全文获取类型
收费全文 | 6465篇 |
免费 | 73篇 |
国内免费 | 94篇 |
专业分类
电工技术 | 1404篇 |
综合类 | 142篇 |
化学工业 | 83篇 |
金属工艺 | 126篇 |
机械仪表 | 90篇 |
建筑科学 | 64篇 |
矿业工程 | 33篇 |
能源动力 | 162篇 |
轻工业 | 40篇 |
水利工程 | 107篇 |
石油天然气 | 18篇 |
武器工业 | 4篇 |
无线电 | 155篇 |
一般工业技术 | 138篇 |
冶金工业 | 3864篇 |
原子能技术 | 28篇 |
自动化技术 | 174篇 |
出版年
2021年 | 4篇 |
2019年 | 6篇 |
2018年 | 10篇 |
2017年 | 57篇 |
2016年 | 6篇 |
2015年 | 11篇 |
2014年 | 30篇 |
2013年 | 68篇 |
2012年 | 52篇 |
2011年 | 226篇 |
2010年 | 87篇 |
2009年 | 95篇 |
2008年 | 71篇 |
2007年 | 114篇 |
2006年 | 50篇 |
2005年 | 89篇 |
2004年 | 541篇 |
2003年 | 185篇 |
2002年 | 164篇 |
2001年 | 139篇 |
2000年 | 71篇 |
1999年 | 370篇 |
1998年 | 1341篇 |
1997年 | 759篇 |
1996年 | 499篇 |
1995年 | 293篇 |
1994年 | 233篇 |
1993年 | 305篇 |
1992年 | 75篇 |
1991年 | 50篇 |
1990年 | 55篇 |
1989年 | 58篇 |
1988年 | 44篇 |
1987年 | 39篇 |
1986年 | 37篇 |
1985年 | 32篇 |
1982年 | 24篇 |
1981年 | 27篇 |
1980年 | 28篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 64篇 |
1976年 | 150篇 |
1975年 | 4篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1970年 | 13篇 |
1969年 | 4篇 |
1968年 | 4篇 |
排序方式: 共有6632条查询结果,搜索用时 31 毫秒
81.
82.
83.
R Pratesi L Gandolfi H Friedman L Farage CA de Castro C Catassi 《Canadian Metallurgical Quarterly》1998,33(8):817-821
BACKGROUND: Our objective was to determine the possible presence of IgA antibodies directed against human central nervous system (CNS) structures in sera from coeliac disease (CD) patients. METHODS: Serum samples were collected from 4 patients with active CD on a gluten-containing diet, 11 biopsy-proven CD patients on a gluten-free diet (GFD), and 52 non-coeliac gastrointestinal controls. In all patients IgA antigliadin antibody (AGA) titres were determined with enzyme-linked immunoassay (ELISA), and IgA antiendomysium antibodies (EMA) with indirect immunofluorescence on human umbilical cord. Cryostat sections of human brain occipital cortex were incubated with the patients' sera and subsequently labelled with anti-human IgA fluorescein conjugate. RESULTS: All sera from patients with active CD on a gluten-containing diet yielded positive results in both the IgG-AGA and EMA test and in indirect immunofluorescence on brain tissue, disclosing a strong fluorescence over blood-vessels structures. All sera from CD patients on a GFD and from non-coeliac gastrointestinal controls gave a negative result on both the EMA test and the immunofluorescence reaction on human brain. CONCLUSIONS: Sera from patients with active CD contain IgA antibodies that react with human brain vessel structures, giving intense fluorescence. These antibodies are not present in sera from coeliac patients on a GFD or non-coeliac controls. This finding might be involved in the abnormal nervous system manifestations frequently described in association with coeliac disease. 相似文献
84.
Zhang Zhiming Lu Daohua Li Zhonglin Harbin Institute of Technology Feng Qiting Peng Chuanliou Heilongjiang Electric Power Electrode Manufacturer Harbin Wang Ruilin Northeast Electric Power Test Institute Shenyang 《中国焊接》1992,(2)
The welded joint of dissimilar heat-resisting steels 20Crl2MoV(F12)and 12 Cr2MoWVTiB(102)generally works around 600°C.In this paperthree kinds of ferritic electrodes are used for testing.They are R817 high-strength electrode(CrllMoVNi),R347 low-strength electrode(Cr2MoVWB)and newly-developed R507MoNb medium-strength electrode.The study on theinfluence of those three different electrodes on carbon migration,HIC and hy-drogen diffusion shows that medium-strength electrodes can well control thecarbon migration,and that the tendency to HIC in the joint formed by R817 issmaller than that by R347 instead.Considering the effect of weld metal transfor-mation on the restraint stress and hydrogen concentration of a joint,the hydro-gen distribution in the heat-affected zone(HAZ)is calculated by using finite ele-ment method(FEM)with stress and strain changing,and so the effect of thetransformation behaviour on HIC is revealed.In addition,newly-developedR507MoNb electrodes,tested the elevated-temperature property,oxidation re-sistance and creep rupture strength,have fulfilled the technical standards con-cerned and passed the examination of on-the-spot operation. 相似文献
85.
86.
RS Mehta SR Harris CA Gunnett OR Bunce DK Hartle 《Canadian Metallurgical Quarterly》1993,14(8):1693-1696
Chronic caloric restriction has been shown to inhibit mammary tumor promotion in the 7,12-dimethyl-benz[a]anthracene (DMBA) rat mammary tumor model. The objectives of this study were to determine (i) the effects of chronic caloric cycling (yo-yo dieting) on mammary tumor promotion by high fat diets and (ii) the effect of three dietary regimens +/- superimposed mammary tumor burden on plasma endothelin-1,2 (ET) levels. Female Sprague-Dawley rats were treated with DMBA (5 mg/rat) and divided into three dietary groups: ad libitum (AL) (containing 15% corn oil); 40% calorie restricted (CR) (containing 20% corn oil so consumption of fat was equivalent between AL and CR); a calorie cycled (CC) group fed alternatively AL and CR diets each 48 h period. After 10 weeks, tumor incidences were: AL, 63%; CR, 27%; CC, 57% (AL versus CR, P < 0.05; CC versus CR, P < 0.05; AL versus CC, NSD). ET levels (pg/ml plasma) were: AL, 16.0 +/- 6.54; CR, 32.31 +/- 0.34; CC, 23.44 +/- 5.04 (AL versus CR, P < 0.01; CC versus CR, P < 0.01; AL versus CC, P < 0.05). Plasma ET levels were independent of tumor incidence and tumor burden, but plasma ET levels were significantly increased in rats with a prior history of calorie restriction. As expected, maintained caloric restriction reduced mammary tumor incidence but intermittent caloric restriction (caloric cycling or yo-yo dieting) was without similar benefit. 相似文献
87.
蔡清伟 《广东输电与变电技术》2003,(4):49-52
本文提出了建立新一代的开放式自动抄表平台的思想,并着重介绍了构建平台的基本原则、技术要求和设计方式。 相似文献
88.
89.
Seventeen years after the introduction of x-ray digital subtraction angiography (DSA), gadolinium-enhanced magnetic resonance (MR) angiography techniques have become available for the performance of MR-DSA. For the purposes of this article, we will consider this to include two-dimensional and three-dimensional approaches using time-resolved and non-time-resolved applications. Magnetic resonance-DSA is one in a historical progression of techniques which have aimed to produce less invasive forms of angiography. After outlining some historical milestones, several current issues regarding current methods for MR-DSA are discussed. 相似文献
90.
Melanomas develop with high frequency in transgenic mice in which oncogenic sequences of the SV40 DNA tumor virus have been specifically targeted to melanocytes. To investigate the role of SV40 in melanomagenesis, cultured human melanocytes were transformed with a retroviral shuttle vector encoding the SV40 large T antigen and examined for changes in cell-cycle kinetics and growth-factor dependence. Colonies expressing the viral oncogene were morphologically indistinguishable from their non-T-antigen-transformed counterparts. Also like normal melanocytes, the infected cells remained anchorage dependent and non-tumorigenic in nude mice. However, T-antigen-positive cultures exhibited significantly accelerated population doubling times, increased saturation densities with highly confluent monolayers and a three- to fourfold extended life span. Most interestingly, cell-cycle analysis revealed a measurable shift from quiescent to cycling cells in T-antigen-expressing cultures and an acquired ability to progress more rapidly through G1. Moreover, T-antigen-positive melanocytes proliferated in the absence of PMA and required markedly reduced levels of exogenous bFGF. These studies indicate that the viral oncogen of simian virus 40 provides melanocytes with distinct growth advantages that may render these cells unusually susceptible to additional environmental challenges necessary for full expression of the malignant phenotype. 相似文献