全文获取类型
收费全文 | 3993篇 |
免费 | 89篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 122篇 |
综合类 | 2篇 |
化学工业 | 453篇 |
金属工艺 | 74篇 |
机械仪表 | 68篇 |
建筑科学 | 121篇 |
矿业工程 | 8篇 |
能源动力 | 46篇 |
轻工业 | 415篇 |
水利工程 | 21篇 |
石油天然气 | 7篇 |
无线电 | 265篇 |
一般工业技术 | 458篇 |
冶金工业 | 1462篇 |
原子能技术 | 36篇 |
自动化技术 | 529篇 |
出版年
2021年 | 45篇 |
2020年 | 32篇 |
2019年 | 50篇 |
2018年 | 61篇 |
2017年 | 45篇 |
2016年 | 41篇 |
2015年 | 40篇 |
2014年 | 68篇 |
2013年 | 184篇 |
2012年 | 116篇 |
2011年 | 143篇 |
2010年 | 127篇 |
2009年 | 102篇 |
2008年 | 140篇 |
2007年 | 139篇 |
2006年 | 118篇 |
2005年 | 94篇 |
2004年 | 78篇 |
2003年 | 93篇 |
2002年 | 83篇 |
2001年 | 58篇 |
2000年 | 71篇 |
1999年 | 104篇 |
1998年 | 361篇 |
1997年 | 219篇 |
1996年 | 146篇 |
1995年 | 98篇 |
1994年 | 93篇 |
1993年 | 102篇 |
1992年 | 49篇 |
1991年 | 40篇 |
1990年 | 41篇 |
1989年 | 50篇 |
1988年 | 36篇 |
1987年 | 40篇 |
1986年 | 34篇 |
1985年 | 54篇 |
1984年 | 35篇 |
1983年 | 41篇 |
1982年 | 46篇 |
1981年 | 37篇 |
1980年 | 42篇 |
1979年 | 30篇 |
1978年 | 31篇 |
1977年 | 38篇 |
1976年 | 65篇 |
1975年 | 32篇 |
1973年 | 24篇 |
1972年 | 24篇 |
1971年 | 17篇 |
排序方式: 共有4087条查询结果,搜索用时 31 毫秒
71.
Jonathan Boudreau Ross F. Nelson Hank A. Margolis André Beaudoin Luc Guindon Daniel S. Kimes 《Remote sensing of environment》2008,112(10):3876-3890
Aboveground dry biomass was estimated for the 1.3 M km2 forested area south of the treeline in the eastern Canadian province of Québec by combining data from an airborne and spaceborne LiDAR, a Landsat ETM+ land cover map, a Shuttle Radar Topographic Mission (SRTM) digital elevation model, ground inventory plots, and vegetation zone maps. Plot-level biomass was calculated using allometric relationships between tree attributes and biomass. A small footprint portable laser profiler then flew over these inventory plots to develop a generic airborne LiDAR-based biomass equation (R2 = 0.65, n = 207). The same airborne LiDAR system flew along four portions of orbits of the ICESat Geoscience Laser Altimeter System (GLAS). A square-root transformed equation was developed to predict airborne profiling LiDAR estimates of aboveground dry biomass from GLAS waveform parameters combined with an SRTM slope index (R2 = 0.59, n = 1325).Using the 104,044 quality-filtered GLAS pulses obtained during autumn 2003 from 97 orbits over the study area, we then predicted aboveground dry biomass for the main vegetation areas of Québec as well as for the entire Province south of the treeline. Including cover type covariances both within and between GLAS orbits increased standard errors of the estimates by two to five times at the vegetation zone level and as much as threefold at the provincial level. Aboveground biomass for the whole study area averaged 39.0 ± 2.2 (standard error) Mg ha? 1 and totalled 4.9 ± 0.3 Pg. Biomass distributions were 12.6% northern hardwoods, 12.6% northern mixedwood, 38.4% commercial boreal, 13% non-commercial boreal, 14.2% taiga, and 9.2% treed tundra. Non-commercial forests represented 36% of the estimated aboveground biomass, thus highlighting the importance of remote northern forests to C sequestration. This study has shown that space-based forest inventories of northern forests could be an efficient way of estimating the amount, distribution, and uncertainty of aboveground biomass and carbon stocks at large spatial scales. 相似文献
72.
Identifying discriminating variables between teachers who fully integrate computers and teachers with limited integration 总被引:1,自引:0,他引:1
Julie Mueller Eileen Wood Teena Willoughby Craig Ross Jacqueline Specht 《Computers & Education》2008,51(4):1523-1537
Given the prevalence of computers in education today, it is critical to understand teachers’ perspectives regarding computer integration in their classrooms. The current study surveyed a random sample of a heterogeneous group of 185 elementary and 204 secondary teachers in order to provide a comprehensive summary of teacher characteristics and variables that best discriminate between teachers who integrate computers and those who do not. Discriminant Function Analysis indicated seven variables for elementary teachers and six for secondary teachers (accounting for 74% and 68% of the variance, respectively) that discriminated between high and low integrators. Variables included positive teaching experiences with computers; teacher’s comfort with computers; beliefs supporting the use of computers as an instructional tool; training; motivation; support; and teaching efficacy. Implications for support of computer integration in the classroom are discussed. 相似文献
73.
An evaluation of new heuristics for the location of cross-docks distribution centers in supply chain network design 总被引:3,自引:0,他引:3
This paper addresses an evaluation of new heuristics solution procedures for the location of cross-docks and distribution centers in supply chain network design. The model is characterized by multiple product families, a central manufacturing plant site, multiple cross-docking and distribution center sites, and retail outlets which demand multiple units of several commodities. This paper describes two heuristics that generate globally feasible, near optimal distribution system design and utilization strategies utilizing the simulated annealing (SA) methodology. This study makes two important contributions. First, we continue the study of location planning for the cross-dock and distribution center supply chain network design problem. Second, we systematically evaluate the computational performance of this network design location model under more sophisticated heuristic control parameter settings to better understand interaction effects among the various factors comprising our experimental design, and present convergence results. The central idea of the paper is to evaluate the impact of geometric control mechanism vis-a-vis more sophisticated ones on solution time, quality, and convergence for two new heuristics. Our results suggest that integrating traditional simulated annealing with TABU search is recommended for this supply chain network design and location problem. 相似文献
74.
Hartsough NE Barrett HH Barber HB Woolfenden JM 《IEEE transactions on medical imaging》1995,14(2):259-265
Accurate tumor staging depends on finding all tumor sites, and curative surgery requires the removal of ail cancerous tissue from those sites. One technique for locating tumors is to inject patients before surgery with a radiotracer that is preferentially taken up by cancerous tissue. Then, an intraoperative gamma-sensitive probe is used to locate the tumors. Small (<1-cm diameter) tumors, often undetectable by external imaging and by the standard surgical inspection with sight and touch, can be found with probes, Simple calculations and measurements with radioactive tumor models show that small tumors should be detected by single-element probes, but often such probes fail to detect these small tumors in practice. This discrepancy is often caused by the use of a uniform background to predict probe performance, Real backgrounds are nonuniform and can decrease probe performance dramatically. Dual-element, coincidence, or imaging probes may solve the background problem. The authors devised a method to predict probe performance in a realistic background which includes variations in normal organ uptakes. They predict the relative performance of both existing probes and those in the design stage so that optimal detector and collimator configurations can be determined. The procedure includes a Monte-Carlo-calculated point-response function, a numerical torso phantom, and measured biodistributions of a monoclonal antibody. The Hotelling Trace Value, a measure of tumor-detection performance, is computed from the probe responses in simulated studies. 相似文献
75.
Masoud Alahbakhshi Aditya Mishra Grigorii Verkhogliadov Emigdio E. Turner Ross Haroldson Austen C. Adams Qing Gu Jeffrey J. Rack Jason D. Slinker Anvar A. Zakhidov 《Advanced functional materials》2023,33(28):2214315
Perovskite light-emitting diodes (PeLEDs) are advancing because of their superior external quantum efficiencies (EQEs) and color purity. Still, additional work is needed for blue PeLEDs to achieve the same benchmarks as the other visible colors. This study demonstrates an extremely efficient blue PeLED with a 488 nm peak emission, a maximum luminance of 8600 cd m−2, and a maximum EQE of 12.2% by incorporating the double-sided ethane-1,2-diammonium bromide (EDBr2) ligand salt along with the long-chain ligand methylphenylammonium chloride (MeCl). The EDBr2 successfully improves the interaction between 2D perovskite layers by reducing the weak van der Waals interaction and creating a Dion–Jacobson (DJ) structure. Whereas the pristine sample (without EDBr2) is inhibited by small stacking number (n) 2D phases with nonradiative recombination regions that diminish the PeLED performance, adding EDBr2 successfully enables better energy transfer from small n phases to larger n phases. As evidenced by photoluminescence (PL), scanning electron microscopy (SEM), and atomic force microscopy (AFM) characterization, EDBr2 improves the morphology by reduction of pinholes and passivation of defects, subsequently improving the efficiencies and operational lifetimes of quasi-2D blue PeLEDs. 相似文献
76.
Sheng Ying Zohar Yoni Ringeissen Christophe Lange Jane Fontaine Pascal Barrett Clark 《Journal of Automated Reasoning》2022,66(3):331-355
Journal of Automated Reasoning - Algebraic datatypes, and among them lists and trees, have attracted a lot of interest in automated reasoning and Satisfiability Modulo Theories (SMT). Since its... 相似文献
77.
Machine Learning - Mapping data from and/or onto a known family of distributions has become an important topic in machine learning and data analysis. Deep generative models (e.g., generative... 相似文献
78.
This paper examines the dynamics of entrepreneurial acquisitions undertaken by UK high growth small and medium enterprises (SMEs). While entrepreneurial acquisitions are increasingly deployed by SMEs, little is known about their antecedents, motivational drivers and organisational outcomes. Drawing on detailed case study evidence from Scotland, the key factor found to be driving these acquisitions was the desire to augment and exploit technological complementarities between the acquiring and acquired firms. Acquisition can therefore be conceptualised as an advanced stage of the outside-in ‘open innovation’ strategies proactively used within these innovative SMEs. Firms executing this strategy typically have an acute propensity for risk, a desire for close customer engagement, effective business models and strong external orientation. The work suggests that greater attention should be paid within M&A theory to the dynamics of these types of smaller scale entrepreneurial acquisitions. 相似文献
79.
Detecting Periods of Significant Increased Communication Levels for Subgroups of Targeted Individuals
下载免费PDF全文
![点击此处可从《Quality and Reliability Engineering International》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ross Sparks 《Quality and Reliability Engineering International》2016,32(5):1871-1888
This paper investigates detecting significant increases in communication patterns and levels between small groups of individuals within a moderate‐size targeted group. Potential applications range from trying to establish emerging thought leaders within an organisation to the detection of the planning stages of a crime. The scan statistic is a popular choice for monitoring and detecting spatio‐temporal outbreaks, but it is difficult to apply to large‐scale target groups because of the computational effort required. When monitoring communication levels between thousands of people, the number of combinations of people whose communication may have increased is very high, and to scan through all of these to find which combinations have increased communications significantly is an enormous task. A successful surveillance plan will have early communication outbreak detection properties and good diagnostic capabilities for identifying individuals contributing to this outbreak. This paper proposes a new computationally feasible approach for detecting communication outbreaks based on exponentially weighted moving average smoothed communication counts between individuals within the network. We apply a cumulative sum of ordered signal‐to‐noise (SN) ratios for communication counts to flag significant departures from their respective median values. This plan is demonstrated to be efficient at detecting changes in communication levels for a small part of the network and diagnosing who is involved in the outbreak. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
80.
Maureen T. Ross Rena Cruz Trent L. Brooks-Richards Louise M. Hafner Sean K. Powell Maria A. Woodruff 《Virtual and Physical Prototyping》2018,13(4):255-265
Congenital facial anomalies, such as microtia (malformation of the external ear), lead to significant psychosocial effects starting from early childhood. Three-dimensional (3D) scanning and advanced manufacturing are being investigated as a cheaper and more personalised method of fabricating reconstructive treatments for patients compared to traditional approaches. To date, most case studies have used expensive 3D scanners, yet, there is potential for low-cost devices to provide comparable results. This study aimed to investigate these different approaches. Both ears of 16 adult participants were scanned with three devices: Artec Spider (Artec Group), Intel® RealSense? (Intel), and the Apple iPhone® 7 (Apple Inc.) combined with photogrammetry using 90, 60 and 30 photographs. The scanning time, processing time, accuracy, completeness, resolution and repeatability of each technique were assessed using the Artec Spider as a reference scanner. Our results show that the iPhone had the longest processing time however, this decreased nine-fold when reducing the number of photos from 90 to 30. There was no significant difference in the accuracy, completeness or repeatability of the iPhone scans with 90 photographs (1.4?±?0.6?mm, 79.9%, 1.0?±?0.1?mm), 60 photographs (1.2?±?0.2, 79.3%, 0.9?±?0.2?mm) or 30 photographs (1.2?±?0.3?mm, 74.3%, 1.0?±?0.2?mm). The Intel RealSesne performed significantly worse in each parameter (1.8?±?03?mm; 46.6%, 1.4?±?0.5). Additionally, the RealSense had significantly lower resolution with not enough detail captured for the application. These results demonstrate that the ear can be accurately 3D scanned using iPhone photographs. We would recommend capturing between 30 and 60 photographs of the ear to create a scan that is accurate but without the downfall of long processing time. Using these methods we aim to provide a more comfortable setting for the patient and a lower-cost and more personalised ear prosthesis. 相似文献