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   4100篇
  免费   244篇
  国内免费   58篇
电工技术   19篇
综合类   145篇
化学工业   1410篇
金属工艺   125篇
机械仪表   49篇
建筑科学   34篇
矿业工程   50篇
能源动力   240篇
轻工业   1121篇
水利工程   20篇
石油天然气   130篇
武器工业   2篇
无线电   107篇
一般工业技术   526篇
冶金工业   63篇
原子能技术   18篇
自动化技术   343篇
  2024年   19篇
  2023年   134篇
  2022年   182篇
  2021年   160篇
  2020年   199篇
  2019年   145篇
  2018年   125篇
  2017年   164篇
  2016年   217篇
  2015年   270篇
  2014年   329篇
  2013年   297篇
  2012年   226篇
  2011年   226篇
  2010年   173篇
  2009年   178篇
  2008年   68篇
  2007年   217篇
  2006年   131篇
  2005年   88篇
  2004年   48篇
  2003年   65篇
  2002年   122篇
  2001年   78篇
  2000年   41篇
  1999年   59篇
  1998年   41篇
  1997年   16篇
  1996年   27篇
  1995年   20篇
  1994年   24篇
  1993年   16篇
  1992年   14篇
  1991年   14篇
  1990年   14篇
  1989年   17篇
  1988年   28篇
  1987年   77篇
  1986年   59篇
  1985年   13篇
  1984年   10篇
  1983年   6篇
  1982年   10篇
  1981年   5篇
  1980年   10篇
  1979年   9篇
  1978年   4篇
  1976年   6篇
  1973年   1篇
排序方式: 共有4402条查询结果,搜索用时 0 毫秒
1.
The falling down problem has become one of the very important issues of global public health in an aging society. The specific equipment was adopted as the detection device of falling-down in the early studies, but it is inconvenient for the elderly and difficult for future application. The smart phone more commonly used than the specific fall detection equipment is selected as a mobile device for human fall detection, and a fall detection algorithm is developed for this purpose. What the user has to do is to put the smart phone in his/her thigh pocket for falling down detection. The signals detected by the tri-axial G-sensor are converted into signal vector magnitudes as the basis of detecting a human body in a stalling condition. The Z-axis data sets are captured for identification of human body inclination and the occurrence frequencies at the peak of the area of use are used as the input parameters. A high-level fuzzy Petri net is used for the analysis and the development of identifying human actions, including normal action, exercising, and falling down. The results of this study can be used in the relevant equipments or in the field of home nursing.  相似文献   
2.
Buffalo milk proteins (casein, co-precipitate or whey protein concentrate) were phosphorylated with phosphorus oxychloride (POCl3) at three different pH values (5.0, 7.0 and 9.0). The solubilities of phosphorylated milk proteins were examined over the pH range 3.0–9.0 in water and ionic (0.1 m NaCl or 10–70 mm Ca2+) systems. The solubilities of buffalo milk proteins decreased at pH 3.0, while there was an increase in the solubilities of casein and co-precipitate near their isoelectric points upon phosphorylation. Solubilities of these phosphorylated milk proteins were pH dependent in 0.1 m NaCl but there was a decrease in their solubilities with increase in calcium ion concentration. This alteration could be due to the shifting of isoionic points of phosphorylated buffalo milk proteins towards acidic pH.  相似文献   
3.
New book titles     
《Polymer Contents》2005,22(4):287-288
  相似文献   
4.
An updated and statistically-rigorous correlation is provided for crack-arrest toughness values versus normalized temperature for light-water nuclear reactor pressure vessel (RPV) steels. The database used in this effort is larger than applied heretofore and includes results from tests of laboratory-size specimens and from tests of large-scale specimens, which contain features prototypical of operating RPVs. The mathematical methodology used is based on a lognormal distribution, with its parameters calculated by orthogonal distance regression. This correlation was developed as one of several items updated for use in the US Nuclear Regulatory Commission's extensive program to evaluate and potentially revise its rule for ensuring structural integrity of operating RPVs when subjected to pressurized thermal-shock transients.  相似文献   
5.
6.
7.
Five commercial samples of sodium copper chlorophyllin, a green food colorant, were analysed by high-performance liquid chromatography (HPLC) using diode-array detection (DAD) and mass spectrometry (MS). Some of the constituents were identified using authentic standards, whereas others were identified tentatively based on their absorption spectra and mass data. The composition of three of the samples was very similar, whereas the other two were quite different. In the three former samples, the three largest peaks could be assigned to Cu chlorin e6, Cu chlorin p6, and Cu isochlorin e4. In one of the two other samples, these three compounds were also among the largest peaks, whereas Cu chlorin e6 was a small peak in the last sample and Cu chlorin p6 was absent altogether. Porphyrins were also present in the samples, while except in one of the samples chlorins derived from chlorophyll b were largely absent.Industrial relevanceSodium copper chlorophyllin is a green food colorant made from chlorophyll. Sodium copper chlorophyllin is made by saponifying chlorophyll and coppering the resulting product. This processing leads to a complex mixture of compounds. An analytical method was developed that can be used to identify many of these compounds and show the extent of coppering and degradation of sodium copper chlorophyllin, which may be used industrially to optimize the production of sodium copper chlorophyllin.  相似文献   
8.
The photocatalytic oxidation of resorcinol, a potent endocrine disrupting chemical, in oxygenated aqueous suspensions of pure and cupric ions modified Degussa P25 titanium dioxide has been investigated at pH 3.0 ± 0.5. The initial rate of photocatalytic oxidation of resorcinol increased until an optimum dissolved cupric ions concentration was reached at 1.04 mM. At the optimum concentration of cupric ions, the initial rate of photocatalytic mineralisation and degradation of resorcinol was improved by 400%. The observed beneficial effect of cupric ions on the initial rate of resorcinol oxidation could be attributed to the formation of complex and its participation in the photoredox cyclic reaction.Two of the initial oxidation intermediates detected were 1,2,3-trihydroxybenzene and 1,2,4-trihydroxybenzene. These intermediates were formed via hydroxylation of the aromatic ring of resorcinol. Evidences have revealed that 1,2,4-trihydroxybenzene interacted strongly with cupric ions forming copper(II)-trihydroxybenzoate complexes that possessed good adsorption onto TiO2 surface. These dual-effects help to draw the metal ions closer to the photocatalyst surface and subsequently trigger the electron trapping mechanism by cupric ions. As a result, this improved the charge carriers’ separation. Furthermore, in the presence of oxygen, reoxidation of photoreduced cupric ions occurred and this eliminated the possibility of copper photodeposition, while inducing a photoredox cyclic reaction to regenerate copper species that may potentially act as co-catalyst for the oxidation of 1,2,4-trihydroxybenzene. In contrast, no obvious complex formation was seen between 1,2,3-trihydroxybenzene and cupric ions. This pointed to an intriguing finding which indicates that the positioning of functional group on benzene ring influences the role of cupric ions.  相似文献   
9.
曾桂萍  孙福强 《化学世界》2005,46(12):732-733,725
以邻氨基苯甲酸为原料,以不同的中间体和不同的脱水剂对2-甲基-3-甲苯基喹唑啉-4-酮的合成进行研究比较,寻找较佳的合成路径。  相似文献   
10.
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