全文获取类型
收费全文 | 26897篇 |
免费 | 1715篇 |
国内免费 | 26篇 |
专业分类
电工技术 | 167篇 |
综合类 | 10篇 |
化学工业 | 5638篇 |
金属工艺 | 422篇 |
机械仪表 | 567篇 |
建筑科学 | 832篇 |
矿业工程 | 52篇 |
能源动力 | 512篇 |
轻工业 | 5536篇 |
水利工程 | 311篇 |
石油天然气 | 120篇 |
武器工业 | 1篇 |
无线电 | 1055篇 |
一般工业技术 | 4361篇 |
冶金工业 | 5404篇 |
原子能技术 | 70篇 |
自动化技术 | 3580篇 |
出版年
2024年 | 66篇 |
2023年 | 281篇 |
2022年 | 285篇 |
2021年 | 733篇 |
2020年 | 668篇 |
2019年 | 683篇 |
2018年 | 1244篇 |
2017年 | 1214篇 |
2016年 | 1269篇 |
2015年 | 968篇 |
2014年 | 1125篇 |
2013年 | 2318篇 |
2012年 | 1774篇 |
2011年 | 1587篇 |
2010年 | 1279篇 |
2009年 | 1101篇 |
2008年 | 1156篇 |
2007年 | 1068篇 |
2006年 | 676篇 |
2005年 | 562篇 |
2004年 | 537篇 |
2003年 | 511篇 |
2002年 | 439篇 |
2001年 | 324篇 |
2000年 | 264篇 |
1999年 | 313篇 |
1998年 | 1898篇 |
1997年 | 1196篇 |
1996年 | 731篇 |
1995年 | 393篇 |
1994年 | 305篇 |
1993年 | 318篇 |
1992年 | 87篇 |
1991年 | 73篇 |
1990年 | 60篇 |
1989年 | 59篇 |
1988年 | 81篇 |
1987年 | 74篇 |
1986年 | 61篇 |
1985年 | 73篇 |
1984年 | 61篇 |
1983年 | 35篇 |
1982年 | 36篇 |
1981年 | 61篇 |
1980年 | 59篇 |
1978年 | 31篇 |
1977年 | 105篇 |
1976年 | 207篇 |
1975年 | 33篇 |
1973年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
M Flores-Díaz A Alape-Girón B Persson P Pollesello M Moos C von Eichel-Streiber M Thelestam I Florin 《Canadian Metallurgical Quarterly》1997,272(38):23784-23791
We previously isolated a mutant cell that is the only mammalian cell reported to have a persistently low level of UDP-glucose. In this work we obtained a spontaneous revertant whose UDP-glucose level lies between those found in the wild type and the mutant cell. The activity of UDP-glucose pyrophosphorylase (UDPG:PP), the enzyme that catalyzes the formation of UDP-glucose, was in the mutant 4% and in the revertant 56% of the activity found in the wild type cell. Sequence analysis of UDPG: PP cDNAs from the mutant cell showed one missense mutation, which changes amino acid residue 115 from glycine to aspartic acid. The substituted glycine is located within the largest stretch of strictly conserved residues among eukaryotic UDPG:PPs. The analysis of the cDNAs from the revertant cell indicated the presence of an equimolar mixture of the wild type and the mutated mRNAs, suggesting that the mutation has reverted in only one of the alleles. In summary, we demonstrate that the G115D substitution in the Chinese hamster UDPG:PP dramatically impairs its enzymatic activity, thereby causing cellular UDP-glucose deficiency. 相似文献
33.
34.
A lectin-like protein was isolated from L. muta venom by gel filtration on BIO Gel P-100 followed by column Chromatography on DEAE-sephades A-50. The protein eluted at 0.4 M Nacl in 0.01 Tris pH 7.3 and exhibited agglutinin activity toward 0+ human erythrocytes. The protein is a dimer with Mr 28 kDa. Amino acid analysis revealed high content of tryptophan and acid recidues and low content of cysteine and methionine residues. No neutral carbohydrates and sialic acid were detected. Circular dichroic spectrum shows 78% of B structure and 1% of alpha structure. In vitro experiments with erythrocytes from rat, rabbit and dog revealed strong agglutination while red blood cells from mice, sheep and goat were not agglutinated. In vivo experiments using anesthetized rats, a sharp and prolonged fall in the blood pressure was observed at protein dose of 1.5 mg/kg. Double dose of protein caused the death of the animal. 相似文献
35.
P Sánchez García 《Canadian Metallurgical Quarterly》1997,114(1):157-63; discussion 164-7
36.
37.
38.
Summary The thermal properties of an epoxy resin (diglycidyl ether Bisphenol A, DGEBA) cured with a primary amine (ethylenediamine, ETDA) and filled with 10, 20 and 30 wt. % of ultra fine copper particles were analyzed. The thermal results were evaluated by means of the Romero-Garcia method, which allowed to obtain the resin degradation kinetic parameters, as well as the possible decomposition mechanism. From the obtained results is possible to infer that higger copper content strongly affects the degradation process of the epoxy resin, which causes a drop off on the composites thermal stability. This behavior could be attributed to water presence, being this effect less pronounced for the resin with 10 wt. % copper and unfilled resin. Regarding to decomposition mechanism, three way transport showed the best correlation for all samples. 相似文献
39.
Lime mortars are often used for repairs to historic buildings. This paper investigates two forms of lime binder: fat and feebly-hydraulic,
in order to predict their long-term behaviours and hence ascertain which of the two possesses greater durability, so that
they may be used more efficiently in restoration. Mortars were tested for properties governing moisture movement and also
subject to durability cycles. The resistance to damage under freezing conditions was evaluated with the saturation coefficient.
Thermal cycles had no effect on the mortars and gave no indication of the relative durabilities of the binders. Salt crystallization
cycles, though effective in distinguishing the more durable of the two, were too aggressive to gauge a clear profile of salt
weathering and succeeded in rapidly decomposing the samples. Tests on the properties governing moisture movement produced
good indications of the degree to which the mortars permit flow through their fabrics. According to the results obtained,
fat lime mortars are more durable than those made with feebly-hydraulic lime. The results also suggest that the feebly-hydraulic
lime mortars are at a higher risk of decomposition by granular disintegration whereas fat lime mortars are better suited to
damp, slightly exposed conditions. These results disagree with the general opinion that hydraulic limes are more durable than
fat limes due to the additional strength and water insolubility arising from their hydraulicity. 相似文献
40.
B González-Grajera R Mendoza Espejo J Hinojosa Díaz F Buitrago 《Canadian Metallurgical Quarterly》1995,16(7):433-436
OBJECTIVE: To assess the correctness and diagnostic concordance in referrals of patients to hospital Casualty Departments (CD); and the possible differences between rural and urban health centres (HC) as well as between general practitioners (GP) and family and community medicine (FCM) specialists. DESIGN: Observational study of a crossover nature. SETTING: Health area 1 in the province of Badajoz. PATIENTS AND OTHER PARTICIPANTS: 800 patients, referred to their local hospital Casualty Department. MEASUREMENTS AND MAIN RESULTS: 50.5% of all referrals were considered justified. 15.1% of the patients referred were admitted to hospital. 50.7% of referrals from GPs were found to be correct, against 47% from FCM specialists; and 49% of those referred from rural HCs were correct, as against 45.9% of those referred from urban HCs (no significant differences). Only 54% of referrals had a diagnostic hypothesis, with diagnostic concordance at 50%. There was diagnostic concordance in 28.1% of GP referrals, against 33.3% of FCM specialists; and in 27.5% of those from rural HCs against 26.1% from urban HCs (no significant differences). CONCLUSIONS: We found no differences in the correctness of referrals or diagnostic concordance of patients seen in the CD of our city's health area, neither between patients referred from rural and urban HCs, nor between patients referred by GPs and FCM specialists. 相似文献