全文获取类型
收费全文 | 57986篇 |
免费 | 7114篇 |
国内免费 | 3920篇 |
专业分类
电工技术 | 4745篇 |
技术理论 | 3篇 |
综合类 | 5165篇 |
化学工业 | 8708篇 |
金属工艺 | 3399篇 |
机械仪表 | 3774篇 |
建筑科学 | 4778篇 |
矿业工程 | 1874篇 |
能源动力 | 1748篇 |
轻工业 | 6066篇 |
水利工程 | 1407篇 |
石油天然气 | 2540篇 |
武器工业 | 712篇 |
无线电 | 6939篇 |
一般工业技术 | 5617篇 |
冶金工业 | 2023篇 |
原子能技术 | 549篇 |
自动化技术 | 8973篇 |
出版年
2024年 | 453篇 |
2023年 | 1437篇 |
2022年 | 2848篇 |
2021年 | 3611篇 |
2020年 | 2518篇 |
2019年 | 1959篇 |
2018年 | 2066篇 |
2017年 | 2194篇 |
2016年 | 1913篇 |
2015年 | 2901篇 |
2014年 | 3460篇 |
2013年 | 3724篇 |
2012年 | 4584篇 |
2011年 | 4710篇 |
2010年 | 4000篇 |
2009年 | 3873篇 |
2008年 | 3671篇 |
2007年 | 3366篇 |
2006年 | 2967篇 |
2005年 | 2418篇 |
2004年 | 1799篇 |
2003年 | 1641篇 |
2002年 | 1816篇 |
2001年 | 1488篇 |
2000年 | 965篇 |
1999年 | 666篇 |
1998年 | 374篇 |
1997年 | 324篇 |
1996年 | 249篇 |
1995年 | 219篇 |
1994年 | 178篇 |
1993年 | 147篇 |
1992年 | 110篇 |
1991年 | 83篇 |
1990年 | 55篇 |
1989年 | 40篇 |
1988年 | 40篇 |
1987年 | 30篇 |
1986年 | 26篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 18篇 |
1981年 | 11篇 |
1980年 | 22篇 |
1979年 | 9篇 |
1978年 | 1篇 |
1959年 | 2篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Retrieving soil temperature profile by assimilating MODIS LST products with ensemble Kalman filter 总被引:7,自引:0,他引:7
Proper estimation of initial state variables and model parameters are vital importance for determining the accuracy of numerical model prediction. In this work, we develop a one-dimensional land data assimilation scheme based on ensemble Kalman filter and Common Land Model version 3.0 (CoLM). This scheme is used to improve the estimation of soil temperature profile. The leaf area index (LAI) is also updated dynamically by MODIS LAI production and the MODIS land surface temperature (LST) products are assimilated into CoLM. The scheme was tested and validated by observations from four automatic weather stations (BTS, DRS, MGS, and DGS) in Mongolian Reference Site of CEOP during the period of October 1, 2002 to September 30, 2003. Results indicate that data assimilation improves the estimation of soil temperature profile about 1 K. In comparison with simulation, the assimilation results of soil heat fluxes also have much improvement about 13 W m− 2 at BTS and DGS and 2 W m− 2 at DRS and MGS, respectively. In addition, assimilation of MODIS land products into land surface model is a practical and effective way to improve the estimation of land surface variables and fluxes. 相似文献
993.
Real-time modeling and rendering of raining scenes 总被引:1,自引:0,他引:1
Wang Changbo Zhangye Wang Xin Zhang Lei Huang Zhiliang Yang Qunsheng Peng 《The Visual computer》2008,24(7-9):605-616
Real-time modeling and rendering of a realistic raining scene is a challenging task. This is because the visual effects of raining involve complex physical mechanisms, reflecting the physical, optical and statistical characteristics of raindrops, etc. In this paper, we propose a set of new methods to model the raining scene according to these physical mechanisms. Firstly, by adhering to the physical characteristic of raindrops, we model the shapes, movements and intensity of raindrops in different situations. Then, based on the principle of human vision persistence, we develop a new model to calculate the shapes and appearances of rain streaks. To render the foggy effect in a raining scene, we present a statistically based multi-particles scattering model exploiting the particle distribution coherence along each viewing ray. By decomposing the conventional equations of single scattering of non-isotropic light into two parts with the physical parameter independent part precalculated, we are able to render the respective scattering effect in real time. We also realize diffraction of lamps, wet ground, the ripples on puddles in the raining scene, as well as the beautiful rainbow. By incorporating GPU acceleration, our approach permits real-time walkthrough of various raining scenes with average 20 fps rendering speed and the results are quite satisfactory. 相似文献
994.
<正> 带有触摸屏界面的液晶显示屏(LCD)为众多消费电子产品提供了出色的易操作性,也成为越来越多的消费电子设备的必备组件。为了帮助在工业人机界面(HMI)应用中加快基于触摸的控制的部署,飞思卡尔推出了具有集成触摸屏控制器的 ColdFire~LCD 微处理器。这个先进的32位器件为那些需要出色性能、集成和设计灵活性的人控商业和工业应用提供了非常理想的嵌入式 相似文献
995.
996.
By splitting a large broadcast message into segments and broadcasting the segments in a pipelined fashion, pipelined broadcast can achieve high performance in many systems. In this paper, we investigate techniques for efficient pipelined broadcast on clusters connected by multiple Ethernet switches. Specifically, we develop algorithms for computing various contention-free broadcast trees that are suitable for pipelined broadcast on Ethernet switched clusters, extend the parametrized LogP model for predicting appropriate segment sizes for pipelined broadcast, show that the segment sizes computed based on the model yield high performance, and evaluate various pipelined broadcast schemes through experimentation on Ethernet switched clusters with various topologies. The results demonstrate that our techniques are practical and efficient for contemporary fast Ethernet and Giga-bit Ethernet clusters. 相似文献
997.
Ahmad Faraj Pitch Patarasuk Xin Yuan 《International journal of parallel programming》2008,36(4):426-453
Clusters of workstations employ flexible topologies: regular, irregular, and hierarchical topologies have been used in such
systems. The flexibility poses challenges for developing efficient collective communication algorithms since the network topology
can potentially have a strong impact on the communication performance. In this paper, we consider the all-to-all broadcast
operation on clusters with cut-through and store-and-forward switches. We show that near-optimal all-to-all broadcast on a
cluster with any topology can be achieved by only using the links in a spanning tree of the topology when the message size
is sufficiently large. The result implies that increasing network connectivity beyond the minimum tree connectivity does not
improve the performance of the all-to-all broadcast operation when the most efficient topology specific algorithm is used.
All-to-all broadcast algorithms that achieve near-optimal performance are developed for clusters with cut-through and clusters
with store-and-forward switches. We evaluate the algorithms through experiments and simulations. The empirical results confirm
our theoretical finding. 相似文献
998.
This paper describes a new aerial image segmentation algorithm by level set. The non-subsampled contourlet transform (NSCT)
is selected to represent the image features for the classification of man-made object. NSCT can avoid pseudo-Gibbs phenomena
around singularities during the process of image denoising, owing to the properties of shift-invariant. NSCT also enriches
the set of basis functions which makes it possible to extract some critical signal features. The optimization of basis selection
is applied in the NSCT to ensure the decomposition based on the maximum information content. Another kind of feature named
RMSerror is also extracted from fBm model. Then a modified Mumford-Shah model which comprises the NSCT features and RMSerror features extracted from the aerial images is built to segment the aerial image by a necessary level set evolution. At last
the proposed method is proven to be effective by the results of experiments. 相似文献
999.
在移动自组网(MANET)与Internet互联的网络结构中,由于移动节点的能量是影响网络性能的重要因素,因此必须考虑节点的负载及能量问题.本文针对这些问题提出一种基于负载均衡和不对称多径传输的路由机制LBAMR(Load-Balanced and Asymmetrical Multipath Routing),并用NS2软件对其进行了仿真.仿真结果表明,该路由机制能够有效地均衡网络负载并保护网络中的低能量节点,尽可能地延长网络寿命. 相似文献
1000.
在无线传感器网络的拓扑控制(TC)中,基于Cell的TC算法被认为是一类可以节省传感器节点能量并延长网络生命周期的方法,但是其需要较多的骨干网节点并且无法保证连通性.通过分析现今算法的内在局限性,提出了一种1-Con思想:当一个Cell的头节点被加入当前骨干网时,所有其可以连接的Cell使用该节点连入拓扑结构,然后此新骨干网递归地继续扩大.基于此思想,设计了一种基于可连Cell的拓扑控制算(CCTC),并从理论上证明:1)CCTC可以保证其所形成的拓扑结构维持网络连通;2)每一轮用于形成骨干网的工作节点非常少.CCTC的计算复杂度是线性的,空间复杂度和信息交换量都是常数量级.仿真实验同样显示,CCTC可以在提供良好鲁棒性和较少的消息交换的情况下,更有效地节省节点能耗并延长网络生命周期. 相似文献