurement of the cleanliness of the surface. We also developed a reference sample for calibration, based on a uniform distribution of dots printed on white paper. The density and the dot size can be easily modified providing a homogeneous, uniform and reproducible standard for the measurement. Based on this method, we designed, developed and patented the first industrial instrument for on-line determination of the degree of cleanliness of manufactured cold rolled steel plate bobbins. PACS 79.20.D; 81.70.C; 42.62. 相似文献
988.
S. O. Olabanji O. R. Omobuwajo D. Ceccato M. C. Buoso M. De Poli G. Moschini 《Journal of Radioanalytical and Nuclear Chemistry》2006,270(3):515-521
Summary Analysis of thirteen medicinal plants of various biological activities commonly used in South-western Nigeria was carried
out using PIXE technique. Nine of these plants are anti-cancer while four are antimicrobial. PIXE measurements were carried
out using collimated proton beams delivered by the 2. 5 MV AN 2000 Van de Graaff accelerator at the Istituto Nazionale di
Fisica Nucleare (INFN), (LNL) Legnaro, (Padova), Italy. The results showed the presence of twenty three different elements
in the plants and none of them contains any toxic heavy metals. Only Chenopodium ambrosioides showed detectable levels of selenium which is considered important in cancer prevention. 相似文献
989.
E. K. Sadykov V. V. Arinin G. I. Petrov A. V. Pyataev F. G. Vagizov O. A. Kocharovskaya 《Hyperfine Interactions》2006,167(1-3):893-896
The role of quantum interference (QI) in spectra of the resonant Mössbauer scattering is investigated. As a mechanism ensuring the QI conditions, the radio-frequency (RF) mixing of the spin sublevels of the excited nuclear state is considered. It is shown that QI leads to a significant intensity redistribution of the elastic and Raman scattering. 相似文献
990.
E. J. S. Lage 《Physica A》1987,140(3):629-636
We study critical dynamics of general q-state Potts models on d-dimensional hypercubic lattices. The master equation is formulated according to a theory recently presented by the author. A simple bond moving technique, followed by decimation, is used to obtain the dynamical exponents. Although this approximation yields poor results for the static exponents, the dynamic behaviour is closer to Monte Carlo simulations. We compare our results with those obtained with a different formulation of dynamics. A final discussion is included. 相似文献