首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   47757篇
  免费   2084篇
  国内免费   1929篇
电工技术   1660篇
技术理论   18篇
综合类   5158篇
化学工业   5668篇
金属工艺   1329篇
机械仪表   2288篇
建筑科学   8155篇
矿业工程   3083篇
能源动力   1645篇
轻工业   3660篇
水利工程   2384篇
石油天然气   3878篇
武器工业   263篇
无线电   1708篇
一般工业技术   2460篇
冶金工业   4121篇
原子能技术   152篇
自动化技术   4140篇
  2024年   50篇
  2023年   297篇
  2022年   609篇
  2021年   999篇
  2020年   1021篇
  2019年   685篇
  2018年   638篇
  2017年   844篇
  2016年   1057篇
  2015年   1134篇
  2014年   2737篇
  2013年   2448篇
  2012年   2992篇
  2011年   3576篇
  2010年   3073篇
  2009年   2951篇
  2008年   2531篇
  2007年   3342篇
  2006年   3441篇
  2005年   3154篇
  2004年   2684篇
  2003年   2396篇
  2002年   1943篇
  2001年   1689篇
  2000年   1441篇
  1999年   991篇
  1998年   732篇
  1997年   512篇
  1996年   389篇
  1995年   285篇
  1994年   217篇
  1993年   147篇
  1992年   130篇
  1991年   81篇
  1990年   70篇
  1989年   61篇
  1988年   37篇
  1987年   29篇
  1986年   35篇
  1985年   44篇
  1984年   27篇
  1983年   17篇
  1982年   18篇
  1981年   21篇
  1980年   14篇
  1979年   14篇
  1965年   11篇
  1963年   10篇
  1959年   11篇
  1955年   16篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
61.
2019年底,湖北武汉暴发了2019新型冠状病毒感染疾病(COVID-19),并快速在全国蔓延,且在多个国家发现病例。其感染病例和死亡病例在短时间内快速超过重症急性呼吸综合征(SARS),给中国带来了不可估量的损失。中国科研人员在短时间内,快速锁定病原体为2019-nCoV(或hCoV-19或SARS-CoV-2),并且在不同层面开展了相关抗病毒药物的研发工作。本文介绍了抗2019-nCoV新药研发的现状。同时,鉴于突发病原体的药物研发过程相对迟缓,我们建议对于潜在流行可能性的病原体,其药物研发要具有前瞻性,国家层面要推进广谱药物的研发和临床试验,以应对可能出现的疫情风险。  相似文献   
62.
介绍了动物和植物型非常规蛋白资源的种类及其制备蛋白基木材胶黏剂的研究现状和存在的问题,展望了非常规蛋白胶黏剂的发展前景。  相似文献   
63.
Grand environmental and societal challenges have drawn increasing attention to system innovation and socio-technical transitions. A recent Deep Transitions framework has provided a comprehensive theory of the co-evolutionary patterns of multiple socio-technical systems over the last 250 years. However, so far the framework has not been subjected to systematic empirical exploration. In this paper we address this gap by exploring the co-evolutionary model linking niche-level dynamics, transitions in single systems and ‘great surges of development’, as conceptualized by Schot and Kanger (2018) [1]. For this purpose, we conduct a case study on the historical evolution of mass production in the Transatlantic region from 1765 to 1972. Instead of focusing on dominant technologies or common practices the development of mass production is understood as the emergence of a meta-regime, i.e. a set of mutually aligned rules guiding production activities in multiple socio-technical systems. The results broadly confirm the overall model but also enable to extend the Deep Transitions framework by uncovering new mechanisms and patterns in the variation, diffusion and contestation of meta-regimes.  相似文献   
64.
The present study explored the relation between exchanging social support on online teacher groups and teacher self-efficacy. An online survey was conducted inside a massive Facebook teacher group, and 584 elementary school teachers provided information regarding Facebook use, self-efficacy for creative teaching, and the extent to which they provided and received support on the online teacher group. Results showed that teacher self-efficacy varied as a function of years of teaching experience, length of group membership, and the extent to which teachers provided and received social support on the online teacher group. Furthermore, the providing of online support predicted teacher self-efficacy after taking into account the effects of teaching experience and group membership. The findings are discussed in terms of the features and importance of social support exchange on online teacher support groups.  相似文献   
65.
Like in many industries, knowledge management is the key to the successful developments of new drugs and other commercialized products in the pharmaceutical sector. Prior studies have shown that knowledge management requires effective external knowledge sourcing strategies. We argue that both the geographic distance to external knowledge sources and the diversity of such sources have strong influences on the success of the search process and the development of new drugs. We test these theoretical assumptions by applying several advanced estimation techniques on a combined broad set of data from the U.S. Patent and Trademarks Office (USPTO) and U.S. Food and Drug Administration (FDA). We find empirical evidence that the intensity of external knowledge sourcing activities has a positive effect on new drugs approval and commercialization. Specifically, our models predict that a higher number of references to prior patents increases the probability of a new patented drug to be approved and commercialized. Furthermore, the geographic distance covered in the search for external knowledge also positively contributes to drug commercialization. Important management implications derived from these findings are also discussed in the paper.  相似文献   
66.
我国铅锌矿产资源丰富,生产能力、消费量、出口量居世界前列,是我国的优势矿种。以10个铅锌矿能源资源基地为研究对象,对基地分布、矿山数量、产能结构、开发利用指标、矿业固废循环利用指标等进行了分析研究。研究表明,2018年,我国铅锌矿大型资源基地的矿业集中度和铅锌矿的综合利用率均高于全国平均水平。  相似文献   
67.
为了推进煤矿智能化转型升级,提升煤矿安全生产水平,增强煤矿企业的核心竞争力,对煤矿智能化建设目标和总体框架进行了研究,提出了煤矿智能化建设“四横四纵”总体框架,并详细介绍了智能化的生产系统、高速安全的传输网络系统、智能支撑平台、智慧协同管控系统的煤矿智能化主要系统建设以及安全可靠的运行保障体系、严谨全面的标准规范体系、统一完备的煤矿智能化工作机制以及创新实用的产学研用机制的煤矿智能化体系与机制建设。  相似文献   
68.
This article mainly discusses the research status and development trends of ceramics for automotive disc-brakes. According to the ceramic disc-brakes, various properties and characteristics, including fracture toughness, strength, compactness, corrosion resistance, wear resistance, micro-morphology, and thermal stabilities are analyzed. In the field of disc-brakes research, the research directions of the ceramics, including high-temperature performance, bionic structure, layered structure, porous structure, eutectic performance, superhard structure, and machinability are analyzed. The analysis of ceramics is expected to find disc-brake materials in line with the future development trends.  相似文献   
69.
Tunneling nanotubes (TNTs) are recognized long membrane nanotubes connecting distance cells. In the last decade, growing evidence has shown that these subcellular structures mediate the specific transfer of cellular materials, pathogens, and electrical signals between cells. As intercellular bridges, they play a unique role in embryonic development, collective cell migration, injured cell recovery, cancer treatment resistance, and pathogen propagation. Although TNTs have been considered as potential drug targets for treatment, there is still a long way to go to translate the research findings into clinical practice. Herein, we emphasize the heterogeneous nature of TNTs by systemically summarizing the current knowledge on their morphology, structure, and biogenesis in different types of cells. Furthermore, we address the communication efficiency and biological outcomes of TNT-dependent transport related to diseases. Finally, we discuss the opportunities and challenges of TNTs as an exciting therapeutic approach by focusing on the development of efficient and safe drugs targeting TNTs.  相似文献   
70.
通过对荔浦市境内碳酸盐岩区岩质崩塌及该区域地质环境条件的调查,总结了岩质崩塌的规模、发育高度、控制结构面等发育特征,分析了岩质崩塌形成条件,并判断岩质崩塌的失稳运动特征。本文以一处危岩为例,用无人机进行三维扫描并分析其形成原因及预测其失稳运动特征。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号