全文获取类型
收费全文 | 3096篇 |
免费 | 461篇 |
国内免费 | 217篇 |
专业分类
化学 | 1070篇 |
晶体学 | 30篇 |
力学 | 708篇 |
综合类 | 42篇 |
数学 | 360篇 |
物理学 | 1564篇 |
出版年
2024年 | 3篇 |
2023年 | 27篇 |
2022年 | 60篇 |
2021年 | 68篇 |
2020年 | 70篇 |
2019年 | 63篇 |
2018年 | 72篇 |
2017年 | 116篇 |
2016年 | 97篇 |
2015年 | 94篇 |
2014年 | 142篇 |
2013年 | 226篇 |
2012年 | 147篇 |
2011年 | 189篇 |
2010年 | 160篇 |
2009年 | 172篇 |
2008年 | 164篇 |
2007年 | 199篇 |
2006年 | 212篇 |
2005年 | 150篇 |
2004年 | 158篇 |
2003年 | 161篇 |
2002年 | 133篇 |
2001年 | 86篇 |
2000年 | 102篇 |
1999年 | 124篇 |
1998年 | 91篇 |
1997年 | 84篇 |
1996年 | 62篇 |
1995年 | 50篇 |
1994年 | 42篇 |
1993年 | 43篇 |
1992年 | 35篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 18篇 |
1988年 | 7篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 16篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1976年 | 8篇 |
1959年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有3774条查询结果,搜索用时 15 毫秒
781.
A simple and effective method to measure an electromagnetic wave polarization plane's weak rotations in various media is proposed. The specific features of the polarization plane's rotation amplification for the light reflection and transmission through the absorbing and amplifying isotropic layers are calculated. The amplification effects on an anisotropic and cholesteric liquid crystal (CLC) layers are also considered. In conclusion the question of probable choice of the amplifier's noise/signal ratio is discussed. 相似文献
782.
研制了一种用于同位素分离在线穆斯堡尔谱学的平行板雪崩计数器,计数器仅重40g。用它测量由穆斯堡尔共振吸收后放出的内转换电子,采用85%^119Sn同位素增丰的SnO2作为阴极吸收材料,测得的穆斯堡尔谱的信噪比为11,是一种适合在线穆斯堡尔实验的计数器。对该计数器的性能进行了讨论。A Parallel Plate Avalanche Counter (PPAC) with weighted about 40 g was developed for isotope separator on-line Moessbauer Spectroscopy. It detects the internal conversion electrons emitted from the resonance Moessbauer nuclide. The signal-to-noise ratio of the spectra reaches 11 for 85% enriched ^119SnO2 cathode and absorber. It is an effective detector for on-line Moessbauer experiments. The perform ance of the counter was discussed in detail. 相似文献
783.
L. V. Perova 《Computational Mathematics and Mathematical Physics》2006,46(5):891-906
Propagation of small perturbations in a homogeneous inviscid liquid rotating with a constant angular velocity in the lower half-space is considered. The source of excitation is a plane wave traveling on the free surface of the liquid. The explicit analytical solution to the problem is constructed. Uniqueness and existence theorems are proved. The wave pattern in the liquid at large times is examined. 相似文献
784.
Ioannis Dimitriou 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2007,58(1):100-120
The paper studies the geometrical aspects of steady, two-dimensional potential flows and their relation to the physics that
governs them. To achieve this, the streamline curvature of a flow is determined when the vector velocity field describing
it, is known. Two methods, which allow the calculation of streamline curvature at every point of a flow field, are developed:
the ‘Method of Rotation’ and the ‘Method of Directional Derivative’. Especially the first method reveals an interesting feature of curvature, allowing it to be interpreted kinematically. Furthermore,
an attempt has been made towards the formulation of a potential theory from a geometrical perspective. For this reason the
concept of ‘Global Curvature’ is introduced, being a measure of both stream and potential line curvature. It has been proven that it contains all the
information needed to determine the physical quantities of velocity and static pressure throughout a potential flow, thus
depicting the strong link between geometry and physics. 相似文献
785.
786.
787.
The dragging of the Kerr-NUT solution does not tend to zero at infinity. To modify this solution in order to produce a good asymptotic behaviour we transform it by introducing two further parameters with the aid of a SU(1,1) transformation followed by a unitary transformation. By imposing a certain relation between these parameters we obtain a new solution with a good asymptotic behaviour for any value of l, the NUT parameter. The new solution corresponds to a parametrized Kerr solution and we show that l is linked to the form of its ergosphere. 相似文献
788.
Asao Mizoguchi Kensuke Harada Mitsuaki Shirasaka 《Journal of Molecular Spectroscopy》2003,222(1):74-85
Millimeter-wave absorption spectroscopy combined with a pulsed jet expansion technique was applied to measure the internal rotation j=2-1 hot band of the Ar-HCN complex in the frequency region of 147-287 GHz. In total 153 rovibrational lines, split into hyperfine components due to the nitrogen nucleus, were assigned to the Σ2-Σ1, Σ2-Π1, Π2-Σ1, Π2-Π1, Δ2-Σ1, and Δ2-Π1 subbands. A set of molecular constants for the Σ2, Π2, and Δ2 internal rotation substates, including subband origins, rotational constants, nuclear quadrupole coupling constants, and Coriolis interaction constants, was determined. The internal rotation energy for the Σ2 state, 412.8949 GHz, is higher than those for the Π2 and Δ2 states, 392.3974 and 355.9570 GHz, by 20.498 and 56.938 GHz, respectively, in contrast to the Σ1 state located by 17.094 GHz lower than the Π1 state, the anisotropy of potential energy surface affecting the j=2 and j=1 states differently. The rotational and quadrupole coupling constants in the j=2 excited state are quite different from those in the ground state, indicating drastic change in the average structure in the j=2 state from the ground state. The determined molecular constants were compared with those calculated from the potential energy surface computed at the CCSD(T) level. 相似文献
789.
二次谐波产生的非线性相移的解析研究 总被引:5,自引:0,他引:5
给出一种分析二阶非线性级联效应的解析方法,对Ⅱ型二次谐波产生的非线性级联效应进行了详细的理论研究和分析。结果表明倍频晶体中正交输入两个振幅不相等的基波分量时,在近相位匹配下二阶非线性级联效应能够产生大的相移。利用本文的解析方法可以对任意二阶非线性相移产生的过程进行优化,从而以最小的需求输入功率来获得特定的相移。还对由非线性相移诱导的且与光强有关的偏振旋转效应和一种基于偏振旋转效应的全光偏振开关进行了分析和讨论。本文的结果对于建立一种基于Ⅱ型倍频晶体中非线性相移诱导偏振旋转效应的新全固化被动锁模飞秒激光装置具有十分重要的意义。 相似文献
790.
Methods of internal-category theory are applied to show that the split epimorphisms in a category C are exactly the morphisms which are effective for descent with respect to any fibration over C (or to any C-indexed category). In the same context, composition-cancellation rules for effective descent morphisms are established and being applied to (suitably defined) locally-split epimorphisms. 相似文献