全文获取类型
收费全文 | 3793篇 |
免费 | 515篇 |
国内免费 | 103篇 |
专业分类
电工技术 | 31篇 |
综合类 | 234篇 |
化学工业 | 989篇 |
金属工艺 | 52篇 |
机械仪表 | 12篇 |
建筑科学 | 370篇 |
矿业工程 | 43篇 |
能源动力 | 174篇 |
轻工业 | 1606篇 |
水利工程 | 118篇 |
石油天然气 | 240篇 |
武器工业 | 2篇 |
无线电 | 27篇 |
一般工业技术 | 123篇 |
冶金工业 | 66篇 |
原子能技术 | 7篇 |
自动化技术 | 317篇 |
出版年
2024年 | 32篇 |
2023年 | 96篇 |
2022年 | 189篇 |
2021年 | 255篇 |
2020年 | 232篇 |
2019年 | 231篇 |
2018年 | 184篇 |
2017年 | 164篇 |
2016年 | 208篇 |
2015年 | 175篇 |
2014年 | 219篇 |
2013年 | 277篇 |
2012年 | 263篇 |
2011年 | 255篇 |
2010年 | 193篇 |
2009年 | 175篇 |
2008年 | 142篇 |
2007年 | 170篇 |
2006年 | 163篇 |
2005年 | 146篇 |
2004年 | 109篇 |
2003年 | 77篇 |
2002年 | 116篇 |
2001年 | 43篇 |
2000年 | 40篇 |
1999年 | 34篇 |
1998年 | 18篇 |
1997年 | 31篇 |
1996年 | 22篇 |
1995年 | 19篇 |
1994年 | 11篇 |
1993年 | 20篇 |
1992年 | 12篇 |
1991年 | 15篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 8篇 |
1977年 | 1篇 |
1954年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有4411条查询结果,搜索用时 15 毫秒
31.
生物絮凝剂及其在水处理中的应用进展 总被引:7,自引:0,他引:7
介绍了微生物絮凝剂的种类、特点、絮凝机理和近几年来国内在不同废水处理中的应用情况,并对它的研究及应用前景做出展望。 相似文献
32.
Online learning has grown exponentially in recent years; however, dropout problem remains challenging for some online programmes. The dropout problem can be attributed to a number of reasons, with a lack of interaction between learners and the instructor constituting one of the main reasons. The lack of interaction also leads to learners' feeling of isolation. Learning communities can provide learners with an environment conducive to increased interactions and alleviate their feeling of isolation. Unfortunately, there are no clear rules that instructors can follow to help learners create learning communities. In this paper, we propose guidelines for online instructors to facilitate the development of learning communities in online courses. We first review the definition of a learning community, importance of a learning community and factors affecting the development of a learning community. Afterwards, based on a review of the existing guidelines and other relevant literature, we propose guidelines for facilitating the development of learning communities in online courses. 相似文献
33.
Sari M Soini Kari T Koskinen Matti J Vilenius Jaakko A Puhakka 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2002,77(8):903-909
Water hydraulic systems use water as a pressure medium and, thus, do not pose such adverse environmental impacts as oil hydraulics. Microbial deterioration of the pressure medium and biofouling of the surfaces restrict the applicability of the water‐based technology. The potential of microbial growth control by UV‐irradiation and filtration was studied in a pilot‐scale water hydraulic system. The UV‐irradiation (25 m Ws cm?2) of the pressure medium reduced the total viable counts of bacteria by 1–2 log10 cfu cm?3, whereas the total microbial cell numbers and the numbers of surface‐attached microorganisms remained unaffected. Prefiltration (1.2 µm, absolute) of the pressure medium decreased the total microbial cell number in the water phase and retarded the attachment of bacteria. The filtration during the operation (2 µm, absolute) decreased the total numbers of microbial cells and the total viable counts in the pressure medium, and microbial attachment on the surfaces. Microbial attachment was not prevented by filtration. The microbial water quality obtained by pre‐ and on‐line filtration of the pressure medium was sufficient to ensure the long‐term operation of the water hydraulic system assuming that clean work practices are complied with in assembly and during the operation. © 2002 Society of Chemical Industry 相似文献
34.
《Expert systems with applications》2014,41(13):5733-5750
The study of criminal networks using traces from heterogeneous communication media is acquiring increasing importance in nowadays society. The usage of communication media such as mobile phones and online social networks leaves digital traces in the form of metadata that can be used for this type of analysis. The goal of this work is twofold: first we provide a theoretical framework for the problem of detecting and characterizing criminal organizations in networks reconstructed from phone call records. Then, we introduce an expert system to support law enforcement agencies in the task of unveiling the underlying structure of criminal networks hidden in communication data. This platform allows for statistical network analysis, community detection and visual exploration of mobile phone network data. It enables forensic investigators to deeply understand hierarchies within criminal organizations, discovering members who play central role and provide connection among sub-groups. Our work concludes illustrating the adoption of our computational framework for a real-word criminal investigation. 相似文献
35.
Transformations of residual fertilizer P in a semi-arid tropical soil under eight-year peanut-wheat rotation 总被引:1,自引:0,他引:1
Long-term transformations of residual phosphorus (P) governs the availability of phosphorus to crops. Very limited information is available on the transformations of residual fertilizer P in semi-arid tropical soils under long-term crop rotations. Therefore, using sequential phosphorus fractionation procedure, we studied changes in labile and stable forms of inorganic and organic P in a semi-arid alluvial soil (Typic Ustisamments) after eight years of annual fertilizer P application either to one crop (alternate) or to both crops (cumulative) in a peanut (Arachis hypogaea) — wheat (Triticum aestivum) rotation.Total residual fertilizer P in soil (P recovered from P-fertilized minus control plots) ranged from 62 to 176 mg P kg–1. In the alternate P treatments (P applied to peanut or wheat only), on an average of 3 rates of applied P (13, 26 and 39 kg P ha–1), in surface (0–15 cm) and subsurface (15 to 30 cm) soil, respectively, residual fertilizer P consisted of 14.8 and 2.2% resin-P, 8.6 and 2.8% NaHCO3-P, 6.3 and 0% microbial-P, 31.4 and 4.2% NaOH-P, 7.8 and 3.0% aggregate protected-P, 12.5 and 3.0% HCl-P, 3.4 and 0% H2SO4-P. The corresponding values for surface and subsurface soils of cumulative P treatments (P applied to both peanut and wheat) were: 12.8 and 1.6% resin-P, 6.9 and 2.3% NaHCO3-P, 4.7 and 0% microbial-P, 32.5 and 4.2% NaOH-P, 5.6 and 2.0% aggregate protected-P, 14.8 and 3.8% HCl-P, 6.7 and 2.1% H2SO4-P. Considerable lower values for the 15–30 cm depth indicate only a very small movement of residual P to the subsoil.Significantly lower amount of fertilizer P (28% and 44%) found in labile (resin, NaHCO3 and microbial P) and semi-labile (NaOH and sonicated NaOH P) fractions for the cumulative P treatment than alternate P treatment (35 and 46%, respectively) suggests that increased rates and frequency of applied P tend to enhance the conversion of residual P to stable forms which are less available to plants. About 12 to 19% of residual fertilizer P found as organic P in labile and semi-labile forms confirmed that organic P increased with long-term fertilizer management. In conclusion, the results of our study suggest that the alternate application of fertilizer P to a crop, as is shown for wheat, helps reduce the transformations of residual P to stable P forms. 相似文献
36.
Different particulate solids such as glass powder, various types of activated carbon and bentonite suspended in Thiobacillus ferrooxidans cultures produce very different effects on the oxidizing activity of the microorganism. The atmospheric oxygen uptake by Thiobacillus ferrooxidans in Warburg respirometer flasks containing 9K medium with ferrous sulfate as energy source and suspended bentonite is 2.8 times that in the absence of solids. The dissolution rate of pure pyrite in 250 cm3 shake flasks containing 9K medium and bentonite is considerably enhanced over that where the only solid phase is pyrite. Conversely, the oxidizing ability of the microorganism seems to be inhibited by all the activated carbons tested. The effect of ground glass seems to be related to its particle size distribution. Implications for the bioleaching of sulfide ores and coal pyrite are discussed in the light of current knowledge on the adsorption of Thiobacillus ferrooxidans cells on solid surfaces. 相似文献
37.
Effects of Microbial Utilization of Phenolic Acids and their Phenolic Acid Breakdown Products on Allelopathic Interactions 总被引:18,自引:0,他引:18
Udo Blum 《Journal of chemical ecology》1998,24(4):685-708
Reversible sorption of phenolic acids by soils may provide some protection to phenolic acids from microbial degradation. In the absence of microbes, reversible sorption 35 days after addition of 0.5–3 mol/g of ferulic acid or p-coumaric acid was 8–14% in Cecil Ap horizon and 31–38% in Cecil Bt, horizon soil materials. The reversibly sorbed/solution ratios (r/s) for ferulic acid or p-coumaric acid ranged from 0.12 to 0.25 in Ap and 0.65 to 0.85 in Bt horizon soil materials. When microbes were introduced, the r/s ratio for both the Ap and Bt horizon soil materials increased over time up to 5 and 2, respectively, thereby indicating a more rapid utilization of solution phenolic acids over reversibly sorbed phenolic acids. The increase in r/s ratio and the overall microbial utilization of ferulic acid and/or p-coumaric acid were much more rapid in Ap than in Bt horizon soil materials. Reversible sorption, however, provided protection of phenolic acids from microbial utilization for only very short periods of time. Differential soil fixation, microbial production of benzoic acids (e.g., vanillic acid and p-hydroxybenzoic acid) from cinnamic acids (e.g., ferulic acid and p-coumaric acid, respectively), and the subsequent differential utilization of cinnamic and benzoic acids by soil microbes indicated that these processes can substantially influence the magnitude and duration of the phytoxicity of individual phenolic acids. 相似文献
38.
Henry?S.?Lam Andrew?ProctorEmail author 《Journal of the American Oil Chemists' Society》2003,80(6):563-567
The changes in milled rice FFA content and composition and in conjugated diene (CD) content and bacterial, yeast, and mold
counts were determined at 24, 37, and 50°C and 70% RH over 50 d. There was a rapid rate of FFA formation during the first
few days of storage, which was optimal at 37°C, but that slowed after 2, 4, and 5 d at 37, 24, and 50°C, respectively. There
was a second increase in FFA after about day 12 that increased with increasing temperature, indicating nonlipase hydrolysis.
Linoleic and oleic acids were the main components of the total FFA produced on the surface of milled rice. The pattern of
CD development followed that of FFA increase. Bacterial growth correlated with increased FFA levels after 12 d of storage,
suggesting that bacterial lipase rather than bran lipase may be responsible for rice lipid hydrolysis 相似文献
39.
40.
序批式生物膜反应器(sequencing biofilm batch reactor, SBBR)是应用广泛的污水处理方法。为探究不同时期排泥对SBBR污染物去除效果与微生物群落结构的影响,本研究设置了挂膜初期、中期和后期进行排泥的反应器处理生活污水,同时结合16S rDNA高通量测序技术对微生物群落结构进行分析,并采用机器学习(machine learning, ML)的方法,在传统的微生物优势种分析基础上,对测序数据进行深度挖掘,寻找造成组间差异的关键物种。水质测定结果显示,COD去除效果在不同时期排泥的SBBR间没有明显差异,出水COD均低于30mg/L。挂膜中期排泥的SBBR的NH3-N去除率先达到稳定且高于前期和后期排泥的系统。高通量测序结果显示,各SBBR中微生物优势种均以降解有机物的物种为主。挂膜中期排泥的SBBR中,ML筛选得到的NH3-N去除相关物种(Hydrogenophaga、Gemmata和Nitrospira)与差异关键物种丰度更高,微生物群落结构稳定性更强,可从微生物层面解释分析SBBR污染物去除效果的差异。 相似文献