全文获取类型
收费全文 | 51576篇 |
免费 | 5178篇 |
国内免费 | 3207篇 |
学科分类
工业技术 | 59961篇 |
出版年
2024年 | 135篇 |
2023年 | 917篇 |
2022年 | 1474篇 |
2021年 | 2210篇 |
2020年 | 1732篇 |
2019年 | 1660篇 |
2018年 | 1686篇 |
2017年 | 1818篇 |
2016年 | 1529篇 |
2015年 | 2155篇 |
2014年 | 2586篇 |
2013年 | 2999篇 |
2012年 | 3180篇 |
2011年 | 3325篇 |
2010年 | 3090篇 |
2009年 | 2852篇 |
2008年 | 2822篇 |
2007年 | 2627篇 |
2006年 | 2551篇 |
2005年 | 2090篇 |
2004年 | 1857篇 |
2003年 | 2387篇 |
2002年 | 3244篇 |
2001年 | 2709篇 |
2000年 | 1472篇 |
1999年 | 1155篇 |
1998年 | 672篇 |
1997年 | 595篇 |
1996年 | 567篇 |
1995年 | 457篇 |
1994年 | 375篇 |
1993年 | 255篇 |
1992年 | 219篇 |
1991年 | 125篇 |
1990年 | 111篇 |
1989年 | 81篇 |
1988年 | 68篇 |
1987年 | 32篇 |
1986年 | 35篇 |
1985年 | 27篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1965年 | 1篇 |
1959年 | 6篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
132.
本文通过分析筼筜湖的自然概况、防汛排涝系统设施及实际运行等资料,提出进一步提高筼筜湖防汛排涝能力的对策。 相似文献
133.
Tian Xiao Qing Huo Liu 《Antennas and Propagation, IEEE Transactions on》2008,56(3):765-773
In this paper, we present an enlarged cell technique (ECT) to avoid the time step reduction encountered in the conformal finite-difference time-domain (CFDTD) method due to small irregular cells truncated by metallic boundaries. We focus our efforts on the discussion of the accuracy and stability of the ECT and its comparison with other conformal methods, especially the one called the uniformly stable conformal (USC) method. We also provide a simplified ECT, which is much easier to implement. In the ECT, a stability criterion is first constructed to identify instable irregular cells, i.e., those having so small an area to cause instability. Those instable cells are then enlarged into their adjacent cells to obtain a large, stable area. Careful treatment is performed on the communication between the intruding and intruded cells in terms of electromotive force by keeping the total electromotive force conservative. This technique is verified by several 3-D numerical experiments. Results show that the ECT is second-order accurate and numerically stable at the regular Courant time step limit. 相似文献
134.
Preparation and Properties of Rare Earth Modified Carbon Black/Natural Rubber Composites 总被引:2,自引:2,他引:0
Lin Yaling Xiao Kongqing Zhang Anqiang Wang Lianshi 《中国稀土学报(英文版)》2005,23(6):720-720
The oxides Eu, Ho, Er and Dy were used to prepare the hydroxides of rare earth modified carbon black. Then natural rubber latex (NRL) was added into the reactor. The system reacted at 85 ℃ with stirring for 1 h to prepare powdered HAF-Ln(OH)3/NR composites. The effects of the kind and content of Ln on the particle size distribution of P [ NR/HAF-Ln (OH)3 ] and mechanical properties of its vulcanizate were studied respectively. It is found that rare earth can help to get the powder of the composite, the product particle with a diameter less than 0.9mm will be get when the composites containing the compound of Ho, Er and Dy with dosage of 1.0, 1.0, O. 5 percent, respectively. The adding of Ln can improve the tensile strength and tear strength of the vulcanizate effectively, what's more, Er and Dy can decrease the permanent set of vulcanizate significantly. The SEM studies shows that P[ NR/HAF-Dy (OH)3 ] vulcanizate shows superior mechanical properties that depend primarily on the absence of free carbon black, the fine dispersion of carbon black in the rubber matrix and better polymer-filler interaction. 相似文献
135.
136.
137.
138.
肖先进 《自动化与仪器仪表》2004,(4):38-42
在对韶关电厂200MW机组DEH系统改造过程中,控制系统采用数字式电液控制系统(DEH),汽机基本控制部分采用一对互为冗余数据处理单元(DPU)完成,并采用专用的硬件来实现超速控制和超速保护功能。汽机保护系统(ETS)采用独立的系统可编程控制器PLC来实现。 相似文献
139.
The effects of yttrium and cerium on microstructures and properties of Nb-Si system composites were investigated by scanning electron microscopy( SEM), energy dispersive spectrum(EDS), X-ray diffraction(XRD) and high temperature oxidation experiments.It is found that the coarse primary silicide phase became finer and more homogeneous with Y and Ce addition.The results of high temperature oxidation experiments show that the oxidation rates of NbSi system composites with an appropriate amount of Y and Ce decrease compared with those of alloys without Y or Ce addition, and oxidation products mainly distribute along the phase boundaries between the Nb solid solution and silicide. 相似文献
140.