全文获取类型
收费全文 | 5765篇 |
免费 | 93篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 37篇 |
综合类 | 1篇 |
化学工业 | 617篇 |
金属工艺 | 126篇 |
机械仪表 | 103篇 |
建筑科学 | 118篇 |
矿业工程 | 5篇 |
能源动力 | 72篇 |
轻工业 | 289篇 |
水利工程 | 19篇 |
石油天然气 | 8篇 |
无线电 | 540篇 |
一般工业技术 | 698篇 |
冶金工业 | 2889篇 |
原子能技术 | 33篇 |
自动化技术 | 311篇 |
出版年
2021年 | 32篇 |
2019年 | 27篇 |
2018年 | 40篇 |
2017年 | 28篇 |
2016年 | 37篇 |
2015年 | 30篇 |
2014年 | 52篇 |
2013年 | 148篇 |
2012年 | 91篇 |
2011年 | 95篇 |
2010年 | 99篇 |
2009年 | 117篇 |
2008年 | 121篇 |
2007年 | 115篇 |
2006年 | 101篇 |
2005年 | 100篇 |
2004年 | 86篇 |
2003年 | 104篇 |
2002年 | 78篇 |
2001年 | 91篇 |
2000年 | 114篇 |
1999年 | 152篇 |
1998年 | 836篇 |
1997年 | 525篇 |
1996年 | 366篇 |
1995年 | 229篇 |
1994年 | 194篇 |
1993年 | 219篇 |
1992年 | 69篇 |
1991年 | 91篇 |
1990年 | 102篇 |
1989年 | 95篇 |
1988年 | 72篇 |
1987年 | 73篇 |
1986年 | 55篇 |
1985年 | 73篇 |
1984年 | 68篇 |
1983年 | 62篇 |
1982年 | 53篇 |
1981年 | 72篇 |
1980年 | 60篇 |
1979年 | 43篇 |
1978年 | 28篇 |
1977年 | 112篇 |
1976年 | 171篇 |
1975年 | 37篇 |
1974年 | 36篇 |
1973年 | 45篇 |
1972年 | 23篇 |
1970年 | 24篇 |
排序方式: 共有5866条查询结果,搜索用时 15 毫秒
51.
52.
53.
Mann-Fu Rau David Rieck James W. Evans 《Metallurgical and Materials Transactions B》1987,18(1):257-278
An “environmental cell” located in a high voltage transmission electron microscope has been used to study the reduction of
single crystal iron oxides by hydrogen and hydrogen-argon mixtures. The cell enables a direct observation of the solid during
reaction, thus permitting the nucleation and growth of solid reaction products to be observed. Hematite was reduced at temperatures
in the range 387 to 610°C with gas pressures up to 5.3 kP. Reduction with pure hydrogen was considerably faster than when
argon was present. Lath magnetite which rapidly transforms to porous magnetite and thence (more slowly) to porous iron was
observed. The reduction of magnetite and of wustite single crystals was observed in the temperature range 300 to 514°C using
both hydrogen and hydrogen-argon mixtures at gas pressures up to 6.6 kP. Incubation periods were found for magnetite reduction;
during these periods faceted pits formed in the oxide. Iron formed in the early stages was epitaxial with the host magnetite;
at later stages the epitaxy was lost and fissures frequently formed in the metal. The morphology of the iron differed between
the gas mixtures. Disproportionation accompanied the reduction of wustite, producing intermediate polycrystalline magnetite
despite reducing conditions. The disproportionation appeared to be promoted by the reduction reaction. For both oxides, reduction
in the hydrogen-argon mixture was slower than in pure hydrogen. 相似文献
54.
In Situ Formation of a Novel Nanocomposite Structure Based on MCM-41 and Polyethylene 总被引:1,自引:0,他引:1
M41S materials are prepared by in situ assembly of inorganic precursors and organic template and can be viewed as nanocomposites of the siliceous phase and organic surfactant. Calcination of these precursors gives the M41S materials that have been used to prepare novel nanocomposite structures, in which the organic phase inside the nano-sized pores is isolated by the nano-sized inorganic pore walls. The nanocomposite structures can be formed by in situ polymerization of monomers inside the channels. Polymerization of ethylene takes place inside the nano-sized pores, producing the desired nanocomposite structure. The resulting polyethylene was found to be a mixture of crystalline and amorphous phases. 相似文献
55.
HM Kepplinger 《The Journal of communication》1997,47(4):102-117
The author discusses Christopher Simpson's (1996) article, 'Elisabeth Noelle-Neumann's 'Spiral of Silence' and the Historical Context of Communication Theory.' He questions the relevance of biographical data for the evaluation of scientific theories and methods, and analyzes the rhetorical structure of Simpson's arguments. He concludes that Simpson's claims about the influence of Noelle's biography on her scholarly work are not grounded in evidence. 相似文献
56.
Based on successful results in animal models, it has been proposed that high-dose myeloablative therapy followed by autologous bone marrow or stem cell transplantation (ABMT/ASCT) may cure autoimmune disease. The coexistence of autoimmune disease and hematologic malignancy provides an opportunity to examine the response of autoimmune disease to ABMT or ASCT. We describe 4 patients with autoimmune disease (3 with psoriasis and 1 with rheumatoid arthritis) and hematologic malignancy. In each patient, the autoimmune disease remitted posttransplantation, but, in 4 patients with long-term followup, it recurred at 8-24 months. The earliest relapse occurred in a patient treated with interferon-alpha. Our experience suggests that a single autograft with unpurged stem cells is unlikely to cure autoimmune disease, but that other strategies building on this approach are worthy of investigation. 相似文献
57.
P Dhordain O Albagli RJ Lin S Ansieau S Quief A Leutz JP Kerckaert RM Evans D Leprince 《Canadian Metallurgical Quarterly》1997,94(20):10762-10767
58.
59.
60.
J Aronowski E Samways R Strong HM Rhoades JC Grotta 《Canadian Metallurgical Quarterly》1996,16(4):705-713
We tested the hypothesis that increasing durations of focal ischemia that have been shown to result in enlargement of cortical infarct will be associated with progression of behavioral dysfunction that can be measured by a battery of tests sufficiently sensitive and reproducible to detect a positive effect of pharmacotherapy. Untreated or N-methyl-D-aspartate receptor antagonist (CNS-1102)-treated spontaneously hypertensive rats underwent 45, 60, 90, or 120 min of tandem middle cerebral and common carotid artery occlusion followed by reperfusion. We then evaluated the extent of damage and its recovery for up to 21 days using nine behavioral tests aimed at analyzing strength, coordination, and bilateral asymmetry. Also using a graded bioassay that employs a curve-fitting computer program (ALLFIT) to correlate duration of ischemia with degree of behavioral dysfunction, we calculated the average of maximal behavioral dysfunction and duration of ischemia required to produce half-maximal behavioral dysfunction and compared these values in untreated controls with analogous values obtained from animals treated with CNS-1102. Three behavioral tests, forearm flex, tape (somatosensory neutralization), and foot-fault placing, were each separately and combined able to distinguish between the degrees of damage produced by increasing durations of ischemia. The behavioral abnormalities assessed using the tape test were reversible within a week, whereas those using forearm flex or foot-fault tests persisted for at least 21 days. CNS-1102 significantly reduced behavioral dysfunction measured by all three tests. This analysis of behavioral dysfunction represents a useful experimental model to grade efficacy of therapies aimed at protecting the brain from damage produced by acute stroke and might also be used to assess recovery from preexisting ischemic damage. 相似文献