首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   294篇
  免费   3篇
  国内免费   8篇
化学   124篇
晶体学   1篇
力学   10篇
数学   42篇
物理学   128篇
  2022年   3篇
  2020年   5篇
  2019年   5篇
  2014年   5篇
  2013年   7篇
  2012年   14篇
  2011年   8篇
  2010年   13篇
  2009年   8篇
  2008年   5篇
  2007年   13篇
  2006年   10篇
  2005年   12篇
  2004年   12篇
  2003年   5篇
  2002年   6篇
  2001年   6篇
  2000年   7篇
  1999年   7篇
  1998年   5篇
  1997年   5篇
  1995年   5篇
  1994年   3篇
  1993年   2篇
  1992年   5篇
  1991年   4篇
  1990年   5篇
  1989年   5篇
  1987年   3篇
  1986年   2篇
  1985年   4篇
  1984年   5篇
  1983年   5篇
  1982年   5篇
  1981年   14篇
  1980年   10篇
  1979年   7篇
  1978年   5篇
  1977年   5篇
  1976年   6篇
  1975年   4篇
  1974年   5篇
  1973年   4篇
  1972年   4篇
  1969年   2篇
  1942年   2篇
  1933年   2篇
  1931年   2篇
  1923年   2篇
  1893年   2篇
排序方式: 共有305条查询结果,搜索用时 31 毫秒
211.
Zinc–bromine flow batteries are promising for stationary energy storage, and bromine‐complexing agents have been used to form phase‐separated liquid polybromide products. However, an understanding of the dynamics of polybromide nucleation is limited due to the beam sensitivity and complexity of polybromides. Here we report an in operando platform composed of dark‐field light microscopy and a transparent electrochemical cell to reveal the dynamics of polybromide formation in their native environment. Using our platform, we confirm and reveal the liquid nature, chemical composition, pinning effect (strong interaction with Pt), residual effect (residual charge products on the surface), self‐discharging, and over‐oxidation of the polybromide products. The results provide insights into the role of complexing agents and guide the future design of zinc–bromine flow batteries. Furthermore, our in operando platform can potentially be used to study sensitive species and phases in other electrochemical reactions.  相似文献   
212.
The frequency fluctuation correlation function (FFCF) measures the spectral diffusion of a state's transition while the frequency fluctuation cross‐correlation function (FXCF) measures the correlation dynamics between the transitions of two separate states. These quantities contain a wealth of information on how the chromophores or excitonic states interact and couple with its environment and with each other. We summarize the experimental implementations and theoretical considerations of using two‐dimensional electronic spectroscopy to characterize FFCFs and FXCFs. Applications can be found in systems such as the chlorophyll pigment molecules in light‐harvesting complexes and CdSe nanomaterials.  相似文献   
213.
A general formula is established for the rate at which acoustic energy is dissipated at the sharp edges of a rigid boundary by the generation of vorticity in the presence of a low, subsonic mean flow of uniform mean density. Experimental results relating to the radiation of sound from a jet pipe are used to show how the formula can be used to make quantitative predictions in the absence of a detailed knowledge of the unsteady flow field.  相似文献   
214.
It has previously been demonstrated that baculovirus infection of the Spodoptera frugiperda Sf-9 (Sf-9) and Trichoplusia ni BTI-Tn-5B1-4 (Tn-5B1-4) insect cell lines leads to oxidative stress as measured by protein and membrane lipid oxidation and that this oxidative damage contributes to cell death. As a result of these findings, it was hypothesized that baculovirus infection stimulates superoxide radical (O 2 ·— synthesis in the mitochondria and that the resulting O 2 ·— accumulation overwhelms the cells’ antioxidant defenses. We investigated the ability of manganese superoxide dismutase (MnSOD) expression (which reduces O 2 ·— to H2O2) to overcome the oxidative damage caused by baculovirus infection. It was found that MnSOD expression significantly reduced oxidative damage in baculovirus-infected Tn-5B1-4 cells but had no significant effect on oxidative damage in baculovirus-infected Sf-9 cells. The results are consistent with the hypothesis that O 2 ·— accumulation in the mitochondria is at least partially responsible for the oxidative damage resulting from the baculovirus infection of insect cells.  相似文献   
215.
An approximate analytical theory is proposed for calculatingthe compression wave generated when a train enters a tunnelfitted with an entrance hood with an open window. The pressurerise ahead of the entering train causes air to exhaust fromthe window in the form of a high-speed jet. The profile of thecompression wave transmitted into the tunnel is modified by theinteraction of the train nose with the window, by multiple reflectionsof wave energy between the window and the hood portal priorto transmission into the tunnel, and in addition by the productionof a pressure pulse by the jet. The wave generation problemcan be formulated in a quasi-one-dimensional manner, wherebythe pressure field generated in front of and to the sides ofthe train in the absence of the window is assumed to be scatteredby the window. A self-consistent solution is obtained by evaluatingthe jet flow from the window using a nonlinear empirical quationproposed and validated by Cummings (1984, Amer. Inst. Aeron.Astron. J., 22, 786–792; 1986, J. Acoust. Soc. Amer.,79, 942–951) for the velocity in the window-exit plane.Predictions are found to be in excellent agreement with measurementsof compression wave profiles obtained in model scale experimentsreported by Howe et al. (2003, J. Fluid Mech., 487, 211–243)at train speeds 350 km h–1.  相似文献   
216.
217.
van Howe J  Xu C 《Optics letters》2005,30(1):99-101
We demonstrate an all-fiber, programmable, ultrafast optical delay line based on reversible frequency conversion by use of a time-prism pair. Using electro-optic phase modulators to provide the time-prism phase profile, we show a record scanning rate of 0.5 GHz and a delay range of 19.0 ps. Computer modeling suggests that aberration correction in the time-prism system can extend the delay range to 28.0 ps. Finally, limitations and potential improvement of our techniques are discussed.  相似文献   
218.
We compared plastic (polycarbonate) and high-quality glass support materials for gold-coated slides, when performing a model immunoassay against rabbit IgG using fluorescently labeled (AlexaFluor-647) anti-rabbit IgG, and detecting surface plasmon-coupled emission (SPCE) signals. Both, glass and plastic slides were simultaneously coated with a 48-nm layer of gold and protected with a 10-nm layer of silica. The maximum SPCE signal of AlexaFluor-647 was only two- to three-fold smaller on plastic slides than on glass slides. A small difference in the SPCE angles on glass (θ F = 55°) and plastic (θ F = 52.5°) slides was observed and can be explained with a slightly smaller refractive index of the plastic. We have not found any difference in the angle distribution (sharpness of the fluorescence signal at optimal SPCE angle) for the plastic slide compared to the glass slide. The kinetics of binding was monitored on the plastic slide as well as on the glass slide. Optically dense samples, a 4% red blood cell suspension and a 15% hemoglobin solution, are causing a reduction in the immunoassay SPCE signal by approximately 15% and three times, respectively, and the percentage of the reduction is the same for plastic and for glass slides. We believe that plastic substrates can be readily used in any SPCE assay, with only marginally lower total signal compared to high-quality glass slides.  相似文献   
219.
This paper is a discussion of the theory of diffraction and scattering of bending waves by mass-impedance loadings of an infinite plane plate. Emphasis is placed on the case of heavy loadings, at which deflexions of the plate are precluded and the scattering is the strongest possible. Examples treated in detail include the diffraction grating, diffraction by a semi-infinite rib, and diffraction by a comb of semi-inifinite ribs.  相似文献   
220.
The fundamental processes of protonation and ethylation, occurring in a methane chemical ionization source, have been investigated for a variety of aromatic amines. The positions of protonation and ethylation on the substrate amines were determined by generating isomeric ions either by protonation of neutral ethyl substituted amines or by ethylation of the amines themselves. The product ions were investigated for structural differences via collision induced dissociation and subsequent analysis via mass analysed ion kinetic energy spectrometry. Similarities and differences between mass analysed ion kinetic energy/collision induced dissociation spectra of these isomeric ions were used to determine protonation and ethylation sites for imidazole, benzimidazole, indazole, pyrrole, pyridine and aniline.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号