全文获取类型
收费全文 | 312795篇 |
免费 | 24262篇 |
国内免费 | 12552篇 |
专业分类
电工技术 | 17459篇 |
技术理论 | 33篇 |
综合类 | 19489篇 |
化学工业 | 53476篇 |
金属工艺 | 18194篇 |
机械仪表 | 20115篇 |
建筑科学 | 24897篇 |
矿业工程 | 10425篇 |
能源动力 | 8812篇 |
轻工业 | 18525篇 |
水利工程 | 5414篇 |
石油天然气 | 21151篇 |
武器工业 | 2472篇 |
无线电 | 34201篇 |
一般工业技术 | 36770篇 |
冶金工业 | 16058篇 |
原子能技术 | 3097篇 |
自动化技术 | 39021篇 |
出版年
2024年 | 1325篇 |
2023年 | 5069篇 |
2022年 | 8853篇 |
2021年 | 12652篇 |
2020年 | 9390篇 |
2019年 | 7966篇 |
2018年 | 8914篇 |
2017年 | 10056篇 |
2016年 | 8744篇 |
2015年 | 12264篇 |
2014年 | 15076篇 |
2013年 | 18015篇 |
2012年 | 19576篇 |
2011年 | 21184篇 |
2010年 | 18372篇 |
2009年 | 17375篇 |
2008年 | 16935篇 |
2007年 | 16450篇 |
2006年 | 17208篇 |
2005年 | 15158篇 |
2004年 | 9854篇 |
2003年 | 8746篇 |
2002年 | 8302篇 |
2001年 | 7405篇 |
2000年 | 7623篇 |
1999年 | 8839篇 |
1998年 | 7003篇 |
1997年 | 5962篇 |
1996年 | 5581篇 |
1995年 | 4592篇 |
1994年 | 3821篇 |
1993年 | 2706篇 |
1992年 | 2181篇 |
1991年 | 1635篇 |
1990年 | 1195篇 |
1989年 | 951篇 |
1988年 | 777篇 |
1987年 | 529篇 |
1986年 | 402篇 |
1985年 | 271篇 |
1984年 | 187篇 |
1983年 | 124篇 |
1982年 | 133篇 |
1981年 | 93篇 |
1980年 | 75篇 |
1979年 | 30篇 |
1978年 | 2篇 |
1965年 | 2篇 |
1959年 | 4篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
��Consulting the relevant documents at home and abroad,the author finisheid the derivation of quations about critical flow quantity,critical flow rate,contrast flow quantity,contrast flow rate which are necessary to the continuous water withdrawal through the flow string with different diameters and the rational flow string formula that should be selected when the contrust parameter1.The author also works out the solving programme for TI-59 computer and designs and draws up the nomograrn of mathematical mode.The evident economical results have been obtained from practice of optimizing the flow string for water withdrawal in gas production in Southern Sichuan and from studying the gas-water two-phase flow characteristics through vertical pipe. 相似文献
992.
Failure analysis and a study of the wear mechanism were performed on a heavily loaded carburized gear with some unusual features. The analysis showed that the different failure forms on the tooth surface of the gear were dependent on the sub-surface shearing stress, the lubrication conditions and the surface roughness. Delaminations formed on the addendum surface were the main reason for the gear failure. A suggestion for improvement has been tried, and a desirable result has been obtained. 相似文献
993.
994.
995.
Zheng Qi; Yang Wan-Ming; Yu Wen-Hao; Cai Bin; Teng Xin-Chen; Xie Yi; Sun Hong-Zhe; Zhang Ming-Jie; Huang Zhong-Xian 《Protein engineering, design & selection : PEDS》2003,16(12):865-870
MT3 shows apparently different properties and function fromMT1 even though they have 70% sequence homology. Possibly thetwo inserts, Thr5 and a negatively charged hexapeptide at position-55in MT3, play important roles. A series of MT3 variants aroundthe EAAEAE hexapeptide have been prepared by site-directed mutagenesisand their properties and reactivity towards pH, EDTA and DTNBhave been studied. Our detailed studies revealed that the EAAEAEinsert is essential to the property of MT3. It is the hexapeptideinsert, to some extent, making the MT3 相似文献
996.
ZhangXiaojing QinRuyi LiuJinlong 《中国炼油与石油化工》2003,(4):31-35
This article refers to the procedure for selection, evaluation and development of the LADS-D desorption agent associated with the LADS-A adsorbent used in the non-hydroprocessing adsorptive desulfurization (LADS) process for FCC naphtha developed by LPEC Refining Research Institute. The LADS-D desorption agent can effectively remove the sulfides adsorbed on the LADS-A adsorbent. The saturated LADS-A adsorbent can be instantly regenerated by the LADS-D desorption agent to recover its adsorption activity. The LADS-D desorption agent can not only effectively remove all impurities adsorbed on the adsorbent, but also has strong ability to dissolve the impurities to keep a stable desorption efficiency of adsorbent to be basically commensurate with fresh adsorbent after extended use. 相似文献
998.
999.
A novel methanol-tolerant oxygen-reduction catalyst, Iridium-selenium (Ir-Se) chalcogenide, was synthesized by chemical precipitation in an organic solvent. Auger electron spectroscopy (AES) analysis confirmed that the synthesized Ir-Se chalcogenide had a chemical formula of Ir4Se. This chalcogenide showed strong catalytic activity towards the oxygen reduction reaction (ORR) and a high methanol tolerance. It was found that most of the oxygen could be directly reduced to water through a four-electron pathway with less than 10% hydrogen peroxide (H2O2) being produced during the ORR. The improvement in catalytic activity of the Ir-Se chalcogenide in comparison with that of pure Ir might be attributed to the effect of a bimetallic interaction. 相似文献
1000.
利用二元理论,在准正交线法轴面流动计算以及逐点积分法的基础上,编程实现了离心泵叶轮水力设计。设计提出了新的过流断面线计算方法,克服了传统过流断面面积内切圆检查方法效率低,精度差的缺点。改进了传统的逐点积分法,设计可以方便地对叶片包角进行控制。叶片采用给定其圆周方向厚度的方法进行加厚,解决了轴面流动计算中排挤系数无法确定的问题。对加厚后的叶片头部出现尖锐形状进行了修圆处理。 相似文献