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   5417篇
  免费   294篇
  国内免费   490篇
化学   4863篇
晶体学   91篇
力学   25篇
综合类   4篇
数学   8篇
物理学   1210篇
  2024年   3篇
  2023年   125篇
  2022年   69篇
  2021年   72篇
  2020年   114篇
  2019年   101篇
  2018年   151篇
  2017年   166篇
  2016年   131篇
  2015年   128篇
  2014年   248篇
  2013年   225篇
  2012年   724篇
  2011年   361篇
  2010年   299篇
  2009年   300篇
  2008年   327篇
  2007年   404篇
  2006年   305篇
  2005年   278篇
  2004年   250篇
  2003年   194篇
  2002年   146篇
  2001年   135篇
  2000年   119篇
  1999年   126篇
  1998年   121篇
  1997年   85篇
  1996年   96篇
  1995年   78篇
  1994年   58篇
  1993年   51篇
  1992年   60篇
  1991年   51篇
  1990年   38篇
  1989年   21篇
  1988年   7篇
  1987年   4篇
  1986年   7篇
  1985年   6篇
  1984年   5篇
  1983年   2篇
  1981年   1篇
  1980年   3篇
  1979年   2篇
  1975年   1篇
  1974年   1篇
  1969年   1篇
  1966年   1篇
排序方式: 共有6201条查询结果,搜索用时 750 毫秒
141.
Kadara RO  Tothill IE 《Talanta》2005,66(5):1089-1093
As copper(II) is a common ion in a variety of analytical samples, its effect on the stripping response of lead(II) at bismuth film screen-printed carbon electrode (BFSPCE) was investigated. The study was conducted using a screen-printed three-electrode system (working, counter and reference electrodes), with the carbon-working electrode plated in situ with bismuth film. Copper present at significant concentration level in samples was found to affect the sensitivity of the electrode by reducing the constant current stripping chronopotentiometric (CCSCP) response of lead(II). Recovery of the lead stripping response at the BFSPCE in the presence of copper was obtained when 0.1 mM ferricyanide was added to the test solution. The ferricyanide added circumvents the detrimental effect of copper(II) by selectively masking the copper ions by forming a complex. The analytical utility of the procedure is illustrated by the stripping chronopotentiometric determinations of lead(II) in soil extracts.  相似文献   
142.
铜(Ⅱ)和锌(Ⅱ)分别在0.1mol/LKH_2PO_4-Na_2HPO_4缓冲溶液(pH6.5)和0.25mol/LNH_4Cl溶液中,与氟哌酸形成良好的络合吸附波,峰电位分别为-0.26V和-1.28V(vs;SCE);络合比分别为1:3和1:2;峰电流与铜(Ⅱ)和锌(Ⅱ)的浓度均在4.0×10 ̄(-7)~5.0×10 ̄(-6)mol/L范围内呈线性关系,检测限分别为7.0×10 ̄(-8)和5.0×10 ̄(-8)mol/L。用线性扫描和循环伏安法等手段研究体系的行为,表明均具吸附性,而铜(Ⅱ)-氟哌酸体系属络合物中铜(Ⅱ)的两电子还原的可逆过程。  相似文献   
143.
PiezoelectricFiber-opticSpectroelectrochemistry──ANewTechniqueofSpectroelectrochemistryinCombinationWithPiezoelectricQuartzCr...  相似文献   
144.
乙醇对合成醇用Cu-Co-Fe催化剂的修饰效应   总被引:2,自引:0,他引:2  
徐杰  王向宇  杜宝石  辛勤  李灿 《催化学报》1998,19(3):264-267
乙醇对合成醇用Cu┐Co┐Fe催化剂的修饰效应徐杰王向宇杜宝石(郑州大学化学系,郑州450052)辛勤李灿(中国科学院大连化学物理研究所,大连116023)关键词铜,钴,铁,合成醇,乙醇,修饰作用分类号O643/O647自70年代以来,已对多种CO加...  相似文献   
145.
Properties of Sr2Cu(PO4)2 and Ba2Cu(PO4)2 having [Cu(PO4)2] linear chains in their structures with Cu-O-P-O-Cu linkages were studied by magnetic susceptibility (T=2-400 K, H=100 Oe) and specific heat measurements (T=0.45-21 K). Magnetic susceptibility versus temperature curves, χ(T), showed broad maxima at TM=92 K for Sr2Cu(PO4)2 and TM=82 K for Ba2Cu(PO4)2 characteristic of quasi-one-dimensional systems. The χ(T) data were excellently fitted by the spin susceptibility curve for the uniform S=1/2 chain (plus temperature-independent and Curie-Weiss terms) with g=2.153(4) and J/kB=143.6(2) K for Sr2Cu(PO4)2 and g=2.073(4) and J/kB=132.16(9) K for Ba2Cu(PO4)2 (Hamiltonian H=JΣSiSi+1). The similar J/kB values were obtained from the specific heat data. No anomaly was observed on the specific heat from 0.45 to 21 K for both compounds indicating that the temperatures of long-range magnetic ordering, TN, were below 0.45 K. Sr2Cu(PO4)2 and Ba2Cu(PO4)2 are an excellent physical realization of the S=1/2 linear chain Heisenberg antiferromagnet with kBTN/J<0.34% together with Sr2CuO3 (kBTN/J≈0.25%) and γ-LiV2O5 (kBTN/J<0.16%). Sr2Cu(PO4)2 and Ba2Cu(PO4)2 were stable in air up to 1280 and 1150 K, respectively.  相似文献   
146.
The reaction of the ortho-alkynylarylimines 1 with allyltributylstannane and allyl chloride in the presence of allylpalladium chloride dimer (5 mol %) and Cu(OAc)2 (20 mol %) in CH3CN at 50 °C gave the 1,4-diallyl-1,2-dihydroisoquinolines 2 in good yields. Most probably, the reaction proceeds through tandem bis-allylation of the imine-alkyne functional groups with bis-π-allylpalladium.  相似文献   
147.
A new Alkaline-Earth Platinum Copper Oxide: Ca3.5Cu0.5PtO6 Ca3.5Cu0.5PtO6 was prepared and investigated by single crystal X-ray work. (Space group C? C12/m1; a = 9.0743; b = 9.2527; c = 6.4840 Å; β = 91.448°; Z = 4). The crystal structure of the previously unknown compound is closely related to the structure of Sr3PtCuO6 and Sr3IrCuO6 as well as the rhombohedral phases M4PtO6 (M = Ba, Sr, Ca). Typical features of the crystal chemistry are isolated chains of PtO6 octahedra, alternately allyed by square CuO4 polygones and trigonal prisms of O2? around Ca2+.  相似文献   
148.
微量稀土对超导稳定化基体铜材的性能和组织的影响   总被引:4,自引:0,他引:4  
研究了微量稀土元素对铜的机械性能、导电性和组织的影响,在铜中加入微量钇、钕、镝、铒和富铈混合稀土后,使铜的抗拉强度有所提高,并保持良好的塑性和导电性。  相似文献   
149.
Various combinations of Cu(0), CuCl, 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen) were used as catalysts for the grafting polymerizations of styrene from polysiloxane macroinitiators functionalized with benzyl chloride. While Cu(0)/bpy alone promotes the grafting, narrower polydispersities were obtained in the presence of CuCl. Analysis of the Cu(0) surface before and after polymerization by a combination of AFM, TGA and FTIR investigations reveals the formation of bpy or phen films on Cu(0). In the presence of CuCl, the ligand film appears decorated with CuCl particles which increase in size with increasing the CuCl concentration. The initial layer occurs most likely as a result of complexation between the ligands and the Cu(0) surface and acts as a support for the rest of the film. These observations are consistent with the film formation on Cu(0) from related nitrogen donors and indicate that the reactivity of the Cu surface may depend not only on its prior treatment but also on the deposition of ligands from the reaction mixture.  相似文献   
150.
用1-(2-吡啶偶氮)-2-萘酚-6-磺酸(PAN-S)水溶液处理201×7强碱性阴离子交换树脂,制备了具有PAN-S功能团的浸渍树脂。经过最佳条件选择,在同一水样中,可以同时富集Pb2 、Cu2 、Zn2 、Cd2 。实验结果表明,PAN-S树脂用于痕量元素的分离富集具有交换速度快、易于洗脱、富集倍数大、选择性好等优点。建立了PAN-S树脂富集-分离铅、镉、铜和锌离子的方波溶出法的测定方法,并可用于海水中的测定,结果令人满意。  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