全文获取类型
收费全文 | 497579篇 |
免费 | 5633篇 |
国内免费 | 1825篇 |
专业分类
电工技术 | 9248篇 |
综合类 | 410篇 |
化学工业 | 75637篇 |
金属工艺 | 21180篇 |
机械仪表 | 14583篇 |
建筑科学 | 12274篇 |
矿业工程 | 2260篇 |
能源动力 | 12186篇 |
轻工业 | 45730篇 |
水利工程 | 4734篇 |
石油天然气 | 8274篇 |
武器工业 | 19篇 |
无线电 | 57995篇 |
一般工业技术 | 94797篇 |
冶金工业 | 96476篇 |
原子能技术 | 10630篇 |
自动化技术 | 38604篇 |
出版年
2021年 | 3437篇 |
2019年 | 3210篇 |
2018年 | 5639篇 |
2017年 | 5518篇 |
2016年 | 5998篇 |
2015年 | 4135篇 |
2014年 | 6957篇 |
2013年 | 21472篇 |
2012年 | 11464篇 |
2011年 | 15883篇 |
2010年 | 12928篇 |
2009年 | 14568篇 |
2008年 | 15373篇 |
2007年 | 15327篇 |
2006年 | 13802篇 |
2005年 | 12794篇 |
2004年 | 12099篇 |
2003年 | 11917篇 |
2002年 | 11936篇 |
2001年 | 11903篇 |
2000年 | 11093篇 |
1999年 | 11760篇 |
1998年 | 29447篇 |
1997年 | 21246篇 |
1996年 | 16421篇 |
1995年 | 12360篇 |
1994年 | 10994篇 |
1993年 | 10805篇 |
1992年 | 7951篇 |
1991年 | 7897篇 |
1990年 | 7347篇 |
1989年 | 7297篇 |
1988年 | 7188篇 |
1987年 | 6111篇 |
1986年 | 6067篇 |
1985年 | 7082篇 |
1984年 | 6583篇 |
1983年 | 6025篇 |
1982年 | 5618篇 |
1981年 | 5768篇 |
1980年 | 5541篇 |
1979年 | 5304篇 |
1978年 | 5372篇 |
1977年 | 6373篇 |
1976年 | 8747篇 |
1975年 | 4791篇 |
1974年 | 4570篇 |
1973年 | 4586篇 |
1972年 | 3913篇 |
1971年 | 3600篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Over the last five years, many activities have focused on the unexploited field of carrying out reactions on small scales. Due to the rapid development of new components, this paper deals with recent developments only in a compressed form. An important point is the analysis of possible plant concepts for microreactors and whether these are a sensible option. Due to the enormous difference in size between the microchannels and the fluid periphera of possible components this is not just a technical question. It touches on the microtechnology concept as a whole. The direction in which the field should be developed and which measures can be taken to influence its development are questions that are addressed here with respect to the big industrial interest in microreactors. 相似文献
52.
In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves. 相似文献
53.
Scale Up from Small Oven-Drying Tests of Mineral Concentrate to Pilot-Scale Drying with a Heated Pad
While Fickian diffusion models are commonly used in other applications, there are few reports of them being applied to the batch drying of a mineral concentrate. Diffusion coefficients estimated from small-scale oven-drying tests were used to predict the drying behavior of a concentrate sample 1 m × 1 m in area and 50 cm deep, with a heated bottom pad. These pilot-scale tests included both daily turning of the sample and turning every three days. The excellent quantitative agreement between the predicted and observed pilot-scale behavior gives a high level of confidence in the model predictions and suggests that a Fickian diffusion model is adequate to predict the behavior of mineral concentrates at the low moisture contents used here. 相似文献
54.
G. Murali Dhar B. N. Srinivas M. S. Rana Manoj Kumar S. K. Maity 《Catalysis Today》2003,86(1-4):45-60
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al2O3 containing mixed oxide supports, TiO2 containing mixed oxide supports, ZrO2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO2 containing mixed oxides received maximum attention, especially TiO2–Al2O3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication. 相似文献
55.
56.
Mathematical models of thermomechanical processes which are based on the laws of rational thermodynamics of irreversible processes are treated. Singular features of the unsteady-state behavior of a continuous medium are demonstrated within different models, such as a medium with internal parameters of state, a medium with memory, and a medium of the velocity type. 相似文献
57.
Managing sewerage systems is a highly complex task due to the dynamic nature of the facilities. Their performance strongly depends on the know-how applied by the operators. In order to define optimal operational settings, two decision support tools based on mathematical models have been developed. Moreover, easy-to-use interfaces have been created as well, aiding operators who presumably do not have the necessary skills to use modelling software. The two developed programs simulate the behaviour of both wastewater treatment plants (WWTP) and sewer network systems, respectively. They have essentially the same structure, including raw data management and statistical analysis, a simulation layer using the application programming interface of the applied software and a layer responsible for the representation of the obtained results. Four user modes are provided in the two software including the simulation of historical data using the applied and novel operational settings, as well as modes concerning prediction of possible operation periods and updates. Concerning the WWTP software, it was successfully installed in Nantes (France) in June 2004. Moreover, the one managing sewer networks has been deployed in Saint-Malo (France) in January 2005. This paper presents the structure of the developed software and the first results obtained during the commissioning phase. 相似文献
58.
59.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9 相似文献
60.
Biryukov S.V. Polevoi V.G. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(6):1160-1170
For pt.I see ibid., vol.43, no.6, pp.1150-9 (1996). An exact solution of the electrostatic problem for calculating the surface charge and electric field distributions in an arbitrary periodic interdigital transducer (IDT) is given using the results of our companion paper. An arbitrary external electric field may be specified along the electrode structure with the unit cell containing one electrode, or several electrodes, of different widths. The potentials of the electrodes that may be specified are also arbitrary. It is shown that in the case without an external field, the solution includes all the known results as special cases. The case of shorted electrodes in the external electric field is investigated in detail. The surface charge and electric field distributions are calculated for a spatially harmonic external field with an arbitrary wavenumber. The results of the calculations are represented graphically for various ratios between the period of the electrode structure and the wavelength of the external field for the case of a unit cell containing one or two electrodes of different widths 相似文献