全文获取类型
收费全文 | 513746篇 |
免费 | 7727篇 |
国内免费 | 4511篇 |
专业分类
化学 | 258066篇 |
晶体学 | 7860篇 |
力学 | 25393篇 |
综合类 | 248篇 |
数学 | 71470篇 |
物理学 | 162947篇 |
出版年
2021年 | 3649篇 |
2020年 | 4106篇 |
2019年 | 4429篇 |
2018年 | 12594篇 |
2017年 | 13278篇 |
2016年 | 11223篇 |
2015年 | 6156篇 |
2014年 | 8110篇 |
2013年 | 19179篇 |
2012年 | 19101篇 |
2011年 | 28981篇 |
2010年 | 19036篇 |
2009年 | 18951篇 |
2008年 | 25692篇 |
2007年 | 28485篇 |
2006年 | 16334篇 |
2005年 | 19828篇 |
2004年 | 15841篇 |
2003年 | 14408篇 |
2002年 | 12652篇 |
2001年 | 12824篇 |
2000年 | 10052篇 |
1999年 | 7604篇 |
1998年 | 6463篇 |
1997年 | 6334篇 |
1996年 | 6374篇 |
1995年 | 5600篇 |
1994年 | 5614篇 |
1993年 | 5451篇 |
1992年 | 5755篇 |
1991年 | 5908篇 |
1990年 | 5492篇 |
1989年 | 5340篇 |
1988年 | 5309篇 |
1987年 | 5139篇 |
1986年 | 4969篇 |
1985年 | 6654篇 |
1984年 | 6839篇 |
1983年 | 5702篇 |
1982年 | 5997篇 |
1981年 | 5779篇 |
1980年 | 5411篇 |
1979年 | 5747篇 |
1978年 | 5998篇 |
1977年 | 5875篇 |
1976年 | 5965篇 |
1975年 | 5447篇 |
1974年 | 5605篇 |
1973年 | 5709篇 |
1972年 | 4200篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Nonlinear susceptibility of a quantum dot (QD) embedded in a two-sided cavity, is studied theoretically from a weak-coupling to a strong-coupling regime. In the relevance of a quantum logic gate, the corresponding nonlinear phase shifts (Kerr effect) are estimated for coherent wavepackets including one photon on average. In the weak-coupling regime, the phase shift enhances strongly as a function of a coupling constant between the cavity photon and QD, and eventually saturates in the strong-coupling regime. We also show transmission spectra to evaluate the efficiency of the phase shift. Although the efficiency decreases monotonically in the weak-coupling regime, it rises in the strong-coupling regime. 相似文献
992.
V. A. Reznikov 《Technical Physics》2003,48(9):1216-1218
A shell model that describes the formation of molecular complexes around a C60 molecule upon the solid-phase interaction of the powders is considered. From the absorption spectra, it follows that a reacting
particle is a fullerene dimer. 相似文献
993.
994.
T. M. Shneidman G. G. Adamian N. V. Antonenko S. P. Ivanova R. V. Jolos W. Scheid 《Physics of Atomic Nuclei》2003,66(2):206-217
Based on the dinuclear system concept, the role of bending vibrations in creation of the angular momentum of primary fission fragments is investigated. For 252Cf spontaneous fission, the angular momenta of the fragments are calculated as a function of the neutron multiplicity and compared with available experimental data. Different cluster compositions of the 252Cf fission modes at the scission point are considered. 相似文献
995.
Results of investigations into the physical properties of a number of new nonlinear crystals are presented. The parameters of frequency converters manufactured on their basis are compared, and second-harmonic generation of CO2 lasers first excited by frequency conversion in LiInSe2, AgGa1– x
InxSe2, AgxGaxGexS2(1 + x), and Hg1–x
CdxGa2S4 crystals is investigated. The superiority of HgGa2S4, Hg1–x
CdxGa2S4, and AgGa1–x
InxSe2 over the well-known crystals has been demonstrated for frequency conversion both within the middle-IR range and from the visible range to the middle-IR range. Advantages of LiInSe2 and AgGa1–x
InxSe2 crystals are demonstrated for the direct frequency conversion of femtosecond laser radiation to the middle-IR range compared to the cascade frequency conversion and direct frequency conversion in LiInS2 crystals. 相似文献
996.
997.
The general theory on the transformation of elastic waves at a rigid nodal junction of an arbitrary number of thin plates is considered. The notion of transformation marix is introduced, and a way for computing it and numerical examples are given. Properties of the transformation matrix resulted from the reciprocity principle and the energy conservatin law are studied. In particular, a new relation that expresses the energy conservation low for the case where a wave damped in the direction of the joint of plates is a source of a field is obtained. Bibliography: 18 titles. 相似文献
998.
999.
P. M. Larionov A. N. Malov M. M. Mandrik N. A. Maslov A. M. Orishich 《Journal of Applied Spectroscopy》2003,70(1):38-42
We investigated the laser-induced fluorescence spectra (LIF) of porcine cardiac tissues with different degrees of viability. The data obtained are compared with the results of routine histological investigations and also with the experiments performed with the use of fluorescent probes. It has been found with a high degree of reliability that the loss of the viability of the myocardium tissue leads to the alteration of its LIF spectra. This can be used for low-invasive rapid control of transplant viability in the process of its preparation and during surgery. 相似文献
1000.
Double adaptive notch filter for mechanical grain flow sensors 总被引:2,自引:0,他引:2
Nowadays, commercial combine harvesters are equipped with special sensors for the purposes of precision farming. Sensors are installed to measure the harvested surface and mass flow each second. Hence, grain yield maps are constructed, approximating the actual grain yield on the field before harvesting.Most grain flow sensors are installed on the paddle elevator before storage in the grain tank. At the elevator exit, paddles throw packs of grain against a curved plate on which a force transducer is attached. Therefore, the measured flow signal is heavily disturbed by the paddle rate and resonance frequency of the mechanical sensor.In this study, a computationally cheap method is presented to track both frequencies in the measured flow signal. Based on these frequency trackers, a double notch filter is tuned continuously to remove both disturbances. Moreover, the knowledge about the frequency content can be used to monitor the condition of the mechanical sensor and the paddle elevator. 相似文献