全文获取类型
收费全文 | 8441篇 |
免费 | 483篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 114篇 |
综合类 | 23篇 |
化学工业 | 2204篇 |
金属工艺 | 246篇 |
机械仪表 | 155篇 |
建筑科学 | 592篇 |
矿业工程 | 98篇 |
能源动力 | 286篇 |
轻工业 | 597篇 |
水利工程 | 50篇 |
石油天然气 | 20篇 |
武器工业 | 1篇 |
无线电 | 662篇 |
一般工业技术 | 1746篇 |
冶金工业 | 483篇 |
原子能技术 | 51篇 |
自动化技术 | 1605篇 |
出版年
2024年 | 15篇 |
2023年 | 117篇 |
2022年 | 208篇 |
2021年 | 331篇 |
2020年 | 201篇 |
2019年 | 210篇 |
2018年 | 231篇 |
2017年 | 269篇 |
2016年 | 352篇 |
2015年 | 294篇 |
2014年 | 379篇 |
2013年 | 600篇 |
2012年 | 536篇 |
2011年 | 719篇 |
2010年 | 511篇 |
2009年 | 479篇 |
2008年 | 486篇 |
2007年 | 424篇 |
2006年 | 379篇 |
2005年 | 303篇 |
2004年 | 253篇 |
2003年 | 187篇 |
2002年 | 165篇 |
2001年 | 104篇 |
2000年 | 99篇 |
1999年 | 114篇 |
1998年 | 123篇 |
1997年 | 99篇 |
1996年 | 87篇 |
1995年 | 54篇 |
1994年 | 63篇 |
1993年 | 37篇 |
1992年 | 48篇 |
1991年 | 27篇 |
1990年 | 39篇 |
1989年 | 25篇 |
1988年 | 28篇 |
1987年 | 29篇 |
1986年 | 27篇 |
1985年 | 20篇 |
1984年 | 29篇 |
1983年 | 19篇 |
1982年 | 19篇 |
1981年 | 16篇 |
1980年 | 23篇 |
1977年 | 20篇 |
1976年 | 27篇 |
1975年 | 15篇 |
1974年 | 12篇 |
1969年 | 12篇 |
排序方式: 共有8933条查询结果,搜索用时 0 毫秒
921.
A number of critiques have been published drawing attention to the gaps in research methods applied to issues surrounding homelessness and service utilisation in Britain. This paper discusses the use of social identity, a theory drawn from the field of applied social psychology, and synthesises it with the pathways model, thereby providing a framework to further explore service utilisation. The synthesised framework was used to predict the uptake of outreach services in a prospective study of 121 homeless people in a major UK city. In general, homeless people's use of intervention services was affected by the extent to which they identified with the support services themselves. The study demonstrates the central role of social identity in understanding service utilisation patterns, and shows the importance of applying fresh techniques to fine-tune our understanding of uptake in the long term. 相似文献
922.
Khaled Ameur Christian MassonPeter J. Eecen 《Journal of Wind Engineering & Industrial Aerodynamics》2011,99(8):833-844
Two-dimensional axisymmetric and three-dimensional steady turbulent flow computations around two horizontal-axis wind turbines (Nordex N80 and Jeumont J48) are carried out to investigate the wind-rotor/nacelle interaction and quantify its effects on the wind speed at the nacelle anemometry. The actuator disk concept has been used to model the action of the blades. For both turbines, the geometry of the nacelle was reproduced as faithfully as possible. The terrain was represented by an appropriate law of the wall to account for roughness with particular attention paid to the boundary conditions in order to reproduce the neutral atmospheric boundary layer. The calculated velocity field in the vicinity of the nacelle exhibits good agreement with available experimental data. The results also show that for a complex nacelle geometry, like that of the N80, a three-dimensional calculation is necessary to obtain a good prediction of the velocity field in the near wake. The hub height effect is evaluated for the J48 by raising the nacelle from a height of 36 to 60 m. No significant impact is noted on the ratio nacelle wind speed/freestream wind speed. 相似文献
923.
Prof. Dr. Walter Semmler (1903–1990) was a ground-breaking German hydrogeologist who conducted practical mine water research in Germany, mainly related to dewatering, but also on tracer tests and potential environmental impacts of mine water. In addition, his contributions to professional associations in Germany and the formation of water authorities in the Ruhr Coal Mining District was noteworthy. 相似文献
924.
Dipl.-Ing. Dr. mont. Pawel Krajewski Christian Bernhard Roman Krobath Thomas Schaden Sergiu Ilie 《BHM Berg- und Hüttenm?nnische Monatshefte》2014,159(7):304-305
Continuous casting of steel free of surface cracks is still one of the major quality challenges in the whole steel production. The key roles for the phenomenon of surface cracking are played by the critical strain and the temperature-dependent material’s phenomena. The new In-Situ Characterization Bending (IMC-B) method will enable the investigation of the critical strains with respect to the cracking under the main continuous casting boundaries. This publication presents potential and interesting results of the IMC-B experiment. 相似文献
925.
Augusto Hernandez-Solis Christian Ekberg Arvid Ödegård Jensen 《Nuclear Engineering and Design》2011,241(9):3697-3706
In recent years, more realistic safety analyses of nuclear reactors have been based on best estimate (BE) computer codes. The need to validate and refine BE codes that are used in the predictions of relevant reactor safety parameters, led to the organization of international benchmarks based on high quality experimental data. The OECD/NRC BWR full-size fine-mesh bundle test (BFBT) benchmark offers a good opportunity to assess the accuracy of thermal-hydraulic codes in predicting, among other parameters, single and two phase bundle pressure drop, cross-sectional averaged void fraction distributions and critical powers under a wide range of system conditions. The BFBT is based on a multi-rod assembly integral test facility which is able to simulate the high pressure, high temperature fluid conditions found in BWRs through electrically heated rod bundles. Since code accuracy is unavoidably affected by models and experimental uncertainties, an uncertainty analysis is fundamental in order to have a complete validation study. In this paper, statistical uncertainty and sensitivity analyses are used to validate the thermal-hydraulic features of the POLCA-T code, based on a one dimensional model of the following macroscopic BFBT exercises: (1) single and two phase bundle pressure drop, (2) steady-state cross-sectional averaged void fraction, (3) transient cross-sectional averaged void fraction and (4) steady-state critical power tests. The Latin hypercube sampling (LHS) strategy was chosen since it densely stratifies across the range of each uncertain input probability distribution, allowing a much better coverage of the input uncertainties than simple random sampling (SRS). The results show that POLCA-T predictions on pressure drop and void fractions under a wide range of conditions are within the validation limits imposed by the uncertainty analysis, while the accuracy of critical power predictions depends much on the boundary and input conditions. 相似文献
926.
The present paper is related to the dynamic (shock) analysis of a naval propulsion (on-board) reactor with fluid–structure interaction modelling. In a previous study, low frequency analysis has been performed; the present study deals with high frequency analysis, i.e. taking into account compressibility effects in the fluid medium. Elasto-acoustic coupling effects are studied and described in the industrial case. The coupled problem is formulated using the so-called (u, p, φ) formulation which yields symmetric matrices. A modal analysis is first performed on the fluid problem alone, then for the coupled fluid–structure problem in the following cases: (i) with incompressible fluid; (ii) with compressible fluid at standard pressure and temperature conditions; (iii) with compressible fluid at the operating pressure and temperature conditions. Elasto-coupling effects are then highlighted, in particular through the calculation of an elastic energy ratio. As a general conclusion, compressibility effects are proved significant in the dynamic response of the reactor in the high frequency range. 相似文献
927.
Computer aided design of microwave monolithic integrated circuits must combine two different fields. The first domain is the simulation of microwave circuits taking into account non linear aspects development of time domain and harmonic balance simulation algorithms specialized for microwave circuits. In the second place are found, the layout algorithms which were developed for logic circuits (on Si or GaAs). The association of these two types of algorithms leads to the constitution of aCad workstation for microwave monolithic integrated circuits. Two examples of design and realization of integrated circuits with these tools are presented. 相似文献
928.
Mayer Richard E.; Stiehl C. Christian; Greeno James G. 《Canadian Metallurgical Quarterly》1975,67(3):331
4 experiments examined effects of a total of 224 college students' aptitudes, preinstructional experience, method of instruction, and differences among posttest items. Instruction that emphasized meanings of concepts led to better performance on posttest items requiring understanding, but Ss with emphasis on computation performed better on simple problems. Ss with higher measured aptitudes directly relevant to instruction or given relevant preinstructional experience had more success in meaningful instruction than did Ss with lower aptitude scores, but little or no aptitude difference was found for instruction emphasizing algorithms. 2 kinds of operations were distinguished-identifying relevant information in the problem situation and carrying out computations. The former appears more closely related to conceptual understanding, the latter to computational skill. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
929.
A method for determining hydrogen in steel by melting with nitrogen as a carrier gas was adapted for aluminum and its alloys. Dehydrogenationvs temperature was investigated in order to define an optimal sequence of operating conditions. The results obtained by the method were systematically compared to those given by the reference vacuum hot extraction method. The essential characteristics of this new method can be summarized as follows: 1) The detection limit is 0.02 ml/100 g (0.02 ppm H2). 2) The method is valid for any alloy, even for those with high volatile constituent content such as Zn or Mg. 3) The bulk hydrogen content is not significantly different from that given by the vacuum hot extraction method. 4) “Surface” hydrogen could be eliminated by a thermal treatment at 400°C prior to melting. 5) Correlations appeared between changes in thermal and dehydrogenation curves, the last one representing a characteristic spectrum of the alloy studied. 6) A complete analysis requires 15 min instead of several hours for the hot extraction method. It is thus applicable in routine industrial work. 相似文献
930.
Pipe fabrication for the repair sector. The paper discusses the changes in pipe fabrication that have taken place in recent years. These enable repair work to be carried out more efficiently, without thereby impairing the flexibility and speed of operation that are essential to maintenance work. A prerequisite for this is that work on the pipes be transferred to workshops. Only here is it possible for manual operations, such as manual welding, to be reduced to a minimum and be replaced by mechanized or semi-mechanized welding methods. The use of modern machines for bending the pipes is more economic than the welding in of pipe bends. Necking out of the pipes by mechanical means or the use of mechanically pre-fabricated connections permit optimum preparation of the weld seam for branch fittings. Any additional work on the pipes, where this is necessary, is carried out at workplaces specially designed for the purpose. 相似文献