全文获取类型
收费全文 | 9262篇 |
免费 | 570篇 |
国内免费 | 43篇 |
专业分类
电工技术 | 178篇 |
综合类 | 68篇 |
化学工业 | 2127篇 |
金属工艺 | 247篇 |
机械仪表 | 287篇 |
建筑科学 | 253篇 |
矿业工程 | 37篇 |
能源动力 | 378篇 |
轻工业 | 1600篇 |
水利工程 | 95篇 |
石油天然气 | 65篇 |
无线电 | 579篇 |
一般工业技术 | 1366篇 |
冶金工业 | 1484篇 |
原子能技术 | 64篇 |
自动化技术 | 1047篇 |
出版年
2024年 | 32篇 |
2023年 | 98篇 |
2022年 | 248篇 |
2021年 | 422篇 |
2020年 | 289篇 |
2019年 | 339篇 |
2018年 | 375篇 |
2017年 | 393篇 |
2016年 | 364篇 |
2015年 | 255篇 |
2014年 | 363篇 |
2013年 | 653篇 |
2012年 | 516篇 |
2011年 | 589篇 |
2010年 | 410篇 |
2009年 | 451篇 |
2008年 | 382篇 |
2007年 | 324篇 |
2006年 | 280篇 |
2005年 | 185篇 |
2004年 | 198篇 |
2003年 | 238篇 |
2002年 | 246篇 |
2001年 | 192篇 |
2000年 | 133篇 |
1999年 | 143篇 |
1998年 | 453篇 |
1997年 | 297篇 |
1996年 | 225篇 |
1995年 | 139篇 |
1994年 | 98篇 |
1993年 | 107篇 |
1992年 | 43篇 |
1991年 | 35篇 |
1990年 | 42篇 |
1989年 | 29篇 |
1988年 | 44篇 |
1987年 | 19篇 |
1986年 | 28篇 |
1985年 | 24篇 |
1984年 | 9篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 12篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 19篇 |
1976年 | 61篇 |
1975年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有9875条查询结果,搜索用时 15 毫秒
1.
2.
讨论了在VMI管理思想下对具有随机需求特性的多客户库存分配问题 ,重点论述了有效近似算法的设计过程 ,最后基于一组模拟数据给出了一个算例。 相似文献
3.
Piedade M. Sousa L. A. de Almeida T. M. Germano J. da Costa B. A. Lemos J. M. Freitas P. P. Ferreira H. A. Cardoso F. A. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(11):2384-2395
This paper presents a hand-held microsystem based on new fully integrated magnetoresistive biochips for biomolecular recognition (DNA hybridization, antibody antigen interaction, etc.). Magnetoresistive chip surfaces are chemically treated, enabling the immobilization of probe biomolecules such as DNA or antibodies. Fluid handling is also integrated in the biochip. The proposed microsystem not only integrates the biochip, which is an array of 16times16 magnetoresistive sensors, but it also provides all the electronic circuitry for addressing and reading out each transducer. The proposed architecture and circuits were specifically designed for achieving a compact, programmable and portable microsystem. The microsystem also integrates a hand-held analyzer connected through a wireless channel. A prototype of the system was already developed and detection of magnetic nanoparticles was obtained. This indicates that the system may be used for magnetic label based bioassays 相似文献
4.
5.
Marcia Cristina Kaezer Fran a Rosane Aguiar da Silva San Gil Jean-Guillaume Eon 《Catalysis Today》2003,78(1-4):105-115
γ-Al2O3 supported vanadium oxides were modified by tungsten and molybdenum oxides in order to improve dispersion and selectivity towards olefins in propane oxidative dehydrogenation (ODH). Both vanadium–tungsten and vanadium–molybdenum catalysts were obtained by adsorption of mixed isopolyanions (VW5O195−, V2W4O194−, VMo5O195− and V2Mo4O194−) from aqueous solutions. The isopolyanion solutions were characterized by UV-Vis and 51V NMR spectroscopy. Vanadium, vanadium–tungsten and vanadium–molybdenum precursors and catalysts were also characterized by UV-Vis (diffuse reflectance) and solid state 51V NMR spectroscopy. An improved selectivity to propene in the presence of tungsten and molybdenum in VOx/γ-Al2O3 was observed and attributed to dilution of vanadium by tungsten or molybdenum oxides on the γ-Al2O3 surface. 相似文献
6.
7.
A longitudinal study to estimate the serum calcium, phosphate and alkaline phosphatase levels of 89 ambulatory epileptic children, aged between 3 years and 12 years, and having generalised tonic-clonic seizures, was carried out. None was on any form of medication for the treatment of seizures prior to presentation. Each patient received only phenobarbitone during the period of study. Serum levels of the biochemical parameters were determined at presentation, 6 months and 12 months, while serum phenobarbitone levels were estimated at 6 months and 12 months. Mean serum calcium, phosphate and alkaline phosphatase of the patients remained within the normal range. Using the paired 't' test, the differences in the levels of the parameters at the three measurements were not statistically significant (P > 0.05). Serum phenobarbitone levels remained within the therapeutic range during the period of study. Our results show that over a 12-month period, serum levels of calcium, phosphate, and alkaline phosphatase, remain normal in ambulant epileptic children treated with phenobarbitone. 相似文献
8.
9.
Larissa Canilha Walter Carvalho Marco Giulietti Maria Das Graças Almeida Felipe João Batista Almeida E Silva 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(5):715-721
BACKGROUND: Xylitol bioproduction from lignocellulosic residues comprises hydrolysis of the hemicellulose, detoxification of the hydrolysate, bioconversion of the xylose, and recovery of xylitol from the fermented hydrolysate. There are relatively few reports on xylitol recovery from fermented media. In the present study, ion‐exchange resins were used to clarify a fermented wheat straw hemicellulosic hydrolysate, which was then vacuum‐concentrated and submitted to cooling in the presence of ethanol for xylitol crystallization. RESULTS: Sequential adsorption into two anion‐exchange resins (A‐860S and A‐500PS) promoted considerable reductions in the content of soluble by‐products (up to 97.5%) and in medium coloration (99.5%). Vacuum concentration led to a dark‐colored viscous solution that inhibited xylitol crystallization. This inhibition could be overcome by mixing the concentrated medium with a commercial xylitol solution. Such a strategy led to xylitol crystals with up to 95.9% purity. The crystallization yield (43.5%) was close to that observed when using commercial xylitol solution (51.4%). CONCLUSION: The experimental data demonstrate the feasibility of using ion‐exchange resins followed by cooling in the presence of ethanol as a strategy to promote the fast recovery and purification of xylitol from hemicellulose‐derived fermentation media. Copyright © 2008 Society of Chemical Industry 相似文献
10.
Cypriano G da Trindade Neto Ana LP Fernandes Ana IB Santos Waldenice A Morais Marcos VM Navarro Tereza NC Dantas Mrcia R Pereira Jos LC Fonseca 《Polymer International》2005,54(4):659-666
Complexation of chitosan in aqueous solutions by low molecular weight electrolytes is one of the simplest methods for the preparation of aqueous chitosan dispersions. In this work, the influence of storage time, sulfate concentration, method of preparation and surfactant content on some properties of the resultant chitosan dispersions (turbidity, viscosity and zeta potential) was analyzed. Turbidimetry was adequate to monitor the formation of particles, while viscometry was suitable to monitor changes in the dispersing phase. An analysis of the properties of these systems, mainly in terms of particle–particle and macromolecule–macromolecule interactions was carried out. Copyright © 2004 Society of Chemical Industry 相似文献