全文获取类型
收费全文 | 457136篇 |
免费 | 2927篇 |
国内免费 | 882篇 |
专业分类
化学 | 218102篇 |
晶体学 | 7140篇 |
力学 | 24410篇 |
综合类 | 7篇 |
数学 | 61461篇 |
物理学 | 149825篇 |
出版年
2021年 | 4078篇 |
2020年 | 4527篇 |
2019年 | 5375篇 |
2018年 | 7677篇 |
2017年 | 7811篇 |
2016年 | 10253篇 |
2015年 | 5202篇 |
2014年 | 9335篇 |
2013年 | 19210篇 |
2012年 | 15544篇 |
2011年 | 18440篇 |
2010年 | 14324篇 |
2009年 | 14405篇 |
2008年 | 17403篇 |
2007年 | 17398篇 |
2006年 | 15991篇 |
2005年 | 14085篇 |
2004年 | 13416篇 |
2003年 | 12184篇 |
2002年 | 12321篇 |
2001年 | 12813篇 |
2000年 | 10053篇 |
1999年 | 7565篇 |
1998年 | 6717篇 |
1997年 | 6566篇 |
1996年 | 5999篇 |
1995年 | 5495篇 |
1994年 | 5410篇 |
1993年 | 5299篇 |
1992年 | 5658篇 |
1991年 | 6012篇 |
1990年 | 5921篇 |
1989年 | 5708篇 |
1988年 | 5556篇 |
1987年 | 5624篇 |
1986年 | 5187篇 |
1985年 | 6338篇 |
1984年 | 6783篇 |
1983年 | 5692篇 |
1982年 | 6082篇 |
1981年 | 5750篇 |
1980年 | 5408篇 |
1979年 | 5935篇 |
1978年 | 6103篇 |
1977年 | 6195篇 |
1976年 | 6351篇 |
1975年 | 5875篇 |
1974年 | 5716篇 |
1973年 | 6002篇 |
1972年 | 4578篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
We exhibit a family of homogeneous hypersurfaces in affine space, one in each dimension, that generalize the Cayley surface. 相似文献
952.
A. F. Semenchev V. G. Gavrilyachenko E. M. Kuznetsova E. N. Sklyarova 《Physics of the Solid State》2006,48(6):1146-1148
The details of the mechanical effects (twinning and microcracking) are clarified at various stages of dynamic fatigue of PbTiO3 crystals using a polarization microscope and selective etching. 相似文献
953.
S. N. Vdovichev B. A. Gribkov S. A. Gusev V. L. Mironov D. S. Nikitushkin A. A. Fraerman V. B. Shevtsov 《Physics of the Solid State》2006,48(10):1902-1905
The statistics of left-and right-handed vortical magnetization states in a system of submicron-sized ferromagnetic disks is studied experimentally. Lattices of elliptic cobalt particles with a planar size of 750 × 450 nm and a thickness of 25 nm were formed using high-resolution electronic lithography. To visualize the magnetization distributions in the disks, magnetic force microscopy was used. The experimental results indicate the conservation of magnetic chiral symmetry in cobalt ferromagnetic particles of the above size and shape. 相似文献
954.
955.
We consider a single machine scheduling problem with two min-sum objective functions: the sum of completion times and the sum of weighted completion times. We propose a simple polynomial time (1+(1/γ),1+γ)-approximation algorithm, and show that for γ>1, there is no (x,y)-approximation with 1<x<1+(1/γ) and 1<y<1+(γ-1)/(2+γ). 相似文献
956.
Y. Zhang T. M. Benson P. Sewell A. Vukovic D. Zhang W. J. Pan A Loni D. Furniss A. B. Seddon 《Optical and Quantum Electronics》2006,38(1-3):97-110
This paper presents our recent simulation results and novel designs of single mode large cross-section glass-based waveguides for photonic integrated circuits (PICs). Simulations were performed using an in-house Finite Difference (FD) based mode solver and the FD Beam propagation Method (FD-BPM). Our simulation results show that this innovative technology could provide a simplified means to couple optical energy efficiently between optical components in a single chip. This would provide the base for the future large-scale integration of optical components in PICs. The novel idea of using single mode large cross-section glass-based waveguides as an optical integration platform is an evolutionary innovative solution for the monolithic integration of optical components, in which the glass-based structures act both as waveguides and as an optical bench for integration. This allows easy and efficient optical coupling between optical components and optical fibres, removing costly and tedious alignment problems and considerably reducing optical coupling losses in PICs. We expect that the glass-based waveguide PICs technology will enable the emergence of a new generation of compact, reliable, high speed, and multifunctional devices. 相似文献
957.
S.N. Vdovichev B.A. Gribkov S.A. Gusev E. Il’ichev Yu.N. Nozdrin G.L. Pakhomov A.V. Samokhvalov R. Stolz A.A. Fraerman 《Journal of magnetism and magnetic materials》2006
The effect of an array of ferromagnetic nanoparticles on the field-dependent critical current of the short overlap Josephson junction is experimentally studied. Large reversible variations of the maximum critical current are observed depending on the magnetic state of the particles. The pronounced commensurability effects are detected which are proved by the additional peaks of magnetic field induced diffraction pattern. 相似文献
958.
It is shown that the presence of mixed-culture growth in batch fermentation processes can be very accurately inferred from total biomass data by means of the wavelet analysis for singularity detection. This is accomplished by considering simple phenomenological models for the mixed growth and the more complicated case of mixed growth on a mixture of substrates. The main quantity provided by the wavelet analysis is the Hölder exponent of the singularity that we determine for our illustrative examples. The numerical results point to the possibility that Hölder exponents can be used to characterize the nature of the mixed-culture growth in batch fermentation processes with potential industrial applications. Moreover, the analysis of the same data affected by the common additive Gaussian noise still lead to the wavelet detection of the singularities although the Hölder exponent is no longer a useful parameter. 相似文献
959.
960.
V. S. Klimov 《Mathematical Notes》2007,81(1-2):61-71
We study homology characteristics of critical values and extremals of Lipschitz functionals defined on bounded closed convex subsets of a reflexive space that are invariant under deformations. Sufficient conditions for the existence of a bifurcation point of a multivalued potential operator (the switch principle for the typical number of an extremal) are established. 相似文献