全文获取类型
收费全文 | 19027篇 |
免费 | 2096篇 |
国内免费 | 1253篇 |
专业分类
化学 | 12746篇 |
晶体学 | 46篇 |
力学 | 1315篇 |
综合类 | 93篇 |
数学 | 585篇 |
物理学 | 7591篇 |
出版年
2024年 | 44篇 |
2023年 | 246篇 |
2022年 | 590篇 |
2021年 | 451篇 |
2020年 | 637篇 |
2019年 | 581篇 |
2018年 | 558篇 |
2017年 | 806篇 |
2016年 | 905篇 |
2015年 | 882篇 |
2014年 | 1004篇 |
2013年 | 1249篇 |
2012年 | 1279篇 |
2011年 | 1281篇 |
2010年 | 976篇 |
2009年 | 1120篇 |
2008年 | 1131篇 |
2007年 | 1183篇 |
2006年 | 1014篇 |
2005年 | 916篇 |
2004年 | 854篇 |
2003年 | 745篇 |
2002年 | 586篇 |
2001年 | 494篇 |
2000年 | 427篇 |
1999年 | 354篇 |
1998年 | 309篇 |
1997年 | 269篇 |
1996年 | 235篇 |
1995年 | 220篇 |
1994年 | 170篇 |
1993年 | 141篇 |
1992年 | 114篇 |
1991年 | 108篇 |
1990年 | 82篇 |
1989年 | 76篇 |
1988年 | 61篇 |
1987年 | 51篇 |
1986年 | 33篇 |
1985年 | 42篇 |
1984年 | 37篇 |
1983年 | 26篇 |
1982年 | 30篇 |
1981年 | 18篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1976年 | 7篇 |
1973年 | 4篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
41.
Mass distributions of fragments in the low-energy fission of nuclei from 187Ir to 213At have been analysed. This analysis has shown that shell effects in symmetric-mode fragment mass yields from the fission of pre-actinide nuclei could be described if one assumes the existence of two strongly deformed neutron shells in the arising fragments with neutron numbers N1 ≈ 52 and N2 ≈ 68. A new method has been proposed for quantitatively describing the mass distributions of the symmetric fission mode for pre-actinides with A ≈ 180–220. 相似文献
42.
B. Sadashive Gowda G.S.V.L. Narasimham M.V. Krishna Murthy 《International Journal of Heat and Fluid Flow》1997,18(6):613-624
In this paper, a mathematical model for forced-air precooling of spherical food products in bulk is developed. The foods are arranged in horizontal layers stacked one above the other to form a rectangular parallelepiped with a vertical gap in between the product layers. The foods are cooled by chilled air blown along the height of the package. The governing equations for the conduction heat transfer in the foods, simultaneous heat and mass transfer at the food-air interface and in the air stream are solved numerically using finite-difference methods. A comprehensive numerical study is performed by varying the process parameters over a wide range. Typical results showing the variation of moist air properties along the height of the package and the effect of each parameter on the process time are presented. The ranges of parameters for advantageous operation of the precooling system are identified. Correlations are obtained for the process time based on the product center and mass-averaged temperatures in terms of process parameters. 相似文献
43.
44.
描述了简并V型三能级原子与单模相干态光场的Raman相互作用,获得了处于激发态单态的原子与相干态光场相互作用的结果.利用探测原子与光场的相互作用将原子和光场制备成最大缠结态,并注入待测原子,通过原子与腔模构成的Bell基矢演化,对腔场进行选择性探测,获得探测原子相互作用后可能的量子状态,然后对待测原子与腔场进行联合探测,接着对探测原子的量子状态实施幺正变换,就将探测原子制备到待测原子的初始量子态上,从而实现未知原子态的隐形传送. 相似文献
45.
46.
用实验的方法,研究电流并联负反馈对放大器性能的改善,提出电流型、并联型负反馈放大器性能参数的测量方法。 相似文献
47.
G. Carelli N. Ioli A. Messina A. Moretti S. Schepis F. Strumia 《International Journal of Infrared and Millimeter Waves》1998,19(9):1191-1199
We measured the dependence of the reflectivity of InSb crystals upon temperature in the submillimeter region using monochromatic radiation from an optically pumped far infrared (FIR) laser. The measures allowed us to determine the value of the electron effective mass at low temperatures with radiations of different frequencies. Our measurements extend the results obtained recently on pure crystals with magneto-optical methods to the low temperatures region where only old measures were available. 相似文献
48.
本文介绍了多路逆磁测量方法及利用这一方法在HER装置上测量热电子环沿轴向的长度与晃荡电子密度的轴向分布的实验结果。 相似文献
49.
Ralf Jäger Anatolij I. Saprykin J. Sabine Becker Hans -Joachim Dietze José A. C. Broekaert 《Mikrochimica acta》1997,125(1-4):41-44
The analytical capabilities of a high-resolution mass spectrometer in combination with a 13.56 MHz glow discharge ion source for the analysis of semiconducting materials (silicon carbide and gallium arsenide) were studied. It was shown that single positively charged ions of sample material have about 10 eV higher average energy than the ions of the discharge and residual gas. Therefore effective energy separation of the ions of analyte from the ions of the discharge and residual gas was achieved by adjusting the ion transfer optics (breadth and position of energy slit), which improves the analytical capabilities of the developed method.Some analytical applications are presented to illustrate the performance of r.f. GDMS for the bulk analysis of semiconducting materials. The results of the trace element analysis of gallium arsenide and silicon carbide samples are compared with data of independent methods (LIMS, ICP-AES, SIMS).Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthdayOn leave from the Institute of Inorganic Chemistry, 630090 Novosibirsk, Russia 相似文献
50.
A. S. Lobach B. P. Tarasov Yu. M. Shul'ga A. A. Perov A. N. Stepanov 《Russian Chemical Bulletin》1996,45(2):464-465
Fullerene deuteride was obtained by the reaction of deuterium with solid palladium fulleride C60Pd4.9 under fairly mild conditions. The compound was identified by FD-MS, UV-Vis and IR spectroscopies, and TLC.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 483–484, February, 1996 相似文献