全文获取类型
收费全文 | 136698篇 |
免费 | 8386篇 |
国内免费 | 4106篇 |
专业分类
电工技术 | 6306篇 |
技术理论 | 8篇 |
综合类 | 12608篇 |
化学工业 | 9286篇 |
金属工艺 | 5289篇 |
机械仪表 | 14211篇 |
建筑科学 | 32929篇 |
矿业工程 | 4423篇 |
能源动力 | 3114篇 |
轻工业 | 5093篇 |
水利工程 | 4071篇 |
石油天然气 | 7954篇 |
武器工业 | 1451篇 |
无线电 | 7737篇 |
一般工业技术 | 14146篇 |
冶金工业 | 3077篇 |
原子能技术 | 743篇 |
自动化技术 | 16744篇 |
出版年
2024年 | 494篇 |
2023年 | 1358篇 |
2022年 | 2355篇 |
2021年 | 3009篇 |
2020年 | 3365篇 |
2019年 | 2570篇 |
2018年 | 2565篇 |
2017年 | 3055篇 |
2016年 | 3587篇 |
2015年 | 3855篇 |
2014年 | 9720篇 |
2013年 | 7748篇 |
2012年 | 9792篇 |
2011年 | 10482篇 |
2010年 | 8710篇 |
2009年 | 9039篇 |
2008年 | 8089篇 |
2007年 | 9642篇 |
2006年 | 8133篇 |
2005年 | 7205篇 |
2004年 | 5784篇 |
2003年 | 5446篇 |
2002年 | 4319篇 |
2001年 | 3648篇 |
2000年 | 2950篇 |
1999年 | 2334篇 |
1998年 | 1923篇 |
1997年 | 1606篇 |
1996年 | 1342篇 |
1995年 | 1060篇 |
1994年 | 901篇 |
1993年 | 613篇 |
1992年 | 494篇 |
1991年 | 417篇 |
1990年 | 281篇 |
1989年 | 263篇 |
1988年 | 191篇 |
1987年 | 141篇 |
1986年 | 84篇 |
1985年 | 95篇 |
1984年 | 124篇 |
1983年 | 82篇 |
1982年 | 92篇 |
1981年 | 32篇 |
1980年 | 61篇 |
1979年 | 36篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1959年 | 15篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
41.
The limited research on the geopolymer concrete mix design for targeting a specific strength is identified an obstacle for their effective design and wide use. In this paper, a mix design procedure has been proposed for fly-ash based geopolymer concrete and its use as infill hybrid composite beam is investigated. Then, the structural performance of geopolymer concrete filled hybrid composite beam is investigated to determine their possible application in civil infrastructure. Firstly, a detailed procedure of mix design for fly-ash based geopolymer concrete is presented. Secondly, three hybrid beams filled with geopolymer concrete were prepared and tested in a four-point bending setup to evaluate their flexural modulus and modulus of rupture. Numerical and analytical evaluation of the behaviour of hybrid beam were performed and results showed a good agreement with the experimental investigation. Thirdly, the suitability of the beam for a composite railway sleeper is evaluated and compared with existing timber and composite sleepers. Finally, the beams’ performance in a ballast railway track is analysed using Strand7 finite element simulation software and the results showed that the new concept of using geopolymer concrete as infill to pultruded composite section satisfied the stiffness and strength requirements for a railway sleeper. 相似文献
42.
Based on the phase transformation theories, especially the T0 concept of bainite transformation, alloy optimisation of bainitic steel with carbides has been carried out aiming at the produce of plastic mould with large cross-section. The effect of manganese and silicon on proeutectoid ferrite and bainite transformation is explored by dilatometric analysis, XRD and different microscopy techniques. The results show that after the alloy optimisation, the transformation of proeutectoid ferrite is suppressed and when the cooling rate is lower than 0·1°C?s??1, the new lower bainite transformation appears by decreasing carbon capacity of austenite and promoting carbide precipitation. Industrial production proves that the optimised alloy SDP1 can meet the demand for the plastic mould with the thickness of 1050?mm. 相似文献
43.
The perpetual energy production of a wind farm could be accomplished (under proper weather conditions) if no failures occurred. But even the best possible design, manufacturing, and maintenance of a system cannot eliminate the failure possibility. In order to understand and minimize the system failures, the most crucial components of the wind turbines, which are prone to failures, should be identified. Moreover, it is essential to determine and classify the criticality of the system failures according to the impact of these failure events on wind turbine safety. The present study is processing the failure data from a wind farm and uses the Fault Tree Analysis as a baseline for applying the Design Structure Matrix technique to reveal the failure and risk interactions between wind turbine subsystems. Based on the analysis performed and by introducing new importance measures, the “readiness to fail” of a subsystem in conjunction with the “failure riskiness” can determine the “failure criticality.” The value of the failure criticality can define the frame within which interventions could be done. The arising interventions could be applied either to the whole system or could be focused in specified pairs of wind turbine subsystems. In conclusion, the method analyzed in the present research can be effectively applied by the wind turbine manufacturers and the wind farm operators as an operation framework, which can lead to a limited (as possible) design‐out maintenance cost, failures' minimization, and safety maximization for the whole wind turbine system. 相似文献
44.
通过对大直径平底负压容器平底板的设计计算,平底板计算厚度很厚。通过分析,提出了对平底板采取加强措施,从而减薄平底板计算厚度的方法。该容器在实际生产过程中性能可靠、稳定,对类似设备设计具有借鉴意义。 相似文献
45.
This work is concerned with the prediction of visual colour difference between pairs of palettes. In this study, the palettes contained five colours arranged in a horizontal row. A total of 95 pairs of palettes were rated for visual difference by 20 participants. The colour difference between the palettes was predicted using two algorithms, each based on one of six colour-difference formulae. The best performance (r2 = 0.86 and STRESS = 16.9) was obtained using the minimum colour-difference algorithm (MICDM) using the CIEDE2000 equation with a lightness weighing of 2. There was some evidence that the order (or arrangement) of the colours in the palettes was a factor affecting the visual colour differences although the MICDM algorithm does not take order into account. Application of this algorithm is intended for digital design workflows where colour palettes are generated automatically using machine learning and for comparing palettes obtained from psychophysical studies to explore, for example, the effect of culture, age, or gender on colour associations. 相似文献
46.
47.
Kinetic,thermodynamic parameters and in vitro digestion of tannase from Aspergillus tamarii URM 7115
Amanda Reges de Sena Tonny Cley Campos Leite Talita Camila Evaristo da Silva Nascimento Anna Carolina da Silva Catiane S. Souza Antônio Fernando de Mello Vaz 《Chemical Engineering Communications》2018,205(10):1415-1431
Tannase is an enzyme used in various industries and produced by a large number of microorganisms. The aim of this study was to evaluate tannase production to determine the biochemical, kinetic, and thermodynamic properties and to simulate tannase in vitro digestion. The tannase-producing fungal strain was isolated from “jamun” leaves and identified as Aspergillus tamarii. Temperature at 26°C for 67?h was the best combination for maximum tannase activity (6.35-fold; initial activity in Plackett–Burman design—15.53?U/mL and average final activity in Doehlert design—98.68?U/mL). The crude extract of tannase was optimally active at 40°C, pH 5.5 and 6.5. Moreover, tannase was stimulated by Na+, Ca2+, Mg2+, and Mn2+. The half-life at 40°C lasted 247.55?min. The free energy of Gibbs, enthalpy, and entropy, at 40°C, was 81.47, 16.85, and ?0.21?kJ/mol?·?K, respectively. After total digestion, 123.95% of the original activity was retained. Results suggested that tannase from A. tamarii URM 7115 is an enzyme of interest for industrial applications, such as gallic acid production, additive for feed industry, and for beverage manufacturing, due to its catalytic and thermodynamic properties. 相似文献
48.
49.
张峰水库溢洪道体型优化设计 总被引:1,自引:0,他引:1
本文对已设计的张峰水库溢洪道进行了模型试验,根据对试验结果分析,认为原方案设计存在一些问题,并针对问题进行了优化设计。通过对修改方案模型试验结果分析,得出修改方案改进了原方案中存在的不足,优化合理,是可以采用的。 相似文献
50.
气烟囱效应——礁滩相岩性气藏的典型地震响应特征 总被引:14,自引:0,他引:14
品质良好的地震剖面上出现的地震模糊带称为气烟囱,发现和识别气烟囱是寻找大型气藏的有效方法。四川盆地东北部长兴组气藏是礁滩相岩性气藏,礁、滩作为一个独立的岩性体,与周围的地层、岩性结构差异较大,由此在构造应力场中形成力学尖点,从而产生气烟囱效应。已知的黄龙场、普光等气田,其气烟囱普遍存在。点礁通常形成下方的气烟囱,台缘礁通常在上方形成气烟囱;礁滩相在构造运动中控制了断层的发育过程,凸起的礁滩相上方可能发育对冲断层;斜坡较陡的台缘礁可能发育叠置的逆冲断层;礁、滩两侧边缘的断层一般都比较发育。断层发育加强了气烟囱效应。模拟试验验证了地震剖面解释结果。根据气烟囱地震相特征,预测黑池梁存在一个大型气藏。 相似文献