全文获取类型
收费全文 | 65613篇 |
免费 | 7843篇 |
国内免费 | 3248篇 |
专业分类
电工技术 | 3858篇 |
技术理论 | 6篇 |
综合类 | 5893篇 |
化学工业 | 15468篇 |
金属工艺 | 1822篇 |
机械仪表 | 3481篇 |
建筑科学 | 5044篇 |
矿业工程 | 1645篇 |
能源动力 | 5621篇 |
轻工业 | 3632篇 |
水利工程 | 1532篇 |
石油天然气 | 2163篇 |
武器工业 | 578篇 |
无线电 | 5003篇 |
一般工业技术 | 7695篇 |
冶金工业 | 3024篇 |
原子能技术 | 1031篇 |
自动化技术 | 9208篇 |
出版年
2024年 | 289篇 |
2023年 | 1008篇 |
2022年 | 1637篇 |
2021年 | 2026篇 |
2020年 | 2182篇 |
2019年 | 1914篇 |
2018年 | 1847篇 |
2017年 | 2151篇 |
2016年 | 2460篇 |
2015年 | 2578篇 |
2014年 | 3755篇 |
2013年 | 4458篇 |
2012年 | 4191篇 |
2011年 | 4716篇 |
2010年 | 3505篇 |
2009年 | 3759篇 |
2008年 | 3524篇 |
2007年 | 4103篇 |
2006年 | 3844篇 |
2005年 | 3434篇 |
2004年 | 2876篇 |
2003年 | 2668篇 |
2002年 | 2177篇 |
2001年 | 1800篇 |
2000年 | 1474篇 |
1999年 | 1146篇 |
1998年 | 963篇 |
1997年 | 807篇 |
1996年 | 659篇 |
1995年 | 615篇 |
1994年 | 476篇 |
1993年 | 391篇 |
1992年 | 382篇 |
1991年 | 255篇 |
1990年 | 264篇 |
1989年 | 196篇 |
1988年 | 154篇 |
1987年 | 116篇 |
1986年 | 100篇 |
1985年 | 205篇 |
1984年 | 324篇 |
1983年 | 331篇 |
1982年 | 236篇 |
1981年 | 321篇 |
1980年 | 128篇 |
1979年 | 42篇 |
1978年 | 41篇 |
1975年 | 24篇 |
1974年 | 25篇 |
1951年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
[Correction Notice: An erratum for this article was reported in Vol 20(2) of Canadian Journal of Behavioural Science Revue canadienne des Sciences du comportement (see record 2007-09831-001). The abstract accompanying the original article was incorrect; the correct abstract (in French) is presented in the erratum.] We know little about individuals who are declared unfit to stand trial and/or not guilty by reason of insanity. The few existing studies are characterized by methodological weaknesses, notably by short follow-up periods and a lack of external validity. The present investigation, which aims to evaluate and explain readmissions that occurred during a seven- to nine-year period, corrects only some of these weaknesses. Sixty-one per cent of the subjects were rehospitalized during the period of study. It proved difficult to identify the factors associated with readmission. However, males with a diagnosis of schizophrenia and who had committed violent crimes were found the most likely to be readmitted. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
102.
Wenwei He Wuping Liao Weiwei Wang Deqian Li Chunji Niu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(9):1314-1320
BACKGROUND: Thermodynamics and kinetics data are both important to explain the extraction property. In order to develop a novel separation technology superior to current extraction systems, many promising extractants have been developed including calixarene carboxylic acids. The extraction thermodynamics behavior of calix[4]arene carboxylic acids has been reported extensively. In this study, the mass transfer kinetics of neodymium(III) and the interfacial behavior of calix[4]arene carboxylic acid were investigated. RESULTS: The rate constant (Kao) becomes constant when the stirring speed was controlled between 250 rpm and 400 rpm. The activation energy (Ea) was calculated to be 21·41 kJ mol?1 or 88·17 kJ mol?1 (dependent on temperature) from the slope of log Kao against 1000/T. The linear relationship between the specific area and the extraction rate is the characteristic of an interfacial reaction control. The minimum bulk concentration of the extractant necessary to saturate the interface (Cmin) is lower than 4·19 × 10?4 mol L?1. CONCLUSION: The effect of stirring speed, temperature, and species concentration on the extraction rate demonstrates that the extraction regime depends on the extraction conditions. The chemical reaction control governs the extraction regime at temperatures below 303 K and a mixed control regime occurs when the temperature is between 303 K and 318 K. The probable locale for the chemical reaction is at the liquid–liquid interface and the rate equation is deduced to be: ? d[Nd3+](a)/dt = kf[Nd3+](a)[H4A](o)0·727[H+](a)?0·978. The rate‐controlling step was suggested by the analysis of the experimental results. Copyright © 2008 Society of Chemical Industry 相似文献
103.
104.
Experiments were performed to investigate the heat transfer characteristics of a row of three premixed, laminar, butane/air flame jets impinging on a water-cooled flat plate. The between-jet interference was found to reduce the heat transfer rate in the jet-to-jet interacting zone due to the depressed combustion. The interference became stronger when the jet-to-jet spacing and/or the nozzle-to-plate distance were/was small. The positive pressure existed in the between-jet interacting zone caused the asymmetric flame and heat transfer distribution of the side jet. The meeting point of the spreading wall jets of the central and the side jets did not occur at the midpoint of the neighboring jets, but at a location shifted slightly outwards. The maximum local heat flux and the maximum area-averaged heat flux occurred at a moderate nozzle-to-plate distance of 5d with a moderate jet-to-jet spacing of 5d. The lowest area-averaged heat flux was produced when both the jet-to-jet spacing and the nozzle-to-plate distance were small. Comparing with a single jet under the same experimental conditions, the heat transfer rates in both the stagnation point and the maximum heat transfer point were shown to be enhanced in a row of three-jet-impingement system. The present study provided detailed information on the heat transfer characteristics of a row of three in-line impinging flame jets, which had rarely been reported in previous study. 相似文献
105.
L. V. El’nikova 《Journal of Superconductivity and Novel Magnetism》2007,20(2):197-199
We describe the lyotropic liquid crystalline phase transitions in the lipid mixture dipalmitoil-PC/dilauroy-PC/cholesterol
by 3D spin-1 lattice model. The formation of nanoscale domains with the characteristic size about 300 nm was studied in experiments
on confocal fluorescence microscopy (CFM) (G. V. Feigenson and J. T. Buboltz, Biophys. J.
80, 2775 (2001)). The structure parameters of the lamellar vesicle in dipalmitoil-PC-rich phase, corresponding to these regions,
are verified by numerical Monte Carlo simulations on the lattice. We point its superconductivity analogy properties at the
region of phase stability for composition-dependent nanoscopic region. 相似文献
106.
A motivational model of rural students' intentions to persist in, versus drop out of, high school. 总被引:1,自引:0,他引:1
Using self-determination theory, the authors tested a motivational model to explain the conditions under which rural students formulate their intentions to persist in, versus drop out of, high school. The model argues that motivational variables underlie students' intentions to drop out and that students' motivation can be either supported in the classroom by autonomy-supportive teachers or frustrated by controlling teachers. LISREL analyses of questionnaire data from 483 rural high school students showed that the provision of autonomy support within classrooms predicted students' self-determined motivation and perceived competence. These motivational resources, in turn, predicted students' intentions to persist, versus drop out, and they did so even after controlling for the effect of achievement. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
107.
In Part I of this paper, a theoretical basis is presented using a two-degrees-of-freedom model. In this second part of the study, the passive control and the two types of semiactive controls introduced in Part I are examined numerically for a taut cable experiencing wind-induced galloping motion. The passive and the semiactive control schemes for taut cables show a good similarity with the results obtained for the two-degrees-of-freedom model. The potential of using these control schemes in practical applications to flexible structures is demonstrated. 相似文献
108.
Hussain Sheikha Anil K. Mehrotra Mehran Pooladi-Darvish 《Journal of Petroleum Science and Engineering》2006,53(3-4):189-202
An inverse solution methodology is developed for the estimation of diffusion coefficient of gases in highly viscous, oil-sands bitumens from isothermal, pressure-decay measurements. The approach involves modeling the rate of change in pressure using the diffusion equation for the liquid phase coupled with a mass balance equation for the gas phase. The inverse solution framework is utilized to arrive at two graphical techniques for estimating the diffusion coefficient. Both techniques involve the determination of the slope of a straight line resulting from plotting the experimental data in accordance with the developed model. An advantage of the proposed techniques is that the diffusion coefficient is estimated directly, i.e. without making it an adjustable parameter. The novelty of the proposed method is in its simplicity as well as its ability to isolate portions of the pressure-decay data affected by experimental fluctuations. The effect of the initial pressure on the predicted diffusion coefficient and pressure-decay profile was also investigated. The diffusion coefficients of CO2, CH4, C2H6 and N2 in Athabasca bitumen at 50–90 °C and about 8 MPa were estimated and compared with literature values. 相似文献
109.
110.
Michael V. Antony 《Minds and Machines》1991,1(3):321-341
Fodor and Pylyshyn (1988) have argued that the cognitive architecture is not Connectionist. Their argument takes the following form: (1) the cognitive architecture is Classical; (2) Classicalism and Connectionism are incompatible; (3) therefore the cognitive architecture is not Connectionist. In this essay I argue that Fodor and Pylyshyn's defenses of (1) and (2) are inadequate. Their argument for (1), based on their claim that Classicalism best explains the systematicity of cognitive capacities, is an invalid instance of inference to the best explanation. And their argument for (2) turns out to be question-begging. The upshot is that, while Fodor and Pylyshyn have presented Connectionists with the important empirical challenge of explaining systematicity, they have failed to provide sufficient reason for inferring that the cognitive architecture is Classical and not Connectionist. 相似文献