全文获取类型
收费全文 | 12931篇 |
免费 | 606篇 |
国内免费 | 98篇 |
专业分类
电工技术 | 288篇 |
综合类 | 33篇 |
化学工业 | 2729篇 |
金属工艺 | 278篇 |
机械仪表 | 343篇 |
建筑科学 | 349篇 |
矿业工程 | 37篇 |
能源动力 | 788篇 |
轻工业 | 1196篇 |
水利工程 | 142篇 |
石油天然气 | 196篇 |
武器工业 | 4篇 |
无线电 | 1548篇 |
一般工业技术 | 2526篇 |
冶金工业 | 988篇 |
原子能技术 | 140篇 |
自动化技术 | 2050篇 |
出版年
2024年 | 37篇 |
2023年 | 281篇 |
2022年 | 668篇 |
2021年 | 923篇 |
2020年 | 613篇 |
2019年 | 646篇 |
2018年 | 762篇 |
2017年 | 585篇 |
2016年 | 631篇 |
2015年 | 399篇 |
2014年 | 567篇 |
2013年 | 1002篇 |
2012年 | 644篇 |
2011年 | 724篇 |
2010年 | 471篇 |
2009年 | 389篇 |
2008年 | 378篇 |
2007年 | 339篇 |
2006年 | 287篇 |
2005年 | 234篇 |
2004年 | 186篇 |
2003年 | 183篇 |
2002年 | 176篇 |
2001年 | 113篇 |
2000年 | 112篇 |
1999年 | 139篇 |
1998年 | 276篇 |
1997年 | 232篇 |
1996年 | 169篇 |
1995年 | 151篇 |
1994年 | 111篇 |
1993年 | 105篇 |
1992年 | 75篇 |
1991年 | 66篇 |
1990年 | 62篇 |
1989年 | 71篇 |
1988年 | 70篇 |
1987年 | 57篇 |
1986年 | 60篇 |
1985年 | 70篇 |
1984年 | 74篇 |
1983年 | 69篇 |
1982年 | 38篇 |
1981年 | 34篇 |
1980年 | 40篇 |
1979年 | 31篇 |
1978年 | 34篇 |
1977年 | 37篇 |
1976年 | 53篇 |
1972年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Gilbert A. Hartley Ahmed Abdel-Akher Peilei Chen 《International journal for numerical methods in engineering》1992,35(9):1771-1785
Procedures are described for modelling a structural system consisting of thin Kirchhoff plates with internal patch areas capable of displacing as rigid flat surfaces. The physical prototype for these patches could be interconnection points for one-dimensional frame type elements of various shapes and layout, rigidly connected at these finite size 'joints' in the plate. The numerical procedure for modelling the thin plate is the Direct Boundary Element Method (DBEM) and a simple overview of this procedure is provided. Potential trouble spots, of which the user should be aware, are described. The paper will be of interest to structural engineers for analysis of frames having both plate and simple frame elements, for example, building frames; and also to researchers seeking the greater detail that this refined procedure can provide. As a practical tool, the methods described are computationally competitive with existing procedures, including the more rugged approaches used by building structural engineers for dynamic and torsional analysis. 相似文献
12.
13.
Second-law-based thermodynamic analysis of two-stage and mechanical-subcooling refrigeration cycles 总被引:1,自引:0,他引:1
Thermodynamic analysis of HFC-134a vapor-compression refrigeration cycles is investigated by both the first and second laws of thermodynamics. Second-law analysis is carried out for both two-stage and mechanical-subcooling refrigeration cycles. The analysis is performed on each of the system components to determine their individual contribution to the overall system irreversible losses. It is found that most of the losses are due to a low compressor efficiency. Irreversibilities of expansion valves and condenser are also significant. In addition, it is shown that the optimum inter-stage pressure for two-stage and mechanical-subcooling refrigeration systems is very close to the saturation pressure corresponding to the arithmetic mean of the refrigerant condensation and evaporation temperatures. These results are compared with the existing practice in the industry. Furthermore, theoretical results of a two-stage refrigeration system performance are also compared with experimental values for a CFC-22 system. 相似文献
14.
Nanotechnology research is booming worldwide, having an impact on multiple sectors and with a general belief that medical
and biological applications will form the greatest area of expansion over the next decade, driven by an attempt to bring radical
solutions to areas of unmet medical need. What is true in the USA is also being fulfilled in Europe, though generally at a
significantly lower investment level, even for ’large’ capital infrastructure and interdisciplinary centres. Against this,
the UK and its European partners are following the maxim ’small is beautiful’ and are attempting to identify and grow academic
research and commercial businesses in areas that traditional nanotechnology developments out of engineering or physics find
challenging. Thus, University College London and Imperial College, in a major joint project linked to other centres of excellence
both in the UK and in the rest of Europe, are building upon their internationally competitive medical and hard-matter research
activities to focus on and develop nanotechnology as a major sector of research activity. The two universities together form
one of the largest centres of biomedical research outside the USA. A novel approach to commercialisation has been taken, exemplified
by the establishment with government and private equity funds of a ‘Bionanotechnology Centre’ — this will act as a portal
for UK industry to access specialist skills to solve issues relating to developing nanotechnology-based medical applications,
for example, for environmental screening, diagnostics and therapy. This paper reviews our academic and business strategy with
examples from our current research portfolio, biased towards medicine as the London Centre for Nanotechnology’s most rapidly
growing area. 相似文献
15.
KS Min AR Khan MK Kwon YJ Jung Z Yun Y Kiso 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(8):909-915
The performance of a laboratory‐scale anaerobic acidogenic fermenter fed with a mixture of blended kitchen food‐waste and primary sludge from a sewage treatment plant was investigated for the production of volatile fatty acids (VFA). The operating variables for acidogenic fermentation were kitchen food‐waste content (10 and 25 wt %), hydraulic retention time (HRT: 1, 3 and 5 days), temperature (ambient: 18 ± 2 °C, and mesophilic: 35 ± 2 °C) and pH (varied from 5.2 to 6.7). The experimental results indicated that effluent VFA concentrations and VFA production rates were higher at ambient temperature than at mesophilic conditions. The net amount of VFA with 10 wt % food‐waste increased up to 920 mg dm?3 with an increase of HRT, but contrasting results (a decrease of 2610 mg dm?3) were found due to the conversion of VFA into biogas in the case of 25 wt % food‐waste, which increased significantly at HRT of 3–5 days. In terms of biogas composition (CO2 and CH4), the organic matter was converted into CO2 through the oxidative pathway by facultative species at low temperature while mesophilic temperature and optimum pH (6.3–7.8) played a pivotal role in increasing rate of conversion of VFA into biogas by methanogenesis. Rates of VFA production and their conversion are dependent on the food‐waste content in the mixture. Yet, the higher concentration of food‐waste (25% compared with 10%) did not produce VFA proportionally due to the increased rate of conversion of VFA into gaseous products. The maximum VFA production rate (0.318 g VFAproduced g?1 VSfed day?1) was achieved in the 10 wt % food‐waste at ambient temperature and at a 5‐day HRT. Copyright © 2005 Society of Chemical Industry 相似文献
16.
A novel rapid power-on operational amplifier and a current modulation technique are used in a 10-bit 1.5-bit/stage pipelined ADC in 0.18-/spl mu/m CMOS to realize power scalability between 1 kS/s (15 /spl mu/W) and 50 MS/s (35 mW), while maintaining an SNDR of 54-56 dB for all sampling rates. The current modulated power scaling (CMPS) technique is shown to enhance the power scaleable range of current scaling by 50 times, allowing ADC power to be varied by a factor of 2500 while only varying bias currents by a factor of 50. Furthermore, the nominal power is reduced by 20%-30% by completely powering off the rapid power-on opamps during the sampling phase in the pipeline's sample-and-holds. 相似文献
17.
An analytical method for calculating static characteristics of linear dc step motors (LSM) is described. These multiphase passive-armature motors are now being developed for control rod drives (CRD) in large nuclear reactors. The static characteristics of such LSM is defined by the variation of electromagnetic force with armature displacement and it determines motor performance in its standing and dynamic modes of operation. The proposed analytical technique for calculating this characteristic is based on the permeance analysis method applied to phase magnetic circuits of LSM. Reluctances of various parts of phase magnetic circuit is calculated analytically by assuming probable flux paths and by taking into account complex nature of magnetic field distribution in it. For given armature positions stator and armature iron saturations are taken into account by an efficient iterative algorithm which gives fast convergence. The method is validated by comparing theoretical results with experimental ones which shows satisfactory agreement for small stator currents and weak iron saturation 相似文献
18.
19.
Calcified and fibrotic coronary artery lesions cannot always be dilated with conventional balloon angioplasty even at high pressures. This study examines the success of excimer laser facilitated angioplasty in 38 lesions in 37 patients with lesions that failed balloon angioplasty alone. 相似文献
20.
Adrian Thomas Christopher D. Gilson Tanveer Ahmed 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,64(1):73-79
Equipment was developed to measure the time for complete gelling of sodium alginate fibres in calcium chloride solution, taken as the time to achieve maximum tensile strength. The effects of fibre diameter, alginate concentration, alginate composition and calcium chloride concentration on gelling time were investigated. A diffusional model, developed to predict the gelling time, agreed with experimental results except for the effect of calcium ion concentration which was modelled empirically. 相似文献