全文获取类型
收费全文 | 22347篇 |
免费 | 1389篇 |
国内免费 | 43篇 |
专业分类
电工技术 | 209篇 |
综合类 | 119篇 |
化学工业 | 6216篇 |
金属工艺 | 523篇 |
机械仪表 | 435篇 |
建筑科学 | 693篇 |
矿业工程 | 68篇 |
能源动力 | 735篇 |
轻工业 | 4743篇 |
水利工程 | 173篇 |
石油天然气 | 170篇 |
武器工业 | 1篇 |
无线电 | 979篇 |
一般工业技术 | 3677篇 |
冶金工业 | 1991篇 |
原子能技术 | 124篇 |
自动化技术 | 2923篇 |
出版年
2024年 | 48篇 |
2023年 | 216篇 |
2022年 | 695篇 |
2021年 | 921篇 |
2020年 | 585篇 |
2019年 | 645篇 |
2018年 | 847篇 |
2017年 | 833篇 |
2016年 | 937篇 |
2015年 | 698篇 |
2014年 | 1031篇 |
2013年 | 1896篇 |
2012年 | 1452篇 |
2011年 | 1597篇 |
2010年 | 1273篇 |
2009年 | 1130篇 |
2008年 | 995篇 |
2007年 | 843篇 |
2006年 | 651篇 |
2005年 | 522篇 |
2004年 | 454篇 |
2003年 | 490篇 |
2002年 | 385篇 |
2001年 | 313篇 |
2000年 | 258篇 |
1999年 | 268篇 |
1998年 | 773篇 |
1997年 | 522篇 |
1996年 | 382篇 |
1995年 | 237篇 |
1994年 | 221篇 |
1993年 | 180篇 |
1992年 | 102篇 |
1991年 | 76篇 |
1990年 | 67篇 |
1989年 | 75篇 |
1988年 | 75篇 |
1987年 | 69篇 |
1986年 | 47篇 |
1985年 | 95篇 |
1984年 | 87篇 |
1983年 | 72篇 |
1982年 | 70篇 |
1981年 | 72篇 |
1980年 | 86篇 |
1979年 | 57篇 |
1978年 | 50篇 |
1977年 | 60篇 |
1976年 | 87篇 |
1973年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
In this study, nitrogen removal was investigated in pilot-scale subsurface flow (SSF) and in free water surface flow (FWS) constructed wetlands installed in the campus of TUBITAK-Marmara Research Center, Gebze, near Istanbul, Turkey. The main purposes of this study are to apply constructed wetlands for the protection of water reservoirs and to reuse wastewater. Experiments were carried out at continuous flow reactors. The effects of the type of plants on the removal were investigated by using emergent (Canna, Cyperus, Typhia spp., Phragmites spp., Juncus, Poaceae, Paspalum and Iris.), submerged (Elodea, Egeria) and floating (Pistia, Salvina and Lemna) marsh plants at different conditions. During the study period HLRs were 30, 50, 70, 80 and 120 L m(2)d(-1) respectively. The average annual NH4-N, NO(3)-N, organic N and TN treatment efficiencies in SSF and FWS wetlands are 81% and 68%, 37% and 49%, 75% and 68%, 47% and 53%, respectively. Nitrification, denitrification and ammonification rate constant (k20) values in SSF and FNS systems have been found as 0.898 d(-1) and 0.541 d(-1), 0.488 d(-1) and 0.502 d(-1), 0.986 d(-1) and 0.908 respectively. Two types of the models (first-order plug flow and multiple regression) were tried to estimate the system performances. 相似文献
62.
The therapeutic panorama of immunomodulation and its effects on the modification of the immune reaction is reviewed. Particular reference is made to the transfer factor as a therapeutic element in bronchial asthma, which insures its efficacy or innocuity. 相似文献
63.
E Aida Pea‐Ramos Youling L Xiong Guillermo E Arteaga 《Journal of the science of food and agriculture》2004,84(14):1908-1918
Whey protein isolate (WPI) was hydrolysed for 1 h using Alcalase, Protamex and Flavourzyme. Native WPI, hydrolysed WPI and two commercial WPI hydrolysates were subjected to fractionation by size exclusion chromatography. Antioxidant activity of WPI fractions was measured with a liposome‐oxidising system (50 µM FeCl3/0.1 µM ascorbate, pH 7.0). Lipid oxidation was measured as thiobarbituric acid‐reactive substances (TBARS). Gel electrophoresis and amino acid analysis were run to identify the peptide composition. The influence of amino acid composition on antioxidant activity was evaluated using multivariate analysis methods (correlation analysis, principal component analysis, multiple linear regression and discriminant analysis). TBARS assays indicated the presence of antioxidant activity in all protein fractions, including non‐hydrolysed WPI. For native and hydrolysed WPI samples the first fraction (> 45 kDa) showed a higher TBARS inhibition effect (24–27%) when compared with lower‐molecular‐weight fractions and hydrolysate mixtures. In contrast, for commercial WPI hydrolysates a higher inhibitory effect was found in most of the lower‐molecular‐weight fractions (30–55%). The ability of WPI fractions to delay lipid oxidation was found to be related to the prevalence of histidine and hydrophobic amino acids. Copyright © 2004 Society of Chemical Industry 相似文献
64.
65.
Baudilio Coto Carmen Martos Jos L. Pea Juan J. Espada María D. Robustillo 《Fuel》2008,87(10-11):2090-2094
Wax precipitation is one of the most important flow assurance problems. Unfortunately, experimental data are very scarce to confirm existing models for prediction of such precipitation problem. This work reports a new experimental method. Multistage fractional wax precipitation was carried out by decreasing the temperature of crude oil. No solvent dilution was used, so the effect of solvent on temperature wax precipitation was avoided. The reproducibility of the method was tested with comparable results. The precipitation curve and the wax appearance temperature were obtained for two crude oils with different chemical nature using the reported method. 相似文献
66.
Renato Cataluña Rosângela da Silva Eliana Weber de Menezes Ricardo Boeira Ivanov 《Fuel》2008,87(15-16):3362-3368
Oxygenated fuels increase fuel consumption due to their low enthalpy of combustion; however, their high antiknock index renders them suitable for use in engines with a high compression rate, increasing their thermal yield. This study evaluated the performance of biorenewable oxygenated fuels (ethanol and isoamyl alcohol) and partially renewable fuels (ETBE: ethyl tert-butyl ether, TAEE: tert-amyl ethyl ether and di-TAE: di-tert-amyl ether) with high degree of purity and in mixtures with automotive gasoline, based on tests with Otto cycle engines. Among the oxygenated fuels evaluated here, di-TAE was found to present the best characteristics of performance, both individually and in mixtures with gasoline. 相似文献
67.
In this work the use of chemical materials (additives) in order to reduce the biomass ash sintering tendency is investigated. A total of seven additives (kaolin, limestone, lime, dolomite, calcined dolomite, ophite and alumina) and silica utilised as reference material were mixed in different proportions with the ash of five different biomasses, and then a laboratory sintering test was performed on the mixtures to determine the effect of the additives on the sintering. The biomasses studied in this work were: thistle biomass, brassica carinata biomass, barley straw, almond shell and orujillo (olive oil extraction residue). The sintering decrease among the additives was studied using X-ray diffraction.Kaolin, lime, calcined dolomite and ophite are proved to be suitable to reduce the biomass sintering in all the considered cases. Dolomite, limestone and, particularly, the tabular alumina, offer poorer results. The dilution of the biomass ash is considered the main process involved in the decrease of the sintering for most of the additives, with the exception of kaolin whose chemical reactions could be more important than the dilution effect. 相似文献
68.
The nonisothermal crystallization kinetics of a metallocene-made isotactic polypropylene (m-iPP) and its compounds with 0.1 wt % and 0.3 wt % of a sorbitol derivative [1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS); an α nucleator] were investigated by differential scanning calorimetry at different cooling rates from the melt. The nucleation efficiency was proved by a significant increase in the crystallization temperatures (accompanied by a slight augmentation of the degree of crystallinity and a decrease in the crystal sizes). This increase in the crystallization temperatures led to higher amounts of fractional content in the γ polymorph, even though DMDBS was supposed to be a nucleator for the α form. The Avrami and Ozawa methods effectively described only the early stage of crystallization, whereas a combined Avrami–Ozawa method was valid for the whole crystallization process. The values of the exponent for this method decreased for nucleated samples in the later stage of crystallization, especially in the case of m-iPP with 0.3 wt % DMDBS added (m-iPP03). The activation energy of the process and the surface free energy were also estimated. The production of considerable proportions of the γ polymorph in m-iPP03 corresponded to higher values of the activation energy and lower values of the surface free energy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
69.
Linear oligosiloxanes functionalized with bulky side chain tris(trimethylsilyl)hexyl (TTSH) substituents were transformed into cross-linked materials by UV 193 nm excimer pulsed laser ablation. The process occurred without any catalyst, by reactions of radicals formed in UV laser induced photolysis of side tris(trimethylsilyl)hexyl groups. Chemical changes were monitored by FTIR, LC/UV, GC/MS and solubility tests. 相似文献
70.