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   117487篇
  免费   3291篇
  国内免费   439篇
电工技术   1026篇
综合类   2333篇
化学工业   18535篇
金属工艺   5476篇
机械仪表   3777篇
建筑科学   3120篇
矿业工程   639篇
能源动力   1785篇
轻工业   9343篇
水利工程   1551篇
石油天然气   464篇
武器工业   5篇
无线电   10458篇
一般工业技术   22081篇
冶金工业   10634篇
原子能技术   435篇
自动化技术   29555篇
  2023年   320篇
  2022年   357篇
  2021年   894篇
  2020年   744篇
  2019年   859篇
  2018年   15546篇
  2017年   14434篇
  2016年   11222篇
  2015年   1742篇
  2014年   1598篇
  2013年   3100篇
  2012年   5138篇
  2011年   11092篇
  2010年   9712篇
  2009年   6840篇
  2008年   7960篇
  2007年   8847篇
  2006年   958篇
  2005年   1900篇
  2004年   1770篇
  2003年   1748篇
  2002年   1115篇
  2001年   540篇
  2000年   587篇
  1999年   509篇
  1998年   2445篇
  1997年   1673篇
  1996年   1098篇
  1995年   655篇
  1994年   510篇
  1993年   595篇
  1992年   234篇
  1991年   241篇
  1990年   163篇
  1989年   171篇
  1988年   186篇
  1987年   157篇
  1986年   133篇
  1985年   170篇
  1984年   147篇
  1983年   120篇
  1982年   158篇
  1981年   177篇
  1980年   187篇
  1979年   117篇
  1978年   115篇
  1977年   316篇
  1976年   660篇
  1975年   87篇
  1973年   100篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
Journal of Chemical Ecology - Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical...  相似文献   
4.
Water Resources Management - The water evaluation and planning (WEAP) approach and the invasive weed optimization algorithm (IWOA) are herein employed to determine the optimal operating policies in...  相似文献   
5.
Photoresponsive biomaterials are experiencing a transition from in vitro models to in vivo demonstrations that point toward clinical translation. Dynamic hydrogels for cell encapsulation, light-responsive carriers for controlled drug delivery, and nanomaterials containing photosensitizers for photodynamic therapy are relevant examples. Nonetheless, the step to the clinic largely depends on their combination with technologies to bring light into the body. This review highlights the challenge of photoactivation in vivo, and presents strategies for light management that can be adopted for this purpose. The authors’ focus is on technologies that are materials-driven, particularly upconversion nanoparticles that assist in “direct path” light delivery through tissue, and optical waveguides that “clear the path” between external light source and in vivo target. The authors’ intention is to assist the photoresponsive biomaterials community transition toward medical technologies by presenting light delivery concepts that can be integrated with the photoresponsive targets. The authors also aim to stimulate further innovation in materials-based light delivery platforms by highlighting needs and opportunities for in vivo photoactivation of biomaterials.  相似文献   
6.
The constructive analysis of Madrid's old timber-framed collective courtyard buildings, whether demolished, preserved intact, or enlarged, has achieved the dating of relevant case studies. New parameters established in this study set a chronology based on front sector original projects: old (1737–1788), pre-modern (1788–1847) and modern (1847–1892). The on-site inspection and archival research point to ongoing misleading construction in the historic Southern area. Some modern corralas erected on top of pre-existing buildings confirm the initial hypothesis. First dimensioning rules for new façades and the stability required in old ones before adding new storeys, maintaining the original masonry or double-layered system, are discovered. Undated buildings suggest their possible origin a la malicia and a later transformation into transitional corralas. Finally, an analysis of the demolished courtyards narrows down the dating and points to new conjectures in some preserved by showing their uneven layout, old features, and structural discordances in each sector.  相似文献   
7.
Recent advancements in isolation and stacking of layered van der Waals materials have created an unprecedented paradigm for demonstrating varieties of 2D quantum materials. Rationally designed van der Waals heterostructures composed of monolayer transition-metal dichalcogenides (TMDs) and few-layer hBN show several unique optoelectronic features driven by correlations. However, entangled superradiant excitonic species in such systems have not been observed before. In this report, it is demonstrated that strong suppression of phonon population at low temperature results in a formation of a coherent excitonic-dipoles ensemble in the heterostructure, and the collective oscillation of those dipoles stimulates a robust phase synchronized ultra-narrow band superradiant emission even at extremely low pumping intensity. Such emitters are in high demand for a multitude of applications, including fundamental research on many-body correlations and other state-of-the-art technologies. This timely demonstration paves the way for further exploration of ultralow-threshold quantum-emitting devices with unmatched design freedom and spectral tunability.  相似文献   
8.
9.
10.
The aim of this work was to investigate the physical and mechanical performance of architectural polyester (PES)–poly(vinyl chloride) (PVC) membranes exposed to different artificial aging conditions. Two commercially available architectural membranes were chosen as research objects. The durability of the PES/PVC fabrics was evaluated by the loss in mechanical performance, scanning electron microscopy, and X-ray diffraction analysis in order to understand the effect of the degradation agents on the surface of the membranes. The mechanical performance of the PES/PVC membranes was unchanged. Scanning electron microscopy images of the tested materials showed initial cracks after aging. The X-ray fluorescence analysis showed that at the time of aging, the amount of Cl and Si decreased slightly, while Ti decreased by half, and Ca by volume increased twice. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47523.  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