全文获取类型
收费全文 | 22722篇 |
免费 | 2684篇 |
国内免费 | 1583篇 |
专业分类
电工技术 | 1763篇 |
技术理论 | 2篇 |
综合类 | 2722篇 |
化学工业 | 2427篇 |
金属工艺 | 502篇 |
机械仪表 | 1072篇 |
建筑科学 | 2539篇 |
矿业工程 | 1332篇 |
能源动力 | 1009篇 |
轻工业 | 1874篇 |
水利工程 | 1694篇 |
石油天然气 | 1334篇 |
武器工业 | 229篇 |
无线电 | 1932篇 |
一般工业技术 | 2098篇 |
冶金工业 | 785篇 |
原子能技术 | 308篇 |
自动化技术 | 3367篇 |
出版年
2024年 | 92篇 |
2023年 | 334篇 |
2022年 | 676篇 |
2021年 | 802篇 |
2020年 | 825篇 |
2019年 | 735篇 |
2018年 | 713篇 |
2017年 | 833篇 |
2016年 | 980篇 |
2015年 | 978篇 |
2014年 | 1519篇 |
2013年 | 1655篇 |
2012年 | 1685篇 |
2011年 | 1883篇 |
2010年 | 1368篇 |
2009年 | 1331篇 |
2008年 | 1266篇 |
2007年 | 1517篇 |
2006年 | 1319篇 |
2005年 | 1133篇 |
2004年 | 915篇 |
2003年 | 777篇 |
2002年 | 602篇 |
2001年 | 500篇 |
2000年 | 407篇 |
1999年 | 406篇 |
1998年 | 306篇 |
1997年 | 269篇 |
1996年 | 223篇 |
1995年 | 196篇 |
1994年 | 172篇 |
1993年 | 125篇 |
1992年 | 76篇 |
1991年 | 87篇 |
1990年 | 64篇 |
1989年 | 48篇 |
1988年 | 40篇 |
1987年 | 19篇 |
1986年 | 23篇 |
1985年 | 8篇 |
1984年 | 17篇 |
1983年 | 16篇 |
1982年 | 14篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1959年 | 2篇 |
1958年 | 2篇 |
1955年 | 2篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
81.
黄运平 《武汉理工大学学报(材料科学英文版)》2002,17(1)
The topological index F* is defined and obtained by the method of a non-dimensional unit calculation in which three matrices multiply with each other. These matrices represent the connective cases of atoms in a molecule, the structural features of atoms on top and the bonded cases of the adjacent atoms respectively. The standard formation enthalpies of ABn(g) molecules were correlated with F'* (A = C, Al, Si, Ti, Zr, B = F, Cl, Br, I, H, n=1 -4) and these correlation coefficients are all more than 0.96. Some molecules (e.g CH4, SiH4,etc. )can be preferably handled by F* but can not be dealt with by other topological indices. By contrast to traditional hydrogen suppressed graph, the contribution of hydrogen atoms to structures and properties of molecules is considered. 相似文献
82.
83.
84.
Xin'an LIANG 《材料科学技术学报》2002,18(1):95-96
Skeletal form of KnbO3 crystals growing in Li2B4O7 solvent was in-situ observed at 900℃ and it was found that shallow depression started to develop on the surface of KnbO3 crystals when the crystal size exceeded several micron,typically 7 micron.Based on the quantitative criterion derived by Chernov,the estimated critical size of KNbO3 crystals was 1 micron,which was consistent with the experimental measurement.The kinetic coefficients,Kcorner and Kcr,in the criterion were experimentally obtained in the diffusive-convective and diffusive-advective flow states respectively. 相似文献
85.
The effect of plasma elongation on the second‐stable spherical tokamak (ST) was numerically studied using the experimentally measured pressure and current profiles of ultrahigh‐beta STs. The maximum beta of ST over 50% was obtained in the TS‐3 ST/CT experiment by applying an external toroidal field to an FRC. It was found that the marginal beta for the ballooning instability increased with the plasma elongation κ of ST. The elongated STs with κ > 2 have the magnetic shear (S)–pressure gradient (α) profiles located in the second‐stable regime for the ballooning mode and the stability margin increased with κ. The close relation between the absolute minimum‐B profile and the second stability was documented. The effect of elongation on maximum beta was observed to saturate when κ exceed 3, indicating that the optimized elongation for high‐beta STs is located around 2 < κ < 3. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(4): 1–6, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20132 相似文献
86.
Jianlong Zou Xikui Ma Chi K. Tse Dong Dai 《International Journal of Circuit Theory and Applications》2006,34(3):251-264
In this paper, we derive the discrete‐time model for the power‐factor‐correction (PFC) buck‐boost converter in terms of a stroboscopic switching map. Fast‐scale instability is analysed through a fold diagram, which exposes the periodicity of the operation as well as the locations of the critical phase angles of the line voltage at which instability begins to occur along a half‐line cycle. The asymmetrical locations of the critical phase angles along a half‐line cycle is explained in terms of ‘under‐developed’ bifurcation. Border collision bifurcations are observed and analysed in detail. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
87.
88.
C R Chakravorty 《Bulletin of Materials Science》1994,17(6):733-745
Magnesium-lithium alloys are among the lowest density metallic materials. Addition of lithium, with a relative density of
0·53, in magnesium reduces the density of the alloy significantly. Furthermore, addition of nearly 11 wt.% lithium converts
hexagonal close packed structure of pure magnesium to a body centered cubic lattice, markedly improving formability of the
alloy. The development of these alloys, however, had been hampered due to the high reactivity of lithium and magnesium in
the molten state and also, due to poor creep resistance and instability of mechanical properties at room temperature. In an
attempt to indigenize these ultra light alloys for possible applications in Indian satellite programme, detailed research
work was initiated in DMRL. The difficulties associated with producing sound cast ingots have been overcome by controlling
melting and casting parameters of these alloys. Extensive work has been done on structure-property correlation of alloys with
varying lithium content and minor alloying additions. Based on these work, advanced magnesium-lithium alloys have been developed
with improved tensile properties, room temperature stability and creep resistance. Wrought products (plates/sheets) of magnesium-lithium
alloy have been supplied to ISAC, Bangalore and are being used in their INSAT-2 programme. This paper describes the systematic
studies carried out in the laboratory to indigenize these ultra light alloys. 相似文献
89.
自聚焦棒耦合性能的分析 总被引:1,自引:0,他引:1
本文采用光线光学的原理分析了自聚焦棒(GRIN)的光学性能,在折射率分布为抛物线近似的条件下,推导出较为简单的GRIN中的光线轨迹方程,并实验测量了GRIN的耦合效率,从而由理论和实验两方面讨论GRIN的聚焦特性。 相似文献
90.
He Ping 《电子科学学刊(英文版)》1994,11(4):296-302
The minimum squared Euclidean distance(MSED) of binary multi-h phase codes is presented. The signal segregation degree(SSD) has been put forward to determine MSED of multi-h phase codes. In order to maximize MSED, SSD should be as large as possible. The necessary and sufficient conditions of maximizing
SSD are derived. Finally, SSD and the exact formulae for MSED of binary 2-h phase codes are also presented. 相似文献