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   4192篇
  免费   229篇
  国内免费   138篇
电工技术   83篇
综合类   332篇
化学工业   610篇
金属工艺   668篇
机械仪表   302篇
建筑科学   241篇
矿业工程   43篇
能源动力   35篇
轻工业   417篇
水利工程   6篇
石油天然气   64篇
武器工业   30篇
无线电   117篇
一般工业技术   380篇
冶金工业   849篇
原子能技术   14篇
自动化技术   368篇
  2024年   10篇
  2023年   45篇
  2022年   184篇
  2021年   188篇
  2020年   112篇
  2019年   81篇
  2018年   102篇
  2017年   95篇
  2016年   99篇
  2015年   107篇
  2014年   155篇
  2013年   234篇
  2012年   187篇
  2011年   333篇
  2010年   256篇
  2009年   334篇
  2008年   277篇
  2007年   276篇
  2006年   285篇
  2005年   249篇
  2004年   179篇
  2003年   148篇
  2002年   115篇
  2001年   89篇
  2000年   53篇
  1999年   41篇
  1998年   34篇
  1997年   39篇
  1996年   23篇
  1995年   24篇
  1994年   30篇
  1993年   29篇
  1992年   13篇
  1991年   3篇
  1990年   16篇
  1989年   20篇
  1988年   16篇
  1987年   12篇
  1986年   13篇
  1985年   9篇
  1984年   3篇
  1981年   2篇
  1979年   4篇
  1967年   3篇
  1966年   4篇
  1964年   3篇
  1963年   5篇
  1961年   2篇
  1955年   2篇
  1954年   1篇
排序方式: 共有4559条查询结果,搜索用时 0 毫秒
31.
We examined the effects of a set of four biosynthetically related iridoid glycosides, aucubin, catalpol, loganin, and asperuloside, on larvae of a generalist,Lymantria dispar (Lymantriidae), the gypsy moth, and an adapted specialist, the buckeye,Junonia coenia (Nymphalidae). In general,L. dispar grew and survived significantly less well on artificial diets containing iridoid glycoside, compared to a control diet without iridoid glycosides. In choice tests, previous exposure to a diet containing iridoid glycosides caused larvae subsequently to prefer iridoid glycoside-containing diets even though they were detrimental to growth and survival. In contrast,J coenia larvae grew and survived better on diets with aucubin and catalpol, the two iridoid glycosides found in the host plantPlantago lanceolata (Plantaginaceae), than on diets with no iridoid glycoside or with loganin and asperuloside. The results of choice tests of diets with and without iridoid glycosides and between diets with different iridoid glycosides reflected these differences as well. These results are discussed in terms of (1) differences between generalists and specialists in their response to qualitative variation in plant allelochemical content, (2) the induction of feeding preferences, and (3) the evolution of qualitative allelochemical variation as a plant defense.  相似文献   
32.
以自制苯并噻唑离子液体([HBth]HSO4)为活性组分,HZSM-5分子筛为载体,通过过量溶剂浸渍法制备了固载型苯并噻唑离子液体催化剂([HBth]HSO4/HZSM-5)并用于催化合成烷基糖苷,通过傅立叶变换红外光谱、N2物理脱附、场发射电子显微镜和X射线衍射对催化剂结构进行表征,结果表明,[HBth]HSO4被成功地引入到HZSM-5载体的表面及孔道内。当催化剂用量为1.5 wt%,反应温度为105℃,醇糖摩尔比n(葡萄糖):n(辛醇)=6:1时,辛基糖苷得率达148.8%(产物质量/葡萄糖的质量?100%)。底物拓展及催化剂稳定性研究结果表明,[HBth]HSO4/HZSM-5对烷基糖苷及其衍生物都具有良好的催化效果,且催化剂能稳定循环使用四次,活性组分流失是催化剂失活的主要原因。通过对烷基糖苷催化合成机理和动力学的研究,确定了动力学方程。  相似文献   
33.
Epoxide hydrolase catalyzes a simple hydrolysis of reactive cyclic ethers that may otherwise alkylate and impair critical proteins and nucleic acids required for life. Although much less studied than the cytochrome P-450 monooxygenases that produce epoxides, differences in subcellular, tissue, pH, substrate, and inhibitor specificities argue for at least three forms of insect epoxide hydrolase. Increasing numbers of epoxides are being identified as plant allelochemicals, antifeedants, and essential hormones or precursors for herbivorous arthropods, and in many cases an associated alkene to diol pathway of metabolism is found. A role for epoxide hydrolase in arthropod-plant interactions is strongly supported by species comparisons and by age-activity and induction studies. Two major limitations for study in biochemical ecology of epoxide hydrolase are the lack of an effective in vivo inhibitor and a range of commercially available radiolabeled substrates for the enzymes.  相似文献   
34.
地月系共线平动点附近的Halo轨道族,能够提供从L1点至月球再至L2点的广泛空间的多种轨道应用需要,但2个轨道族内轨道的稳定性差异较大。文章引入稳定系数和线性稳定阶数2个指标来判断轨道的稳定性,并用数值模拟分别分析了百米和千米量级的初始轨道误差在数天后所引起的轨道偏差,得出结论:两轨道族内接近平动点的部分轨道稳定性较差,其余部分轨道稳定性相差不大,L1点附近Halo轨道族内轨道较为稳定的是0.85~0.92之间的轨道,L2点较为稳定的是1.02~1.1之间的轨道。  相似文献   
35.
家庭暴力是近年来我国婚姻领域的突出问题,家庭暴力事件呈上升趋势,男尊女卑、父权制的封建陋习造成家庭暴力的受害者多为女性,而家庭暴力行为的隐秘性、残暴性、反复性,使得反家庭暴力存在困难。立足于中国的实际,文章以家庭暴力的法律规制为切入点,反思家庭暴力的产生原因,并对防止和制裁家庭暴力问题展开深入的理论研究,以期为我国的家庭暴力规制制度的完善尽一份绵薄之力。  相似文献   
36.
Product family design and product configuration based on data mining technology is identified as an intelligent and automated means to improve the efficiency of product development. However, few of previous literatures have proposed systematic product family design method based on data mining technology. To make up for this deficiency, this research put forward a systematic data-mining-based method for product family design and product configuration. First, the customer requirement information and product engineering information in the historical order are formatted into structural data. Second, principal component analysis is performed on historical orders to extract the customers' differentiated needs. Third, association rule algorithm is introduced to mine the rules between differentiated needs and module instances in the historical orders, thus obtained the configuration knowledge between customer needs and product engineer. Forth, the mined rules are used to construct association rule-based classifier (CBA) that is employed to sort out the best product configuration schemes as popular product variants. Fifth, sequence alignment technique is employed to identify modules for popular product variants, so that the module instances are divided into optional, common and special module, respectively, thereby the product platform is generated based on common modules. Finally, according to new customer needs, the CBA classifier is used to recommend the best configuration schemes, and then popular product variants are configured based on the product platform. The feasibility of the proposed method is demonstrated by the product family design example of desktop computer hosts.  相似文献   
37.
王鹏  朱韦龙 《图学学报》2021,42(6):1051-1060
为提升产品造型意象成族的准确性,增强感性工学研究中意象词汇提取的规范性和知识重用性。 首先从同族、泛族、异族的概念切入,对目标产品族的造型意象本体进行了定义;再借助 word2vec 工具和主 成分分析法(PCA)分别完成了对产品族意象词汇的关联性联想和降维提取,从而构建了意象词汇挖掘机制,通 过此机制可以辅助设计师利用网络大数据资源更高效、准确地进行目标产品意象的挖掘,一定程度上解决了传 统感性工学在意象挖掘方法中模糊性。最后结合意象词汇与造型特征的映射关系,利用 Protege 工具构建了产 品族造型意象的本体模型,对目标产品的造型意象知识进行了逻辑化表征,为下一代产品继承并发展原产品族 造型意象提供参考。以马自达 MX-5 车系的造型意象为例构建了本体模型,并进行了子代产品前脸的概念设计。  相似文献   
38.
产品族竞争优势是产品族在市场上比其他同类产品更能带来利润或效益的优势。产品族以大规模定制的方式实现了大规模生产不具备的定制化优势和单一方式不具备的规模优势。通过梳理产品族架构的过程,提出产品族架构的金字塔结构,并分析了影响产品族架构的其他因素;分析了产品族竞争优势,将产品族竞争优势分为规模优势和定制化优势;描述了产品族架构与市场、供应链、企业技术能力、企业制造能力等影响因素对产品族竞争优势的影响的分析模型。  相似文献   
39.
40.
Processing map for hot working of as extruded AZ31B magnesium alloy   总被引:1,自引:0,他引:1  
The deformation behavior of AZ31B magnesium alloy as extruded under hot compression conditions was characterized in the temperature range of 200 - 400 ℃ and strain rate range of 0. 001 - 1 s^-1. The processing maps were obtained at different strains. The results show that the map exhibits flow instabilities as two domains. The domain at beyond 300 ℃ and strain rate of 1 s^-1 appears with a peak efficiency of power dissipation about 56% occurring. This domain is expected to happen in a hot process, such as hot rolling, hot extrusion and hot forging. There is high efficiency of power dissipation at temperature beyond 350 ℃ and strain rate 0. 001 s^-1. Such domains suggest the occurrence of superplastic deformation.  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