全文获取类型
收费全文 | 15007篇 |
免费 | 1391篇 |
国内免费 | 882篇 |
学科分类
工业技术 | 17280篇 |
出版年
2024年 | 49篇 |
2023年 | 287篇 |
2022年 | 456篇 |
2021年 | 667篇 |
2020年 | 536篇 |
2019年 | 424篇 |
2018年 | 465篇 |
2017年 | 526篇 |
2016年 | 458篇 |
2015年 | 643篇 |
2014年 | 801篇 |
2013年 | 886篇 |
2012年 | 940篇 |
2011年 | 1058篇 |
2010年 | 923篇 |
2009年 | 881篇 |
2008年 | 838篇 |
2007年 | 842篇 |
2006年 | 855篇 |
2005年 | 718篇 |
2004年 | 498篇 |
2003年 | 405篇 |
2002年 | 426篇 |
2001年 | 378篇 |
2000年 | 428篇 |
1999年 | 386篇 |
1998年 | 277篇 |
1997年 | 243篇 |
1996年 | 229篇 |
1995年 | 168篇 |
1994年 | 147篇 |
1993年 | 94篇 |
1992年 | 79篇 |
1991年 | 69篇 |
1990年 | 40篇 |
1989年 | 42篇 |
1988年 | 31篇 |
1987年 | 18篇 |
1986年 | 17篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1965年 | 1篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 818 毫秒
1.
飞机从一个航段飞向下一个航段时,需要对下个航段是否激活进行判断.提出了一种新的飞行计划航段自动激活方法,通过获取飞机当前位置及其磁差,并结合临近的3个航路点对应位置的磁差经纬度,分别计算3个航路点与飞机位置对应的磁航向角,通过磁航向角之间做差进行比较,进而判断是否被激活.算法推导完成后,通过基于模型的系统工程工具SCADE SUITE进行了建模,并结合杰普逊航图进行了实际数据采样与仿真.仿真结果表明:该航段自动激活方法能够有效稳定地激活下一航段,比传统方法计算简便,方法实用有效.已在实际飞行中成功应用,达到了预期效果. 相似文献
2.
3.
Electronic Commerce Research - We consider a platform providing free content for users and earning profit from the sale of advertising. The platform can collect and analyze personal data to... 相似文献
4.
Mitigating gibbsite particle cracking and breakage during industrial alumina production can increase the quality of smelter grade alumina product by reducing the ultrafine particle content. Therefore, it is essential to investigate the particle cracking during static calcination and the breakage of calcined gibbsite particles under external force. In this work, we investigated the impact of the calcination ramping rate and the crystallite size on gibbsite particle cracking during static calcination. A slow ramping rate and a large pristine crystallite size tend to increase particle cracking. Apart from the study of particle cracking behaviour, we also investigated the breakage of calcined gibbsite particle under external force. Cracks on the particle surface can initiate breakage within the crystallite and along the grain boundary under external force. The breakage within crystallite occurs as the cleavage of the crystallite, while the breakage along the grain boundary leads to the shedding of a whole crystallite. We further explored the factors influencing the strength of calcined gibbsite particles. With increasing calcination temperature, the strength of particle increases when gibbsite converts to boehmite, and then decreases when boehmite converts into amorphous alumina. Particles containing smaller crystallites and calcined with fast ramping rates exhibit higher resistance to breakage. 相似文献
5.
6.
Zhongyu Qiu Xiaowen Ge Naibao Huang Shixian Zhou Junjie Zhang Jiaping Xuan 《International Journal of Hydrogen Energy》2021,46(3):2952-2959
Polyethylene oxide (PEO)-polypropylene oxide (PPO)-polyethylene oxide block copolymer having different molecular weights are used as precursors of carbon materials to prepare Hollow -Derivatives carbon material as an electrocatalyst through block copolymer self-assembly. The composition and microstructure of the prepared catalysts are shown by Raman spectroscopy, X-ray diffraction (XRD), Test of nitrogen adsorption and desorption curves, High resolution transmission electron microscopy (HR-TEM) and scanning electron microscopy (HR-SEM). Oxygen was passed into alkaline electrolyte solution until the solution reached saturation state. With molecular weight increasing, the obtained sample gradually changed from block to hollow and spherical. When the molecular weight was 12600 g mol?1, the evenly hollow carbon nanocages was acquired (C-12600). In O2 saturated alkaline electrolyte (0.1 M KOH solution), C-12600's limited current density,half-wave potential and initial potential are 5.23 mA cm?2@0.4 V, 0.72 V and 0.81 V, respectively. And most important is that half-wave potential and onset potential have barely change after 2000 cycles of cyclic voltammetry. As a result, the porous carbon materials exhibited excellent electrocatalytic activity while maintaining high stability in alkaline KOH solution. 相似文献
7.
8.
9.