全文获取类型
收费全文 | 1457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 | 308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 | 71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 | 30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 | 9篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 8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1529条查询结果,搜索用时 31 毫秒
41.
Pre-processing is one of the vital steps for developing robust and efficient recognition system. Better pre-processing not
only aid in better data selection but also in significant reduction of computational complexity. Further an efficient frame
selection technique can improve the overall performance of the system. Pre-quantization (PQ) is the technique of selecting
less number of frames in the pre-processing stage to reduce the computational burden in the post processing stages of speaker
identification (SI). In this paper, we develop PQ techniques based on spectral entropy and spectral shape to pick suitable
frames containing speaker specific information that varies from frame to frame depending on spoken text and environmental
conditions. The attempt is to exploit the statistical properties of distributions of speech frames at the pre-processing stage
of speaker recognition. Our aim is not only to reduce the frame rate but also to maintain identification accuracy reasonably
high. Further we have also analyzed the robustness of our proposed techniques on noisy utterances. To establish the efficacy
of our proposed methods, we used two different databases, POLYCOST (telephone speech) and YOHO (microphone speech). 相似文献
42.
Automatic MR brain image segmentation using a multiseed based multiobjective clustering approach 总被引:2,自引:2,他引:0
In this paper, the automatic segmentation of a multispectral magnetic resonance image of the brain is posed as a clustering
problem in the intensity space. The automatic clustering problem is thereafter modelled as solving a multiobjective optimization
(MOO) problem, optimizing a set of cluster validity indices simultaneously. A multiobjective clustering technique, named MCMOClust, is used to solve this problem. MCMOClust utilizes a recently developed simulated annealing based multiobjective optimization method as the underlying optimization
strategy. Each cluster is divided into several small hyperspherical subclusters and the centers of all these small sub-clusters
are encoded in a string to represent the whole clustering. For assigning points to different clusters, these local sub-clusters
are considered individually. For the purpose of objective function evaluation, these sub-clusters are merged appropriately
to form a variable number of global clusters. Two cluster validity indices, one based on the Euclidean distance, XB-index,
and another recently developed point symmetry distance based cluster validity index, Sym-index, are optimized simultaneously to automatically evolve the appropriate number of clusters present in MR brain images.
A semi-supervised method is used to select a single solution from the final Pareto optimal front of MCMOClust. The present method is applied on several simulated T1-weighted, T2-weighted and proton density normal and MS lesion magnetic
resonance brain images. Superiority of the present method over Fuzzy C-means, Expectation Maximization clustering algorithms
and a newly developed symmetry based fuzzy genetic clustering technique (Fuzzy-VGAPS), are demonstrated quantitatively. The
automatic segmentation obtained by multiseed based multiobjective clustering technique (MCMOClust) is also compared with the available ground truth information. 相似文献
43.
Bhattacharya D Saha S Basu S Chakravarty S Chakravarty A Banerjee D Chakrabarti A 《Proteomics. Clinical applications》2010,4(5):480-488
Purpose: In (hemoglobin, Hb) HbEβ‐thalassemia, HbE (β‐26 Glu→Lys) interacts with β‐thalassemia to produce clinical manifestation of varying severity. This is the first proteomic effort to study changes in protein levels of erythrocytes isolated from HbEβ‐thalassemic patients compared to normal. Experimental design: We have used 2‐DE and MALDI‐MS/MS‐based techniques to investigate the differential proteome profiling of membrane and Hb‐depleted fraction of cytosolic proteins of erythrocytes isolated from the peripheral blood samples of HbEβ‐thalassemia patients and normal volunteers. Results: Our study showed that redox regulators such as peroxiredoxin 2, Cu‐Zn superoxide dismutase and thioredoxin and chaperones such as α‐hemoglobin stabilizing protein and HSP‐70 were upregulated in HbEβ‐thalassemia. We have also observed larger amounts of membrane associated globin chains and indications of disruption of spectrin‐based junctional complex in the membrane skeleton of HbEβ‐thalassemic erythrocytes upon detection of low molecular weight fragments of β‐spectrin and decrease in β‐actin and dematin content. Conclusion and clinical relevance: We have observed interesting changes in the proteomic levels of redox regulators and chaperons in the thalassemic hemolysates and have observed strong correlation or association of the extent of such proteomic changes with HbE levels. This could be important in understanding the role of HbE in disease progression and pathophysiology. 相似文献
44.
Sumit Misra Sanjoy Kumar Saha Chandan Mazumdar 《Innovations in Systems and Software Engineering》2017,13(4):261-269
Multiple data streams coming out of a complex system form the observable state of the system. The streams may correspond to various sensors attached with the system or outcome of internal processes. Such stream data may consist of multiple attributes and may differ in terms of their frequency of generation and observation. The streams may have dependency among themselves. One will have to rely on such data streams for monitoring the health of the system or to take any corrective measure. Predicting the value of certain stream data is an important task that can help one to take decision and act accordingly. In this work, a simple but generic visualization of a complex system is presented and thereafter a linear regression-based dynamic model for short-term prediction is proposed. The model is based on the past history of the attributes of multiple streams as suggested by the domain experts. But, it automatically determines the meaningful attributes and reformulates the model. The model is also re-computed if the prediction error exceeds the allowable tolerance. All these make the model dynamic. Experiment is carried out with stock market data streams to predict the close value well in advance. It is observed that in terms of quality of prediction and performance metric, the proposed model is quite effective. 相似文献
45.
Saha P.K. Udupa J.K. 《IEEE transactions on pattern analysis and machine intelligence》2001,23(7):689-706
Thresholding is a popular image segmentation method that converts a gray-level image into a binary image. The selection of optimum thresholds has remained a challenge over decades. Besides being a segmentation tool on its own, often it is also a step in many advanced image segmentation techniques in spaces other than the image space. We introduce a thresholding method that accounts for both intensity-based class uncertainty-a histogram-based property-and region homogeneity-an image morphology-based property. A scale-based formulation is used for region homogeneity computation. At any threshold, intensity-based class uncertainty is computed by fitting a Gaussian to the intensity distribution of each of the two regions segmented at that threshold. The theory of the optimum thresholding method is based on the postulate that objects manifest themselves with fuzzy boundaries in any digital image acquired by an imaging device. The main idea here is to select that threshold at which pixels with high class uncertainty accumulate mostly around object boundaries. To achieve this, a threshold energy criterion is formulated using class-uncertainty and region homogeneity such that, at any image location, a high energy is created when both class uncertainty and region homogeneity are high or both are low. Finally, the method selects that threshold which corresponds to the minimum overall energy. The method has been compared to a maximum segmented image information method. Superiority of the proposed method was observed both qualitatively on clinical medical images as well as quantitatively on 250 realistic phantom images generated by adding different degrees of blurring, noise, and background variation to real objects segmented from clinical images 相似文献
46.
A stability-based distributed routing mechanism to support unicast and multicast routing in ad hoc wireless network 总被引:6,自引:0,他引:6
An ad hoc network can be envisioned as a collection of mobile routers, each equipped with a wireless transceiver, which are free to move about arbitrarily. In ad hoc wireless networks, even if two nodes are outside the wireless transmission range of each other, they may still be able to communicate in multiple hops using other intermediate nodes. However, the dynamics of these networks, as a consequence of mobility and disconnection of mobile hosts, pose a number of problems in designing routing schemes for effective communication between any pair of source and destination. In this paper, a stability-based unicast routing mechanism, that considers both link affinity and path stability in order to find out a stable route from source to destination, is proposed. It is then extended to support multicast routing as well where only local state information (at source) is utilized for constructing a multicast tree. The performance of the proposed scheme is evaluated on a simulated environment to show that the stability-based scheme provides a unified framework for both unicast and multicast routing and reduces the probability of route error drastically in both the cases. 相似文献
47.
Nanocomposites of polyfuran (PF) and polythiophene (PTP) with montmorillonite clay (MMT) were prepared and modified by loading
of polyaniline (PANI) and polypyrrole (PPY) moieties via polymerization of aniline (ANI) and pyrrole (PY) in aqueous dispersions
of PF-MMT and PTP-MMT nanocomposites. Formation of PANI and PPY and their subsequent incorporation in the PF-MMT and PTP-MMT
composites was confirmed by FTIR absorption studies. X-ray diffraction (XRD) patterns of PANI and PPY modified PF-MMT and
PTP-MMT composites showed that PF-MMT and PTP-MMT intercalates were still present in the modified composites. Scanning electron
microscopic analysis revealed distinctive morphological patterns of the various composite particles. The dc conductivity values
of PANI and PPY modified PF-MMT and PTP-MMT composites were in the order of 10−2 S/cm in either system – a value much improved compared to the same for both of the unmodified PF-MMT (10−7 S/cm) and PTP-MMT (10−5 S/cm) nanocomposites respectively. 相似文献
48.
Pervasive computing: a paradigm for the 21st century 总被引:4,自引:0,他引:4
Pervasive computing promises to make life simpler via digital environments that sense, adapt, and respond to human needs. Yet we still view computers as machines that run programs in a virtual environment. Pervasive computing presumes a different vision. A device can be a portal into an application-data space, not just a repository of custom software a user must manage. An application is a means by which a user performs a task, not software written to exploit a device's capabilities. And a computing environment is an information-enhanced physical space, not a virtual environment that exists to store and run software. Pervasive computing is close to technical and economic viability. 相似文献
49.
This paper describes the investigation of the insulation condition of a number of power and distribution type transformers of different manufacturing dates and with different operating histories. Return voltage measurements were conducted for these transformers. Effects of moisture and aging on the oil-paper insulation of these transformers were investigated and results are presented in this paper. Moisture in oil samples at known temperature was measured for these transformers. Previously accelerated aging experiments were performed on paper wrapped insulated conductors in different environments over a temperature range of 115 to 145/spl deg/C. Results from the measurements on transformers are compared with those of the accelerated aged samples and are described in this paper. 相似文献
50.
O. Auciello S. Saha D.Y. Kaufman S.K. Streiffer W. Fan B. Kabius J. Im P. Baumann 《Journal of Electroceramics》2004,12(1-2):119-131
Thin films of Ba1?x Sr x Ti1+y O3+z (BST), were fabricated using both by RF-magnetron sputtering and MOCVD to demonstrate application to high frequency devices. Precise control of composition and microstructure is critical for the production of (Ba x Sr1?x )Ti1+y O3+z (BST) dielectric thin films with the large dependence of permittivity on electric field, low losses, and high electrical breakdown fields that are required for successful integration of BST into tunable high frequency devices. Here we review results on composition-microstructure-electrical property relationships of polycrystalline BST films produced by magnetron sputter deposition that are appropriate for microwave devices such as phase shifters. BST films with a multilayer structure were also developed with different Ti-elemental ratio in each layer to minimize losses and leakage current. Interfacial contamination from C and H species was studied and implications on electrical properties are highlighted. Finally, York's group at the University of California-Santa Barbara successfully integrated our BST films onto phase shifter arrays. The results show potential of BST films in such applications. Results from initial work on the integration of Cu-electrodes with BST films are also presented. 相似文献