全文获取类型
收费全文 | 2813篇 |
免费 | 103篇 |
国内免费 | 25篇 |
专业分类
化学 | 1870篇 |
晶体学 | 11篇 |
力学 | 67篇 |
数学 | 519篇 |
物理学 | 474篇 |
出版年
2023年 | 23篇 |
2022年 | 73篇 |
2021年 | 69篇 |
2020年 | 63篇 |
2019年 | 60篇 |
2018年 | 63篇 |
2017年 | 60篇 |
2016年 | 111篇 |
2015年 | 69篇 |
2014年 | 102篇 |
2013年 | 199篇 |
2012年 | 175篇 |
2011年 | 209篇 |
2010年 | 157篇 |
2009年 | 139篇 |
2008年 | 163篇 |
2007年 | 170篇 |
2006年 | 153篇 |
2005年 | 141篇 |
2004年 | 102篇 |
2003年 | 80篇 |
2002年 | 84篇 |
2001年 | 45篇 |
2000年 | 33篇 |
1999年 | 19篇 |
1998年 | 26篇 |
1997年 | 34篇 |
1996年 | 35篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 20篇 |
1992年 | 14篇 |
1991年 | 22篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 13篇 |
1987年 | 9篇 |
1986年 | 16篇 |
1985年 | 22篇 |
1984年 | 8篇 |
1983年 | 12篇 |
1982年 | 21篇 |
1981年 | 22篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1971年 | 3篇 |
1957年 | 2篇 |
排序方式: 共有2941条查询结果,搜索用时 15 毫秒
1.
Mohammad A. Khalilzadeh Soo Young Kim Ho Won Jang Rafael Luque Rajender S. Varma Richard A. Venditti Mohammadreza Shokouhimehr 《Materials Today Chemistry》2022
The requirement of green and sustainable materials to prepare heterogeneous catalysts has intensified for practical reasons over the past few decades. Carbohydrates are possibly the most plentiful and renewable organic materials in nature with inimitable physiochemical properties, plausible low-cost and large-scale production, and sustainability features could be exploited in the generation of nanostructured heterogeneous catalysts. This review article outlines the organic transformations catalyzed by diverse carbohydrate-based nanostructured catalysts in greener and environmentally friendly processes. Selected examples are highlighted for a variety of organic reactions exploiting the proposed catalysts’ reactivity and reusability, and interactions with the intrinsic nature of the applied carbohydrate supports; advantages and speculated challenges of the introduced catalysts are deliberated as well. 相似文献
2.
BIT Numerical Mathematics - In this article we address the problem of minimizing a strictly convex quadratic function using a novel iterative method. The new algorithm is based on the well-known... 相似文献
3.
4.
Nonlinear Dynamics - Introduction of stiffness nonlinearities to broaden the frequency bandwidth of vibratory energy harvesters has the adverse influence of complicating the response behavior of... 相似文献
5.
Rafael López 《Annals of Global Analysis and Geometry》1997,15(3):201-210
In this paper we study constant mean curvature compact surfaces with two Jordan curves in parallel planes as boundary and we investigate the point at which the surface inherits the symmetries of its boundary. 相似文献
6.
Composition of corrosion layers on steel 20 in aerated solutions with hydrazine concentrations less than 11 ppm was studied at 50, 60, and 80°C in dynamic conditions by transmission Mössbauer spectroscopy and X-ray diffraction as supplementary technique. Corrosion rates were determined by gravimetric method. A comparison with corrosion in water at 80°C was made. The observed layers have not any protective character. For 0.1 m/s linear velocity, they are composed by nonstoichiometric magnetite, (Fe3?x O4,x=0.02–0.04) with lepidocrocite (γ-FeOOH) as secondary phase at 50°C. Haematite (α-Fe2O3) is observed at 60 and 80°C with a 19 nm particle size. It becomes smaller for higher velocity (0.7 m/s). 相似文献
7.
Ilda Abe Rafael E. de Ges Jos L. Fabris Hypolito J. Kalinowski Mrcia Müller Meire C. Fugihara Rosane Falate Barbara W. Diesel Ricardo C. Kamikawachi Carmen L. Barbosa 《Optics and Lasers in Engineering》2003,39(5-6):537-548
In this work, we report production and modelling of both Bragg gratings and rocking filters in high birefringence fibre optics. Bragg gratings are produced by UV (257.0 nm) external interferometric exposition of a frequency-doubled Ar+ ion laser, whereas for rocking filters formation the visible Ar+ ion laser lines in 488.0 and 514.5 nm are used in an internal method. The spectral characteristics due to the birefringence properties are studied through numerical methods and experimental techniques. The spectral responsivity of the structures under temperature changes and stress application is presented. 相似文献
8.
Rafael Tiedra de Aldecoa 《Annales Henri Poincare》2006,7(1):105-124
Although many physical arguments account for using a modified definition of time delay in multichannel-type scattering processes,
one can hardly find rigorous results on that issue in the literature. We try to fill in this gap by showing, both in an abstract
setting and in a short-range case, the identity of the modified time delay and the Eisenbud-Wigner time delay in waveguides.
In the short-range case we also obtain limiting absorption principles, state spectral properties of the total Hamiltonian,
prove the existence of the wave operators and show an explicit formula for the S-matrix. The proofs rely on stationary and commutator methods.
Communicated by Yosi Avron
submitted 12/04/05, accepted 13/05/05 相似文献
9.
Rafael Ortega 《Journal of Dynamics and Differential Equations》1992,4(4):651-665
This paper gives sufficient conditions for the existence of periodic solutions of twist type of a time-dependent differential equation of the second order. The concept of periodic solution of twist type is defined in terms of the corresponding Birkhoff normal form and, in particular, implies that the solution is Lyapunov stable. Some applications to nonlocal problems are given. 相似文献
10.
Currently, most combinatorial optimisation problems have to be solved, if the optimum solution is sought, using general techniques
to explore the space of feasible solutions and, more specifically, through exploratory enumerative procedures in trees and
search graphs. We propose Branch and Win, a general formulation for understanding and synthesising the different tree search
procedures that have been presented in the literature of operations research as well as in that of artificial intelligence.
Several general ideas are also presented, whose application allows designing new hybrid search algorithms, in order to implement
the procedure. 相似文献