全文获取类型
收费全文 | 2202篇 |
免费 | 56篇 |
国内免费 | 4篇 |
专业分类
化学 | 1326篇 |
晶体学 | 26篇 |
力学 | 53篇 |
数学 | 203篇 |
物理学 | 654篇 |
出版年
2024年 | 8篇 |
2023年 | 20篇 |
2022年 | 57篇 |
2021年 | 46篇 |
2020年 | 47篇 |
2019年 | 62篇 |
2018年 | 54篇 |
2017年 | 58篇 |
2016年 | 92篇 |
2015年 | 46篇 |
2014年 | 87篇 |
2013年 | 153篇 |
2012年 | 136篇 |
2011年 | 142篇 |
2010年 | 97篇 |
2009年 | 93篇 |
2008年 | 136篇 |
2007年 | 119篇 |
2006年 | 81篇 |
2005年 | 63篇 |
2004年 | 49篇 |
2003年 | 40篇 |
2002年 | 42篇 |
2001年 | 33篇 |
2000年 | 29篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 17篇 |
1995年 | 23篇 |
1994年 | 22篇 |
1993年 | 34篇 |
1992年 | 26篇 |
1991年 | 25篇 |
1990年 | 23篇 |
1989年 | 25篇 |
1988年 | 12篇 |
1987年 | 28篇 |
1986年 | 19篇 |
1985年 | 21篇 |
1984年 | 15篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 20篇 |
1978年 | 7篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1965年 | 7篇 |
排序方式: 共有2262条查询结果,搜索用时 15 毫秒
181.
Stokes-flow reversibility is violated in electrolyte solutions by a streaming-potential mechanism, where nonuniform convective currents within Debye layers surrounding charged particles induce electric fields in the electroneutral Ohmic bulk. We demonstrate the irreversibility consequences of this phenomenon for the problem of particle-pair sedimentation, where the two particles experience a repulsive force driven by bulk Maxwell stresses. At small separations the force scales inversely with the third power of separation distance. This singular behavior is associated with the counterrotation of the two torque-free particles, which leads through a lubrication mechanism to an intense electric field in the narrow gap between them. At large separations the force follows an inverse dependence upon the fourth power of separation, now associated with rectilinear particle motion. 相似文献
182.
We present an all-fiber bidirectional passively mode-locked soliton laser with what we believe is a novel cavity configuration. Using a four-port circulator, we incorporate two different semiconductor saturable absorber mirrors (SESAMs) into the laser cavity, which enables bidirectional mode locking. The laser allows the generation of two independent countercirculating mode-locked pulse trains, each with an individual fundamental repetition rate that can be adjusted by varying the SESAM pigtail length. Two countercirculating pulse trains with repetition rates of 21.3 and 15.2 MHz are obtained simultaneously. By controlling the intracavity loss imposed on these two pulse trains, either one of the two pulse trains can be switched on or off. The bidirectional operation with other repetition rates is also demonstrated. 相似文献
183.
184.
185.
S. K. Mohanta S. N. Mishra S. M. Davane Neeraj Kumar A. Thamizhavel S. Layek Z. Hossain S. K. Srivastava 《Hyperfine Interactions》2013,221(1-3):23-27
Employing the γ-ray perturbed angular distribution technique, we have measured the magnetic hyperfine field of 54Fe in tetragonal and orthorhombic structural phases of SrFe2As2. In the tetragonal phase, the magnetic response of 54Fe shows Curie-Weiss type local susceptibility, indicating the presence of localized moment on Fe. The temperature dependence of the hyperfine field of 54Fe reflects quasi-two dimensional first order magnetic transition at 200 K. Our data indicate that Fe moments in the magnetically ordered phase of SrFe2As2 may be canted out of the ab-plane. 相似文献
186.
187.
A simple and efficient methodology for Markovnikov addition of azoles with vinyl acetate catalyzed by potassium tert-butoxide is described.N-heterocyclic compounds are synthesized from simple and commercially available starting materials under mild conditions in high yields. 相似文献
188.
This note reports the dependence of shape factor corresponding to the portion of wall behind a berm and above the ground on the angle of berm; the results have been obtained by thermal simulation of heat transfer between the ground and the wall through the berming. 相似文献
189.
Shalini Bagchi Kasturi Roychowdhury A.P. Mishra A. Roy Chowdhury 《Communications in Nonlinear Science & Numerical Simulation》2010,15(2):275-280
Excitation of nonlinear waves in a quantum dusty plasma with various effects is analyzed when the geometry is cylindrical.This introduces the effect of finite boundary conditions on the solitary waves so generated. it is observed that the nonlinear equation deduced is cylindrical KP–Burger type leading to the generation of Shock Wave. Different situations which arises in various parameter regions are considered separately and the form of the nonlinear excitations are obtained explicitly. 相似文献
190.
Anamika Mishra Karel Matou? Kumud B. Mishra Ladislav Nedbal 《Journal of fluorescence》2009,19(5):905-913
Automatic discrimination of plant species is required for precision farming and for advanced environmental protection. For
this task, reflected sunlight has already been tested whereas fluorescence emission has been only scarcely considered. Here,
we investigated the discriminative potential of chlorophyll fluorescence imaging in a case study using three closely related
plant species of the family Lamiaceae. We compared discriminative potential of eight classifiers and four feature selection methods to identify the fluorescence
parameters that can yield the highest contrast between the species. Three plant species: Ocimum basilicum, Origanum majorana and Origanum vulgare were grown separately as well as in pots where all three species were mixed. First, eight statistical classifiers were applied
and tested in simulated species discrimination. The performance of the Quadratic Discriminant Classifier was found to be the
most efficient. This classifier was further applied in combination with four different methods of feature selection. The Sequential
Forward Floating Selection was found as the most efficient method for selecting the best performing subset of fluorescence
images. The ability of the combinatorial statistical techniques for discriminating the species was also compared to the resolving
power of conventional fluorescence parameters and found to be more efficient. 相似文献