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   383304篇
  免费   4592篇
  国内免费   1499篇
电工技术   6244篇
综合类   2612篇
化学工业   59194篇
金属工艺   16688篇
机械仪表   12464篇
建筑科学   8997篇
矿业工程   2375篇
能源动力   7840篇
轻工业   33376篇
水利工程   4428篇
石油天然气   7231篇
武器工业   72篇
无线电   39973篇
一般工业技术   73683篇
冶金工业   58402篇
原子能技术   8310篇
自动化技术   47506篇
  2021年   2807篇
  2019年   2610篇
  2018年   18760篇
  2017年   17676篇
  2016年   14729篇
  2015年   3551篇
  2014年   5302篇
  2013年   13249篇
  2012年   11037篇
  2011年   19692篇
  2010年   16469篇
  2009年   14733篇
  2008年   16216篇
  2007年   17235篇
  2006年   8779篇
  2005年   8773篇
  2004年   8423篇
  2003年   8244篇
  2002年   7619篇
  2001年   7058篇
  2000年   6952篇
  1999年   6675篇
  1998年   15734篇
  1997年   11139篇
  1996年   8538篇
  1995年   6640篇
  1994年   5871篇
  1993年   5812篇
  1992年   4517篇
  1991年   4318篇
  1990年   4491篇
  1989年   4349篇
  1988年   4108篇
  1987年   3632篇
  1986年   3677篇
  1985年   4181篇
  1984年   3857篇
  1983年   3541篇
  1982年   3308篇
  1981年   3406篇
  1980年   3274篇
  1979年   3163篇
  1978年   3201篇
  1977年   3608篇
  1976年   4608篇
  1975年   2869篇
  1974年   2721篇
  1973年   2839篇
  1972年   2388篇
  1971年   2224篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
This review examines the application, limitations, and potential alternatives to the Hagberg–Perten falling number (FN) method used in the global wheat industry for detecting the risk of poor end-product quality mainly due to starch degradation by the enzyme α-amylase. By viscometry, the FN test indirectly detects the presence of α-amylase, the primary enzyme that digests starch. Elevated α-amylase results in low FN and damages wheat product quality resulting in cakes that fall, and sticky bread and noodles. Low FN can occur from preharvest sprouting (PHS) and late maturity α-amylase (LMA). Moist or rainy conditions before harvest cause PHS on the mother plant. Continuously cool or fluctuating temperatures during the grain filling stage cause LMA. Due to the expression of additional hydrolytic enzymes, PHS has a stronger negative impact than LMA. Wheat grain with low FN/high α-amylase results in serious losses for farmers, traders, millers, and bakers worldwide. Although blending of low FN grain with sound wheat may be used as a means of moving affected grain through the marketplace, care must be taken to avoid grain lots from falling below contract-specified FN. A large amount of sound wheat can be ruined if mixed with a small amount of sprouted wheat. The FN method is widely employed to detect α-amylase after harvest. However, it has several limitations, including sampling variability, high cost, labor intensiveness, the destructive nature of the test, and an inability to differentiate between LMA and PHS. Faster, cheaper, and more accurate alternatives could improve breeding for resistance to PHS and LMA and could preserve the value of wheat grain by avoiding inadvertent mixing of high- and low-FN grain by enabling testing at more stages of the value stream including at harvest, delivery, transport, storage, and milling. Alternatives to the FN method explored here include the Rapid Visco Analyzer, enzyme assays, immunoassays, near-infrared spectroscopy, and hyperspectral imaging.  相似文献   
22.
Journal of Materials Science - For transformers and inductors to meet the world’s growing demand for electrical power, more efficient soft magnetic materials with high saturation magnetic...  相似文献   
23.
24.
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   
25.
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   
26.
Kirovskaya  I. A.  Filatova  T. N.  Nor  P. E. 《Semiconductors》2021,55(2):228-233
Semiconductors - According to developed methods, in the fields of the mutual solubility of initial binary compounds (InP, InSb, and CdS), solid solutions of the InP–CdS and InSb–CdS...  相似文献   
27.
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   
28.
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   
29.
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   
30.
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