全文获取类型
收费全文 | 4530篇 |
免费 | 430篇 |
国内免费 | 536篇 |
专业分类
化学 | 2608篇 |
晶体学 | 55篇 |
力学 | 31篇 |
综合类 | 16篇 |
数学 | 240篇 |
物理学 | 1886篇 |
综合类 | 660篇 |
出版年
2024年 | 9篇 |
2023年 | 29篇 |
2022年 | 84篇 |
2021年 | 89篇 |
2020年 | 89篇 |
2019年 | 94篇 |
2018年 | 135篇 |
2017年 | 158篇 |
2016年 | 166篇 |
2015年 | 126篇 |
2014年 | 216篇 |
2013年 | 895篇 |
2012年 | 241篇 |
2011年 | 237篇 |
2010年 | 192篇 |
2009年 | 251篇 |
2008年 | 274篇 |
2007年 | 300篇 |
2006年 | 222篇 |
2005年 | 238篇 |
2004年 | 223篇 |
2003年 | 196篇 |
2002年 | 188篇 |
2001年 | 123篇 |
2000年 | 109篇 |
1999年 | 80篇 |
1998年 | 117篇 |
1997年 | 54篇 |
1996年 | 49篇 |
1995年 | 53篇 |
1994年 | 45篇 |
1993年 | 45篇 |
1992年 | 25篇 |
1991年 | 18篇 |
1990年 | 24篇 |
1989年 | 16篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有5496条查询结果,搜索用时 15 毫秒
41.
Changyao Shan Baishu Li Li Li Beibei Li YongLin Ren Tao Liu 《Molecules (Basel, Switzerland)》2022,27(14)
The metabolites produced by the larvae of Bactrocera dorsalis (Diptera: Tephritidae) exposed to different doses of irradiation were analyzed using solid phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS), and a metabonomic analysis method of irradiated insects based on GC-MS was established. The analysis revealed 67 peaks, of which 23 peaks were identified. The metabolites produced by larvae treated with different irradiation doses were compared by multivariate statistical analysis, and eight differential metabolites were selected. Irradiation seriously influenced the fatty acid metabolic pathway in larvae. Using the R platform combined with the method of multivariate statistical analysis, changes to metabolite production under four irradiation doses given to B. dorsalis larvae were described. Differential metabolites of B. dorsalis larvae carried chemical signatures that indicated irradiation dose, and this method is expected to provide a reference for the detection of irradiated insects. 相似文献
42.
43.
分析了双轴应变Si p型金属氧化物半导体场效应晶体管(PMOSFET)在γ射线辐照下载流子的微观输运过程, 揭示了γ射线的作用机理及器件电学特性随辐照总剂量的演化规律, 建立了总剂量辐照条件下的双轴应变Si PMOSFET 阈值电压与跨导等电学特性模型, 并对其进行了模拟仿真. 由仿真结果可知, 阈值电压的绝对值会随着辐照总剂量的积累而增加, 辐照总剂量较低时阈值电压的变化与总剂量基本呈线性关系, 高剂量时趋于饱和; 辐照产生的陷阱电荷增加了沟道区载流子之间的碰撞概率, 导致了沟道载流子迁移率的退化以及跨导的降低. 在此基础上, 进行实验验证, 测试结果表明实验数据与仿真结果基本相符, 为双轴应变Si PMOSFET辐照可靠性的研究和应变集成电路的应用与推广提供了理论依据和实践基础.
关键词:
应变Sip型金属氧化物半导体场效应晶体管
总剂量辐照
阈值电压
跨导 相似文献
44.
离散元与壳体有限元结合的多尺度方法及其应用 总被引:5,自引:1,他引:4
在深入研究复杂结构和非均质材料冲击响应和破坏机理的过程中,往往遇到多尺度计算问题。本文尝试建立三维离散元与壳体有限元结合的多尺度方法用于处理圆柱壳问题,该方法采用三维离散元对感兴趣的局域进行局部模拟,利用平板壳体有限元进行整体模拟,采用一种特殊的过渡层使离散元区和有限元区能很好的衔接。我们将这一方法应用于激光辐照下充压柱壳的热/力耦合冲击破坏响应,得到的模拟结果与文献报道有较好的吻合。 相似文献
45.
Xiangli Qian Huiying Sun Tianlu Chen Danzengluobu Youliang Feng Qi Gao Quanbu Gou Yiqing Guo Hongbo Hu Mingming Kang Haijin Li Cheng Liu Maoyuan Liu Wei Liu Bingqiang Qiao Xu Wang Zhen Wang Guangguang Xin Yuhua Yao Qiang Yuan Yi Zhang 《Frontiers of Physics》2022,17(6):64602
The High Altitude Detection of Astronomical Radiation (HADAR) experiment is a refracting terrestrial telescope array based on the atmospheric Cherenkov imaging technique. It focuses the Cherenkov light emitted by extensive air showers through a large aperture water-lens system for observing very-high-energy γ-rays and cosmic rays. With the advantages of a large field-of-view (FOV) and low energy threshold, the HADAR experiment operates in a large-scale sky scanning mode to observe galactic sources. This study presents the prospects of using the HADAR experiment for the sky survey of TeV γ-ray sources from TeVCat and provids a one-year survey of statistical significance. Results from the simulation show that a total of 23 galactic point sources, including five supernova remnant sources and superbubbles, four pulsar wind nebula sources, and 14 unidentified sources, were detected in the HADAR FOV with a significance greater than 5 standard deviations (σ). The statistical significance for the Crab Nebula during one year of operation reached 346.0 σ and the one-year integral sensitivity of HADAR above 1 TeV was ~1.3%–2.4% of the flux from the Crab Nebula. 相似文献
46.
建立了坑点型划痕的旋转抛物面模型, 用三维时域有限差分方法研究了熔石英后表面坑点型划痕随深度、 宽度、 间距以及酸蚀量变化对波长λ =355 nm入射激光的调制.研究表明, 这类划痕调制最强区位于相邻两坑点的连接区, 且越靠近表面调制越强.当其宽深比为2.0---3.5、 坑点间距约为坑点宽度的1/2时, 可获得最大光场调制, 最大光强增强因子(LIEF)为11.53; 当坑点间距大于坑点宽度时, 其调制大为减弱, 相当于单坑的场调制.对宽为60δ (δ =λ/12), 深和间距均为30δ的坑点型划痕进行刻蚀模拟, 刻蚀过程中最大LIEF为11.0, 当间距小于300 nm时, 相邻坑点由于衍射形成场贯通. 相似文献
47.
48.
Kawaljeet Singh Samra Ravinder Singh Lakhwant Singh 《Journal of Macromolecular Science: Physics》2013,52(10):691-698
Polyethylene terephthalate (PET) films of 50?μm thickness were exposed to swift-heavy 50?MeV copper and 84?MeV oxygen ions, with fluence varying from 1?×?1011 to 1?×?1013 ions cm?2. Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) and UV-visible spectroscopic techniques were used to characterize the irradiated samples. The XRD and DSC analysis indicated the loss of crystallinity during/after the irradiation. The FTIR spectra revealed the formation of alkyne end groups, C═C groups and structural deformation with increase of ion fluence. Considerable reduction in the value of the optical bandgap was inferred from the study of the UV-visible absorption curves. 相似文献
49.
O. Merwitz H. M. Nitzsche E. Hochhäuser 《Isotopes in environmental and health studies》2013,49(4):319-322
Abstract The dose-dependent isotope fractionation during decarboxylation (13C/12C) amplifies the radiation effect in the relatively low dose range. The fractionation of the nitrogen isotopes during deamination (15N/14N) at the dose of 17 Gy was found to be smaller than that of decarboxylation. 相似文献
50.
A. M. El-Agramy B. A. Henaish A. A. Shabaka 《Isotopes in environmental and health studies》2013,49(10):479-482
Radiophotolumenescence (RPL) of irradiated and non irradiated thin films of polymethylmethacrylate (PMMA) doped with anthracene (Anth) as a donor, and tetracyanoquinodimethane (TCNQ) as an acceptor, has been investigated. The RPL – glow spectrum was recorded to study the characterizing emission bands from the point of view of glow peak position and intensity and hence the prospective relative sensitivities. RFL – signal fading after one month storage in dark at room temperature post gamma irradiation was also studied. PMMA doped with 6:4 donor to acceptor ratio has been proved to be the most sensitive one with less fading regarding gamma detection. On the other hand 2 Anth: 8 TCNQ was found to be the proper dopant concentration ratio for thermal neutron detection. 相似文献