全文获取类型
收费全文 | 40347篇 |
免费 | 2678篇 |
国内免费 | 64篇 |
专业分类
电工技术 | 357篇 |
综合类 | 34篇 |
化学工业 | 8901篇 |
金属工艺 | 740篇 |
机械仪表 | 827篇 |
建筑科学 | 1313篇 |
矿业工程 | 74篇 |
能源动力 | 1054篇 |
轻工业 | 7521篇 |
水利工程 | 439篇 |
石油天然气 | 193篇 |
武器工业 | 3篇 |
无线电 | 1920篇 |
一般工业技术 | 6466篇 |
冶金工业 | 7307篇 |
原子能技术 | 181篇 |
自动化技术 | 5759篇 |
出版年
2024年 | 69篇 |
2023年 | 347篇 |
2022年 | 443篇 |
2021年 | 1269篇 |
2020年 | 956篇 |
2019年 | 1038篇 |
2018年 | 1714篇 |
2017年 | 1646篇 |
2016年 | 1696篇 |
2015年 | 1284篇 |
2014年 | 1632篇 |
2013年 | 3120篇 |
2012年 | 2507篇 |
2011年 | 2516篇 |
2010年 | 1986篇 |
2009年 | 1812篇 |
2008年 | 1786篇 |
2007年 | 1658篇 |
2006年 | 1193篇 |
2005年 | 978篇 |
2004年 | 903篇 |
2003年 | 847篇 |
2002年 | 758篇 |
2001年 | 571篇 |
2000年 | 496篇 |
1999年 | 517篇 |
1998年 | 2620篇 |
1997年 | 1656篇 |
1996年 | 1079篇 |
1995年 | 627篇 |
1994年 | 480篇 |
1993年 | 491篇 |
1992年 | 163篇 |
1991年 | 155篇 |
1990年 | 131篇 |
1989年 | 124篇 |
1988年 | 134篇 |
1987年 | 123篇 |
1986年 | 118篇 |
1985年 | 127篇 |
1984年 | 104篇 |
1983年 | 77篇 |
1982年 | 80篇 |
1981年 | 114篇 |
1980年 | 104篇 |
1979年 | 53篇 |
1978年 | 57篇 |
1977年 | 153篇 |
1976年 | 288篇 |
1973年 | 60篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
111.
112.
113.
114.
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
115.
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
116.
A simple apparatus for elongational test of molten polymers is presented. Its realiability is demonstrated by means of stress growth in constant stretching rate experiments and relaxation test on a low density polyethylene sample. 相似文献
117.
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
118.
A Symbolic Pole/Zero Extraction Methodology Based on Analysis of Circuit Time-Constants 总被引:1,自引:0,他引:1
O. Guerra J. D. Rodríguez-García F. V. Fernández A. Rodríguez-Vázquez 《Analog Integrated Circuits and Signal Processing》2002,31(2):101-118
This paper introduces a methodology for symbolic pole/zero extraction based on the formulation of the time-constant matrix of the circuits. This methodology incorporates approximation techniques specifically devoted to achieve an optimum trade-off between accuracy and complexity of the symbolic root expressions. The capability to efficiently handle even large circuits will be demonstrated through several practical circuits. 相似文献
119.
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
120.
Inaki Arrazola Agn s Plainfoss Henri Prade Claudette Testemale 《Information Systems》1989,14(6):487-492
This paper presents different approaches which enable a data base management system to obtain a plausible fuzzy estimate for an attribute value of an item for which the information is not explicitly stored in the data base. This can be made either by a kind of analogical reasoning from information about particular items or by means of expert rules which specify the (fuzzy) sets of possible values of the attribute under consideration, for various classes of items. Another kind of expert rules enables the system to compute an estimate from the attribute value of another item provided that, in other respects, this latter item sufficiently resembles the item, the value of which we are interested in; then these expert rules are used either for controlling the analogical reasoning process or for enlarging the scope of application of the first kind of expert rules. The different approaches are discussed in the framework of possibility theory. 相似文献