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   168417篇
  免费   16639篇
  国内免费   8998篇
电工技术   11533篇
技术理论   11篇
综合类   11982篇
化学工业   26049篇
金属工艺   10249篇
机械仪表   11838篇
建筑科学   14020篇
矿业工程   5886篇
能源动力   4969篇
轻工业   11429篇
水利工程   3431篇
石油天然气   10570篇
武器工业   1715篇
无线电   19650篇
一般工业技术   18369篇
冶金工业   7477篇
原子能技术   1995篇
自动化技术   22881篇
  2024年   892篇
  2023年   3067篇
  2022年   5875篇
  2021年   8094篇
  2020年   6192篇
  2019年   4812篇
  2018年   5287篇
  2017年   5965篇
  2016年   5365篇
  2015年   7736篇
  2014年   9399篇
  2013年   11020篇
  2012年   12426篇
  2011年   13089篇
  2010年   11429篇
  2009年   10743篇
  2008年   10320篇
  2007年   9477篇
  2006年   9141篇
  2005年   7705篇
  2004年   4932篇
  2003年   4111篇
  2002年   3804篇
  2001年   3297篇
  2000年   3064篇
  1999年   3293篇
  1998年   2488篇
  1997年   2088篇
  1996年   2015篇
  1995年   1668篇
  1994年   1358篇
  1993年   879篇
  1992年   747篇
  1991年   533篇
  1990年   409篇
  1989年   349篇
  1988年   273篇
  1987年   177篇
  1986年   142篇
  1985年   79篇
  1984年   64篇
  1983年   47篇
  1982年   52篇
  1981年   39篇
  1980年   45篇
  1979年   32篇
  1978年   3篇
  1976年   2篇
  1959年   16篇
  1951年   11篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
91.
92.
Cao  Zehui  Zhao  Jing  Sun  Shiliang 《Neural Processing Letters》2021,53(1):339-353
Neural Processing Letters - The beta processes (BP) is a powerful nonparametric tool in feature learning, which is often used as the prior of Bernoulli process for choosing features from a feature...  相似文献   
93.
94.
以2,6-二甲基苯胺为原料,通过重氮化反应制备2,6-二甲基苯腈,经水蒸汽蒸馏法提纯后,采用75%硫酸酸化,再经酸碱法对产物进行脱色和纯化得产物2,6-二甲基苯甲酸,总收率68.4%。工艺简单、操作安全、适合工业化生产。  相似文献   
95.
Directionally solidified microstructures of Al2O3-Er3Al5O12 eutectic and off-eutectic in situ composite ceramics were explored under abrupt-change pulling rate conditions. Corresponding temperature distributions and interface locations were studied. In eutectic composition, fluctuation of eutectic spacing occurred when the pulling rate increased abruptly. A gradually increase or abrupt increase in eutectic spacing was observed when the pulling rate decreased abruptly. In hypoeutectic and hypereutectic compositions, formation of the primary phases were suppressed when the pulling rate increased abruptly from 10?µm/s to 100?µm/s, while primary phases precipitated when the pulling rate decreased abruptly from 100?µm/s to 10?µm/s. The interface altitude decreased after the pulling rate increased abruptly, but increased after the pulling rate decreased abruptly. The liquid composition restriction (around the eutectic composition) at the eutectic interface plays an important role in the suppression of the primary dendrite and coupled eutectic oxides can be obtained in off-eutectic compositions even under higher solidification rate conditions.  相似文献   
96.
Hydrocracking of a bitumen‐derived asphaltene over NiMo/γ‐Al2O3 was investigated in a microbatch reactor at varying temperatures. The molar kinetics of asphaltene cracking reaction was examined by fitting the experimental data. Below a defined temperature, the molar reaction showed the first‐order kinetic feature while at higher temperatures secondary reactions such as coke formation became significant, causing deviation of the reaction behavior from the proposed first‐order kinetic model. Selectivity analysis proved that dominant products varied from gases to liquids to gases with increasing temperature, shifting the dominant reaction from C–S bonds cleavage to C–C bonds cleavage.  相似文献   
97.
98.
Journal of Mechanical Science and Technology - Real-time monitoring and rapid evaluation of bearing operating conditions, especially for the reliability evaluation and remaining useful life (RUL)...  相似文献   
99.
Structures and properties of myofibrillar protein gel prepared at different power (300–800 W) were evaluated. Amino acid analysis demonstrated that changes in microwave power did not alter primary structure of gel. However, an increase in microwave power could change higher structures of gel. As microwave power increased, α-helix content decreased and β-sheet content increased. Increased microwave power probably facilitated protein to unfold and expose the internal groups, causing surface hydrophobicity and the formation of disulphide bonds were enhanced, which indicated changes in tertiary and quaternary structures of protein. At 500 W, gel had the best ultrastructure where surface morphology, springiness and water holding capacity reached the optimum. Our findings suggested that microwave at an appropriate power (500 W) could change higher structures of myofibrillar protein gel to achieve desired processing and quality protein gel characteristics.  相似文献   
100.
Abstract

Lignin biochar-catalytic depolymerization using biochar Fe-600, Fe-800, Ni-600, Ni-800 catalysts under microwave-heating (180?°C for 30?min) was explored in an ethanol/formic acid (1:1) media. Non-catalyst depolymerization was also studied and compared with the biochar-catalysts results. Characteristics of the bio-char catalysts were analyze by BET, XRD, and FT-IR. GPC, FT-IR, and MALDI-TOF MS spectrometry were also used to characterize the depolymerization products. The experimental results showed that the SBET, Vt, and Vmec and average pore diameter of the biochars are considerably dependent on the preparation temperature and type of cation (Ni2+ or Fe3+). The maximum yield of bio-oil product was obtained as 85?wt% with the addition of biochar Ni-600 and the total amount of oligomers or monomers with a molecular weight of 164 to 446 reaches 80.4%.  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