全文获取类型
收费全文 | 21950篇 |
免费 | 570篇 |
国内免费 | 357篇 |
专业分类
化学 | 13921篇 |
晶体学 | 129篇 |
力学 | 574篇 |
综合类 | 30篇 |
数学 | 2931篇 |
物理学 | 5292篇 |
出版年
2022年 | 296篇 |
2021年 | 341篇 |
2020年 | 287篇 |
2019年 | 293篇 |
2018年 | 262篇 |
2017年 | 255篇 |
2016年 | 576篇 |
2015年 | 459篇 |
2014年 | 586篇 |
2013年 | 1134篇 |
2012年 | 1018篇 |
2011年 | 1216篇 |
2010年 | 810篇 |
2009年 | 785篇 |
2008年 | 1119篇 |
2007年 | 1147篇 |
2006年 | 949篇 |
2005年 | 974篇 |
2004年 | 881篇 |
2003年 | 863篇 |
2002年 | 846篇 |
2001年 | 563篇 |
2000年 | 524篇 |
1999年 | 390篇 |
1998年 | 309篇 |
1997年 | 285篇 |
1996年 | 326篇 |
1995年 | 325篇 |
1994年 | 309篇 |
1993年 | 264篇 |
1992年 | 221篇 |
1991年 | 230篇 |
1990年 | 243篇 |
1989年 | 208篇 |
1988年 | 178篇 |
1987年 | 184篇 |
1986年 | 161篇 |
1985年 | 264篇 |
1984年 | 292篇 |
1983年 | 213篇 |
1982年 | 228篇 |
1981年 | 194篇 |
1980年 | 190篇 |
1979年 | 174篇 |
1978年 | 146篇 |
1977年 | 188篇 |
1976年 | 163篇 |
1975年 | 139篇 |
1974年 | 126篇 |
1973年 | 129篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Given a smooth Lagrangian path, both in the finite and in the infinite dimensional (Fredholm) case, we introduce the notion of partial signatures at each isolated intersection of the path with the Maslov cycle. For real-analytic paths, we give a formula for the computation of the Maslov index using the partial signatures; a similar formula holds for the spectral flow of real-analytic paths of Fredholm self-adjoint operators on real separable Hilbert spaces. As applications of the theory, we obtain a semi-Riemannian version of the Morse index theorem for geodesics with possibly conjugate endpoints, and we prove a bifurcation result at conjugate points along semi-Riemannian geodesics. To cite this article: R. Giambò et al., C. R. Acad. Sci. Paris, Ser. I 338 (2004). 相似文献
72.
We review the proof of a conjecture concerning the reality of the spectra of certain PT-symmetric quantum mechanical systems, obtained via a connection between the theories of ordinary differential equations and integrable models. Spectral equivalences inspired by the correspondence are also discussed. 相似文献
73.
We consider a SOS type model of interfaces on a substrate which is both heterogeneous and rough. We first show that, for appropriate values of the parameters, the differential wall tension that governs wetting on such a substrate satisfies a generalized law which combines both Cassie and Wenzel laws. Then in the case of an homogeneous substrate, we show that this differential wall tension satisfies either the Wenzel's law or the Cassie's law, according to the values of the parameters. 相似文献
74.
Marialuigia Macchione Giovanni De Filpo Fiore P. Nicoletta Giuseppe Chidichimo 《Liquid crystals》2005,32(3):315-319
Control of light intensity and colour are two of the major features required in the realization of smart windows. We designed a bi-functional polymer dispersed liquid crystal (PDLC) film in order to satisfy such requirements, i.e. it is able both to modulate the optical transmission, if an external electric field is applied, and to change colour if exposed to sunlight. A monomer/liquid crystal mixture was doped with a small amount of photochromic material and homeotropically aligned by means of rough surfaces. A transparent and pale pink coloured film was achieved after photopolymerization. Such a film changes colour upon exposure for some seconds to sunlight or ultraviolet radiation in a persistent but reversible manner. In addition, the film appears transparent without the application of an electric field (OFF state) and becomes opaque on application of a driving voltage of about 75 V (ON state), and thus the film operates in reverse mode with respect to conventional PDLCs. 相似文献
75.
76.
Luciano Galeone Roberto Garrappa 《Journal of Computational and Applied Mathematics》1997,80(2):377-195
We study convergence properties of time-point relaxation (TR) Runge-Kutta methods for linear systems of ordinary differential equations. TR methods are implemented by decoupling systems in Gauss-Jacobi, Gauss-Seidel and successive overrelaxation modes (continuous-time iterations) and then solving the resulting subsystems by means of continuous extensions of Runge-Kutta (CRK) methods (discretized iterations). By iterating to convergence, these methods tend to the same limit called diagonally split Runge-Kutta (DSRK) method. We prove that TR methods are equivalent to decouple in the same modes the linear algebraic system obtained by applying DSRK limit method. This issue allows us to study the convergence of TR methods by using standard principles of convergence of iterative methods for linear algebraic systems. For a particular problem regions of convergence are plotted. 相似文献
77.
We classify smooth subvarieties of codimension twoX⊂P
n
, 4≤n≤5, which are arithmetically Cohen-Macaulay and of non general type. By the way we exhibit some classes of non extendable
subvarieties. Then we give new proofs of the classification of scrolls inP
4; finally we consider smooth surfaces of non general type inP
4 arising from rank three vector bundles.
Sunto Classifichiamo le sottovarietà lisce di codimensione dueX⊂P n , 4≤n≤5, aritmeticamente Cohen-Macaulay e non di tipo generale. Nel contempo descriviamo alcune classi di sottovarietà non estendibili. Diamo poi due nuove dimostrazioni della classificazione degli scrolls inP 4; infine consideriamo superfici lisce inP 4, non di tipo generale, associate a fibrati di rango tre.相似文献
78.
A. Paesano Jr. S. C. Zanatta S. N. De Medeiros L. F. CÓtica J. B. M. Da Cunha 《Hyperfine Interactions》2005,161(1-4):211-220
We have investigated the mechanosynthesis of gadolinium and yttrium iron garnets by high-energy ball-milling of α-Fe2O3 and Gd2O3 or α-Fe2O3 and Y2O3, respectively, followed by short thermal annealings conducted at moderate temperatures. The samples were characterized by X-ray diffraction and Mössbauer spectroscopy, in order to determine the influence of the milling time and annealing conditions on the final products. For as-milled samples of each rare-earth system, the results revealed the formation of perovskite phases, in relative amounts that depend on the milling time. The formation of garnet phases was observed in as-annealed samples treated at 1000°C for 2 h or 1100°C for 3 h, i.e., at very modest annealing requirements when compared with ordinary solid-state-reaction processes performed without previous high-energy milling. Also, the occurrence was verified of a milling time for which the relative amount of garnet phases formed by annealing was maximized. This time depends on the rare-earth composing the garnet phase and on the annealing temperature. 相似文献
79.
A. Fernndez-Mateos E.M. Martín de la Nava R. Rabanedo Clemente R. Rubio Gonzlez M.S.J. Simmonds 《Tetrahedron》2005,61(52):12264-12274
A diastereoselective synthesis of the model insect antifeedant 29 a CDE molecular fragment of 12-ketoepoxyazadiradione has been achieved in ten steps from indenone 9 in 44% overall yield. Several of the compounds obtained along the synthesis related to model compound 29 show significant antifeedant activity against Spodoptera littoralis and Spodoptera frugiperda. 相似文献
80.
Long-Mei Zeng Xiong Fu Jing-Yu Su Florecita De Guzman J. Francis Schmitz M. Bilayet Hossain Dick van Der Helm 《中国化学》1991,9(2):136-143
Three pyrrololactam alkaloids have been isolated from the marine sponge Phacellia fusca Schmidt collected from the South China Sea, and their structures were determined as 1–3 , on the grounds of spectral data. This is the first report of these compounds from this sponge. The structure of 1 was confirmed by X-ray analysis. 相似文献