全文获取类型
收费全文 | 1341篇 |
免费 | 42篇 |
国内免费 | 73篇 |
专业分类
化学 | 416篇 |
晶体学 | 4篇 |
力学 | 15篇 |
综合类 | 3篇 |
数学 | 456篇 |
物理学 | 227篇 |
综合类 | 335篇 |
出版年
2023年 | 8篇 |
2022年 | 20篇 |
2021年 | 15篇 |
2020年 | 8篇 |
2019年 | 23篇 |
2018年 | 22篇 |
2017年 | 17篇 |
2016年 | 26篇 |
2015年 | 32篇 |
2014年 | 52篇 |
2013年 | 76篇 |
2012年 | 48篇 |
2011年 | 61篇 |
2010年 | 58篇 |
2009年 | 69篇 |
2008年 | 74篇 |
2007年 | 61篇 |
2006年 | 50篇 |
2005年 | 56篇 |
2004年 | 45篇 |
2003年 | 43篇 |
2002年 | 56篇 |
2001年 | 34篇 |
2000年 | 48篇 |
1999年 | 27篇 |
1998年 | 19篇 |
1997年 | 23篇 |
1996年 | 23篇 |
1995年 | 22篇 |
1994年 | 17篇 |
1993年 | 7篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1985年 | 28篇 |
1984年 | 23篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 37篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 21篇 |
1977年 | 28篇 |
1976年 | 22篇 |
1975年 | 16篇 |
1974年 | 18篇 |
1973年 | 19篇 |
排序方式: 共有1456条查询结果,搜索用时 31 毫秒
181.
Several characteristics of fission accompanied by long range alpha particles (LRA) have been studied in the thermal neutron
induced fission of235U. The kinetic energies of fission fragments and the LRA were measured with a back-to-back ionization chamber and semiconductor
detectors respectively. The kinetic energies of the two fragments and the LRA in LRA fission, along with the energies of pair
fragments in the normal binary fissions, were recorded event by event on a magnetic tape by means of a four-parameter data
acquisition system. The data were analysed to study the dependence of different quantities in LRA fission on the fragment
mass ratio, LRA energy and the total kinetic energy of the fission fragments. It is seen that the most probable energy of
LRA increases significantly for near symmetric mass divisions. The total kinetic energy for all mass ratios in LRA fission
is found to be (2.6±0.7) MeV larger than that in binary fission. The difference in the total kinetic energies in LRA and binary
fissions is seen to be dependent on mass ratio. This result may suggest that the scission configuration in LRA fission is
different for different mass ratios. Correlations between the fission fragment and LRA energies have been studied for several
mass ratios. It is seen that the most probable fragment kinetic energyĒ
k varies nearly linearly with the LRA energyE
a for various mass divisions but the variation of the most probable LRA energyĒ
a with fragment kinetic energyE
k is found to deviate from linearity for several mass ratios. From a least square fit to the variation ofĒ
k withE
a it is found that the slope (dĒ
k/dEa) increases with the increase in mass ratio. The present results are discussed to arrive at a better understanding of the
scission configuration in the fission accompanied by LRA emission. 相似文献
182.
James Kao 《Journal of Molecular Structure》1980,63(2):293-300
The structures of S42+ and S42? have been investigated by ab initio calculations using the GAUSSIAN 70 system of programs and the 44-31G basis set. Electronic singlet states of the square form and three possible conformations of the chain structure were examined for both ions, and the singlet rectangle form of S42? was also investigated. The anti chain form of S42+ was found to be 78.3 kJ mol? more stable than the square form, in contrast to previous experimental data. S42?is predicted to adopt the chain structure with the anti conformation. 相似文献
183.
184.
M. Zyskin 《Letters in Mathematical Physics》1996,36(4):427-439
We construct quantum operators solving the quantum versions of the Sturm-Liouville equation and the resolvent equation, and show the existence of conserved currents. The construction depends on the following input data: the basic quantum field O(k) and the regularization. 相似文献
185.
应用单元格试探作用量变分法研究2 1维U(1)格点规范场的相图。解析地计算出序参量——平均元格能量,与MC方法所得结果符合很好。证实2 1维U(1)格点规范理论是禁闭的。消除了以往文献中用单链试探作用量变分法出现的不正确的一级相变点,还可以很方便地计算到比MC方法的β更大的深度弱耦合区。 相似文献
186.
赫英 《西北大学学报(自然科学版)》2002,32(4):341-343
结合实际工作中的体会,探讨了与岩浆有关的热液矿床矿体赋存部位与岩浆岩类型、矿种类型及构造开放条件的关系,并运用连通器原理,解释了一些矿田中常见的矿体等高性的成因。 相似文献
187.
Alexander Scheeline John A. Norris J.C. Travis J.R. Devoe John P. Walters 《Spectrochimica Acta Part B: Atomic Spectroscopy》1981,36(4):373-383
Light scattering was used to demonstrate the presence of small (?1 μm) particles in the immediate surroundings of a stable spark discharge. Several parameters, including electrode composition and surface condition, which are of importance in emission spectrochemical analysis, were found to be of importance in affecting the scattering signal. Electron micrographs of the heaviest particles revealed two distinct types of particles. Analytical implications are discussed. 相似文献
188.
An unusual fragmentation reaction was observed when terramycin is treated with MeI in acetone at room temp. The reaction proceeds with quaternization, loss of trimethylamine, fission of bonds 4a,5 and 12,12a with formation of an aldehydo-lactone derived from rings B, C and D. Additionally some transformations of this lactone are described. 相似文献
189.
Ghitun M Bonneil E Fortier MH Yin H Killeen K Thibault P 《Journal of separation science》2006,29(11):1539-1549
This work reports on the application of a microfluidic device integrating nanoscale LC to nanoelectrospray MS (nano-LC-chip-MS) for the analysis of complex protein digests. Peak profile analyses of more than 700 peptide ions, reproducibly detected across replicate nano-LC-chip-MS runs (n = 5), indicated that the system provided RSD values of 0.24% on retention time, +/- 30 ppm on m/z measurement and +/- 30% variation on intensity over three orders of magnitude. RP adsorbant media with different alkyl chains and particle size packed in both trapping and separation channels were investigated to improve the chromatographic performance of this system. A two-fold improvement in chromatographic peak capacity was achieved using microfluidic devices comprising a 5 mircrom C3 trap with 2.5 microm C18 trap separation channel compared to the traditional 5 microm C18 stationary phase. Enhanced sample selectivity for the identification of phosphopeptides was obtained by combining immobilized metal affinity media prior to peptide separation on the RP microfluidic device. This system was evaluated in the context of differential phosphoproteome analyses to identify changes in signaling events and protein expression of human monocytes following the administration of phorbol ester. 相似文献
190.
李龙途 《贵州大学学报(自然科学版)》2012,29(3):67-70
目前主流品牌的保密U盘均采用硬件加密的方式,安全级别较高,数据加密速度快,应用也比较简单。但由于硬件加密的实现需要用到价位较高的专用芯片,使得这种类型的产品价格也比较昂贵。本文提出一种基于虚拟磁盘的保密U盘实现方案,该方案具有成本低、高效、实用等特点。 相似文献