全文获取类型
收费全文 | 77901篇 |
免费 | 2556篇 |
国内免费 | 252篇 |
专业分类
化学 | 50057篇 |
晶体学 | 453篇 |
力学 | 1523篇 |
综合类 | 1篇 |
数学 | 14075篇 |
物理学 | 14600篇 |
出版年
2023年 | 489篇 |
2022年 | 484篇 |
2021年 | 857篇 |
2020年 | 1150篇 |
2019年 | 1066篇 |
2018年 | 1300篇 |
2017年 | 1214篇 |
2016年 | 2457篇 |
2015年 | 2089篇 |
2014年 | 2129篇 |
2013年 | 4712篇 |
2012年 | 4658篇 |
2011年 | 4976篇 |
2010年 | 2898篇 |
2009年 | 2457篇 |
2008年 | 4310篇 |
2007年 | 4097篇 |
2006年 | 3859篇 |
2005年 | 3782篇 |
2004年 | 3245篇 |
2003年 | 2774篇 |
2002年 | 2492篇 |
2001年 | 1355篇 |
2000年 | 1338篇 |
1999年 | 1017篇 |
1998年 | 841篇 |
1997年 | 787篇 |
1996年 | 1059篇 |
1995年 | 750篇 |
1994年 | 781篇 |
1993年 | 707篇 |
1992年 | 734篇 |
1991年 | 632篇 |
1990年 | 645篇 |
1989年 | 562篇 |
1988年 | 599篇 |
1987年 | 526篇 |
1986年 | 498篇 |
1985年 | 793篇 |
1984年 | 748篇 |
1983年 | 567篇 |
1982年 | 636篇 |
1981年 | 663篇 |
1980年 | 575篇 |
1979年 | 553篇 |
1978年 | 527篇 |
1977年 | 487篇 |
1976年 | 483篇 |
1974年 | 459篇 |
1973年 | 471篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
141.
The purpose of this paper is to give the Reid ``Roundabout Theorem' for quadratic functionals with general boundary conditions.
In particular, we describe the so-called coupled point and regularity condition introduced in [16] in terms of Riccati equation
solutions.
Accepted 27 February 1996 相似文献
142.
A. Sánchez-Lavega A. Salazar A. Ocariz L. Pottier E. Gomez L.M. Villar E. Macho 《Applied Physics A: Materials Science & Processing》1997,65(1):15-22
Received: 16 September 1996/Accepted: 6 January 1997 相似文献
143.
A. Bonilla F. Pérez-González A. Stray R. Trujillo-González 《Journal d'Analyse Mathématique》1997,73(1):65-89
This paper is concerned with several approximation problems in the weighted Hardy spacesH
p(Ω) of analytic functions in the open unit disc D of the complex plane ℂ. We prove that ifX is a relatively closed subset of D, the class of uniform limits onX of functions inH
p(Ω) coincides, moduloH
p(Ω), with the space of uniformly continuous functions on a certain hull ofX which are holomorphic on its interior. We also solve the simultaneous approximation problems of describing Farrell and Mergelyan
sets forH
p(Ω), giving geometric characterizations for them. By replacing approximating polynomials by polynomial multipliers of outer
functions, our results lead to characterizations of the same sets with respect to cyclic vectors in the classical Hardy spacesH
p(D), 1 ⪯p < ∞.
Dedicated to Professor Nácere Hayek on the occasion of his 75th birthday. 相似文献
144.
145.
Some of the motivations for as well as the main points of the quantization of the Nappi-Witten string in the light-cone gauge are reviewed. 相似文献
146.
V.I. Fernández A. Iucci C.M. Naón 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):53-56
We present an extension of the Tomonaga-Luttinger model in which left and right-moving particles have different Fermi velocities.
We derive expressions for one-particle Green's functions, momentum-distributions, density of states, charge compressibility
and conductivity as functions of both the velocity difference ε and the strength of the interaction β. This allows us to identify
a novel restricted region in the parameter space in which the system keeps the main features of a Luttinger liquid but with
an unusual behavior of the density of states and the static charge compressibility κ. In particular κ diverges on the boundary
of the restricted region, indicating the occurrence of a phase transition.
Received 20 May 2002 / Received in final form 23 August 2002 Published online 19 November 2002 相似文献
147.
We clarify the way in which cosmological perturbations of quantum origin, produced during inflation, assume classical properties. Two features play an important role in this process: First, the dynamics of fluctuations which are presently on large cosmological scales leads to a very peculiar state (highly squeezed) that is indistinguishable, in a precise sense, from a classical stochastic process. This holds for almost all initial quantum states. Second, the process of decoherence by interaction with the environment distinguishes the field amplitude basis as the robust pointer basis. We discuss in detail the interplay between these features and use simple analogies such as the free quantum particle to illustrate the main conceptual issues. 相似文献
148.
Theorists often characterize modeling as a cyclic problem-solving process. One builds the model, assesses its validity with regard to the underlying problem situation, and revises accordingly. The process halts when, in the opinion of the modeler, the model generates a valid solution to the underlying problem. Recent research suggests that students, like experts, employ cyclic modeling processes. Extensive observations of university and high school students’ modeling efforts, however, suggest the use of linear rather than cyclic modeling strategies. That is, novice modelers often fail to look back or revise their initial models. This paper offers empirical evidence on behalf of the linear modeling theory and identifies five factors that promote the use of linear modeling strategies: students’ conceptions of models and the modeling process, the perceived objectives of the modeling activity, constraints on time and resources, statistical misconceptions, and an overall lack of interest. The paper concludes with several promising instructional strategies (strategies that address students’ difficulties and promote reflective modeling behavior), as well as suggestions for future research. 相似文献
149.
Ricardo García-Pelayo Iván Salazar William C. Schieve 《Journal of statistical physics》1993,72(1-2):167-187
An analytically solvable model for sand avalanches of noninteracting grains of sand, based on the Chapman-Kolmogorov equations, is presented. For a single avalanche, distributions of lifetimes, sizes of overflows and avalanches, and correlation functions are calculated. Some of these are exponentials, some are power laws. Spatially homogeneous distributions of avalanches are also studied. Computer simulations of avalanches of interacting grains of sand are compared to the solutions to the Chapman-Kolmogorov equations. We find that within the range of parameters explored in the simulation, the approximation of noninteracting grains of sand is a good one. 相似文献
150.
Dr. David J. Lurie I. Nicholson J. S. McLay J. R. Mallard 《Applied magnetic resonance》1992,3(5):917-925
The technique of Field-Cycled Dynamic Nuclear Polarization (FC-DNP) involves the EPR irradiation of a free radical solution and the subsequent observation of the NMR signal, the experiment being carried out at a range of magnetic field strengths in order to measure the free radical’s EPR spectrum. In this work FC-DNP has been used to study the EPR spectrum of DMPO spin-trapped hydroxyl free radicals at magnetic field strengths between 0.5 mT and 13.0 mT (5–130 Gauss). The low-field EPR spectrum contains six separate EPR lines, in contrast to the well-known X-band spectrum where only four are seen. Knowledge of the spin-adduct’s EPR spectrum will be of use to workers involved in low-field EPR, especially those conducting biological or in-vivo spin-trapping experiments. 相似文献