全文获取类型
收费全文 | 155454篇 |
免费 | 25115篇 |
国内免费 | 6658篇 |
专业分类
电工技术 | 8243篇 |
技术理论 | 9篇 |
综合类 | 10037篇 |
化学工业 | 35594篇 |
金属工艺 | 7031篇 |
机械仪表 | 7828篇 |
建筑科学 | 11860篇 |
矿业工程 | 3281篇 |
能源动力 | 4223篇 |
轻工业 | 17197篇 |
水利工程 | 2778篇 |
石油天然气 | 5938篇 |
武器工业 | 1025篇 |
无线电 | 19916篇 |
一般工业技术 | 23793篇 |
冶金工业 | 5543篇 |
原子能技术 | 1474篇 |
自动化技术 | 21457篇 |
出版年
2024年 | 586篇 |
2023年 | 1997篇 |
2022年 | 3456篇 |
2021年 | 5015篇 |
2020年 | 4968篇 |
2019年 | 6168篇 |
2018年 | 6345篇 |
2017年 | 7026篇 |
2016年 | 6974篇 |
2015年 | 8525篇 |
2014年 | 9466篇 |
2013年 | 11641篇 |
2012年 | 10244篇 |
2011年 | 10425篇 |
2010年 | 10017篇 |
2009年 | 9636篇 |
2008年 | 9106篇 |
2007年 | 8506篇 |
2006年 | 8256篇 |
2005年 | 6877篇 |
2004年 | 5613篇 |
2003年 | 5849篇 |
2002年 | 6832篇 |
2001年 | 5791篇 |
2000年 | 4085篇 |
1999年 | 3228篇 |
1998年 | 1963篇 |
1997年 | 1661篇 |
1996年 | 1539篇 |
1995年 | 1298篇 |
1994年 | 995篇 |
1993年 | 742篇 |
1992年 | 617篇 |
1991年 | 404篇 |
1990年 | 321篇 |
1989年 | 262篇 |
1988年 | 217篇 |
1987年 | 120篇 |
1986年 | 112篇 |
1985年 | 77篇 |
1984年 | 61篇 |
1983年 | 40篇 |
1982年 | 34篇 |
1981年 | 31篇 |
1980年 | 43篇 |
1979年 | 17篇 |
1976年 | 7篇 |
1975年 | 4篇 |
1959年 | 6篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
This paper presents a control design for the one‐phase Stefan problem under actuator delay via a backstepping method. The Stefan problem represents a liquid‐solid phase change phenomenon which describes the time evolution of a material's temperature profile and the interface position. The actuator delay is modeled by a first‐order hyperbolic partial differential equation (PDE), resulting in a cascaded transport‐diffusion PDE system defined on a time‐varying spatial domain described by an ordinary differential equation (ODE). Two nonlinear backstepping transformations are utilized for the control design. The setpoint restriction is given to guarantee a physical constraint on the proposed controller for the melting process. This constraint ensures the exponential convergence of the moving interface to a setpoint and the exponential stability of the temperature equilibrium profile and the delayed controller in the norm. Furthermore, robustness analysis with respect to the delay mismatch between the plant and the controller is studied, which provides analogous results to the exact compensation by restricting the control gain. 相似文献
93.
94.
This paper is concerned with the problem of joint input and state estimation for linear stochastic systems with direct feedthrough. Based on the fact that each unknown input between any two time steps is always bounded, a novel improved algorithm is proposed. Compared with existing results, this algorithm can effectively enhance estimation accuracy. Moreover, the stability of the algorithm is also discussed. Finally, an illustrative example is given to demonstrate the effectiveness of the proposed approach. 相似文献
95.
The current study establishes the unprecedented involvement in the evolution and production of novel core–shell nanocomposites composed of nanosized titanium dioxide and aniline‐o‐phenylenediamine copolymer. TiO2@copoly(aniline and o‐phenylenediamine) (TiO2@PANI‐o‐PDA) core–shell nanocomposites were chemically synthesized in a molar ratio of 5:1 of the particular monomers and several weights of nano‐TiO2 via oxidative copolymerization. The construction of the TiO2@PANI‐o‐PDA core–shell nanocomposites was ascertained from Fourier transform IR spectroscopy, UV–visible spectroscopy and XRD. A reasonable thermal behavior for the original copolymer and the TiO2@PANI‐o‐PDA core–shell nanocomposites was investigated. The bare PANI‐o‐PDA copolymer was thermally less stable than the TiO2@PANI‐o‐PDA nanocomposites. The core–shell feature of the nanocomposites was found to have core and shell sizes of 17 nm and 19–26 nm, respectively. In addition, it was found that the addition of a high ratio of TiO2 nanoparticles increases the electrical conductivity and consequently lowers the electrical resistivity of the TiO2@PANI‐o‐PDA core–shell nanocomposites. The hybrid photocatalysts exhibit a dramatic photocatalytic efficacy of methylene blue degradation under solar light irradiation. A plausible interpretation of the photocatalytic degradation results of methylene blue is also demonstrated. Our setup introduces a facile, inexpensive, unique and efficient technique for developing new core–shell nanomaterials with various required functionalities and colloidal stabilities. © 2018 Society of Chemical Industry 相似文献
96.
97.
98.
Lecture capture with real‐time rearrangement of visual elements: impact on student performance
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)
The primary goal of this study is to create and test a lecture‐capture system that can rearrange visual elements while recording is still taking place, in such a way that student performance can be positively influenced. The system we have devised is capable of integrating and rearranging multimedia sources, including learning content, the instructor and students' images, into lecture videos that are embedded in a website for students to review after school. The present study employed a two‐group experimental design, with 153 participants (145 females and 8 males) making up an experimental group in which lecture courses were recorded using the new lecture‐capture system, and 149 participants (140 females and 9 males) forming a control group whose lectures were recorded by traditional means. All participants were in the freshman college and studying Introduction to Computer and Information Science in one of six classes, and were randomly assigned to one of the two groups. The participants' midterm examination and final examination scores were collected as indicators of their academic performance, with their mathematics entrance scores used as a pre‐test. The findings obtained from analysis of covariance (ANCOVA) suggest that appropriate rearrangement of visual elements in lecture videos can significantly impact students' learning performance. 相似文献
99.
Abiodun B. Ogbesejana Zhong Ningning Oluwadayo O. Sonibare 《Petroleum Science and Technology》2019,37(18):1969-1977
The occurrence and distributions of dibenzofurans (DBFs) and benzo[b]naphthofurans were investigated in crude oils from Niger Delta, Nigeria, by gas chromatography-mass spectrometry-mass spectrometry. The distribution of DBFs was characterized by the predominance of C2-dibenzofurans. 4-Methyldibenzofuran was the most abundant among the methyldibenzofurans isomers while dimethyldibenzofuran-2 (DMDBF-2), ethyldibenzofuran-1, DMDBF-3, and DMDBF-6 occurred in higher amounts when compared with other DMDBFs. Among the benzonaphthofurans, the abundance of benzo[b]naphtho[2,1-d]furan was higher than other isomers. The DBFs distributions in the oils were not affected by source facies and depositional environments. However, the DBFs concentrations increased with increasing maturity in oils from ADL and MJO oilfields. 相似文献
100.
Zhang Huawei Yang Zhi Wu Zhaoyu Hong Xiaoyu Li Zhong Xu Yulai Li Jun Ni Gaojin Xiao Xueshan 《Oxidation of Metals》2019,92(1-2):49-65
Oxidation of Metals - The isothermal oxidation behavior and oxide-scale evolution on a newly developed Ni–Fe-based superalloy were investigated. Three oxidation stages were generally... 相似文献