全文获取类型
收费全文 | 29303篇 |
免费 | 2601篇 |
国内免费 | 1309篇 |
专业分类
电工技术 | 4555篇 |
技术理论 | 2篇 |
综合类 | 2840篇 |
化学工业 | 2019篇 |
金属工艺 | 2240篇 |
机械仪表 | 3914篇 |
建筑科学 | 1502篇 |
矿业工程 | 1465篇 |
能源动力 | 1718篇 |
轻工业 | 954篇 |
水利工程 | 637篇 |
石油天然气 | 1131篇 |
武器工业 | 406篇 |
无线电 | 2291篇 |
一般工业技术 | 1866篇 |
冶金工业 | 2459篇 |
原子能技术 | 163篇 |
自动化技术 | 3051篇 |
出版年
2024年 | 91篇 |
2023年 | 276篇 |
2022年 | 636篇 |
2021年 | 648篇 |
2020年 | 811篇 |
2019年 | 572篇 |
2018年 | 610篇 |
2017年 | 807篇 |
2016年 | 928篇 |
2015年 | 1031篇 |
2014年 | 1766篇 |
2013年 | 1375篇 |
2012年 | 2201篇 |
2011年 | 2382篇 |
2010年 | 1709篇 |
2009年 | 1657篇 |
2008年 | 1527篇 |
2007年 | 2048篇 |
2006年 | 1884篇 |
2005年 | 1659篇 |
2004年 | 1277篇 |
2003年 | 1358篇 |
2002年 | 1064篇 |
2001年 | 1024篇 |
2000年 | 816篇 |
1999年 | 647篇 |
1998年 | 475篇 |
1997年 | 420篇 |
1996年 | 343篇 |
1995年 | 269篇 |
1994年 | 220篇 |
1993年 | 136篇 |
1992年 | 108篇 |
1991年 | 74篇 |
1990年 | 62篇 |
1989年 | 78篇 |
1988年 | 43篇 |
1987年 | 34篇 |
1986年 | 16篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1965年 | 7篇 |
1964年 | 10篇 |
1962年 | 10篇 |
1960年 | 6篇 |
1959年 | 9篇 |
1958年 | 6篇 |
1956年 | 5篇 |
1955年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Small object detection is challenging and far from satisfactory. Most general object detectors suffer from two critical issues with small objects: (1) Feature extractor based on classification network cannot express the characteristics of small objects reasonably due to insufficient appearance information of targets and a large amount of background interference around them. (2) The detector requires a much higher location accuracy for small objects than for general objects. This paper proposes an effective and efficient small object detector YOLSO to address the above problems. For feature representation, we analyze the drawbacks in previous backbones and present a Half-Space Shortcut(HSSC) module to build a background-aware backbone. Furthermore, a coarse-to-fine Feature Pyramid Enhancement(FPE) module is introduced for layer-wise aggregation at a granular level to enhance the semantic discriminability. For loss function, we propose an exponential L1 loss to promote the convergence of regression, and a focal IOU loss to focus on prime samples with high classification confidence and high IOU. Both of them significantly improves the location accuracy of small objects. The proposed YOLSO sets state-of-the-art results on two typical small object datasets, MOCOD and VeDAI, at a speed of over 200 FPS. In the meantime, it also outperforms the baseline YOLOv3 by a wide margin on the common COCO dataset. 相似文献
2.
3.
对鞍钢股份无缝钢管厂连轧机前毛管坯横移装置存在的设计缺陷进行了分析,并提出改进方案,将原横移装置由高架轨道横移机构及上下升降链传动装置,改进为地面轨道横移系统及同步旋转臂实现取管、放管过程。实施后消除了生产故障,缩短了轧制周期,降低生产成本。 相似文献
4.
Data fitting with B-splines is a challenging problem in reverse engineering for CAD/CAM, virtual reality, data visualization, and many other fields. It is well-known that the fitting improves greatly if knots are considered as free variables. This leads, however, to a very difficult multimodal and multivariate continuous nonlinear optimization problem, the so-called knot adjustment problem. In this context, the present paper introduces an adapted elitist clonal selection algorithm for automatic knot adjustment of B-spline curves. Given a set of noisy data points, our method determines the number and location of knots automatically in order to obtain an extremely accurate fitting of data. In addition, our method minimizes the number of parameters required for this task. Our approach performs very well and in a fully automatic way even for the cases of underlying functions requiring identical multiple knots, such as functions with discontinuities and cusps. To evaluate its performance, it has been applied to three challenging test functions, and results have been compared with those from other alternative methods based on AIS and genetic algorithms. Our experimental results show that our proposal outperforms previous approaches in terms of accuracy and flexibility. Some other issues such as the parameter tuning, the complexity of the algorithm, and the CPU runtime are also discussed. 相似文献
5.
Very high resolution inverse synthetic aperture radar (ISAR) imaging of fast rotating targets is a complicated task. There may be insufficient pulses or may introduce migration through range cells (MTRC) during the coherent processing interval (CPI) when we use the conventional range Doppler (RD) ISAR technique. With compressed sensing (CS) technique, we can achieve the high-resolution ISAR imaging of a target with limited number of pulses. Sparse representation based method can achieve the super resolution ISAR imaging of a target with a short CPI, during which the target rotates only a small angle and the range migration of the scatterers is small. However, traditional CS-based ISAR imaging method generally faced with the problem of basis mismatch, which may degrade the ISAR image. To achieve the high resolution ISAR imaging of fast rotating targets, this paper proposed a pattern-coupled sparse Bayesian learning method for multiple measurement vectors, i.e. the PC-MSBL algorithm. A multi-channel pattern-coupled hierarchical Gaussian prior is proposed to model the pattern dependencies among neighboring range cells and correct the MTRC problem. The expectation-maximization (EM) algorithm is used to infer the maximum a posterior (MAP) estimate of the hyperparameters. Simulation results validate the effectiveness and superiority of the proposed algorithm. 相似文献
6.
Sirshendu Guha 《American Institute of Chemical Engineers》2022,68(3):e17505
In continuation to my previous work (Guha S. AIChE J. 2013;59(4):1390-1399), in this work, effects of ionic migration are evaluated for disk region of a rotating ring disk electrode system by numerically solving complex differential equations, developed for mass transfer along with kinetic complication in presence of ionic migration under limiting current condition. The system for simulation is 0.01 M Fe2(SO4)3 solution with H2SO4 as supporting electrolyte. Simulation cases are presence and absence of ionic migration with kinetic complication (oxidation of Fe2+ to Fe3+ under O2 pressure). Results show that concentration boundary layer thickness of reactant Fe3+ reduces appreciably and steady-state disk current reduces substantially in presence of migration. Simulated steady-state disk current in absence of migration case agrees well with published data. Results indicate higher Fe2+ concentration in presence of migration and thereby higher rate of oxidation of Fe2+ to Fe3+ at all rate constant values. 相似文献
7.
Although previous research has investigated widespread use of social media, especially Facebook, by youth attending college, the conditions under which these media foster adjustment to college remain unclear. This study tested a model illuminating pathways linking social competence to college adjustment via students’ perceptions about the usefulness of Facebook and ways in which they used the medium. Self-report survey data from 321 college students (M age = 20.09; 58% female; 84% Caucasian) attending a major Midwestern university supported the proposed model, indicating that higher social competence could foster or impede college adjustment, depending upon how it was related to beliefs about the usefulness of different Facebook functions and how these perceptions, in turn, were associated with patterns of Facebook use. Findings underscore the importance of considering connections among personal attributes, perception of media effectiveness, and media behaviors in assessing the implications of social media for users’ psychosocial well-being. 相似文献
8.
M1080B无心外圆磨床砂轮及导轮宽度较窄,磨削轴承套圈外圆时,磨削效率低,托板架调整较为繁琐、皮带打滑、磨损较为严重。针对上述问题,提出了相应的解决办法,提高了磨削效率。 相似文献
9.
介绍了高压变频调速变压器及高压变频器系统的基本原理及结构,详细论述了系统各组成部分的功能,并进行了举例说明。 相似文献
10.
运用过程中各类相关因子的变化,会使得机车柴油机配气相位出现一定程度变化,采取某种措施调整或是处理可以解决动力不足的问题。 相似文献