全文获取类型
收费全文 | 11976篇 |
免费 | 1063篇 |
国内免费 | 487篇 |
专业分类
电工技术 | 428篇 |
技术理论 | 1篇 |
综合类 | 913篇 |
化学工业 | 920篇 |
金属工艺 | 2100篇 |
机械仪表 | 659篇 |
建筑科学 | 1367篇 |
矿业工程 | 166篇 |
能源动力 | 410篇 |
轻工业 | 1131篇 |
水利工程 | 208篇 |
石油天然气 | 392篇 |
武器工业 | 62篇 |
无线电 | 499篇 |
一般工业技术 | 1116篇 |
冶金工业 | 1814篇 |
原子能技术 | 155篇 |
自动化技术 | 1185篇 |
出版年
2024年 | 43篇 |
2023年 | 229篇 |
2022年 | 374篇 |
2021年 | 440篇 |
2020年 | 436篇 |
2019年 | 326篇 |
2018年 | 272篇 |
2017年 | 398篇 |
2016年 | 463篇 |
2015年 | 453篇 |
2014年 | 695篇 |
2013年 | 704篇 |
2012年 | 830篇 |
2011年 | 856篇 |
2010年 | 659篇 |
2009年 | 745篇 |
2008年 | 560篇 |
2007年 | 793篇 |
2006年 | 699篇 |
2005年 | 586篇 |
2004年 | 483篇 |
2003年 | 435篇 |
2002年 | 411篇 |
2001年 | 337篇 |
2000年 | 283篇 |
1999年 | 206篇 |
1998年 | 148篇 |
1997年 | 151篇 |
1996年 | 118篇 |
1995年 | 69篇 |
1994年 | 73篇 |
1993年 | 56篇 |
1992年 | 38篇 |
1991年 | 28篇 |
1990年 | 30篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 12篇 |
1983年 | 11篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1964年 | 4篇 |
1958年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
1.
The existing analytical average bit error rate (ABER) expression of conventional generalised spatial modulation (CGSM) does not agree well with the Monte Carlo simulation results in the low signal‐to‐noise ratio (SNR) region. Hence, the first contribution of this paper is to derive a new and easy way to evaluate analytical ABER expression that improves the validation of the simulation results at low SNRs. Secondly, a novel system termed CGSM with enhanced spectral efficiency (CGSM‐ESE) is presented. This system is realised by applying a rotation angle to one of the two active transmit antennas. As a result, the overall spectral efficiency is increased by 1 bit/s/Hz when compared with the equivalent CGSM system. In order to validate the simulation results of CGSM‐ESE, the third contribution is to derive an analytical ABER expression. Finally, to improve the ABER performance of CGSM‐ESE, three link adaptation algorithms are developed. By assuming full knowledge of the channel at the receiver, the proposed algorithms select a subset of channel gain vector (CGV) pairs based on the Euclidean distance between all CGV pairs, CGV splitting, CGV amplitudes, or a combination of these. 相似文献
2.
Colour remains one of the key factors in presenting an object and, consequently, has been widely applied in retrieval of images based on their visual contents. However, a colour appearance changes with the change of viewing surroundings, the phenomenon that has not been paid attention yet while performing colour‐based image retrieval. To comprehend this effect, in this article, a chromatic contrast model, CAMcc, is developed for the application of retrieval of colour intensive images, cementing the gap that most of existing colour models lack to fill by taking simultaneous colour contrast into account. Subsequently, the model is applied to the retrieval task on a collection of museum wallpapers of colour‐rich images. In comparison with current popular colour models including CIECAM02, HSI and RGB, with respect to both foreground and background colours, CAMcc appears to outperform the others with retrieved results being closer to query images. In addition, CAMcc focuses more on foreground colours, especially by maintaining the balance between both foreground and background colours, while the rest of existing models take on dominant colours that are perceived the most, usually background tones. Significantly, the contribution of the investigation lies in not only the improvement of the accuracy of colour‐based image retrieval but also the development of colour contrast model that warrants an important place in colour and computer vision theory, leading to deciphering the insight of this age‐old topic of chromatic contrast in colour science. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 361–373, 2015 相似文献
3.
Rectangular section control technology(RSCT)was introduced to achieve high-precision profile control during silicon steel rolling.The RSCT principle and method were designed,and the whole RSCT control strategy was developed.Specifically,RSCT included roll contour design,rolling technology optimization,and control strategy development,aiming at both hot strip mills(HSMs)and cold strip mills(CSMs).Firstly,through the high-performance variable crown(HVC)work roll optimization design in the upper-stream stands and the limited shifting technology for schedule-free rolling in the downstream stands of HSMs,a hot strip with a stable crown and limited wedge,local spot,and single wave was obtained,which was suitable for cold rolling.Secondly,an approximately rectangular section was obtained by edge varying contact(EVC)work roll contour design,edge-drop setting control,and closed loop control in the upper-stream stands of CSMs.Moreover,complex-mode flatness control was realized by coordinating multiple shape-control methods in the downstream stands of CSMs.In addition,the RSCT approach was applied in several silicon-steel production plants,where an outstanding performance and remarkable economic benefits were observed. 相似文献
4.
5.
Nathan M. Wilbur Antin M. O'Sullivan Kerry T. B. MacQuarrie Tommi Linnansaari R. Allen Curry 《河流研究与利用》2020,36(5):769-783
Anthropogenic influences, including climate change, are increasing river temperatures in northern and temperate regions and threatening the thermal habitats of native salmonids. When river temperatures exceed the tolerance levels of brook trout and Atlantic salmon, individuals exhibit behavioural thermoregulation by seeking out cold‐water refugia – often created by tributaries and groundwater discharge. Thermal infrared (TIR) imagery was used to map cold‐water anomalies along a 53 km reach of the Cains River, New Brunswick. Trout and salmon parr did not use all identified thermal anomalies as refugia during higher river temperature periods (>21°C). Most small‐bodied trout (8–30 cm) were observed in 80% of the thermal anomalies sampled. Large‐bodied trout (>35 cm) required a more specific set of physical habitat conditions for suitable refugia, that is, 100% of observed large trout used 30% of the anomalies sampled and required water depths >65 cm within or adjacent to the anomaly. Densities of trout were significantly higher within anomalies compared with areas of ambient river temperature. Salmon parr were less aligned with thermal anomalies at the observed temperatures, that is, 59% were found in 65% of the sampled anomalies; and densities were not significantly different within/ outside anomalies. Salmon parr appeared to aggregate at 27°C, and after several events over 27°C variability in aggregation behaviour was observed – some fish aggregated at 25°C, others did not. We stipulate this is due to variances of thermal fatigue. Habitat suitability curves were developed for velocity, temperature, depth, substrate, and deep water availability to characterize conditions preferred by fish during high‐temperature events. These findings are useful for managers as our climate warms, and can potentially be used as a tool to help conserve and enhance thermal refugia for brook trout and Atlantic salmon in similar systems. 相似文献
6.
This paper proposes the application of Covariance Matrix Adaptation Evolution Strategy (CMA-ES) in fixed structure H∞ loop shaping controller design. Integral Time Absolute Error (ITAE) performance requirement is incorporated as a constraint with an objective of maximization of stability margin in the fixed structure H∞ loop shaping controller design problem. Pneumatic servo system, separating tower process and F18 fighter aircraft system are considered as test systems. The CMA-ES designed fixed structure H∞ loop-shaping controller is compared with the traditional H∞ loop shaping controller, non-smooth optimization and Heuristic Kalman Algorithm (HKA) based fixed structure H∞ loop shaping controllers in terms of stability margin. 20% perturbation in the nominal plant is used to validate the robustness of the CMA-ES designed H∞ loop shaping controller. The effect of Finite Word Length (FWL) is considered to show the implementation difficulties of controller in digital processors. Simulation results demonstrated that CMA-ES based fixed structure H∞ loop shaping controller is suitable for real time implementation with good robust stability and performance. 相似文献
7.
8.
轧制速度是三辊式冷轧成形过程中关键的工艺参数,决定其力学特征及温升情况。基于此,本文以冷轧AZ31镁合金管材为研究对象,通过全流程数值仿真计算,对比分析不同轧制速度在各特征变形段对等效应力、等效塑性应变及节点温度的影响规律。结果表明,等效应力、等效塑性应变及节点温度均随轧制速度的增大而增大。通过元胞自动机模型及实验等手段,探明了晶粒在轧制过程中产生连续再结晶并细化的初步组织演变规律;对比分析实验与模拟结果并结合多方面因素,得到800mm/s的轧制速度可以更好的满足工艺要求的结果,为冷轧镁合金管材轧制速度的选择提供依据。 相似文献
9.
本文分析了燃气热水器行业针对无回水管水路系统实现零冷水功能的现有技术方案,指出现有技术方案存在的一些缺陷,并结合试验研究,对无回水管水路系统提出了一套全新的实现零冷水功能的技术解决方案。 相似文献
10.
使用真空电弧炉熔炼出(Fe50Mn30Co10Cr10)94Al6合金,利用冷轧及在不同温度对合金进行退火,以期望得到由多尺度再结晶晶粒构成的层状结构;并对不同退火温度的样品进行拉伸性能测试。利用扫描电镜和EBSD对合金组织形貌进行表征,采用X射线衍射方法研究其相组成。结果表明:合金在铸态和冷轧后相组成未发生变化,700 ℃退火得到较好的多尺度再结晶晶粒的层状结构,其屈服强度为487 MPa,抗拉强度为708 MPa,断后伸长率为39%,表现出良好的综合力学性能。 相似文献