全文获取类型
收费全文 | 5393篇 |
免费 | 743篇 |
国内免费 | 273篇 |
专业分类
电工技术 | 200篇 |
综合类 | 621篇 |
化学工业 | 260篇 |
金属工艺 | 107篇 |
机械仪表 | 602篇 |
建筑科学 | 308篇 |
矿业工程 | 63篇 |
能源动力 | 96篇 |
轻工业 | 477篇 |
水利工程 | 49篇 |
石油天然气 | 99篇 |
武器工业 | 77篇 |
无线电 | 1366篇 |
一般工业技术 | 1289篇 |
冶金工业 | 98篇 |
原子能技术 | 57篇 |
自动化技术 | 640篇 |
出版年
2024年 | 1篇 |
2023年 | 93篇 |
2022年 | 167篇 |
2021年 | 203篇 |
2020年 | 213篇 |
2019年 | 152篇 |
2018年 | 143篇 |
2017年 | 187篇 |
2016年 | 189篇 |
2015年 | 215篇 |
2014年 | 395篇 |
2013年 | 323篇 |
2012年 | 408篇 |
2011年 | 387篇 |
2010年 | 319篇 |
2009年 | 321篇 |
2008年 | 255篇 |
2007年 | 346篇 |
2006年 | 337篇 |
2005年 | 269篇 |
2004年 | 219篇 |
2003年 | 189篇 |
2002年 | 152篇 |
2001年 | 151篇 |
2000年 | 128篇 |
1999年 | 107篇 |
1998年 | 83篇 |
1997年 | 76篇 |
1996年 | 54篇 |
1995年 | 71篇 |
1994年 | 62篇 |
1993年 | 44篇 |
1992年 | 33篇 |
1991年 | 29篇 |
1990年 | 28篇 |
1989年 | 14篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1972年 | 1篇 |
1963年 | 2篇 |
1961年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1955年 | 4篇 |
排序方式: 共有6409条查询结果,搜索用时 15 毫秒
1.
Carlo Dal Lin Claudia Maria Radu Giuseppe Vitiello Paola Romano Albino Polcari Sabino Iliceto Paolo Simioni Francesco Tona 《International journal of molecular sciences》2021,22(1)
Mechanical vibrations seem to affect the behaviour of different cell types and the functions of different organs. Pressure waves, including acoustic waves (sounds), could affect cytoskeletal molecules via coherent changes in their spatial organization and mechano-transduction signalling. We analyzed the sounds spectra and their fractal features. Cardiac muscle HL1 cells were exposed to different sounds, were stained for cytoskeletal markers (phalloidin, beta-actin, alpha-tubulin, alpha-actinin-1), and studied with multifractal analysis (using FracLac for ImageJ). A single cell was live-imaged and its dynamic contractility changes in response to each different sound were analysed (using Musclemotion for ImageJ). Different sound stimuli seem to influence the contractility and the spatial organization of HL1 cells, resulting in a different localization and fluorescence emission of cytoskeletal proteins. Since the cellular behaviour seems to correlate with the fractal structure of the sound used, we speculate that it can influence the cells by virtue of the different sound waves’ geometric properties that we have photographed and filmed. A theoretical physical model is proposed to explain our results, based on the coherent molecular dynamics. We stress the role of the systemic view in the understanding of the biological activity. 相似文献
2.
3.
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
4.
基于硅介质柱型光子晶体,采用时域有限差分方法(FDTD),探究高斯光束在光子晶体界面的逆古斯汉欣(GH)位移。通过在光子晶体下表面添加硅透镜,研究高斯光束的入射角度、硅透镜的曲率半径以及温度对光子晶体逆GH位移的影响。研究结果表明,发生最大逆GH位移的角度大于几何理想全反射角。添加焦点位于光子晶体表面中心的硅透镜可以使逆GH位移显著增强,且当硅透镜的曲率半径为170时,逆GH位移增大为不加透镜时的1.7倍。研究不同入射角度下温度对光子晶体的逆GH位移的影响发现,当高斯光束的入射角为26o时,逆GH位移随着温度的变化最大且线性度较好,便于温度监测。 相似文献
5.
《Contact lens & anterior eye》2022,45(1):101443
PurposeWith active investigation underway for embedded-circuit contact lenses, safe oxygen supply of these novel lenses remains a question. Central-to-peripheral corneal edema for healthy eyes during wear of soft contact (SCL) and scleral lenses (SL) with embedding components is assessed.MethodsVarious 2-dimensional (2D) designs of SL and SCL with embedded components are constructed on Comsol Multiphysics 5.5. Local corneal swelling associated with the designed lenses is determined by a recently developed 2D metabolic-swelling model. Settled central post-lens tear-film thicknesses (PoLTFs) are set at 400 μm and 3 μm for SL and SCL designs, respectively. Each lens design has an axisymmetric central and an axisymmetric peripheral embedment. Oxygen permeability (Dk) of the lens and the embedments ranges from 0 to 200 Barrer. Dimensions and location of the embedments are varied to assess optimal-design configurations to minimize central-to-peripheral corneal edema.ResultsBy adjusting oxygen Dk of the central embedment, the peripheral embedment, or the lens matrix polymer, corneal swelling is reduced by up to 2.5 %, 1.5 %, or 1.4 % of the baseline corneal thickness, respectively, while keeping all other parameters constant. A decrease in PoLTF thickness from 400 μm to 3 μm decreases corneal edema by up to 1.8 % of the baseline corneal thickness. Shifting the peripheral embedment farther out towards the periphery and towards the anterior lens surface reduces peak edema by up to 1.3 % and 0.6 % of the baseline corneal thickness, respectively.ConclusionsTo minimize central-to-peripheral corneal edema, embedments should be placed anteriorly and far into the periphery to allow maximal limbal metabolic support and oxygen transport in the polar direction (i.e., the θ-direction in spherical coordinates). High-oxygen transmissibility for all components and thinner PoLTF thickness are recommended to minimize corneal edema. Depending on design specifications, less than 1 % swelling over the entire cornea is achievable even with oxygen-impermeable embedments. 相似文献
6.
采用超声波协同臭氧工艺进行剩余污泥溶胞减量,考察了工艺条件对污泥减量效果的影响,并分析了处理过程中污泥性质的变化情况。结果表明:采用超声波和臭氧同时作用工艺,在超声波频率为20 kHz,声能密度为0.5 W/mL,臭氧投加速率为100 mg/min,反应时间为60 min的最佳条件下,污泥减量率达到40.11%,并且污泥粒径由处理前的29.76 μm降至处理后的10.01 μm,沉降比由0.93降至0.11,溶解性化学需氧量、总氮、总磷质量浓度依次由45,8,0.20 mg/L上升至1 242,129,12.41 mg/L,挥发性悬浮固体物与总悬浮固体物质量浓度比则由0.79降至0.63。 相似文献
7.
在物理模拟实验中对水合物微观赋存模式和饱和度进行准确控制和评价尚存在技术困难,仅依赖实验技术研究含水合物沉积物声学特性、建立储层参数解释模型存在局限性。采用基于有限元的数字岩石物理技术,针对悬浮、接触和胶结三种典型的水合物微观赋存模式分别建立多孔介质的三维电-力-声多物理场耦合模型,考察了微观赋存模式和水合物饱和度对多孔介质声速和衰减的影响规律,对比了声速数值模拟与理论模型计算结果,建立了声波衰减参数与水合物饱和度之间的关系式。研究结果表明:(1)对于三种水合物赋存模式,由于水合物相比孔隙水具有更高的弹性模量,多孔介质的声速随着水合物饱和度的增大而增大;水合物的存在导致声波在传播过程中遇到更多不连续的声阻抗界面,声衰减随着水合物饱和度的增大而近似线性增大;(2)悬浮和接触赋存模式条件下,水合物饱和度对多孔介质的声速和衰减影响规律基本一致;对于相同的水合物饱和度,胶结模式条件下含水合物多孔介质具有更高的声速和更小的声衰减;(3)通过合理选择参数值,利用权重方程与Lee改进的Biot-Gassmann Theory(BGTL)模型估算的含悬浮和接触模式水合物多孔介质的声速较为准确;通过等效介质理论模型C计算的含胶结模式水合物多孔介质的声速更为准确。研究结果可为获取复杂条件下含水合物沉积物的声学特性提供数值建模方法,为基于声波测井数据的水合物储层精细评价提供理论支撑。 相似文献
8.
提出了一种针对无限共轭距显微物镜的数值孔径测量方法,采用载玻片与空气界面处的全反射效应以及其在物镜的后焦面产生的全反射圆作为数值孔径参考基准,根据阿贝正弦定理推导出物镜的数值孔径。完成了基于该原理的实验测试系统的研发,包括光学系统、控制系统和完整的后焦面算法流程。其中的图像处理算法采用了二维傅立叶相关分析和灰度统计。对若干实际的油浸物镜的数值孔径进行了测量,结果表明本方法相对误差低于1%,远低于本文对比的其它方法。本方法对应的实验测量装置简单,可快速、全自动化地对实际的油浸物镜的数值孔径进行测量,且测量结果具有高精度和高重复性的优势,能直接用于无限共轭距油浸物镜的数值孔径测量,解决当前制约我国高端镜头检测方面的困难,具有很好的应用前景。 相似文献
9.
通过流场-声场同步测试实验,观测自由液面处双悬停气泡几近同时破裂,引起液面波动的瞬态流动行为与声学特性。利用短时傅里叶变换提取了声音信号的时-频谱图,同步分析了气泡破裂过程图像和声压图谱。结果表明,双悬停气泡相继破裂,气泡Ⅰ射流形成和气泡Ⅱ体积急剧收缩的时刻重叠,存在高于单气泡破裂0.5 Pa的声压激增现象,该声压峰值均大于单气泡破裂、体积急剧收缩、射流引起的声压幅值。双悬停气泡破裂引起的液面波动相向传播重叠时刻,也存在明显的声压峰值。其中,气泡Ⅰ射流形成和气泡Ⅱ体积急剧收缩重叠时刻的声信号中心频率约为1078 Hz;双悬停气泡破裂引起的液面振动波叠加时刻具有两个频域峰值,中心频率分别为1242 Hz和2063 Hz。 相似文献
10.
《Contact lens & anterior eye》2021,44(2):192-219
This paper outlines changes to the ocular surface caused by contact lenses and their degree of clinical significance. Substantial research and development to improve oxygen permeability of rigid and soft contact lenses has meant that in many countries the issues caused by hypoxia to the ocular surface have largely been negated. The ability of contact lenses to change the axial growth characteristics of the globe is being utilised to help reduce the myopia pandemic and several studies and meta-analyses have shown that wearing orthokeratology lenses or soft multifocal contact lenses can reduce axial length growth (and hence myopia).However, effects on blinking, ptosis, the function of Meibomian glands, fluorescein and lissamine green staining of the conjunctiva and cornea, production of lid-parallel conjunctival folds and lid wiper epitheliopathy have received less research attention. Contact lens wear produces a subclinical inflammatory response manifested by increases in the number of dendritiform cells in the conjunctiva, cornea and limbus. Papillary conjunctivitis is also a complication of all types of contact lenses. Changes to wear schedule (daily disposable from overnight wear) or lens materials (hydrogel from SiHy) can reduce papillary conjunctivitis, but the effect of such changes on dendritic cell migration needs further study. These changes may be associated with decreased comfort but confirmatory studies are needed. Contact lenses can affect the sensitivity of the ocular surface to mechanical stimulation, but whether these changes affect comfort requires further investigation.In conclusion, there have been changes to lens materials, design and wear schedules over the past 20+ years that have improved their safety and seen the development of lenses that can reduce the myopia development. However, several changes to the ocular surface still occur and warrant further research effort in order to optimise the lens wearing experience. 相似文献