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   488篇
  免费   23篇
  国内免费   1篇
化学   401篇
晶体学   2篇
力学   1篇
数学   9篇
物理学   99篇
  2021年   1篇
  2020年   1篇
  2019年   3篇
  2018年   3篇
  2017年   1篇
  2016年   13篇
  2015年   15篇
  2014年   7篇
  2013年   9篇
  2012年   40篇
  2011年   38篇
  2010年   21篇
  2009年   11篇
  2008年   40篇
  2007年   44篇
  2006年   38篇
  2005年   29篇
  2004年   29篇
  2003年   29篇
  2002年   16篇
  2001年   14篇
  2000年   11篇
  1999年   4篇
  1998年   1篇
  1997年   4篇
  1996年   3篇
  1995年   7篇
  1994年   8篇
  1993年   4篇
  1992年   10篇
  1991年   4篇
  1990年   9篇
  1989年   3篇
  1988年   1篇
  1987年   5篇
  1986年   3篇
  1985年   6篇
  1984年   4篇
  1983年   4篇
  1982年   2篇
  1981年   2篇
  1980年   2篇
  1979年   1篇
  1978年   2篇
  1977年   4篇
  1976年   2篇
  1975年   1篇
  1974年   1篇
  1968年   1篇
  1967年   1篇
排序方式: 共有512条查询结果,搜索用时 31 毫秒
41.
The recent progress in the nanofabrication of superconducting films opens the road toward detectors with highly improved performances. This is the case for superconducting nano-striplines where the thickness and the width are pushed down to the extreme limits to realize detectors with unprecedented sensitivity and ultra fast response time. In this way quantum detectors for single photons at telecommunication wavelengths and for macromolecules such as proteins can be realized. As is often the case in applied nanotechnology, it is a challenge to make devices with the necessary macroscopic dimensions that are needed to interface present technologies, while maintaining the performance improvements. For nano-stripline detectors, both the fast temporal response and the device sensitivity is generally degraded when the area is increased. Here, we present how such detectors can be scaled up to macroscopic dimensions without losing the performance of the nano-structured active elements by using an innovative configuration. In order to realize ultrathin superconducting film the nano-layer is growth with a careful setup of the deposition technique which guarantees high quality and thickness uniformity at the nano-scale size. The active nano-strips are defined with the state-of-the-art electron beam nanolithography to achieve a highly uniform linewidth. We present working detectors based on nano-strips with thicknesses 9–40 nm and widths of 100–1000 nm which exhibit unprecedented speed and area coverage (40 × 40 μm2 for single photon detectors and 1 × 1 mm2 for single molecule detectors) based on niobium nitride thus enabling practical use of this nanotechnology.  相似文献   
42.
43.
The effects of dipotassium glycyrrhizinate (GLYK) on the dissolution behavior and bioavailability of amphotericin B (AMB) were investigated. The mixtures of AMB and GLYK were prepared at different molar ratios by lyophilization. Lyophilization resulted in amorphous AMB either alone or in the mixture. Dissolution rates of AMB of the mixtures were markedly faster than that of lyophilized AMB alone, which was followed by a decrease of dissolution. The initially-enhanced dissolution rate was likely to be due to the improvement of surface wettability of drug particles with GLYK rather than the amorphous state of AMB. A phase solubility study of AMB with GLYK indicated that the increasing solubility was caused by micellar solubilization. The in vitro release rate of AMB from suppositories containing the lyophilized mixtures was significantly accelerated by increasing the amount of GLYK. The rectal absorption of AMB from suppositories containing either the drug alone, a physical mixture or a lyophilized mixture was studied using rabbits. The absorption of the mixture (AMB/GLYK = 1/9) was about 35 times greater in the area under the serum concentration-time curve (0-24 h) than that of lyophilized AMB alone. These results suggest that GLYK is useful for improving the dissolution property of AMB and the bioavailability of the drug incorporated in suppositories.  相似文献   
44.
In the (6Li,d) reaction on36Ar, the strongly excited seventeen levels were observed at excitation energies above 11 MeV in40Ca. On the basis of the result of the DWBA analysis, these levels may correspond to the members of the higher nodal α-clusterK n =O+ band with prinicpal quantum numberN=14.  相似文献   
45.
Electrical characteristics of Mg-doped p-GaN activated with Ni catalytic layers have been investigated by means of temperature-dependent Hall effect measurements. It has been revealed that the Ni layer on GaN enhances activation of the acceptor in the whole annealing temperature range. This enhancement is remarkable especially at temperatures below 500 °C and can be attributed to the catalytic effect for the hydrogen desorption. We have found that the donor concentrations in the samples activated with the Ni catalysts are also higher than those activated without Ni. This is probably due to the catalytic effect of Ni for the nitrogen desorption. In addition, it has been found that the ionization energies of the Mg acceptors in GaN activated with the Ni layer are decreased from 170 to 118 meV as the acceptor concentration increases.  相似文献   
46.
The energy spectrum and α-spectroscopic factors of40Ca are calculated by using an α+36Ar orthogonality condition model. Overall agreement is obtained with the experimental data. The model successfully produces the parity-doubletK π=O + and O? α+36Ar cluster bands. It is shown that the coexistence and interference of α-cluster states and shell-model states are indispensable to understand the structure of40Ca.  相似文献   
47.
The time-differential perturbed angular correlation (TDPAC) method was applied to a study on the behavior of 140Ce atoms implanted in highly oriented pyrolytic graphite (HOPG). Exponential-type gradual attenuation of the directional anisotropy of the relevant γ-ray cascade was observed in the perturbation patterns. From temperature dependence of the relaxation rate, a thermally activated dynamic motion of the probe atoms was suggested.  相似文献   
48.
The transition metal phosphorus trichalcogenides MnPS3 and the FePS3 are CdCl2 type layered compounds, where the transition metal ions form a hexagonal lattice. While these compounds order anti-ferromagnetically at low temperature, the magnetic structures are different. We have reported that these mixtures Mn0.5Fe0.5PS3 is a spin glass with a glass transition temperature T g=33.7 K. Then, in this work, we report that the results of the temperature variation of the 57Fe Mössbauer spectra of FePS3 and Mn0.5Fe0.5PS3, in detail. In the anti-ferromagnetic state of FePS3, the hyperfine magnetic field H int increases with decreasing temperature and the Isomer shift I. S. increases slightly with decreasing temperature. However in Mn0.5Fe0.5PS3, the two broadened peaks are observed and the two peaks became a single peak with decreasing temperature at about 50.0 K, which is higher than T g=33.7 K. In the spin glass Mn0.5Fe0.5PS3, the Mössbauer spectra suggest that the magnetic interactions exist far above T g.  相似文献   
49.
It is suggested that weak coupling picture for theα-cluster states holds not only in the44Ti~40Ca region but also in the upper part of thesd-shell region. To confirm this experimentally, theα-clustering aspects of38Ar is investigated.  相似文献   
50.
A series of coronenetetraimide (CorTIm)‐centered cruciform pentamers containing multiporphyrin units, in which four porphyrin units are covalently linked to a CorTIm core through benzyl linkages, were designed and synthesized to investigate their structural, spectroscopic, and electrochemical properties as well as photoinduced electron‐ and energy‐transfer dynamics. These systems afforded the first synthetic case of coroneneimide derivatives covalently linked with dye molecules. The steady‐state absorption and electrochemical results indicate that a CorTIm and four porphyrin units were successfully characterized by the corresponding reference monomers. In contrast, the steady‐state fluorescence measurements demonstrated that strong fluorescence quenching relative to the corresponding monomer units was observed in these pentamers. Nanosecond laser flash photolysis measurements revealed the occurrence of intermolecular electron transfer from triplet excited state of zinc porphyrins to CorTIm. Femtosecond laser‐induced transient absorption measurements for excitation of the CorTIm unit clearly demonstrate the sequential photoinduced energy and electron transfer between CorTIm and porphyrins, that is, occurrence of the initial energy transfer from CorTIm (energy donor) to porphyrins (energy acceptor) and subsequent electron transfer from porphyrins (electron donor) to CorTIm (electron acceptor) in these pentamers, whereas only the electron‐transfer process from porphyrins to CorTIm was observed when we mainly excite porphyrin units. Finally, construction of high‐order supramolecular patterning of these pentamers was performed by utilizing self‐assembly and physical dewetting during the evaporation of solvent.  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