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   1083篇
  免费   10篇
化学工业   53篇
金属工艺   2篇
机械仪表   13篇
建筑科学   34篇
矿业工程   2篇
能源动力   5篇
轻工业   30篇
水利工程   5篇
石油天然气   4篇
无线电   23篇
一般工业技术   76篇
冶金工业   789篇
原子能技术   8篇
自动化技术   49篇
  2022年   5篇
  2017年   5篇
  2016年   7篇
  2015年   3篇
  2014年   9篇
  2013年   13篇
  2012年   13篇
  2011年   10篇
  2010年   12篇
  2009年   18篇
  2008年   13篇
  2007年   13篇
  2006年   6篇
  2005年   8篇
  2004年   7篇
  2003年   11篇
  2002年   8篇
  2001年   6篇
  2000年   6篇
  1999年   30篇
  1998年   242篇
  1997年   126篇
  1996年   78篇
  1995年   50篇
  1994年   36篇
  1993年   45篇
  1992年   19篇
  1991年   13篇
  1990年   9篇
  1989年   15篇
  1988年   13篇
  1987年   20篇
  1986年   11篇
  1985年   11篇
  1984年   11篇
  1983年   9篇
  1982年   11篇
  1981年   13篇
  1980年   9篇
  1979年   6篇
  1978年   10篇
  1977年   30篇
  1976年   63篇
  1973年   3篇
  1972年   3篇
  1968年   3篇
  1967年   2篇
  1966年   2篇
  1964年   4篇
  1962年   2篇
排序方式: 共有1093条查询结果,搜索用时 15 毫秒
1.
Levels of temporary invalidity because of catching cold were analyzed in 101 working women over two years and these women's levels of serum iron, total iron-binding capacity of the serum, transferrin saturation with iron, serum ferritin, and red cell ferritin measured. Women with stable iron reserves in the body virtually have no sick leaves because of catching cold, whereas in those with iron deficiency susceptibility to catching cold is increased, and if iron metabolism intensity in the body grows, invalidity periods are much longer. Normalization of not only iron reserves in the body, but correction of iron metabolism as well should be regarded as a factor exerting a favorable effect on body resistance to catching cold.  相似文献   
2.
3.
Nuclear magnetism in the second layer of 3He films on graphite has been studied as a function of density in the zero-field limit at temperatures down to 300 µK. Total surface coverages in this study ranged from 20 atoms/nm2 (the lowest coverage at which the effective exchange parameter turns ferromagnetic) through the two-phase region (ending at about 24 atoms/nm2) and into the single-phase imcommensurate solid region up to 31.2 atoms/nm2. The surface layers were studied using both pulsed and cw NMR measured with our SQUID NMR system in magnetic fields of 500 µT and lower. As the surface density continues to increase in the single-phase region, the exchange constant decreases consistently with a picture of steric hindrance impeding ferromagnetic exchange. Several different observational features scale with this inferred exchange: low-field magnetization, NMR frequency shift, and the temperature of onset of significant magnetization.  相似文献   
4.
5.
Two cases of fibromatosis of the breast, characterized by a proliferation of spindle cells containing intracytoplasmic, spherical, eosinophilic inclusion bodies, are reported. The light and electron microscopic features, as well as the immunohistochemical features, are indistinguishable from those found in infantile digital fibromatosis. The proliferating spindle cells are characterized as myofibroblasts, whereas the inclusion bodies show an immunohistochemically nonreactive, hollow-like pattern with peripheral reactivity for actin filaments. This lesion, observed for the first time in the breast, expands the number of extradigital inclusion body fibromatoses.  相似文献   
6.
It has previously been shown that the Copenhagen (COP) rat contains several genetic loci that contribute to its mammary tumor-resistant phenotype after 7,12-dimethylbenz(a)anthracene (DMBA) administration. One of these loci, mammary carcinoma susceptibility 1 (Mcs1), is located on the centromeric end of chromosome 2 and appears to act in a semidominant fashion. To confirm the existence and independent action of this locus and also aid in the identification of the physical location of the Mcs1 gene, congenic lines were generated by transferring the Mcs1 COP allele onto a Wistar Furth (WF) genetic background. Male carriers were genotyped using microsatellite markers spanning 20-30 cM of the Mcs1 locus. One of the congenic lines minimally retained the COP allele at D2Mit29 on the centromeric end of chromosome 2 and extended distally to D2Rat201. Heterozygous Mcs1 carrier rats were interbred, and the female offspring were treated with DMBA. The female rats from the Mcs1 congenic line that carried one or two COP alleles of the Mcs1 region had a significantly reduced (65 and 85%, respectively) tumor development (P < 0.001) compared with rats carrying zero COP alleles at this locus. A WF.COP-D2Mit29/D2Rat201 homozygous congenic strain derived at the N10 generation was treated with DMBA, and the COP homozygous rats developed 1.5 +/- 0.3 carcinomas/rat versus 6.3 +/- 0.5 in WF control rats (P < 0.0001). Fine mapping of this congenic interval using several recombinant lines identified three genetic loci within the Mcs1 congenic region that independently supported a tumor resistance phenotype. These genetic loci have been termed Mcs1a, Mcs1b, and Mcs1c. In rats for which each locus was homozygous for the COP allele, tumor development was reduced by approximately 60% compared with littermate controls. The identification of these independent loci within the Mcs1 COP allele provide a model of the genetic complexity of cancer.  相似文献   
7.
8.
9.
The design of a single-chip VLSI system to implement the Zigangirov-Jelinek sequential decoding algorithm for bit-error-correction is described and the dependence of performance on design parameters is discussed. By virtue of being self-contained, having few input and output pins, and processing stack elements once each clock cycle, the system should be capable of high-speed decoding. For constraint length 21, rate 1/2 codes, and 3-b soft decision detection, it is found that a system containing approximately 25000 stack cells reduces errors in a 3-dB signal-to-noise level environment, corresponding to 7.8% hard decision error rate, by two orders of magnitude. Higher decoding gain is obtained at lower noise levels through the use of a relatively long constraint length. The constraint length is not limited by the architecture. Chip area estimates needed to obtain prescribed decoded error rates and average decoding rates are also described and indicate that an effective system is potentially achievable with current technology  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