全文获取类型
收费全文 | 289424篇 |
免费 | 2020篇 |
国内免费 | 849篇 |
专业分类
化学 | 122407篇 |
晶体学 | 3554篇 |
力学 | 17129篇 |
综合类 | 5篇 |
数学 | 63630篇 |
物理学 | 85568篇 |
出版年
2018年 | 18104篇 |
2017年 | 18735篇 |
2016年 | 10310篇 |
2015年 | 2667篇 |
2014年 | 1831篇 |
2013年 | 5339篇 |
2012年 | 10856篇 |
2011年 | 25350篇 |
2010年 | 14614篇 |
2009年 | 14825篇 |
2008年 | 20135篇 |
2007年 | 25447篇 |
2006年 | 4631篇 |
2005年 | 12512篇 |
2004年 | 8497篇 |
2003年 | 8428篇 |
2002年 | 5484篇 |
2001年 | 3980篇 |
2000年 | 3277篇 |
1999年 | 2393篇 |
1998年 | 2130篇 |
1997年 | 2043篇 |
1996年 | 2138篇 |
1995年 | 2002篇 |
1994年 | 1717篇 |
1993年 | 1721篇 |
1992年 | 1832篇 |
1991年 | 1811篇 |
1990年 | 1735篇 |
1989年 | 1757篇 |
1988年 | 1776篇 |
1987年 | 1765篇 |
1986年 | 1658篇 |
1985年 | 2250篇 |
1984年 | 2382篇 |
1983年 | 1985篇 |
1982年 | 2319篇 |
1981年 | 2132篇 |
1980年 | 2174篇 |
1979年 | 2182篇 |
1978年 | 2315篇 |
1977年 | 2122篇 |
1976年 | 2176篇 |
1975年 | 2096篇 |
1974年 | 1930篇 |
1973年 | 2200篇 |
1972年 | 1329篇 |
1969年 | 1000篇 |
1968年 | 1163篇 |
1967年 | 1140篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Algorithm for Optimal Triangulations in Scattered Data Representation and Implementation 总被引:2,自引:0,他引:2
Scattered data collected at sample points may be used to determine simple functions to best fit the data. An ideal choice for these simple functions is bivariate splines. Triangulation of the sample points creates partitions over which the bivariate splines may be defined. But the optimality of the approximation is dependent on the choice of triangulation. An algorithm, referred to as an Edge Swapping Algorithm, has been developed to transform an arbitrary triangulation of the sample points into an optimal triangulation for representation of the scattered data. A Matlab package has been completed that implements this algorithm for any triangulation on a given set of sample points. 相似文献
942.
G. Kocher-Oberlehner W. Jantsch L. Palmetshofer A. Ulyashin 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):347
Erbium (Er)- and oxygen (O)-doped Cz–Si was additionally doped with hydrogen, using plasma enhanced chemical vapour deposition. Photoluminescence (PL) spectra show a large enhancement especially for samples treated with solid phase epitaxy before hydrogenation and annealing at 900°C later. Secondary ion mass spectroscopy measurements give evidence for an enhanced diffusion of O and Er at this temperature towards the surface. Etching shows that the PL does not stem from the heavily doped surface layer but from a deeper region with lower Er concentration. This conclusion is supported by the appearance of the so-called “cubic” centre with low solubility. Comparing the PL yield of the hydrogenated samples to that of samples with similar Er volume concentration but without hydrogenation still gives a large enhancement. We thus conclude that hydrogen can enhance the solubility of the cubic centre in Si:Er,O. 相似文献
943.
I. V. Bodnar 《Technical Physics》2003,48(5):587-591
The thermal expansion coefficients and the thermal conductivity of Bridgman-grown crystals of CuGa1−x
InxTe2 solid solutions are investigated. It is found that the thermal expansion coefficient varies with x linearly, while the thermal conductivity is minimal when x=0.5. The Debye temperature and the rms dynamic atomic displacements are calculated from experimental data. It is shown that
the Debye temperature decreases and the rms displacements in the crystal lattice sharply increase as the In content in the
solid solutions grows. 相似文献
944.
Surface free energy of a solid surface gives a direct measure of intermolecular interactions at interfaces and has a strong influence on adsorption and adhesion behaviour. However few data are available for the surface free energies of electroless Ni–P based composition coatings. In this paper, the electroless Ni–P, Ni–P-surfactant, Ni–Cu–P, Ni–P–PTFE and Ni–Cu–P–PTFE composite coatings were prepared under various coating conditions. The chemical compositions, surface morphology and thickness of the coatings were measured using an energy dispersive X-ray microanalysis (EDX), a scanning electron microscope (SEM) and a digital micrometer respectively. The contact angles of water, diiodomethane and ethylene glycol on the coatings were measured automatically using dataphysics OCA-20 contact angle analyser. The surface free energy of the coatings and their components (e.g. dispersion, polar or acid/base portions) were calculated using various methods. The experimental results showed that the incorporation of surfactant or PTFE particles into Ni–P matrixes has a significant influence on the surface free energy of the coatings, while the incorporation of copper into Ni–P matrixes has no significant influence on the surface free energy of the coatings. 相似文献
945.
§ 1 IntroductionLetRn×mdenotetherealn×mmatrixspace ,Rn×mr itssubsetwhoseelementshaverankr ,ORn×nthesetofalln×northogonalmatrices,SRn×n(SRn×n≥ ,SRn×n>)thesetofalln×nrealsymmetric (symmetricpositivesemidefinite ,positivedefinite)matrices.ThenotationA>0 (≥ 0 ,<0 ,≤ 0 )m… 相似文献
946.
E. Sh. Gutshabash 《JETP Letters》2003,78(11):740-744
The integration procedure based on the generalized Darboux transform is suggested for the Ishimori magnet model. Exact solutions are constructed for the model on the background of spiral structures. The possibility of phase transition in the system is hypothesized. 相似文献
947.
L. Yu. Kolotilina 《Journal of Mathematical Sciences》2004,121(4):2481-2507
In this paper, bounds and inequalities for the Perron root of a nonnegative matrix, extending and complementing the classical theorems of Frobenius and Ostrowski in terms of (deleted) row and column sums, are presented. All the results are derived by using the same approach, based on the monotonicity property of the Perron root. Bibliography: 12 titles. 相似文献
948.
A new double pass long wavelength band erbium-doped fiber amplifier with enhanced noise figure characteristics is demonstrated. The noise figure is improved by about 2.6 dB with the incorporation of broadband conventional-band fiber Bragg grating (FBG) in between the two segments of erbium-doped fiber. By incorporating both the pre-amplifier and the FBG, the noise figure is further improved, which varies from 4.0 to 5.0 dB in the flat gain region from 1570 to 1600 nm. The gain varies from 32.0 to 33.4 dB within this region. The new amplifier with high gain and low noise figure can be useful as an inline amplifier in a wavelength division multiplexing transmission system. 相似文献
949.
950.
Donald W. Barnes 《Transactions of the American Mathematical Society》2003,355(7):2755-2769
The concept of a spectral sequence constructor is generalised to Hopf Galois extensions. The spectral sequence constructions that are given by Guichardet for crossed product algebras are also generalised and shown to provide examples. It is shown that all spectral sequence constructors for Hopf Galois extensions construct the same spectral sequence. 相似文献