全文获取类型
收费全文 | 2272篇 |
免费 | 20篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 14篇 |
化学工业 | 146篇 |
金属工艺 | 9篇 |
机械仪表 | 17篇 |
建筑科学 | 31篇 |
矿业工程 | 3篇 |
能源动力 | 37篇 |
轻工业 | 51篇 |
水利工程 | 7篇 |
石油天然气 | 4篇 |
无线电 | 156篇 |
一般工业技术 | 133篇 |
冶金工业 | 1542篇 |
原子能技术 | 14篇 |
自动化技术 | 131篇 |
出版年
2021年 | 11篇 |
2020年 | 7篇 |
2019年 | 10篇 |
2017年 | 14篇 |
2016年 | 9篇 |
2015年 | 14篇 |
2014年 | 22篇 |
2013年 | 66篇 |
2012年 | 30篇 |
2011年 | 31篇 |
2010年 | 20篇 |
2009年 | 26篇 |
2008年 | 28篇 |
2007年 | 33篇 |
2006年 | 33篇 |
2005年 | 24篇 |
2004年 | 33篇 |
2003年 | 25篇 |
2002年 | 21篇 |
2001年 | 21篇 |
2000年 | 18篇 |
1999年 | 62篇 |
1998年 | 453篇 |
1997年 | 258篇 |
1996年 | 193篇 |
1995年 | 117篇 |
1994年 | 99篇 |
1993年 | 114篇 |
1992年 | 21篇 |
1991年 | 32篇 |
1990年 | 24篇 |
1989年 | 25篇 |
1988年 | 33篇 |
1987年 | 17篇 |
1986年 | 30篇 |
1985年 | 29篇 |
1984年 | 13篇 |
1983年 | 14篇 |
1982年 | 19篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 46篇 |
1976年 | 79篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1971年 | 5篇 |
1970年 | 6篇 |
1968年 | 5篇 |
排序方式: 共有2295条查询结果,搜索用时 31 毫秒
81.
Yeast/E. coli shuttle vectors with multiple unique restriction sites 总被引:239,自引:0,他引:239
Two yeast/E. coli shuttle vectors have been constructed. The two vectors, YEp351 and YEp352, have the following properties: (1) they can replicate autonomously in Saccharomyces cerevisiae and in E. coli; (2) they contain the beta-lactamase gene and confer ampicillin resistance to E. coli; (3) they contain the entire sequence of pUC18; (4) all ten restriction sites of the multiple cloning region of pUC18 including EcoRI, SacI, KpnI, SmaI, BamHI, XbaI, SalI, PstI, SphI and HindIII are unique in YEp352; these sites are also unique in YEp351 except for EcoRI and KpnI, which occur twice; (5) recombinant plasmids with DNA inserts in the multiple cloning region of YEp351 and YEp352 can be recognised by loss of beta-galactosidase function in appropriate E. coli hosts; (6) YEp351 and YEp352 contain the yeast LEU2 and URA3 genes, respectively, allowing for selection of these auxotrophic markers in yeast and E. coli; (7) both plasmids are retained with high frequency in yeast grown under non-selective conditions indicative of high plasmid copy number. The above properties make the shuttle vectors suitable for construction of yeast genomic libraries and for cloning of DNA fragments defined by a large number of different restriction sites. The two vectors have been further modified by deletion of the sequences necessary for autonomous replication in yeast. The derivative plasmids YIp351 and YIp352 can therefore be used to integrate specific sequences into yeast chromosomal DNA. 相似文献
82.
83.
Building mounted micro-wind turbines and photovoltaics have the potential to provide widely applicable carbon free electricity generation at the building level. Photovoltaic systems are well understood and it is easy to predict performance using software tools or widely accepted yield estimates. Micro-wind, however, is far more complex and in comparison poorly understood. This paper presents the key findings of the building mounted (<2 kWp) turbine component of the UK micro-wind trial undertaken by the Energy Saving Trust in 2008/09. The monitored performance of 39 horizontal axis turbines in urban, suburban and rural locations is discussed alongside the accuracy of predictive wind speed tools for the sites. The performance of urban and suburban micro-wind sites in the trial was poor with annual generation of less than 75 kWh/m2 swept area, the majority of which were less than 25 kWh/m2. Good rural sites had an annual generation of between 100 and 280 kWh/m2, far less than the nominal 360 kWh/m2 (10% load factor for a typical turbine) that is often assumed. In the light of these findings, the potential impact of the UK’s latest policy instrument, the 2010 micro-generation tariffs, is considered for both micro-wind and photovoltaics. 相似文献
84.
Dowell Myers 《Journal of the American Planning Association. American Planning Association》2013,79(4):383-397
Demographic futures are proposed as an empirical and normative guide for planning. Projections of demographic change help planners prepare future-oriented plans that are better targeted to the needs of a changing clientele. As an example, population changes in California highlight the growing importance of Latinos to the development of more compact cities. Demographic futures also entail normative interpretations of future scenarios as much as they do empirical relationships projected into the future. Several alternative stories are related of Latinos' future situation, each highlighting different value premises, problems, and conclusions. To effectively use demographic futures, planners must be conversant with both projected trends and competing interpretive stories. 相似文献
85.
Tim G. Myers 《Microfluidics and nanofluidics》2011,10(5):1141-1145
A possible explanation for the enhanced flow in carbon nanotubes is given using a mathematical model that includes a depletion
layer with reduced viscosity near the wall. In the limit of large tubes the model predicts no noticeable enhancement. For
smaller tubes the model predicts enhancement that increases as the radius decreases. An analogy between the reduced viscosity
and slip-length models shows that the term slip-length is misleading and that on surfaces which are smooth at the nanoscale
it may be thought of as a length-scale associated with the size of the depletion region and viscosity ratio. The model therefore
provides a physical interpretation of the classical Navier slip condition and explains why ‘slip-lengths’ may be greater than
the tube radius. 相似文献
86.
The behaviour of two‐phase gas‐liquid flows in a stopper‐rod controlled submerged entry nozzle (SEN) is investigated in water model experiments. The observed two‐phase flow patterns can be classified into either bubble coring or bubbly slug. The scaling of the two‐phase flows by means of similarity parameters is discussed. In the experiments, it is found that the liquid flow rates depend strongly on the two‐phase flow patterns. Additionally, the influence of swirl on the flow patterns is investigated in detail. It is shown that swirl has a marked impact on the transition from bubble coring to bubbly slug. Finally, an estimation of the two‐phase argon‐steel flow patterns in industrialscale SEN flows is given. 相似文献
87.
Katherine Donaldson Gregory K. Myers 《International Journal on Document Analysis and Recognition》2005,7(2-3):159-167
To increase the range of sizes of video scene text recognizable by optical character recognition (OCR), we developed a Bayesian super-resolution algorithm that uses a text-specific bimodal prior. We evaluated the effectiveness of the bimodal prior, compared and in conjunction with a piecewise smoothness prior, visually and by measuring the accuracy of the OCR results on the variously super-resolved images. The bimodal prior improved the readability of 4- to 7-pixel-high scene text significantly better than bicubic interpolation and increased the accuracy of OCR results better than the piecewise smoothness prior. 相似文献
88.
Bradley T. Vander Zanden Richard Halterman Brad A. Myers Rob Miller Pedro Szekely Dario A. Giuse David Kosbie Rich McDaniel 《Software》2005,35(13):1275-1298
One‐way constraints have been incorporated in many graphical user interface toolkits because they are simple to learn, easy to write, and can express many types of useful graphical relationships. This paper is an evaluative paper that examines users' experience with one‐way constraints in two user interface development toolkits, Garnet and Amulet, over a 15‐year time span. The lessons gained from this examination can help guide the design of future constraint systems. The most important lessons are that (1) constraints should be allowed to contain arbitrary code that is written in the underlying toolkit language and does not require any annotations, such as parameter declarations, (2) constraints are difficult to debug and better debugging tools are needed, and (3) programmers will readily use one‐way constraints to specify the graphical layout of an application, but must be carefully and time‐consumingly trained to use them for other purposes. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
89.
Avila Matthew T.; Robles Olalla; Hong L. Elliot; Blaxton Theresa A.; Myers Carol S.; Wonodi Ikwunga; Gold James; Thaker Gunvant K. 《Canadian Metallurgical Quarterly》2006,115(4):771
Individuals with schizophrenia spectrum personality disorders (SSPD) and schizophrenia show similar cognitive impairments. The authors examined the contributions of SSPD symptoms and familial risk for schizophrenia to impairments on the Continuous Performance Test-Identical Pairs Version. Participants included 103 schizophrenia patients, 66 first-degree relatives (29 SSPD), and 103 community controls (26 SSPD) screened for family history of psychosis. Patients and SSPD relatives performed significantly worse than non-SSPD relatives and SSPD and non-SSPD community controls. No differences in performance were observed among non-SSPD relatives and SSPD and non-SSPD community controls. Results suggest a continuum in which risk for schizophrenia-related cognitive impairments is highest among patients and SSPD relatives, intermediate among non-SSPD relatives, and lowest among SSPD and non-SSPD community controls. Results suggest that SSPD in the absence of a family history of psychosis may be a phenocopy. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
90.
Controlling Home and Office Appliances with Smart Phones 总被引:1,自引:0,他引:1
Most home and office appliances contain microprocessors. All these appliances have some user interface, but many users become frustrated with their appliances' difficult, complex functions. However, a new framework, the personal universal controller (PUC), lets users interact with appliances through a separate user interface device that they carry. Smart phones are good candidates for providing interfaces because they're common, their communication capabilities connect users to appliances, and they're already being used for a wide range of applications. The framework includes an abstract specification language for describing appliances, a two-way communication protocol, and automatic interface generation software that customizes user interfaces. This article overviews the PUC system and describes in detail the design and implementation of automatic interface generation for Microsoft's Smartphone platform. 相似文献