全文获取类型
收费全文 | 11070篇 |
免费 | 422篇 |
国内免费 | 295篇 |
专业分类
化学 | 4772篇 |
晶体学 | 249篇 |
力学 | 806篇 |
综合类 | 5篇 |
数学 | 1329篇 |
物理学 | 4626篇 |
出版年
2023年 | 86篇 |
2022年 | 170篇 |
2021年 | 181篇 |
2020年 | 180篇 |
2019年 | 176篇 |
2018年 | 197篇 |
2017年 | 166篇 |
2016年 | 258篇 |
2015年 | 210篇 |
2014年 | 317篇 |
2013年 | 535篇 |
2012年 | 718篇 |
2011年 | 832篇 |
2010年 | 617篇 |
2009年 | 636篇 |
2008年 | 663篇 |
2007年 | 600篇 |
2006年 | 593篇 |
2005年 | 454篇 |
2004年 | 396篇 |
2003年 | 317篇 |
2002年 | 269篇 |
2001年 | 485篇 |
2000年 | 400篇 |
1999年 | 272篇 |
1998年 | 208篇 |
1997年 | 188篇 |
1996年 | 207篇 |
1995年 | 161篇 |
1994年 | 150篇 |
1993年 | 111篇 |
1992年 | 116篇 |
1991年 | 132篇 |
1990年 | 112篇 |
1989年 | 85篇 |
1988年 | 68篇 |
1987年 | 49篇 |
1986年 | 43篇 |
1985年 | 52篇 |
1984年 | 46篇 |
1983年 | 25篇 |
1982年 | 39篇 |
1981年 | 35篇 |
1980年 | 29篇 |
1979年 | 25篇 |
1978年 | 26篇 |
1977年 | 21篇 |
1976年 | 18篇 |
1975年 | 21篇 |
1974年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
21.
We present some algorithms related to rings of Ore polynomials (or, briefly, Ore rings) and describe a computer algebra library
for basic operations in an arbitrary Ore ring. The library can be used as a basis for various algorithms in Ore rings, in
particular, in differential, shift, and q-shift rings.
__________
Translated from Sovremennaya Matematika i Ee Prilozheniya (Contemporary Mathematics and Its Applications), Vol. 13, Algebra,
2004. 相似文献
22.
本文提出从高分辨电子显微像中,利用光学、全息和部分相干等方法,提取传递函数,制作相位和振幅滤波器,实现解卷,提高高分辨电子显微像的分辨率. 相似文献
23.
Tereza C. R. dos Santos Ricardo Q. Aucélio Reinaldo C. Campos 《Mikrochimica acta》2003,142(1-2):63-66
A simple and direct spectrofluorimetric method has been developed for the determination of aluminum using alizarin red PS
(1,2,4-trihydroxy 9,10-anthraquinone-3-sulfonic acid). The method is based on the strong fluorescence (480/564 nm) of Al3+ and alizarin red. Experimental parameters such as pH, concentration of the ligand, ionic strength of the solution, reaction
time and temperature were optimized in order to maximize the analytical signal. Interferences of several ions (anions and
cations) were studied and evaluated. The linear range of the method extends from 3 to 100 μg L−1. Limit of detection (3sb) was 0.9 μg L−1. The method was tested with a silicate certified reference material. Interferences were eliminated by a liquid extraction
with cupferron.
Author for correspondence. E-mail: aucelior@rdc.puc-rio.br
Received September 10, 2002; accepted January 15, 2003
Published online May 5, 2003 相似文献
24.
Liang Liao Yi Pang Liming Ding Frank E. Karasz 《Journal of polymer science. Part A, Polymer chemistry》2003,41(20):3149-3158
A soluble cyano‐substituted poly[(1,3‐phenylene vinylene)‐alt‐(1,4‐phenylene vinylene)] derivative ( 9 ) was synthesized and characterized. Comparison between 9 and its model compound ( 10 ) showed that the chromophore in 9 remained to be well defined as a result of a π‐conjugation interruption at adjacent m‐phenylene units. The attachment of a cyano substituent only at the β position of the vinylene allowed the maximum electronic impact of the cyano group on the optical properties of the poly(p‐phenylene vinylene) material. At a low temperature (?108 or ?198 °C), the vibronic structures of 9 and 10 were partially resolved. The absorption and emission spectra of a film of 9 were less temperature‐dependent than those of a film of 10 , indicating that the former had a lower tendency to aggregate. A light‐emitting diode (LED) based on 9 emitted yellow light (λmax ≈ 578 nm) with an external quantum efficiency of 0.03%. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3149–3158, 2003 相似文献
25.
K.B. Welter Q. Wu Y. You K. Abel D. McCreary S.M. Bajorek J.N. Reyes Jr 《International Journal of Multiphase Flow》2004,30(12):407-1484
This article describes a comprehensive literature review of liquid entrainment in horizontal pipes with vertical-up branches. Deficiencies in the available data and correlations were identified. The Air–water Test Loop for Advanced Thermal–hydraulic Studies (ATLATS) was constructed and entrainment onset and steady-state data were collected for a wide range of flow conditions. Using new insights gained from experimental testing, the authors developed a model for predicting the onset of entrainment and steady-state entrainment rate. Previously published correlations, along with the new model, are compared against all available data. The new model shows very good agreement with the onset data, but is not very good at predicting branch quality at high liquid flow rates. 相似文献
26.
Richard Kotek Kyeong Pang Ben Schmidt Alan Tonelli 《Journal of Polymer Science.Polymer Physics》2004,42(23):4247-4254
Poly(ethylene isophthalate) (PEI) was synthesized for this research with essentially a condensation polymerization of isophthalic acid and ethylene glycol catalyzed by zinc acetate and antimony trioxide. Several samples were obtained, and their characteristics were observed and compared with poly(ethylene terephthalate) (PET). The synthesized PEI samples were chemically identified by 1H NMR. Thermal analysis with differential scanning calorimetry (DSC) yielded results that indicate the samples were primarily amorphous, with a glass‐transition temperature of 55–60 °C. Molecular weights of these PEI samples were also obtained through intrinsic viscosity measurements (Mark–Houwink equation). Molecular weights varied with conditions of the polymerization, and the highest molecular weight achieved was 21,000 g/mol. Finally, the diffusion coefficient, solubility, and permeability of CO2 gas in PEI were measured and found to be substantially lower than in PET, as anticipated from their isomeric chemical structures. This is because in PET the phenyl rings are substituted in the para (1,4) positions, which allows for their facile flipping, effectively permitting gases to pass through. However, the meta‐substituted phenyl rings in PEI do not permit such ring flipping, and thus PEI may be more suitable for barrier applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4247–4254, 2004 相似文献
27.
For vector quasivariational inequalities involving multifunctions in topological vector spaces, an existence result is obtained without a monotonicity assumption and with a convergence assumption weaker than semicontinuity. A new type of quasivariational inequality is proposed. Applications to quasicomplementarity problems and traffic network equilibria are considered. In particular, definitions of weak and strong Wardrop equilibria are introduced for the case of multivalued cost functions. 相似文献
28.
29.
In this article we have studied the nonlinear interaction between ellipticity and dissipation in a set of model equations (1.1) and established the relation between this interaction and chaos. In addition to theoretical investigations, extensive numerical simulations with these equations have been made, and different routes to chaos have been found. The numerical studies have revealed the chaotic nature of the solutions. 相似文献
30.
W. A. Rodrigues Jr. Q. A. G. de Souza J. Vaz Jr. P. Lounesto 《International Journal of Theoretical Physics》1996,35(9):1849-1900
In this paper we study Dirac-Hestenes spinor fields (DHSF) on a four-dimensional Riemann-Cartan spacetime (RCST). We prove that these fields must be defined as certain equivalence classes of even sections of the Clifford bundle (over the RCST), thereby being certain particular sections of a new bundle named the spin-Clifford bundle (SCB). The conditions for the existence of the SCB are studied and are shown to be equivalent to Geroch's theorem concerning the existence of spinor structures in a Lorentzian spacetime. We introduce also the covariant and algebraic Dirac spinor fields and compare these with DHSF, showing that all three kinds of spinor fields contain the same mathematical and physical information. We clarify also the notion of (Crumeyrolle's) amorphous spinors (Dirac-Kähler spinor fields are of this type), showing that they cannot be used to describe fermionic fields. We develop a rigorous theory for the covariant derivatives of Clifford fields (sections of the Clifford bundle, CB) and of Dirac-Hestenes spinor fields. We show how to generalize the original Dirac-Hestenes equation in Minkowski spacetime for the case of RCST. Our results are obtained from a variational principle formulated through the multiform derivative approach to Lagrangian field theory in the Clifford bundle. 相似文献