全文获取类型
收费全文 | 206篇 |
免费 | 11篇 |
国内免费 | 19篇 |
专业分类
化学 | 50篇 |
力学 | 116篇 |
综合类 | 8篇 |
数学 | 8篇 |
物理学 | 54篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 11篇 |
2014年 | 8篇 |
2013年 | 18篇 |
2012年 | 7篇 |
2011年 | 12篇 |
2010年 | 6篇 |
2009年 | 7篇 |
2008年 | 11篇 |
2007年 | 16篇 |
2006年 | 14篇 |
2005年 | 12篇 |
2004年 | 11篇 |
2003年 | 8篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有236条查询结果,搜索用时 15 毫秒
71.
从弹塑性基本关系、流动关系准则及Hooke定律出发,应用介质的动三轴、单轴和静水压实验规律,导出了物质的塑性势方程。对具体物质得到的塑性势F(ij,),在主应力和剪应力平面上为一闭合曲线,得到的本构关系表达式,对于砂土和玻璃钢两种介质进行计算,结果与实测值符合得很好。 相似文献
72.
73.
A high-speed digital camera is used to record the saltation of three sand samples(diameter range:300–500,200–300 and100–125μm).This is followed by an overlapping particle tracking algorithm to reconstruct the saltating trajectory and the differential scheme to abstract the kinetic parameters of saltating grains.The velocity results confirm the propagating feature of saltation in maintaining near-face aeolian sand transport.Moreover,the acceleration of saltating sand grains was obtained directly from the reconstructed trajectory,and the results reveal that the climbing stage of the saltating trajectory represents an critical process of energy transfer while the sand grains travel through air. 相似文献
74.
A kind of octanol-modifded silica nanoparticle was fabricated and employed as a framework to form‘‘soggy sand’’electrolyte along with 1-butyl-3-methylimidazolium tetrafluoroborate.‘‘Soggy sand’’and poly(vinylidene fluoride-hexafluoropropylene)composite electrolyte membranes were electrospun for the frst time.The properties of this membrane electrolyte have been evaluated by the mechanical test and electrochemical test.The Young’s modulus increased by 275%from 6.8 MPa to 25.5 MPa and the electrical conductivity increased to 7.6 10à5S/cm at 290.15 K when compared to pristine P(VdF-HFP)membrane electrolyte.The conductivity is 3.1 10à4S/cm at 323.15 K. 相似文献
75.
A semi‐quantitative approach for the rapid screening and mass profiling of naphthenic acids directly in contaminated aqueous samples 下载免费PDF全文
Kyle D. Duncan Dane R. Letourneau Gregory W. Vandergrift Karl Jobst Eric Reiner Chris G. Gill Erik T. Krogh 《Journal of mass spectrometry : JMS》2016,51(1):44-52
We report the use of a direct sampling, online analytical approach for the determination of acid extractable naphthenic acids in complex aqueous samples, known as condensed phase membrane introduction mass spectrometry (CP‐MIMS). The technique employs a capillary hollow fibre semi‐permeable membrane probe configured for immersion into a pH adjusted sample. A continuously flowing methanol acceptor phase transfers naphthenic acids to an electrospray ionization source, operated in negative ion mode, whereupon they are analysed by mass spectrometry as [M–H]? ions. High‐resolution mass spectrometry is used to characterize the influence of sample pH on membrane transport of multiple components of complex naphthenic acid mixtures. We demonstrate the use of CP‐MIMS for semi‐quantitative analysis of real‐world samples using selected ion monitoring and full scan mass spectra at unit mass resolution. The technique has also been employed to continuously monitor the temporal evolution in the mass profile and concentrations of individual naphthenic acid isomer classes in heterogeneous solutions during adsorption processes. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
76.
为了使干旱沙漠地区的电子系统能够全天候的工作, 必须开展沙尘大气的电磁波多重散射及衰减特性研究. 根据Mie理论、沙尘大气粒子尺寸分布和能见度的关系得到了电磁波沙尘大气传播衰减的计算方法, 计算了不同沙尘大气能见度的37 GHz电磁波的衰减, 与其他经验公式及文献中的实验结果进行比较, 文中方法得到的结果更接近于测量结果. 为了研究较低能见度沙尘暴中电磁波的传播特性, 需研究沙尘大气的多重散射效应. 应用Monte Carlo模拟方法, 在沙尘粒子为干燥和5%水含量时, 模拟了37 GHz和93 GHz电磁波在沙尘大气中传播时考虑多重散射效应的衰减, 并与基于Mie理论的计算结果进行比较, 结果显示, 在37 GHz时, 沙尘大气的多重散射对衰减的影响小, 在93 GHz时多重散射显著, 沙尘大气能见度越低, 多重散射的影响越显著. 粒子水含量增加使电磁波的衰减显著增大, 对多重散射的影响不明显. 因此, 在相同大气能见度下, 沙尘天气越干燥, 多重散射影响越大, 电磁波衰减减小越显著. 相似文献
77.
78.
Dependence of effective screening length in granular columns on bead and silo sizes and their ratio 下载免费PDF全文
Apparent mass measurements at the bottom of silos have been carried out. An important parameter in the Janssen model known as the effective screening length has been investigated for different bead and silo diameters as well as of their ratios. It is found that the effective screening length augments with the grain diameter d in addition to the granular column size. It is also revealed that λ exhibits stronger correlation with the bead diameter than that of the silo. This phenomenon is attributed to the reduced-shielding of the vertical stresses to the horizontal ones. 相似文献
79.
Khalid Khan Muhammad Rizwan Khalid Abdul Jabbar Perveen Akhter 《Isotopes in environmental and health studies》2013,49(2):286-294
Natural and anthropogenic radioactivity of sand and water samples collected from the four big rivers of Punjab province, Pakistan, was measured using a high-purity germanium detector coupled with a high resolution multichannel analyser. The average concentration of the naturally occurring radionuclides 226Ra, 232Th and 40K in all the sand samples from the rivers Jhelum, Chenab, Ravi and Indus was found to be 22±0.6, 36±1 and 287±10 Bq?kg ?1, respectively, while the concentration of the anthropogenic radionuclide 137Cs was found to be below the minimum detectable activity, i.e. ~ 1.2 Bq?kg ?1. All the sand samples have Raeq concentrations lower than the limit of 370 Bq?kg ?1. Indoor (H in) and outdoor (H out) radiation hazard indices were calculated for the samples to assess the radiation hazards arising due to the use of this sand in construction, and were found to be less than unity in the study area. Calculated values of the absorbed dose rate were less than the typical world average value of 59 nGy?h ?1, and the annual effective dose rate was also less than the typical world value of 70 μSv, except in the Indus river, in which it is slightly higher then the world average. Results show that the measured values are comparable with other global radioactivity measurements. None of the studied riverbeds was considered a radiological hazard, and their sand can be safely used in construction. 相似文献
80.