全文获取类型
收费全文 | 772篇 |
免费 | 28篇 |
国内免费 | 4篇 |
专业分类
化学 | 492篇 |
晶体学 | 10篇 |
力学 | 12篇 |
数学 | 91篇 |
物理学 | 199篇 |
出版年
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 19篇 |
2018年 | 8篇 |
2017年 | 9篇 |
2016年 | 25篇 |
2015年 | 15篇 |
2014年 | 8篇 |
2013年 | 27篇 |
2012年 | 36篇 |
2011年 | 42篇 |
2010年 | 25篇 |
2009年 | 25篇 |
2008年 | 62篇 |
2007年 | 50篇 |
2006年 | 58篇 |
2005年 | 37篇 |
2004年 | 21篇 |
2003年 | 23篇 |
2002年 | 35篇 |
2001年 | 29篇 |
2000年 | 14篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 19篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1971年 | 2篇 |
1930年 | 2篇 |
排序方式: 共有804条查询结果,搜索用时 15 毫秒
1.
When an organization solves a portfolio problem with public projects evaluated by multiple criteria, in which the economic dimension is not essential or not well characterized, the classical methods are not useful. We propose a non-linear preference model developed from normative Value Theory and using fuzzy sets to model some sources of imprecision. This model can be considered as a generalization of the classical approaches. However, the optimization problem is very complex in order to be solved with non-linear programming techniques. Therefore, the model is exploited by an evolutionary algorithm, able to achieve a strong improvement of the quality of solution. 相似文献
2.
E. Casarejos P. Armbruster L. Audouin J. Benlliure M. Bernas A. Boudard R. Legrain S. Leray B. Mustapha S. Czajkowski T. Enqvist B. Fernandez J. Pereira M. Pravikoff F. Rejmund K. -H. Schmidt C. Stephan J. Taieb L. Tassan-Got C. Villagrasa C. Volant W. Wlazlo 《Physics of Atomic Nuclei》2003,66(8):1413-1420
The isotopic production cross sections of heavy residues in relativistic heavy-ion collisions have been investigated in inverse kinematics. The primary reaction products were fully identified in mass and atomic number prior to beta decay using the fragment separator FRS. The huge collection of data obtained helps in the understanding of the two main reaction mechanisms involved: fragmentation and fission. These data provide basic information for future radioactive ion beam facilities and for technical applications like intense neutron sources by means of spallation targets. 相似文献
3.
In quasi-steady operation, convection currents in a Bridgmandevice, used for producing a semi-conductor crystal, createinhomogeneities that may make the crystal unusable. It has oftenbeen suggested that additional forces due to rotation or magnetismmight be efficacious in reducing the segregation of the elementsof the alloy. It has been found that, over a wide range of rotationrates, there is no improvement in performance due to rotationabout the vertical axis. However, numerical results that havebeen obtained previously (Lee & Pearlstein, J. Crys. Growth240, 2002) indicate that, when effects of centrifugal buoyancyare introduced, a substantial reduction in segregation is achieved.In the work reported here, by contrast, in which we extend previouslarge-Rayleigh-number asymptotic analysis to include centrifugalbuoyancy, we find no improvement in radial segregation, butrather increasing segregation with increasing rotation rate. 相似文献
4.
Novel oscillatory flow results of phenoxy/organoclay nanocomposites are analysed considering the blocking effect of nanostructure on polymer chain mobility. The modification provoked by this hindering effect on loss tangent spectrum is investigated. The study of three different systems, involving a pristine montmorillonite and two montmorillonites modified with one alkyl tail and two alkyl tails, respectively, leads to conclude that polymer-alkyl repulsive interactions play the most important role in the chain mobility obstruction process. Our results suggest that polymer-alkyl interactions increase with temperature. 相似文献
5.
Weir AJ Klein SR Abrams G Adolphsen CE Akerlof C Alexander JP Alvarez M Amidei D Baden AR Ballam J Barish BC Barklow T Barnett BA Bartelt J Blockus D Bonvicini G Boyarski A Boyer J Brabson B Breakstone A Brom JM Bulos F Burchat PR Burke DL Butler F Calvino F Cence RJ Chapman J Cords D Coupal DP DeStaebler HC Dorfan DE Dorfan JM Drell PS Feldman GJ Fernandez E Field RC Ford WT Fordham C Frey R Fujino D Gan KK Gidal G Gladney L Glanzman T Gold MS Goldhaber G Green A Grosse-Wiesmann P Haggerty J 《Physical review D: Particles and fields》1990,41(5):1384-1388
6.
N. S. Nesterenko F. Thibault-Starzyk V. Montouilliout V. V. Yushchenko C. Fernandez J.-P. Gilson F. Fajula I. I. Ivanova 《Kinetics and Catalysis》2006,47(1):40-48
A new approach to the evaluation of the accessibility of acid sites in microporous/mesoporous materials is developed and tested
using a series of dealuminated mordenites. This approach is based on an IR-spectroscopic study of the consecutive adsorption
of substituted alkylpyridines (pyridine, 2,4,6-trimethylpyridine, and 2,4,6-triethylpyridine) and carbon monoxide. This method
allowed us to determine the strength and number of acid sites with various degrees of accessibility. The adsorption of 2,4,6-triethylpyridine
on various types of materials is studied. The extinction coefficients of alkylpyridines are determined using a McBain balance
placed in a cell for IR-spectroscopic measurements.
Original Russian Text N.S. Nesterenko, F. Thibault-Starzyk, V. Montouilliout, V.V. Yushchenko, C. Fernandez, J.-P. Gilson,
F. Fajula, I.I. Ivanova, 2006, published in Kinetika i Kataliz, 2006, Vol. 47, No. 1, pp. 45–53. 相似文献
7.
Joan Albaigés Josep M. Bayona Pilar Fernandez Joan Grimalt Antoni Rosell Rafel Simó 《Mikrochimica acta》1991,104(1-6):13-27
An analytical procedure is described for a comprehensive determination of the composition of hydrocarbons in the atmosphere, based on: (a) aerosol filtration and subsequent adsorption of the vapor phase onto active charcoal and polyurethane foam; (b) GPC and HPLC fractionation of the extracts, and (c) analysis of the fractions by GC-MS under EI and NICI modes. Special emphasis is placed onn-alkanes, PAHs and their oxygenated derivatives.The characterization of samples collected in a coastal urban area (Barcelona city), and far away over the Western Mediterranean, at sea level and at 1100 m of altitude, revealed significant changes in the aerosol composition, mainly attributed to initial vapor-particle partitioning processes, influenced by ambient temperature variations, and to others taking place during long-range atmospheric transport, related with the different compound photoreactivities and with an unexplained source-decoupling phenomenon. 相似文献
8.
A. Caubet A. Labarta R. Rodríguez A. Fernandez E. Molins V. Moreno J. Tejada 《Hyperfine Interactions》1986,28(1-4):773-776
By means of57Co Mössbauer emission spectroscopy and magnetic susceptibility measurements, the local symmetries and electronic structure of the Co(II) ions in the Co-5IMO and Co-5GMP complexes in the hydrated and dehydrated forms have been determined. 相似文献
9.
Rüdiger O Abad JM Hatchikian EC Fernandez VM De Lacey AL 《Journal of the American Chemical Society》2005,127(46):16008-16009
The orientation of hydrogenase bound covalently to a pyrolytic graphite edge electrode modified with a 4-aminophenyl monolayer can be modulated via electrostatic interactions during the immobilization step. At low ionic strength and when the amino groups of the electrode surface are mostly protonated, the hydrogenase is immobilized with the negatively charged region that surrounds its 4Fe4S cluster nearer to the protein surface facing the electrode. This allows direct electron transfer between the immobilized hydrogenase and the electrode, which is observed by the strong catalytic currents measured in the presence of the H2 substrate. Therefore, a very stable enzymatic electrode is produced that catalyzes nonmediated H2 oxidation. 相似文献
10.
Calculations involving molecular orbitals have appeared in the chemical literature over the past few years, but all have used smalltrans-polyenes. We now report extended Huckel molecular orbital calculations ontrans-polyenes of up to 18 double bonds (36 carbons and 38 hydrogen atoms). Information obtained from these calculations include total energies, bond gaps, and net charges on each atom. Also found is that the band gap approaches 1.41 eV as the number of double bonds approaches infinity. This value is quite close to reported experimental values. Data are also presented for polyenes assuming equal C-C bond lengths. 相似文献