全文获取类型
收费全文 | 98588篇 |
免费 | 3358篇 |
国内免费 | 3426篇 |
专业分类
化学 | 40366篇 |
晶体学 | 1113篇 |
力学 | 7705篇 |
综合类 | 232篇 |
数学 | 34015篇 |
物理学 | 21941篇 |
出版年
2024年 | 65篇 |
2023年 | 332篇 |
2022年 | 696篇 |
2021年 | 732篇 |
2020年 | 759篇 |
2019年 | 805篇 |
2018年 | 10908篇 |
2017年 | 10788篇 |
2016年 | 6917篇 |
2015年 | 1799篇 |
2014年 | 1575篇 |
2013年 | 1853篇 |
2012年 | 5585篇 |
2011年 | 12302篇 |
2010年 | 7005篇 |
2009年 | 7351篇 |
2008年 | 8155篇 |
2007年 | 10012篇 |
2006年 | 1444篇 |
2005年 | 2399篇 |
2004年 | 2371篇 |
2003年 | 2704篇 |
2002年 | 1846篇 |
2001年 | 866篇 |
2000年 | 773篇 |
1999年 | 552篇 |
1998年 | 530篇 |
1997年 | 401篇 |
1996年 | 460篇 |
1995年 | 313篇 |
1994年 | 278篇 |
1993年 | 255篇 |
1992年 | 216篇 |
1991年 | 222篇 |
1990年 | 154篇 |
1989年 | 174篇 |
1988年 | 116篇 |
1987年 | 109篇 |
1986年 | 111篇 |
1985年 | 94篇 |
1984年 | 70篇 |
1983年 | 63篇 |
1982年 | 59篇 |
1981年 | 52篇 |
1980年 | 60篇 |
1979年 | 51篇 |
1978年 | 47篇 |
1914年 | 45篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Jem‐Kun Chen I‐Kuan Lin Fu‐Hsiang Ko Chih‐Feng Huang Kuo‐Shen Chen Chia‐Hao Chan Feng‐Chih Chang 《Journal of Polymer Science.Polymer Physics》2004,42(22):4063-4074
Polybenzoxazine (PBZZ) thin films can be fabricated by the plasma‐polymerization technique with, as the energy source, plasmas of argon, oxygen, or hydrogen atoms and ions. When benzoxazine (BZZ) films are polymerized through the use of high‐energy argon atoms, electronegative oxygen atoms, or excited hydrogen atoms, the PBZZ films that form possess different properties and morphologies in their surfaces. High‐energy argon atoms provide a thermodynamic factor to initiate the ring‐opening polymerization of BZZ and result in the polymer surface having a grid‐like structure. The ring‐opening polymerization of the BZZ film that is initiated by cationic species such as oxygen atoms in plasma, is propagated around nodule structures to form the PBZZ. The excited hydrogen atom plasma initiates both polymerization and decomposition reactions simultaneously in the BZZ film and results in the formation of a porous structure on the PBZZ surface. We evaluated the surface energies of the PBZZ films polymerized by the action of these three plasmas by measuring the contact angles of diiodomethane and water droplets. The surface roughness of the films range from 0.5 to 26 nm, depending on the type of carrier gas and the plasma‐polymerization time. By estimating changes in thickness, we found that the PBZZ film synthesized by the oxygen plasma‐polymerization process undergoes the slowest rate of etching in CF4 plasma. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4063–4074, 2004 相似文献
52.
53.
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
54.
55.
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
56.
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
57.
58.
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
59.
Zhaoyang Yin 《Monatshefte für Mathematik》2004,141(4):337-344
We prove under quite general assumptions the existence of a bounded positive solution to the semilinear Schrödinger equation in a two-dimensional exterior domain. 相似文献
60.
Shea-Ming Oon 《Periodica Mathematica Hungarica》2004,49(2):107-118
In this paper we study some pseudo-random properties related to the prime factors of integers. We prove some results concerning the well distribution of the greatest prime factor modulo 4, and give some computational insight on the correlations, which seem to be beyond reach of proof. 相似文献