全文获取类型
收费全文 | 1849篇 |
免费 | 88篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 22篇 |
综合类 | 9篇 |
化学工业 | 338篇 |
金属工艺 | 29篇 |
机械仪表 | 35篇 |
建筑科学 | 107篇 |
矿业工程 | 1篇 |
能源动力 | 79篇 |
轻工业 | 288篇 |
水利工程 | 14篇 |
石油天然气 | 9篇 |
无线电 | 124篇 |
一般工业技术 | 247篇 |
冶金工业 | 322篇 |
原子能技术 | 12篇 |
自动化技术 | 308篇 |
出版年
2023年 | 14篇 |
2022年 | 18篇 |
2021年 | 44篇 |
2020年 | 26篇 |
2019年 | 35篇 |
2018年 | 47篇 |
2017年 | 53篇 |
2016年 | 41篇 |
2015年 | 33篇 |
2014年 | 50篇 |
2013年 | 112篇 |
2012年 | 88篇 |
2011年 | 109篇 |
2010年 | 83篇 |
2009年 | 87篇 |
2008年 | 97篇 |
2007年 | 119篇 |
2006年 | 87篇 |
2005年 | 61篇 |
2004年 | 67篇 |
2003年 | 57篇 |
2002年 | 49篇 |
2001年 | 34篇 |
2000年 | 27篇 |
1999年 | 27篇 |
1998年 | 34篇 |
1997年 | 23篇 |
1996年 | 32篇 |
1995年 | 31篇 |
1994年 | 29篇 |
1993年 | 27篇 |
1992年 | 31篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 20篇 |
1986年 | 18篇 |
1985年 | 23篇 |
1984年 | 17篇 |
1983年 | 21篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 11篇 |
1974年 | 6篇 |
排序方式: 共有1944条查询结果,搜索用时 546 毫秒
51.
We present a real-time method for rendering global illumination effects from large area and environmental lights on dynamic height fields. In contrast to previous work, our method handles inter-reflections (indirect lighting) and non-diffuse surfaces. To reduce sampling, we construct one multi-resolution pyramid for height variation to compute direct shadows, and another pyramid for each indirect bounce of incident radiance to compute inter-reflections. The basic principle is to sample the points blocking direct light, or shedding indirect light, from coarser levels of the pyramid the farther away they are from a given receiver point. We unify the representation of visibility and indirect radiance at discrete azimuthal directions (i.e., as a function of a single elevation angle) using the concept of a "casting set" of visible points along this direction whose contributions are collected in the basis of normalized Legendre polynomials. This analytic representation is compact, requires no precomputation, and allows efficient integration to produce the spherical visibility and indirect radiance signals. Sub-sampling visibility and indirect radiance, while shading with full-resolution surface normals, further increases performance without introducing noticeable artifacts. Our method renders 512×512 height fields (> 500K triangles) at 36Hz. 相似文献
52.
We present a real-time relighting and shadowing method for dynamic scenes with varying lighting, view and BRDFs. Our approach is based on a compact representation of reflectance data that allows for changing the BRDF at run-time and a data-driven method for accurately synthesizing self-shadows on articulated and deformable geometries. Unlike previous self-shadowing approaches, we do not rely on local blocking heuristics. We do not fit a model to the BRDF-weighted visibility, but rather only to the visibility that changes during animation. In this manner, our model is more compact than previous techniques and requires less computation both during fitting and at run-time. Our reflectance product operators can re-integrate arbitrary low-frequency view-dependent BRDF effects on-the-fly and are compatible with all previous dynamic visibility generation techniques as well as our own data-driven visibility model. We apply our reflectance product operators to three different visibility generation models, and our data-driven model can achieve framerates well over 300Hz. 相似文献
53.
Ian Scott Evans Jessica Miki Jessee Ho Derek T. Robinson 《International journal of remote sensing》2016,37(6):1411-1430
Topographic and elevation data are essential in the development of supporting infrastructure around mining sites. The de facto standard for acquiring elevation data is through light detection and ranging (lidar). The high labour and monetary cost of acquiring lidar has fostered more cost-effective approaches for creating elevation models that use stereo photogrammetry. To assess the accuracy of stereo-photogrammetry-derived elevation models and their potential application, we benchmark satellite (Worldview-2) and aircraft (South Central Ontario Orthoimagery Project; SCOOP) stereo-derived digital surface models (DSMs) against a lidar-derived DSM. Our results show that both stereo-derived DSMs have strong monotonic correlations with lidar across a range of land-cover types and slopes. The overall vertical accuracy of Worldview-2 and SCOOP DSMs are similar and do not meet the United States National Digital Elevation Program (NDEP) standards. However, accuracy assessment across land-cover types and slope categories show that specific land cover types (i.e. grass, row crops/pasture, sparse vegetation and marsh) on gently sloping terrain compare well to lidar data and meet NDEP accuracy standards. We situate the presented research in the context of northern resource development and discuss opportunities to improve the vertical accuracy of stereo-derived DSMs, for example, through unmanned aerial systems. 相似文献
54.
Adrian Blumer Jan Novák Ralf Habel Derek Nowrouzezahrai Wojciech Jarosz 《Computer Graphics Forum》2016,35(7):461-473
Aggregate scattering operators (ASOs) describe the overall scattering behavior of an asset (i.e., an object or volume, or collection thereof) accounting for all orders of its internal scattering. We propose a practical way to precompute and compactly store ASOs and demonstrate their ability to accelerate path tracing. Our approach is modular avoiding costly and inflexible scene‐dependent precomputation. This is achieved by decoupling light transport within and outside of each asset, and precomputing on a per‐asset level. We store the internal transport in a reduced‐dimensional subspace tailored to the structure of the asset geometry, its scattering behavior, and typical illumination conditions, allowing the ASOs to maintain good accuracy with modest memory requirements. The precomputed ASO can be reused across all instances of the asset and across multiple scenes. We augment ASOs with functionality enabling multi‐bounce importance sampling, fast short‐circuiting of complex light paths, and compact caching, while retaining rapid progressive preview rendering. We demonstrate the benefits of our ASOs by efficiently path tracing scenes containing many instances of objects with complex inter‐reflections or multiple scattering. 相似文献
55.
This paper presents the comparison for the role of bi-articular and mono-articular actuators in human and bipedal robot legs, in particular the hip and knee joint, for driving the design of a humanoid robot with inspirations from the biological system. The various constraints driving the design of both systems are also compared. Additional factors particular to robotic system are identified and incorporated in the design process. To do this, a dynamic simulation is used to determine loading conditions and the forces and power produced by each actuator under various arrangements. It is shown that while the design principles of humans and humanoids are similar, other constraints ensure that robots are still merely inspired by humans, and not direct copies. A simple design methodology that captures the complexity and constraints of such a system in this paper is proposed. Finally, a full-size humanoid robot that demonstrates the newfound principle is highlighted. 相似文献
56.
Derek S.Speed 《程序员》2008,(7):68-70
市场上出现了一种新的设备,它能够访问Internet上丰富的内容,同时没有与PC相关的复杂性。这些设备以各种形式出现,从移动互联网设备(Mobile Internet Devices,MID)、便携式媒体播放器(PMP)到个人导航设备(PND)、数码机顶盒(STB)到笔记本电脑。Moblin.org项目由Intel于2007年7月正式启动,它的目的是推动此类设备所需的最新技术的发展。 相似文献
57.
Fault diagnosis is very important for modern production technology and has received increasing theoretical and practical attention during the last few years. This paper presents a model-based diagnostic method for industrial systems. An online, real-time, deep knowledge based fault detection system has been developed by combining different development environments and tools. The system diagnoses, predicts and compensates faults by coupling symbolic and numerical data in a new environment suitable for the interaction of different sources of knowledge and has been successfully implemented and tested on a real hydraulic system. 相似文献
58.
The complex shear acoustic impedance of liquid He II has been measured at frequenciesf(=/2) of 20.5, 34.1, and 47.8 MHz from 30 mK to the -point T (2.176 K). The impedanceZ was found from the temperature dependence of the quality factor and the resonant frequency of a thickness shear mode quartz crystal resonator immersed in the liquid. The relationship for a hydrodynamic viscous liquidZ(T)=(1–i)(f
n
)1/2 was used to measure the temperature dependence of the viscosity (T) using tabulated values of the normal fluid density
n
(T). Deviations from hydrodynamic behavior occurred when the viscous penetration depth was less than the superfluid healing length, the phonon mean free path, and the roton mean free path. Near the -point,Z(T)/Z(T) was frequency dependent and a value for the superfluid healing lengtha=(0.10±0.01)–2/3 nm was found, where =(T–T)/T. The effects of van der Waals forces near the crystal surface were also observed and a layer model was used to interpret the measurements. Below 1.8 K only rotons contribute significantly toZ and we determined the roton relaxation time as
r
=8.5×10–14
T
–1/3 exp (8.65/T) sec. Below 1.2 K,
r
>1 and we investigated the breakdown of hydrodynamics in this region. ForT<0.6 K the resonant frequency of the crystals decreased by f/f=2×10–7, but the origin of this effect is not yet known.Financial support provided by the SERC, Bedford College, and the Central Research Fund, University of London. 相似文献
59.
Geoffrey Levine Ugur Kuter Antons Rebguns Derek Green Diana Spears 《Computational Intelligence》2012,28(3):329-357
We present a Bayesian approach to learning flexible safety constraints and subsequently verifying whether plans satisfy these constraints. Our approach, called the Safety Constraint Learner/Checker (SCLC), infers safety constraints from a single expert demonstration trace and minimal background knowledge, and applies these constraints to the solutions proposed by multiple planning agents in an integrated and heterogeneous ensemble. The SCLC calculates how much to blame plan fragments (partial solutions) generated by the individual planning agents. This information is used when composing these fragments into a final overall plan. In particular, fragments whose safety violations exceed a threshold are rejected. This facilitates the generation of safe plans. We have integrated the SCLC within the Generalized Integrated Learning Architecture, which was designed for Defense Advanced Research Projects Agency (DARPA)’s Integrated Learning (IL) program. The main goal of the IL program is to promote the development and success of sophisticated systems that learn to solve challenging real‐world problems based on a simple demonstration by a human expert and exiguous domain knowledge. We present experimental results showing the advantages of the SCLC on two multiagent problem‐solving tasks that were benchmark applications in DARPA’s IL program. 相似文献
60.
Jan Novák Derek Nowrouzezahrai Carsten Dachsbacher Wojciech Jarosz 《Computer Graphics Forum》2012,31(4):1407-1413
A recent technique that forms virtual ray lights (VRLs) from path segments in media, reduces the artifacts common to VPL approaches in participating media, however, distracting singularities still remain. We present Virtual Beam Lights (VBLs), a progressive many‐lights algorithm for rendering complex indirect transport paths in, from, and to media. VBLs are efficient and can handle heterogeneous media, anisotropic scattering, and moderately glossy surfaces, while provably converging to ground truth. We inflate ray lights into beam lights with finite thicknesses to eliminate the remaining singularities. Furthermore, we devise several practical schemes for importance sampling the various transport contributions between camera rays, light rays, and surface points. VBLs produce artifact‐free images faster than VRLs, especially when glossy surfaces and/or anisotropic phase functions are present. Lastly, we employ a progressive thickness reduction scheme for VBLs in order to render results that converge to ground truth. 相似文献