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611.
Vishwakarma Singh Punitha VedanthamVinayak V Kane Kurt Polborn 《Tetrahedron letters》2003,44(3):475-478
A new synthesis of 3-oxatricyclo[7.2.2.01,7]tridecenones via intramolecular π4s+π2s cycloaddition in cyclohexa-2,4-dienones is described. Their photochemical reactions leading to oxepane-diquinane and oxepane-sterpurane hybrids are depicted. The crystal structure of a key intermediate is also presented. 相似文献
612.
发现了一种对异戊二烯聚合立体选择性较敏感的稀士催化体系:(β-CH_3-allyl)_2LnCl_5Mg·2T的ED(Ln)-R_3Al(Al)(Ln=Nd、Ce和La,T的ED:N,N,N′,N′-四甲基乙二胺;R=Me一,Et一,i-Bu一和Oct一).该催化体系在改变聚合温度、聚合时间、Al/Ln摩尔比、溶剂等时,可使聚异戊二烯的立体现整度有较大的改变,其中顺式-1,4、反式-1,4和3,4-链节含量的变化范围分别为19%~79%、17%~78%和0%~3.5%,还可获得较低分子量的聚合物。 相似文献
613.
含咪唑基配体的Co(Ⅱ)超分子配合物的合成、晶体结构和光谱性质 总被引:6,自引:0,他引:6
采用改进的固相Wittig反应, 合成了一种新型的具有电子给受体和π共轭结构的咪唑衍生物1-{反式4-[4-(-N,N-二乙基氨基)苯乙烯基]苯}咪唑(C21H23N3, 简作L). 室温下, 将L与Co(SCN)2在甲醇中反应, 合成了配合物Co(SCN)2(C21H23N3)4. X射线单晶衍射分析结果表明, 该晶体属于三斜晶系, P1空间群, 晶胞参数a=0.931 7(3) nm, b=1.275 3(4) nm, c=1.669 1(5) nm, α= 89.521(5)°, β=84.591(5)°, γ=80.052(5)°, V=1.944 6(11) nm3, Z=1, μ=0.329 mm-1, Dc=1.234 Mg/m3, F(000)=765, R1=0.060 1, wR=0.138 1, GOF=1.030, 中心原子Co(Ⅱ)的配位数为6, 分别与来自4个L的咪唑N及2个SCN-的N配位, 形成八面体的空间构型. 配合物分子通过非典型氢键和π-π堆积作用形成三维超分子结构. 研究结果表明, 配合物具有很好的光学性质. 相似文献
614.
Photocatalytic H2 evolution reactions on pristine graphitic carbon nitrides (g-C3N4), as a promising approach for converting solar energy to fuel, are attractive for tackling global energy concerns but still suffer from low efficiencies. In this article, we report a tractable approach to modifying g-C3N4 with vanadyl phthalocyanine (VOPc/CN) for efficient visible-light-driven hydrogen production. A non-covalent VOPc/CN hybrid photocatalyst formed via π-π stacking interactions between the two components, as confirmed by analysis of UV-vis absorption spectra. The VOPc/CN hybrid photocatalyst shows excellent visible-light-driven photocatalytic performance and good stability. Under optimal conditions, the corresponding H2 evolution rate is nearly 6 times higher than that of pure g-C3N4. The role of VOPc in promoting hydrogen evolution activity was to extend the visible light absorption range and prevent the recombination of photoexcited electron-hole pairs effectively. It is expected that this facile modification method could be a new inspiration for the rational design and exploration of g-C3N4-based hybrid systems with strong light absorption and high-efficiency carrier separation. 相似文献
615.
Dr. Martin Mayer Dr. Markus Rohdenburg Sebastian Kawa Francine Horn Harald Knorke Prof. Dr. Carsten Jenne Prof. Dr. Ralf Tonner Prof. Dr. Knut R. Asmis Dr. Jonas Warneke 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(40):10274-10281
Electrophilic anions of type [B12X11]− posses a vacant positive boron binding site within the anion. In a comparatitve experimental and theoretical study, the reactivity of [B12X11]− with X=F, Cl, Br, I, CN is characterized towards different nucleophiles: (i) noble gases (NGs) as σ-donors and (ii) CO/N2 as σ-donor-π-acceptors. Temperature-dependent formation of [B12X11NG]− indicates the enthalpy order (X=CN)>(X=Cl)≈(X=Br)>(X=I)≈(X=F) almost independent of the NG in good agreement with calculated trends. The observed order is explained by an interplay of the electron deficiency of the vacant boron site in [B12X11]− and steric effects. The binding of CO and N2 to [B12X11]− is significantly stronger. The B3LYP 0 K attachment enthapies follow the order (X=F)>(X=CN)>(X=Cl)>(X=Br)>(X=I), in contrast to the NG series. The bonding motifs of [B12X11CO]− and [B12X11N2]− were characterized using cryogenic ion trap vibrational spectroscopy by focusing on the CO and N2 stretching frequencies and , respectively. Observed shifts of and are explained by an interplay between electrostatic effects (blue shift), due to the positive partial charge, and by π-backdonation (red shift). Energy decomposition analysis and analysis of natural orbitals for chemical valence support all conclusions based on the experimental results. This establishes a rational understanding of [B12X11]− reactivety dependent on the substituent X and provides first systematic data on π-backdonation from delocalized σ-electron systems of closo-borate anions. 相似文献
616.
比较了含有配位不饱和过渡金属原子簇合物Mo_2S_4(dtp)_2,(Ⅰ)和Mo_3S_4(dtp)_4·Py,(Ⅱ)的紫外—可见电子吸收光谱实验数据和半经验的量子化学方法INDO计算得到的电子跃迁能,讨论了(d-p)π型共轭作用对其电子吸收光谱位移的影响。结果表明,过渡金属簇合物中电子吸收光谱位移,与有机共轭体系有着类似的变化规律,即随着共轭π键数目增加,π-π电子跃迁的吸收光谱红移。 相似文献
617.
We determine the maximal number of conjugacy classes of maximal elementary abelian subgroups of rank 2 in a finite p-group G, for an odd prime p. Namely, it is p if G has rank at least 3 and it is p+1 if G has rank 2. More precisely, if G has rank 2, there are exactly 1,2,p+1, or possibly 3 classes for some 3-groups of maximal nilpotency class. 相似文献
618.
CHEN Hui-Fen ;LI Yan ;WANG Ming-Sheng ;WU A-Qing ;GUO Guo-Cong ;HUANG Jin-Shun 《结构化学》2008,(11):1398-1403
The reaction of 6,7-dicyanodipyridoquinoxaline (DICNQ) with AgNO3 in a 1:1 molar ratio by solution method gave a new complex [Ag(DICNQ)2]NO3 1. Single-crystal X-ray diffraction analysis reveals that the complex crystallizes in the space group Ibca of orthorhombic system with eight formula units in a cell. Crystal data for 1: a = 15.7055(17), b = 18.411(2), c = 20.680(2)A, V = 5979.7(11)A3, Z = 8, C32Hl2AgN13O3, Mr = 734.42, Dc = 1.632 g/cm3, μ= 0.734 mm-1, F(000) = 2928, S = 1.023 and T= 293(2) K. The final R = 0.0659 and wR = 0.1927 for 2118 observed reflections with I 〉 2σ(I), and R = 0.0801 and wR = 0.2196 for all data. The complex builds up a packing structure by π-π stacking interactions and shows a luminescent feature. 相似文献
619.
The class of the regular p-groups is one of the important classes in p-groups. Not only it has many similar properties as abelian p-groups, but also many of the p-groups belong to this class. In this paper, using the algorithms for determining the isomorphic regular p-groups, we give a complete classification of the regular p-groups with e-invariants (e, 2, 1).Supported by SXYSF 991003. 相似文献
620.
Mariusz Michalczyk Dr. Wiktor Zierkiewicz Dr. Rafał Wysokiński Prof. Steve Scheiner 《Chemphyschem》2019,20(7):959-966
In order to accommodate the approach of two NCH bases, a tetrahedral TF4 molecule (T=Si, Ge, Sn, Pb) distorts into an octahedral structure in which the two bases can be situated either cis or trans to one another. The square planar geometry of TF4, associated with the trans arrangement of the bases, is higher in energy than its see-saw structure that corresponds to the cis trimer. On the other hand, the square geometry offers an unobstructed path of the bases to the π-holes above and below the tetrel atom and hence enjoys a higher interaction energy than is the case for the σ-holes approached by the bases in the cis arrangement. When these two effects are combined, the total binding energies are more exothermic for the cis than for the trans complexes. This preference amounts to some 3 kcal mol−1 for Sn and Pb, but is amplified for the smaller tetrel atoms. 相似文献