全文获取类型
收费全文 | 19963篇 |
免费 | 2701篇 |
国内免费 | 1767篇 |
专业分类
化学 | 7760篇 |
晶体学 | 80篇 |
力学 | 2653篇 |
综合类 | 84篇 |
数学 | 1914篇 |
物理学 | 7436篇 |
综合类 | 4504篇 |
出版年
2024年 | 73篇 |
2023年 | 294篇 |
2022年 | 710篇 |
2021年 | 683篇 |
2020年 | 768篇 |
2019年 | 704篇 |
2018年 | 591篇 |
2017年 | 691篇 |
2016年 | 871篇 |
2015年 | 806篇 |
2014年 | 1025篇 |
2013年 | 1591篇 |
2012年 | 1225篇 |
2011年 | 1242篇 |
2010年 | 983篇 |
2009年 | 1180篇 |
2008年 | 1208篇 |
2007年 | 1340篇 |
2006年 | 1153篇 |
2005年 | 970篇 |
2004年 | 750篇 |
2003年 | 731篇 |
2002年 | 660篇 |
2001年 | 527篇 |
2000年 | 542篇 |
1999年 | 459篇 |
1998年 | 421篇 |
1997年 | 322篇 |
1996年 | 284篇 |
1995年 | 240篇 |
1994年 | 229篇 |
1993年 | 195篇 |
1992年 | 160篇 |
1991年 | 161篇 |
1990年 | 125篇 |
1989年 | 93篇 |
1988年 | 84篇 |
1987年 | 86篇 |
1986年 | 47篇 |
1985年 | 37篇 |
1984年 | 30篇 |
1983年 | 21篇 |
1982年 | 30篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 16篇 |
1978年 | 9篇 |
1976年 | 9篇 |
1971年 | 8篇 |
1957年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
Piotr Garbaczewski 《Journal of statistical physics》2006,123(2):315-355
We analyze the functioning of Gibbs-type entropy functionals in the time domain, with emphasis on Shannon and Kullback-Leibler entropies of time-dependent continuous probability distributions. The Shannon entropy validity is extended to probability distributions inferred from L
2(R
n
) quantum wave packets. In contrast to the von Neumann entropy which simply vanishes on pure states, the differential entropy quantifies the degree of probability (de)localization and its time development. The associated dynamics of the Fisher information functional quantifies nontrivial power transfer processes in the mean, both in dissipative and quantum mechanical cases.
PACS NUMBERS: 05.45.+b, 02.50.-r, 03.65.Ta, 03.67.-a 相似文献
22.
G. Tiana M.H. Jensen K. Sneppen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):135-140
A feedback mechanism that involves the proteins p53 and mdm2, induces cell death as a controlled response to severe DNA damage.
A minimal model for this mechanism demonstrates that the response may be dynamic and connected with the time needed to translate
the mdm2 protein. The response takes place if the dissociation constant k between p53 and mdm2 varies from its normal value. Although it is widely believed that it is an increase in k that triggers the response, we show that the experimental behaviour is better described by a decrease in the dissociation
constant. The response is quite robust upon changes in the parameters of the system, as required by any control mechanism,
except for few weak points, which could be connected with the onset of cancer.
Received 8 May 2002 / Received in final form 9 July 2002 Published online 17 September 2002 相似文献
23.
We investigate an operator renormalization group method to extract and describe the relevant degrees of freedom in the evolution of partial differential equations. The proposed renormalization group approach is formulated as an analytical method providing the fundamental concepts of a numerical algorithm applicable to various dynamical systems. We examine dynamical scaling characteristics in the short-time and the long-time evolution regime providing only a reduced number of degrees of freedom to the evolution process. 相似文献
24.
25.
B.I. Sturman A.S. Gorkunova K.H. Ringhofer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):291-297
We investigate analytically and numerically the influence of the type of the photorefractive nonlinear response on the periodic
states (attractors) which occur during feedback controlled 2W-coupling and correspond to almost 100% diffraction efficiency
of the dynamic index grating. In addition to the case of the local response typical, for example, for LiNbO3 crystals we consider the cases of nonlocal (diffusive) response (BaTiO3, SBN) and resonant response (DC-biased BSO, BTO, and BGO crystals). It is shown that the conditions for the transition to
the periodic states and their apparent characteristics are strongly different for the two limiting cases above.
Received 16 July 2002 / Received in final form 29 October 2002 Published online 4 March 2003 相似文献
26.
TANG Chen ZHANG Fang YAN Hai-Qing CHEN Zhan-Qing LUO Tao 《理论物理通讯》2005,44(3):435-439
We develop the three-step explicit and implicit schemes of exponential fitting methods. We use the three- step explicit exponential fitting scheme to predict an approximation, then use the three-step implicit exponential fitting scheme to correct this prediction. This combination is called the three-step predictor-corrector of exponential fitting method. The three-step predictor-corrector of exponential fitting method is applied to numerically compute the coupled nonlinear Schroedinger equation and the nonlinear Schroedinger equation with varying coefficients. The numerical results show that the scheme is highly accurate. 相似文献
27.
Architecture, engineering, and construction (AEC) global project teamwork is communication intensive and relies heavily on synchronous and asynchronous information and collaboration technologies (ICT). We explore in this paper how an asynchronous ICT, called ThinkTank, reshaped the work practice of design-construction global teams, and how the interaction with this ICT reshaped the purpose and benefits of its use. ThinkTank is a web-based asynchronous collaboration and discussion forum. We introduce the influence diffusion model (IDM) that formalizes the process of identifying the influence of people, messages, and terms mathematically. Discovering who the influence leaders in project teams are can be beneficial and critical from a corporate management perspective, since they can guide or motivate the team towards successful actions and outcomes. We present the ThinkTank-IDM integrated system and its validation with a testbed of 53 AEC global team project archived in ThinkTank over 8 years. 相似文献
28.
Nanograins are characterized by a typical grain size from lto 100 nm.Mclecular dynamics aimubations have been carried out for the nanograin sphere with the diameters from 1.45 to 10.12 nm.We study the influence of grain size on structure and diffusion properties of the nanograins.The results reveal that as the grain size is reduced,the fraction of grain surface increases significantly,and the surface width is approximately constant;the diffusicn coefficlent is increased sharply,and the relation of the diffusion coefficient and the grain size is close to exponential relation below 10nm. 相似文献
29.
《Surface and interface analysis : SIA》2003,35(2):146-150
We report the first application of pump–probe second harmonic generation (SHG) measurements to characterize optically induced magnetization in non‐magnetic multilayer semiconductors. In the experiment, spin‐polarized electrons are excited selectively by a pump beam in the GaAs layer of GaAs/GaSb/InAs structures. However, the resulting net magnetization manifests itself through the induced SHG probe signal from the GaSb/InAs interface, thus indicating a spin‐polarized electron transport across the heterostructure. We find that the magnetization dynamics are governed by an interplay between the spin density evolution at the interfaces and the spin relaxation. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
30.