全文获取类型
收费全文 | 38282篇 |
免费 | 2324篇 |
国内免费 | 44篇 |
专业分类
电工技术 | 347篇 |
综合类 | 16篇 |
化学工业 | 8645篇 |
金属工艺 | 686篇 |
机械仪表 | 905篇 |
建筑科学 | 1209篇 |
矿业工程 | 87篇 |
能源动力 | 1026篇 |
轻工业 | 7292篇 |
水利工程 | 421篇 |
石油天然气 | 193篇 |
武器工业 | 1篇 |
无线电 | 1773篇 |
一般工业技术 | 6183篇 |
冶金工业 | 6298篇 |
原子能技术 | 154篇 |
自动化技术 | 5414篇 |
出版年
2024年 | 100篇 |
2023年 | 402篇 |
2022年 | 710篇 |
2021年 | 1259篇 |
2020年 | 995篇 |
2019年 | 1108篇 |
2018年 | 1675篇 |
2017年 | 1661篇 |
2016年 | 1681篇 |
2015年 | 1312篇 |
2014年 | 1591篇 |
2013年 | 3246篇 |
2012年 | 2476篇 |
2011年 | 2436篇 |
2010年 | 1879篇 |
2009年 | 1757篇 |
2008年 | 1731篇 |
2007年 | 1556篇 |
2006年 | 1101篇 |
2005年 | 882篇 |
2004年 | 790篇 |
2003年 | 778篇 |
2002年 | 660篇 |
2001年 | 474篇 |
2000年 | 416篇 |
1999年 | 460篇 |
1998年 | 2123篇 |
1997年 | 1389篇 |
1996年 | 896篇 |
1995年 | 499篇 |
1994年 | 383篇 |
1993年 | 397篇 |
1992年 | 133篇 |
1991年 | 111篇 |
1990年 | 101篇 |
1989年 | 96篇 |
1988年 | 117篇 |
1987年 | 94篇 |
1986年 | 85篇 |
1985年 | 98篇 |
1984年 | 77篇 |
1983年 | 47篇 |
1982年 | 56篇 |
1981年 | 74篇 |
1980年 | 76篇 |
1978年 | 54篇 |
1977年 | 113篇 |
1976年 | 233篇 |
1975年 | 45篇 |
1973年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
R Herruzo-Cabrera L Malo-González ME Calle Purón MJ Vizcaíno-Alcaide J Del Rey-Calero 《Canadian Metallurgical Quarterly》1993,9(4):442-446
A cross-sectional study was performed to obtain risk factors for hepatitis B disease, HBsAg carriers and immunised personnel, among 2470 workers in a general hospital in Madrid, Spain. The data obtained were analyzed with multiple logistic regression to obtain beta coefficients for variables. The results of the analysis show that being a nurse or being regularly exposed to blood are the most important risk factors for hepatitis B acquisition. The length of time working at the same job activity was also a risk factor. The resulting beta coefficients allow the construction for a hepatitis non-immunised, HBsAg carrier and immunised HBV status, which can select subjects for a hepatitis B vaccination program. 相似文献
13.
María P. Albano Liliana B. Garrido 《Journal of Materials Synthesis and Processing》2002,10(4):211-218
Si3N4powders coated with 6 wt% Y2O3and 4 wt% Al2O3were prepared by coprecipitation. The resulting powders were dispersed in water at different pH values and with addition of various amounts of ammonium polyacrylate (NH4PA) to produce 32 vol% slips. The influence of the amount of NH4PA solution added and pH on the rheological properties of 32 vol% coated Si3N4slips were studied. In addition, the sintered density of cast samples was determined and related to the degree of slip dispersion. The adsorption of the NH4PA on the coated particle surface was rather high and the surface became saturated near 0.86 mg/m2at pH 9.2. High NH4PA concentrations (1.7–3 wt%) were necessary to obtain well dispersed 32 vol% coated Si3N4slips at pH 9.2. The best stabilization was obtained with the addition of 2.3 wt% NH4PA; in this condition, the viscosity reached a minimum value of 35 mPa.s at 100 s–1. The slip viscosity increased with increasing pH from 9.2 to 10.2. Slips with low viscosities gave a more dense packing of cast samples and consequently higher sintered density values. 相似文献
14.
Generation of Technology-Independent Retargetable Analog Blocks 总被引:1,自引:0,他引:1
R. Castro-López F. V. Fernández F. Medeiro A. Rodríguez-Vázquez 《Analog Integrated Circuits and Signal Processing》2002,33(2):157-170
This paper introduces a complete methodology for retargeting of analog cells to different sets of specifications. This methodology is technology-independent, thus allowing the migration, from one technology to another, of the circuit under retargeting. Careful integration of the device sizing and layout generation tasks via the incorporation of layout constraints during the sizing process allows to generate fully functional designs in a few minutes. The methodology is illustrated via the retargeting of a fully-differential Miller-compensated two-stage operational amplifier for a new set of specifications and two different technological processes.An erratum to this article can be found at 相似文献
15.
Kunkel Mark A.; Hector Mark A.; Góngora Coronado Elías; Castillo Vales Victor 《Canadian Metallurgical Quarterly》1989,36(3):322
Conducted a study of client expectations of psychological services in Yucatán, Mexico, under the sponsorship of a grant from the Organization of American States. The Expectations about Counseling–Brief form (EAC-B) questionnaire was translated and administered to 488 subjects across age, sex, and experience with psychological services. Subsequent analyses supported the reliability and robustness of the Spanish EAC-B, with factor structure similar to the EAC-B in English. Some relation was found among age, sex, prior counseling experience, and expectations about counseling. Implications of these data for future research and comparison with U.S. subjects are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
16.
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
17.
In this article, a general synthesis method is proposed for the design of discontinuous feedback strategies leading to asymptotically stabilizing sliding regimes. The method is applicable to the class of nonlinear dynamical systems possessing constant equilibrium points. A family of nonlinear stabilizing sliding manifolds, parametrized by generic desired equilibrium point, is specified on the basis of the extended linearization approach. Some examples including simulations are presented for illustrative purposes.
Editor: S. Zak 相似文献
18.
There are some foods that contain mutagenic or carcinogenic agents, some of which occur naturally and others that may be formed during preparation or cooking. Several foods such as legumes, also contain natural antimutagens and/or anticarcinogens. Lupine is one such legume that contains high amounts of protein (40%) and oils (14%). About 90 species of lupine have been reported throughout Mexico. However, the use of this crop as a source of food has been limited by the presence of antinutritional agents such as phenolic compounds (PC), carbohydrates (CH) and quinolizidinic alkaloids (Qas). It has also been suggested that consuming these compounds can affect human health and may even reduce the risk of disease. The objective of this work was to determine the effect of PC, CH and Qas, isolated and quantified from Lupinus campestris on the mutagenicity of 1-nitropyrene (1-NP) as a model mutagen and we used the Salmonella typhimurium tester strain YG1024 by the Kado microsuspension method. The results indicate that L. campestris seeds have 11 mg (+)catechin equivalent g(-1) seed coat; 120.3 mg g(-1) seeds and 2.13 mg g(-1) seeds of PC, CH and Qas, respectively. 1-NP mutagenicity was inhibited by 86% for PC, 76% for CH and 75% for Qas at concentrations of 200, 512 and 13.6 microg/tube, respectively. 相似文献
19.
Daniel X. Gouveia Odair P. Ferreira Antonio G. Souza Filho M. G. da Silva J. A. C. de Paiva Oswaldo L. Alves Josué Mendes Filho 《Journal of Materials Science》2007,42(2):534-538
The thermal decomposition properties of Mg–Fe hydrotalcites were studied through in situ 57Fe Mössbauer spectroscopy and in situ X-ray diffraction. Abrupt changes in the quadrupolar splitting measured in the Mössbauer spectra revealed a phase transition from the starting lamellar structure to a new crystalline arrangement. By analyzing the Mössbauer parameters we show that the material is highly disordered in the 300–400 °C temperature range. This hypothesis is confirmed by the X-ray results whose diffractograms indicated the collapse of the lamellar structure and the formation of a solid solution. 相似文献
20.