全文获取类型
收费全文 | 37108篇 |
免费 | 3730篇 |
国内免费 | 1892篇 |
专业分类
电工技术 | 2221篇 |
技术理论 | 1篇 |
综合类 | 2531篇 |
化学工业 | 6377篇 |
金属工艺 | 1680篇 |
机械仪表 | 1760篇 |
建筑科学 | 2971篇 |
矿业工程 | 842篇 |
能源动力 | 1031篇 |
轻工业 | 3646篇 |
水利工程 | 756篇 |
石油天然气 | 1234篇 |
武器工业 | 283篇 |
无线电 | 4327篇 |
一般工业技术 | 4730篇 |
冶金工业 | 2425篇 |
原子能技术 | 388篇 |
自动化技术 | 5527篇 |
出版年
2024年 | 226篇 |
2023年 | 837篇 |
2022年 | 1479篇 |
2021年 | 2040篇 |
2020年 | 1404篇 |
2019年 | 1190篇 |
2018年 | 1279篇 |
2017年 | 1363篇 |
2016年 | 1225篇 |
2015年 | 1481篇 |
2014年 | 1932篇 |
2013年 | 2482篇 |
2012年 | 2386篇 |
2011年 | 2569篇 |
2010年 | 2051篇 |
2009年 | 2025篇 |
2008年 | 1968篇 |
2007年 | 1863篇 |
2006年 | 1690篇 |
2005年 | 1439篇 |
2004年 | 1099篇 |
2003年 | 1041篇 |
2002年 | 1091篇 |
2001年 | 912篇 |
2000年 | 688篇 |
1999年 | 613篇 |
1998年 | 571篇 |
1997年 | 421篇 |
1996年 | 404篇 |
1995年 | 287篇 |
1994年 | 257篇 |
1993年 | 212篇 |
1992年 | 188篇 |
1991年 | 156篇 |
1990年 | 126篇 |
1989年 | 150篇 |
1988年 | 114篇 |
1987年 | 106篇 |
1986年 | 114篇 |
1985年 | 106篇 |
1984年 | 119篇 |
1983年 | 94篇 |
1982年 | 92篇 |
1981年 | 96篇 |
1980年 | 81篇 |
1979年 | 71篇 |
1978年 | 66篇 |
1977年 | 69篇 |
1976年 | 87篇 |
1975年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
991.
992.
993.
994.
We propose an adaptive and energy-efficient TDMA-based MAC protocol that significantly reduces energy consumption in the network, while efficiently handling network traffic load variations and optimizing channel utilization through a timeslot stealing mechanism and a timeslot reassignment procedure. We have analytically derived the average delay performance of our MAC protocol, with and without the timeslot stealing mechanism. Our delay model, validated via simulations, shows that the timeslot stealing mechanism can substantially improve the protocol throughput in scenarios with varying and asymmetric traffic patterns. Evaluation results show that the timeslot reassignment procedure is efficient in handling the longer timescale changes in the traffic load, while the timeslot stealing mechanism is better in handling the shorter timescale changes in the traffic patterns. 相似文献
995.
Andrew J. Berry Jeremy Howitt Da-Wei Gu Ian Postlethwaite 《Journal of Intelligent and Robotic Systems》2012,66(4):477-494
As the complexity of an unmanned vehicle’s operational environment increases so does the need to consider the obstacle space
continually, and this is aided by splitting the motion planning functionality into distinct global and local layers. This
paper presents a new continuous local motion planning framework, where the output and control space elements of the traditional
receding horizon control problem are separated into distinct layers. This separation reduces the complexity of the local motion
trajectory optimisation, enabling faster design and increased horizon length. The focus of this paper is on the output space
component of this framework. Bezier polynomial functions are used to describe local motion trajectories which are constrained
to vehicle performance limits and optimised to track a global trajectory. Development and testing is in simulation, targeted
at a nonlinear model of a quadrotor unmanned air vehicle. The defined framework is used to provide situation-aware tracking of a global trajectory in the presence of static and dynamic obstacles, as well as realistic turbulence and gusts.
Also demonstrated is the immediate-term decentralised deconfliction of multiple unmanned vehicles, and multiple formations of unmanned vehicles. 相似文献
996.
Orientation pattern is an important feature for characterizing fingerprint and plays critical roles in fingerprint recognition and fingerprint classification. This paper proposes a framework for modeling the fingerprint orientation field based on the variational principle, where the orientation pattern can be estimated through solving the associated Euler–Lagrange equation. Compared with existing methods, our proposed method has the following features. Firstly, it does not require any prior information about the structure of the acquired fingerprint, such as location of singular point(s). Secondly, it explicitly provides freedom for modeling the singularity in the orientation field. Thirdly, it has less number of parameters. Comparison has been made with respect to state-of-the-arts in fingerprint orientation modeling in terms of modeling accuracy, fingerprint enhancement and singular point detection. Advantages of the proposed method are demonstrated. 相似文献
997.
Arterial bypass grafts tend to fail after some years due to the development of intimal thickening (restenosis). Non-uniform hemodynamics following a bypass operation contributes to restenosis and bypass failure can occur due to the focal development of anastomotic intimal hyperplasia. Additionally, surgical injury aggravated by compliance mismatch between the graft and artery has been suggested as an initiating factor for progress of wall thickening along the suture line Vascular grafts that are small in diameter tend to occlude rapidly. Computational fluid dynamics (CFD) methods have been effectively used to simulate the physical and geometrical parameters characterizing the hemodynamics of various arteries and bypass configurations. The effects of such changes on the pressure and flow characteristics as well as the wall shear stress during a cardiac cycle can be simulated. Recently, utilization of fluid and structure interactions have been used to determine fluid flow parameters and structure forces including stress and strains relationships under steady and transient conditions. In parallel to this, experimental diagnostics techniques such as Laser Doppler Anemometry, Particle Image Velocimetry, Doppler Guide wire and Magnetic Resonance Imaging have been used to provide essential information and to validate the numerical results. Moreover, clinical imaging techniques such as magnetic resonance or computed tomography have assisted considerably in gaining a detailed patient-specific picture of the blood flow and structure dynamics. This paper gives a review of recent numerical investigations of various configurations of coronary artery bypass grafts (CABG). In addition, the paper ends with a summary of the findings and the future directions. 相似文献
998.
In this paper, we seek to eliminate the noise caused by caustic paths during progressive Monte Carlo path tracing. We employ a filtering strategy over path space, handling each subspace using specialized derivations of path tracing and progressive photon mapping. Evaluating diffuse paths with path tracing allows the use of sample stratification over both pixels and the image as a whole, whilst sharp detailed caustics are produced using progressive photon mapping. This is an efficient, low noise progressive algorithm with vanishing bias combining the advantages of both Monte Carlo methods, and particle tracing. 相似文献
999.
In many applications, the properties of an object being modeled are stored as labels on vertices or edges of a graph. In this paper, we consider succinct representation of labeled graphs. Our main results are the succinct representations of labeled and multi-labeled graphs (we consider planar triangulations, planar graphs and k-page graphs) to support various label queries efficiently. The additional space cost to store the labels is essentially the information-theoretic minimum. As far as we know, our representations are the first succinct representations of labeled graphs. We also have two preliminary results to achieve the main contribution. First, we design a succinct representation of unlabeled planar triangulations to support the rank/select of edges in ccw (counter clockwise) order in addition to the other operations supported in previous work. Second, we design a succinct representation for a k-page graph when k is large to support various navigational operations more efficiently. In particular, we can test the adjacency of two vertices in O(lg?k) time, while previous work uses O(k) time. 相似文献
1000.
Modeling and experimental investigation for electrolytic corrosion prevention in high frequency micro EDM using deionized water 总被引:1,自引:0,他引:1
The characteristics of the prevention of electrolytic corrosion during micro electrical discharge machining (EDM) using deionized water and high frequency bipolar pulse were investigated. Electrolytic corrosion during micro EDM using deionized water was analyzed using an equivalent electrical circuit based on the electrical double layer theory. Based on the analysis and experimental verification, a narrow positive pulse duration should be provided to the workpiece to prevent corrosion. A negative voltage with zero average applied voltage (Vavg, app) is also essential for this purpose. If Vavg, app is positive or negative, electrolytic corrosion occurs on the workpiece or tool, respectively. Micro holes and 3D structures without corrosion were successfully fabricated using a high frequency bipolar pulse with a pulse duration of 0.2?μs and a period of 1?μs, as well as Vavg, app?=?0?V. 相似文献