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   4369篇
  免费   1022篇
  国内免费   612篇
化学   3428篇
晶体学   171篇
力学   115篇
综合类   41篇
数学   241篇
物理学   2007篇
  2024年   15篇
  2023年   69篇
  2022年   178篇
  2021年   189篇
  2020年   224篇
  2019年   195篇
  2018年   177篇
  2017年   153篇
  2016年   251篇
  2015年   219篇
  2014年   238篇
  2013年   650篇
  2012年   306篇
  2011年   280篇
  2010年   223篇
  2009年   243篇
  2008年   243篇
  2007年   262篇
  2006年   234篇
  2005年   231篇
  2004年   196篇
  2003年   180篇
  2002年   178篇
  2001年   93篇
  2000年   92篇
  1999年   70篇
  1998年   84篇
  1997年   80篇
  1996年   88篇
  1995年   68篇
  1994年   39篇
  1993年   28篇
  1992年   30篇
  1991年   22篇
  1990年   22篇
  1989年   25篇
  1988年   19篇
  1987年   13篇
  1986年   3篇
  1985年   15篇
  1984年   7篇
  1983年   13篇
  1982年   10篇
  1980年   3篇
  1979年   8篇
  1978年   4篇
  1976年   3篇
  1975年   7篇
  1974年   7篇
  1973年   6篇
排序方式: 共有6003条查询结果,搜索用时 15 毫秒
151.
王焕华 《物理》2012,41(12):783-788
现代光电子产品和能源技术都大量使用透明导电氧化物(TCO)薄膜.由于太阳能电池、平板显示器、发光二极管、短波长激光器、节能玻璃窗等应用领域日益增长的需求,TCO薄膜获得了越来越广泛的应用.文章总结了TCO薄膜的功能原理、应用需求和当前的研究方向,重点分析了p型TCO薄膜研究所要解决的关键问题(其中包括掺杂非对称性,性能退化与缺陷的生成,结构和变化的关系),指出了p型TCO薄膜制备的关键因素,研究的热点问题和蕴藏的研究机会.  相似文献   
152.
153.
154.
Radioaktiv markierte Präparate haben in denletzten Jahren in schnell zunehmendem Maße Eingang in die klinische Medizin gefunden. Sie sind beieiner Reihe von Indikationen schon jetzt außerordentlich wertvolle Hilfsmittel bei der Diagnose, besonders bei der Prüfung von Organfunktionen.  相似文献   
155.
The tandem dual C−H amination of tetrahydroquinoxalines with free amines under aerobic copper catalysis conditions has been demonstrated. The synthetic protocol proceeds with good substrate and functional group compatibility, mild reaction conditions, short reaction time, the use of the naturally abundant [Cu]/O2 catalyst system, excellent chemoselectivity and synthetic efficiency, and with no need for the pre-installation of specific aminating agents, which offers a practical platform for the rapid and diverse synthesis of diaminoquinoxalines. Moreover, this work has shown the potential of single-electron-oxidation-induced C−H functionalization of N-heterocycles, and its application in the development of optoelectronic materials.  相似文献   
156.
通过低温燃烧法(LCS)制备了不同金属硝酸盐与柠檬酸物质的量比的系列Mn-CeO_x(LCS)锰铈催化剂,将其与共沉淀法(CP)制备的Mn-CeO_x(CP)锰铈催化剂相对比,结合XRD、XPS、FESEM和H2-TPR等技术表征,对其NH_3-SCR脱硝催化性能进行了研究。结果表明,金属硝酸盐与柠檬酸的物质的量比是影响Mn-CeO_x(LCS)催化剂脱硝性能的重要因素。虽然两种催化剂中的锰氧化物组分均为无定型,但相较于Mn-CeO_x(CP),Mn-CeO_x(LCS)表面具有较高的锰含量与Oα/(Oα+Oβ)比,其脱硝催化性能也较高;同时,Mn-CeO_x(LCS)锰铈催化剂上有更多的多级孔,有利于气体在催化剂上的吸附和反应。硝酸盐与柠檬酸物质的量比为36∶22的Mn-CeO_x(LCS)锰铈催化剂在80-180℃下脱硝率可达75%-100%;即使通入SO2,180℃下的脱硝率仍可稳定于74%。  相似文献   
157.
A theoretical approach is developed that describes the formation of a thin-film of AB-compound layer under the influence of radiation-induced vacancy. The AB-compound layer is formed as a result of a chemical reaction between the atomic species of A and B immiscible layers. The two layers are irradiated with a beam of energetic particles and this process leads to several vacant lattice sites creation in both layers due to the displacement of lattice atoms by irradiating particles. A- and B-atoms diffuse via these lattice sites by means of a vacancy mechanism in considerable amount to reaction interfaces A/AB and AB/B. The reaction interfaces increase in thickness as a result of chemical transformation between the diffusing species and surface atoms (near both layers). The compound layer formation occurs in two stages. The first stage begins as an interfacial reaction controlled process, and the second as a diffusion controlled process. The critical thickness and time are determined at a transition point between the two stages. The influence of radiation-induced vacancy on layer thickness, speed of growth, and reaction rate is investigated under irradiation within the framework of the model presented here. The result obtained shows that the layer thickness, speed of growth, and reaction rate increase strongly as the defect generation rate rises in the irradiated layers. It also shows the feasibility of producing a compound layer (especially in near-noble metal silicide considered in this study) at a temperature below their normal formation temperature under the influence of radiation.  相似文献   
158.
Artemisinin‐based combination therapy is widely used for the treatment of uncomplicated Plasmodium falciparum malaria, and piperaquine (PQ) is one of important partner drugs. The pharmacokinetics of PQ is characterized by a low clearance and a large volume of distribution; however, metabolism of PQ has not been thoroughly investigated. In this work, the metabolite profiling of PQ in human and rat was studied using liquid chromatography tandem high‐resolution LTQ‐Orbitrap mass spectrometry (HRMS). The biological samples were pretreated by solid‐phase extraction. Data processes were carried out using multiple data‐mining techniques in tandem, i.e., isotope pattern filter followed by mass defect filter. A total of six metabolites (M1–M6) were identified for PQ in human (plasma and urine) and rat (plasma, urine and bile). Three reported metabolites were also found in this study, which included N‐oxidation (M1, M2) and carboxylic products (M3). The subsequent N‐oxidation of M3 resulted in a new metabolite M4 detected in urine and bile samples. A new metabolic pathway N‐dealkylation was found for PQ in human and rat, leading to two new metabolites (M5 and M6). This study demonstrated that LC‐HRMSn in combination with multiple data‐mining techniques in tandem can be a valuable analytical strategy for rapid metabolite profiling of drugs. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
159.
Retaining nitrogen for polyacrylonitrile (PAN) based carbon anode is a cost-effective way to make full use of the advantages of PAN for sodium-ion batteries (SIBs). Here, a simple strategy has been successfully adopted to retain N atoms in situ and increase production yield of a novel composite PAZ by mixing 3 wt % of zinc borate (ZB) with poly (acrylonitrile-co-itaconic acid) (PANIA). Among the prepared carbonised fibre (CF) samples, PAZ-CF-700 maintains the highest N content, retaining 90 % of the original N from PANIA. It represents the highest capacity storage contribution (80.55 %) and the lowest impedance Rct (117 Ω). Consequently, the specific capacity increases from 60 mAh g−1 of PANIA-CF-700 to 190 mAh g−1 of PAZ-CF-700 at a current density of 100 mA g−1. At the same time, PAZ-CF-700 exhibits a good rate performance and excellent long-term cycling stability with a specific capacity of 94 mAh g−1 after 4000 cycles at 1.6 A g−1.  相似文献   
160.
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