全文获取类型
收费全文 | 25741篇 |
免费 | 471篇 |
国内免费 | 100篇 |
专业分类
化学 | 14401篇 |
晶体学 | 171篇 |
力学 | 772篇 |
综合类 | 9篇 |
数学 | 3552篇 |
物理学 | 7407篇 |
出版年
2023年 | 117篇 |
2022年 | 336篇 |
2021年 | 410篇 |
2020年 | 371篇 |
2019年 | 328篇 |
2018年 | 416篇 |
2017年 | 381篇 |
2016年 | 648篇 |
2015年 | 534篇 |
2014年 | 625篇 |
2013年 | 1029篇 |
2012年 | 1321篇 |
2011年 | 1486篇 |
2010年 | 840篇 |
2009年 | 797篇 |
2008年 | 1240篇 |
2007年 | 1210篇 |
2006年 | 1087篇 |
2005年 | 1520篇 |
2004年 | 1567篇 |
2003年 | 1095篇 |
2002年 | 738篇 |
2001年 | 608篇 |
2000年 | 564篇 |
1999年 | 357篇 |
1998年 | 301篇 |
1997年 | 311篇 |
1996年 | 363篇 |
1995年 | 324篇 |
1994年 | 311篇 |
1993年 | 339篇 |
1992年 | 327篇 |
1991年 | 267篇 |
1990年 | 219篇 |
1989年 | 207篇 |
1988年 | 182篇 |
1987年 | 175篇 |
1986年 | 177篇 |
1985年 | 231篇 |
1984年 | 216篇 |
1983年 | 188篇 |
1982年 | 189篇 |
1981年 | 186篇 |
1980年 | 170篇 |
1979年 | 151篇 |
1978年 | 177篇 |
1977年 | 138篇 |
1976年 | 134篇 |
1974年 | 132篇 |
1973年 | 122篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
The critical limit of the eight-vertex model eigenvectors obtained by means of the generalized Bethe Ansatz is shown to give the six-vertex eigenvectors as constructed in a previous paper by two of the authors. Furthermore, an explicit mapping is established between these eigenvectors and the usual Bethe Ansatz eigenvectors of the six-vertex model. This allows one to show that the indexv labeling the eight-vertex eigenstates becomes exactly the third component of the total spin in the critical limit. 相似文献
42.
Cornelis Van de Panne 《The Journal of the Operational Research Society》1992,43(12):1159-1171
The paper deals with the appropriate form of interaction between two refineries with different demand patterns. This problem can be formulated as finding a decentralized solution of linear programming problems linked by buying and selling activities. The complete problem is first solved for central values of product demands and costs and revenues. The structure of the basis then determines the organization of the interaction in terms of which unit sets quantities and which prices, or whether centralized decisions should be made. If, for expected values of product demand and costs, the structure of the basis is the same then the related organization of trading can be used for day-to-day transactions. For a well-known oil refinery model it is found that, for fairly large demand variations, decentralized interaction is effective, but that the structure of the basis changes easily with crude price variations, and that simulations did not converge for these variations. 相似文献
43.
L. S. de C. Oliveira M. T. X. Silva A. Vasquez J. A. H. da Jornada 《Hyperfine Interactions》1991,66(1-4):267-270
An exploratory Mössbauer spectroscopy study of the Fe-C system in the C rich region, prepared by high pressure-high temperature treatment near the graphite-diamond stability line, was made. The results obtained for the different processing conditions give no evidence of Fe intercalation in graphite. The presence of some water in the cell produced hydrated Fe complexes, which can explain the deleterious effect of water or hydrogen in the high pressure diamond synthesis. 相似文献
44.
Miloslav Duchoň Anatolij Dvurečenskij Paolo de Lucia 《International Journal of Theoretical Physics》1997,36(9):1941-1958
We present a solution to the moment problem for effect algebras, concerning mean values of all powers of an observable concentrated
on the interval [0, 1] for states from a convex set. We give a solution for particular examples, e.g., for the set of all
effect operators. We examine how this problem is related to a socalled E-property. Finally, we give a solution for observables
studied in the operational approach to physical theories. 相似文献
45.
J.-J. Sauvain L. F. de Alencastro J. Tarradellas R. Camenzind G. Karlaganis C. Vuilleumier 《Fresenius' Journal of Analytical Chemistry》1994,350(7-9):555-562
The analysis of PCB in transformer oils has been achieved with three HRGC/ECD based methods, proposed by the International Electrotechnical Commission (IEC/TC 10), by the Comité Européen de Normalisation (CEN/TC 19/WG 22) and by the Deutsches Institut für Normung (DIN 51 527). The same clean-up, described in the CEN/TC 19/WG 22, has been used for all the samples, allowing a comparison of the quantification procedure only. The total chlorine content has also been determined with X-ray fluorescence. These different methods of quantification are compared and their application for legislative purposes is discussed.Dedicated to Professor Dr Dieter Klockow on the occasion of his 60th birthday 相似文献
46.
Patricia Smichowski María Beatriz de la Calle Guntiñas Carmen Cámara 《Fresenius' Journal of Analytical Chemistry》1994,348(5-6):380-384
Summary A method is described for antimony preconcentration based on retention on a column of activated alumina. Recovery is 80% when no pH-control and 4 mol/l HCl as eluent are used. The preconcentration factor is 400. The method was applied to the determination of antimony in spiked tap and sea water. The analytical performance of the method is discussed. 相似文献
47.
Principles and recent developments in ultrasound contrast agents 总被引:6,自引:1,他引:5
The behaviour of gas bubbles and gas encapsulated spheres as echographic contrast agents is reviewed. Compared with rigid spheres, gas bubbles are superior scattering agents and they offer a number of useful properties which can be exploited in a variety of ways. The analysis of their velocity of sound, back-scatter intensity, second harmonic emission and resonant frequency opens up new perspectives in the development of contrast agents for echocardiographic research with potential clinical applications. 相似文献
48.
C. Caldera N. Caponio C. de Bernardi F. Delpiano G. Destefanis S. Morasca M. Puleo G. Schiavini F. Schiattone A. Stano E. Legros M. Billard 《Optical and Quantum Electronics》1994,26(5):S529-S545
Optical waveguide 3-dB couplers integrated on semicondutors have been studied, designed and fabricated, using both bulk and diluted multi-quantum-well InGaAsP/InP-based materials, grown by MOCVD. The device structure is based on the two-mode interference (TMI) principle and is fully compatible for integration with the optoelectronic and electronic components of a coherent receiver. Bulk material couplers provide an output balanced within 0.05 dB per nanometer and an excess loss of 1.4 dB, compared to a straight guide, while coupling loss to a tapered-lensed single mode fibre is 4 dB.Improved coupling efficiency to single-mode fibres is achieved by use of moderately diluted multi-quantum-well waveguides, which include InGaAsP wells and InP barriers: coupling loss to a tapered-lensed single-mode fibre as low as 0.5 dB and excess loss of 1.8 dB are featured. Couplers fabricated with this waveguide structure have a balance sensitivity of 0.03 to 0.04 dB per nanometer.A moderately diluted multi-quantum-well 3-dB coupler has been permanently pigtailed and butt-coupled to a dual balanced PIN photoreceiver. This hybrid assembly was tested in a coherent transmission system at 155 and 622 Mbits-1 showing sensitivities, for 10-9 BER, of about-38.0 dBm and-28.8 dBm, respectively. 相似文献
49.
Maurits de Graaf 《Discrete Mathematics》2004,280(1-3):219-223
We show that each directed graph (with no parallel arcs) on n vertices, each with indegree and outdegree at least n/twhere t=2.888997… contains a directed circuit of length at most 3. 相似文献
50.
A time‐marching formulation is derived from the space–time integrated least squares (STILS) method for solving a pure hyperbolic convection equation and is numerically compared to various known methods. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献