全文获取类型
收费全文 | 1419篇 |
免费 | 17篇 |
专业分类
电工技术 | 6篇 |
化学工业 | 49篇 |
金属工艺 | 4篇 |
机械仪表 | 34篇 |
建筑科学 | 6篇 |
能源动力 | 6篇 |
轻工业 | 32篇 |
水利工程 | 4篇 |
石油天然气 | 2篇 |
无线电 | 53篇 |
一般工业技术 | 118篇 |
冶金工业 | 1044篇 |
原子能技术 | 1篇 |
自动化技术 | 77篇 |
出版年
2023年 | 5篇 |
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 6篇 |
2019年 | 16篇 |
2018年 | 9篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 8篇 |
2014年 | 17篇 |
2013年 | 37篇 |
2012年 | 13篇 |
2011年 | 29篇 |
2010年 | 21篇 |
2009年 | 14篇 |
2008年 | 14篇 |
2007年 | 12篇 |
2006年 | 13篇 |
2005年 | 13篇 |
2004年 | 14篇 |
2003年 | 20篇 |
2002年 | 13篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 44篇 |
1998年 | 310篇 |
1997年 | 200篇 |
1996年 | 125篇 |
1995年 | 70篇 |
1994年 | 66篇 |
1993年 | 62篇 |
1992年 | 13篇 |
1991年 | 22篇 |
1990年 | 21篇 |
1989年 | 27篇 |
1988年 | 25篇 |
1987年 | 22篇 |
1986年 | 23篇 |
1985年 | 13篇 |
1983年 | 2篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 11篇 |
1976年 | 23篇 |
1975年 | 3篇 |
1972年 | 2篇 |
1955年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有1436条查询结果,搜索用时 15 毫秒
101.
102.
103.
Li Wang ping Mechanics Department Huazhong University of Science Technology Wuhan P.R.China Yeo K.S. Khoo B.C. Mechanical Production Engineering Department National University of Singapore 《水动力学研究与进展(B辑)》1999,(3)
1. INTRODUCTIONThemaingoalofthispaperistoexplorethepossibilitytolearnmoreaboutthemechanismofturbulentboundarylayerflowinteractionsanditseffectsoncompliantwallperformance.Therearecertainprerequisiteconditionstofurtherthestudyonthemechanism,i.e.theco… 相似文献
104.
In this work, we investigated the immobilization of methylene blue in a methyltrimethoxysilane sol-gel ceramic film on a glassy carbon electrode. Up to a certain saturation level, under our conditions, it was found that the methylene blue was tightly held and did not leach out into aqueous solutions, even with continuous immersion for up to 1 month. The electrochemical behavior of the immobilized methylene blue was then studied. pH variation revealed that there were two distinct redox couples whose existences were pH-dependent. The methylene blue/sol-gel film was also examined as an electrocatalytic system for ascorbic and uric acid oxidations. It was revealed that this system was highly sensitive for ascorbic and uric acid sensing (practical determination limits of 5.00 nM and 1.00 nM for ascorbic acid and uric acid, respectively) and also allowed simultaneous determination of these biomolecules. The simultaneous determination of these two analytes in a human urine sample was demonstrated. The stability of the methylene blue/sol-gel film/glassy carbon electrode sensing system was good, with up to at least a month of continual operation. 相似文献
105.
Vicent Giner‐Bosch Kim Phuc Tran Philippe Castagliola Michael Boon Chong Khoo 《Quality and Reliability Engineering International》2019,35(6):1515-1541
Monitoring the multivariate coefficient of variation over time is a natural choice when the focus is on stabilising the relative variability of a multivariate process, as is the case in a significant number of real situations in engineering, health sciences, and finance, to name but a few areas. However, not many tools are available to practitioners with this aim. This paper introduces a new control chart to monitor the multivariate coefficient of variation through an exponentially weighted moving average (EWMA) scheme. Concrete methodologies to calculate the limits and evaluate the performance of the chart proposed and determine the optimal values of the chart's parameters are derived based on a theoretical study of the statistic being monitored. Computational experiments reveal that our proposal clearly outperforms existing alternatives, in terms of the average run length to detect an out‐of‐control state. A numerical example is included to show the efficiency of our chart when operating in practice. 相似文献
106.
RN Shain JM Piper ER Newton ST Perdue R Ramos JD Champion FA Guerra 《Canadian Metallurgical Quarterly》1999,340(2):93-100
Using annual bite-wing radiographs, the incidence and progression of approximal caries (4d-7m) were assessed longitudinally in teenagers and adolescents whose treatment had been based on remineralizing rather than restorative strategies. A closed cohort of 536 children initially was followed from 11 to 22 years of age. The scoring system was: 0 = no visible radiolucency; 1-2 = radiolucency in the enamel up to the enamel-dentin border; 3 = radiolucency with a broken enamel-dentin border but with no obvious progression in the dentin; 4 = radiolucency with obvious spread in the outer half of the dentin, and 5 = radiolucency in the inner half of the dentin. Caries rates were estimated as the number of new lesions/100 tooth surface-years, and the Kaplan-Meier estimate was used to calculate the cumulative survival time of each approximal surface. Three events were used: the transitions from states 0 to 2, 2 to 4 and 3 to 4. The results showed a considerable variation between the surfaces in both caries rates and survival time. For all surfaces combined, the median caries rate from state 0 to 2 was 3.9 new lesions/100 tooth surface-years; from state 2 to 4, the rate was 5.4, and from state 3 to 4 it was 20.3. Of the sound surfaces (state 0), 75% survived 6.3 years without reaching state 2. Given state 2, 75% survived 4.8 years without reaching the outer half of the dentin (state 4), while given a lesion at the enamel-dentin border (state 3), 75% survived 1.3 years without doing the same. The median survival time of lesions from state 3 to 4 was 3.1 years. The group with DMFSappr>1 at the age of 11-12 years had a risk of new approximal enamel lesions (state 0-2) that was 2.5 times greater than that of the group with DMFSappr = 0-1. 相似文献
107.
The frog intermediate lobe consists of a single endocrine cell type, the melanotrope cells, which are under the tonic inhibitory control of dopamine. Separation of dispersed pars intermedia cells in a Percoll density gradient has revealed the existence of two melanotrope cell subpopulations, referred to as high-density (HD) and low-density (LD) cells. The aim of the present study was to investigate the effects of dopamine on each of these melanotrope cell subsets. Increasing doses of dopamine, ranging from 10(-9)-10(-6) M, inhibited the release of alpha-melanocyte-stimulating hormone (alpha-MSH) in LD (but not in HD) melanotrope cells. In addition, dopamine provoked a significant reduction of the rate of acetylation of alpha-MSH in LD cells but not in HD cells. Similarly, dopamine significantly decreased the accumulation of POMC messenger RNA in LD cells, whereas it did not affect POMC gene expression in the HD melanotrope subset. On the other hand, microfluorimetric studies revealed that dopamine induced a significant reduction of KCl-stimulated cytosolic free calcium concentration in both LD and HD cells. The present study provides additional evidence for functional heterogeneity of melanotrope cells in the frog pars intermedia. Because dopamine plays a pivotal role in the regulation of alpha-MSH secretion, these data suggest the involvement of cell heterogeneity in the physiological process of background color adaptation in amphibians. 相似文献
108.
109.
110.
RNase H1 from Escherichia coli cleaves single strand RNA extending 3' from an RNA-DNA duplex. Substrates consisting of a 25-mer RNA annealed to complementary DNA ranging in length from 9-17 nucleotides were designed to create overhanging single strand RNA regions extending 5' and 3' from the RNA-DNA duplex. Digestion of single strand RNA was observed exclusively within the 3' overhang region and not the 5' overhang region. RNase H digestion of the 3' overhang region resulted in digestion products with 5'-phosphate and 3'-hydroxyl termini. The number of single strand RNA residues cleaved by RNase H is influenced by the sequence of the single strand RNA immediately adjacent to the RNA-DNA duplex and appears to be a function of the stacking properties of the RNA residues adjacent to the RNA-DNA duplex. RNase H digestion of the 3' overhang region was not observed for a substrate that contained a 2'-methoxy antisense strand. The introduction of 3 deoxynucleotides at the 5' terminus of the 2'-methoxy antisense oligonucleotide resulted in cleavage. These results offer additional insights into the binding directionality of RNase H with respect to the heteroduplex substrate. 相似文献