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   1334篇
  免费   121篇
  国内免费   554篇
化学   1459篇
晶体学   35篇
力学   10篇
综合类   16篇
数学   47篇
物理学   442篇
  2024年   1篇
  2023年   4篇
  2022年   34篇
  2021年   31篇
  2020年   32篇
  2019年   19篇
  2018年   19篇
  2017年   65篇
  2016年   62篇
  2015年   83篇
  2014年   93篇
  2013年   118篇
  2012年   201篇
  2011年   163篇
  2010年   93篇
  2009年   92篇
  2008年   129篇
  2007年   141篇
  2006年   63篇
  2005年   85篇
  2004年   85篇
  2003年   50篇
  2002年   52篇
  2001年   30篇
  2000年   33篇
  1999年   36篇
  1998年   27篇
  1997年   25篇
  1996年   32篇
  1995年   11篇
  1994年   25篇
  1993年   11篇
  1992年   6篇
  1991年   7篇
  1990年   11篇
  1989年   9篇
  1988年   7篇
  1987年   6篇
  1986年   1篇
  1985年   3篇
  1984年   1篇
  1983年   1篇
  1982年   3篇
  1981年   1篇
  1980年   1篇
  1979年   2篇
  1978年   1篇
  1977年   1篇
  1975年   1篇
  1973年   2篇
排序方式: 共有2009条查询结果,搜索用时 15 毫秒
91.
乐学义  童明良 《无机化学学报》2002,18(10):1023-1027
The complex [Cu(L-met)(phen)(H2O)]NO3·H2O has been synthesized and investigated by elemental analysis, molar conductivity, spectroscopic and X-ray diffraction methods, where phen=1,10-phenanthroline and L-met=L-methioninate group. The complex crystallized in the monoclinic space group P21 with a=12.053(2)?, b=6.886(1)?, c=13.385(3)?, β=113.59(3)°, V=1018.1(3)?3, Z=2,Dc=1.598g·cm-3, μ=1.223mm-1, F(000)=506, R1=0.0306, and wR2=0.0742. The copper(Ⅱ) atom is ligated in a distorted square-pyramidal geometry by two nitrogen atoms of one phen and the amino nitrogen atom , one carboxylate oxygen atom of L-met in the base plane, and an aqua at the apical position. A one-dimensional chain configuration formed by the hydrogen-bonding and weak Cu-O (the uncoordinated carboxyl oxygen atom) coordination interactions be-tween neighboring [Cu(L-met)(phen)(H2O)]+ cations. CCDC: 183368.  相似文献   
92.
在HF和MP2水平用全电子(AE)和相对论有效芯势(RECP)方法研究了Ⅰa、Ⅰb、Ⅱa和Ⅱb族金属离子与β D 核糖(RI)的相互作用. 结果表明, RECP能可靠地用于重金属离子;二价金属离子(M2+)比一价金属离子(M+)更易使β D 核糖(RI)变形;二价金属离子络合物(RI M2+)比一价金属离子络合物(RI M+)稳定. 电荷布居分析的结果支持上述结论.  相似文献   
93.
米常焕  夏熙  张校刚 《物理化学学报》2002,18(11):1038-1042
采用循环伏安法对Mn(Ⅱ)/Mn(Ⅲ)电对在硫酸溶液中铂电极上的氧化还原与Mn(Ⅱ)浓度、酸浓度、扫描速率、温度以及对流因素的函数关系进行了研究.结果发现,Mn(Ⅱ)在铂电极上Mn(Ⅱ)的氧化及Mn(Ⅲ)的还原均受扩散控制;升高温度和磁搅拌均能增加Mn(Ⅱ)氧化为Mn(Ⅲ)的速率;增加酸浓度和Mn(Ⅱ)浓度有利于增加Mn(Ⅲ)的稳定性,减少Mn(Ⅲ)的歧化和水解.  相似文献   
94.

Reaction of the ligand 2,2′-diphenyl-4,4′-bithiazole (DPBTZ) with Hg(SCN)2, Tl(NO3)3, CuCl, and PdCl2 gives complexes with stoichiometry [Hg(DPBTZ)(SCN)2], [Tl(DPBTZ)(NO3)3], [Cu(DPBTZ)(H2O)Cl], and [Pd(DPBTZ)Cl2]. The new complexes were characterized by elemental analyses and infrared spectroscopy. The crystal structure of [Hg(DPBTZ)(SCN)2] determined by X-ray crystallography. The Hg atom in the title monomeric complex, (2,2′-diphenyl-4,4′-bithiazole)mercury(II)bisthiocyanate, [Hg(C18H12N2S2)(SCN)2], is four-coordinate having an irregular tetrahedral geometry composed of two S atoms of thiocyanate ions [Hg-S 2.4025(15) and 2.4073(15) Å] and two N atoms of 2,2′-diphenyl-4,4′-bithiazole ligand [Hg-N 2.411(4) and 2.459(4) Å]. The bond angle S(3)-Hg(1)-S(4) of 147.46(5)° has the greatest derivation from ideal tetrahedral geometry. Intermolecular interaction between Hg(1) and two S atoms of two neighboring molecules, 3.9318(15) and 3.9640(18) Å, make the Hg(1) distort from a tetrahedron to a disordered octahedron. The attempts for preparation complexes of Tl(I), Pb(II), Bi(III), Cd(II) ions with 2,2′-diphenyl-4,4′-bithiazole ligand were not successful and also the attempts for preparation complexes of 4,4′,5,5′-tetraphenyl-2,2′-bithizole ligand with Cu(II), Ni(II), Co(II), Co(III), Mn(II), Mn(III), Fe(II), Fe(III), Cr(III), Zn(II), Tl(III), Pb(II), Hg(II), Cu(I), Pd(II) were not successful. This point can be regarded as the initial electron withdrawing of phenyl rings and also their spatial steric effects.  相似文献   
95.
A new 1,3,4 thiadiazole-derivative ligand 2,5-(s-acetic acid) dimercapto-1,3,4 thiadiazole (H2ADTZ) and its one-dimensional manganese polymer Mn(ADTZ)·4H2O had been synthesized and structurally characterized by X-ray single crystal diffraction in this paper. The Mn(Ⅱ) ion is coordinated with a distorted octahedron by two oxygen atoms from neighboring two deprotonated ligands ADTZ2- and other four oxygen atoms from four coordinated water molecules. The structural feature of the title compound is the formation of one-dimensional manganese chains polymer through the bridging of dioxygen O-O units. In the solid state structure of the complex, one-dimensional manganese chains are joined together by the weak intermolecular hydrogen bonds and vander Waals interactions forming a two-dimensional supramolecular compound. Furthermore, the UV spectra and electro-chemical properties of the title compound were also investigated. CCDC: 260532.  相似文献   
96.
制备了锌修饰铂电极,建立了一种新的测定Zn(Ⅱ)的示波双电位滴定法。在六次甲基四胺溶液(1.0mol/L)中(pH=5.5),用制备的修饰铂电极作为双指示电极,以EDTA标准溶液滴定Zn(Ⅱ),利用示波器屏幕上荧光点的显著最大位移指示滴定终点。在3.0×10-4~2.0×10-3mol/L的浓度范围内,Zn(Ⅱ)的回收率为99.9%~100.2%。该修饰电极具有良好的稳定性和重现性,对Zn(Ⅱ,1.0×10-3mol/L)溶液连续11次测定,所得终点电位值均在10.1mV左右,其相对标准偏差(RSD)为0.5%。用来测定含锌的实际样品,其结果与指示剂法测定的值基本一致。  相似文献   
97.

The transport of Hg (II) ions from an aqueous solution into an aqueous receiving solution through bulk and supported liquid membranes containing a calix[4]arene derivative 1 as a carrier was examined. The kinetic parameters of bulk liquid membrane studies were analyzed assuming two consecutive, irreversible first‐order reactions. The influence of temperature, stirring rate, carrier concentration and solvent on the kinetic parameters (k1, k2, Rm max, tmax, Jd max, Ja max) has also been investigated. The membrane entrance rate, k1, and the membrane exit rate, k2, increased with increasing temperature and stirring rate. The activation energy values are calculated as 4.87 and 48.63 kj mol?1 for extraction and reextraction, respectively. The values of calculated activation energy indicate that the process is diffusionally controlled by species. Also, the transport behavior of Hg2+ from aqueous solution through a flat‐sheet supported liquid membrane has been investigated by the use of calix[4]arene derivative 1 as carrier and Celgard 2500 as the solid support. A Danesi mass transfer model was used to calculate the permeability coefficients for each parameter studied. The highest values of permeability were obtained with 2‐nitrophenyloctyl‐ether (NPOE) solvent and the influence was found to be in the order of NPOE>chloroform>xylene.  相似文献   
98.
《Electroanalysis》2005,17(14):1317-1324
The electrochemical processes of sulfide in NaCl electrolyte solutions were studied using stripping cyclic voltammetry, differential capacity and chronoamperometric measurements. Some new effects were observed and are here discussed. At potentials around ?0.1 to ?0.3 V a pair of Faradaic adsorptive peaks, which can only be observed in the presence of chloride, is attributed to the formation of HgCl ion from the deposited layer of HgS. A second pair of peaks of purely capacitive character was observed at ?0.4 V. This is the result of the reorientation and partial desorption or transformation of HgS layers. The formation and dissolution of HgS layers on mercury has been well investigated previously. We observed some new effects after depositing approximately ten layers of HgS and attributed this to the formation of polysulfides at positive potentials.  相似文献   
99.
Two cadmium arsonate coordination polymers, Cd(HL1)2 (1, H2L1 = 4-aminophenylarsonatic acid) and Cd(H2L2)2·2H2O (2, H3L2 = 2-(4-arsonphenylamino)acetic acid), have been synthesized and characterized by IR and single-crystal X-ray diffraction. Crystal data for 1: triclinic, space group P1 with a = 5.7559(12), b = 7.0903(14), c = 8.9925(18), α = 89.04(3), β = 80.79(3), γ = 85.09(3)o, Dc = 2.496 g·cm-3, μ = 6.095 mm-1, F(000) = 260, Z = 1, the final R = 0.0574 and wR = 0.1376 for 1489 observed reflections with I > 2σ(I). And those for 2: monoclinic, space group P21/c with a = 4.7595(10), b = 9.925(2), c = 22.609(5), β = 91.81(3)°, Dc = 2.167 g·cm-3, μ = 4.168 mm-1, F(000) = 684, Z = 2, the final R = 0.0335 and wR = 0.0815 for 2340 observed reflections with I > 2σ(I). The structure of 1 shows a two-dimensional layer consisting of inorganic chains of {CdN2(AsO3)2} along the a axis linking with the phenyl groups. These layers are further linked through strong interlayer hydrogen bonding interaction to form a three-dimensional hydrogen bond supramolecular architecture. Compound 2 has inorganic chains of {CdO2(AsO3)2} similar to 1, which connect with four adjacent inorganic chains forming a three-dimensional framework.  相似文献   
100.
Two novel mono-nuclear zinc(Ⅱ) complexes with oligoaniline-functionalized terpyridine ligands have been synthesized and verified by 1H-NMR,13C-NMR,Elemental Analysis (EA) and X-ray Diffraction (XRD). The UV-vis spectra show the ligand-centered (LC) π-π* transitions and intra-ligand charge transfer (1ILCT) transitions,and the 1ILCT band red-shifts with the increasing number of aromatic amine groups in the ligands. Complex [Zn(L1)2](PF6)2 with an aromatic amine group in ligand shows a strong emission peak at 523 nm in the MeCN solution at 293 K and a blue-shifted band at 517 nm in the alcoholic glass at 77 K. However,for complex [Zn(L2)2](PF6)2 containing aniline dimer modified ligand,no apparent emission can be observed in the MeCN solution at room temperature due to a PET non-radiative decay pathway. Both of them show multiplicate redox processes based on oligoaniline and terpyridine units. The shifts of redox potentials also reflect the D-A interactions between the oligoaniline units and [Zn(TPY)2]2+ core.  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