全文获取类型
收费全文 | 118235篇 |
免费 | 10220篇 |
国内免费 | 5270篇 |
专业分类
电工技术 | 7007篇 |
技术理论 | 5篇 |
综合类 | 7921篇 |
化学工业 | 19637篇 |
金属工艺 | 6891篇 |
机械仪表 | 7771篇 |
建筑科学 | 9048篇 |
矿业工程 | 3863篇 |
能源动力 | 3297篇 |
轻工业 | 7581篇 |
水利工程 | 2070篇 |
石油天然气 | 7596篇 |
武器工业 | 1035篇 |
无线电 | 13540篇 |
一般工业技术 | 14222篇 |
冶金工业 | 5429篇 |
原子能技术 | 1191篇 |
自动化技术 | 15621篇 |
出版年
2024年 | 469篇 |
2023年 | 1996篇 |
2022年 | 3246篇 |
2021年 | 4793篇 |
2020年 | 3728篇 |
2019年 | 3162篇 |
2018年 | 3483篇 |
2017年 | 3856篇 |
2016年 | 3436篇 |
2015年 | 4598篇 |
2014年 | 5815篇 |
2013年 | 6755篇 |
2012年 | 7515篇 |
2011年 | 8313篇 |
2010年 | 7051篇 |
2009年 | 6660篇 |
2008年 | 6498篇 |
2007年 | 6174篇 |
2006年 | 6634篇 |
2005年 | 5535篇 |
2004年 | 3901篇 |
2003年 | 3381篇 |
2002年 | 3160篇 |
2001年 | 2796篇 |
2000年 | 2817篇 |
1999年 | 3181篇 |
1998年 | 2748篇 |
1997年 | 2352篇 |
1996年 | 2103篇 |
1995年 | 1752篇 |
1994年 | 1474篇 |
1993年 | 1022篇 |
1992年 | 827篇 |
1991年 | 613篇 |
1990年 | 461篇 |
1989年 | 372篇 |
1988年 | 296篇 |
1987年 | 185篇 |
1986年 | 152篇 |
1985年 | 97篇 |
1984年 | 60篇 |
1983年 | 44篇 |
1982年 | 55篇 |
1981年 | 33篇 |
1980年 | 37篇 |
1979年 | 16篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 14篇 |
1975年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
101.
针对目标探测类空间红外相机大范围成像、高灵敏度探测、高精度定位等应用需求,文中提出采用像方远心光路和低温光学技术结合的解决方案,设计了物方视场角8°×8°、入瞳口径265 mm、工作温度200 K的像方远心折射式光学系统。镜头最大口径280 mm,采用多级分散的弹性支撑设计,解决大口径低温透镜装框、透镜组件支撑和镜头整体安装各环节的热应力卸载问题。在保证高刚度和低漏热的情况下,使低温下透镜的热应力对镜头能量集中度的影响降低到可接受范围内。镜头完成装调及室温下像质确认后,进行了力学振动试验,并将其制冷到200 K水平测试像质,测试结果表明,镜头能量集中度达到轴上75%,边缘视场72%。 相似文献
103.
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
104.
Yingchao Hu Wenqiang Liu Yuandong Yang Xianliang Tong Qianjun Chen Zijian Zhou 《Ceramics International》2018,44(14):16668-16677
Li4SiO4 sorbents for high-temperature CO2 removal have drawn extensive attention owing to their potential application in carbon capture and storage (CCS). The major challenge in the application lies in the poor CO2 capture performance under realistic conditions of low CO2 concentrations, owing to the dense structure and poor porosity. In this work, Li4SiO4 sorbents were prepared with porous micromorphologies and large contact areas using a variety of organometallic Li-precursors, achieving fast CO2 sorption kinetics, high capacity and excellent cyclic stability at a low CO2 concentration (15?vol%). It was found that a high conversion of ~?74% was maintained for pure Li4SiO4 even after 100 sorption/desorption cycles. Moreover, by doping with Na2CO3 to reduce the CO2 diffusion resistance, the conversion of the sorbent was further enhanced to 93.2%. The enhancement mechanism of alkali carbonate have been proven here to be ascribed to the formation of the eutectic melt of Li/Na carbonates, the existence and function of which has been confirmed in this study. 相似文献
105.
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
106.
入侵检测是保障网络安全的重要手段,针对现有入侵检测系统中告警数量多、协调性差等问题,论文提出了一种具有告警融合与关联功能的告警处理系统模型,该模型冗余告警量少、整体检测能力强,并能进行攻击企图的预测,能有效提高入侵检测的效率,有助于进一步增强网络的健壮性。 相似文献
107.
Wang Xuping Wang Jiyang Hu Xiaobo Zhang Jianxiu Zhao Hongyang Huang Wanxia Zhu Peiping 《中国稀土学报(英文版)》2006,24(Z1)
Langasite single crystal was grown by the Czochralski method and its perfection was assessed by white beam synchrotron radiation topography. It is found that the growth core and the growth striations are the primary growth defects and they show strong X-ray kinematical contrast in the topographs. Another typical defect in LGS crystal is dislocation. The formation mechanisms of these growth defects in LGS crystals were discussed. 相似文献
108.
109.
110.