全文获取类型
收费全文 | 1696篇 |
免费 | 70篇 |
国内免费 | 5篇 |
专业分类
化学 | 1355篇 |
晶体学 | 9篇 |
力学 | 38篇 |
数学 | 140篇 |
物理学 | 229篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 62篇 |
2021年 | 67篇 |
2020年 | 59篇 |
2019年 | 64篇 |
2018年 | 57篇 |
2017年 | 46篇 |
2016年 | 76篇 |
2015年 | 63篇 |
2014年 | 56篇 |
2013年 | 109篇 |
2012年 | 116篇 |
2011年 | 139篇 |
2010年 | 80篇 |
2009年 | 73篇 |
2008年 | 119篇 |
2007年 | 117篇 |
2006年 | 80篇 |
2005年 | 91篇 |
2004年 | 76篇 |
2003年 | 38篇 |
2002年 | 42篇 |
2001年 | 24篇 |
2000年 | 22篇 |
1999年 | 12篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1771条查询结果,搜索用时 15 毫秒
81.
Leonid Kikot Alexander Lyapunov Tatiana Bogaschenko Sergey Smola Catherine Kulygina 《合成通讯》2013,43(4):478-484
A new facile synthetic route to benzils containing fragments of 12-crown-4, 15-crown-5, and 18-crown-6 by oxidation of corresponding stilbenes was developed. The first representative of a new family of fluorescent sensors was obtained by reaction of bis(15-crown-5)benzil with o-phenylenediamine. The latter exhibits great fluorescence enhancement upon association with K+ and Rb+ compared to Na+ and Cs+. 相似文献
82.
83.
An efficient semiclassical approach is developed and used to calculate the coherent-control map and time dependent decoherence measure for the excited-state proton transfer dynamics associated with the keto-enolic tautomerization reaction of 2-(2'-hydroxyphenyl)-oxazole. The method extends the usual bichromatic coherent-control scenario to simulate control at finite times after photoexcitation of the system. Extensive coherent control is demonstrated in a large molecule despite the ultrafast decoherence phenomena, providing results of broad theoretical and experimental interest. 相似文献
84.
Batista CD 《Physical review letters》2002,89(16):166403
I show that a spontaneous electric polarization exists in the solution of the Falicov-Kimball model by mapping the strong coupling limit of this Hamiltonian into an xxz spin 1/2 model with a magnetic field. In this way, I determine the phase diagram of the strongly interacting model and show the existence of a transition to a mixed-valence regime containing two phases: an orbitally ordered state and a Bose-Einstein condensation of excitons with a built-in electric polarization. 相似文献
85.
86.
We obtain pulse-driven Rabi oscillations guided by a generalization of the rotating-wave approximation to include, in the optical-Bloch equations, two-level systems with a time-varying transition energy. We achieve this by using chirped pulses with the central frequency given by the time-varying transition energy. Using this approach, we predict Rabi oscillations in intersubband transitions in a two-subband n-type modulation-doped quantum well by taking into account the time-dependent intersubband energy-gap renormalization due to depolarization-shift effects. We obtain Rabi oscillations for jpi (j=0,1,2, ) pulses in the presence of dephasing. 相似文献
87.
We introduce a frustrated spin 1/2 Hamiltonian which is an extension of the two dimensional J1-J2 Heisenberg model. The ground states of this model are exactly obtained at a first-order quantum phase transition between two valence bond crystals. At this point, the low energy excitations are deconfined spinons and spin-charge separation occurs under doping in the limit of low concentration of holes. In addition, this point is characterized by the proliferation of topological defects. 相似文献
88.
Pacheco Santos V Del Colle V Batista de Lima R Tremiliosi-Filho G 《Langmuir : the ACS journal of surfaces and colloids》2004,20(25):11064-11072
In the present work, ethanol electrooxidation on a Pt(100) electrode modified by different coverage degrees of osmium nanoislands obtained by spontaneous depositions, was extensively studied employing in situ FTIR spectroscopy. A collection of spectra of the ethanol adsorption and oxidation processes was acquired during the first series of a positive potential step, to determine the intermediate species, as well as the main products formed. The spectroscopic results obtained were correlated with conventional electrochemical results obtained by cyclic voltammetry. It was shown that the catalytic activity of Pt(100) for ethanol oxidation increases significantly after osmium deposition and that the mechanistic pathway for this reaction depends directly on the osmium coverage degree. Thus, for low osmium coverage (theta;( Os) up to 0.15) the formation of CO as an intermediate was favored and hence the full oxidation of adsorbed ethanol to CO(2) was increased. For higher osmium coverages (theta;(Os) up to 0.33), the higher the coverage is, the more the direct ethanol oxidation to acetaldehyde and acetic acid is favored. For osmium coverage degree of 0.40, the catalytic activity of the electrode for ethanol oxidation decreased. On an almost complete osmium layer (theta;(Os) = 0.92) obtained by electrodeposition at 50 mV vs reversible hydrogen electrode, the catalytic activity for ethanol oxidation shows a much lower value. 相似文献
89.
[reaction: see text] A new and convenient three-step synthesis of pentafluorosulfanylbenzene from 1,4-cyclohexadiene with an overall yield of >70% is reported along with a number of derivatization reactions. 相似文献
90.
Yurij?Stoyan Guntram?ScheithauerEmail author Nikolay?Gil Tatiana?Romanova 《4OR: A Quarterly Journal of Operations Research》2004,2(1):69-84
Within two-dimensional cutting and packing problems with irregular shaped objects, the concept of
-functions has been proven to be very helpful for several solution approaches. In order to construct such
-functions a previous work, in which so-called primary objects are considered, is continued. Now
-functions are constructed for pairs of objects which can be represented as a finite combination (union, intersection, complement) of primary objects which allows the handling of arbitrary shaped objects by appropriate approximations of sufficient accuracy.Received: October 2002, Revised: October 2003, AMS classification:
65K05, 90C26, 90B06All correspondence to: Guntram Scheithauer 相似文献