全文获取类型
收费全文 | 407707篇 |
免费 | 3450篇 |
国内免费 | 951篇 |
专业分类
化学 | 189741篇 |
晶体学 | 6450篇 |
力学 | 21390篇 |
综合类 | 7篇 |
数学 | 59854篇 |
物理学 | 134666篇 |
出版年
2021年 | 3127篇 |
2020年 | 3330篇 |
2019年 | 3762篇 |
2018年 | 11918篇 |
2017年 | 12618篇 |
2016年 | 10500篇 |
2015年 | 4817篇 |
2014年 | 7122篇 |
2013年 | 16002篇 |
2012年 | 15763篇 |
2011年 | 24769篇 |
2010年 | 16808篇 |
2009年 | 16792篇 |
2008年 | 21813篇 |
2007年 | 24596篇 |
2006年 | 12304篇 |
2005年 | 15892篇 |
2004年 | 12517篇 |
2003年 | 11452篇 |
2002年 | 9859篇 |
2001年 | 10518篇 |
2000年 | 7932篇 |
1999年 | 5998篇 |
1998年 | 5002篇 |
1997年 | 4823篇 |
1996年 | 4645篇 |
1995年 | 3958篇 |
1994年 | 3904篇 |
1993年 | 3777篇 |
1992年 | 4160篇 |
1991年 | 4375篇 |
1990年 | 4167篇 |
1989年 | 4083篇 |
1988年 | 3862篇 |
1987年 | 3994篇 |
1986年 | 3756篇 |
1985年 | 4713篇 |
1984年 | 4777篇 |
1983年 | 3975篇 |
1982年 | 4055篇 |
1981年 | 3781篇 |
1980年 | 3734篇 |
1979年 | 4015篇 |
1978年 | 4016篇 |
1977年 | 3931篇 |
1976年 | 3940篇 |
1975年 | 3722篇 |
1974年 | 3663篇 |
1973年 | 3723篇 |
1972年 | 2638篇 |
排序方式: 共有10000条查询结果,搜索用时 20 毫秒
281.
Many operators in Banach spaces occur as the integration operator of a suitable vector measure; their compactness is completely described in [19]. However, many important spaces X in analysis (and integration operators in such spaces) do not fall into this scheme because X is not normable. Characterizing the compactness of integration operators in this setting is the aim of this note. The methods and techniques employed are quite different to the Banach space arguments used in [19]. 相似文献
282.
Necessary conditions for the Gâteaux differentiability of the distance function to a set are considered. A series of characterizing results is obtained. 相似文献
283.
P Vincent A BrioudeC Journet S RabasteS.T Purcell J Le BrusqJ.C Plenet 《Journal of Non》2002,311(2):130-137
We report here the successful inclusion of carbon nanotubes (CNs) into a TiO2 matrix prepared by a sol-gel method. The presence of CNs in the sol-gel matrix and the structure of the film were analyzed principally by transmission electron microscopy. Complementary information about the behavior of embedded carbon nanotubes versus heat treatment and ion irradiation were obtained by X-ray photoelectron spectroscopy. The elaboration of an inorganic matrix containing embedded carbon nanotubes leads to a new nanocomposite. The possible applications of this nanocomposite are discussed. 相似文献
284.
A comprehensive study of the excited electronic states of HCl is reported. Using resonance enhanced multiphoton ionization ((2 + 1) REMPI) and time-of-flight mass spectrometry (TOFMS) over 120 band systems are analyzed. Supersonic jet techniques are used to prepare rotationally cold species for laser spectroscopy in the 77 000 to 96 000 cm−1 region. At least 50 new electronic states are characterized as well as several features only tentatively assigned previously. A long vibrational progression consisting of 29 vibrational levels of the deeply bound V1Σ+(0+) valence/ion-pair state is studied. We also extend the identification and analysis to high vibrational levels of low-lying Rydberg states. The assignments of [2Πi] Rydberg state complexes are evaluated in terms of spin-orbit coupling and united-atom calculations. In several band systems, the spectra exhibit anomalous rotational line intensities and broadened linewidths which are consistent with predissociation. Multiphoton ionization with mass spectrometry permits the investigation of isotope effects as well as the appearance of fragment species associated with repulsive potential curves. 相似文献
285.
The variational problem of contact equilibrium of a punch and an elastic body is considered. An equivalent formulation of the problem is given in variational inequality form. Existence and uniqueness of the solution is investigated in a particular case. A penalty method is proposed for approximate solution of the problem.Translated from Vychislitel'naya i Prikladnaya Matematika, No. 56, pp. 97–103, 1985. 相似文献
286.
D. A. Tikhomirov O. S. Slyadevskaya A. V. Eremeev 《Chemistry of Heterocyclic Compounds》1991,27(9):966-969
A convenient method of synthesis of 2-(methoxycarbonylmethylene)-substituted imidazolidines and imidazolidinium bromides, and also of bicyclic diazo compounds has been developed starting from methyl bromopropiolate and ethylenediamine and its derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1205–1208, September, 1991. 相似文献
287.
288.
289.
The theory of free-carrier absorption (FCA) is developed, in the extreme quantum limit when the carriers are assumed to populate
only the lowest quantized energy level, for quasi-two and one-dimensional semiconducting quantum well structures where the
carriers are scattered by ionized impurities. The radiation field is assumed to be polarized in the plane of the layer in
the quasi-two-dimensional case and along the length of the wire in the quasi-one-dimensional case. Expressions for FCA are
obtained for the cases where the impurities are either in the well (background impurities) or outside the well (remote impurities).
Variation of FCA is numerically studied with photon frequency and well width. 相似文献
290.
A firm's logistics cost, including shipping and inventory-carrying, is a substantial percentage of its sales. Nevertheless, typical inventory-control methods ignore or insufficiently represent the shipping cost. This paper describes a recursive algorithm that determines the reorder cycle-time that minimizes total logistics cost. It allows for a realistic accounting of shipping cost, which is modelled here as a function of shipping distance and weight. The algorithm uses a relaxation procedure to identify a suitable initial approximation to the optimal order cycle-time and then, through a series of recursive steps, moves to the optimal result. We demonstrate the algorithm with a single item, with a group of items that share a common order cycle, and with multi-items when item demands are random variables. Experience with this algorithm indicates that it converges to the optimal result in a very few steps. 相似文献