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   302205篇
  免费   7124篇
  国内免费   1166篇
电工技术   4846篇
综合类   444篇
化学工业   46523篇
金属工艺   9223篇
机械仪表   8346篇
建筑科学   8431篇
矿业工程   683篇
能源动力   8552篇
轻工业   36271篇
水利工程   2600篇
石油天然气   2077篇
武器工业   16篇
无线电   36199篇
一般工业技术   54087篇
冶金工业   58058篇
原子能技术   3643篇
自动化技术   30496篇
  2022年   1533篇
  2021年   3140篇
  2020年   2387篇
  2019年   2843篇
  2018年   4275篇
  2017年   4298篇
  2016年   4662篇
  2015年   3515篇
  2014年   5411篇
  2013年   15335篇
  2012年   9392篇
  2011年   12463篇
  2010年   9632篇
  2009年   10454篇
  2008年   10853篇
  2007年   10728篇
  2006年   9554篇
  2005年   8773篇
  2004年   8492篇
  2003年   8269篇
  2002年   7757篇
  2001年   7914篇
  2000年   7059篇
  1999年   7572篇
  1998年   19749篇
  1997年   13671篇
  1996年   10141篇
  1995年   7520篇
  1994年   6484篇
  1993年   6443篇
  1992年   4337篇
  1991年   4192篇
  1990年   3866篇
  1989年   3669篇
  1988年   3593篇
  1987年   2851篇
  1986年   2729篇
  1985年   3424篇
  1984年   3019篇
  1983年   2724篇
  1982年   2569篇
  1981年   2620篇
  1980年   2446篇
  1979年   2193篇
  1978年   2018篇
  1977年   2557篇
  1976年   3504篇
  1975年   1703篇
  1974年   1570篇
  1973年   1654篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Journal of Materials Science -  相似文献   
3.
Xiao  Zhu  Chen  Yanxun  Jiang  Hongbo  Hu  Zhenzhen  Lui  John C. S.  Min  Geyong  Dustdar  Schahram 《Wireless Networks》2022,28(7):3305-3322
Wireless Networks - Unmanned aerial vehicles (UAV) have been widely used in various fields because of their high mobility and portability. At the same time, due to the rapid development of...  相似文献   
4.
5.
Transmission electron microscopy (TEM) is an important analysis technique to visualize (bio)macromolecules and their assemblies, including collagen fibers. Many protocols for TEM sample preparation of collagen involve one or more washing steps to remove excess salts from the dispersion that could hamper analysis when dried on a TEM grid. Such protocols are not standardized and washing times as well as washing solvents vary from procedure to procedure, with each research group typically having their own protocol. Here, we investigate the influence of washing with water, ethanol, but also methanol and 2-propanol, for both mineralized and unmineralized collagen samples via a protocol based on centrifugation. Washing with water maintains the hydrated collagen structure and the characteristic banding pattern can be clearly observed. Conversely, washing with ethanol results in dehydration of the fibrils, often leading to aggregation of the fibers and a less obvious banding pattern, already within 1 min of ethanol exposure. As we show, this process is fully reversible. Similar observations were made for methanol and propanol. Based on these results, a standardized washing protocol for collagenous samples is proposed.  相似文献   
6.
7.
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   
8.
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   
9.
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   
10.
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   
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