全文获取类型
收费全文 | 71773篇 |
免费 | 7110篇 |
国内免费 | 4609篇 |
专业分类
电工技术 | 4853篇 |
技术理论 | 3篇 |
综合类 | 6132篇 |
化学工业 | 11248篇 |
金属工艺 | 3979篇 |
机械仪表 | 4205篇 |
建筑科学 | 6112篇 |
矿业工程 | 1974篇 |
能源动力 | 2176篇 |
轻工业 | 6294篇 |
水利工程 | 1498篇 |
石油天然气 | 3404篇 |
武器工业 | 602篇 |
无线电 | 8496篇 |
一般工业技术 | 7820篇 |
冶金工业 | 3052篇 |
原子能技术 | 1009篇 |
自动化技术 | 10635篇 |
出版年
2024年 | 330篇 |
2023年 | 1285篇 |
2022年 | 2221篇 |
2021年 | 2987篇 |
2020年 | 2360篇 |
2019年 | 2140篇 |
2018年 | 2197篇 |
2017年 | 2492篇 |
2016年 | 2078篇 |
2015年 | 2992篇 |
2014年 | 3718篇 |
2013年 | 4234篇 |
2012年 | 4591篇 |
2011年 | 4789篇 |
2010年 | 4555篇 |
2009年 | 4221篇 |
2008年 | 4207篇 |
2007年 | 3978篇 |
2006年 | 3752篇 |
2005年 | 3100篇 |
2004年 | 2632篇 |
2003年 | 3082篇 |
2002年 | 3981篇 |
2001年 | 3356篇 |
2000年 | 1922篇 |
1999年 | 1476篇 |
1998年 | 909篇 |
1997年 | 769篇 |
1996年 | 732篇 |
1995年 | 588篇 |
1994年 | 487篇 |
1993年 | 315篇 |
1992年 | 286篇 |
1991年 | 168篇 |
1990年 | 155篇 |
1989年 | 113篇 |
1988年 | 84篇 |
1987年 | 39篇 |
1986年 | 41篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1980年 | 17篇 |
1979年 | 7篇 |
1977年 | 1篇 |
1965年 | 1篇 |
1959年 | 6篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
51.
Xiangrong Ma Rui Dang Ning Yang Xiao Li Ya zhang Ying Gong Zhipan Liu Wei Guo Yuanyuan Zhang Chunyan Li 《International Journal of Hydrogen Energy》2021,46(44):22842-22851
The high cost of noble metal catalysts has been a great bottleneck for the catalyst industry. Using the noble metal at a single-atom level for catalytic applications could dramatically decrease the cost. The impacts of single Pt atoms on the photocatalytic performance of Ag3VO4 have been investigated and reported. In this report, single Pt atoms were anchored on the surface of Ag3VO4 (AVO) as a cocatalyst, and the resultant composite photocatalyst has been studied for photocatalytic H2 production from water driven by visible light. The as-prepared AVO particles are hollow nanospheres in the monoclinic phase with a bandgap of 2.20 eV. The light absorption edge of AVO/Pt is slightly red-shifted compared to that of the pristine AVO, indicating more visible light absorption of AVO/Pt. The XPS peaks of Ag, V, and Pt exhibit a significant shift after AVO and Pt get into contact, suggesting the strong interaction between the surface Ag and V atoms, and single Pt atoms. After 3-h illumination, the photocatalytic H2 evolution amount from AVO/Pt is improved up to 1400 μmol, which is 2.8 times that on the bare AVO. Such efficient photocatalytic H2 evolution on AVO/Pt is still maintained after five reaction cycles. The better photocatalytic performance of AVO/Pt has been attributed to the more efficient visible light utilization and the lower interfacial charge transfer resistance, as demonstrated in the DRS and EIS spectra. The presence of the surface Pt atoms also leads to a higher amount of reactive radicals, which could efficiently promote the surface redox reactions. 相似文献
52.
53.
The titanium carbides are potential candidates to achieve both high hardness and refractory property. We carried out a structural search for titanium carbides at three pressures of 0 GPa, 30 GPa and 50 GPa. A phase diagram of the Ti-C system at 0 K was obtained by elucidating formation enthalpies as a function of compositions, and their mechanical and metallic properties of titanium carbides were investigated systematically. We also discussed the relation of titanium concentration to the both mechanical and metallic properties of titanium carbides. It has been found that the average valence electron density and tractility improved at higher concentrations of titanium, while the degree of covalent bonding directionality decreased. To this effect, the hardness of titanium carbide decreases as the content of titanium increases. Our results indicated that the titanium content significantly affected the metallic properties of the Ti-C system. 相似文献
54.
宁东供水工程供水水泵共有卧式和立式离心泵2种方案可供选择,也是工程论证时争论的焦点,经综合比较及主机设备的国际招标,最终确定了奥地利安德里兹公司的卧式双吸中开式离心泵为宁东供水工程的供水水泵。 相似文献
55.
当前脉冲发生器里的脉冲形成器件,大部分是用火花气隙(spark gap)和高压电子开关(high voltageswitch).采用火花气隙充当脉冲形成器件有很多弊病:(1)火花气隙在低于1kV时,在机械和电气上不稳定,所以对低于2kV的试验电压要通过分压器来得到. 相似文献
56.
Al2O3陶瓷激光铣削试验研究 总被引:9,自引:1,他引:8
采用Nd∶YAG脉冲激光器对Al2 O3陶瓷进行铣削加工试验。系统研究了工艺参数对铣削量和铣削面质量的影响规律 ,并利用优化的铣削工艺对Al2 O3陶瓷进行多种形状的铣削加工。 相似文献
57.
概述了Windows2000即插即用系统组成及其实现过程,结合实例介绍了Windows2000设备驱动程序如何支持用户即插即用的功能。 相似文献
58.
In this paper, we consider the problem of designing optimal asynchronous wake-up schedules to facilitate distributed power management and neighbor discovery in multihop wireless networks. We first formulate it as a block design problem and derive the fundamental trade-offs between wake-up latency and the average duty cycle of a node. After the theoretical foundation is laid, we then devise a neighbor discovery and schedule bookkeeping protocol that can operate on the optimal wake-up schedule derived. To demonstrate the usefulness of asynchronous wake-up, we investigate the efficiency of neighbor discovery and the application of on-demand power management, which overlays a desirable communication schedule over the wake-up schedule mandated by the asynchronous wake-up mechanism. Simulation studies demonstrate that the proposed asynchronous wake-up protocol has short discovery time which scales with the density of the network; it can accommodate various traffic characteristics and loads to achieve an energy savings that can be as high as 70 percent, while the packet delivery ratio is comparable to that without power management. 相似文献
59.
SO4^2-/ZrO2固体超强酸的制备及其催化合成ETBE的研究 总被引:5,自引:2,他引:3
采用沉淀一浸渍法制备了负载型SO4^2-/ZrO2固体超强酸催化剂,运用IR、XRD等方法表征所制备催化剂的物化性质。结果表明,所制备的催化剂具有固体超强酸催化剂的特征,酸性与焙烧温度有关,适当提高焙烧温度有利于样品酸强度的提高,但焙烧温度过高会导致脱硫;浸渍液H2SO4浓度高有利于提高催化剂的硫含量,但是浓度过高,会在催化剂上形成硫酸盐,从而降低催化剂的比表面积和酸性。采用制备的催化剂气相催化乙醇与叔丁醇合成乙基叔丁基醚反应,乙基叔丁基醚的选择性为54.71%。 相似文献
60.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献