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   233篇
  免费   7篇
  国内免费   1篇
化学   179篇
晶体学   4篇
力学   5篇
数学   18篇
物理学   35篇
  2023年   1篇
  2022年   6篇
  2021年   1篇
  2020年   2篇
  2019年   4篇
  2018年   4篇
  2017年   1篇
  2016年   3篇
  2015年   8篇
  2014年   4篇
  2013年   13篇
  2012年   13篇
  2011年   15篇
  2010年   9篇
  2009年   7篇
  2008年   16篇
  2007年   24篇
  2006年   11篇
  2005年   11篇
  2004年   9篇
  2003年   8篇
  2002年   1篇
  2000年   3篇
  1999年   5篇
  1998年   2篇
  1997年   5篇
  1996年   2篇
  1995年   3篇
  1994年   3篇
  1993年   5篇
  1992年   4篇
  1991年   3篇
  1990年   5篇
  1989年   5篇
  1988年   3篇
  1987年   3篇
  1986年   3篇
  1985年   3篇
  1984年   2篇
  1982年   2篇
  1980年   1篇
  1979年   1篇
  1974年   3篇
  1972年   1篇
  1967年   1篇
  1935年   2篇
排序方式: 共有241条查询结果,搜索用时 31 毫秒
121.
This study analyzed photobiomodulation therapy (PBMT) effects on regenerative, antioxidative, anti-inflammatory and angiogenic markers in the dystrophic skeletal muscle of mdx mice, the experimental model of Duchenne muscular dystrophy (DMD), during the acute phase of dystrophy disease. The following groups were set up: Ctrl (control group of normal wild-type mice; C57BL/10); mdx (untreated mdx mice); mdxPred (mdx mice treated with prednisolone) and mdxLA (mdx mice treated with PBMT). The PBMT was carried out using an Aluminum Gallium Arsenide (AIGaAs; IBRAMED® laserpulse) diode, 830 nm wavelength, applied on the dystrophic quadriceps muscle. The mdxLA group showed a degenerative and regenerative area reduction simultaneously with a MyoD level increase, ROS production and inflammatory marker reduction and up-regulation in the VEGF factor. In addition, PBMT presented similar effects to prednisolone treatment in most of the parameters analyzed. In conclusion, our results indicate that PBMT in the parameters selected attenuated the dystrophic phenotype of mdx mice, improving skeletal muscle regeneration; reducing the oxidative stress and inflammatory process; and up-regulating the angiogenic marker.  相似文献   
122.
A divergent method for the synthesis of α,α′‐diarylacenaphtho[1,2‐c]phosphole P‐oxides has been established; α,α′‐dibromoacenaphtho[c]phosphole P‐oxide, which was prepared through a TiII‐mediated cyclization of 1,8‐bis(trimethylsilylethynyl)naphthalene, underwent a Stille coupling with three different kinds of aryltributylstannanes to afford the α,α′‐diarylacenaphtho[c]phosphole P‐oxides in moderate to good yields. X‐ray crystallographic analyses and UV/Vis absorption/fluorescence measurements have revealed that the degree of π‐conjugation, the packing motif, the electron‐accepting ability, and the thermal stability of the acenaphtho[c]phosphole π‐systems are finely tunable with the α‐aryl substituents. All the P?O and P?S derivatives exhibited high stability in their electrochemically reduced state. To use this class of arene‐fused phosphole π‐systems as n‐type semiconducting materials, we evaluated device performances of the bulk heterojunction organic photovoltaics (OPV) that consist of poly(3‐hexylthiophene), an indene‐C70 bisadduct, and a cathode buffer layer. The insertion of the diarylacenaphtho[c]phosphole P‐oxides as the buffer layer was found to improve the power conversion efficiency of the polymer‐based OPV devices.  相似文献   
123.
124.
A biosensor was developed for the detection of L-phenylalanine (Phe) and demonstrated for use in the diagnosis of phenylketonuria (PKU). It consists of L-phenylalanine dehydrogenase (L-PheDH) immobilized on a membrane, an ultraviolet light-emitting diode excitation system, and a photomultiplier tube. The L-PheDH was immobilized on a teflon membrane modified with 2-methacryloyloxyethyl phosphorylcholine and placed at the distal and of an optical fiber. The concentration of Phe was determined by immersing the sensor into a sample solution that also contained NAD+ and measurement of the fluorescence of the NADH produced by enzymatic reaction. Two L-PheDHs (from Thermoactinomyces intermedius and Sporosarcina sp.) were studied and compared. The fluorescence intensities of the biosensor are linearly related to the L-Phe concentrations in the range from 10 μmol L?1 to 10 mmol L?1. The sensor also was operated in the kinetic mode by differential determination of the slope of the signal within 2 min. The analytical range of the sensor is adequate for application in the genotypic diagnosis of PKU (diagnostic value >600 μmol L?1). High sensitivity, good cost-benefit ratio, and low power consumption are typical features of this biosensing system that can can be applied to routine screening of newborn.
Figure
Nicotinamide adenine dinucleotide (NADH) detecting biosensor of L-phenylalanine (Phe) was developed and demonstrated for diagnosis of phenylketonuria. This biosensor was comprised of L-phenylalanine dehydrogenase immobilized membrane, an ultra violet light-emitting diodes excitation system and a photomultiplier tube. The sensor was sufficient to clinical application of genotypic diagnosis for phenylketonuria.  相似文献   
125.
Commercial purity aluminium sheets were severely plastic deformed by accumulative roll bonding (ARB). Changes in electrical resistivity at 77 K and microstructure during the ARB process were traced up to 12 cycles, which corresponded to an equivalent strain of 10. The resistivity at 77 K increased with increasing number of ARB cycles, then saturated after about the sixth ARB cycle with a maximum increment of resistivity from starting material of about 1.1 nΩ m. Since lattice defects affect the resistivity of metals, the internal dislocation density and the density of grain boundaries were evaluated from scanning transmission electron microscopy images using Ham's method and grain boundary maps obtained from electron back-scattering diffraction, respectively. The relationship between the change in resistivity and the lattice defects is discussed.  相似文献   
126.
Samples of CaF2 irradiated for millions of years in nature were studied by several methods, including X-Ray diffraction, positron annihilation spectroscopy (PAS), photoluminescence spectroscopy (PLS) and transmission electron microscopy (TEM). It was found that the unexpectedly high density of radiation-induced defects present in the fluorite structure (documented by TEM) causes significant micro-strains. Even annealing up to 450°C cannot completely remove these micro-strains, which are stabilised by impurities. PAS and subsequent theoretical calculations revealed the behaviour of the defects during heating. The PL spectra of irradiated fluorite were also interpreted.  相似文献   
127.
Compared with cyclo -triphosphate anions, cyclo -tri- w -imidotriphosphate anions (Figure 1), cP 3 (NH) 3 3 m , form stable complexes with transition metal ions. Two experimental procedures, potentiometry and spectroscopy, have been applied to determine the stability constants of the complexes with Co 2+ , Ni 2+ , and Cu 2+ ions at 25;C and at I = 0.10 (NaClO 4 ). One-to-one (ML) complex formation has been assumed for the analyses. In the presence of sufficiently high concentration of metal ions, the log g 1 values determined by both methods are consistent with each other, whereas the log g 1 value determined by spectroscopy decreases with the decrease in metal ion concentration. This peculiar phenomenon cannot be explained by the presence of additional complexes, that is, ML 2 or M 2 L. One possible reasoning is agglomeration formation of ligand molecules mediated by countercations in aqueous solution.  相似文献   
128.
129.
The untapped potential of radical thiol-yne mono-addition chemistry is exploited to overcome the known limitations of thiol-ene chemistry in polymer coupling and block copolymer formation. By careful choice of alkyne, the reaction can selectively lead to the mono-addition product with efficiencies surpassing those achieved by traditional thiol-ene chemistry. This improvement is illustrated by the nearly quantitative synthesis of a variety of diblock and graft copolymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 319–326  相似文献   
130.
K Katayama  K Miyajima  M Ashida  T Itoh 《J Phys Condens Matter》2012,24(32):325801, 1-325801, 6
In Cd(0.8)Mn(0.2)Te, nonlinear photoluminescence (PL) appears only when localized excitons are selectively excited to high-density states. Here, the effect of a magnetic field is compared between nonlinear PL and PL due to localized magnetic polarons. Nonlinear PL shows a shift towards lower energy under an applied magnetic field, whereas PL of a localized magnetic polaron band shows a slight shift towards higher energy. The experimental results support the hypothesis that the origin of the nonlinear PL is a spin-aligned state of high-density exciton magnetic polarons. In the spin-aligned state, most spins of electrons (holes) in many magnetic polarons point in the same direction. In this new high-density photoexcited state, the s, p-d exchange interaction between photoexcited electrons (holes) and magnetic ions plays an important role.  相似文献   
[首页] « 上一页 [8] [9] [10] [11] [12] 13 [14] [15] [16] [17] [18] 下一页 » 末  页»
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