全文获取类型
收费全文 | 3436篇 |
免费 | 709篇 |
国内免费 | 1211篇 |
专业分类
化学 | 2665篇 |
晶体学 | 190篇 |
力学 | 189篇 |
综合类 | 112篇 |
数学 | 563篇 |
物理学 | 1637篇 |
出版年
2024年 | 7篇 |
2023年 | 60篇 |
2022年 | 136篇 |
2021年 | 149篇 |
2020年 | 153篇 |
2019年 | 153篇 |
2018年 | 130篇 |
2017年 | 190篇 |
2016年 | 140篇 |
2015年 | 223篇 |
2014年 | 217篇 |
2013年 | 308篇 |
2012年 | 321篇 |
2011年 | 357篇 |
2010年 | 344篇 |
2009年 | 343篇 |
2008年 | 366篇 |
2007年 | 306篇 |
2006年 | 265篇 |
2005年 | 213篇 |
2004年 | 178篇 |
2003年 | 124篇 |
2002年 | 112篇 |
2001年 | 115篇 |
2000年 | 91篇 |
1999年 | 81篇 |
1998年 | 33篇 |
1997年 | 26篇 |
1996年 | 19篇 |
1995年 | 19篇 |
1994年 | 22篇 |
1993年 | 32篇 |
1992年 | 21篇 |
1991年 | 13篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1964年 | 1篇 |
1959年 | 3篇 |
排序方式: 共有5356条查询结果,搜索用时 18 毫秒
91.
Fe(OH)2悬浮液在EDTA作用下氧气氧化生成δ-FeOOH的机理研究 总被引:1,自引:0,他引:1
At room temperature and in the presence of trace EDTA, the formation of δ-FeOOH was studied by the rapid oxidation of Fe(OH)2 suspension with O2. The structural and morphological changes were characterized by various techniques such as XRD, FTIR and TEM. γ-FeOOH and (δ-FeOOH) formed simutaneously in the early period of oxidation. But as the rate of mass transfer was in equilibrium, trace (γ-FeOOH) vanished gradually. Accordingly, pure phase δ-FeOOH was obtained. At the same time, critical amount ratio K of EDTA to Fe2+ was verified. The experiments show that the reactivity, rate of the oxidizing agent and pH of the initial medium were important factors for the formation of pure phase (δ-FeOOH). Under the auxiliary effect of EDTA, the reactivity of O2 was nearly improved to that of H2O2. And the process of the oxidation that Fe(OH)2 suspension was oxidized by O2 under that condition was discussed. 相似文献
92.
合成了锑-镨与乙二胺四乙酸形成的新颖三维配合物[Sb2-μ4-(EDTA)2Pr(H2O)5]NO3·4H2O,用元素分析、红外光谱、热分析及X射线单晶衍射法等进行了组成和结构表征.结果表明该配合物属正交晶系,空间群Pnn2;晶胞参数:a=1.07031(2)nm,b=2.30805(4)nm,c=0.72343(2)nm,V=1.78711(7)nm3,Z=2,Dc=2.202g/cm3,F(000)=1164,μ=2.955mm-1,GOF=1.000,最终偏离因子R1=0.0203,wR2=0.0545[I>2σ(Ⅰ)].在标题化合物中,每个镨(Ⅲ)离子的配位数为9,与五个水分子中的五个氧原子和四个羧基氧原子配位,形成三帽三角棱柱空间配位多面体.锑(Ⅲ)与EDTA离子中的四个氧原子和两个氮原子配位,在赤道平面上有一孤对电子.同时讨论了配合物的热分解过程. 相似文献
93.
94.
Tapping mode atomic force microscope has been applied to observe single-chain PMMAparticles which were stored for six months at room temperature after sprayed from verydilute solutions in good solvents, good/poor mixed solvents, and a theta solvent. Monodis-perse PMMA standards of molecular weights ranging from 7.90×10~4 to 1.3×10~6 wereused to investigate the effect of molecular weight oh the size of the single-chain PMMAparticles. These single-chain particles showed close to spherical shapes. The morphologyof single-chain PMMA particles of a given molecular weight was found to be identical inspite of different solvents used for solution spraying. Molecular weigh dependence of theparticle dimension was also found. The diameters of single-chain PMMA particles aftercorrection of tlp-geometry effect were compared to the values estimated from molecularweight and density. 相似文献
95.
A novel organic-inorganic hybrid compound {[Cu(2,2′-bpy)2]2Mo8O26} has been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group, Pna21,with a=2.4164(5),b=1.8281(4),c=1.1877(2)nm,V=5.247(2)nm^3,Z=4,and final R1=0.0331,wR2=0.0727.The structure consists of discrete {[Cu(2,2′-bpy)2]2Mo8O26} clusters,constructed from a β-octamolybdate subunit[Mo8O26]^4- covalently bonded to two [Cu(2,2′-bpy)2]^2 coordination complex cations via bridging oxo groups.In addition,the spectroscopic properties and thernal behavior of this compound have been investigated by spectroscopic techniques (UV-vis,IR,Raman and EPR spectra) and TG analysis. 相似文献
96.
A new polyoxomolybdate complex HNa7[Mo36O112(H2O)16]·47H2O 1 has been prepared in the beaker solution and characterized by single-crystal X-ray diffraction and elemental analyses. Crystal data: H127Mo36Na7O175, Mr = 6542.79, monoclinic, C2/c, a = 40.891(6), b = 17.900(3), c = 25.580(4) , β = 125.673(2)°, V = 15210(4) 3, Z = 4, Dc = 2.857 g/cm3, F(000) = 12464, μ = 3.013 mm-1, R = 0.0633 and wR = 0.1654 (I > 2σ(I)). With the bridging sodium cations, the [Mo36O112(H2O)16]8- units in compound 1 are linked to form a one-dimensional structure, on the basis of which a three-dimensional architecture is further constructed via other sodium cations and complicated hydrogen bonds. 相似文献
97.
98.
苯基荧光酮荧光分光光度法测定痕量锗的研究 总被引:10,自引:0,他引:10
锗具有增血、抗炎症、抗衰老等多种医疗功能 ,因此 ,越来越受到人们的关注。荧光光度法测定微量锗已有报道[1~ 4] 。用苯基荧光酮荧光度法测定锗未见报道。本文利用苯基荧光酮与锗在醋酸 醋酸钠缓冲溶液中络合物形成速度快的优势 ,使其先在缓冲溶液中显色 ,然后在 0 .3mol LHCl介质中测定其荧光强度 ,用于粉煤灰中痕量锗的测定 ,得到满意结果。1 实验部分1 1 仪器与试剂RF - 5 4 0荧光分光光度计 (日本岛津 )。锗标准溶液 ( 1g L) :称取 0 .1 0 0 0g纯锗粉于 5 0ml小烧杯中 ,加入 5mlNaOH ,再加入几滴 30 %H2 O2… 相似文献
99.
ZHANG Dan JIA Shu-yong WANG Yue YAO Jie WANG Gong-ying 《高等学校化学研究》2007,23(2):173-175
IntroductionDimethyl carbonate(DMC) is known to be a novelbuilding block in organic synthesis. As an environmen-tally benign compound and a unique intermediate,DMC has attracted much attention[1,2]. Among the va-rious methods for synthesizing DMC, the tra… 相似文献
100.