全文获取类型
收费全文 | 5013篇 |
免费 | 297篇 |
国内免费 | 19篇 |
专业分类
电工技术 | 77篇 |
综合类 | 8篇 |
化学工业 | 1010篇 |
金属工艺 | 116篇 |
机械仪表 | 124篇 |
建筑科学 | 176篇 |
矿业工程 | 8篇 |
能源动力 | 177篇 |
轻工业 | 321篇 |
水利工程 | 32篇 |
石油天然气 | 22篇 |
无线电 | 945篇 |
一般工业技术 | 960篇 |
冶金工业 | 430篇 |
原子能技术 | 29篇 |
自动化技术 | 894篇 |
出版年
2024年 | 8篇 |
2023年 | 93篇 |
2022年 | 98篇 |
2021年 | 272篇 |
2020年 | 214篇 |
2019年 | 180篇 |
2018年 | 221篇 |
2017年 | 186篇 |
2016年 | 273篇 |
2015年 | 167篇 |
2014年 | 223篇 |
2013年 | 351篇 |
2012年 | 264篇 |
2011年 | 298篇 |
2010年 | 218篇 |
2009年 | 212篇 |
2008年 | 210篇 |
2007年 | 186篇 |
2006年 | 142篇 |
2005年 | 126篇 |
2004年 | 101篇 |
2003年 | 87篇 |
2002年 | 75篇 |
2001年 | 82篇 |
2000年 | 53篇 |
1999年 | 61篇 |
1998年 | 201篇 |
1997年 | 95篇 |
1996年 | 81篇 |
1995年 | 74篇 |
1994年 | 47篇 |
1993年 | 70篇 |
1992年 | 37篇 |
1991年 | 36篇 |
1990年 | 24篇 |
1989年 | 34篇 |
1988年 | 21篇 |
1987年 | 19篇 |
1986年 | 22篇 |
1985年 | 21篇 |
1984年 | 25篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1975年 | 7篇 |
1973年 | 8篇 |
排序方式: 共有5329条查询结果,搜索用时 245 毫秒
81.
Li-Piin Sung Joan Jasmin Xiaohong Gu Tinh Nguyen Jonathan W. Martin 《Journal of Coatings Technology and Research》2004,1(4):267-276
Laser scanning confocal microscopy (LSCM) has been used to characterize the changes in film thickness and local surface morphology
of polymer coatings during the UV degradation process. With the noninvasive feature of LSCM, one can obtain thickness information
directly and nondestructively at various exposure times without destroying the specimens or deriving the thickness values
from IR measurement by assuming uniform film ablation. Two acrylic polymer coatings were chosen for the study, and the physical
and chemical changes of the two systems at various exposure times were measured and analyzed. Those measurable physical changes
caused by UV exposure include film ablation, formation of pits and other surface defects, and increases in surface roughness.
It was found in both coatings that changes in measured film thickness by LSCM were not correlated linearly to the predicted
thickness loss using the changes in the CH band obtained by the Fourier Transform Infrared (FTIR) spectroscopy measurements
in the later degradation stages. This result suggested it was not a uniform film ablation process during the UV degradation.
At later stages, where surface deformation became severe, surface roughness and profile information using LSCM were also proven
to be useful for analyzing the surface degradation process
Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 13–14, 2004 in Philadelphia,
PA. 相似文献
82.
D. Wiesenborn Z. Zbikowski H. Nguyen 《Journal of the American Oil Chemists' Society》1995,72(2):183-188
Extract of purple sunflower hulls is a potential red food colorant; however, suitable process conditions must still be identified.
Selected process variables were studied using bench-scale units to prepare, clarify, concentrate and spray dry extracts. Concentration
by evaporation at 32°C and addition of maltodextrin to 15% (wt/dry wt) prior to drying largely eliminated pigment degradation
during those steps. Relative to water extracts, extracts prepared with 5 to 15% ethanol in water generally yielded more pigment
with similar levels of degradation and loss during subsequent processing. Use of 5% ethanol/2% citric acid reduced yield by
about half relative to water, but gave a powder with a lower degradation index and wetting time. Percentage recovery of pigment
during concentration and drying was not greatly affected by solvent type or extraction temperature. 相似文献
83.
Thao P. Nghiem Kiki Maulana Kinh Nguyen David Green Agustinus Borgy Waluyo David Taniar 《Journal of Parallel and Distributed Computing》2014
The increasing use of mobile communications has raised many issues of decision support and resource allocation. A crucial problem is how to solve queries of Reverse Nearest Neighbour (RNN). An RNN query returns all objects that consider the query object as their nearest neighbour. Existing methods mostly rely on a centralised base station. However, mobile P2P systems offer many benefits, including self-organisation, fault-tolerance and load-balancing. In this study, we propose and evaluate 3 distinct P2P algorithms focusing on bichromatic RNN queries, in which mobile query peers and static objects of interest are of two different categories, based on a time-out mechanism and a boundary polygon around the mobile query peers. The Brute-Force Search Algorithm provides a naive approach to exploit shared information among peers whereas two other Boundary Search Algorithms filter a number of peers involved in query processing. The algorithms are evaluated in the MiXiM simulation framework with both real and synthetic datasets. The results show the practical feasibility of the P2P approach for solving bichromatic RNN queries for mobile networks. 相似文献
84.
Francis W. Maloba Michael L. Rooney Paul Wormell Minh Nguyen 《Journal of the American Oil Chemists' Society》1996,73(2):181-185
The oxidative stability of sunflower oil (SFO) was measured during storage at 23 and 37°C in the presence of a novel oxygen-scavenging
film that contained polyfuryloxirane (PFO). Commercially refined and deodorized SFO was stored in a lighted room in sealed
transparent packages containing either PFO film or an antioxidant, 0.02% butylated hydroxytoluene (BHT). Oxidative stability
was evaluated by determination of peroxide values and gas-chromatographic measurement of headspace hexanal. SFO stored in
the presence of the oxygen-scavenging film was more stable than oil stored without the film, or than film stored with 0.02%
BHT. The PFO film scavenges oxygen through energy-transfer sensitization of singlet oxygen. The film is doped with eosin and
the naturally-occurring dye, curcumin, which absorb over a wide range of visible wavelengths. Curcumin transfers its absorbed
energy to eosin, which sensitizes the production of singlet oxygen. The singlet oxygen is scavenged by PFO. The use of two
dyes increases the efficiency of the sensitization process, reducing the illumination time and intensity required for effective
oxygen scavenging. 相似文献
85.
Thin Nguyen Dinh Phung Brett Adams Svetha Venkatesh 《Knowledge and Information Systems》2014,39(3):667-702
We present a large-scale mood analysis in social media texts. We organise the paper in three parts: (1) addressing the problem of feature selection and classification of mood in blogosphere, (2) we extract global mood patterns at different level of aggregation from a large-scale data set of approximately 18 millions documents (3) and finally, we extract mood trajectory for an egocentric user and study how it can be used to detect subtle emotion signals in a user-centric manner, supporting discovery of hyper-groups of communities based on sentiment information. For mood classification, two feature sets proposed in psychology are used, showing that these features are efficient, do not require a training phase and yield classification results comparable to state of the art, supervised feature selection schemes; on mood patterns, empirical results for mood organisation in the blogosphere are provided, analogous to the structure of human emotion proposed independently in the psychology literature; and on community structure discovery, sentiment-based approach can yield useful insights into community formation. 相似文献
86.
A streaming time series is a continuous and unbounded group of chronological observations that are found in many scientific and business applications. Motifs that are frequent subsequences are highly representative for the time series and play an important role in time series mining. Discovering motifs in time series has received much attention during recent years, and several algorithms have been proposed to solve this problem. However, these algorithms can only find motifs with a predefined length, which greatly affects their performance and practicality. Recent algorithms can discover motifs with different lengths, but require multiple scanning of the time series and are thus not applicable to streaming time series. In addition, it is difficult to determine the optimal length of interesting motifs; a suboptimal choice results in missing the key motifs or having too many redundant motifs. To overcome this challenge, we introduce the notion of a \(closed\) motif; a motif is \(closed\) if there is no motif with a longer length having the same number of occurrences. We propose a novel algorithm \(closedMotif\) to discover closed motifs in a single scan for streaming time series. We also use the nearest neighbor classifier with the most distinctive closed motifs to validate their potential in time series classification. Extensive experiments show that our approach can efficiently discover motifs with different lengths. In addition, our closed-motif-based classifier is shown to be more accurate than \(Logical\text{- }Shapelet\) , a state-of-the-art time series classifier. Finally, we demonstrate the scalability of \(closedMotif\) on several large datasets in diverse domains like video surveillance, sensor networks, and biometrics. 相似文献
87.
Tuan D. Pham Dinh T.P. Le Jinwei Xu Duc T. Nguyen Robert G. Martindale Clifford W. Deveney 《Computer methods and programs in biomedicine》2014
An abdominal wall hernia is a protrusion of the intestine through an opening or area of weakness in the abdominal wall. Correct pre-operative identification of abdominal wall hernia meshes could help surgeons adjust the surgical plan to meet the expected difficulty and morbidity of operating through or removing the previous mesh. First, we present herein for the first time the application of image analysis for automated identification of hernia meshes. Second, we discuss the novel development of a new entropy-based image texture feature using geostatistics and indicator kriging. Third, we seek to enhance the hernia mesh identification by combining the new texture feature with the gray-level co-occurrence matrix feature of the image. The two features can characterize complementary information of anatomic details of the abdominal hernia wall and its mesh on computed tomography. Experimental results have demonstrated the effectiveness of the proposed study. The new computational tool has potential for personalized mesh identification which can assist surgeons in the diagnosis and repair of complex abdominal wall hernias. 相似文献
88.
Tristan Allard Benjamin Nguyen Philippe Pucheral 《Distributed and Parallel Databases》2014,32(2):191-244
The goal of Privacy-Preserving Data Publishing (PPDP) is to generate a sanitized (i.e. harmless) view of sensitive personal data (e.g. a health survey), to be released to some agencies or simply the public. However, traditional PPDP practices all make the assumption that the process is run on a trusted central server. In this article, we argue that the trust assumption on the central server is far too strong. We propose Met ??P, a generic fully distributed protocol, to execute various forms of PPDP algorithms on an asymmetric architecture composed of low power secure devices and a powerful but untrusted infrastructure. We show that this protocol is both correct and secure against honest-but-curious or malicious adversaries. Finally, we provide an experimental validation showing that this protocol can support PPDP processes scaling up to nation-wide surveys. 相似文献
89.
Nguyen Van Nguu 《Nutrient Cycling in Agroecosystems》1987,14(2):135-142
The shortening of fallow period in several areas in tropical Africa has reduced soil fertility and exposed soils to erosion and run-off. Fertilizer application and crop conservation practices are needeed to sustain high crop yield and to conserve the natural resource base for upland crop production in the continent. Field trials were carried out to evaluate the effect of fertilizer application and soil and crop residues management practices on yield of maize (Zea mays L.) planted on a Plinthudult soil at Bertoua, Eastern Cameroon. Maize yields increased significantly with nitrogen and phosphorus fertilizer application. Under the rainfall pattern prevailing in the area, the amount of nitrogen required for maximum yield was higher in the second season. On the other hand, the amount of phosphorus required for maximum yield appeared to decrease with time. The burning of crop residues and weeds prior to planting together with no-till practive gave higher yield of maize than other soil and crop residues management practices. 相似文献
90.
The packing stage starts at the end of mold filling. During this stage, additional material is forced into the mold to compensate for the shrinkage during subse-quent cooling. Underpacking results in molded parts with dimensional variation. Overpacking causes flash at the parting lines, stick during ejection, and excess residual stresses resulting in warpage. The packing stage is thus extremely important in the determination of the final quality of the product. Despite its importance, analysis of the packing stage has been relatively ignored, particularly the viscoelastic effect. In this work, the analysis of the isothermal packing stage is presented for a Maxwell fluid. A set of governing equations is derived for a two-dimensional mold and solved using the Galerkin finite element method. In addition to the distribution of velocity and pressure, the model predicts the stresses in the planar direction, which could be used for subsequent calculation of the residual stresses. 相似文献