全文获取类型
收费全文 | 3288篇 |
免费 | 121篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 32篇 |
综合类 | 4篇 |
化学工业 | 755篇 |
金属工艺 | 102篇 |
机械仪表 | 71篇 |
建筑科学 | 85篇 |
矿业工程 | 6篇 |
能源动力 | 102篇 |
轻工业 | 131篇 |
水利工程 | 17篇 |
石油天然气 | 10篇 |
无线电 | 298篇 |
一般工业技术 | 695篇 |
冶金工业 | 661篇 |
原子能技术 | 26篇 |
自动化技术 | 431篇 |
出版年
2023年 | 18篇 |
2022年 | 34篇 |
2021年 | 62篇 |
2020年 | 53篇 |
2019年 | 47篇 |
2018年 | 72篇 |
2017年 | 55篇 |
2016年 | 74篇 |
2015年 | 55篇 |
2014年 | 72篇 |
2013年 | 188篇 |
2012年 | 112篇 |
2011年 | 153篇 |
2010年 | 139篇 |
2009年 | 160篇 |
2008年 | 128篇 |
2007年 | 124篇 |
2006年 | 107篇 |
2005年 | 91篇 |
2004年 | 107篇 |
2003年 | 86篇 |
2002年 | 84篇 |
2001年 | 77篇 |
2000年 | 66篇 |
1999年 | 75篇 |
1998年 | 119篇 |
1997年 | 76篇 |
1996年 | 69篇 |
1995年 | 53篇 |
1994年 | 59篇 |
1993年 | 67篇 |
1992年 | 60篇 |
1991年 | 50篇 |
1990年 | 46篇 |
1989年 | 55篇 |
1988年 | 44篇 |
1987年 | 31篇 |
1986年 | 37篇 |
1985年 | 40篇 |
1984年 | 40篇 |
1983年 | 38篇 |
1982年 | 23篇 |
1981年 | 26篇 |
1980年 | 30篇 |
1979年 | 15篇 |
1978年 | 21篇 |
1977年 | 27篇 |
1976年 | 32篇 |
1974年 | 19篇 |
1973年 | 24篇 |
排序方式: 共有3426条查询结果,搜索用时 31 毫秒
91.
Under-segmentation of an image with multiple objects is a common problem in image segmentation algorithms. This paper presents a novel approach for splitting clumps formed by multiple objects due to under-segmentation. The proposed algorithm includes three steps: (1) decide whether to split a candidate connected component by application-specific shape classification; (2) find a pair of points for clump splitting and (3) join the pair of selected points. In the first step, a shape classifier is applied to determine whether a connected component should be split. In the second step, a pair of points for splitting is detected using a bottleneck rule, under the assumption that the desired objects have roughly a convex shape. In the third step, the selected splitting points from step two are joined by finding the optimal splitting line between them, based on minimizing an image energy. The shape classifier is built offline via various shape features and a support vector machine. Steps two and three are application-independent. The performance of this method is evaluated using images from various applications. Experimental results show that the proposed approach outperforms the state-of-the-art algorithms for the clump splitting problem. 相似文献
92.
Amir Talaei-Khoei Terje Solvoll Pradeep Ray Nandan Parameshwaran 《Journal of Computer and System Sciences》2012,78(1):370-391
The field of computer supported cooperative work aims at providing information technology models, methods, and tools that assist individuals to cooperate. The presented paper is based on three main observations from literature. First, one of the problems in utilizing information technology for cooperation is to identify the relevance of information, called awareness. Second, research in computer supported cooperative work proposes the use of agent technologies to aid individuals to maintain their awareness. Third, literature lacks the formalized methods on how software agents can identify awareness. This paper addresses the problem of awareness identification. The main contribution of this paper is to propose and evaluate a formalized structure, called Policy-based Awareness Management (PAM). PAM extends the logic of general awareness in order to identify relevance of information. PAM formalizes existing policies into Directory Enabled Networks-next generation structure and uses them as a source for awareness identification. The formalism is demonstrated by applying PAM to the space shuttle Columbia disaster occurred in 2003. The paper also argues that efficacy and cost-efficiency of the logic of general awareness will be increased by PAM. This is evaluated by simulation of hypothetical scenarios as well as a case study. 相似文献
93.
Purnendu Parhi Satya Sadhan Singh Alok R. Ray A. Ramanan 《Bulletin of Materials Science》2006,29(2):115-118
This communication reports a novel mechanochemically assisted room temperature solid state metathesis reaction for the synthesis
of submicron-size alkaline-earth molybdates crystallizing in a tetragonal Scheelite structure. The solids were characterized
by powder XRD, FTIR, TGA, DTA, SEM, EDAX and TEM to ascertain their composition, phase homogeneity and morphology. 相似文献
94.
J. Theo Kloprogge Maarten Broekmans Loc V. Duong Wayde N. Martens Liesel Hickey Ray L. Frost 《Journal of Materials Science》2006,41(11):3535-3539
Lecontite, (NH4)Na(SO4).2H2O, was synthesised at room temperature in high purity compared to earlier work with a minor impurity of mascagnite, (NH4)2SO4. Rietveld refinement of the XRD results confirmed the crystal structure and unit cell dimensions as published earlier. Raman
and Infrared spectroscopy, in conjunction with factor group analysis, resulted in a complex pattern of overlapping sulphate,
NH and OH modes. The NH modes υ1 was observed around 2880 cm−1, υ2 around 1700 cm−1 overlapping with water OH-bending modes, υ3 around 3300 cm−1 overlapping with water OH-stretching modes around 3023, 3185 and 3422 cm−1, and υ4 around 1432, 1447 and 1462 cm−1. The sulphate group in the crystal structure displays a decrease in symmetry from Td as evidenced by the activation of the ν1 mode at 982 cm−1 and the ν2 mode around 452 cm−1 in the Infrared spectrum. The υ3 mode shows clear splitting in the infrared spectra with a strong band at 1064 cm−1 accompanied by two shoulders at 1107 and 1139 cm−1. The Raman spectra show three weak bands at 1068, 1109 and 1135 cm−1 with a shoulder at 1155 cm−1. Similar splitting was observed for the υ4 mode around 611 and 632 cm−1 in the Infrared and Raman spectra, respectively. 相似文献
95.
K. K. Makhija Arabinda Ray R. M. Patel U. B. Trivedi H. N. Kapse 《Bulletin of Materials Science》2005,28(1):9-17
A sensor for ammonia gas and ethanol vapour has been fabricated using indium oxide thin film as sensing layer and indium tin
oxide thin film encapsulated in poly(methyl methacrylate) (PMMA) as a miniature heater. For the fabrication of miniature heater
indium tin oxide thin film was grown on special high temperature corning glass substrate by flash evaporation method. Gold
was deposited on the film using thermal evaporation technique under high vacuum. The film was then annealed at 700 K for an
hour. The thermocouple attached on sensing surface measures the appropriate operating temperature.
The thin film gas sensor for ammonia was operated at different concentrations in the temperature range 323–493 K. At 473 K
the sensitivity of the sensor was found to be saturate. The detrimental effect of humidity on ammonia sensing is removed by
intermittent periodic heating of the sensor at the two temperatures 323K and 448 K, respectively. The indium oxide ethanol
vapour sensor operated at fixed concentration of 400 ppm in the temperature range 293–393 K. Above 373 K, the sensor conductance
was found to be saturate. With various thicknesses from 150–300 nm of indium oxide sensor there was no variation in the sensitivity
measurements of ethanol vapour. The block diagram of circuits for detecting the ammonia gas and ethanol vapour has been included
in this paper. 相似文献
96.
A general formulation for modeling frictional contact interactions in a constrained multi-flexible body system is outlined in this paper. The governing differential-algebraic equations (DAE) for the constrained motion contains not only a frictional term but also, the unknown contact conditions. These contact conditions are characterized by a set of nonlinear complementarity equations. To demonstrate the model, a falling-spinning beam impacting a rough elastic ground with damping is solved and comparison with Stewart-Trinkles' results provided. 相似文献
97.
The effect of melting temperature, time, and the type of raw material, NaNO3 or Na2CO3, as a source for Na2O on the glass formation for a Na2O·4TeO2(NT4) melt was investigated. Melting with NaNO3 at 750°C for a short time (15 min) produced a glass that is slightly more chemically durable and more resistant to crystallization than glasses melted at a higher temperature (800°C), or for a longer time (60 min), or using Na2CO3. A thin surface layer (<1.5 nm) that contains some nitrogen and a higher concentration of bridging oxygen is suspected to be the reason for the higher chemical durability and higher resistance to crystallization for this glass. However, melting at 800°C for 60 min produced a glass, whose properties were independent of the type of raw material, NaNO3 or Na2CO3, used. 相似文献
98.
This paper reports the presence of Al- O- Al linkages in an aluminosilicate glass where Si/Al = 1 by using 2D17O triple quantum MAS NMR technique (3Q MASNMR). The experiments were performed at external magnetic fields of 8.4 and 14.4T.
Despite17OMAS NMR spectra of the sample in both fields do not give much information about the different kinds of linkages in the sample,
3Q MAS NMR spectrum shows clear evidence that there are some amounts of Al-O-Al linkages in the sample giving two completely
resolved peaks. These two peaks were attributed to the Si-O-Al and Al-O-Al linkages on the basis of their chemical shifts
and, quadrupolar coupling constants which are quite sensitive to the local structure. 相似文献
99.
Lake RE Dean A Maheswaranathan N Lange AP Ray MP Sosolik CE 《The Review of scientific instruments》2008,79(1):013703
We demonstrate that scanning tunneling microscope tip-surface crash events can be utilized as an efficient means for the creation of predefined island configurations for diffusion studies. Using this method, islands of varying size can be created and placed in close proximity, increasing the probability of initiating and observing coalescence events. Data obtained from crash initiated events on a Ag(111) surface are presented. Relaxation time exponents extracted from these data confirm that our method gives results consistent with previous, sputter-obtained island coalescence studies. We also describe an instrument-control routine developed for these measurements that utilizes commercial imaging and off-the-shelf automation software to automate the tracking of islands or other features by the microscope. 相似文献
100.
Conley R Liu C Qian J Kewish CM Macrander AT Yan H Kang HC Maser J Stephenson GB 《The Review of scientific instruments》2008,79(5):053104
A multilayer Laue lens (MLL) is an x-ray focusing optic fabricated from a multilayer structure consisting of thousands of layers of two different materials produced by thin-film deposition. The sequence of layer thicknesses is controlled to satisfy the Fresnel zone plate law and the multilayer is sectioned to form the optic. An improved MLL geometry can be created by growing each layer with an in-plane thickness gradient to form a wedge, so that every interface makes the correct angle with the incident beam for symmetric Bragg diffraction. The ultimate hard x-ray focusing performance of a wedged MLL has been predicted to be significantly better than that of a nonwedged MLL, giving subnanometer resolution with high efficiency. Here, we describe a method to deposit the multilayer structure needed for an ideal wedged MLL and report our initial deposition results to produce these structures. 相似文献