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   537945篇
  免费   6559篇
  国内免费   1603篇
电工技术   10585篇
综合类   593篇
化学工业   75967篇
金属工艺   23703篇
机械仪表   19413篇
建筑科学   12737篇
矿业工程   2491篇
能源动力   13268篇
轻工业   41098篇
水利工程   5349篇
石油天然气   7685篇
武器工业   80篇
无线电   68777篇
一般工业技术   107978篇
冶金工业   95539篇
原子能技术   10367篇
自动化技术   50477篇
  2021年   3876篇
  2020年   2901篇
  2019年   3652篇
  2018年   12962篇
  2017年   13544篇
  2016年   10511篇
  2015年   4683篇
  2014年   7515篇
  2013年   21460篇
  2012年   13921篇
  2011年   23142篇
  2010年   19472篇
  2009年   20330篇
  2008年   21013篇
  2007年   22701篇
  2006年   14068篇
  2005年   15544篇
  2004年   13765篇
  2003年   13554篇
  2002年   12010篇
  2001年   11952篇
  2000年   11350篇
  1999年   11799篇
  1998年   29217篇
  1997年   20526篇
  1996年   15899篇
  1995年   12210篇
  1994年   10883篇
  1993年   10787篇
  1992年   8004篇
  1991年   7622篇
  1990年   7349篇
  1989年   6938篇
  1988年   6703篇
  1987年   5806篇
  1986年   5638篇
  1985年   6409篇
  1984年   5921篇
  1983年   5500篇
  1982年   5163篇
  1981年   5119篇
  1980年   4902篇
  1979年   4665篇
  1978年   4324篇
  1977年   5253篇
  1976年   6838篇
  1975年   3884篇
  1974年   3789篇
  1973年   3781篇
  1972年   3144篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Theoretical Foundations of Chemical Engineering - The effect of the electrolyte composition, mass-transfer conditions, pore diameter, interpore distance, and electric parameters on the formation of...  相似文献   
42.
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   
43.
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   
44.
Chronic stress is a combination of nonspecific adaptive reactions of the body to the influence of various adverse stress factors which disrupt its homeostasis, and it is also a corresponding state of the organism’s nervous system (or the body in general). We hypothesized that chronic stress may be one of the causes occurence of several molecular and cellular types of stress. We analyzed literary sources and considered most of these types of stress in our review article. We examined genes and mutations of nuclear and mitochondrial genomes and also molecular variants which lead to various types of stress. The end result of chronic stress can be metabolic disturbance in humans and animals, leading to accumulation of reactive oxygen species (ROS), oxidative stress, energy deficiency in cells (due to a decrease in ATP synthesis) and mitochondrial dysfunction. These changes can last for the lifetime and lead to severe pathologies, including neurodegenerative diseases and atherosclerosis. The analysis of literature allowed us to conclude that under the influence of chronic stress, metabolism in the human body can be disrupted, mutations of the mitochondrial and nuclear genome and dysfunction of cells and their compartments can occur. As a result of these processes, oxidative, genotoxic, and cellular stress can occur. Therefore, chronic stress can be one of the causes forthe occurrence and development of neurodegenerative diseases and atherosclerosis. In particular, chronic stress can play a large role in the occurrence and development of oxidative, genotoxic, and cellular types of stress.  相似文献   
45.
46.
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   
47.
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   
48.
Russian Engineering Research - Models based on regression analysis for predicting the operational efficiency of high-pressure roller crushers are considered. A systematized and structured...  相似文献   
49.
Journal of Machinery Manufacture and Reliability - A device based on smart alloys has been designed for use in machine building items, in particular, in nuclear engineering, for preventing...  相似文献   
50.
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   
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