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   205篇
  免费   42篇
  国内免费   3篇
化学   135篇
晶体学   3篇
力学   12篇
综合类   7篇
数学   61篇
物理学   32篇
  2024年   1篇
  2023年   7篇
  2022年   8篇
  2021年   25篇
  2020年   22篇
  2019年   20篇
  2018年   13篇
  2017年   8篇
  2016年   15篇
  2015年   9篇
  2014年   14篇
  2013年   14篇
  2012年   14篇
  2011年   10篇
  2010年   8篇
  2009年   4篇
  2008年   2篇
  2007年   8篇
  2006年   5篇
  2005年   10篇
  2004年   1篇
  2003年   1篇
  2001年   3篇
  2000年   1篇
  1999年   1篇
  1997年   4篇
  1996年   3篇
  1995年   2篇
  1994年   3篇
  1993年   1篇
  1992年   1篇
  1990年   1篇
  1989年   1篇
  1986年   2篇
  1985年   6篇
  1984年   2篇
排序方式: 共有250条查询结果,搜索用时 78 毫秒
1.
The potential of X-ray nanotomography hosted in a SEM in presented in this paper. In order to improve the detail detectability of this system, which is directly related to the X-ray source size, thin metal layers have been studied and installed in the equipment. A 3D resolution pattern has been created in order to determine the smallest detectable features by this setup. This sample is a 25 μm diameter copper pillar in which size-controlled holes have been milled using a plasma-focused ion beam. This pattern has then been scanned and the resulting 3D reconstruction demonstrates that the instrument is able to detect 500 nm diameter voids in a copper interconnection, as used in 3D integration.  相似文献   
2.
基于色谱-质谱联用的新型有机污染物分析方法与技术   总被引:1,自引:0,他引:1  
赵晓峰  李云  张海军  倪余文  陈吉平 《色谱》2010,28(5):435-441
新型有机污染物是目前国内外关注的热点。在发现和分析新型有机污染物方面色谱-质谱联用技术发挥着至关重要的作用。本文对5类新型有机污染物(全氟化合物、药物、饮用水消毒副产物、农药转化产物和新农药、溴化阻燃剂)的主要色谱-质谱联用技术进行了介绍和评价,并对色谱-质谱联用的发展趋势进行了展望。  相似文献   
3.
The self‐inclusion behavior of monoester copillar[5]arenes depends on the position of the ester group, which causes different guest selectivities. Monoester copillar[5]arenes bearing an acetate chain can form stable self‐inclusion complexes in low‐ and high‐concentration solution and exhibit high guest selectivity. However, a monoester copillar[5]arene bearing a butyrate chain can not form a self‐inclusion complex and exhibits low guest selectivity. Thus, a new class of stable self‐inclusion complexes of copillar[5]arenes was explored to improve the selectivity of molecular recognition.  相似文献   
4.
本文运用面板数据模型,对我国各省1996-2005年人均GDP及三次产业产值比重的关系分别进行了模型拟合,结论认为:我国经济增长对产业结构变化的影响显著,而后者对前者的影响在统计上并不显著,我国经济增长模式是需求导向型的。其次,就各次产业与人均GDP的关系看,第一产业与人均GDP呈现负相关关系,而第二、三产业与人均GDP呈现正相关关系。  相似文献   
5.
《Electroanalysis》2018,30(1):109-118
The differential pulse adsorptive cathodic stripping voltammetry (DP‐AdsCSV) employing the hanging mercury drop electrode (HMDE) was used towards the determination of two psychotropic drugs in environmental samples. Voltammetric and experimental conditions to Clonazepam (CLO) and diazepam (DIAZ) were optimized and the methods were in‐house validated. Accumulation potentials were −0.3 V to CLO and −0.6 V to DIAZ at 120 s of accumulation time. Pulse amplitude, pulse time and scan rate were 80 mV, 20 ms and 25 mV s−1 to CLO and 100 mV, 20 ms and 40 mV s−1 to DIAZ, respectively. Recovery tests were done in three different concentrations to evaluate methods’ accuracy and the results were from 88±6 to 120±13 %. In precision tests, standard deviations were lower than 15 % for both methods. Goods limits of quantification 0.65 and 0.27 μg L−1 to CLO and DIAZ respectively were achieved without pre‐concentration steps such as SPE, etc. Voltammetry employing HMDE was first used for the determination of CLO and DIAZ in natural water. Natural samples were spiked and recovery tests confirmed the applicability of the methods developed. Nine samples from Parana state, Brazil, were analyzed and CLO and DIAZ values were below the limits of detection in all samples.  相似文献   
6.
The synthesis and characterization of a polyrotaxanated covalent organic network (CON) based on the association between the viologen and pillar[5]arene (P[5]OH) units are reported. The mechanical bond allows for the irreversible insertion of n-type redox centers (P[5]OH macrocycles) within a pristine structure based on p-type viologen redox centers. Both redox units are active on a narrow potential range and, in water, the presence of P[5]OH greatly increases the electroactivity of the material.  相似文献   
7.
Stable pillar[5]arene-containing [2]rotaxane building blocks with pentafluorophenyl ester stoppers have been efficiently prepared on a multi-gram scale. Reaction of these building blocks with various nucleophiles gave access to a wide range of [2]rotaxanes with amide, ester or thioester stoppers in good to excellent yields. The rotaxane structure is fully preserved during these chemical transformations. Actually, the addition-elimination mechanism at work during these transformations totally prevents the unthreading of the axle moiety of the mechanically interlocked system. The stopper exchange reactions were optimized both in solution and under mechanochemical solvent-free conditions. While amide formation is more efficient in solution, the solvent-free conditions are more powerful for the transesterification reactions. Starting from a fullerene-functionalized pillar[5]arene derivative, this new strategy gave easy access to a photoactive [2]rotaxane incorporating a C60 moiety and two Bodipy stoppers. Despite the absence of covalent connectivity between the Bodipy and the fullerene moieties in this photoactive molecular device, efficient through-space excited state interactions have been evidenced in this rotaxane.  相似文献   
8.
The pace of industrialization and rapid population growth in countries such as India entail an increased input of industrial and sanitary organic micropollutants, the so-called emerging contaminants (EC), into the environment. The emission of EC, such as pharmaceuticals, reaching Indian water bodies causes a detrimental effect on aquatic life and ultimately on human health. However, the financial burden of expanding sophisticated water treatment capacities renders complementary, cost-efficient alternatives, such as adsorption, attractive. Here we show the merits of washed and milled pigeon pea husk (PPH) as low-cost adsorbent for the removal of the EC trimethoprim (TMP) and atenolol (ATN) that are among the most detected pharmaceuticals in Indian waters. We found a linear increase in adsorption capacity of PPH for TMP and ATN at concentrations ranging from 10 to 200 μg/L and from 50 to 400 μg/L, respectively, reflecting the concentrations occurring in Indian water bodies. Investigation of adsorption kinetics using the external mass transfer model (EMTM) revealed that film diffusion resistance governed the adsorption process of TMP or ATN onto PPH. Moreover, analysis of the adsorption performance of PPH across an extensive range of pH and temperature illustrated that the highest adsorption loadings achieved concurred with actual conditions of Indian waters. We anticipate our work as starting point towards the development of a feasible adsorbent system aiming at low-cost water treatment.  相似文献   
9.
Organometallic complexes (OMCs) consisting of organic and metal active moieties have shown immense potential for application in solar cells. The diverse structure, rich porosity, and unique charge centers of OMCs enable them to be functional in solar cells. In this review, we introduced four types of OMCs, such as crown organometallic complexes, β-diketone metal complexes, cyclometallic complexes, and main chain metal-containing polymers, providing an in-depth analysis of the structure-performance relationship. OMCs could serve as active or interlayer materials in a variety of solar cell systems such as organic solar cells, perovskite solar cells, and dye-sensitized solar cells, especially some metals to improve the photoelectric performance of the device as dopants. In the end, perspectives on the opportunities and challenges of OMCs are given.  相似文献   
10.
Water bodies located nearby cities are much prone to pollution, especially in the developing countries, where effluents treatment facilities are generally lacking. The main reason for this phenomenon is the increasing population in the cities, and the large number of industries located near them. This leads to generation of huge amounts of domestic and industrial sewage that is discharged into the water bodies, increasing their organic pollutant load and resulting in the depletion of dissolved oxygen. In this paper, we propose a mathematical model for this situation, focusing especially on the resulting quality of the water, determined by the level of dissolved oxygen. The model also accounts for resources needed for the population survival and for the industrial operations. In addition, we describe also the decomposition of organic pollutants by bacteria in the aquatic medium. Feasibility conditions and stability criteria of the system's equilibria are determined analytically. The results show that human population and industries are relevant influential factors responsible for the increase in organic pollutants and the decrease in dissolved oxygen in the water body, in the sense that they may exert a destabilizing effect on the system. The numerical simulations confirm the analytical results. Copyright © 2016 John Wiley & Sons, Ltd.  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