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   458101篇
  免费   6099篇
  国内免费   2002篇
电工技术   8603篇
综合类   349篇
化学工业   67473篇
金属工艺   18791篇
机械仪表   15290篇
建筑科学   9825篇
矿业工程   2550篇
能源动力   12882篇
轻工业   33701篇
水利工程   4907篇
石油天然气   9469篇
武器工业   55篇
无线电   54344篇
一般工业技术   94894篇
冶金工业   84353篇
原子能技术   11041篇
自动化技术   37675篇
  2021年   4438篇
  2020年   3389篇
  2019年   4318篇
  2018年   7520篇
  2017年   7561篇
  2016年   8128篇
  2015年   5016篇
  2014年   8250篇
  2013年   22670篇
  2012年   13131篇
  2011年   17331篇
  2010年   13911篇
  2009年   15621篇
  2008年   15970篇
  2007年   15708篇
  2006年   14031篇
  2005年   12577篇
  2004年   11889篇
  2003年   11778篇
  2002年   11131篇
  2001年   11021篇
  2000年   10398篇
  1999年   10705篇
  1998年   27109篇
  1997年   18694篇
  1996年   14305篇
  1995年   10680篇
  1994年   9413篇
  1993年   9413篇
  1992年   6811篇
  1991年   6507篇
  1990年   6486篇
  1989年   6139篇
  1988年   5759篇
  1987年   5105篇
  1986年   4985篇
  1985年   5555篇
  1984年   5027篇
  1983年   4584篇
  1982年   4198篇
  1981年   4277篇
  1980年   3969篇
  1979年   3821篇
  1978年   3790篇
  1977年   4333篇
  1976年   5575篇
  1975年   3292篇
  1974年   3071篇
  1973年   3154篇
  1972年   2651篇
排序方式: 共有10000条查询结果,搜索用时 328 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.
The influence of the microstructure on the corrosion rate of three monolithic SiC samples in FLiNaK salt at 900 °C for 250 h was studied. The SiC samples, labeled as SiC-1, SiC-2, and SiC-3, had corrosion rates of 0.137, 0.020, and 0.043 mg/cm2h, respectively. Compared with grain size and the presence of special grain boundaries (i.e., Σ3), the content of high-angle grain boundaries (HAGBs) appeared to have the strongest influence on the corrosion rate of SiC in FLiNaK salt, since the corrosion rate increased six times as the concentration of high-angle grain boundaries increased from 19 to 32% for SiC-2 and SiC-1, respectively. These results stress the importance of controlling the content of HAGBs during the production process of SiC.  相似文献   
43.
Theoretical Foundations of Chemical Engineering - The corona onset voltage is an important operating parameter in the electrostatic precipitation of nanoparticulate, however, its experimental...  相似文献   
44.
Herein, we report the photosensing property of CdS thin films. CdS thin films were coated onto glass substrates via a spray pyrolysis method using different spray pressures. Prepared films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical and photoluminescence spectroscopy. XRD analysis demonstrated the growth of crystalline CdS films with crystallite sizes varying from 26 to 29 nm depending on the pressure. The SEM and EDAX analyses revealed nearly-stoichiometric CdS films with smooth surfaces and slight variation in grain morphology due to pressure changes. Optical measurements showed a direct bandgap varying from 2.37 eV to 2.42 eV due to pressure changes. A photodetector was also fabricated using the grown CdS films; the fabricated photodetector exhibited good performance depending on the spray pressure. A spray pressure of 1.5 GPa resulted in high photoresponsivity and external quantum efficiency.  相似文献   
45.
NiO nanostructure was synthesized using a simple co-precipitation method and was embedded on reduced graphene oxide surface via ultrasonication. Structural investigations were made through X-ray diffraction (XRD) and functional groups were confirmed by Fourier transform infrared spectroscopy (FTIR). XRD analysis revealed the grain size reduction with doping. Fourier transform infrared spectroscopy confirmed the presence of metal-oxygen bond in pristine and doped NiO nanostructure as well as the presence of carbon containing groups. Scanning electron microscopy (SEM) indicated that the particle size decreased when NiO nanostructure was doped with copper. BET surface area was found to increase almost up to 43 m2/g for Cu doped NiO nanostructure/rGO composite. Current-voltage measurements were performed using two probe method. UV–Visible spectroscopic profiles showed the blue and red shift for Cu doped NiO nanostructure and Cu doped NiO Nanostructure/rGO composite respectively. Rate constant for Cu doped NiO nanostructure/rGO composite found to increase 4.4 times than pristine NiO nanostructure.  相似文献   
46.
Golubev  N. V.  Ignat’eva  E. S.  Maurus  A. A.  Ziyatdinova  M. Z.  Lopatina  E. V.  Lorenzi  R.  Paleari  A.  Sigaev  V. N. 《Glass and Ceramics》2021,77(11-12):415-418
Glass and Ceramics - The influence of Al2O3 as an additive and the heat-treatment regime on the luminescence spectra of gallate glass-ceramics was investigated. It is shown that its luminescence...  相似文献   
47.
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   
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.
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   
50.
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