全文获取类型
收费全文 | 1450篇 |
免费 | 65篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 51篇 |
综合类 | 1篇 |
化学工业 | 305篇 |
金属工艺 | 38篇 |
机械仪表 | 32篇 |
建筑科学 | 21篇 |
矿业工程 | 1篇 |
能源动力 | 136篇 |
轻工业 | 67篇 |
水利工程 | 7篇 |
石油天然气 | 6篇 |
无线电 | 154篇 |
一般工业技术 | 304篇 |
冶金工业 | 163篇 |
原子能技术 | 20篇 |
自动化技术 | 216篇 |
出版年
2024年 | 4篇 |
2023年 | 21篇 |
2022年 | 28篇 |
2021年 | 62篇 |
2020年 | 50篇 |
2019年 | 60篇 |
2018年 | 63篇 |
2017年 | 48篇 |
2016年 | 60篇 |
2015年 | 43篇 |
2014年 | 51篇 |
2013年 | 115篇 |
2012年 | 73篇 |
2011年 | 92篇 |
2010年 | 71篇 |
2009年 | 74篇 |
2008年 | 49篇 |
2007年 | 56篇 |
2006年 | 43篇 |
2005年 | 28篇 |
2004年 | 28篇 |
2003年 | 37篇 |
2002年 | 19篇 |
2001年 | 23篇 |
2000年 | 28篇 |
1999年 | 18篇 |
1998年 | 37篇 |
1997年 | 34篇 |
1996年 | 26篇 |
1995年 | 12篇 |
1994年 | 19篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有1522条查询结果,搜索用时 15 毫秒
101.
The search for fresh or potable water remains a pressing concern throughout many regions of the world. Although most of the Earth's surface is covered by oceans, the effort to provide for the world's inhabitants with fresh or potable water seems to be insurmountable; at least one billion people do not have access to clean and fresh water. The World Health Organization (WHO) reported that about 41% of the Earth's population lives in water-stressed areas, and the number of people in the water scarce regions may climb to 3.5 billion by the year 2025. Thus, innovative and cost-effective desalination technologies for producing fresh water are needed to provide practical solutions. 相似文献
102.
Suvash C. Saha John C. Patterson Chengwang Lei 《International Journal of Thermal Sciences》2010,49(9):1600-1612
The natural convection thermal boundary-layer adjacent to an inclined flat plate subject to sudden heating and a temperature boundary condition which follows a ramp function up until a specified time and then remains constant is investigated. The development of the flow from start-up to a steady state has been described based on scaling analyses and verified by numerical simulations. Different flow regimes based on the Rayleigh number are discussed with numerical results for both boundary conditions. For ramp heating, the boundary-layer flow depends on the comparison of the time at which the ramp heating is completed and the time at which the boundary layer completes its growth. If the ramp time is long compared with the steady-state time, the layer reaches a quasi-steady mode in which the growth of the layer is governed solely by the thermal balance between convection and conduction. On the other hand, if the ramp is completed before the layer becomes steady; the subsequent growth is governed by the balance between buoyancy and inertia, as for the case of instantaneous heating. 相似文献
103.
This paper presents a review of studies on natural convection heat transfer in the triangular enclosure namely, in attic-shaped space. Much research activity has been devoted to this topic over the last three decades with a view to providing thermal comfort to the occupants in attic-shaped buildings and to minimising the energy costs associated with heating and air-conditioning. Two basic thermal boundary conditions of attic are considered to represent hot and cold climates or day and night time. This paper also reports on a significant number of studies which have been performed recently on other topics related to the attic space, for example, attics subject to localized heating and attics filled with porous media. 相似文献
104.
Sourabh K. Saha S.K. Choudhury 《International Journal of Machine Tools and Manufacture》2009,49(3-4):297-308
Dry electric discharge machining (EDM) is an environment-friendly modification of the oil EDM process in which liquid dielectric is replaced by a gaseous medium. In the current work, parametric analysis of the process has been performed with tubular copper tool electrode and mild steel workpiece. Experiments have been conducted using air as the dielectric medium to study the effect of gap voltage, discharge current, pulse-on time, duty factor, air pressure and spindle speed on material removal rate (MRR), surface roughness (Ra) and tool wear rate (TWR). First, a set of exploratory experiments has been performed to identify the optimum tool design and to select input parameters and their levels for later stage experiments. Empirical models for MRR, Ra and TWR have then been developed by performing a designed experiment based on the central composite design of experiments. Response surface analysis has been done using the developed models. Analysis of variance (ANOVA) tests were performed to identify the significant parameters. Current, duty factor, air pressure and spindle speed were found to have significant effects on MRR and Ra. However, TWR was found to be very small and independent of the input parameters. 相似文献
105.
Badal C Saha Michael A Cotta 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2007,82(10):913-919
BACKGROUND: The objective of this work is to develop an efficient pretreatment method that can help enzymes break down the complex carbohydrates present in wheat straw to sugars, and to then ferment of all these sugars to ethanol. RESULTS: The yield of sugars from wheat straw (8.6%, w/v) by lime pretreatment (100 mg g?1 straw, 121 °C, 1 h) and enzymatic hydrolysis (45 °C, pH 5.0, 120 h) using a cocktail of three commercial enzyme preparations (cellulase, β‐glucosidase, and xylanase) at the dose level of 0.15 mL of each enzyme preparation g?1 straw was 568 ± 13 mg g?1 (82% yield). The concentration of ethanol from lime pretreated enzyme saccharified wheat straw (78 g) hydrolyzate by recombinant Escherichia coli strain FBR5 at pH 6.5 and 35 °C in 24 h was 22.5 ± 0.6 g L?1 with a yield of 0.50 g g?1 available sugars (0.29 g g?1 straw). The ethanol concentration was 20.6 ± 0.4 g L?1 with a yield of 0.26 g g?1 straw in the case of simultaneous saccharification and fermentation by the E. coli strain at pH 6.0 and 35 °C in 72 h. CONCLUSION: The results are important in choosing a suitable pretreatment option for developing bioprocess technologies for conversion of wheat straw to fuel ethanol. Copyright © 2007 Society of Chemical Industry 相似文献
106.
The spi gene of Streptococcus pneumoniae was cloned and its nucleotide sequence was determined. It encodes a protein of 204 amino acids that is homologous to bacterial signal peptidase I proteins. The S. pneumoniae protein contains all of the conserved amino acid sequence motifs previously identified in this enzyme from both prokaryotic and eukaryotic sources. Sequence comparisons revealed several additional motifs characteristic of the enzyme. The cloned S. pneumoniae gene complemented an Escherichia coli mutant defective in its leader peptidase gene. Expression of the spi gene in S. pneumoniae appeared to be essential for viability. The cloned gene was shown to produce a polypeptide of approximately 20 kDa. Overproduction of the S. pneumoniae spi gene in an E. coli expression system gave a native protein product, soluble in the presence of a non-ionic detergent, which should be amenable to structural determination. 相似文献
107.
Sandip Ghosh Deb Mukhopadhyay Samir Kumar Saha 《International Journal of Pressure Vessels and Piping》2011,88(8-9):281-289
The work presented here is an experimental investigation of the critical flashing flow of initially subcooled water through circumferential slits in pipes. The study provides first hand information about the prediction of leak flow rates in piping and pressure vessels retaining high temperature and high pressure. The dedicated experimental facility loop simulates the thermal hydraulic condition of Pressurized Heavy Water Reactors (PHWR). The critical flow characteristics found for varying leakage cross sections at different stagnation pressure and different degree of subcooling has been demonstrated in this paper. A marked decrease in mass flux has been found as subcooling decreases for a fixed stagnation pressure. More observation has revealed that the tighter slits or openings with very short duct as small as 0.8 cm flow length have different flow behavior than greater opening dimensions or with longer flow channels or that for nozzles. The critical flow has been seen to occur at higher pressure differentials along the flaws and prominent changes in the flow rate is reported to occur with varying dimensional parameters of the slit or cracks. 相似文献
108.
Fair-exchange is an important property that must be ensured in all electronic commerce environments where the merchants and the customers are reluctant to trust each other. This property guarantees that none of the transacting parties suffer because of the fraudulent behavior of the other party in the transaction. In this paper, we describe our experiences in developing a new e-commerce protocol to address the problem of fair-exchange for digital products. The protocol is based on a novel cryptographic technique that we had proposed earlier. We show how to use common off-the-shelf software components to develop such a protocol. 相似文献
109.
HD Kalter M Hossain G Burnham NZ Khan SK Saha MA Ali RE Black 《Canadian Metallurgical Quarterly》1999,13(1):99-113
The objective of this study was to validate retrospective caregiver interviews for diagnosing major causes of severe neonatal illness and death. A convenience sample of 149 infants aged < 28 days with one or more suspected diagnoses of interest (low birthweight/severe malnutrition, preterm birth, birth asphyxia, birth trauma, neonatal tetanus, pneumonia, meningitis, septicaemia, diarrhoea, congenital malformation or injury) was taken from patients admitted to two hospitals in Dhaka, Bangladesh. Study paediatricians performed a standardised history and physical examination and ordered laboratory and radiographic tests according to study criteria. With a median interval of 64.5 days after death or hospital discharge, caregivers of 118 (79%) infants were interviewed about their child's illness. Using reference diagnoses based on predefined clinical and laboratory criteria, the sensitivity and specificity of particular combinations of signs (algorithms) reported by the caregivers were ascertained. Sufficient numbers of children with five reference standard diagnoses were studied to validate caregiver reports. Algorithms with sensitivity and specificity > 80% were identified for neonatal tetanus, low birthweight/severe malnutrition and preterm delivery. Algorithms with specificities > 80% for birth asphyxia and pneumonia had sensitivities < 70%, or alternatively had high sensitivity with lower specificity. In settings with limited access to medical care, retrospective caregiver interviews provide a valid means of diagnosing several of the most common causes of severe neonatal illness and death. 相似文献
110.
Kasztenny B. Rosolowski E. Saha M.M. Hillstrom B. 《Power Delivery, IEEE Transactions on》1997,12(3):1119-1127
In the paper the fuzzy logic based multi-criteria protective relay for a three-phase power transformer is presented. Twelve criteria used to stabilize the relay are introduced and integrated by means of multi-objective decision-making methods. The introduced protection scheme contains several internal functions and coefficients which are subject to off-line pre-installation self-setting. Three unique procedures are delivered for self-adjusting the relay, and thus, making it self-organized. The results of testing show significant gains in both sensitivity and selectivity of the self-organized relay compared with traditional approaches 相似文献