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   545篇
  免费   16篇
  国内免费   1篇
化学   355篇
晶体学   9篇
力学   3篇
数学   27篇
物理学   168篇
  2023年   3篇
  2022年   4篇
  2021年   9篇
  2020年   12篇
  2019年   12篇
  2018年   3篇
  2017年   8篇
  2016年   9篇
  2015年   9篇
  2014年   14篇
  2013年   28篇
  2012年   29篇
  2011年   38篇
  2010年   15篇
  2009年   13篇
  2008年   34篇
  2007年   20篇
  2006年   23篇
  2005年   26篇
  2004年   25篇
  2003年   21篇
  2002年   23篇
  2001年   8篇
  2000年   10篇
  1999年   7篇
  1998年   5篇
  1997年   7篇
  1996年   13篇
  1995年   8篇
  1994年   6篇
  1993年   11篇
  1992年   13篇
  1991年   3篇
  1990年   5篇
  1988年   4篇
  1987年   5篇
  1986年   4篇
  1985年   10篇
  1982年   3篇
  1981年   5篇
  1979年   5篇
  1978年   6篇
  1976年   5篇
  1973年   7篇
  1968年   4篇
  1967年   2篇
  1966年   4篇
  1956年   2篇
  1955年   2篇
  1954年   2篇
排序方式: 共有562条查询结果,搜索用时 15 毫秒
81.
The influences of two structural modifications on the photocurrent generation performance of the Langmuir–Blodgett (LB) film of the 6-O-phthalocyaninyl cellulose derivative were investigated. These structural modifications were the substituent groups at the O-2 and O-3 positions, and the central metal of the phthalocyanine moiety. Specifically, 6-O-Zn/phthalocyaninyl- (8a) and Pd/phthalocyaninyl (8b) -2,3-di-O-myristoylcelluloses were prepared instead of 6-O-Zn/phthalocyaninyl-2,3-di-O-myristylcellulose (2). The LB monolayer film of compound 8a on an indium thin oxide electrode showed higher photocurrent generation performance than that of compound 2. This suggested that myristoyl groups (C-14 acyl groups) were more beneficial to photocurrent generation than myristyl groups (C-14 alkyl groups), as the substituent at the O-2 and O-3 positions. The LB monolayer film of compound 8b showed photocurrent generation from 500 to 700 nm, although a blue-shift in the Q-band maximum was observed. The photocurrent generation performance of compound 8b was significantly higher than that of compound 8a. This indicated that Pd was more beneficial to photocurrent generation than Zn. The film of compound 8b prepared by the horizontal lifting method showed better photocurrent generation performance than that prepared by the vertical dipping method. Consequently, compound 8b is a complementary material to the porphyrin-appended cellulose derivative (1) for photocurrent generation system.  相似文献   
82.
In this study, we show that earnings forecasting creates an index-tracking portfolio that dominates the historical model trade-off curve. We find that using Toyo Keizai earnings forecasts improves geometric means by over 300 basis points compared to the historical model. Weighted latent root regression is used in this study to create portfolios that have outperformed the Japanese market in backtest and in real-time performance.  相似文献   
83.
84.
85.
2-(2-Dithianyl)benzhydrols (2 a-c) undergo facile cycloaddition reaction with maleic anhydride under thermal conditions to give 1-phenyl-naphthalenes (7 a-c) in one step. The naphthalenes (7 a-c) have been converted into the naphthalene lignan lactones, (9 a-c) and (10 a-c).  相似文献   
86.
Yb(Ba1−xSrx)2Cu4O8 (0.1x0.3) superconductors of the YBa2Cu4O8(“124”) structure were successfully synthesized using an O2-hot-isostaticc-pressing (HIP) technique. The samples were characterized with respect to the crystal structure and superconducting properties. The lattice parameters of the samples decreased as the substitution of Sr for Ba proceeded. The superconducting transition temperatures of all the Yb-“124” samples were more or less the same, being around 80 K.  相似文献   
87.
Homoorientaline 4 was oxidised with homogenised potato peelings along, followed by acetylation, to give 1-hydroxyhomoorientaline triacetate 9, the structure of which was determined by spectroscopic data and an alternative synthesis.  相似文献   
88.
The problem of multivariate information analysis is considered. First, the interaction information in each dimension is defined analogously according to McGill [4] and then applied to Markov chains. The property of interaction information zero deeply relates to a certain class of weakly dependent random variables. For homogeneous, recurrent Markov chains with m states, mn ≥3, the zero criterion of n-dimensional interaction information is achieved only by (n ? 2)-dependent Markov chains, which are generated by some nilpotent matrices. Further for Gaussian Markov chains, it gives the decomposition rule of the variables into mutually correlated subchains.  相似文献   
89.
A sharp feature in the charge-density excitation spectra of single-crystal MgB2, displaying a remarkable cosinelike, periodic energy dispersion with momentum transfer (q) along the c* axis, has been observed for the first time by high-resolution nonresonant inelastic x-ray scattering (NIXS). Time-dependent density-functional theory calculations show that the physics underlying the NIXS data is strong coupling between single-particle and collective degrees of freedom, mediated by large crystal local-field effects. As a result, the small-q collective mode residing in the single-particle excitation gap of the B pi bands reappears periodically in higher Brillouin zones. The NIXS data thus embody a novel signature of the layered electronic structure of MgB2.  相似文献   
90.
Simultaneous measurements of stress relaxation and differential dynamic modulus were made at 268 K over a time scale of 10 to 1045 s for nearly monodisperse polybutadiene (M w =2.2x105, 1,2-structure 70%, M e =3600) and also one having coarse cross-linking (M c =29000). Static shear strain ranged from 0.1 to 2.0. In a long-time region (t> k ), the relaxation modulus G (; t) could be expressed by the product G (0; t) h (y). The observed h() agreed well with the Doi-Edwards theory without use of IA approximation. Both the cured and uncured samples showed initial drop of the differential storage modulus G (), ; t) followed by gradual recovery, but did not attain the value before shearing G (, ; t) for the uncured sample showed smaller values than that for the cured one in the whole measured time scale at the higher strain, confirming the two origins of nonlinear viscoelasticity of well entangled polymer; induced chain anisotropy and induced decrement in entanglement density. G (, ; t) curves for the cured sample agreed well with the BKZ predictions. But the curves for the uncured sample agreed well with the BKZ prediction only at the time scale of t< k . BKZ prediction showed significant upward deviations at t> k . Such the differences are discussed in terms of the two origins.Dedicated to Prof. John D. Ferry on the occasion of his 85th birthday.  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