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951.
The computation of intrinsic, geodesic distances and geodesic paths on surfaces is a fundamental low‐level building block in countless Computer Graphics and Geometry Processing applications. This demand led to the development of numerous algorithms – some for the exact, others for the approximative computation, some focussing on speed, others providing strict guarantees. Most of these methods are designed for computing distances according to the standard Riemannian metric induced by the surface's embedding in Euclidean space. Generalization to other, especially anisotropic, metrics – which more recently gained interest in several application areas – is not rarely hampered by fundamental problems. We explore and discuss possibilities for the generalization and extension of well‐known methods to the anisotropic case, evaluate their relative performance in terms of accuracy and speed, and propose a novel algorithm, the Short‐Term Vector Dijkstra. This algorithm is strikingly simple to implement and proves to provide practical accuracy at a higher speed than generalized previous methods. 相似文献
952.
Capturing fine details of turbulence on a coarse grid is one of the main tasks in real‐time fluid simulation. Existing methods for doing this have various limitations. In this paper, we propose a new turbulence method that uses a refined second vorticity confinement method, referred to as robust second vorticity confinement, and a synthesis scheme to create highly turbulent effects from coarse grid. The new technique is sufficiently stable to efficiently produce highly turbulent flows, while allowing intuitive control of vortical structures. Second vorticity confinement captures and defines the vortical features of turbulence on a coarse grid. However, due to the stability problem, it cannot be used to produce highly turbulent flows. In this work, we propose a robust formulation to improve the stability problem by making the positive diffusion term to vary with helicity adaptively. In addition, we also employ our new method to procedurally synthesize the high‐resolution flow fields. As shown in our results, this approach produces stable high‐resolution turbulence very efficiently. 相似文献
953.
Hai Jin Xiao Ling Shadi Ibrahim Wenzhi Cao Song Wu Gabriel Antoniu 《Future Generation Computer Systems》2013,29(8):2222-2238
While virtualization enables multiple virtual machines (VMs)—with multiple operating systems and applications—to run within a physical server, it also complicates resource allocations trying to guarantee Quality of Service (QoS) requirements of the diverse applications running within these VMs. As QoS is crucial in the cloud, considerable research efforts have been directed towards CPU, memory and network allocations to provide effective QoS to VMs, but little attention has been devoted to disk resource allocation.This paper presents the design and implementation of Flubber, a two-level scheduling framework that decouples throughput and latency allocation to provide QoS guarantees to VMs while maintaining high disk utilization. The high-level throughput control regulates the pending requests from the VMs with an adaptive credit-rate controller, in order to meet the throughput requirements of different VMs and ensure performance isolation. Meanwhile, the low-level latency control, by the virtue of the batch and delay earliest deadline first mechanism (BD-EDF), re-orders all pending requests from VMs based on their deadlines, and batches them to disk devices taking into account the locality of accesses across VMs. We have implemented Flubber and made extensive evaluations on a Xen-based host. The results show that Flubber can simultaneously meet the different service requirements of VMs while improving the efficiency of the physical disk. The results also show improvement of up to 25% in the VM performance over state-of-art approaches: for example, in contract to the default Xen disk I/O scheduler—Completely Fair Queueing (CFQ)—besides achieving the desired QoS of each VM, Flubber speeds up the sequential and random reads by 17% and 25%, respectively, due to the efficient physical disk utilization. 相似文献
954.
We present anefficient algorithm for determining an aesthetically pleasing shape boundary connecting all the points in a given unorganized set of 2D points, with no other information than point coordinates. By posing shape construction as a minimisation problem which follows the Gestalt laws, our desired shape is non‐intersecting, interpolates all points and minimizes a criterion related to these laws. The basis for our algorithm is an initial graph, an extension of the Euclidean minimum spanning tree but with no leaf nodes, called as the minimum boundary complex . and can be expressed similarly by parametrizing a topological constraint. A close approximation of , termed can be computed fast using a greedy algorithm. is then transformed into a closed interpolating boundary in two steps to satisfy ’s topological and minimization requirements. Computing exactly is an NP (Non‐Polynomial)‐hard problem, whereas is computed in linearithmic time. We present many examples showing considerable improvement over previous techniques, especially for shapes with sharp corners. Source code is available online. 相似文献
955.
We present a novel methodology that utilizes four‐dimensional (4D) space deformation to simulate a magnification lens on versatile volume datasets and textured solid models. Compared with other magnification methods (e.g. geometric optics, mesh editing), 4D differential geometry theory and its practices are much more flexible and powerful for preserving shape features (i.e. minimizing angle distortion), and easier to adapt to versatile solid models. The primary advantage of 4D space lies at the following fact: we can now easily magnify the volume of regions of interest (ROIs) from the additional dimension, while keeping the rest region unchanged. To achieve this primary goal, we first embed a 3D volumetric input into 4D space and magnify ROIs in the fourth dimension. Then we flatten the 4D shape back into 3D space to accommodate other typical applications in the real 3D world. In order to enforce distortion minimization, in both steps we devise the high‐dimensional geometry techniques based on rigorous 4D geometry theory for 3D/4D mapping back and forth to amend the distortion. Our system can preserve not only focus region, but also context region and global shape. We demonstrate the effectiveness, robustness and efficacy of our framework with a variety of models ranging from tetrahedral meshes to volume datasets. 相似文献
956.
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959.
详细论述了一种基于单片机为核心的四轴飞行器无刷电机驱动系统,主要包括大功率驱动模块,反向电动势检测模块,PWM输出模块,转速测量模块等四部分。系统可通过I2C通讯接受到主控板发来的信号进行相应的调速,减少控制周期,提高电机的响应频率。 相似文献
960.
Pascal Gautron Cyril Delalandre Jean‐Eudes Marvie Pascal Lecocq 《Computer Graphics Forum》2013,32(7):305-314
We introduce Boundary‐Aware Extinction Maps for interactive rendering of massive heterogeneous volumetric datasets. Our approach is based on the projection of the extinction along light rays into a boundary‐aware function space, focusing on the most relevant sections of the light paths. This technique also provides an alternative representation of the set of participating media, allowing scattering simulation methods to be applied on arbitrary volume representations. Combined with a simple out‐of‐core rendering framework, Boundary‐Aware Extinction Maps are valuable tools for interactive applications as well as production previsualization and rendering. 相似文献