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   655篇
  免费   23篇
  国内免费   3篇
化学   449篇
晶体学   5篇
力学   30篇
数学   79篇
物理学   118篇
  2022年   18篇
  2021年   25篇
  2020年   26篇
  2019年   18篇
  2018年   30篇
  2017年   23篇
  2016年   35篇
  2015年   15篇
  2014年   12篇
  2013年   55篇
  2012年   37篇
  2011年   37篇
  2010年   25篇
  2009年   32篇
  2008年   29篇
  2007年   22篇
  2006年   22篇
  2005年   17篇
  2004年   10篇
  2003年   19篇
  2002年   13篇
  2001年   7篇
  2000年   7篇
  1998年   8篇
  1997年   9篇
  1996年   6篇
  1995年   7篇
  1994年   6篇
  1993年   3篇
  1992年   5篇
  1991年   6篇
  1990年   5篇
  1989年   6篇
  1988年   5篇
  1986年   4篇
  1985年   7篇
  1984年   4篇
  1983年   9篇
  1982年   3篇
  1981年   9篇
  1980年   3篇
  1979年   3篇
  1978年   3篇
  1977年   4篇
  1976年   3篇
  1975年   5篇
  1974年   5篇
  1973年   3篇
  1970年   3篇
  1961年   3篇
排序方式: 共有681条查询结果,搜索用时 31 毫秒
1.

Polyacrylonitrile/ferrocyanide composite incorporated with cetrimonium bromide (PFICB) was synthesized and evaluated as a novel bifunctional adsorbent for coremoval of Cs+ and HCrO4?. Results of the reaction time effect showed that adsorption of Cs+ and HCrO4? onto PFICB were rapid processes. The effect of the solution pH in the range 2.5–10 revealed that PFICB had the ability to simultaneously remove Cs+ and HCrO4?. The maximum adsorption capacity of PFICB was found to be 41.79 mg/g for Cs+ and 19.39 mg/g for HCrO4?. These values were compared with those reported in literature using other adsorbents.

  相似文献   
2.
3.
4.
5.
This paper applies the entropy-based fractal indexing scheme that enables the grid environment for fast indexing and querying. It addresses the issue of fault tolerance and load balancing-based fractal management to make computational grids more effective and reliable. A fractal dimension of a cloud of points gives an estimate of the intrinsic dimensionality of the data in that space. The main drawback of this technique is the long computing time. The main contribution of the suggested work is to investigate the effect of fractal transform by adding R-tree index structure-based entropy to existing grid computing models to obtain a balanced infrastructure with minimal fault. In this regard, the presented work is going to extend the commonly scheduling algorithms that are built based on the physical grid structure to a reduced logical network. The objective of this logical network is to reduce the searching in the grid paths according to arrival time rate and path’s bandwidth with respect to load balance and fault tolerance, respectively. Furthermore, an optimization searching technique is utilized to enhance the grid performance by investigating the optimum number of nodes extracted from the logical grid. The experimental results indicated that the proposed model has better execution time, throughput, makespan, latency, load balancing, and success rate.  相似文献   
6.
The current study attempted, for the first time, to qualitatively and quantitatively determine the phytochemical components of Elatostema papillosum methanol extract and their biological activities. The present study represents an effort to correlate our previously reported biological activities with a computational study, including molecular docking, and ADME/T (absorption, distribution, metabolism, and excretion/toxicity) analyses, to identify the phytochemicals that are potentially responsible for the antioxidant, antidepressant, anxiolytic, analgesic, and anti-inflammatory activities of this plant. In the gas chromatography-mass spectroscopy analysis, a total of 24 compounds were identified, seven of which were documented as being bioactive based on their binding affinities. These seven were subjected to molecular docking studies that were correlated with the pharmacological outcomes. Additionally, the ADME/T properties of these compounds were evaluated to determine their drug-like properties and toxicity levels. The seven selected, isolated compounds displayed favorable binding affinities to potassium channels, human serotonin receptor, cyclooxygenase-1 (COX-1), COX-2, nuclear factor (NF)-κB, and human peroxiredoxin 5 receptor proteins. Phytol acetate, and terpene compounds identified in E. papillosum displayed strong predictive binding affinities towards the human serotonin receptor. Furthermore, 3-trifluoroacetoxypentadecane showed a significant binding affinity for the KcsA potassium channel. Eicosanal showed the highest predicted binding affinity towards the human peroxiredoxin 5 receptor. All of these findings support the observed in vivo antidepressant and anxiolytic effects and the in vitro antioxidant effects observed for this extract. The identified compounds from E. papillosum showed the lowest binding affinities towards COX-1, COX-2, and NF-κB receptors, which indicated the inconsequential impacts of this extract against the activities of these three proteins. Overall, E. papillosum appears to be bioactive and could represent a potential source for the development of alternative medicines; however, further analytical experiments remain necessary.  相似文献   
7.
A straightforward strategy to prepare nanoporous metal oxides with well‐defined shapes is highly desirable. Through thermal treatment and a proper selection of metal‐cyanide coordination polymers, nanoporous nickel‐cobalt mixed oxides with different shapes (i.e., flakes and cubes) can be easily prepared. Our nanoporous materials demonstrate high electrocatalytic activity for oxygen evolution reaction.  相似文献   
8.
Controllable tailoring of metal-free/carbon-based nanostructures tends an encouraging way to enhance the bifunctional activity of electrodes, but a great challenge owing to the sluggish kinetics of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, a facile tempted-defects assisted fractionation strategy is presented to synthesize N, S, and O tri-doped metal-free catalyst (DE-TDAP). Due to this effective tempted-defects and heteroatoms interlinking in DE-TDAP, it delivers the lowest overpotential toward both the OER (346 mV) and HER (154 mV) at 10 mA cm?2. Remarkably, the DE-TDAP-electrode carries only a cell voltage of 1.81 V at 10 mA cm?2 for overall water splitting and long-term stability. Considerably, the density functional theory (DFT) calculation exposes that the tailored-defects in tri-doped interlinking could enhance bifunctional catalytic performance devising from lower Gibbs free energy of OER/HER intermediates on active sites. This struggle henceforth provides a perceptive understanding of the synergetic principles of heteroatom-interlinking-tailoring nanostructures in water splitting.  相似文献   
9.
Mesoporous silica SBA‐15 was synthesized and silanized with azidopropyl triethoxysilane in order to design a clickable material. Fourier transform infrared analysis permitted to prove the attachment of the azidopropylene groups to SBA‐15 resulting in the reactive and functional material N3‐SBA‐15. X‐ray photoelectron spectroscopy was used to determine the surface composition of SBA‐15. However, we unexpectedly found that the surface bound azido groups undergo X‐ray induced decomposition during the X‐ray photoelectron spectroscopy analysis resulting in the formation of nitrenes. These are very reactive groups able to intercalate C―C and C―H bonds of the propylene chains as judged from the N1s peak shape. Possible mechanisms of intercalation are suggested. C1s and N1s peaks were recorded at different exposure time. N/C, N+/N and N+/C undergo exponential decay. N+/N reaches the value of zero in less than 80 min of exposure to the X‐ray source. The N+/C decay plot was fitted with first‐order kinetics, and the decomposition kinetic constant (kdec) was found to equal to 516.4 s?1. This is a fast X‐ray induced degradation which must be considered with care when examining clickable materials with surface bound alkyl azido groups. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
10.
Alkylation of N,N-dialkylcarboxamides with 1,3-dehydroadamantane has been accomplished for the first time. The reaction involves the C–H bond in the α-position with respect to the carbonyl group and provides a convenient one-step preparation of substituted carboxylic acid amides containing an 1-adamantyl substituent and a pharmacophoric group in the amide moiety.  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