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   14693篇
  免费   557篇
  国内免费   60篇
电工技术   174篇
综合类   44篇
化学工业   3203篇
金属工艺   254篇
机械仪表   354篇
建筑科学   868篇
矿业工程   41篇
能源动力   395篇
轻工业   1125篇
水利工程   109篇
石油天然气   42篇
武器工业   1篇
无线电   1094篇
一般工业技术   2587篇
冶金工业   2347篇
原子能技术   116篇
自动化技术   2556篇
  2023年   110篇
  2022年   233篇
  2021年   323篇
  2020年   235篇
  2019年   292篇
  2018年   378篇
  2017年   245篇
  2016年   348篇
  2015年   319篇
  2014年   439篇
  2013年   906篇
  2012年   699篇
  2011年   885篇
  2010年   657篇
  2009年   647篇
  2008年   698篇
  2007年   693篇
  2006年   562篇
  2005年   502篇
  2004年   457篇
  2003年   390篇
  2002年   371篇
  2001年   258篇
  2000年   261篇
  1999年   227篇
  1998年   487篇
  1997年   349篇
  1996年   256篇
  1995年   246篇
  1994年   199篇
  1993年   206篇
  1992年   188篇
  1991年   119篇
  1990年   123篇
  1989年   110篇
  1988年   131篇
  1987年   100篇
  1986年   73篇
  1985年   107篇
  1984年   114篇
  1983年   75篇
  1982年   90篇
  1981年   112篇
  1980年   90篇
  1979年   106篇
  1978年   85篇
  1977年   93篇
  1976年   101篇
  1975年   71篇
  1973年   56篇
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
991.
992.
Canola oil is not presently permitted in infant formulations in the United States because of lack of information concenring the effects of feeding canola oil to the newborn. We have previously reported a transient decrease in platelet counts and an increase in platelet size in newborn piglets fed canola oil for 4 wk, and have confirmed this in the present study. In canola oil-fed piglets, changes in platelet size and number were overcome by adding either long-chain saturated fatty acids from cocoa butter (16:0 and 18:0), or shorter-chain saturates from coconut oil (12:0 and 14:0). Feeding a high erucic acid rapeseed (HEAR) oil, with 20% 22:1n−9, led to an even greater platelet reduction and increased platelet size throughout the 4-wk trial. Bleeding times were longer in piglets fed canola oil or HEAR oil compared to sow-reared and soybean oil-fed piglets. There were no other diet-related changes. Diet-induced platelet changes were not related to platelet lipid class composition, but there were fatty acid changes. The incorporation of 22:1n−9 into platelet phospholipids of piglets fed canola oil was low (0.2–1.2%), and even for the HEAR oil group ranged from only 0.2% in phosphatidylinositol to 2.4% in phosphatidylserine. A much greater change was observed in the concentration of 24:1n−9 and in the 24:1n−9/24:0 ratio in platelet sphingomyelin (SM). The 24:1n−9 increased to 49% in the HEAR oil group compared to about 12% in animals fed the control diets (sow-reared piglets and soybean oil-fed group), while the 24:1n−9/24:0 ratio increased from about 1 to 12. Even feeding canola oil, prepared to contain 2% 22:1n−9, led to a marked increase in 24:1n−9 to 29% and had a 24:1n−9/24:0 ratio of 5. The canola oil/cocoa butter group, which also contained 2% 22:1n−9, showed a lower level of 24:1n−9 (20%) and the 24:1n−9/24:0 ratio (3) compared to the canola oil group. The results suggest that the diet-related platelet changes in newborn piglets may be related to an increase in 24:1n−9 in platelet SM, resulting from chain elongation of 22:1n−9. The inclusion of canola oil as the sole source of fat in the milk-replacer diets of newborn piglets resulted in significant platelet and lipid changes.  相似文献   
993.
Lower moisture content in wood, preferably 5–6%, is desirable for many chemical modification reactions. Economically, it is not feasible to dry timber to such low moisture content by conventional drying without drying degrades. Microwave heating was evaluated and found to be effective in reducing the moisture content of radiata pine from 13% to 6% in a microwave cycle of two minutes. The energy consumption is about 55 kWh/m3. Moisture distribution profiles demonstrate very uniform drying across the sample thickness. The findings suggest that microwave heating can potentially be applied to condition wood in a very short period of time.  相似文献   
994.
995.
The thermodynamics of nanocrystalline TiO2 ceramics during the whole sintering process were analyzed using differential scanning calorimetry (DSC) for different heating rates (10, 20 and 30 °C/min). The raw TiO2 powder was also studied comparably. The DSC and specific heat capacity (Cp) were also studied. The results show that there is no obvious endothermic or exothermic peak at the stage where the maximum densification rate occurred for TiO2 ceramics. The ordering process induced by the microstructural densification counteracts the disordering process induced by increasing the sintering temperature. The sintering process is a result of combination of the ordering process and the disordering one. The activation energy of nanometer TiO2 ceramics determined by Kissinger method is 103.8 kJ/mol.  相似文献   
996.
Multiple-bonded iron-oxo and -nitrido species have been identified or proposed as key intermediates in a range of important chemical transformations. The reported model complexes feature various coordination geometries and distinct electronic structures, and therefore exhibit diverse reactivity. The present contribution highlights the synergy from both experimental and theoretical standpoints to elucidate their different bonding situations and delineate their common mechanistic features in hydrogen-atom abstraction processes. Our analysis reveals that a radical centered on the abstracting atom E (E=O, N), which is generated via homolysis of covalent Fe−E bonds upon approaching the transition state, is an intrinsic C−H cleaving agent. The iron-oxo species is predicted to be more reactive than its nitride congener, in general, because the O−H bond formed in the H-atom transfer process is often stronger than the corresponding N−H bond.  相似文献   
997.
998.
Diffusion tensor imaging is of high value in neurosurgery, providing information about the location of white matter tracts in the human brain. For their reconstruction, streamline techniques commonly referred to as fiber tracking model the underlying fiber structures and have therefore gained interest. To meet the requirements of surgical planning and to overcome the visual limitations of line representations, a new real-time visualization approach of high visual quality is introduced. For this purpose, textured triangle strips and point sprites are combined in a hybrid strategy employing GPU programming. The triangle strips follow the fiber streamlines and are textured to obtain a tube-like appearance. A vertex program is used to orient the triangle strips towards the camera. In order to avoid triangle flipping in case of fiber segments where the viewing and segment direction are parallel, a correct visual representation is achieved in these areas by chains of point sprites. As a result, a high quality visualization similar to tubes is provided allowing for interactive multimodal inspection. Overall, the presented approach is faster than existing techniques of similar visualization quality and at the same time allows for real-time rendering of dense bundles encompassing a high number of fibers, which is of high importance for diagnosis and surgical planning.  相似文献   
999.
1000.
OBJECTIVES: The choice of cell line for in vitro biological tests which assess the cytotoxicity of dental materials remains controversial, yet this issue is important because these tests are widely used to rate the biocompatibility of new and existing materials, and many different cell lines are commonly used. The purpose of the current study was to quantify the responses of four cell lines (Balb/c 3T3, L929, ROS 17/2.8 and WI-38) to 14 metal ions which are released from dental materials, and relate these responses to the metabolic activity and population doubling times of these cells. METHODS: Succinic dehydrogenase (SDH) activity was used to monitor metabolic activity and cytotoxic response. RESULTS: The cell lines responded differently to most metal ions. In general, the Balb/c 3T3 line was the most sensitive, and the WI-38 line was the least sensitive. However, there were many exceptions depending on the metal ion. The passage number of the cells also affected the cytotoxic response. It was concluded that the cytotoxicity of materials which release metal ions will be significantly different depending on which cell line is selected and its passage number. SIGNIFICANCE: Based on the findings that cell lines ranked the toxicities of the metal ions similarly, it seems reasonable to use these types of in vitro tests to rank the cytotoxicities of materials. However, if these types of tests are used to predict in vivo cytotoxicity, care should be taken to choose conditions and cells which are relevant.  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