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   887篇
  免费   18篇
  国内免费   8篇
电工技术   13篇
综合类   1篇
化学工业   158篇
金属工艺   19篇
机械仪表   18篇
建筑科学   40篇
矿业工程   15篇
能源动力   31篇
轻工业   78篇
水利工程   12篇
石油天然气   4篇
无线电   119篇
一般工业技术   122篇
冶金工业   93篇
原子能技术   4篇
自动化技术   186篇
  2023年   5篇
  2022年   8篇
  2021年   14篇
  2020年   11篇
  2019年   17篇
  2018年   24篇
  2017年   7篇
  2016年   23篇
  2015年   18篇
  2014年   26篇
  2013年   65篇
  2012年   40篇
  2011年   55篇
  2010年   49篇
  2009年   50篇
  2008年   43篇
  2007年   43篇
  2006年   55篇
  2005年   40篇
  2004年   38篇
  2003年   23篇
  2002年   23篇
  2001年   16篇
  2000年   14篇
  1999年   17篇
  1998年   24篇
  1997年   17篇
  1996年   5篇
  1995年   10篇
  1994年   10篇
  1993年   11篇
  1992年   9篇
  1991年   4篇
  1990年   2篇
  1989年   13篇
  1988年   6篇
  1987年   13篇
  1986年   8篇
  1985年   5篇
  1984年   6篇
  1982年   7篇
  1981年   4篇
  1980年   7篇
  1979年   7篇
  1978年   4篇
  1977年   3篇
  1976年   4篇
  1973年   3篇
  1972年   2篇
  1955年   1篇
排序方式: 共有913条查询结果,搜索用时 15 毫秒
51.
52.
The non-digestible fraction (NDF) of common bean (Phaseolus vulgaris L.) cultivar Bayo Madero was evaluated for its chemopreventive effect on azoxymethane (AOM) induced aberrant crypt foci (ACF) in rats. Diets containing cooked beans (CB) or its non-digestible fraction (NDF) were fed to 72 male rats after 2 azoxymethane injections (15 mg kg(-1) of body weight once a week for 2 weeks). ACF number, short chain fatty acids (SCFA) and β-glucuronidase activity were measured in colon sections from rats sacrificed 7 weeks after the last AOM injection. Food intake and weight gain of rats were unaffected by CB and NDF. CB and NDF suppressed the AOM-induced formation of ACF (0.8 and 1.5 ACF/distal zone, respectively vs. 6.6 ACF/distal zone based on methylene blue stain) and lowered β-glucuronidase activity in cecal, colonic and fecal content compared to AOM group. SCFA production was not significantly different among fecal, cecal and colonic content. These results indicate that CB and NDF from Bayo Madero provide direct chemoprotection against early stage of azoxymethane (AOM)-induced colon cancer in rats.  相似文献   
53.
The following column on methodology topic was prepared by AOCS Technical Director Dave Berner. Questions on these or other topics concerning analytical methodology of fats and oils or related products may be directed to Dave Berner, AOCS, PO Box 3489, Champaign, IL 61821-0489, USA  相似文献   
54.
55.
Segmented mirrors present unique challenges to fabrication and testing that are absent for monolithic optics. Since traditional asphere tests do not address segmented optics adequately, we validate a previously developed method to test large quantities of segments accurately, quickly, and economically. In this test, the aspheric shape of each segment is controlled to high accuracy by use of computer-generated holograms, and the radius of curvature is tightly controlled by use of the reference plate. In an adjoining paper [Appl Opt 43, 5303 (2004)] we developed the theory for this test, and now we present a complete system design and optimization for measuring the 1.4-m segments from a 30-m F/1 primary. A complete tolerance analysis predicts a test accuracy of 4.8-nm rms surface and excellent accuracy for controlling the geometry of the segment. In addition, a laboratory demonstration using 30-cm optics is presented that demonstrated 3.9-nm rms surface accuracy.  相似文献   
56.
4 experiments provided support for the hypothesis that tonic immobility (TI) in chickens, which may be analogous to response suppression in the rat, is a result of fear and is mediated by central cholinergic systems. A total of 124 experimental and 54 control, White Leghorn cockerel chicks were the Ss. Exp I established that scopolamine, a central and peripheral acting anticholinergic, will reduce the duration of TI, whereas methylscopolamine, which acts only peripherally, will not. Exp II established a dose-response curve for scopolamine and TI. Exp III demonstrated that scopolamine increased activity and that this increase may be a factor in reducing the duration of TI. Exp IV showed that physostigmine, which blocks acetylcholinesterase and allows longer action of acetylcholine at the synapse, increased the duration of TI. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
57.
58.
59.
Clavibacter sp. ALA2 oxidized n−3 and n−6 PUFA into a variety of oxylipins. Structures of products converted from EPA and DHA were determined as 15,18-dihydroxy-14,17-epoxy-5(Z),8(Z),11(Z)-eicosatrienoic acid and 17,20-dihydroxy-16,19-epoxy-4(Z),7(Z),10(Z),13(Z)-docosatetraenoic acid by GC-MS and NMR analyses. In contrast, γ-linolenic acid and arachidonic acid were converted to diepoxy bicyclic FA, tetrahydrofuranyl monohydroxy FA, and trihydroxy FA. Thus, the structures of bioconversion products were different between n−3 and n−6 PUFA. Furthermore, strain ALA2 placed hydroxy groups and cyclic structures at the same position from the ω-terminal despite the number of carbons in the chain and the double bonds in the PUFA.  相似文献   
60.
Control over the surface functionality and microporosity in conjugated microporous polymers (CMPs) has been achieved by the post-synthetic modification of amines into amides of with different alkyl chains, one of which was chiral. The surface areas, pore volumes, carbon dioxide uptakes and isosteric heat of adsorption for carbon dioxide can be rationally tuned.  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