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   991篇
  免费   31篇
  国内免费   3篇
化学   791篇
晶体学   4篇
力学   6篇
数学   91篇
物理学   133篇
  2023年   4篇
  2021年   6篇
  2020年   8篇
  2019年   12篇
  2018年   8篇
  2017年   9篇
  2016年   19篇
  2015年   18篇
  2014年   23篇
  2013年   33篇
  2012年   54篇
  2011年   76篇
  2010年   33篇
  2009年   35篇
  2008年   54篇
  2007年   74篇
  2006年   66篇
  2005年   43篇
  2004年   54篇
  2003年   53篇
  2002年   50篇
  2001年   9篇
  2000年   16篇
  1999年   16篇
  1998年   16篇
  1997年   8篇
  1996年   19篇
  1995年   5篇
  1994年   16篇
  1993年   11篇
  1992年   14篇
  1991年   7篇
  1990年   4篇
  1988年   7篇
  1987年   14篇
  1986年   7篇
  1985年   17篇
  1984年   16篇
  1983年   5篇
  1982年   8篇
  1981年   10篇
  1980年   8篇
  1979年   13篇
  1978年   11篇
  1977年   6篇
  1976年   6篇
  1975年   4篇
  1973年   5篇
  1972年   5篇
  1964年   2篇
排序方式: 共有1025条查询结果,搜索用时 31 毫秒
131.
We discuss the properties of algebraic-geometric codes defined by a vector bundle on a curve X over a finite field. We investigate the correction capacities of the codes defined from vector bundles constructed by means of finite coverings of X.  相似文献   
132.
[Structure: see text] The morphinan skeleton was effectively synthesized by an intramolecular Mannich-type reaction. Further transformation led to total synthesis of morphine.  相似文献   
133.
We report electrically detected electron spin resonance (ESR) measurements of a high mobility two-dimensional (2D) electron system formed in a Si/SiGe quantum well, with millimeter wave in a high magnetic field . The negative ESR signal observed under an in-plane magnetic field gives direct evidence that the spin polarization leads to a resistance increase in the 2D metallic state. Suppression of spin decoherence was observed in the quantum Hall state at the Landau level filling factor ν=2. Strength of the nuclear magnetic field in the resonance is evaluated to be less than , much smaller than that reported for GaAs/AlGaAs heterostructures.  相似文献   
134.
Tohru Ozawa 《Mathematische Nachrichten》2013,286(17-18):1792-1796
We study an initial boundary value problem for a time‐dependent 3D Ginzburg‐Landau model of superconductivity with partial viscous terms. We prove the global existence of strong solutions.  相似文献   
135.
Photo-induced magnetic phase transitions observed in Co—Fe Prussian blue analogues are discussed from a theoretical point of view. In this material a magnetization is induced by visible light, and the induced magnetization can be completely diminished not only by thermal annealing but also by irradiation of infra red light. After a brief survey of relevant experiments, we present an overview of our theoretical approaches to clarify the underlying mechanism of this interesting phenomenon. The ligand field at the Co site is shown to be the most relevant variable controlling spin states. The presence of Fe vacancies and the resultant ligand substitution by water molecules turns to be an essential prerequisite for the photoinduced magnetization.  相似文献   
136.
Salinipostins are cyclic enol-phosphotriesters isolated from a marine-derived Salinispora sp. as antimalarial compounds. Herein, the first enantioselective synthesis of salinipostin A was achieved. Organocatalyst-mediated asymmetric cyclopropanation and regioselective cyclopropane ring opening were the key steps.  相似文献   
137.
We report three self‐assembled iron complexes that comprised an anti‐parallel open form (o‐ L anti), a parallel open form (o‐ L syn), and a closed form (c‐ L ) of diarylethene conformers. Under kinetic control, FeII2(o‐ L anti)3 was isolated, which exhibited a dinuclear structure with diamagnetic properties. Under light‐irradiation control, FeII2(c‐ L )3 was prepared and exhibited paramagnetism and spin‐crossover behaviour. Under thermodynamic control and in the presence of indispensable [FeIII(Tp*)(CN)3]?, FeII2(o‐ L anti)3 and FeII2(c‐ L )3 transformed into tetranuclear FeIII2FeII2(o‐ L syn)2, which exhibited complete spin‐crossover behaviour at T1/2=353 K.  相似文献   
138.
Linezolid is an antimicrobial agent for the treatment of multiresistant Gram‐positive infections. A practical high‐performance liquid chromatography method was developed for the determination of linezolid in human plasma and saliva. Linezolid and an internal standard (o‐ethoxybenzamide) were extracted from plasma and saliva with ethyl acetate and analyzed on a Capcell Pak C18 MG column with UV detection at 254 nm. The calibration curve was linear through the range 0.5–50 µg/mL using a 200 μL sample volume. The intra‐ and interday precisions were all <6.44% for plasma and 5.60% for saliva. The accuracies ranged from 98.8 to 110% for both matrices. The mean recoveries of linezolid were 80.8% for plasma and 79.0% for saliva. This method was used to determine the plasma and saliva concentrations of linezolid in healthy volunteers who were orally administered a 600 mg dose of linezolid. Our liquid–liquid extraction procedure is easy and requires a small volume of plasma or saliva (200 μL). This small volume can be advantageous in clinical pharmacokinetic studies, especially if children participate. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
139.
Cobalt hexacyanoferrate of various compositions was prepared in flow mode and the role of the vacancy on the structure, thermogravimetric (TG) properties, and the adsorption efficiency was studied. The material, NayCo[Fe(CN)6]1−xz H2O, with a minimum vacancy of x=0.014 to the highest x=0.47, was obtained. The TG-differential scanning calorimetry (DSC) profile showed a distinct influence of the vacancy on the water release temperature. Materials with x>0.35 showed a smooth release of water at a relatively lower temperature. However, for the materials with x<0.35, water release took place in multiple steps, suggesting the existence of various forms of water. The FTIR profiles supported the existence of free and bonded water molecules. However, the materials with multiple water peaks in the FTIR spectra showed a shift of the major XRD peaks when heated at 285 °C in N2 atmosphere. Regarding the effect of the vacancy on the adsorption behavior, for NH4, the adsorption was found to be proportional to the number of Na atoms in the material, confirming the ion-exchange process. On the contrary, the materials with low vacancy and high Na content showed nominal Cs adsorption capacity. Interestingly, the K adsorption capacity was found to be in between that of the other two ions. This means the ionic size decides the rate of placement into the interstitial sites. For larger ions like Cs, the ease of percolation via the vacancy decides the overall adsorption efficiency.  相似文献   
140.
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