全文获取类型
收费全文 | 29954篇 |
免费 | 2286篇 |
国内免费 | 1216篇 |
专业分类
电工技术 | 1636篇 |
综合类 | 2294篇 |
化学工业 | 5200篇 |
金属工艺 | 1410篇 |
机械仪表 | 1715篇 |
建筑科学 | 2061篇 |
矿业工程 | 724篇 |
能源动力 | 754篇 |
轻工业 | 2698篇 |
水利工程 | 636篇 |
石油天然气 | 1785篇 |
武器工业 | 213篇 |
无线电 | 3280篇 |
一般工业技术 | 3415篇 |
冶金工业 | 1335篇 |
原子能技术 | 342篇 |
自动化技术 | 3958篇 |
出版年
2024年 | 85篇 |
2023年 | 439篇 |
2022年 | 758篇 |
2021年 | 1107篇 |
2020年 | 864篇 |
2019年 | 717篇 |
2018年 | 778篇 |
2017年 | 938篇 |
2016年 | 817篇 |
2015年 | 1159篇 |
2014年 | 1488篇 |
2013年 | 1841篇 |
2012年 | 2050篇 |
2011年 | 2234篇 |
2010年 | 2053篇 |
2009年 | 1952篇 |
2008年 | 1941篇 |
2007年 | 1832篇 |
2006年 | 1791篇 |
2005年 | 1529篇 |
2004年 | 1079篇 |
2003年 | 819篇 |
2002年 | 746篇 |
2001年 | 593篇 |
2000年 | 604篇 |
1999年 | 598篇 |
1998年 | 492篇 |
1997年 | 416篇 |
1996年 | 405篇 |
1995年 | 317篇 |
1994年 | 244篇 |
1993年 | 193篇 |
1992年 | 150篇 |
1991年 | 115篇 |
1990年 | 64篇 |
1989年 | 67篇 |
1988年 | 68篇 |
1987年 | 26篇 |
1986年 | 25篇 |
1985年 | 18篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1959年 | 1篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
赵霞 《河南机电高等专科学校学报》2013,(1):27-30
实现旅游产业的转型升级是新乡市旅游业发展到一定阶段的必然选择。文章从新乡旅游产业转型升级的背景入手,对制约新乡市旅游产业转型升级的因素进行了深入的分析论证,并提出了相关的对策和建议。 相似文献
52.
Energy flux characteristics of seismic waves at the interface between soil layers with different saturations 总被引:1,自引:0,他引:1
Based on the multiphase poroelasticity theory describing the propagation of waves in the unsaturated fluid-saturated porous medium, the reflection and transmission coefficients of the seismic waves at the interface between soil layers with different saturations are obtained. Our unsaturated model consists of a deformable skeleton in which two compressible and viscous fluids (i.e., water and gas) flow in the interstices. Three compressional waves (i.e., P1, P2, and P3 waves) and one shear (i.e., S wave) wave exist in the unsaturated soils. The expressions for the energy ratios of the various reflected and transmitted waves at the interface during the transmission and reflection processes are presented in explicit forms accordingly. At last, numerical computations are performed and the results obtained are respectively depicted graphically. The variation of the energy ratios with the incident angle, wave frequency and saturation degrees of the upper and lower soil layers is illustrated in detail. The calculation results show that the allocation of incident seismic waves at the interface is influenced not only by the angle and frequency of the incident seismic waves, but also by the saturations of the upper and lower soil layers. It is also verified that, at the interface, the sum of energy ratios of the reflected and transmitted waves is approximately equal to unity as was expected. This study is of importance to several fields such as geotechnical engineering, seismology, and geophysics. 相似文献
53.
曹霞 《湖南工业职业技术学院学报》2012,12(6):82-83
《了不起的盖茨比》生动地描述了二十世纪二十时代的美国社会丰裕物质生活与精神荒原的冲突。美国梦的幻灭、道德和宗教信仰体系的坍塌引发了菲茨杰拉德对美国精神和传统价值观的思索,呼吁回归传统价值观,重塑道德体系。 相似文献
54.
55.
本文重点介绍莱钢1500mm热连轧机中液压AGC的控制性能及其实现方式。 相似文献
56.
Shift-full-rank matrices and applications in space-time trellis codes for relay networks with asynchronous cooperative diversity 总被引:1,自引:0,他引:1
Shang Y. Xia X.-G. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2006,52(7):3153-3167
To achieve full cooperative diversity in a relay network, most of the existing space-time coding schemes require the synchronization between terminals. A family of space-time trellis codes that achieve full cooperative diversity order without the assumption of synchronization has been recently proposed. The family is based on the stack construction by Hammons and El Gamal and its generalizations by Lu and Kumar. It has been shown that the construction of such a family is equivalent to the construction of binary matrices that have full row rank no matter how their rows are shifted, where a row corresponds to a terminal (or transmit antenna) and its length corresponds to the memory size of the trellis code on that terminal. We call such matrices as shift-full-rank (SFR) matrices. A family of SFR matrices has been also constructed, but the memory sizes of the corresponding space-time trellis codes (the number of columns of SFR matrices) grow exponentially in terms of the number of terminals (the number of rows of SFR matrices), which may cause a high decoding complexity when the number of terminals is not small. In this paper, we systematically study and construct SFR matrices of any sizes for any number of terminals. Furthermore, we construct shortest (square) SFR (SSFR) matrices that correspond to space-time trellis codes with the smallest memory sizes and asynchronous full cooperative diversity. We also present some simulation results to illustrate the performances of the space-time trellis codes associated with SFR matrices in asynchronous cooperative communications. 相似文献
57.
58.
根据现行消防技术规范的有关规定,结合建筑工程消防监督审核的工作实践,指出了消防水箱设计中常出现的错误并提出了相应的改正措施。 相似文献
59.
60.