全文获取类型
收费全文 | 7047篇 |
免费 | 160篇 |
国内免费 | 43篇 |
专业分类
化学 | 4105篇 |
晶体学 | 59篇 |
力学 | 227篇 |
数学 | 1281篇 |
物理学 | 1578篇 |
出版年
2021年 | 58篇 |
2020年 | 64篇 |
2019年 | 64篇 |
2018年 | 54篇 |
2017年 | 46篇 |
2016年 | 96篇 |
2015年 | 112篇 |
2014年 | 116篇 |
2013年 | 331篇 |
2012年 | 308篇 |
2011年 | 393篇 |
2010年 | 189篇 |
2009年 | 162篇 |
2008年 | 310篇 |
2007年 | 301篇 |
2006年 | 331篇 |
2005年 | 292篇 |
2004年 | 242篇 |
2003年 | 225篇 |
2002年 | 203篇 |
2001年 | 173篇 |
2000年 | 132篇 |
1999年 | 86篇 |
1998年 | 69篇 |
1997年 | 79篇 |
1996年 | 109篇 |
1995年 | 97篇 |
1994年 | 118篇 |
1993年 | 132篇 |
1992年 | 106篇 |
1991年 | 111篇 |
1990年 | 94篇 |
1989年 | 102篇 |
1988年 | 77篇 |
1987年 | 83篇 |
1986年 | 68篇 |
1985年 | 130篇 |
1984年 | 106篇 |
1983年 | 61篇 |
1982年 | 99篇 |
1981年 | 95篇 |
1980年 | 76篇 |
1979年 | 100篇 |
1978年 | 90篇 |
1977年 | 84篇 |
1976年 | 88篇 |
1975年 | 87篇 |
1974年 | 93篇 |
1973年 | 119篇 |
1972年 | 50篇 |
排序方式: 共有7250条查询结果,搜索用时 15 毫秒
1.
2.
Optics and Spectroscopy - Scattering of light by disordered structures is normally detrimental to their applicability in many optoelectronic devices. However, some micro and nanostructures are... 相似文献
3.
In this paper, we investigate the evolution of joint invariants under invariant geometric flows using the theory of equivariant moving frames and the induced invariant discrete variational complex. For certain arc length preserving planar curve flows invariant under the special Euclidean group , the special linear group , and the semidirect group , we find that the induced evolution of the discrete curvature satisfies the differential‐difference mKdV, KdV, and Burgers' equations, respectively. These three equations are completely integrable, and we show that a recursion operator can be constructed by precomposing the characteristic operator of the curvature by a certain invariant difference operator. Finally, we derive the constraint for the integrability of the discrete curvature evolution to lift to the evolution of the discrete curve itself. 相似文献
4.
5.
Francis Jordan 《Topology and its Applications》2006,153(14):2386-2412
An abstract scheme using particular types of relations on filters leads to general unifying results on stability under supremum and product of local topological properties. We present applications for Fréchetness, strong Fréchetness, countable tightness and countable fan-tightness, some of which recover or refine classical results, some of which are new. The reader may find other applications as well. 相似文献
6.
H E Cline W E Lorensen R J Herfkens G A Johnson G H Glover 《Magnetic resonance imaging》1989,7(1):45-54
A three-dimensional examination of blood vessels is provided using MR data from seven cases. The vascular surfaces are constructed with an algorithm that automatically follows the selected artery or vein and generates a projected three-dimensional gradient shaded image. Fast 3DFT pulse sequences were optimized to enhance the time-of-flight contrast of the intravascular region. By increasing the surface threshold value in a three-dimensional head study, the flesh of a patient's face was peeled away to demonstrate the superfacial temporal artery. Gated cardiac images show the great vessels and cardiac chambers. A three-dimensional view of the aorta shows an irregular surface in the vicinity of an adrenal tumor. 3D MR exams provide a non-invasive technique for assessing vascular morphology in a clinical setting. 相似文献
7.
Francis K. Bell 《Journal of Graph Theory》2003,43(2):137-149
It is shown that, if t is an integer ≥3 and not equal to 7 or 8, then there is a unique maximal graph having the path Pt as a star complement for the eigenvalue ?2. The maximal graph is the line graph of Km,m if t = 2m?1, and of Km,m+1 if t = 2m. This result yields a characterization of L(G ) when G is a (t + 1)‐vertex bipartite graph with a Hamiltonian path. The graphs with star complement Pr ∪ Ps or Pr ∪ Cs for ?2 are also determined. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 137–149, 2003 相似文献
8.
9.
The new Antiproton Accumulator Complex is now in operation at CERN. We consider the possibility of using this facility to
create and store antideuterons and conclude that we could achieve an accumulation rate of about 2·106 particles/day. No major rebuild of the rings is envisaged, but it is thought that modification to existing components and
becoming operational would take about 5 to 6 months. We stress, however, that the operation of such a facility and the use
of any stack of antideuterons for particle physics would be extremely taxing. 相似文献
10.
J. R. Lindle W. W. Bewley I. Vurgaftman J. R. Meyer J. L. Johnson M. L. Thomas W. E. Tennant 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):558
A self-referencing, optical modulation technique was used to measure the negative luminescence efficiencies of an array of mid-wave infrared HgCdTe photodiodes with cutoff wavelength 4.6 μm as a function of sample temperature. The internal efficiency at a wavelength of 4 μm was 93% at 295 K, and nearly independent of temperature in the 240–300 K range. This corresponds to an apparent temperature reduction >50 K at room temperature and >30 K at 240 K. Moreover, the reverse-bias saturation current density was only 0.13 A/cm2. The measured transmission and emission spectra were simulated using empirical HgCdTe absorption formulas from the literature. 相似文献