全文获取类型
收费全文 | 27287篇 |
免费 | 629篇 |
国内免费 | 107篇 |
专业分类
化学 | 15587篇 |
晶体学 | 165篇 |
力学 | 791篇 |
综合类 | 9篇 |
数学 | 3818篇 |
物理学 | 7653篇 |
出版年
2022年 | 274篇 |
2021年 | 439篇 |
2020年 | 400篇 |
2019年 | 367篇 |
2018年 | 440篇 |
2017年 | 402篇 |
2016年 | 698篇 |
2015年 | 588篇 |
2014年 | 674篇 |
2013年 | 1091篇 |
2012年 | 1383篇 |
2011年 | 1602篇 |
2010年 | 925篇 |
2009年 | 847篇 |
2008年 | 1352篇 |
2007年 | 1334篇 |
2006年 | 1200篇 |
2005年 | 1641篇 |
2004年 | 1623篇 |
2003年 | 1169篇 |
2002年 | 797篇 |
2001年 | 641篇 |
2000年 | 592篇 |
1999年 | 369篇 |
1998年 | 321篇 |
1997年 | 312篇 |
1996年 | 385篇 |
1995年 | 332篇 |
1994年 | 321篇 |
1993年 | 356篇 |
1992年 | 339篇 |
1991年 | 286篇 |
1990年 | 235篇 |
1989年 | 220篇 |
1988年 | 189篇 |
1987年 | 188篇 |
1986年 | 185篇 |
1985年 | 235篇 |
1984年 | 228篇 |
1983年 | 206篇 |
1982年 | 205篇 |
1981年 | 203篇 |
1980年 | 184篇 |
1979年 | 164篇 |
1978年 | 183篇 |
1977年 | 152篇 |
1976年 | 148篇 |
1975年 | 119篇 |
1974年 | 139篇 |
1973年 | 132篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Despite the large cost of bodily injury (BI) claims in motor insurance, relatively little research has been done in this area. Many companies estimate (and therefore reserve) bodily injury compensation directly from initial medical reports. This practice may underestimate the final cost, because the severity is often assessed during the recovery period. Since the evaluation of this severity is often only qualitative, in this paper we apply an ordered multiple choice model at different moments in the life of a claim reported to an insurance company. We assume that the information available to the insurer does not flow continuously, because it is obtained at different stages. Using a real data set, we show that the application of sequential ordered logit models leads to a significant improvement in the prediction of the BI severity level, compared to the subjective classification that is used in practice. We also show that these results could improve the insurer’s reserves notably. 相似文献
72.
73.
R. Martínez-Snchez J. A. Matutes-Aquino O. Ayala-Valenzuela S. D. De la Torre 《Physica B: Condensed Matter》2002,320(1-4):285-287
An amorphous phase containing traces of non-transformed Co and Ti powders was obtained by mechanical alloying nominal compositions of Co67Ti33 and Co50Ti50 in a high-energy ball-mill. These alloys were prepared from elemental powders of Co and Ti. The heat treatment of Co67Ti33 at 573, 873 and 1173 K crystallized nanoparticles of Co2Ti and Co3Ti compounds, while the same treatments conducted on Co50Ti50 resulted in the formation of Co2Ti and CoTi nanoparticles. The saturation magnetizations reached a maximum value in the amorphous state and they decreased when the temperatures of the heat treatment rose. Demagnetizing interparticle interaction effects were estimated through hysteresis loops and initial magnetization curves using the Fourier technique. 相似文献
74.
75.
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
76.
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
77.
G.M. Ingo P. Plescia E. Angelini C. Riccucci T. de Caro 《Applied Physics A: Materials Science & Processing》2006,83(4):611-615
The surface microchemical structure of high tin leaded bronze Roman mirrors has been studied by means of scanning electron microscopy combined with energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD) and optical microscopy (OM) techniques. The results allowed understanding of the origin of their high chemical stability and silvery-lustrous appearance. Indeed, some areas of the selected Roman mirrors are still characterised by a highly reflective and silver coloured surface even though they have been buried in the soil for about 2000 years. The micro-chemical results obtained from these areas have revealed that the mirror surface was tin enriched via inverse-segregation phenomenon by tailoring the cooling parameters. Furthermore, the presence of tin could be likely enhanced via cycles of oxidation and selective copper corrosion processes, thus resulting in a tin surface enrichment as a semi-transparent amorphous-like tin oxide (SnO2) film, as well as a copper depletion at the outer surfaces. 相似文献
78.
A. Craig W. H. Jacobson A. Meyer N. Welwart A. Seuthe H. N. Marr B. S. Evans G. E. F. Lundell J. A. Scherrer E. Stelling F. J. Mück A. Kling A. Lassieur L. Bertiaux C. C. Bissett P. de Pauw J. Heslinga A. Bartsch R. E. Lee W. H. Fegeley F. H. Reichel und E. Saz 《Fresenius' Journal of Analytical Chemistry》1927,71(1-2):83-90
Ohne Zusammenfassung 相似文献
79.
We study a class of shape optimization problems for semi-linear elliptic equations with Dirichlet boundary conditions in smooth
domains in ℝ2. A part of the boundary of the domain is variable as the graph of a smooth function. The problem is equivalently reformulated
on a fixed domain. Continuity of the solution to the state equation with respect to domain variations is shown. This is used
to obtain differentiability in the general case, and moreover a useful formula for the gradient of the cost functional in
the case where the principal part of the differential operator is the Laplacian.
Online publication 23 January 2004. 相似文献
80.
Mathilde Kammerer-Colin de Verdière 《Comptes Rendus Mathematique》2004,339(9):625-629
For generic families of vector fields or transformations, normally hyperbolic invariant products of spheres appear near partially elliptic rest points. To cite this article: M. Kammerer-Colin de Verdière, C. R. Acad. Sci. Paris, Ser. I 339 (2004). 相似文献