全文获取类型
收费全文 | 872篇 |
免费 | 14篇 |
国内免费 | 3篇 |
专业分类
化学 | 509篇 |
晶体学 | 11篇 |
力学 | 30篇 |
数学 | 106篇 |
物理学 | 233篇 |
出版年
2022年 | 19篇 |
2021年 | 16篇 |
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 21篇 |
2017年 | 27篇 |
2016年 | 23篇 |
2015年 | 17篇 |
2014年 | 30篇 |
2013年 | 56篇 |
2012年 | 42篇 |
2011年 | 42篇 |
2010年 | 28篇 |
2009年 | 34篇 |
2008年 | 38篇 |
2007年 | 34篇 |
2006年 | 23篇 |
2005年 | 14篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 16篇 |
2001年 | 9篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 11篇 |
1990年 | 9篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 18篇 |
1982年 | 6篇 |
1981年 | 12篇 |
1980年 | 13篇 |
1979年 | 24篇 |
1978年 | 15篇 |
1977年 | 18篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 13篇 |
1973年 | 14篇 |
1972年 | 8篇 |
1971年 | 8篇 |
1966年 | 6篇 |
1960年 | 5篇 |
1957年 | 7篇 |
1954年 | 5篇 |
排序方式: 共有889条查询结果,搜索用时 15 毫秒
1.
2.
Development of a 100 MeV CW proton LINAC has been planned at CAT. This LINAC will be needing CW rf power in the frequency
ranges of 350 MHz and 700 MHz for its RFQ and DTL/CCDTL/SFDTL structures respectively. The power to the accelerating structures
will be produced by either 1 MW CW or 250 kW CW klystrons/inductive output tubes (HOM IOTs). The power needed by respective
feed points in the structure is max. 250 kW which will be powered by splitting the power from 1 MW klystron/klystrode into
four channels by using a wave-guide system. In case of using 250 kW tubes the power to the structures will be provided directly
from each tube. Two types of wave-guide transmission system have been considered, viz, WR 2300 for 350 MHz rf needs and WR
1500 for 700 MHz rf needs. The typical wave-guide system has been designed using the 1 MW CW klystron followed by wave-guide
filter, dual directional coupler, high-power circulator, three 3 dB magic TEE power dividers to split the main channel into
four equal channels of 250 kW each. Each individual channel has dual directional couplers, flexible wave-guide sections and
high power ceramic vacuum window. The circulator and each power divider is terminated into the isolated ports by high power
CW loads. Out of the four channels three channels have phase shifters. Present paper describes the technological aspects and
design specifications-considerations for these stringent requirements. 相似文献
3.
The 57Fe Mössbauer technique has been used to investigate the effect of zinc oxide substitution in (25???x)MnO–xZnO–15Fe2O3–60B2O3 glass system (x?=?0, 5, 10, 15 and 20 mol% of ZnO ). Mössbauer absorption spectra for all the samples recorded at room temperature suggest the existence of the two paramagnetic quadrupole doublets. The observed variations in hyperfine parameters have been explained on the basis of cations distribution and exchange interaction at the lattice sites and it is concluded that B–B interaction increases while the metal–metal interaction decreases due to replacement of manganese oxide by zinc oxide. These results suggest that the present glass system exhibits a paramagnetic behaviour that changes towards the weak paramagnetic when manganese oxide was replaced with zinc oxide. 相似文献
4.
The collision-generated hybridization which has been found responsible for the on-site mixing of the atomic-likef-state and the band-liked states in mixed valence solids has been studied for the cerium solid. A practical expression which depends on the lattice
constant and temperature has been obtained for the collision-generated hybridization. Numerical calculations show that the
valence varies continuously with lattice constant and that temperature makes the transition smoother. The collision-generated
hybridization is found to be of significant strength in the intermediate valence regime; but over a wide range of the valence
near 3.5 it varies rather slowly without preferring a particular valence. Factors which can assist the collision-generated
hybridization in stabilizing the mixed valence phase at a particular lattice constant are discussed. 相似文献
5.
Adamovich MI Aggarwal MM Alexandrov YA Ameeva ZV Andreeva NP Anzon ZV Arora R Badyal SK Bhalla KB Bhasin A Bhatia VS Bubnov VI Burnett TH Cai X Chasnikov IY Chernova LP Chernyavski MM Dressel B Eligbaeva GZ Eremenko LE Friedlander EM Gadzhieva SI Gaitinov AS Ganssauge ER Garpman S Gerassimov SG Gill A Grote JG Gulamov KG Gulyamov UG Gupta VK Hackel S Heckman HH Haung H Judek B Kachroo S Kadyrov FG Kalyachkina GS Kanygina EK Kaul GL Kaur M Kharlamov SP Koss T Kumar V Lal P Larionova VG 《Physical review letters》1990,65(4):412-415
6.
Results are presented from a study of electrical breakdown of anodic aluminum oxide in a constant field with a platinum pressure electrode. Statistical breakdown parameters and their dependence on the magnitude and polarity of the applied voltage are obtained. Field and temperature dependences of breakdown delay time over the interval 10–6–103 sec are determined. It is shown that the experimental (E) curves can be rectified (in two segments) in the coordinates log E–1. This indicates a possible contribution to the breakdown mechanism by both tunnel injection of electrons from the cathode and subsequent avalanche multiplication of electrons within the dielectric.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 25–29, April, 1990.In conclusion, the authors thank T. V. Shmidt and E. Ya. Khanin for assistance in the study. 相似文献
7.
8.
9.
K. Lal 《Monatshefte für Chemie / Chemical Monthly》1983,114(1):33-36
Reactions of trimethylchlorosilane (Me 3SiCl) with some nitrogen donors viz. pyridine, 2-, 3- and 4-picolines, quinoline and isoquinoline in nitrobenzene have been studied conductometrically. The conductivities of the solutions during these reactions have been interpreted in terms of the formation of (Me 3Si.D)+, (Me 3SiCl2)? andMe 3SiCl.D (D=N-donor molecule) species. 相似文献
10.
The direct oxidation of chiral amide enolates to optically active mandelic acid using 2-sulfonyloxaziridine is described. The diastereoselectivity is counterion dependent. 相似文献