全文获取类型
收费全文 | 471篇 |
免费 | 10篇 |
国内免费 | 3篇 |
专业分类
化学 | 277篇 |
晶体学 | 3篇 |
力学 | 19篇 |
数学 | 95篇 |
物理学 | 90篇 |
出版年
2021年 | 3篇 |
2020年 | 7篇 |
2019年 | 11篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 11篇 |
2014年 | 11篇 |
2013年 | 40篇 |
2012年 | 23篇 |
2011年 | 15篇 |
2010年 | 13篇 |
2009年 | 13篇 |
2008年 | 32篇 |
2007年 | 28篇 |
2006年 | 30篇 |
2005年 | 15篇 |
2004年 | 20篇 |
2003年 | 15篇 |
2002年 | 15篇 |
2001年 | 10篇 |
2000年 | 13篇 |
1999年 | 12篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1992年 | 4篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1970年 | 9篇 |
1966年 | 3篇 |
1959年 | 3篇 |
1943年 | 2篇 |
1934年 | 2篇 |
1933年 | 3篇 |
1930年 | 2篇 |
排序方式: 共有484条查询结果,搜索用时 15 毫秒
61.
C(3)-symmetric, octopolar 1,3,5-alkynylbenzenes with terminal pyridyl substituents are presented which show an increase up to 17-fold in the second-order NLO activity upon protonation while maintaining their octopolar character, as confirmed by the depolarization ratios measured. 相似文献
62.
63.
We prove the local invertibility, up to potential fields, and stability of the geodesic X-ray transform on tensor fields of order 1 and 2 near a strictly convex boundary point, on manifolds with boundary of dimension n ≥ 3. We also present an inversion formula. Under the condition that the manifold can be foliated with a continuous family of strictly convex surfaces, we prove a global result which also implies a lens rigidity result near such a metric. The class of manifolds satisfying the foliation condition includes manifolds with no focal points, and does not exclude existence of conjugate points. 相似文献
64.
Gunther Schmidt 《Applications of Mathematics》2013,58(3):279-307
The paper is devoted to an integral equation algorithm for studying the scattering of plane waves by multilayer diffraction gratings under oblique incidence. The scattering problem is described by a system of Helmholtz equations with piecewise constant coefficients in ?2 coupled by special transmission conditions at the interfaces between different layers. Boundary integral methods lead to a system of singular integral equations, containing at least two equations for each interface. To deal with an arbitrary number of material layers we present the extension of a recursive procedure developed by Maystre for normal incidence, which transforms the problem to a sequence of equations with 2×2 operator matrices on each interface. Necessary and sufficient conditions for the applicability of the algorithm are derived. 相似文献
65.
Substantial research activities have been carried out at HZDR during the last 15 years on the development and qualification of various methods to measure the velocity field in liquid metal flows. In this paper we report on two complementary methods for measuring the local velocity. The potential difference probe is a local sensor which is immersed into the liquid. Such sensors are very effective for investigations of the turbulent fluctuations at a local point. However, the installation of the probe in the bulk of the liquid might disturb the flow to be measured. Ultrasonic techniques are non-invasive, but need a continuous path from the ultrasonic transducer to the liquid under investigation. The ultrasound Doppler method delivers instantaneous profiles of the local velocity. Experimental applications of these measuring techniques in diverse liquid metal flows under the influence of magnetic fields will be presented here showing the capabilities and limitations of both methods. 相似文献
66.
M. Fischer F. Stefani G. Gerbeth 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(4):547-554
Using a spherically symmetric mean-field α2-dynamomodel for Earth’s magnetic field reversals, we show thecoexistence of the noise-induced phenomena coherence resonance
and stochastic resonance. Stochastic resonance was recentlyinvoked to explain the 100 kyr periodicity in the distribution
ofresidence times between reversals.The comparison of the resulting residence time distribution withthe paleomagnetic one
allows for some estimate ofthe effective diffusion time of the Earth’s core which may be100 kyr or slightly below rather than200 kyr
as it would result from the molecular resistivity. 相似文献
67.
68.
Temperature dependence of electrical conductivity, σ(T), thermoelectric power, S(T), and viscosity, η(T), of Pb-based eutectic systems was studied. Anomalous changes of thermophysical properties in liquid binary Pb26.1Sn73.9, Pb44Bi56, Pb83Mg17 and ternary Bi46Pb29Sn25 eutectics occurred well above the liquidus. The temperature range of anomalies reached hundreds of degrees. The obtained results are interpreted assuming that microsegregation areas exist in the eutectic systems. 相似文献
69.
The Surface Structure of a TiNi-Based Powder Alloy Manufactured by the Method of Diffusion Sintering
Anikeev S. G. Artyukhova N. V. Khodorenko V. N. Kaftaranova M. I. Yakovlev E. V. Gunther V. E. 《Russian Physics Journal》2020,63(3):484-490
Russian Physics Journal - The structural features of the surface of a TiNi-based powder alloy produced by diffusion sintering are studied. Two-dimensional porous samples based on a TiNi powder... 相似文献
70.
Dr. Aleksandra Markovic Luca Gerhards Dr. Pia Sander Dr. Carsten Dosche Prof. Dr. Thorsten Klüner Prof. Dr. Rüdiger Beckhaus Prof. Gunther Wittstock 《Chemphyschem》2020,21(22):2506-2514
Multinuclear transition metal complexes bridged by ligands with extended π-electronic systems show a variety of complex electronic transitions and electron transfer reactions. While a systematic understanding of the photochemistry and electrochemistry has been attained for binuclear complexes, much less is known about trinuclear complexes such as hexaphenyl-5,6,11,12,17,18-hexaazatrinaphthylene-tristitanocene [(Cp2Ti)3HATN(Ph)6]. The voltammogram of [(Cp2Ti)3HATN(Ph)6] shows six oxidation and three reduction waves. Solution spectra of [(Cp2Ti)3HATN(Ph)6] and of the electrochemically formed oxidation products show electronic transitions in the UV, visible and the NIR ranges. Density functional theory (DFT) and linear response time-dependent DFT show that the three formally titanium(II) centers transfer an electron to the HATN ligand in the ground state. The optically excited transitions occur exclusively between ligand-centered orbitals. The charged titanium centers only provide an electrostatic frame to the extended π-electronic system. Complete active self-consistent field (CASSCF) calculation on a structurally simplified model compound, which considers the multi-reference character imposed by the three titanium centers, can provide an interpretation of the experimentally observed temperature-dependent magnetic behavior of the different redox states of the title compound in full consistency with the interpretation of the electronic spectra. 相似文献