全文获取类型
收费全文 | 267847篇 |
免费 | 32425篇 |
国内免费 | 21911篇 |
专业分类
电工技术 | 24442篇 |
技术理论 | 5篇 |
综合类 | 27822篇 |
化学工业 | 32916篇 |
金属工艺 | 17629篇 |
机械仪表 | 19032篇 |
建筑科学 | 20820篇 |
矿业工程 | 10940篇 |
能源动力 | 7036篇 |
轻工业 | 28004篇 |
水利工程 | 9096篇 |
石油天然气 | 10213篇 |
武器工业 | 3877篇 |
无线电 | 30292篇 |
一般工业技术 | 23609篇 |
冶金工业 | 10982篇 |
原子能技术 | 4557篇 |
自动化技术 | 40911篇 |
出版年
2024年 | 1823篇 |
2023年 | 4752篇 |
2022年 | 10880篇 |
2021年 | 14119篇 |
2020年 | 10443篇 |
2019年 | 7305篇 |
2018年 | 7661篇 |
2017年 | 8913篇 |
2016年 | 7830篇 |
2015年 | 12678篇 |
2014年 | 15792篇 |
2013年 | 18537篇 |
2012年 | 22653篇 |
2011年 | 23743篇 |
2010年 | 22299篇 |
2009年 | 20852篇 |
2008年 | 21438篇 |
2007年 | 20381篇 |
2006年 | 17574篇 |
2005年 | 14119篇 |
2004年 | 9919篇 |
2003年 | 6645篇 |
2002年 | 6072篇 |
2001年 | 5320篇 |
2000年 | 4320篇 |
1999年 | 1917篇 |
1998年 | 734篇 |
1997年 | 581篇 |
1996年 | 506篇 |
1995年 | 441篇 |
1994年 | 323篇 |
1993年 | 263篇 |
1992年 | 226篇 |
1991年 | 169篇 |
1990年 | 133篇 |
1989年 | 138篇 |
1988年 | 103篇 |
1987年 | 70篇 |
1986年 | 60篇 |
1985年 | 29篇 |
1984年 | 35篇 |
1983年 | 31篇 |
1982年 | 38篇 |
1981年 | 43篇 |
1980年 | 77篇 |
1979年 | 56篇 |
1976年 | 3篇 |
1965年 | 4篇 |
1959年 | 59篇 |
1951年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
2.
利用纤维床生物反应器(FBB)发酵生产链霉素,对发酵培养基氮源进行了优化,并与传统搅拌发酵进行了比较。结果表明,以可溶性有机氮源大豆蛋白胨作为发酵培养基氮源,并添加一定量蔗糖,可以完全替代黄豆粉,在1 LFBB中发酵96 h时链霉素效价达到5 567 U·mL~(-1)。在整个发酵过程中,所有菌体都被固定在纤维床反应器上,而发酵液保持澄清,这不仅有利于从无菌体的发酵液中进行产物的提取和纯化,也可以重复利用菌体生产次级代谢产物,从而缩短发酵周期,进一步提高链霉素在发酵过程中的体积生产率。 相似文献
3.
Yuchuan Lei 《传热工程》2020,41(9-10):768-778
AbstractA numerical study of condensation heat transfer in curved square and triangle microchannels with various curvatures is conducted. The model is based on the volume of fluid approach and user-defined routines. The predictive accuracy of the numerical results is assessed by comparing the heat transfer coefficient with available correlation. After the validation, the effects of the mass flux and heat flux on heat transfer coefficient are analyzed in detail. Increasing mass flux could strengthen heat transfer performance, while wall heat flux has little effect on condensation heat transfer coefficient. The curved microchannels show an advantage in heat transfer enhancement comparing with the straight ones, and the enhancement performs better in curved microchannels with larger curvatures. Besides, the heat transfer performance could be enhanced in triangle microchannels in comparison with square microchannels. 相似文献
4.
阐述了我国钢管行业进入"新常态"时期面临的主要问题,以及钢管企业经营状态;提出我国钢管企业提高生存能力的方向与开发新领域。建议我国钢管企业主动适应"新常态",及时转型,走差异化发展之路;找准生产产品的发展方向和路径;积极开发新领域,研发新产品。 相似文献
5.
Zenan Yu Julian Moore Jean Calderon Lei Zhai Jayan Thomas 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(39):5289-5295
Cable‐shaped supercapacitors (SCs) have recently aroused significant attention due to their attractive properties such as small size, lightweight, and bendability. Current cable‐shaped SCs have symmetric device configuration. However, if an asymmetric design is used in cable‐shaped supercapacitors, they would become more attractive due to broader cell operation voltages, which results in higher energy densities. Here, a novel coil‐type asymmetric supercapacitor electrical cable (CASEC) is reported with enhanced cell operation voltage and extraordinary mechanical‐electrochemical stability. The CASECs show excellent charge–discharge profiles, extraordinary rate capability (95.4%), high energy density (0.85 mWh cm−3), remarkable flexibility and bendability, and superior bending cycle stability (≈93.0% after 4000 cycles at different bending states). In addition, the CASECs not only exhibit the capability to store energy but also to transmit electricity simultaneously and independently. The integrated electrical conduction and storage capability of CASECS offer many potential applications in solar energy storage and electronic gadgets. 相似文献
6.
Rui ZHAO Weikai LI Tian WANG Ke ZHAN Zheng YANG Ya YAN Bin ZHAO Junhe YANG 《材料科学前沿(英文版)》2020,14(2):188
Effective thermal management of electronic integrated devices with high powder density has become a serious issue, which requires materials with high thermal conductivity (TC). In order to solve the problem of weak bonding between graphite and Cu, a novel Cu/graphite film/Cu sandwich composite (Cu/GF/Cu composite) with ultrahigh TC was fabricated by electro-deposition. The micro-riveting structure was introduced to enhance the bonding strength between graphite film and deposited Cu layers by preparing a rectangular array of micro-holes on the graphite film before electro-deposition. TC and mechanical properties of the composites with different graphite volume fractions and current densities were investigated. The results showed that the TC enhancement generated by the micro-riveting structure for Cu/GF/Cu composites at low graphite content was more effective than that at high graphite content, and the strong texture orientation of deposited Cu resulted in high TC. Under the optimizing preparing condition, the highest in-plane TC reached 824.3 W·m−1·K−1, while the ultimate tensile strength of this composite was about four times higher than that of the graphite film. 相似文献
7.
针对基站柜式空调耗电量大的问题,创造性地使用基站分布式冷却的方式,达到精确送风,节能高效的目的.在应用实践中检验了分布式冷却系统实际节能量和应用效果,总结出分布式冷却系统应用场景和范围,为更大范围推广应用DCS分布式冷却系统提供实践依据. 相似文献
8.
Rectangular section control technology(RSCT)was introduced to achieve high-precision profile control during silicon steel rolling.The RSCT principle and method were designed,and the whole RSCT control strategy was developed.Specifically,RSCT included roll contour design,rolling technology optimization,and control strategy development,aiming at both hot strip mills(HSMs)and cold strip mills(CSMs).Firstly,through the high-performance variable crown(HVC)work roll optimization design in the upper-stream stands and the limited shifting technology for schedule-free rolling in the downstream stands of HSMs,a hot strip with a stable crown and limited wedge,local spot,and single wave was obtained,which was suitable for cold rolling.Secondly,an approximately rectangular section was obtained by edge varying contact(EVC)work roll contour design,edge-drop setting control,and closed loop control in the upper-stream stands of CSMs.Moreover,complex-mode flatness control was realized by coordinating multiple shape-control methods in the downstream stands of CSMs.In addition,the RSCT approach was applied in several silicon-steel production plants,where an outstanding performance and remarkable economic benefits were observed. 相似文献
9.
为检查工程质量,查找输水系统可能存在的问题并消除隐患,保障电站安全运行,福建仙游抽水蓄能电站在投产发电前,要对输水发电系统进行充水试验与放空排水试验,在试验过程中监测输水系统的应力、应变与渗漏水情况。本文以尾水系统为例,介绍了试验所应具备的工程条件、工作程序及技术要求、试验成果分析和存在问题处理等。试验表明,仙游抽水蓄能电站尾水系统设计合理,施工质量优良,结构可靠,可供同类工程参考与借鉴。 相似文献
10.