全文获取类型
收费全文 | 53001篇 |
免费 | 6325篇 |
国内免费 | 4030篇 |
专业分类
电工技术 | 4620篇 |
技术理论 | 2篇 |
综合类 | 5176篇 |
化学工业 | 7207篇 |
金属工艺 | 3281篇 |
机械仪表 | 4017篇 |
建筑科学 | 4487篇 |
矿业工程 | 2329篇 |
能源动力 | 1591篇 |
轻工业 | 5099篇 |
水利工程 | 1646篇 |
石油天然气 | 1993篇 |
武器工业 | 684篇 |
无线电 | 5861篇 |
一般工业技术 | 4917篇 |
冶金工业 | 1853篇 |
原子能技术 | 922篇 |
自动化技术 | 7671篇 |
出版年
2024年 | 199篇 |
2023年 | 914篇 |
2022年 | 2171篇 |
2021年 | 2818篇 |
2020年 | 2027篇 |
2019年 | 1522篇 |
2018年 | 1686篇 |
2017年 | 1808篇 |
2016年 | 1555篇 |
2015年 | 2517篇 |
2014年 | 2992篇 |
2013年 | 3600篇 |
2012年 | 4332篇 |
2011年 | 4552篇 |
2010年 | 4038篇 |
2009年 | 3774篇 |
2008年 | 3987篇 |
2007年 | 3760篇 |
2006年 | 3160篇 |
2005年 | 2486篇 |
2004年 | 1981篇 |
2003年 | 1609篇 |
2002年 | 1671篇 |
2001年 | 1507篇 |
2000年 | 988篇 |
1999年 | 514篇 |
1998年 | 215篇 |
1997年 | 182篇 |
1996年 | 170篇 |
1995年 | 111篇 |
1994年 | 88篇 |
1993年 | 97篇 |
1992年 | 67篇 |
1991年 | 43篇 |
1990年 | 36篇 |
1989年 | 36篇 |
1988年 | 25篇 |
1987年 | 18篇 |
1986年 | 18篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 15篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1959年 | 8篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Mutual information-based analysis of JPEG2000 contexts. 总被引:4,自引:0,他引:4
Context-based arithmetic coding has been widely adopted in image and video compression and is a key component of the new JPEG2000 image compression standard. In this paper, the contexts used in JPEG2000 are analyzed using the mutual information, which is closely related to the compression performance. We first show that, when combining the contexts, the mutual information between the contexts and the encoded data will decrease unless the conditional probability distributions of the combined contexts are the same. Given I, the initial number of contexts, and F, the final desired number of contexts, there are S(I, F) possible context classification schemes where S(I, F) is called the Stirling number of the second kind. The optimal classification scheme is the one that gives the maximum mutual information. Instead of using an exhaustive search, the optimal classification scheme can be obtained through a modified generalized Lloyd algorithm with the relative entropy as the distortion metric. For binary arithmetic coding, the search complexity can be reduced by using dynamic programming. Our experimental results show that the JPEG2000 contexts capture the correlations among the wavelet coefficients very well. At the same time, the number of contexts used as part of the standard can be reduced without loss in the coding performance. 相似文献
92.
93.
Experiments were carried out to investigate the characteristics of oil-gas flow in a horizontal pipe on a large scale (with the inner diameter D = 125 mm). With the experimental data, the flow patterns were presented. Through the analyses for the flow regime transition, it was found that there was a critical superficial velocity of liquid phase for the flow regime transiting from stratified flow to slug flow. The slug flow could not occur until the superficial velocity of liquid phase was higher than the critical velocity. For the flow pattern transiting from stratified to slug flow, the transmitting velocity of gas phase decreases with the augmentation of superficial velocity of liquid phase. On the basis of the experiments, numerical simulations of different flow patterns and their transitions were performed with the use of the Volume Of Fluid (VOF) technique. The results of the computations are shown to match well with the measured data in the experiments. 相似文献
94.
95.
苏里格低渗强非均质性气田开发技术对策探讨 总被引:29,自引:2,他引:27
鄂尔多斯盆地苏里格气田储集层具有低渗、强非均质性、中强压敏的特点,气井产能低,稳产期短。根据单井模拟及生产动态分析,气井低产量生产可以降低压敏效应的影响,加强气井低产量生产阶段的管理,有利于合理利用地层能量,提高井控外围低渗区储量动用程度;分层压裂、多层合采可以在纵向上充分动用气井控制储量,增加气井最终累计产气量和稳产时间;地质研究与地震相结合,是提高储集层预测精度和钻井成功率的技术关键;降低成本,争取优惠政策也是提高经济效益的有效途径。 相似文献
96.
97.
JIAHong-bo CHENBao-xue ZHOUJian-zhong ZHAODe-xir LUHong-liang YUANYi-fang ISOMamoru 《半导体光子学与技术》2004,10(1):21-27
Based on the measurement of dispersion characteristic and birefractive index of the fluorinated polyimide film,a statistical optimum design method is proposed and used to realize the design of 32-and 36-wavelengths optical waveguide wavelength-interleave coupler (i,e.,interleaver) with the optimization of polarization fluctuation and wavelength interval of 0.8nm at 1550nm. The largest cross coupling ratios of the two interleavers are respectively less than 1.8% and 3.5%, while the least through coupling ratios are respectively greater than 98. 2% and 96. 5%. The output differences due to polarization fluctuation are less than 1.7% and 3.2% 相似文献
98.
设计了一种适合在低电源电压下工作的前馈型输入级放大结构,在全摆幅的动态工作范围内,输入级跨导保持不变,采用负载电流补偿以保证增益近似恒定,输出采用前馈型AB类输结构,实现全摆幅输出。 相似文献
99.
通过分析PHS网络中各寻呼区的统计指标,剖析指标劣化的根本原因,采取修改相应的参数配置、移站、调整天线等措施进行网络优化,优化实施后再次收集统计指标做对比分析,总结经验。 相似文献
100.