全文获取类型
收费全文 | 42112篇 |
免费 | 5304篇 |
国内免费 | 3050篇 |
专业分类
电工技术 | 4431篇 |
技术理论 | 1篇 |
综合类 | 3173篇 |
化学工业 | 9773篇 |
金属工艺 | 5061篇 |
机械仪表 | 1673篇 |
建筑科学 | 829篇 |
矿业工程 | 669篇 |
能源动力 | 1564篇 |
轻工业 | 2350篇 |
水利工程 | 292篇 |
石油天然气 | 1748篇 |
武器工业 | 387篇 |
无线电 | 6693篇 |
一般工业技术 | 6187篇 |
冶金工业 | 2929篇 |
原子能技术 | 430篇 |
自动化技术 | 2276篇 |
出版年
2024年 | 204篇 |
2023年 | 846篇 |
2022年 | 1189篇 |
2021年 | 1453篇 |
2020年 | 1591篇 |
2019年 | 1517篇 |
2018年 | 1384篇 |
2017年 | 1660篇 |
2016年 | 1673篇 |
2015年 | 1659篇 |
2014年 | 2286篇 |
2013年 | 2497篇 |
2012年 | 2781篇 |
2011年 | 2818篇 |
2010年 | 2025篇 |
2009年 | 2325篇 |
2008年 | 2146篇 |
2007年 | 2634篇 |
2006年 | 2519篇 |
2005年 | 2050篇 |
2004年 | 1713篇 |
2003年 | 1683篇 |
2002年 | 1445篇 |
2001年 | 1306篇 |
2000年 | 1174篇 |
1999年 | 948篇 |
1998年 | 831篇 |
1997年 | 740篇 |
1996年 | 567篇 |
1995年 | 540篇 |
1994年 | 471篇 |
1993年 | 324篇 |
1992年 | 328篇 |
1991年 | 251篇 |
1990年 | 224篇 |
1989年 | 206篇 |
1988年 | 97篇 |
1987年 | 63篇 |
1986年 | 54篇 |
1985年 | 41篇 |
1984年 | 48篇 |
1983年 | 28篇 |
1982年 | 33篇 |
1981年 | 25篇 |
1980年 | 23篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1975年 | 5篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
低相噪,低杂波数字锁相环路滤波器的设计 总被引:11,自引:0,他引:11
较详细地分析数字锁相频率合成器的相位噪声,着重用控制论方法对低相噪、低杂波锁相环的环路滤波器进行设计,并用某S波段频率合成器的实验结果进行了验证。 相似文献
82.
This paper analyses the HIPERLAN channel access mechanism. Both a purely mathematical and a simulation model are built in order to evaluate the two successive phases of the contention scheme. Several optimisations, based on the choice of parametric values, are proposed, evaluated and compared. 相似文献
83.
A Method of Combined SHPB Technique and BP Neural Network to Study Impact Response of Materials 总被引:2,自引:0,他引:2
Abstract: A new method combining the split Hopkinson pressure bar (SHPB) technique with the back-propagation (BP) neural network program is proposed. By this method, the treated strain wave signals become smooth with less noises induced by the transverse inertia. Moreover, the dynamic rate-dependent constitutive behaviour of materials can be identified, without any pre-assumption of a constitutive model. It is found that by taking the experimentally measured data of strain, strain rate and time as 'input' and the corresponding data of stress as 'output' of the BP neural network, the dynamic constitutive behaviour with internal damage or phase transformation evolution is easy to be identified, where the time could represent either the internal damage evolution or phase transformation process accompanied with the deformation process. It is emphasised that the data learnt by the BP neural network must include both loading and unloading processes, if the whole loading and unloading response is to be correctly predicted. The comparisons between the predictions and experimental results are in good agreement for both polyamide (PA) polymer (as an example of nonlinear viscoelastic materials) and Ti–Ni alloy (as an example of superelastic materials with stress-induced phase transformation). 相似文献
84.
A series of polyurethane microcapsules containing a phase change material (PCM) of n‐octadecane was successfully synthesized by an interfacial polymerization in aqueous styrene‐maleic anhydride (SMA) dispersion with diethylene triamine (DETA) as a chain extender reacting with toluene‐2,4‐diisocyanate (TDI). The average diameter of microPCMs is in the range of 5–10 μm under the stirring speed of 3000–4000 rpm. Optical and SEM morphologies of microPCMs had ensured that the shell was regularly fabricated with the influence of SMA. FTIR results confirmed that the shell material was polyurethane and the SMA chains associated on core material reacted with TDI forming a part of shell material. The shell thickness was decreasing in the range of 0.31–0.55 μm with the molar ratio of DETA/TDI from 0.84 to 1.35 and the weight of core material increasing from 40 to 80% (wt %). By controlling the weight ratio of PCM as 40, 50, 60, 70, and 80% in microPCMs, it was found using DSC that the Tm and Tc of microPCMs were in the range of 29.8–31.0oC and 21.1–22.0°C and an obvious phase change had been achieved nearly the same temperature range of that of PCM. The results from release curves of microPCM samples prepared by 1.4, 1.7, and 2.0 g of SMA indicated the release properties were affected by the amount of the dispersant, which attributed to the emulsion effect and shell polymerization structure. The above results suggest that the shell structure of microPCMs can be controlled and the properties of microPCMs determined by shell will perform proper practical usage. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4996–5006, 2006 相似文献
85.
86.
近年来,大电流的监测成了人们十分关心的问题,这是由于大电流有强磁、高压、电流大等一系列的直接监测所不能克服的问题。这就需要把高压大电流的强电信号,经过提取后变成能在实验室中直接观测的弱电信号。为此,如何从高压大电流的信号中提取出随实时信号变化而实时变化的小信号就变成了一个关键问题。详细介绍了监测信号提取的光收发电路原理和后续信号处理电路,分析了各部分的作用,给出了必要的分析结果。 相似文献
87.
NiCuZn铁氧体和银内电极的共烧行为 总被引:2,自引:0,他引:2
NiCuZn铁氧体正作为磁介质广泛地应用于低烧多层片式电感,因此有必要对其与银内电极的共烧行为进行研究。该文主要介绍NiCuZn铁氧体/银内电极多层复合体共烧过程中的烧结收缩、界面反应、扩散对介质性能的影响。尖晶石结构中存在相当数量的空位,这为银离子提供了一定的溶解度,因此在共烧过程中银对铁氧体的相组成影响较小。银对铁氧体性能的影响体现在两个方面。一方面是由于银具有相对低的烧结温度,从而在烧结过程中起到助烧剂的作用,促进致密化过程,提高烧结体的密度和磁导率;另一方面,银促使铁氧体中的铜在晶界处析出,导致晶界处应力,使磁导率降低,晶粒生长也被一定程度地抑制。 相似文献
88.
Rui Morimoto Chisato Yokomori Akiko Kikkawa Akira Izumi Hideki Matsumura 《Thin solid films》2003,430(1-2):230-235
In this paper, bulk-Si metal–oxide–semiconductor field effect transistors (MOSFETs) are fabricated using the catalytic chemical vapor deposition (Cat-CVD) method as an alternative technology to the conventional high-temperature thermal chemical vapor deposition. Particularly, formation of low-resistivity phosphorus (P)-doped poly-Si films is attempted by using Cat-CVD-deposited amorphous silicon (a-Si) films and successive rapid thermal annealing (RTA) of them. Even after RTA processes, neither peeling nor bubbling are observed, since hydrogen contents in Cat-CVD a-Si films can be as low as 1.1%. Both the crystallization and low resistivity of 0.004 Ω·cm are realized by RTA at 1000 °C for only 5 s. It is also revealed that Cat-CVD SiNx films prepared at 250 °C show excellent oxidation resistance, when the thickness of films is larger than approximately 10 nm for wet O2 oxidation at 1100 °C. It is found that the thickness required to stop oxygen penetration is equivalent to that for thermal CVD SiNx prepared at 750 °C. Finally, complementary MOSFETs (CMOSs) of single-crystalline Si were fabricated by using Cat-CVD poly-Si for gate electrodes and SiNx films for masks of local oxidation of silicon (LOCOS). At 3.3 V operation, less than 1.0 pA μm−1 of OFF leakage current and ON/OFF ratio of 107–108 are realized, i.e. the devices can operate similarly to conventional thermal CVD process. 相似文献
89.
旋转场移相器具有移相精度高(均方根误差可小于1°)和温度稳定性好等特点,通过改进射频传输结构,可大大提高他的功率容量。利用旋转场移相器的互易特性和铁氧体圆极化器的非互易特性,设计出高功率双工旋转场移相器。其双工特性可将收/发信号分开,实现移相器和环行器的双重功能,用于天线的收发通道等场合时,可省去一个高功率环行器,结构紧凑。分析了双工旋转场移相器的工作原理,阐述了高功率应用下的设计方法,推导出了管状铁氧体的相移量计算公式,按此方法设计了实用的器件,并给出了试验数据。 相似文献
90.
In keeping with the advance of more compact and more power-saving electronic equipment, the demand is increasing for smaller and more efficient switching power supply. Therefore, it is necessary to provide the adequate magnetic power ferrite materials to satisfy the demand. Such ferrite materials have to meet the following main requirement: 1) high initial permeability (μ i ); 2) high saturation magnetic induction (Bs); 3) high Curie temperature (Tc); 4) high electrical resistivity (ρ ); 5)… 相似文献