全文获取类型
收费全文 | 7995篇 |
免费 | 1070篇 |
国内免费 | 319篇 |
专业分类
电工技术 | 544篇 |
综合类 | 876篇 |
化学工业 | 1005篇 |
金属工艺 | 399篇 |
机械仪表 | 957篇 |
建筑科学 | 466篇 |
矿业工程 | 186篇 |
能源动力 | 487篇 |
轻工业 | 238篇 |
水利工程 | 96篇 |
石油天然气 | 246篇 |
武器工业 | 169篇 |
无线电 | 947篇 |
一般工业技术 | 1708篇 |
冶金工业 | 215篇 |
原子能技术 | 98篇 |
自动化技术 | 747篇 |
出版年
2024年 | 17篇 |
2023年 | 106篇 |
2022年 | 227篇 |
2021年 | 235篇 |
2020年 | 268篇 |
2019年 | 199篇 |
2018年 | 214篇 |
2017年 | 245篇 |
2016年 | 323篇 |
2015年 | 307篇 |
2014年 | 528篇 |
2013年 | 449篇 |
2012年 | 600篇 |
2011年 | 626篇 |
2010年 | 496篇 |
2009年 | 465篇 |
2008年 | 380篇 |
2007年 | 559篇 |
2006年 | 503篇 |
2005年 | 397篇 |
2004年 | 315篇 |
2003年 | 332篇 |
2002年 | 250篇 |
2001年 | 242篇 |
2000年 | 202篇 |
1999年 | 159篇 |
1998年 | 123篇 |
1997年 | 104篇 |
1996年 | 108篇 |
1995年 | 81篇 |
1994年 | 70篇 |
1993年 | 54篇 |
1992年 | 39篇 |
1991年 | 42篇 |
1990年 | 32篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1972年 | 1篇 |
1964年 | 1篇 |
1963年 | 2篇 |
1961年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1955年 | 4篇 |
1951年 | 1篇 |
排序方式: 共有9384条查询结果,搜索用时 22 毫秒
1.
Le Fang Qian Sun Yong-Hong Duan Jing Zhai Dan Wang Jie-Xin Wang 《Frontiers of Chemical Science and Engineering》2021,15(4):902
BaSO4 nanoparticles as important functional materials have attracted considerable research interests, due to their X-rays barrier and absorption properties. However, most of BaSO4 nanoparticles prepared by traditional technology are nanopowders with broad size distribution and poor dispersibility, which may greatly limit their applications. To the best of our knowledge, the synthesis of transparent BaSO4 nanodispersions was rarely reported. Here, we firstly present a novel and efficient method to prepare transparent and stable BaSO4 nanodispersions with a relatively small particle size around 10 to 17 nm using a precipitation method in a rotating packed bed (RPB), followed by a modification treatment using stearic acid. Compared with the BaSO4 prepared in a traditional stirred tank, the product prepared using an RPB has much smaller particle size and narrower size distribution. More importantly, by using RPB, the reaction time can be significantly decreased from 20 min to 18 s. Furthermore, the transparent BaSO4-polyvinyl butyral nanocomposite films with good X-ray shielding performance can be easily fabricated. We believe that the stable BaSO4 nanodispersions may have a wide range of applications for transparent composite materials and coatings with X-ray shielding performance for future research. 相似文献
2.
Real‐time thermal states monitoring of absorber tube for parabolic trough solar collector with non‐uniform solar flux 下载免费PDF全文
With the world energy shortage problem becoming increasingly prominent, more and more attentions have been paid to the development of renewable energies. Among these sources, solar energy has received extensive attention with its excellent characteristics. The thermal state affects the safety of the solar heat collection system. In this paper, real‐time monitoring of the input heat flux on the inside wall and the temperature field simultaneously of an absorber tube for parabolic trough solar collector were studied. Based on the measured temperatures on the outside wall, the fuzzy adaptive Kalman filter coupled with weighted recursive least squares algorithm (WRLSA) was employed to monitor the heat states of the absorber tube inversely, in which WRLSA was used to acquire the heat flux while fuzzy adaptive Kalman filter was adopted to monitor the temperature field. The method showed strong robustness to resist the ill‐posedness. Accurate monitoring results also can be acquired when there are random disturbances of the heat transfer condition on the inner wall. 相似文献
3.
随着网络建设以及信息化教学方法在高校教学过程中的应用普及,越来越多的高校使用在线巡课系统对教师的教学过程进行跟踪和管理,以便发现课堂教学中的亮点、问题和不足。文章提出的在线巡课系统,基于声源定位的技术,对传统的在线巡课系统做出了改进,解决了已有巡课系统中“只闻其声,不见其人”的问题,能够更直观地跟踪到教师的教学过程,包括教学行为以及师生互动过程,有效提升教务人员巡课效果和体验感受。 相似文献
4.
An active band‐notched frequency selective absorber (BNFSA) with switchable notch band is proposed in this article. The BNFSA is a two‐layer structure composed of a lossy layer at the top and a ground plane at the bottom, separated by an air spacer. The element of the lossy layer is a lumped‐resistor‐loaded metallic dipole with a parallel LC resonance structure, which is realized by complementary n‐shaped resonator (CnR) inserted in the center, and PIN diode is welded at two arms of CnR. The bias circuit printed on the back of the substrate of the lossy layer connects to anode and cathode of the diode by via hole and isolates by the inductor. Simulation results show that the notch bands are located at 4.50 and 6.81 GHz when the diode sets to ON and OFF, respectively. To validate the performance of switchable BNFSA, the prototypes are fabricated and measured, reasonable agreement between simulated and measured results is obtained. 相似文献
5.
基于GA-BP的汽车风振噪声声品质预测模型 总被引:1,自引:1,他引:0
目前对于汽车风振噪声的优化研究主要以声压级(Sound pressure level,SPL)作为单一评价指标,既不能全面反映噪声的物理属性,也无法考虑人耳对噪声的主观认知过程。为准确评价风振噪声,引入声品质,运用大涡模拟(Large eddy simulation,LES)对风振噪声进行数值仿真,根据实车道路试验判断仿真的准确性;对仿真结果进行声品质客观评价与主观评价,综合声品质客观评价参数与声品质主观评价试验结果建立BP神经网络预测模型;利用遗传算法(Genetic algorithm,GA),进一步对BP神经网络的结构参数进行优化,建立GA-BP声品质预测模型。研究结果表明,GA-BP声品质预测模型在训练速度和预测精度上都优于BP神经网络预测模型。预测模型基于声品质主客观评价结果,其预测值可以代替传统的声压级评价指标,为风振噪声提供更为准确合理的评价。 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.
Measurement of vertical and horizontal vibrations of a probe for acoustic evaluation of food texture
Two‐dimensional (vertical and horizontal) vibrations of a wedge‐type probe upon food rupture were evaluated separately using two accelerometers placed perpendicular to a guide rod of a swing‐arm device for texture evaluation of the flesh of three varieties of apples and three types of potato chips. Voltage signals from the accelerometers were filtered using a half‐octave band‐pass filter. The energy texture index (ETI), based on kinetic energy of the vertical or horizontal probe vibrations, was calculated over low to high frequency bands (no. 1–21). The spectra for the flesh of the three varieties of apples included two common peaks for vertical ETI at band no. 11 (1,120–1,600 Hz) and 19 (17,920–25,600 Hz) and horizontal ETI at band no. 1 (0–10 Hz) and 15 (4,480–6,400 Hz). The spectra for the three types of potato chips had a common ETI peak at band no. 11 (1,120–1,600 Hz) for horizontal ETI and at no. 15 (4,480–6,400 Hz) for vertical ETI. The three apple varieties gave rise to different intensities of vertical and horizontal ETIs while the two peaks were maintained. The thick potato chip type had higher vertical and horizontal ETIs than the thin and soft varieties in most bands; however, the thin type had the highest vertical ETIs only in lower bands (0–200 Hz). The soft type had the lowest vertical and horizontal ETI. The above results suggest that different food textures can be distinguished by two‐dimensional vibration analyses of probe insertion into a food sample based on frequency bands. 相似文献
8.
9.
10.
为了探索南美白对虾进食前后发声信号特点和规律,首先进行了养殖虾塘环境下的实验,利用水听器与采集器采集信号;然后利用Matlab软件对信号进行频谱分析和时频分析,得到南美白对虾的发声信号规律。实验证明,在淡水养殖环境下,南美白对虾产生的声信号具有一定的规律,一般情况单个脉冲信号时长为0.005 s,主峰频率在2~10 kHz之间,投饵后主峰频率有所扩大,约在5~15 kHz之间。投饵后南美白对虾随着咀嚼活动的展开产生的信号增多,并且时频域特征明显与投饵前不同。该实验结果为利用南美白对虾产生的信号来控制投饵机实现按需投饵提供了可能。 相似文献