全文获取类型
收费全文 | 6163篇 |
免费 | 232篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 55篇 |
综合类 | 6篇 |
化学工业 | 1252篇 |
金属工艺 | 68篇 |
机械仪表 | 121篇 |
建筑科学 | 393篇 |
矿业工程 | 18篇 |
能源动力 | 152篇 |
轻工业 | 598篇 |
水利工程 | 58篇 |
石油天然气 | 22篇 |
武器工业 | 1篇 |
无线电 | 475篇 |
一般工业技术 | 940篇 |
冶金工业 | 1144篇 |
原子能技术 | 28篇 |
自动化技术 | 1067篇 |
出版年
2023年 | 36篇 |
2022年 | 53篇 |
2021年 | 84篇 |
2020年 | 65篇 |
2019年 | 91篇 |
2018年 | 122篇 |
2017年 | 108篇 |
2016年 | 135篇 |
2015年 | 87篇 |
2014年 | 171篇 |
2013年 | 389篇 |
2012年 | 253篇 |
2011年 | 345篇 |
2010年 | 256篇 |
2009年 | 270篇 |
2008年 | 271篇 |
2007年 | 270篇 |
2006年 | 213篇 |
2005年 | 213篇 |
2004年 | 162篇 |
2003年 | 136篇 |
2002年 | 147篇 |
2001年 | 111篇 |
2000年 | 120篇 |
1999年 | 119篇 |
1998年 | 267篇 |
1997年 | 200篇 |
1996年 | 173篇 |
1995年 | 101篇 |
1994年 | 89篇 |
1993年 | 115篇 |
1992年 | 75篇 |
1991年 | 58篇 |
1990年 | 53篇 |
1989年 | 66篇 |
1988年 | 60篇 |
1987年 | 58篇 |
1986年 | 55篇 |
1985年 | 65篇 |
1984年 | 78篇 |
1983年 | 60篇 |
1982年 | 56篇 |
1981年 | 68篇 |
1980年 | 59篇 |
1979年 | 40篇 |
1978年 | 47篇 |
1977年 | 57篇 |
1976年 | 79篇 |
1975年 | 45篇 |
1973年 | 35篇 |
排序方式: 共有6398条查询结果,搜索用时 31 毫秒
51.
52.
Cathodic processes in the leaching and electrochemistry of covellite in mixed sulfate–chloride media
The cathodic processes that occur on a covellite (CuS) surface in mixed sulfate–chloride solutions in the absence and presence
of copper(II) ions have been studied using potentiostatic transients and cyclic voltammetry at rotating disk electrodes in
the potential range 0.3–0.7 V (versus SHE). This range is relevant to the oxidative leaching of this copper mineral in sulfate
and chloride lixiviants. Variations in the concentrations of sulfate and chloride ions had a small effect on the cathodic
reduction of covellite in the potential range of 0.5–0.3 V, although the presence of chloride ion resulted in a significant
increase in the anodic current on the reverse sweep. On the other hand, addition of copper(II) ions resulted in enhanced cathodic
currents and subsequent anodic currents in both sulfate and chloride solutions due to reduction of covellite to an undefined
reduced copper sulfide species. Reduction of copper(II) to copper(I) ions becomes the preferred cathodic reaction as the concentration
of chloride ions increases, becoming mass transport controlled at a rotating disc electrode at potentials below about 0.4 V.
Potentiostatic measurements at potentials negative to the mixed potential in acidic chloride solutions have shown that reduction
of copper(II) ions is reversible and have been used to estimate the rate of oxidative dissolution of the mineral which value
agrees reasonably well with previously reported leaching rates under similar conditions. Reduction of dissolved oxygen has
been found to be very much slower that that of copper(II) ions under ambient conditions. 相似文献
53.
Structural system identification: from reality to models 总被引:2,自引:0,他引:2
The paper is an expository contribution on the subject of structural system identification, measured signal processing and their applications to model-based structural health detection. The materials covered in this paper are by and large extracted from the three theses of the first three authors. The paper focuses on the state-space oriented system identification theory as specialized to structural dynamics governing equations of motion, a judicious use of wavelet transformation techniques for extracting impulse response functions, various input-output combinations for multi-input and multi-output problems, robust ways of identifying both proportional and non-proportional damping parameters, and the use of localized identification theory for damage detection from measured response data. The authors then offer several outstanding challenges in structural system identification theory and their applications. 相似文献
54.
55.
Lowe Rob; Bennett Paul; Walker Ian; Milne Sarah; Bozionelos George 《Canadian Metallurgical Quarterly》2003,22(5):464
The theory of planned behavior suggests attitudes are a product of salient beliefs. This study examined whether aggregating salient beliefs was plausible within a more biologically centered information-processing environment. A neural network was used to examine associations among beliefs relating to exercise intention. Data on intentions and behavioral, normative, and control beliefs from 114 respondents were used to train (by error backpropagation) a neural network to associate beliefs with intention. The R2 between the network's estimated and self-reported intention was .66. The network's representation comprised 6 belief profiles associated with high, moderate, or low behavioral intention. The neural network accommodated complex relationships among beliefs and belief-intention associations and indicated how high-level constructs such as attitudes may be viewed as the best fit (compromise state) between aroused beliefs. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
56.
BACKGROUND: The effects of hypothermic injury to the liver were investigated on an isolated perfusion circuit by comparing porcine livers with varying degrees of preservation injury. METHODS: A group of unstored livers (n = 5) were compared to livers stored in University of Wisconsin (UW) solution for 18 h (n = 5), and a group of livers stored in Hartmann's solution for 18 h (n = 5). RESULTS: We observed that the degree of platelet sequestration was directly related to the severity of the preservation injury. After 2 h of isolated liver perfusion, the perfusate platelet count fell from 148 +/- 14 x 10(9)/L to 84 +/- 13 x 10(9)/L for control livers. In comparison for livers stored in UW solution, the platelet count fell from 173 +/- 43 x 10(9)/L to 61 +/- 14 x 10(9)/L representing a 64.8% fall, while for those stored in Hartmann's solution, an even more profound fall from 152 +/- 36 x 10(9)/L to 19 +/- 9 x 10(9)/L (87.5% fall) was observed. The difference between the UW-stored and Hartmann's-stored livers was significant (P < 0.05). However, using this model, the degree of leukocyte sequestration did not differentiate the groups. Both histological and ultrastructural examination of liver biopsies taken immediately following revascularization demonstrated that for mild degrees of preservation injury following hypothermic storage, changes occur to the sinusoidal lining cells well before changes to the parenchymal elements. CONCLUSIONS: These findings substantiate the hypothesis that the primary injury associated with hypothermia involves the sinusoidal lining cells (non-parenchymal elements), that it is predominantly a reperfusion phenomenon and that efforts at improving preservation should therefore be targeted primarily at these cells and not the hepatocytes. 相似文献
57.
Ian McKeown 《Coloration Technology》1994,110(4):136-137
Over the last few years, Polaroid has been actively trying to reduce the amount of waste produced at its sites. In this article, Ian McKeown looks at the measures taken at the UK site in Scotland to achieve this aim. 相似文献
58.
This paper describes the application of Fault Tree Analysis to the design phase of a robot manipulator for hazardous waste retrieval. The robot is to be deployed in single-shell under-ground storage tanks at the US Department of Energy (DOE) site in Hanford, Washington. These tanks contain a variety of highly radioactive waste types, necessitating extremely safe and reliable manipulator operation. Based on preliminary design drawings of this long-reach manipulator, fault trees were constructed for several critical failure scenarios. Analysis of the trees revealed a number of ways to improve the safety and reliability of the manipulator design. This paper presents a summary of the fault tree analysis, with a discussion of the applicability of qualitative and quantitative fault tree methods to hazardous waste robotics. 相似文献
59.
The extensive heterogeneity of the gonadotrophin hormones, follicle stimulating hormone (FSH) and luteinizing hormone (LH), is due primarily to the heterogeneous nature of their carbohydrate side-chains, in particular sialic acid residues. In this review, we discuss the role of carbohydrate chains in receptor binding and activation, biological activity, and metabolic half-life. The synthesis and secretion of the various glycoforms of both FSH and LH appear to be under endocrine control with gonadotrophin-releasing hormone (GnRH), oestradiol and testosterone playing important roles. Evidence for different glycoforms having variable biopotency or different encoded functions is increasing, and the production and secretion of more or less acidic gonadotrophin species in different physiological states may represent an important mechanism whereby the pituitary regulates gonadal cell and organ function. This has potential importance for the development of new pharmaceutical reagents and new therapeutic regimens in assisted reproduction. It is envisaged that the use of existing and new forms of FSH/LH will allow patients to be treated in a more controlled and physiological manner, with treatment regimens individualized to the needs of the patient. 相似文献
60.
Research has continued in the field sidechain liquid crystal polymers over recent years, but it is becoming clearer that this research is being directed away from the traditional technology areas of electro-optic devices and researchers are developing new and exciting applications for this novel state of matter. 相似文献