全文获取类型
收费全文 | 84364篇 |
免费 | 7007篇 |
国内免费 | 3698篇 |
专业分类
电工技术 | 3114篇 |
技术理论 | 5篇 |
综合类 | 6542篇 |
化学工业 | 16980篇 |
金属工艺 | 8617篇 |
机械仪表 | 5437篇 |
建筑科学 | 6296篇 |
矿业工程 | 3099篇 |
能源动力 | 1949篇 |
轻工业 | 7109篇 |
水利工程 | 1411篇 |
石油天然气 | 3663篇 |
武器工业 | 675篇 |
无线电 | 3872篇 |
一般工业技术 | 7253篇 |
冶金工业 | 9076篇 |
原子能技术 | 515篇 |
自动化技术 | 9456篇 |
出版年
2024年 | 167篇 |
2023年 | 901篇 |
2022年 | 1853篇 |
2021年 | 2239篇 |
2020年 | 2461篇 |
2019年 | 1887篇 |
2018年 | 1604篇 |
2017年 | 2177篇 |
2016年 | 2657篇 |
2015年 | 2817篇 |
2014年 | 5106篇 |
2013年 | 5235篇 |
2012年 | 6235篇 |
2011年 | 6529篇 |
2010年 | 4880篇 |
2009年 | 4953篇 |
2008年 | 4209篇 |
2007年 | 5552篇 |
2006年 | 5288篇 |
2005年 | 4474篇 |
2004年 | 3867篇 |
2003年 | 3453篇 |
2002年 | 3006篇 |
2001年 | 2629篇 |
2000年 | 2209篇 |
1999年 | 1780篇 |
1998年 | 1380篇 |
1997年 | 1077篇 |
1996年 | 965篇 |
1995年 | 774篇 |
1994年 | 651篇 |
1993年 | 423篇 |
1992年 | 372篇 |
1991年 | 294篇 |
1990年 | 200篇 |
1989年 | 173篇 |
1988年 | 121篇 |
1987年 | 76篇 |
1986年 | 65篇 |
1985年 | 48篇 |
1984年 | 44篇 |
1983年 | 36篇 |
1982年 | 22篇 |
1981年 | 20篇 |
1980年 | 28篇 |
1979年 | 13篇 |
1977年 | 14篇 |
1964年 | 9篇 |
1961年 | 9篇 |
1951年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
To effectively analyze the impact of continuous business interruption on the information system,an information system business affecting impact evaluation method (IBAIE) is proposed.First,we identify the main businesses of the system and quantify their vulnerability.Then,we take the businesses as the nodes of network topology and weight nodes based on the business significance.The orderly association between businesses is taken as the edges which are weighted based on the association between asset and business,and the directed weighted business network topology is obtained.Finally,the method of directed weighted network structure entropy is used to evaluate the change of system business network structure during the period from business interruption to recovery.Experiments show that this method has obvious advantages in evaluating accuracy compared to other methods,and can be applied in ensuring information system security. 相似文献
103.
Huifan Liu Sufen Li Yuming Zhong Siqi Lan Charles Stephen Brennan Qin Wang Lukai Ma 《International Journal of Food Science & Technology》2021,56(11):5629-5638
We characterised the formation and dynamic changes in the main aroma compounds produced during the manufacturing process of Jinxuan and Qingxin oolong tea. Thirty-five aroma compounds were investigated. Subsequent principal component and cluster analyses showed that the fresh leaves, spread leaves and rocked leaves of the two varieties of tea were distinguished from each other. Particularly, the aldehyde and ‘other’ compounds showed the highest correlation coefficients (0.71 and −0.70) among the principal. The heat map showed that the proportions of acetic acid, 3-methylbutanal and 2-methylbutanal significantly changed during the manufacturing process of the two tea varieties. The key amino acids (isoleucine, leucine, valine and aspartic acid) and enzymes (branched-chain amino acid aminotransferase, aspartate aminotransferase and acetaldehyde dehydrogenase) involved in the synthesis of 3-methylbutanal and 2-methylbutanal differed between the two varieties during manufacture. Our study reveals the characteristics of different varieties of oolong tea and their aroma formation after manufacture using the same process. 相似文献
104.
针对现有商业化牦牛绒脱色过程复杂、脱色时间长等问题,提出新型过氧化氢/过硫酸铵体系牦牛绒脱色工艺。在尽可能提高纤维白度的前提下尽量减少纤维损伤,通过单因素试验确定了脱色时间、过硫酸铵用量和试剂pH值,对脱色工艺进行探讨并与商业化脱色牦牛绒进行比较。结果表明:采用过硫酸铵质量浓度为400 g/L,试剂pH值为9,在室温下脱色为180 min可达到商业脱色牦牛绒的效果,脱色时间节省至原来的1/8;脱色机制分析发现,脱色过程中硫酸根自由基起主要作用,羟基自由基起次要作用。该脱色工艺简单,为牦牛绒高值化利用提供了新的解决方案。 相似文献
105.
106.
107.
《International Journal of Hydrogen Energy》2019,44(35):19141-19152
Thermochemical hydrogen production has attracted considerable interest as a clean energy solution to address the challenges of climate change and environmental sustainability. The thermochemical water-splitting iodine-sulfur (IS) process uses heat from nuclear or solar power and thus is a promising next-generation thermochemical hydrogen production method that is independent of fossil fuels and can provide energy security. This paper presents the current state of research and development (R&D) of the IS process based on membrane techniques using solar energy at a medium temperature of 600 °C. Membrane design strategies have the most potential for making the IS process using solar energy highly efficient and economical and are illustrated here in detail. Three aspects of membrane design proposed herein for the IS process have led to a considerable improvement of the total thermal efficiency of the process: membrane reactors, membranes, and reaction catalysts. Experimental studies in the applications of these membrane design techniques to the Bunsen reaction, sulfuric acid decomposition, and hydrogen iodide decomposition are discussed. 相似文献
108.
以Orbit专利分析平台为主要研究工具,从专利文献中抽取专利数量指标和专利质量指标来构建评价薄板坯连铸连轧技术竞争力和企业创新能力的指标体系,结合其他文献研究的成果,从产业发展的实际出发做出分析,系统揭示了自薄板坯连铸连轧技术开发以来的技术进步、专利布局、发展演化、国内外发展现状、技术竞争实力等,有助于在专利文献提供的线索启发下开发新产品、新技术,从而有效提高研发效率。 相似文献
109.
C. Doga Demirhan William W. Tso Joseph B. Powell Efstratios N. Pistikopoulos 《American Institute of Chemical Engineers》2019,65(7):e16498
Current ammonia production technologies have a significant carbon footprint. In this study, we present a process synthesis and global optimization framework to discover the efficient utilization of renewable resources in ammonia production. Competing technologies are incorporated in a process superstructure where biomass, wind, and solar routes are compared with the natural gas-based reference case. A deterministic global optimization-based branch-and-bound algorithm is used to solve the resulting large-scale nonconvex mixed-integer nonlinear programming problem (MINLP). Case studies for Texas, California, and Iowa are conducted to examine the effects of different feedstock prices and availabilities. Results indicate that profitability of ammonia production is highly sensitive to feedstock and electricity prices, as well as greenhouse gas (GHG) restrictions. Under strict 75% GHG reductions, biomass to ammonia route is found to be competitive with natural gas route, whereas wind and solar to ammonia routes require further improvement to compete with those two routes. © 2018 American Institute of Chemical Engineers AIChE J, 65: e16498 2019 相似文献
110.
Catalysts of quaternary composition have been prepared and tested for the Sabatier process. For catalyst syntheses the following techniques have been used: sol‐gel methods, wet impregnation and incipient wetness impregnation. The Sabatier reaction was carried out at temperatures between 520 K and 670 K, pressures of 15 bar and 30 bar using a mixture H2:CO2 of 4:1. Activity screening of the microscale wall catalysts was performed by a custom‐built 10‐fold parallel gas‐flow microreactor setup in sequential operating mode. To analyze the gas phase compositions GC‐FID was used. 相似文献