全文获取类型
收费全文 | 167617篇 |
免费 | 13652篇 |
国内免费 | 9787篇 |
专业分类
化学 | 86253篇 |
晶体学 | 1697篇 |
力学 | 12189篇 |
综合类 | 736篇 |
数学 | 42675篇 |
物理学 | 47506篇 |
出版年
2024年 | 288篇 |
2023年 | 1729篇 |
2022年 | 2907篇 |
2021年 | 3059篇 |
2020年 | 3263篇 |
2019年 | 3170篇 |
2018年 | 12583篇 |
2017年 | 12177篇 |
2016年 | 9570篇 |
2015年 | 4814篇 |
2014年 | 5059篇 |
2013年 | 6745篇 |
2012年 | 11250篇 |
2011年 | 17948篇 |
2010年 | 10840篇 |
2009年 | 11129篇 |
2008年 | 12039篇 |
2007年 | 13631篇 |
2006年 | 5112篇 |
2005年 | 5526篇 |
2004年 | 4901篇 |
2003年 | 4556篇 |
2002年 | 3440篇 |
2001年 | 2421篇 |
2000年 | 2234篇 |
1999年 | 2207篇 |
1998年 | 1956篇 |
1997年 | 1699篇 |
1996年 | 1842篇 |
1995年 | 1534篇 |
1994年 | 1401篇 |
1993年 | 1273篇 |
1992年 | 1103篇 |
1991年 | 973篇 |
1990年 | 808篇 |
1989年 | 706篇 |
1988年 | 573篇 |
1987年 | 523篇 |
1986年 | 478篇 |
1985年 | 486篇 |
1984年 | 336篇 |
1983年 | 269篇 |
1982年 | 250篇 |
1981年 | 202篇 |
1980年 | 180篇 |
1979年 | 151篇 |
1978年 | 129篇 |
1977年 | 102篇 |
1975年 | 104篇 |
1973年 | 125篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
According to a multiphase mixture theory, we have mathematically developed a multiphysical model with chemoelectromechanical coupling considerations, termed the multieffect‐coupling electric‐stimulus (MECe) model, to simulate the responsive behavior of electric‐sensitive hydrogels immersed in a bath solution under an externally applied electric field. For solutions of the MECe model consisting of coupled nonlinear partial differential governing equations, a meshless Hermite–Cloud method with a hierarchical iteration technique has been used for a one‐dimensional steady‐state analysis of a hydrogel strip. The computed results are compared with the experimental data, and there is very good agreement. Simulations within the domains of both hydrogels and surrounding solutions also present distributions of the ionic concentrations and electric potential as well as the hydrogel displacement. The effects of various physical parameters on the response behavior of electric‐stimulus responsive hydrogels are discussed in detail. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1514–1531, 2004 相似文献
152.
The structure, morphology, and isothermal and nonisothermal crystallization of isotactic polypropylene/low‐molecular‐mass hydrocarbon resin blends (iPP/HR) (up to 20% in weight of HR) have been studied, using optical and electron microscopy, wide‐ and small‐angle X‐ray and differential scanning calorimetry. New structures and morphologies can be activated, using appropriate preparation and crystallization conditions and blend composition. For every composition and crystallization condition, iPP crystallizes in α‐form, with a spherulitic morphology. The size of iPP spherulites increases with resin content, whereas the long period decreases. In the range of crystallization temperatures investigated, HR modifies the birefringence of iPP spherulites, favoring the formation of radial lamellae and changing the ratio between tangential and radial lamellae. Spherulitic radial growth rates, overall crystallization rates, and melting temperatures are strongly affected by resin, monotonically decreasing with resin content. This confirms miscibility in the melt between the two components of the blends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3368–3379, 2004 相似文献
153.
YAN Xiaomin ZHAO Lin SHAO Jianhui TAN Xin SONG Zhengxiao School of Chemical Engineering Technology Tianjin University Tianjin China Slichem Liquid Material Co. Ltd. Shijiazhuang China 《Chinese Journal of Reactive Polymers》2004,(Z1)
1. INTRODUCTION Methionine, namely 2-amido-4-thiomethyl butyric acid with a structure of CH3SCH2CH2CHCOOH, is one of the essential amino acids and has two natural enantionmers, D and L-methionine. The mixture of L- and D-isomers can be used as analeptics or nutritive additives to maintain the equilibrium of amino acids of feed [1,2]. L-methionine can release active methyl and accelerate the synthesis of choline, which further speeds up the conversion of the lipid accumulated in liv… 相似文献
154.
NianYuanTAN XiaoMingXIAO ZeLinLI TakekoMATSUMURA-INOUE 《中国化学快报》2004,15(6):687-690
A new cobalt(Ⅱ) complex with tridentate ligand 2, 6-bis (benzimidazol-2-yl)pyridine has been synthesized by microwave irradiation method and characterized by elemental analysis,electrochemical and spectral methods. The binding of the complex with calf thymus DNA has also been investigated by absorption and fluorescence spectra. 相似文献
155.
Baker‘s yeast mediated reduction of optically active diketone is described. The two keto groups are efficiently differentiated and the ee value of the recovered material is considerably raised. It affords highly optically active key intermediates efficiently for the synthesis of natural polyhydroxylated agarofuran products. 相似文献
156.
We shall answer several questions concerning additive or multiplicative commutators in a division ring which are algebraic of bounded degree over its center. 相似文献
157.
Panos M. Pardalos Wanpracha Chaovalitwongse Leonidas D. Iasemidis J. Chris Sackellares Deng-Shan Shiau Paul R. Carney Oleg A. Prokopyev Vitaliy A. Yatsenko 《Mathematical Programming》2004,101(2):365-385
There is growing evidence that temporal lobe seizures are preceded by a preictal transition, characterized by a gradual dynamical change from asymptomatic interictal state to seizure. We herein report the first prospective analysis of the online automated algorithm for detecting the preictal transition in ongoing EEG signals. Such, the algorithm constitutes a seizure warning system. The algorithm estimates STLmax, a measure of the order or disorder of the signal, of EEG signals recorded from individual electrode sites. The optimization techniques were employed to select critical brain electrode sites that exhibit the preictal transition for the warning of epileptic seizures. Specifically, a quadratically constrained quadratic 0-1 programming problem is formulated to identify critical electrode sites. The automated seizure warning algorithm was tested in continuous, long-term EEG recordings obtained from 5 patients with temporal lobe epilepsy. For individual patient, we use the first half of seizures to train the parameter settings, which is evaluated by ROC (Receiver Operating Characteristic) curve analysis. With the best parameter setting, the algorithm applied to all cases predicted an average of 91.7% of seizures with an average false prediction rate of 0.196 per hour. These results indicate that it may be possible to develop automated seizure warning devices for diagnostic and therapeutic purposes.Mathematics Subject Classification (1991):20E28, 20G40, 20C20 相似文献
158.
Harish Seshadri 《Mathematische Zeitschrift》2004,247(3):487-503
We study closed Einstein 4-manifolds which admit S1 actions of a certain type, i.e., warped products. In particular, we classify them up to isometry when the fixed point of the S1 action satisfies certain natural geometric conditions. The proof uses the Bochner-Weitzenböck formula for 1-forms and the theory of minimal surfaces in 3-manifolds.in final form: 22 January 2003 相似文献
159.
160.
Fabio A. C. C. Chalub Peter A. Markowich Benoît Perthame Christian Schmeiser 《Monatshefte für Mathematik》2004,142(1-2):123-141
Kinetic models for chemotaxis, nonlinearly coupled to a Poisson equation for the chemo-attractant density, are considered. Under suitable assumptions on the turning kernel (including models introduced by Othmer, Dunbar and Alt), convergence in the macroscopic limit to a drift-diffusion model is proven. The drift-diffusion models derived in this way include the classical Keller-Segel model. Furthermore, sufficient conditions for kinetic models are given such that finite-time-blow-up does not occur. Examples are given satisfying these conditions, whereas the macroscopic limit problem is known to exhibit finite-time-blow-up. The main analytical tools are entropy techniques for the macroscopic limit as well as results from potential theory for the control of the chemo-attractant density.Present address: Centro de Matemática e Aplicações Fundamentais, Universidade de Lisboa, Av. Prof. Gama Pinto 2, 1649-003, Lisboa, Portugal 相似文献