全文获取类型
收费全文 | 4066篇 |
免费 | 104篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 51篇 |
综合类 | 1篇 |
化学工业 | 547篇 |
金属工艺 | 73篇 |
机械仪表 | 66篇 |
建筑科学 | 129篇 |
矿业工程 | 4篇 |
能源动力 | 94篇 |
轻工业 | 306篇 |
水利工程 | 21篇 |
石油天然气 | 3篇 |
无线电 | 359篇 |
一般工业技术 | 642篇 |
冶金工业 | 1213篇 |
原子能技术 | 48篇 |
自动化技术 | 615篇 |
出版年
2022年 | 26篇 |
2021年 | 34篇 |
2019年 | 34篇 |
2018年 | 44篇 |
2017年 | 49篇 |
2016年 | 35篇 |
2015年 | 42篇 |
2014年 | 77篇 |
2013年 | 192篇 |
2012年 | 85篇 |
2011年 | 134篇 |
2010年 | 111篇 |
2009年 | 106篇 |
2008年 | 116篇 |
2007年 | 130篇 |
2006年 | 98篇 |
2005年 | 90篇 |
2004年 | 89篇 |
2003年 | 99篇 |
2002年 | 89篇 |
2001年 | 91篇 |
2000年 | 85篇 |
1999年 | 95篇 |
1998年 | 333篇 |
1997年 | 196篇 |
1996年 | 161篇 |
1995年 | 111篇 |
1994年 | 103篇 |
1993年 | 98篇 |
1992年 | 56篇 |
1991年 | 56篇 |
1990年 | 51篇 |
1989年 | 58篇 |
1988年 | 55篇 |
1987年 | 54篇 |
1986年 | 35篇 |
1985年 | 45篇 |
1984年 | 61篇 |
1983年 | 53篇 |
1982年 | 44篇 |
1981年 | 50篇 |
1980年 | 52篇 |
1979年 | 56篇 |
1978年 | 42篇 |
1977年 | 56篇 |
1976年 | 94篇 |
1975年 | 41篇 |
1974年 | 33篇 |
1972年 | 24篇 |
1966年 | 22篇 |
排序方式: 共有4172条查询结果,搜索用时 15 毫秒
91.
H-Infinity Static Output-feedback Control for Rotorcraft 总被引:1,自引:0,他引:1
Jyotirmay Gadewadikar Frank L. Lewis Kamesh Subbarao Kemao Peng Ben M. Chen 《Journal of Intelligent and Robotic Systems》2009,54(4):629-646
The problem of stabilization of an autonomous rotorcraft platform in a hover configuration subject to external disturbances
is addressed. Necessary and sufficient conditions are presented for static output-feedback control of linear time-invariant
systems using the H-Infinity approach. Simplified conditions are given which only require the solution of two coupled matrix
design equations. This paper also proposes a numerically efficient solution algorithm for the coupled design equations to
determine the output-feedback gain. A major contribution is that an initial stabilizing gain is not needed. The efficacy of
the control law and the disturbance accommodation properties are shown on a rotorcraft design example. The helicopter dynamics
do not decouple as in the fixed-wing aircraft case, so that the design of helicopter flight controllers with a desirable intuitive
structure is not straightforward. In this paper an output feedback approach is given that allows one to selectively close
prescribed multivariable feedback loops using a reduced set of the states. Shaping filters are added that improve performance
and yield guaranteed robustness and speed of response. This gives direct control over the design procedure and performance.
Accurate identification of the System parameters is a challenging task for rotorcraft control, addition of loop shaping facilitates
implementation engineers to counteract unmodeled high frequency dynamics. The net result yields control structures that have
been historically accepted in the flight control community. 相似文献
92.
Steven Hancock Mathias Disney Jan-Peter Muller Philip Lewis Mike Foster 《Remote sensing of environment》2011,115(12):3286-3297
Lidars have the unique ability to make direct, physical measurements of forest height and vertical structure in much denser canopies than is possible with passive optical or short wavelength radars. However the literature reports a consistent underestimate of tree height when using physically based methods, necessitating empirical corrections. This bias is a result of overestimating the range to the canopy top due to background noise and failing to correctly identify the ground.This paper introduces a method, referred to as “noise tracking”, to avoid biases when determining the range to the canopy top. Simulated waveforms, created with Monte-Carlo ray tracing over geometrically explicit forest models, are used to test noise tracking against simple thresholding over a range of forest and system characteristics. It was found that noise tracking almost completely removed the bias in all situations except for very high noise levels and very low (< 10%) canopy covers. In all cases noise tracking gave lower errors than simple thresholding and had a lower sensitivity to the initial noise threshold.Finite laser pulses spread out the measured signal, potentially overriding the benefit of noise tracking. In the past laser pulse length has been corrected by adding half that length to the signal start range. This investigation suggests that this is not always appropriate for simple thresholding and that the results for noise tracking were more directly related to pulse length than for simple thresholding. That this effect has not been commented on before may be due to the possible confounding impacts of instrument and survey characteristics inherent in field data. This method should help improve the accuracy of waveform lidar measurements of forests, whether using airborne or spaceborne instruments. 相似文献
93.
94.
For finite-buffer manufacturing systems, the major stability issue is "deadlock," rather than "bounded-buffer-length stability." The paper introduces the concept of "system deadlock," defined rigorously in Petri net terms, and system operation with uninterrupted part-flow is characterized in terms of the absence of this condition. For a large class of finite-buffer multiclass re-entrant flowline systems, an analysis of "circular waits" yields necessary and sufficient conditions for the occurrence of "system deadlock." This allows the formulation of a maximally permissive one-step-look-ahead deadlock-avoidance control policy for dispatching jobs, while maximizing the percent utilization of resources. The result is a generalized kanban dispatching strategy, which is more general than the standard multiclass last buffer first serve (LBFS) dispatching strategies for finite buffer flowlines that typically under-utilize the resources. The problem of computational complexity associated with Petri net (PN) applications is overcome by using certain sub-matrices of the PN incidence matrix. Computationally efficient matrix techniques are given for implementing the deadlock-free dispatching policy. 相似文献
95.
A desired compensation adaptive law‐based neural network (DCAL‐NN) controller is proposed for the robust position control of rigid‐link robots. The NN is used to approximate a highly nonlinear function. The controller can guarantee the global asymptotic stability of tracking errors and boundedness of NN weights. In addition, the NN weights here are tuned on‐line, with no offline learning phase required. When compared with standard adaptive robot controllers, we do not require linearity in the parameters, or lengthy and tedious preliminary analysis to determine a regression matrix. The controller can be regarded as a universal reusable controller because the same controller can be applied to any type of rigid robots without any modifications. A comparative simulation study with different robust and adaptive controllers is included. 相似文献
96.
Larsen L Griffin LD Grässel D Witte OW Axer H 《Microscopy research and technique》2007,70(10):851-863
Polarized light imaging (PLI) is a method to image fiber orientation in gross histological brain sections based on the birefringent properties of the myelin sheaths. The method uses the transmission of polarized light to quantitatively estimate the fiber orientation and inclination angles at every point of the imaged section. Multiple sections can be assembled into a 3D volume, from which the 3D extent of fiber tracts can be extracted. This article describes the physical principles of PLI and describes two major applications of the method: the imaging of white matter orientation of the rat brain and the generation of fiber orientation maps of the human brain in white and gray matter. The strengths and weaknesses of the method are set out. 相似文献
97.
Griffin LD 《IEEE transactions on pattern analysis and machine intelligence》2007,29(8):1355-1366
Characterization of second order local image structure by a 6D vector (or jet) of Gaussian derivative measurements is considered. We consider the affect on jets of a group of transformations-affine intensity-scaling, image rotation and reflection, and their compositions-that preserve intrinsic image structure. We show how this group stratifies the jet space into a system of orbits. Considering individual orbits as points, a 3D orbifold is defined. We propose a norm on jet space which we use to induce a metric on the orbifold. The metric tensor shows that the orbifold is intrinsically curved. To allow visualization of the orbifold and numerical computation with it, we present a mildly-distorting but volume-preserving embedding of it into euclidean 3-space. We call the resulting shape, which is like a flattened lemon, the second order local-image-structure solid. As an example use of the solid, we compute the distribution of local structures in noise and natural images. For noise images, analytical results are possible and they agree with the empirical results. For natural images, an excess of locally 1D structure is found. 相似文献
98.
Wylie B. Pavlakos C. Lewis V. Moreland K. 《Computer Graphics and Applications, IEEE》2001,21(4):62-69
Sandia National Laboratories use PC clusters and commodity graphics cards to achieve higher rendering performance on extreme data sets. The main obstacle in using cluster-based graphics systems is the difficulty in realizing the full aggregate performance of all the individual graphics accelerators, particularly for very large data sets that exceed the capacity and performance characteristics of any one single node. Based on our efforts to achieve higher performance, we present results from a parallel sort-last implementation that the scalable rendering project at Sandia National Laboratories generated. Our sort-last library (libpglc) can be linked to an existing parallel application to achieve high rendering rates. We ran performance tests on a 64-node PC cluster populated with commodity graphics cards. Applications using libpglc have demonstrated rendering performance of 300 million polygons per second $approximately two orders of magnitude greater than the performance on an SGI Infinite Reality system for similar applications 相似文献
99.
We have discovered a class of fractal functions that are differentiable. Fractal interpolation functions have been used for
over a decade to generate rough functions passing through a set of given points. The integral of a fractal interpolation function
remains a fractal interpolation function, and this new fractal interpolation function is differentiable. Tensor products of
pairs of these fractal functions form fractal surfaces with a well-defined tangent plane. We use this surface normal to shade
fractal surfaces, and demonstrate its use with renderings of fractal mirrors. 相似文献
100.
We have previously demonstrated that mouse brain membrane fractions have a specific, saturable receptor for diadenylated nucleotides. Binding is specific for two adenosines, and the length of the phosphate bridge is critical, with four phosphates being optimal [Hilderman et al. (1991) J. Biol. Chem. 266, 6915-6918]. In this report, we demonstrate that adenosine 5',5"'-P1,P4-tetraphosphate (Ap4A) binding to its receptor is dependent upon an activation step that requires divalent cations and a serine protease. Monoclonal antibodies (Mabs) are identified that inhibit Ap4A binding to its membrane receptor. These antibodies recognize a 212-kDa membrane protein. However, SDS-PAGE analysis of Ap4A cross-linked to membrane fractions reveals that Ap4A is not attached to the 212-kDa peptide but to a 30-kDa polypeptide. Appearance of the 30-kDa polypeptide is dependent on the activation step, and one of the inhibitory antibodies blocks its appearance. We suggest that the protease-dependent processing step involves cleavage of the 212-kDa component with the appearance of an active 30-kDa receptor. 相似文献