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   1965篇
  免费   45篇
  国内免费   608篇
化学   2322篇
晶体学   2篇
力学   8篇
综合类   7篇
数学   11篇
物理学   268篇
  2024年   7篇
  2023年   37篇
  2022年   43篇
  2021年   43篇
  2020年   39篇
  2019年   48篇
  2018年   47篇
  2017年   57篇
  2016年   71篇
  2015年   67篇
  2014年   82篇
  2013年   86篇
  2012年   130篇
  2011年   103篇
  2010年   71篇
  2009年   119篇
  2008年   103篇
  2007年   145篇
  2006年   107篇
  2005年   118篇
  2004年   105篇
  2003年   78篇
  2002年   103篇
  2001年   96篇
  2000年   94篇
  1999年   90篇
  1998年   76篇
  1997年   70篇
  1996年   70篇
  1995年   62篇
  1994年   45篇
  1993年   47篇
  1992年   40篇
  1991年   25篇
  1990年   28篇
  1989年   22篇
  1988年   15篇
  1987年   4篇
  1986年   4篇
  1985年   4篇
  1984年   4篇
  1982年   2篇
  1981年   4篇
  1980年   1篇
  1979年   4篇
  1978年   1篇
  1971年   1篇
排序方式: 共有2618条查询结果,搜索用时 15 毫秒
991.
新型螯合物分离阻化动力学光度法测定痕量镉   总被引:1,自引:0,他引:1  
在碳酸钠介质中,以2,2′ 联吡啶为活化剂,Cd2+对过氧化氢氧化偶氮氯膦Ⅲ褪色反应具有抑制作用。考察了反应动力学条件,建立了一种测量痕量镉的新的动力学光度法。方法的检出限为1.0×10-11g/mL,线性范围为0~2.0μg/10mL。用APDC螯合纤维分离富集后,测定了湖水中痕量镉,并与原子吸收法对照,结果一致。  相似文献   
992.
流动注射催化动力学光度法测定碘的研究   总被引:3,自引:0,他引:3  
本文采用流动注射技术,利用微量碘离子催化铁的硫氰酸配合物与亚硝酸钠的褪色反应,实现水中微量碘离子的催化动力学光度测定。该法测定碘离子的线性范围是1.0~7.0μg/mL,检出限为0.5μg/mL,相对标准偏差为5.0%。方法用于实际水样中微量碘离子的测定,结果令人满意。  相似文献   
993.
在磷酸介质中 ,甲醛可以催化溴酸钾氧化 花青的反应使其退色 ,据此建立了顺序注射催化动力学光度法测定织物和室内空气中痕量甲醛的新方法。方法的线性范围 0 .5~ 7.0 μg mL ,检出限 0 .1 μg mL。用于树脂整理特殊织物和室内空气中痕量甲醛的测定 ,回收率在 97.0 %~ 1 0 5 .0 %之间。  相似文献   
994.
稀土螯合物BCPDA-Eu3+标记蛋白质研究   总被引:3,自引:0,他引:3  
通过自制的双功能螯合剂 4 ,7 二氯磺基苯 1,10啡啉 2 ,9二羧酸 (BCPDA)标记牛血清白蛋白(BSA)实验 ,对于BCPDA标记蛋白质的条件进行研究。结果表明 :BCPDA在温和的条件下能与蛋白质反应 ,并在一定条件下与铕离子形成稳定的BSA BCPDA Eu3 标记物。利用自建的分析方法 ,测定了标记过程的有关参数。并对标记物的某些光学特性进行了研究。  相似文献   
995.
荧光光度法测定血清中碱性磷酸酶   总被引:1,自引:0,他引:1  
合成了一种新的底物水杨酸磷酸酯 (SP),用于荧光光度法测定血清中碱性磷酸酶(ALP)活力.在37.0 ℃的Tris-HCl缓冲液(pH 9.0)条件下, 碱性磷酸酶作用于荧光底物SP,水解生成强荧光产物水杨酸(SA),生成的SA的量与参与反应的ALP 的活力成正比.据此建立了荧光光度法测定血清中碱性磷酸酶活力的新方法.测定碱性磷酸酶的线性范围是0.03~6.00 U/L,检测限为7.04 mU/L.本方法适用于血清中碱性磷酸酶的测定.测定结果与临床上常用的以对硝基苯磷酸酯为底物的分光光度法相比,无显著性差异.  相似文献   
996.
The alternating copolymer poly(3-nitrobenzylidene-1-naphthylamine-co-succinic anhydride) was synthesized from the Schiff base, 3-nitrobenzylidene-1-naphthylamine and succinic anhydride using hydroquinone monomethyl ether under nitrogen atmosphere. The molecular weight of the copolymer was determined by gel permeation chromatography. The metal-polymer complexes were synthesized by the reaction of THF solution of the alternating copolymer with aqueous solution of Cu(II) and Ni(II) acetates. The elemental analysis of the metal-polymer complexes suggests that the metal to ligand ratio is 1:2. The IR spectral data indicate that the metal ions are coordinated through the oxygen of the keto and ester groups. The UV-Visible, magnetic moments and ESR studies indicate square planar geometry for Cu(II) and distorted octahedral geometry for Ni(II) complexes. XRD studies revealed that the copolymer and its Cu(II) complex are crystalline, while the Ni(II) complex is amorphous. The intrinsic viscosity of the copolymer, thermal properties of metal-polymer complexes and their catalytic activity are discussed.  相似文献   
997.
Four new coordination polymers formed by zinc-benzoate with the 1,2-bis(4-pyridyl)ethane (bpe) bridging ligand have been prepared and characterized. Zinc-benzoates can be rationally tuned to form four different structures with a bridging bpe ligand by controlling ligand-to-zinc-benzoate molar ratios and by using different solvent systems, and reveal three coordination polymers having similar one-dimensional characteristics but having different mono-, di-, trinuclear nodes (13), and a dinuclear ring type molecule (4). This work reveals that the ligand-to-metal ratio and solvent play very important roles in the formation of different coordination structures. We have also shown that the compounds 14 catalyzed efficiently the transesterification of a variety of esters. The complex 3 showed the most efficient reactivity and is the best among the catalytic efficiencies reported previously with zinc-containing coordination and polymeric compounds. The substrates with the electron-withdrawing substituents have undergone faster transesterification than those with the electron-donating ones. In addition, the scope of the application of 14 as transesterification catalysts has been expanded to now include ethanol and propanol, suggesting that this catalytic system can be potentially useful for preparing various esters by transesterification. Moreover, the transesterification reaction mechanism was discussed by 1H NMR study.  相似文献   
998.
建立了1,2-萘醌-4-磺酸钠分光光度法测定含羟基药物盐酸吡硫醇的方法.研究表明,在pH=13.00的KCl-NaOH缓冲溶液中,盐酸吡硫醇能够催化氢氧根离子与1,2-萘醌-4-磺酸钠反应形成橙红色的2-羟基-1,4-萘醌,其最大吸收波长为454nm.盐酸吡硫醇浓度在3.2μg/mL~80μg/mL范围内与吸光度呈现良好的线性关系.线性回归方程为A=0.02715+0.02837C(×105 mol/L),线性相关系数r=0.9986.表观摩尔吸光系数、相对标准偏差(R.S.D.)和检测限分别为2.84×103L/mol/cm、1.6%和2.0μg/mL.通过对片剂中的盐酸吡硫醇含量进行测定,回收率在98%~101%.  相似文献   
999.
A facile and high yield method of synthesis of novel and functional poly(methylalkoxy) siloxanes is reported. The Si–H groups of poly(methylhydrogen) siloxanes (PMHS) were treated with various simple (primary, secondary, tertiary) alcohols (1a–10a) in the presence of platinum based catalysts (Speier’s and Karstedt’s catalysts). Also oxyethylene, aldehyde, epoxide, halogen and allyl grafted polysiloxane were smoothly and quantitatively prepared by the alcoholysis between linear siloxanes polymer and functional alcohols (11a–20a) with use of Karstedt’s catalysts. It is found that alcoholysis reaction in the presence of the Karstedt’s catalyst proceed faster than Speier’s catalyst .In addition, the rate of alcoholysis reaction is dependent on amount of the catalyst and reaction temperature. The polymers prepared were characterized by IR, NMR spectroscopy and GPC analysis.  相似文献   
1000.
The direct self-assembly of bis-(1-benzoimidazolymethylene)-(2,5-thiadiazoly)-disulfide (L) with CuSO4, Cu(NO3)2 and CuCl2 affords three novel supramolecular complexes: 1-D ladder-like chain complex {[Cu(SO4)(L)] · (CH3OH)}n (1), dimer complexes {[Cu(L)(CH3O)]2(NO3)2} · 2H2O (2) and [Cu(L)(Cl)(N3)]2 · 2CH3OH (3). The nature of the anions is the underlying reason behind the differences in the structures of this series of complexes. Furthermore, utilizing the coordinatively unsaturated complexes 2 and 3 as precursor complexes, two new derivative complexes [Cu(L)(NCS)(CH3O)]2 · 2CH3OH (2A) and [Cu(L)(ClO4)(N3)]2 · 2CH3OH (3A) are obtained by the addition and exchange reactions of complexes 2 and 3 with anions. X-ray crystallographic analysis shows that the two derivatives retain the skeletons of their precursor complexes, and the anions with the stronger coordination capacity only bind to the active position of precursor complexes. In addition, different from the obvious effects on the structures in the direct self-assembly of the metal and ligand, the change of counteranions has no great impact on the structures in the anion exchange reactions. We also study the catalytic activities of the complexes 2, 2A, 3, and 3A, which have similar skeletons, for the oxidative coupling polymerization of 2,6-dimethylphenol (DMP). And we find that the introductions of different coordination counterions produce significant impacts on the catalytic properties of these complexes.  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