全文获取类型
收费全文 | 749852篇 |
免费 | 8981篇 |
国内免费 | 1932篇 |
专业分类
电工技术 | 13590篇 |
综合类 | 642篇 |
化学工业 | 116726篇 |
金属工艺 | 29555篇 |
机械仪表 | 23842篇 |
建筑科学 | 17594篇 |
矿业工程 | 4738篇 |
能源动力 | 19763篇 |
轻工业 | 64229篇 |
水利工程 | 8409篇 |
石油天然气 | 16578篇 |
武器工业 | 44篇 |
无线电 | 84316篇 |
一般工业技术 | 149122篇 |
冶金工业 | 131044篇 |
原子能技术 | 16899篇 |
自动化技术 | 63674篇 |
出版年
2021年 | 6724篇 |
2020年 | 5041篇 |
2019年 | 6427篇 |
2018年 | 10975篇 |
2017年 | 11177篇 |
2016年 | 11910篇 |
2015年 | 7609篇 |
2014年 | 12805篇 |
2013年 | 35022篇 |
2012年 | 20322篇 |
2011年 | 27906篇 |
2010年 | 22245篇 |
2009年 | 24783篇 |
2008年 | 25393篇 |
2007年 | 25137篇 |
2006年 | 22149篇 |
2005年 | 20107篇 |
2004年 | 19209篇 |
2003年 | 18776篇 |
2002年 | 17970篇 |
2001年 | 17844篇 |
2000年 | 16836篇 |
1999年 | 17050篇 |
1998年 | 39410篇 |
1997年 | 28315篇 |
1996年 | 21943篇 |
1995年 | 16839篇 |
1994年 | 15079篇 |
1993年 | 14799篇 |
1992年 | 11318篇 |
1991年 | 10802篇 |
1990年 | 10638篇 |
1989年 | 10268篇 |
1988年 | 9913篇 |
1987年 | 8702篇 |
1986年 | 8413篇 |
1985年 | 9766篇 |
1984年 | 8855篇 |
1983年 | 8389篇 |
1982年 | 7588篇 |
1981年 | 7737篇 |
1980年 | 7302篇 |
1979年 | 7329篇 |
1978年 | 7112篇 |
1977年 | 7918篇 |
1976年 | 9902篇 |
1975年 | 6340篇 |
1974年 | 6067篇 |
1973年 | 6193篇 |
1972年 | 5171篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
S. K. Chen A. Serquis G. Serrano K. A. Yates M. G. Blamire D. Guthrie J. Cooper H. Wang S. Margadonna J. L. MacManus‐Driscoll 《Advanced functional materials》2008,18(1):113-120
By applying a combination of characterisation tools, changes in structural and superconducting properties with nominal Mg non‐stoichiometry in MgxB2 are found. The non‐stoichiometry produces enhanced in‐field critical current densities (Jc's) and upper critical field / irreversibility field (Hc2/Hirr(T)) values. Upper critical fields of ~ 21 T (4.2 K) were obtained in nominal Mg‐deficient samples compared to ~ 17 T (4.2 K) for near‐stoichiometric samples. 相似文献
992.
Ricardo Beristain‐Cardoso Anne‐Claire Texier Reyes Sierra‐Álvarez Jim A Field Elías Razo‐Flores Jorge Gómez 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(9):1197-1203
BACKGROUND: Simultaneous removal of sulfur, nitrogen and carbon compounds from wastewaters is a commercially important biological process. The objective was to evaluate the influence of the CH3COO?/NO3? molar ratio on the sulfide oxidation process using an inverse fluidized bed reactor (IFBR). RESULTS: Three molar ratios of CH3COO?/NO3? (0.85, 0.72 and 0.62) with a constant S2?/NO3? molar ratio of 0.13 were evaluated. At a CH3COO?/NO3? molar ratio of 0.85, the nitrate, acetate and sulfide removal efficiencies were approximately 100%. The N2 yield (g N2 g?1 NO3?‐N consumed) was 0.81. Acetate was mineralized, resulting in a yield of 0.65 g inorganic‐C g?1 CH3COO?‐C consumed. Sulfide was partially oxidized to S0, and 71% of the S2? consumed was recovered as elemental sulfur by a settler installed in the IFBR. At a CH3COO?/NO3? molar ratio of 0.72, the efficiencies of nitrate, acetate and sulfide consumption were of 100%, with N2 and inorganic‐C yields of 0.84 and 0.69, respectively. The sulfide was recovered as sulfate instead of S0, with a yield of 0.92 g SO42?‐S g?1 S2? consumed. CONCLUSIONS: The CH3COO?/NO3? molar ratio was shown to be an important parameter that can be used to control the fate of sulfide oxidation to either S0 or sulfate. In this study, the potential of denitrification for the simultaneous removal of organic matter, sulfide and nitrate from wastewaters was demonstrated, obtaining CO2, S0 and N2 as the major end products. Copyright © 2008 Society of Chemical Industry 相似文献
993.
Different and alternative methods for the preparation of Ni/pillared clays based on impregnation and encapsulation procedures are reported. Several nickel precursors and metal loadings are considered in order to evaluate their influence on the structural, textural and catalytic properties of the resulting solids. The behaviour of the optimum solids as catalysts has been proved in the selective catalytic reduction of nitrogen oxides with propene, and the relevance of the oxidant nature was checked by changing the composition of the oxidant mixture. Of all the factors studied, the nature of the nickel precursors appears as the most important one, owing to the formation of different active nickel species during the synthesis procedure. 相似文献
994.
The specific features of SPPA-T3000, a new instrumentation and control system intended for automation of processes in power engineering, are briefly described. Distinctive features of the system architecture, central to which is using the model of web systems, are singled out. 相似文献
995.
S. C. Hogg H. V. Atkinson P. Kapranos 《Metallurgical and Materials Transactions A》2004,35(3):899-910
The rheology of Al-30Si-5Cu and Al-30Si-5Cu-2Mg spray-formed alloys has been characterized after holding at various times
and temperatures, using semisolid rapid compression to obtain load-displacement curves. Microstructures were examined after
partial remelting and compression in an attempt to understand the flow behavior. The initial resistance to flow generally
increased with holding time at temperature. This increase was attributed to the increased strength of a three-dimensional
(3-D) solid silicon network present in these alloys in the semisolid state, with the initial resistance to flow smaller in
the magnesium-containing alloys. With increased temperature, the initial resistance decreased due to increased liquid content
and grain spheroidization. The viscosity vs shear rate response was studied using the approach of Laxmanan and Flemings. The materials shear thinned rapidly during the
test conditions, in which the shear rate rapidly increased from approximately 2.5 to 92 s−1. The results were fitted to a power-law model, and the viscosities showed a drop of approximately two to four orders of magnitude
when extrapolated to a shear rate of 1000 s−1 (a typical value in actual component manufacture). The rapid compression test, which is close to conditions present in component
manufacture, was shown to have more in common with a shear rate jump experiment, rather than steady-state viscometry. 相似文献
996.
Hiding biometric data 总被引:5,自引:0,他引:5
Jain A.K. Uludag U. 《IEEE transactions on pattern analysis and machine intelligence》2003,25(11):1494-1498
With the wide spread utilization of biometric identification systems, establishing the authenticity of biometric data itself has emerged as an important research issue. The fact that biometric data is not replaceable and is not secret, combined with the existence of several types of attacks that are possible in a biometric system, make the issue of security/integrity of biometric data extremely critical. We introduce two applications of an amplitude modulation-based watermarking method, in which we hide a user's biometric data in a variety of images. This method has the ability to increase the security of both the hidden biometric data (e.g., eigen-face coefficients) and host images (e.g., fingerprints). Image adaptive data embedding methods used in our scheme lead to low visibility of the embedded signal. Feature analysis of host images guarantees high verification accuracy on watermarked (e.g., fingerprint) images. 相似文献
997.
998.
999.
This paper presents a valve-regulated lead acid (VRLA) battery reserve life estimation scheme. The scheme is adaptive in both type and frequency of involvement. The scheme is based on capacity trending with the support of a number of state-of-health (SOH) indicators. These SOH indicators include accumulated thermal stress, float voltage, and indicators acquired from the start-of-discharge (coup de fouet) region. An implementation test case is given, indicating that the scheme is capable of providing an accurate estimation of reserve life long before the end of life. Furthermore, the estimation accuracy improves as the end of battery life approaches. 相似文献
1000.
Fabrication and thermal characterization of a resistance temperature detector (RTD) heater and microthermocouples (MTs) on silicon substrates have been reported in this paper. The influence of film thickness and nickel-gold (Au) electroplating on RTD on its steady-state temperature with respect to its steady-state electrical power input and resistance is studied. Further, the thermal effects of multiple thermocouples in a thermopile as well as the effects of Au layers in the contact pads of the thermopiles on their open-circuit Seebeck voltage are studied. Therein lies the novelty of this paper. The in situ operating relationships for the RTD heater and the MT are provided 相似文献