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   252496篇
  免费   3185篇
  国内免费   858篇
电工技术   4841篇
综合类   190篇
化学工业   35706篇
金属工艺   9522篇
机械仪表   7562篇
建筑科学   6049篇
矿业工程   876篇
能源动力   7250篇
轻工业   21004篇
水利工程   2207篇
石油天然气   3232篇
武器工业   15篇
无线电   34367篇
一般工业技术   50131篇
冶金工业   48687篇
原子能技术   5101篇
自动化技术   19799篇
  2021年   2157篇
  2020年   1564篇
  2019年   1926篇
  2018年   3275篇
  2017年   3319篇
  2016年   3421篇
  2015年   2229篇
  2014年   3970篇
  2013年   11508篇
  2012年   6268篇
  2011年   8615篇
  2010年   6936篇
  2009年   7903篇
  2008年   8439篇
  2007年   8327篇
  2006年   7390篇
  2005年   6527篇
  2004年   6316篇
  2003年   6574篇
  2002年   6060篇
  2001年   6529篇
  2000年   5995篇
  1999年   6413篇
  1998年   16540篇
  1997年   11446篇
  1996年   8830篇
  1995年   6635篇
  1994年   5922篇
  1993年   5863篇
  1992年   4148篇
  1991年   4034篇
  1990年   3869篇
  1989年   3662篇
  1988年   3571篇
  1987年   3026篇
  1986年   2953篇
  1985年   3220篇
  1984年   2934篇
  1983年   2835篇
  1982年   2644篇
  1981年   2508篇
  1980年   2423篇
  1979年   2271篇
  1978年   2087篇
  1977年   2569篇
  1976年   3526篇
  1975年   1736篇
  1974年   1705篇
  1973年   1635篇
  1972年   1450篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
21.
Mobile Networks and Applications - 5G/6G communication are first generation high speed wireless communication network which integrates the aerial data, terrestrial data and maritime data via...  相似文献   
22.
Journal of Inorganic and Organometallic Polymers and Materials - This paper reports the performance of alizarin based SnO2 dye-sensitized solar cells. A novel template assisted method has been...  相似文献   
23.
A new TiO2-containing bioactive glass and glass-ceramics based on 50SiO2-(45-X)CaO-(XTiO2)-5P2O5 system was designed using a sol–gel technique (where X = 5, 7.5 and 10 wt %). The roles of the crystallization behavior and physicochemical characteristics of the designed glass and glass-ceramics which were played in the introduction of TiO2 substitutions were investigated. Moreover, cell proliferation and differentiation were evaluated against human osteosarcoma cells (Saos-2). The TiO2/CaO replacements led to the formation of a stronger glass structure and thus increased thermal parameters and the chemical stabilization of the designed materials. The FTIR data confirmed the existence of Ti within the glass and glass-ceramics samples, and no remarkable effect on their chemical integrity was observed. The XRD patterns indicated that calcium-containing minerals, including Ca2SiO4,Ca3(PO4)2, Ca(Ti,Si)O5, CaTiSiO5, and Ca15(PO4)2·(SiO4)6 phases were developed as a role of structure/texture under the applied heat-treatment. The results of the cytotoxicity test proved that a safe sample dose is 12–50 μg/ml, at which cell viability is ≥ 85%. The cell differentiation determined by ALP test proved the superiority of glass-ceramics compared with their native glasses. Therefore, the obtained materials could be safely used as novel biocompatible materials for the regeneration of bone tissue.  相似文献   
24.
25.
The germline carrier of the BRCA1 pathogenic mutation has been well proven to confer an increased risk of breast and ovarian cancer. Despite BRCA1 biallelic pathogenic mutations being extremely rare, they have been reported to be embryonically lethal or to cause Fanconi anemia (FA). Here we describe a patient who was a 48-year-old female identified with biallelic pathogenic mutations of the BRCA1 gene, with no or very subtle FA-features. She was diagnosed with ovarian cancer and breast cancer at the ages of 43 and 44 and had a strong family history of breast and gynecological cancers.  相似文献   
26.
Jori  Popat K.  Jadhav  Vrushali H. 《Catalysis Letters》2022,152(6):1703-1710
Catalysis Letters - A new zirconium based carbonaceous solid acid catalyst Zr@CC-PA with both Lewis and Bronsted acidic sites was prepared by simultaneous carbonization and phosphonation of glucose...  相似文献   
27.
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations.  相似文献   
28.
Clean Technologies and Environmental Policy - Food production and consumption is one of the major causes of global environmental degradation. One way to address environmental impacts in the food...  相似文献   
29.
30.
Theoretical Foundations of Chemical Engineering - New research results, as well as those published earlier by the authors, on the synthesis of azo compounds based on nitroanilines obtained by the...  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