全文获取类型
收费全文 | 3635篇 |
免费 | 113篇 |
国内免费 | 25篇 |
专业分类
化学 | 2423篇 |
晶体学 | 30篇 |
力学 | 76篇 |
数学 | 610篇 |
物理学 | 634篇 |
出版年
2023年 | 32篇 |
2022年 | 105篇 |
2021年 | 88篇 |
2020年 | 86篇 |
2019年 | 82篇 |
2018年 | 83篇 |
2017年 | 81篇 |
2016年 | 134篇 |
2015年 | 83篇 |
2014年 | 137篇 |
2013年 | 274篇 |
2012年 | 270篇 |
2011年 | 286篇 |
2010年 | 205篇 |
2009年 | 163篇 |
2008年 | 222篇 |
2007年 | 201篇 |
2006年 | 178篇 |
2005年 | 150篇 |
2004年 | 138篇 |
2003年 | 98篇 |
2002年 | 90篇 |
2001年 | 48篇 |
2000年 | 44篇 |
1999年 | 27篇 |
1998年 | 35篇 |
1997年 | 47篇 |
1996年 | 38篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 32篇 |
1992年 | 22篇 |
1991年 | 23篇 |
1990年 | 14篇 |
1989年 | 10篇 |
1988年 | 17篇 |
1987年 | 9篇 |
1986年 | 22篇 |
1985年 | 26篇 |
1984年 | 11篇 |
1983年 | 18篇 |
1982年 | 26篇 |
1981年 | 21篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1939年 | 2篇 |
排序方式: 共有3773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.
7.
Rafael R. del Río Castillo 《Communications in Mathematical Physics》1991,142(2):421-431
In this work we study the behavior of embedded eigenvalues of Sturm-Liouville problems in the half axis under local perturbations. When the derivative of the spectral function is strictly positive, we prove that the embedded eigenvalues either disappear or remain fixed. In this case we show that local perturbations cannot add eigenvalues in the continuous spectrum. If the condition on the spectral function is removed then a local perturbation can add infinitely many eigenvalues. 相似文献
8.
Marcos Almeida Bezerra Sérgio Mitihiro do Nascimento Maêda Eliane Padua Oliveira Maria de Fátima Batista de Carvalho Ricardo Erthal Santelli 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007
In the present paper a procedure is proposed for the determination of traces of Cd, Co, Mn and Cr in petroleum industry produced water by inductively coupled plasma optical emission spectrometry. The procedure is based on cloud point extraction of these metals, as their dithizonate complexes, into the surfactant-rich phase of octylphenoxypolyethoxyethanol surfactant (Triton X-114). Extractions were carried out in solutions with salinities between 10‰ and 70‰. Since residual salinity in the surfactant-rich phase caused differences in its transport to the plasma, yttrium was used as an internal standard to correct for this effect. The simultaneous metal extraction procedure was optimized by response surface methodology using a Doehlert design and desirability function. Enhancement factors of 21, 21, 9 and 19, along with limits of quantification of 0.093, 0.20, 0.73 and 1.2 μg L− 1, and precision expressed as relative standard deviation (n = 8, 20.0 μg L− 1) of 5.8, 1.2, 1.7 and 5.7% were obtained for Cd, Co, Mn and Cr, respectively. The accuracy was evaluated by spike recovery tests on the high salinity water samples with salinity of 40 and 63‰. 相似文献
9.
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
10.
Rafael Caballero Mercedes González Flor M Guerrero Julián Molina Concepción Paralera 《European Journal of Operational Research》2007
In this work we present a multiobjective location routing problem and solve it with a multiobjective metaheuristic procedure. In this type of problem, we have to locate some plants within a set of possible locations to meet the demands of a number of clients with multiple objectives. This type of model is used to solve a problem with real data in the region of Andalusia (Spain). Thus, we study the location of two incineration plants for the disposal of solid animal waste from some preestablished locations in Andalusia, and design the routes to serve the different slaughterhouses in this region. This must be done while taking into account certain economic objectives (start-up, maintenance, and transport costs) and social objectives (social rejection by towns on the truck routes, maximum risk as an equity criterion, and the negative implications for towns close to the plant). 相似文献