首页 | 官方网站   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   291917篇
  免费   4038篇
  国内免费   1034篇
工业技术   296989篇
  2021年   2186篇
  2020年   1573篇
  2019年   1962篇
  2018年   4201篇
  2017年   4415篇
  2016年   4664篇
  2015年   3104篇
  2014年   4424篇
  2013年   11890篇
  2012年   8328篇
  2011年   11038篇
  2010年   7549篇
  2009年   8616篇
  2008年   8991篇
  2007年   8902篇
  2006年   7898篇
  2005年   10588篇
  2004年   9310篇
  2003年   8895篇
  2002年   6877篇
  2001年   7224篇
  2000年   6244篇
  1999年   6905篇
  1998年   21526篇
  1997年   14498篇
  1996年   10517篇
  1995年   7702篇
  1994年   6742篇
  1993年   6695篇
  1992年   4285篇
  1991年   4199篇
  1990年   4073篇
  1989年   3822篇
  1988年   3735篇
  1987年   3140篇
  1986年   3056篇
  1985年   3297篇
  1984年   2939篇
  1983年   2844篇
  1982年   2702篇
  1981年   2650篇
  1980年   2585篇
  1979年   2309篇
  1978年   2167篇
  1977年   3101篇
  1976年   4662篇
  1975年   1811篇
  1974年   1730篇
  1973年   1667篇
  1972年   1481篇
排序方式: 共有10000条查询结果,搜索用时 250 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.
Protection of Metals and Physical Chemistry of Surfaces - The distribution of the density of the adsorbate inside the transition region of the liquid–vapor interface in a slit pore, in which...  相似文献   
28.
In this paper, we present a novel memory access reduction scheme (MARS) for two-dimension fast cosine transform (2-D FCT). It targets programmable DSPs with high memory-access latency. It reduces the number of memory accesses by: 1) reducing the number of weighting factors and 2) combining butterflies in vector-radix 2-D FCT pruning diagram from two stages to one stage with an efficient structure. Hardware platform based on general purpose processor is used to verify the effectiveness of the proposed method for vector-radix 2-D FCT pruning implementation. Experimental results validate the benefits of the proposed method with reduced memory access, less clock cycle and fewer memory space compared with the conventional implementation.  相似文献   
29.
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   
30.
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   
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-23

京公网安备 11010802026262号