全文获取类型
收费全文 | 186161篇 |
免费 | 23969篇 |
国内免费 | 16746篇 |
专业分类
电工技术 | 17011篇 |
技术理论 | 11篇 |
综合类 | 21959篇 |
化学工业 | 15267篇 |
金属工艺 | 6939篇 |
机械仪表 | 13614篇 |
建筑科学 | 23055篇 |
矿业工程 | 6685篇 |
能源动力 | 7717篇 |
轻工业 | 7210篇 |
水利工程 | 10783篇 |
石油天然气 | 10876篇 |
武器工业 | 3274篇 |
无线电 | 14922篇 |
一般工业技术 | 16541篇 |
冶金工业 | 6701篇 |
原子能技术 | 1926篇 |
自动化技术 | 42385篇 |
出版年
2024年 | 942篇 |
2023年 | 2739篇 |
2022年 | 5400篇 |
2021年 | 6246篇 |
2020年 | 6873篇 |
2019年 | 5756篇 |
2018年 | 5501篇 |
2017年 | 6995篇 |
2016年 | 7937篇 |
2015年 | 8337篇 |
2014年 | 11705篇 |
2013年 | 11908篇 |
2012年 | 13812篇 |
2011年 | 14790篇 |
2010年 | 11528篇 |
2009年 | 11794篇 |
2008年 | 11504篇 |
2007年 | 13200篇 |
2006年 | 11601篇 |
2005年 | 10175篇 |
2004年 | 8242篇 |
2003年 | 7100篇 |
2002年 | 5746篇 |
2001年 | 4790篇 |
2000年 | 4085篇 |
1999年 | 3185篇 |
1998年 | 2646篇 |
1997年 | 2133篇 |
1996年 | 2051篇 |
1995年 | 1742篇 |
1994年 | 1401篇 |
1993年 | 993篇 |
1992年 | 838篇 |
1991年 | 619篇 |
1990年 | 521篇 |
1989年 | 427篇 |
1988年 | 266篇 |
1987年 | 170篇 |
1986年 | 137篇 |
1985年 | 121篇 |
1984年 | 125篇 |
1983年 | 58篇 |
1982年 | 67篇 |
1981年 | 55篇 |
1980年 | 102篇 |
1979年 | 79篇 |
1964年 | 35篇 |
1959年 | 48篇 |
1956年 | 29篇 |
1955年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
The architectural choices underlying Linked Data have led to a compendium of data sources which contain both duplicated and fragmented information on a large number of domains. One way to enable non-experts users to access this data compendium is to provide keyword search frameworks that can capitalize on the inherent characteristics of Linked Data. Developing such systems is challenging for three main reasons. First, resources across different datasets or even within the same dataset can be homonyms. Second, different datasets employ heterogeneous schemas and each one may only contain a part of the answer for a certain user query. Finally, constructing a federated formal query from keywords across different datasets requires exploiting links between the different datasets on both the schema and instance levels. We present Sina, a scalable keyword search system that can answer user queries by transforming user-supplied keywords or natural-languages queries into conjunctive SPARQL queries over a set of interlinked data sources. Sina uses a hidden Markov model to determine the most suitable resources for a user-supplied query from different datasets. Moreover, our framework is able to construct federated queries by using the disambiguated resources and leveraging the link structure underlying the datasets to query. We evaluate Sina over three different datasets. We can answer 25 queries from the QALD-1 correctly. Moreover, we perform as well as the best question answering system from the QALD-3 competition by answering 32 questions correctly while also being able to answer queries on distributed sources. We study the runtime of SINA in its mono-core and parallel implementations and draw preliminary conclusions on the scalability of keyword search on Linked Data. 相似文献
63.
64.
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
65.
A method for estimating the sway angle using an observer has already been proposed. The state observer estimates the sway angle accurately and must use the detected sway angle value. However, the estimated sway angle has an error owing to rope length error, friction force, and wind. Moreover, the container mass cannot be determined, and therefore the observer parameter is not suitable. We already proposed robust antisway control for overcoming rope length error without adding a new sensor. Further, we designed a friction disturbance observer to cancel out the influence of the friction force. In this paper, we first propose a container mass estimation method when a crane system performs rolling up control. The observer parameter can be selected using the estimated mass value. Second, in crane parallel shift control, we propose a robust antisway control even when there is a wind disturbance. We design a wind disturbance observer and propose a wind disturbance estimator to separate the friction observer output from the wind disturbance observer output. We confirm through experiments that the proposed method can reduce vibration. 相似文献
66.
A conceptualization of intended learning outcomes supporting self‐regulated learners in indicating learning paths
下载免费PDF全文
![点击此处可从《Journal of Computer Assisted Learning》网站下载免费的PDF全文](/ch/ext_images/free.gif)
P. Tangworakitthaworn L. Gilbert G.B. Wills 《Journal of Computer Assisted Learning》2015,31(5):393-404
Intended learning outcomes (ILOs) indicate what learners will be able to achieve after they are taught. Traditionally, ILOs are expressed as plain text or unstructured documents. What if all ILOs of a specific course of study can be conceptualized through a structured diagrammatic technique? It was hypothesized that learners can benefit from this conceptualization in learning, especially in self‐regulated learning. The aim of this study was to investigate whether the ILOs represented in unstructured or structured formats can facilitate learners to identify learning paths. The results revealed that the mean ratings of all learning paths were statistically significantly higher with structured ILOs. 相似文献
67.
Shmuel Borenstain Gil Bar-Haim Keren Goldshtein Gili Cohen-Taguri 《Color research and application》2020,45(6):1153-1169
Investigation of ink formulation options with the purpose to obtain color-gamut-optimal set of Cyan Magenta and Yellow CMY inks is reported. Implementation of the thickness dependent Kubelka-Munk model on multiple ink layers having different and well-defined thicknesses, provides characteristic absorption and scattering (K, S ) spectra of the ink ingredients. These data enable accurate computation of the reflectance spectrum and thus the L*a*b* color coordinates for any given ink thickness or substrate. Pigment materials investigated are quinacridone as magenta, copper-phthalocyanine as cyan, and arylide yellow. Scaling the peak of the absorption band to the number of molecules per unit area for the specific pigments studied in this article provides the molar extinction coefficients, 1.21 × 104 , 4.7 × 104 , and 3.3 × 104 cm2/millimole respectively, regardless of the different ink formulations used, in accord with Avogadro's principle. Having a set of three pairs of K, S spectra is used to compute the color gamut of any CMY color combination in the L*a*b* space as a function of ink layer thickness and formulation. Using an iterative algorithm, a color-gamut-optimal set of CMY inks is obtained. 相似文献
68.
对射频电缆幅相稳定性进行了介绍,阐述了射频测试电缆相位和幅度变化的因素,并详细分析了射频电缆相位性能以及幅度性能的不同测试方法,最后通过实测数据的展示,总结说明了在日常测试中该如何正确使用测试电缆。 相似文献
69.
Previous experimental results indicate that the humidification conditions at the anode have an impact on the liquid water distribution in the cathode gas diffusion layer. Numerical simulations are developed to reproduce and analyze this effect. Results consistent with the experimental results are first obtained by playing with the partition coefficients of an advanced pore network model computing the liquid water formation and transfer in the cathode gas diffusion layer (GDL) for a large range of operating conditions. Then, a model for the full anode – cathode assembly is developed by combining the pore network model of the cathode GDL and a 1D model describing the heat and water transfer in the various components of the anode-cathode assembly. This enables one to generalize the dry – wet regime diagram introduced in a previous work by incorporating the effect of the humidity condition at the anode. 相似文献
70.
性能效率是APP软件的重要质量属性,但目前缺乏APP软件性能效率的通用模型。分析了APP软件的性能特征,基于ISO/IEC 25010标准提出了APP软件的性能效率模型,定义了APP软件性能效率的子特性和度量指标。基于提出的APP软件性能效率模型,通过实验对APP软件的性能效率进行了度量及相关分析。 相似文献