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   203731篇
  免费   15038篇
  国内免费   7904篇
电工技术   11108篇
技术理论   12篇
综合类   12159篇
化学工业   32917篇
金属工艺   12322篇
机械仪表   12753篇
建筑科学   12640篇
矿业工程   4975篇
能源动力   4641篇
轻工业   12583篇
水利工程   4031篇
石油天然气   11160篇
武器工业   1475篇
无线电   21093篇
一般工业技术   30274篇
冶金工业   12604篇
原子能技术   5245篇
自动化技术   24681篇
  2024年   775篇
  2023年   2586篇
  2022年   5374篇
  2021年   7252篇
  2020年   5510篇
  2019年   4698篇
  2018年   5876篇
  2017年   6486篇
  2016年   6028篇
  2015年   7069篇
  2014年   9170篇
  2013年   11173篇
  2012年   12258篇
  2011年   13255篇
  2010年   11578篇
  2009年   11354篇
  2008年   11172篇
  2007年   10587篇
  2006年   9921篇
  2005年   8393篇
  2004年   6376篇
  2003年   5899篇
  2002年   5950篇
  2001年   5419篇
  2000年   4504篇
  1999年   3945篇
  1998年   3021篇
  1997年   2561篇
  1996年   2267篇
  1995年   1952篇
  1994年   1665篇
  1993年   1386篇
  1992年   1321篇
  1991年   1174篇
  1990年   1146篇
  1989年   1069篇
  1988年   940篇
  1987年   866篇
  1986年   784篇
  1985年   731篇
  1984年   712篇
  1981年   674篇
  1979年   739篇
  1978年   777篇
  1977年   739篇
  1976年   757篇
  1975年   713篇
  1974年   719篇
  1973年   723篇
  1972年   705篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Pleurotus eryngii, the second largest industrial cultivation mushroom in China, is usually cultivated on substrates mainly consisting of sawdust and corncob. In this study, experiments were performed to determine the effects of different carbon sources and C/N values on nonvolatile taste components of P. eryngii. The effects of different carbon sources on nonvolatile taste components levels revealed that sawdust was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while corncob was beneficial to high contents of carbohydrate, polysaccharides and trehalose. At the similar C/N values, relatively higher sawdust content was beneficial to umami amino acid production, while relatively higher corncob content was beneficial to high contents of carbohydrate, polysaccharides and mannitol. Higher C/N value was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while lower C/N value was beneficial to high contents of carbohydrate, polysaccharides and trehalose. These results provided information for P. eryngii fruit body industrial cultivation to obtain specific nonvolatile taste components with high levels.  相似文献   
63.
64.
65.
66.
  Qing  Xu  Bin  Yu  Yang  Zhan  Wei  Zhao  Yu  Zheng  Jun  Ji  Jian 《Bulletin of Engineering Geology and the Environment》2021,80(8):6513-6525
Bulletin of Engineering Geology and the Environment - Many uncertainties exist in pile-stabilized slopes which make their design substantially complicated. In this paper, a first-order reliability...  相似文献   
67.
A tensile properties testing study was conducted to understand the influence of thickness, cross-head speed (speed of testing), gauge length (GL; specimen test length), and sample shape on important tensile properties of polyvinyl alcohol (PVA) nanofiber webs. The effects of each testing parameter on load at break, extension at break, Young's modulus, and tensile stress–strain curve of PVA nanofiber webs are analyzed. The Welch two sample t-tests show the significant difference among tested data. Using interaction plots, two-way analysis of variance, and margin mean plots, the interaction effects among testing parameters have been analyzed. Of all the factors, cross-head speed, the interaction among GL, and sample thickness (GL: Thickness) and the interaction among GL, testing speed and sample thickness (GL: Speed: Thickness) have significant influence on the tensile properties of PVA nanofiber webs. Moreover, the hypothesized model of mechanism of tensile strain–stress curve of PVA nanofiber webs has been proposed. Based on the model, the tensile strain–stress curve can be split into three stages: linear elastic, partial break up, and complete breakage. This study will provide a better understanding of tensile testing parameters' effects and their interaction effects on the tensile properties of nanowebs.  相似文献   
68.
69.
One-dimensional, diluted magnetic semiconductor nanofibers have attracted increasing attention for their unique magnetic properties, large specific surface area, and high porosity. These qualities lead to excellent performance in magneto-optical devices, magnetic resonance imaging, ferrofluids and magnetic separation. The purpose of this study is to fabricate P-type one dimensional CuAlO2-based diluted magnetic semiconductor nanofibers. First, we fabricated Cu Al0.95Co0.05O2 nanofibers with an average diameter of 1 μm with the electrospinning method. The annealed nanofibers were thermally treated at a temperature of 1 100 ℃ and then shrunk to a diameter of about 650 nm. We used X-ray diffraction measurements and Raman spectra to confirm that the Cu Al0.95Co0.05O2 nanofibers had a single impurity free delafossite phase. The X-ray photoelectron spectroscopy analysis indicates that Co was present in the +2 oxidation state, resulting in an room temperature ferromagnetism in the Cu Al0.95Co0.05O2 fiber. This contrasts with nonmagnetism in pristine CuAlO2 fiber. The coercivity(Hc) value of 65.26 Oe and approximate saturation magnetization(Ms) of 0.012 emu/g demonstrate good evidence of ferromagnetism at room temperature for Cu Al0.95Co0.05O2 nanofibers.  相似文献   
70.
Bochkareva  N. I.  Ivanov  A. M.  Klochkov  A. V.  Kogotkov  V. S.  Rebane  Yu. T.  Virko  M. V.  Shreter  Y. G. 《Semiconductors》2015,49(6):827-835
Semiconductors - It is shown that the emission efficiency and the 1/f noise level in light-emitting diodes with InGaN/GaN quantum wells correlate with how the differential resistance of a diode...  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