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   962篇
  免费   12篇
电工技术   14篇
化学工业   71篇
金属工艺   23篇
机械仪表   26篇
建筑科学   1篇
矿业工程   25篇
能源动力   2篇
轻工业   8篇
水利工程   8篇
石油天然气   21篇
无线电   22篇
一般工业技术   113篇
冶金工业   529篇
原子能技术   58篇
自动化技术   53篇
  2021年   10篇
  2020年   8篇
  2019年   7篇
  2018年   17篇
  2017年   10篇
  2016年   13篇
  2015年   11篇
  2014年   14篇
  2013年   23篇
  2012年   17篇
  2011年   23篇
  2010年   17篇
  2009年   23篇
  2008年   21篇
  2007年   23篇
  2006年   10篇
  2005年   20篇
  2004年   10篇
  2003年   7篇
  2002年   10篇
  2001年   6篇
  2000年   9篇
  1999年   11篇
  1998年   155篇
  1997年   95篇
  1996年   59篇
  1995年   37篇
  1994年   27篇
  1993年   39篇
  1992年   10篇
  1991年   11篇
  1990年   8篇
  1989年   9篇
  1988年   8篇
  1987年   5篇
  1986年   11篇
  1985年   16篇
  1983年   8篇
  1981年   7篇
  1980年   16篇
  1979年   9篇
  1977年   14篇
  1976年   35篇
  1975年   7篇
  1974年   8篇
  1973年   9篇
  1972年   8篇
  1970年   6篇
  1968年   7篇
  1967年   4篇
排序方式: 共有974条查询结果,搜索用时 343 毫秒
1.
2.
The European Electronic Money Directive contains a definition of electronic money. However, determining which systems involving the use of electronic value fall under its scope can be more complicated than one might think. This issue is explored in this article through consideration of the question of whether prepaid mobile phone credits qualify as electronic money—a question that is currently being debated by telecommunications operators and regulators.  相似文献   
3.
The procedure is proposed for estimating the crack resistance and tensile strength of rocks by the results of experiments on disk samples with holes. The gradient approach to the strength problem is employed in processing the experimental data.  相似文献   
4.
5.
Pilot studies in human populations have demonstrated a correlation between the level of antigen receptor trans-rearrangements and risk (at the population level) of lymphoid malignancy. Irradiation of newborn severe combined immune deficiency mice results in an increased risk of subsequent development of thymic lymphoma (100% of mice so irradiated are dead of thymic lymphoma by 20 weeks of age). We, therefore, assayed the occurrence of trans-rearrangements in this well-controlled mouse mutant system and found a 50-100-fold increase in the absolute number of TCRGV-TCRBJ trans-rearrangements compared to unirradiated littermates (and a comparable fold increase over age-matched BALB/c mice) at 2 weeks following irradiation. We also found a marked disproportion in generating trans-rearrangements versus intralocus rearrangements in the severe combined immune deficiency system compared to BALB/c, independent of irradiation. The trans-rearrangements noted were polyclonal in nature. These data, again, suggest that the absolute level of antigen receptor trans-rearrangements may serve as a biomarker of lymphoma risk.  相似文献   
6.
During the last decade, episodes of sepsis have increased and Escherichia coli has remained the most frequent clinical isolate. Lipopolysaccharides (LPS; endotoxin) are the major toxic and antigenic components of gram-negative bacteria and qualify as targets for therapeutic interventions. Molecules that neutralize the toxic effects of LPS are actively investigated. In this paper, we describe a murine monoclonal antibody (MAb; WN1 222-5), broadly cross-reactive and cross-protective for smooth (S)-form and rough (R)-form LPS. As shown in enzyme-linked immunosorbent assay and the passive hemolysis assay, WN1 222-5 binds to the five known E. coli core chemotypes, to Salmonella core, and to S-form LPS having these core structures. In immunoblots, it is shown to react with both the nonsubstituted core LPS and with LPS carrying O-side chains, indicating the exposure of the epitope in both S-form and R-form LPS. This MAb of the immunoglobulin G2a class is not lipid A reactive but binds to E. coli J5, an RcP+ mutant which carries an inner core structure common to many members of the family Enterobacteriaceae. Phosphate groups present in the inner core contribute to the epitope but are not essential for the binding of WN1 222-5 to complete core LPS. Cross-reactivity for clinical bacterial isolates is broad. WN1 222-5 binds to all E. coli clinical isolates tested so far (79 blood isolates, 80 urinary isolates, and 21 fecal isolates) and to some Citrobacter, Enterobacter, and Klebsiella isolates. This pattern of reactivity indicates that its binding epitope is widespread among members of the Enterobacteriaceae. WN1 222-5 exhibits biologically relevant activities. In vitro, it inhibits the Limulus amoebocyte lysate assay activity of S-form and R-form LPS in a dose-dependent manner and it neutralizes the LPS-induced release of clinically relevant monokines (interleukin 6 and tumor necrosis factor). In vivo, WN1 222-5 blocks endotoxin-induced pyrogenicity in rabbits and lethality in galactosamine-sensitized mice. The discovery of WN1 222-5 settles the long-lasting controversy over the existence of anti-core LPS MAbs with both cross-reactive and cross-protective activity, opening new possibilities for the immunotherapy of sepsis caused by gram-negative bacteria.  相似文献   
7.
In exploring the structural features which determine the antitumor activity of 2,4,6-tris-[(hydroxymethyl)methylamino]-1,3,5-triazine (trimelamol, 1), we have synthesized analogues in which the methyl groups have been replaced by the electron-withdrawing substituents 2,2,2-trifluoroethyl (5), propargyl (13), and cyanomethyl (15) via the respective tris(alkylamino)triazines 3, 12, and 14. Three mono[(hydroxymethyl)amino]triazines (4, 7, and 10) were also prepared. All the new tris(hydroxymethyl) derivatives showed cytotoxicities toward a variety of experimental rodent and human ovarian tumor cell lines similar to those shown by 1, the cyanomethyl analogue (15) having the most favorable profile. Mono(hydroxymethyl) derivatives (4 and 7) were ca. one-third as toxic. The new tris(hydroxymethyl) analogues were more stable to aqueous hydrolysis than was 1. Half-life (pH 7.5) values were, for 1, 120 min, for 5, 690 min, for 13, 450 min, and for 15, 275 min, but at pH 2.0, 15 (t1/2 350 min) was the most stable. This cyanomethyl analogue was also the most water-soluble, being comparable to 1 whereas 5 and 13 were poorly soluble.  相似文献   
8.
9.
The notions of dynamical synchronization and adaptive dynamical synchronization problems are introduced. The algorithm solving adaptive synchronization problem for a subclass of Lurie systems with exciting input is proposed. The performance and potentialities of proposed solutions are demonstrated by two examples related to formation control and self‐organization of swarm systems. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
10.
An experimental study was made of the effect of the velocity of an N2+O2 flow and its oxygen content on the rate and nature of combustion of specimens of titanium alloys and St. 20. The limit flow velocities for which combustion is still self-sustaining were obtained as a function of the O2 concentration.N. E. Zhukovskii Central Aero-Hydrodynamics Institute, 140160 Zhukovski. Translated from Fizika Goreniya i Vzryva, Vol. 30, No. 6, pp. 68–71, November–December, 1994.  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