全文获取类型
收费全文 | 7211篇 |
免费 | 223篇 |
国内免费 | 13篇 |
专业分类
化学 | 4879篇 |
晶体学 | 55篇 |
力学 | 184篇 |
综合类 | 5篇 |
数学 | 774篇 |
物理学 | 1550篇 |
出版年
2023年 | 53篇 |
2022年 | 154篇 |
2021年 | 222篇 |
2020年 | 180篇 |
2019年 | 191篇 |
2018年 | 193篇 |
2017年 | 137篇 |
2016年 | 280篇 |
2015年 | 220篇 |
2014年 | 289篇 |
2013年 | 442篇 |
2012年 | 494篇 |
2011年 | 555篇 |
2010年 | 365篇 |
2009年 | 373篇 |
2008年 | 457篇 |
2007年 | 408篇 |
2006年 | 339篇 |
2005年 | 286篇 |
2004年 | 246篇 |
2003年 | 191篇 |
2002年 | 171篇 |
2001年 | 132篇 |
2000年 | 127篇 |
1999年 | 76篇 |
1998年 | 66篇 |
1997年 | 63篇 |
1996年 | 52篇 |
1995年 | 46篇 |
1994年 | 65篇 |
1993年 | 63篇 |
1992年 | 64篇 |
1991年 | 36篇 |
1990年 | 32篇 |
1989年 | 25篇 |
1988年 | 26篇 |
1987年 | 20篇 |
1986年 | 22篇 |
1985年 | 23篇 |
1984年 | 24篇 |
1983年 | 26篇 |
1982年 | 15篇 |
1981年 | 26篇 |
1980年 | 18篇 |
1979年 | 24篇 |
1978年 | 21篇 |
1977年 | 14篇 |
1976年 | 12篇 |
1975年 | 12篇 |
1973年 | 11篇 |
排序方式: 共有7447条查询结果,搜索用时 328 毫秒
991.
L. Jakubowski V.V. Plyusnin K. Malinowski M.J. Sadowski J. Zebrowski M. Rabiński H. Fernandes C. Silva P. Duarte M.J. Jakubowski 《等离子体物理论文集》2013,53(9):615-622
The paper reports on experimental studies of electron beams in the ISTTOK tokamak, those were performed by means of an improved four‐channel detector. The Cherenkov‐type detector measuring head was equipped with four radiators made of two types of alumina‐nitrate (AlN) poly‐crystals: machinable and translucent ones, both of 10 mm in diameter and 2.5 mm in thickness. The movable support that enabled the whole detectors to be placed inside the tokamak vacuum chamber, at chosen positions along the ISTTOK minor radius. Since the electron energy distribution is one of the most important characteristics of tokamak plasmas, the main aim of the study was to perform estimations of an energy spectrum of the recorded electrons. For this purpose the radiators were coated with molybdenum (Mo) layers of different thickness. The technique based on the use of Cherenkov‐type detectors enabled the detection of fast electrons (of energy above 66 keV) and determination of their spatial and temporal characteristics in the ISTTOK experiment. Measurements of hard X‐rays (HXR), which were emitted during ISTTOK discharges, have also been performed. Particular attention was paid to the correlation measurements of HXR pulses with run‐away electron beams. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
992.
Maria das Graças Andrade Korn Elane Santos da Boa Morte Daniele Cristina Muniz Batista dos Santos Jacira Teixeira Castro José Tiago Pereira Barbosa Alete Paixão Teixeira 《应用光谱学评论》2013,48(2):67-92
Abstract The present article gives an overview of recent publications and modern techniques of sample preparation for food analysis employing atomic and inorganic mass spectrometric techniques, such as flame atomic absorption spectrometry, chemical vapor generation atomic absorption and atomic fluorescence spectrometry, graphite furnace atomic absorption spectrometry, inductively coupled plasma optical emission spectrometry, and inductively coupled plasma mass spectrometry. Among the most frequently applied sample preparation techniques for food analysis are dry ashing, usually with the addition of an ashing aid, and acid digestion, preferably with the assistance of microwave energy. Slurry preparation, particularly with the assistance of ultrasound, is increasingly used to reduce acid consumption and sample preparation time. Direct analysis of solid samples is gaining importance in the field of food analysis as it offers the highest sensitivity, avoids the use of acids and other aggressive reagents, makes possible the analysis of micro‐samples, and can be applied for fast screening analysis, e.g., of fresh meat. 相似文献
993.
We present results of calculations of the equilibrium surface tension and density profiles for the liquid-vapour interface of a binary mixture of Lennard-Jones 12-6 fluids. The calculations are based on a density-functional theory for the Helmholtz free energy of the inhomogeneous mixture. This is a ‘microscopic’ generalization of the van der Waals-Cahn-Hilliard theory for the interface of a binary mixture. Our calculations cover the full range of liquid-vapour coexistence and the whole range of concentration. We find a correlation between the excess surface tension of the mixture and the surface segregation (adsorption) of the species with the lower surface tension. The ways in which segregation and excess surface tension depend on the Lennard-Jones parameters of the pure components are briefly discussed. Our results for the excess surface tension of mixtures of Ar and N2 and Ar and CH4 are compared with experiment; the agreement is reasonable. 相似文献
994.
995.
996.
Manuel A.P. Segurado Margarida F.B. Silva Rita Castro 《International Journal of Mathematical Education in Science & Technology》2013,44(5):664-679
The mathematical language and its tools are complementary to the formalism in chemistry, in particular at an advanced level. It is thus crucial, for its understanding, that students acquire a solid knowledge in Calculus and that they know how to apply it. The frequent occurrence of indeterminate forms in multiple areas, particularly in Physical Chemistry, justifies the need to properly understand the limiting process in such cases. This article emphasizes the importance of the L’Hôpital's rule as a practical tool, although often neglected, to obtain the more common indeterminate limits, through the use of some specific examples as the radioactive decay, spectrophotometric error, Planck's radiation law, second-order kinetics, or consecutive reactions. 相似文献
997.
G. C. Bento J. X. da Cruz Neto P. S. M. Santos 《Journal of Optimization Theory and Applications》2013,159(1):108-124
In this paper, we present an inexact version of the steepest descent method with Armijo’s rule for multicriteria optimization in the Riemannian context given in Bento et al. (J. Optim. Theory Appl., 154: 88–107, 2012). Under mild assumptions on the multicriteria function, we prove that each accumulation point (if any) satisfies first-order necessary conditions for Pareto optimality. Moreover, assuming that the multicriteria function is quasi-convex and the Riemannian manifold has nonnegative curvature, we show full convergence of any sequence generated by the method to a Pareto critical point. 相似文献
998.
Viviane Ribeiro Tomaz da Silva 《代数通讯》2013,41(9):3342-3359
Let E be the infinite-dimensional Grassmann algebra over a field F of characteristic zero, and consider L the F-vector space spanned by all generators of E. Let ? l be any fixed automorphism of E of order 2 such that L is an homogeneous subspace. Our goal is to finish the computation of the sequences of ? l -codimensions, by finding its exact value for the unique open case, that is, when the subspace of L corresponding to the eigenvalue 1 is finite-dimensional. As a consequence we get the ?-codimensions for a large amount of arbitrary automorphisms ? of E of order 2. 相似文献
999.
1000.
The notion of hyperdecidability has been introduced as a tool which is particularly suited for granting decidability of semidirect products. It is shown in this paper that the semidirect product of an hyperdecidable pseudovariety with a pseudovariety whose finitely generated free objects are finite and effectively computable is again hyperdecidable. As instances of this result, one obtains, for example, the hyperdecidability of the pseudovarieties of ail finite completely simple semigroups and of all finite bands of left groups. 相似文献