全文获取类型
收费全文 | 106464篇 |
免费 | 9647篇 |
国内免费 | 5649篇 |
专业分类
电工技术 | 6803篇 |
技术理论 | 5篇 |
综合类 | 8194篇 |
化学工业 | 17261篇 |
金属工艺 | 6104篇 |
机械仪表 | 6626篇 |
建筑科学 | 8873篇 |
矿业工程 | 3223篇 |
能源动力 | 3213篇 |
轻工业 | 7564篇 |
水利工程 | 2047篇 |
石油天然气 | 6333篇 |
武器工业 | 879篇 |
无线电 | 12002篇 |
一般工业技术 | 12256篇 |
冶金工业 | 4573篇 |
原子能技术 | 1260篇 |
自动化技术 | 14544篇 |
出版年
2024年 | 363篇 |
2023年 | 1848篇 |
2022年 | 2961篇 |
2021年 | 4427篇 |
2020年 | 3515篇 |
2019年 | 3089篇 |
2018年 | 3265篇 |
2017年 | 3577篇 |
2016年 | 3066篇 |
2015年 | 4289篇 |
2014年 | 5390篇 |
2013年 | 6139篇 |
2012年 | 6572篇 |
2011年 | 7185篇 |
2010年 | 6452篇 |
2009年 | 6001篇 |
2008年 | 5910篇 |
2007年 | 5488篇 |
2006年 | 5510篇 |
2005年 | 4569篇 |
2004年 | 3632篇 |
2003年 | 3933篇 |
2002年 | 4788篇 |
2001年 | 4036篇 |
2000年 | 2711篇 |
1999年 | 2629篇 |
1998年 | 1929篇 |
1997年 | 1678篇 |
1996年 | 1553篇 |
1995年 | 1266篇 |
1994年 | 1021篇 |
1993年 | 723篇 |
1992年 | 625篇 |
1991年 | 381篇 |
1990年 | 320篇 |
1989年 | 244篇 |
1988年 | 185篇 |
1987年 | 108篇 |
1986年 | 96篇 |
1985年 | 68篇 |
1984年 | 52篇 |
1983年 | 38篇 |
1982年 | 39篇 |
1981年 | 25篇 |
1980年 | 28篇 |
1979年 | 12篇 |
1965年 | 2篇 |
1959年 | 6篇 |
1951年 | 4篇 |
1940年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
92.
93.
Ziqian Wang Yalan Chen Yating He Weidong Jiang Yan Long Guangyin Fan 《International Journal of Hydrogen Energy》2021,46(21):11587-11596
Developing high-efficiency and low-cost catalysts for hydrogen evolution from hydrolysis of ammonia borane (AB) is significant and critical for the exploitation and utilization of hydrogen energy. Herein, the in-situ fabrication of well-dispersed and small bimetallic RuNi alloy nanoparticles (NPs) with tuned compositions and concomitant hydrolysis of AB are successfully achieved by using graphitic carbon nitride (g-C3N4) as a NP support without additional stabilizing ligands. The optimized Ru1Ni7.5/g-C3N4 catalyst exhibits an excellent catalytic activity with a high turnover frequency of 901 min?1 and an activation energy of 28.46 kJ mol?1 without any base additives, overtaking the activities of many previously reported catalysts for AB hydrolysis. The kinetic studies indicate that the AB hydrolysis over Ru1Ni7.5/g-C3N4 is first-order and zero-order reactions with respect to the catalyst and AB concentrations, respectively. Ru1Ni7.5/g-C3N4 has a good recyclability with 46% of the initial catalytic activity retained even after five runs. The high performance of Ru1Ni7.5/g-C3N4 should be assigned to the small-sized alloy NPs with abundant accessible active sites and the synergistic effect between the composition-tuned Ru–Ni bimetals. This work highlights a potentially powerful and simple strategy for preparing highly active bimetallic alloy catalysts for AB hydrolysis to generate hydrogen. 相似文献
94.
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
95.
Climate change raises many concerns for urban water management because of the effects on all aspects of the hydrological cycle. Urban water infrastructure has traditionally been designed using historical observations and assuming stationary climatic conditions. The capability of this infrastructure, whether for storm-water drainage, or water supply, may be over- or under-designed for future climatic conditions. In particular, changes in the frequency and intensity of extreme rainfall events will have the most acute effect on storm-water drainage systems. Therefore, it is necessary to take future climatic conditions into consideration in engineering designs in order to enhance water infrastructure investment planning practices in a long time horizon. This paper provides the initial results of a study that is examining ways to enhance urban infrastructure investment planning practices against changes in hydrologic regimes for a changing climate. Design storms and intensity-duration-frequency curves that are used in the engineering design of storm-water drainage systems are developed under future climatic conditions by empirically adjusting the general circulation model output, and using the Gumbel distribution and the Chicago method. Simulations are then performed on an existing storm-water drainage system from NE Calgary to investigate the resiliency of the system under climate change. 相似文献
96.
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
97.
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
98.
99.
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
100.
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