全文获取类型
收费全文 | 1200篇 |
免费 | 55篇 |
国内免费 | 5篇 |
专业分类
化学 | 884篇 |
晶体学 | 5篇 |
力学 | 15篇 |
数学 | 181篇 |
物理学 | 175篇 |
出版年
2023年 | 10篇 |
2022年 | 24篇 |
2021年 | 43篇 |
2020年 | 34篇 |
2019年 | 34篇 |
2018年 | 31篇 |
2017年 | 29篇 |
2016年 | 42篇 |
2015年 | 39篇 |
2014年 | 46篇 |
2013年 | 74篇 |
2012年 | 75篇 |
2011年 | 88篇 |
2010年 | 52篇 |
2009年 | 44篇 |
2008年 | 63篇 |
2007年 | 59篇 |
2006年 | 60篇 |
2005年 | 53篇 |
2004年 | 51篇 |
2003年 | 29篇 |
2002年 | 29篇 |
2001年 | 18篇 |
2000年 | 18篇 |
1999年 | 10篇 |
1997年 | 7篇 |
1996年 | 19篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1969年 | 4篇 |
1961年 | 5篇 |
1934年 | 3篇 |
1932年 | 3篇 |
1912年 | 3篇 |
1906年 | 3篇 |
排序方式: 共有1260条查询结果,搜索用时 15 毫秒
101.
We study theoretically the possibility of performing temporal differentiation of optical signals using a resonant diffraction grating. We demonstrate that the resonant grating allows the calculation of the first-order derivative of an optical signal envelope in the vicinity of waveguide resonant frequencies in the zeroth transmitted diffraction order. The grating is shown to allow the calculation of the fractional derivative of order 1/2 in the vicinity of Rayleigh-Wood anomalies. Numerical simulations based on the rigorous coupled-wave analysis of Maxwell's equations demonstrate the high-quality differentiation of optical signals with temporal features in the picosecond range. 相似文献
102.
Möbius structure (on a set \(X\) ) is a class of metrics having the same cross-ratios. A Möbius structure is Ptolemaic if it is invariant under inversion operations. The boundary at infinity of a \(\mathrm{CAT }(-1)\) space is in a natural way a Möbius space, which is Ptolemaic. We give a free of classification proof of the following result that characterizes the rank one symmetric spaces of noncompact type purely in terms of their Möbius geometry: Let \(X\) be a compact Ptolemy space which contains a Ptolemy circle and allows many space inversions. Then \(X\) is Möbius equivalent to the boundary at infinity of a rank one symmetric space. 相似文献
103.
104.
A new, highly denaturing electrolyte system based on a solution containing 0.01 M NaOH, 0.0015 M Na2B4O5(OH)4 and a replaceable polymer sieving medium was designed for the separation of single-stranded DNA fragments in bare fused-silica capillaries. Extreme denaturing power, together with the optimized composition of the electrolyte, allows for a separation efficiency as high as 2,300,000 height equivalents to a theoretical plate per meter. Sample denaturation in alkaline solutions provides single-stranded DNA fragments without any intra- or intermolecular interactions at room temperature. Their electrophoretic mobilities were found to be twice those of fragments denatured by dimethylformamide or HCl. This can be interpreted in terms of an increased effective charge on the DNA molecules. The surprisingly weak electroosmosis (6 x 10(-10) m2 V-1 s-1) of polymer solutions at pH 12 or higher is considered to be the result of the dissolution of the silica capillary wall. A highly viscous thin layer of dissolved silica probably causes a shift of the slipping plane further away from the wall to the lower value of the zeta potential. Applications of the electrolyte in clinical diagnostics demonstrate its remarkable properties. 相似文献
105.
106.
107.
Viktor O. Iaroshenko Verena SpecowiusKatharina Vlach Marcelo Vilches-HerreraDmytro Ostrovskyi Satenik MkrtchyanAlexander Villinger Peter Langer 《Tetrahedron》2011,67(31):5663-5677
Difluoromethyl-containing heteroannulated pyridines, pyrimidines and pyrazoles are prepared by a two step method. The regioselective cyclizations of electron-excessive aminoheterocycles, hydrazines and amidines with CF2Cl-substituted 1,3-dicarbonyl compounds provide the corresponding CF2Cl-substituted heterocycles. Subsequent radical reactions with trimethylstannane or allyltrimethylstannane gave difluoromethyl-containing heteroannulated pyridines, pyrimidines and pyrazoles, respectively. 相似文献
108.
Several transition metal-mediated oxidations using hypervalent iodine species are reported. A convenient procedure for preparation of iodylarenes via RuCl3-catalyzed oxidation of iodoarenes has been developed. This procedure allows the generation of highly reactive monomeric iodine(V) species, which are excellent oxidants toward alcohols and hydrocarbons in situ. A broad range of substrates can be oxidized to carbonyl compounds by a tandem catalytic system based on the Ru(III)-catalyzed reoxidation of ArIO to ArIO2 using Oxone® as oxidant. It was shown that electrophilic iodine(III) species, originating from oligomeric iodosylbenzene sulfate (PhIO)3SO3, are efficient oxygenating agents in catalytic oxidation of aromatic hydrocarbons in the presence of metalloporphyrin complexes. 相似文献
109.
110.
Sabir Jacquir Stéphane Binczak Jean-Marie Bilbault Viktor Kazantsev Vladimir Nekorkin 《Nonlinear dynamics》2006,44(1-4):29-36
An electrical circuit is proposed to realize an unidirectional coupling between two cells, mimicking chemical synaptic coupling.
Each cell represents the FitzHugh–Nagumo (FHN) model of neuron with a modified exitability (MFHN). We present experimental
results on frequency doublings and on the chaotic dynamics depending on the coupling strength in a master–slave configuration.
In all experiments, we stress the influence of the coupling strength on the control of the slave neuron. 相似文献