全文获取类型
收费全文 | 13951篇 |
免费 | 2059篇 |
国内免费 | 1355篇 |
专业分类
电工技术 | 1060篇 |
综合类 | 1863篇 |
化学工业 | 1296篇 |
金属工艺 | 612篇 |
机械仪表 | 807篇 |
建筑科学 | 1474篇 |
矿业工程 | 271篇 |
能源动力 | 246篇 |
轻工业 | 420篇 |
水利工程 | 367篇 |
石油天然气 | 534篇 |
武器工业 | 237篇 |
无线电 | 2489篇 |
一般工业技术 | 1645篇 |
冶金工业 | 423篇 |
原子能技术 | 83篇 |
自动化技术 | 3538篇 |
出版年
2024年 | 86篇 |
2023年 | 262篇 |
2022年 | 478篇 |
2021年 | 526篇 |
2020年 | 538篇 |
2019年 | 523篇 |
2018年 | 499篇 |
2017年 | 582篇 |
2016年 | 685篇 |
2015年 | 753篇 |
2014年 | 881篇 |
2013年 | 1130篇 |
2012年 | 1062篇 |
2011年 | 1117篇 |
2010年 | 774篇 |
2009年 | 779篇 |
2008年 | 825篇 |
2007年 | 948篇 |
2006年 | 774篇 |
2005年 | 654篇 |
2004年 | 526篇 |
2003年 | 493篇 |
2002年 | 388篇 |
2001年 | 384篇 |
2000年 | 291篇 |
1999年 | 264篇 |
1998年 | 190篇 |
1997年 | 154篇 |
1996年 | 135篇 |
1995年 | 120篇 |
1994年 | 95篇 |
1993年 | 71篇 |
1992年 | 61篇 |
1991年 | 49篇 |
1990年 | 46篇 |
1989年 | 39篇 |
1988年 | 23篇 |
1987年 | 33篇 |
1986年 | 15篇 |
1985年 | 23篇 |
1984年 | 17篇 |
1983年 | 13篇 |
1982年 | 18篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1976年 | 3篇 |
1963年 | 3篇 |
1961年 | 2篇 |
1959年 | 5篇 |
1956年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Danny Barash Tamar Schlick Moshe Israeli Ron Kimmel 《Journal of Mathematical Imaging and Vision》2003,19(1):33-48
Operator splitting is a powerful concept used in many diversed fields of applied mathematics for the design of effective numerical schemes. Following the success of the additive operator splitting (AOS) in performing an efficient nonlinear diffusion filtering on digital images, we analyze the possibility of using multiplicative operator splittings to process images from different perspectives.We start by examining the potential of using fractional step methods to design a multiplicative operator splitting as an alternative to AOS schemes. By means of a Strang splitting, we attempt to use numerical schemes that are known to be more accurate in linear diffusion processes and apply them on images. Initially we implement the Crank-Nicolson and DuFort-Frankel schemes to diffuse noisy signals in one dimension and devise a simple extrapolation that enables the Crank-Nicolson to be used with high accuracy on these signals. We then combine the Crank-Nicolson in 1D with various multiplicative operator splittings to process images. Based on these ideas we obtain some interesting results. However, from the practical standpoint, due to the computational expenses associated with these schemes and the questionable benefits in applying them to perform nonlinear diffusion filtering when using long timesteps, we conclude that AOS schemes are simple and efficient compared to these alternatives.We then examine the potential utility of using multiple timestep methods combined with AOS schemes, as means to expedite the diffusion process. These methods were developed for molecular dynamics applications and are used efficiently in biomolecular simulations. The idea is to split the forces exerted on atoms into different classes according to their behavior in time, and assign longer timesteps to nonlocal, slowly-varying forces such as the Coulomb and van der Waals interactions, whereas the local forces like bond and angle are treated with smaller timesteps. Multiple timestep integrators can be derived from the Trotter factorization, a decomposition that bears a strong resemblance to a Strang splitting. Both formulations decompose the time propagator into trilateral products to construct multiplicative operator splittings which are second order in time, with the possibility of extending the factorization to higher order expansions. While a Strang splitting is a decomposition across spatial dimensions, where each dimension is subsequently treated with a fractional step, the multiple timestep method is a decomposition across scales. Thus, multiple timestep methods are a realization of the multiplicative operator splitting idea. For certain nonlinear diffusion coefficients with favorable properties, we show that a simple multiple timestep method can improve the diffusion process. 相似文献
12.
提出以视觉跟踪为基础并引入通信进行多机器人的编队控制方法,根据需要编写了一种新的通信协议,采用闭环l-Φ实现编队算法.这种多机器人编队控制避免了视觉系统的局限,能够更好地在复杂未知环境中协作完成任务,解决了编队控制的无反馈和实时性不高的问题,使得机器人能够准确迅速地进行跟踪和通信编队,一起顺利达到目标点.试验结果证明了该方法的有效性. 相似文献
13.
Quantification of secondary structure prediction improvement using multiple alignments 总被引:9,自引:0,他引:9
Levin Jonathan M.; Pascarella Stefano; Argos Patrick; Garnier Jean 《Protein engineering, design & selection : PEDS》1993,6(8):849-854
The use of multiple sequence alignments for secondary structurepredictions is analysed. Seven different protein families, containingonly sequences of known structure, were considered to providea range of alignment and prediction conditions. Using alignmentsobtained by spatial superposition of main chain atoms in knowntertiary protein structures allowed a mean of 8% in secondarystructure prediction accuracy, when compared to those obtainedfrom the individual sequences. Substitution of these alignmentsby those determined directly from an automated sequence alignmentalgorithm showed variations in the prediction accuracy whichcorrelated with the quality of the multiple alignments and distanceof the primary sequence. Secondary structure predictions canbe reliably improved using alignments from an automatic alignmentprocedure with a mean increase of 6.87percnt;, giving an overallprediction accuracy of 68.5%, if there is a minimum of 25% sequenceidentity between all sequences in a family. 相似文献
14.
A study has been made of ‘combined’ joints consisting of mechanical fastening and adhesive bonding between rigid adherends. The mechanical characteristics of such ‘hybrid’ butt and lap shear joints have been derived by theoretical analysis. Results from experimental tests in combined joints giver reasonable agreement with the theoretical equations relating joint load to deformation. 相似文献
15.
16.
The objective of this study was to determine how the fracture of adhesive joints depends on elastic beam parameters describing the adherends and the applied loads. The basic specimen geometry was the cracked lap shear joint constructed of aluminium alloy with various adherend and bondline thicknesses. Loads were applied in different combinations of bending, tension and shear to generate a failure envelope for each adhesive and specimen geometry. It was found that crack propagation for precracked specimens occured at a critical strain energy release rate but was also a function of the GI/GII ratio and the bondline thickness. The experiments also showed that the loads required to propagate a crack in a precracked specimen were always lower than the loads required to break the fillet. Hence, by treating uncracked joints as being cracked, where the fictitious crack tip is assumed to coincide with the location of the fillet, a conservative estimate of the failure load is obtained. 相似文献
17.
当前基于迭代最近点拼接的同时定位与建图算法,存在误差积累、无法满足大范围定位精度的缺陷。为此,提出一种融合多帧迭代最近点和图优化的算法。在时域上处理点云拼接问题,将单帧迭代最近点算法推广到多帧进行最近点迭代,提取同一地点在不同时刻的数据特征,形成多个封闭循环,再运用基于最小二乘的图优化方法对点云拼接后的全网数据进行全局优化,消除累计误差,提升整体的定位精度。采用鲁巷和密歇根的数据进行测试,结果表明,该方法在一定程度上减少了匹配误差,平均误差为1.0m,最小误差为0.2m,可以满足大范围同步定位与建图的精度需求。 相似文献
18.
针对多属性群决策中的共识问题, 提出两种使群体达成共识的方法. 假设群体决策的结果以从个体偏好通过集结得到的群体偏好为基础, 在使用算术加权集结算子和几何加权集结算子的条件下, 分别设计相应的共识达成算法, 并对算法的收敛性进行分析. 与已有方法相比, 所提出算法能够体现决策个体的差异和决策个体对群体的影响. 通过某市政图书馆空调系统安装方案的选择表明了所提出方法的合理性和可行性.
相似文献19.
20.