全文获取类型
收费全文 | 74306篇 |
免费 | 2003篇 |
国内免费 | 502篇 |
专业分类
化学 | 45282篇 |
晶体学 | 528篇 |
力学 | 1819篇 |
综合类 | 38篇 |
数学 | 12268篇 |
物理学 | 16876篇 |
出版年
2023年 | 449篇 |
2022年 | 1027篇 |
2021年 | 1266篇 |
2020年 | 1177篇 |
2019年 | 1210篇 |
2018年 | 1368篇 |
2017年 | 1237篇 |
2016年 | 2286篇 |
2015年 | 1931篇 |
2014年 | 2104篇 |
2013年 | 4047篇 |
2012年 | 4212篇 |
2011年 | 4674篇 |
2010年 | 2892篇 |
2009年 | 2686篇 |
2008年 | 3991篇 |
2007年 | 3872篇 |
2006年 | 3598篇 |
2005年 | 3755篇 |
2004年 | 3436篇 |
2003年 | 2700篇 |
2002年 | 2096篇 |
2001年 | 1605篇 |
2000年 | 1439篇 |
1999年 | 1051篇 |
1998年 | 828篇 |
1997年 | 810篇 |
1996年 | 989篇 |
1995年 | 772篇 |
1994年 | 840篇 |
1993年 | 796篇 |
1992年 | 786篇 |
1991年 | 668篇 |
1990年 | 582篇 |
1989年 | 510篇 |
1988年 | 473篇 |
1987年 | 460篇 |
1986年 | 471篇 |
1985年 | 615篇 |
1984年 | 616篇 |
1983年 | 444篇 |
1982年 | 489篇 |
1981年 | 490篇 |
1980年 | 461篇 |
1979年 | 373篇 |
1978年 | 404篇 |
1977年 | 361篇 |
1976年 | 327篇 |
1975年 | 280篇 |
1973年 | 300篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Rodrigo París José Luis de la Fuente 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3538-3549
Different diblock copolymers constituted by one segment of a monomer supporting a reactive functional group, like allyl methacrylate (AMA), were synthesized by atom transfer radical polymerization (ATRP). Bromo‐terminated polymers, like polystyrene (PS), poly(methyl methacrylate) (PMMA), and poly(butyl acrylate) (PBA) were employed as macroinitiators to form the other blocks. Copolymerizations were carried out using copper chloride with N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) as the catalyst system in benzonitrile solution at 70 °C. At the early stage, the ATRP copolymerizations yielded well‐defined linear block copolymers. However, with the polymerization progress a change in the macromolecular architecture takes place due to the secondary reactions caused by the allylic groups, passing to a branched and/or star‐shaped structure until finally yielding gel at monomer conversion around 40% or higher. The block copolymers were characterized by means of size exclusion chromatography (SEC), 1H NMR spectroscopy, and differential scanning calorimetry (DSC). In addition, one of these copolymers, specifically P(BA‐b‐AMA), was satisfactorily modified through osmylation reaction to obtain the subsequent amphiphilic diblock copolymer of P(BA‐b‐DHPMA), where DHPMA is 2,3‐dihydroxypropyl methacrylate; demonstrating the feasibility of side‐chain modification of the functional obtained copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3538–3549, 2007 相似文献
62.
63.
In this paper we propose a general integration scheme for a Multi-Criteria Decision Making model of the Multi-Attribute Utility
Theory in Constraint Programming. We introduce the Choquet integral as a general aggregation function for multi-criteria optimization
problems and define the Choquet global constraint that propagates this function during the Branch-and-Bound search. Finally the benefits of the propagation
of the Choquet constraint are evaluated on the examination timetabling problem. 相似文献
64.
The rutile TiO2(1 1 0) surface is a highly anisotropic surface exhibiting “channels” delimited by oxygen rows. In previous experimental and theoretical DFT works we could identify the molybdenum adsorption sites. They are located inside the channels. Moreover, experimental studies have shown that during subsequent annealing after deposition, special molybdenum nano structures can be formed, especially two monolayer high pyramidal chains of atoms.In order to better understand the dynamics of nano structure formation, we present a kinetic Monte Carlo study on diffusion and adsorption of molybdenum atoms on a TiO2(1 1 0) surface. A quasi one-dimensional lattice gas model has been used which describes the possible adsorption sites of a Mo atom in a single channel of the surface. The atomic positions of a 1.5 monolayer thick Mo film formed of pyramidal chains define the lattice sites of the model. Thereby the formation of three-dimensional clusters could be studied. Here we have studied the cluster formation as a function of parameters that can be controlled in a growth experiment by physical vapor deposition: deposition and annealing temperature, flux and total amount of deposited Mo. Good qualitative agreement with recent experiments is obtained. 相似文献
65.
J. -Ph. Jay J. Ben Youssef H. Le Gall 《Journal of magnetism and magnetic materials》2002,240(1-3):287-290
The dynamic response of trilayer magnetoresistive permalloy/Cu/Co films was studied by high-frequency permeability spectra measurements. The resonance frequency is shown to depend on the interlayer copper thickness. This dependence is related to exchange coupling between permalloy and cobalt and the interaction field is estimated using the Landau–Lifschitz–Gilbert model. 相似文献
66.
67.
A. Ferreira da Silva I. Pepe S.A. Tomás W.M. de Azevedo R. Ahuja 《Applied Surface Science》2006,252(15):5365-5367
In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO2) as nanofilms prepared by the sol-gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO2 thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3 eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eV attributed to TiO2 absorption, which subsequently yields a strong emission band at 600 nm. The electronic band structure and optical properties of the rutile phase of TiO2 are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO2 films prepared for undoped sol-gels and by sputtering is performed. 相似文献
68.
Bernardo Lafuerza-Guillén Donal O’regan Reza Saadati 《Proceedings Mathematical Sciences》2007,117(1):61-70
We introduce the concept of quotient in PN spaces and give some examples. We prove some theorems with regard to the completeness
of a quotient. 相似文献
69.
Bubble pressure points of ethanol–1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea refrigerant) mixtures from the third Industrial Fluid Properties Simulation Challenge are computed using publicly available molecular simulation software. Several published force fields are compared against the known answers provided in the contest guidelines and the best force fields are used to make predictions for the unknown results. 相似文献
70.
Eliza P. de Jager 《Topology and its Applications》2007,154(10):2117-2126
We show that the infimum of any family of proximally symmetric quasi-uniformities is proximally symmetric, while the supremum of two proximally symmetric quasi-uniformities need not be proximally symmetric. On the other hand, the supremum of any family of transitive quasi-uniformities is transitive, while there are transitive quasi-uniformities whose infimum with their conjugate quasi-uniformity is not transitive. Moreover we present two examples that show that neither the supremum topology nor the infimum topology of two transitive topologies need be transitive. Finally, we prove that several operations one can perform on and between quasi-uniformities preserve the property of having a complement. 相似文献