全文获取类型
收费全文 | 202241篇 |
免费 | 1958篇 |
国内免费 | 501篇 |
专业分类
化学 | 110526篇 |
晶体学 | 3647篇 |
力学 | 7996篇 |
综合类 | 11篇 |
数学 | 19193篇 |
物理学 | 63327篇 |
出版年
2020年 | 1724篇 |
2019年 | 1917篇 |
2018年 | 2236篇 |
2017年 | 2355篇 |
2016年 | 3515篇 |
2015年 | 2190篇 |
2014年 | 3546篇 |
2013年 | 9078篇 |
2012年 | 6505篇 |
2011年 | 8009篇 |
2010年 | 5696篇 |
2009年 | 5654篇 |
2008年 | 7154篇 |
2007年 | 7066篇 |
2006年 | 6693篇 |
2005年 | 6051篇 |
2004年 | 5520篇 |
2003年 | 5099篇 |
2002年 | 4867篇 |
2001年 | 6141篇 |
2000年 | 4622篇 |
1999年 | 3518篇 |
1998年 | 2745篇 |
1997年 | 2702篇 |
1996年 | 2591篇 |
1995年 | 2440篇 |
1994年 | 2330篇 |
1993年 | 2165篇 |
1992年 | 2826篇 |
1991年 | 2730篇 |
1990年 | 2672篇 |
1989年 | 2690篇 |
1988年 | 2713篇 |
1987年 | 2721篇 |
1986年 | 2591篇 |
1985年 | 3303篇 |
1984年 | 3313篇 |
1983年 | 2598篇 |
1982年 | 2709篇 |
1981年 | 2763篇 |
1980年 | 2533篇 |
1979年 | 2875篇 |
1978年 | 2860篇 |
1977年 | 2980篇 |
1976年 | 2816篇 |
1975年 | 2553篇 |
1974年 | 2509篇 |
1973年 | 2465篇 |
1972年 | 1702篇 |
1968年 | 1703篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
201.
Laser driven shocks can lead to a dynamic failure, called film spallation. Here, we use a modified laser spallation set-up
to measure the dynamic adhesion of thin films and we propose a novel diagnostic technology. Based on correlation theory, new
spallation criteria for characterizing the progressive damage at the interface between the film and the substrate are established,
such as interface delamination, film spallation and film expulsion. With the help of the theory, the degree of damage and
the dimension of damage (i.e. fracture), such as the minimum width of delamination radius, the thickness of the film etc.,
are estimated. Experiments are carried out on epoxy/stainless steel and epoxy/Al, and the experimental results show that their
dynamic bonding strengths are about 25 MPa and 20 MPa, respectively. The detailed results, analyses and discussions are presented
in this paper.
Received: 6 February 2001 / Accepted: 3 December 2001 / Published online: 11 February 2002 相似文献
202.
A classification has been obtained for spaces which admit complete sets of motion integrals of the (3.1)-type and are spatially homogeneous. The metrics and Killing vectors have been found in explicit form for all types of these spaces. A classification by Bianchi is given for the spaces obtained. 相似文献
203.
M. Gutowski I. Dabkowska J. Rak S. Xu J.M. Nilles D. Radisic K.H. Bowen Jr 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(3):431-439
The photoelectron spectra (PES) of anions of uracil-glycine and uracil-phenylalanine complexes reveal broad features with
maxima at 1.8 and 2.0 eV. The results of ab initio density functional B3LYP and second order M?ller-Plesset theory calculations indicate that the excess electron occupies a
π* orbital localized on uracil. The excess electron attachment to the complex can induce a barrier-free proton transfer (BFPT)
from the carboxylic group of glycine to the O8 atom of uracil. As a result, the four most stable structures of the anion of
uracil-glycine complex can be characterized as the neutral radical of hydrogenated uracil solvated by the anion of deprotonated
glycine. The similarity between the PES spectra for the uracil complexes with glycine and phenylalanine suggests that the
BFPT is also operative in the case of the latter anionic species. The BFPT to the O8 atom of uracil may be related to the
damage of nucleic acid bases by low energy electrons because the O8 atom is involved in a hydrogen bond with adenine in the
standard Watson-Crick pairing scheme.
Received 6 April 2002 Published online 13 September 2002 相似文献
204.
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
205.
206.
207.
Mass transport due to electromigration can be estimated if the diffusion coefficientD and the electromigration effective charge numberZ* are known. Neutron activated tracer scanning method determine the radioactivity at different positions. An automatic scanning
system for determining the radioactive concentration profiles developed using a microprocessor is described in this paper.
Using the radioactive concentration profiles the electromigration shift is determined. From this shift the electromigration
effective charge numberZ* is calculated. The system developed was tested for tin thin films. 相似文献
208.
D. K. Kuznetsov I. S. Baturin V. Ya. Shur N. Menou C. Muller T. Schneller A. Sternberg 《Physics of the Solid State》2006,48(6):1174-1176
The effect of irradiation with electrons and neutrons and of exposure to synchrotron radiation on cyclic switching of polarization in thin films of lead zirconate titanate Pb(Zr,Ti)O3 (PZT) was studied. It is shown that variations in the shape of switching currents are due to the generation of a spatially nonuniform bound internal field with account for an increase in the rate of bulk screening caused by irradiation. A correlation between structural variations and the evolution of the switching current measured during and after irradiation is established. 相似文献
209.
Current techniques of water wave visualization such as shadowgraphy and stereo photography are widely used but are deficient
in many aspects. Refraction based visualization observes the bending of light as it traverses across a liquid-air interface.
This work describes the continued development of techniques to measure the surface height of a liquid free surface. The method,
Reference Image Topography, utilizes refraction of light at the free surface as a function of the local angle of that surface.
Particle Image Velocimetry (PIV) software is used to evaluate apparent dislocations of the target image viewed through the
free surface, which are approximately proportional to the surface angle. High-resolution images are presented of the dynamic
surface topography for a point source and the shallow water flow around a vertical cylinder. 相似文献
210.