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941.
石墨炉原子吸收法测茶叶中铅和镉 总被引:1,自引:0,他引:1
王黎瑾 《广东微量元素科学》2006,13(12):53-56
采用石墨炉原子吸收法测茶叶中铅、镉的含量,方法灵敏、准确,测定时无需富集、萃取,操作简便。铅、镉平均回收率分别为102.05%和94.98%,相对标准偏差不超过4.2%。 相似文献
942.
用密度泛函理论论证了原子价层轨道能与元素电负性之间的密切关系,说明如何用原子价层轨道能对元素电负性的概念进行解释,从而使周期表中元素电负性更容易被理解和计算。 相似文献
943.
微量寡糖的甲基化分析:用于魔芋葡甘多糖酶解产物的结构测定 总被引:4,自引:1,他引:4
本文研究了成功了10-80μg范围的寡糖甲基化方法。用庐方法并与快原子轰击质谱相结合,给出了魔芋葡甘多糖酶解后二糖、三糖异体的结构。 相似文献
944.
Michael Gerken Paul Hazendonk Gary J. Schrobilgen 《Journal of fluorine chemistry》2004,125(7):1163-1168
The xenon fluorides, XeF2, XeF4, and XeF6, were characterized by gas-phase and NMR spectroscopy, providing the first gas-phase NMR spectroscopic data for the xenon fluorides. Xenon difluoride was also characterized in the solid state by static and magic angle spinning (MAS) and NMR spectroscopy, providing experimental values for the (4260±10 ppm) and (125±5 ppm) shielding anisotropies in XeF2. A method for encapsulating reactive fluoride samples for study by MAS NMR spectroscopy is also described. 相似文献
945.
946.
Qun Zhao Jianjun Wang Tatiana Besset Xavier Pannecoucke Jean-Philippe Bouillon Thomas Poisson 《Tetrahedron》2018,74(41):6033-6040
Here we reported a Pd-catalyzed coupling reaction between acrylate derivatives and BTP (2-bromo-3,3,3-trifluoropropene) to access 3-trifluoromethylated 1,3-dienes. The reaction allows the formation of the corresponding products in good to excellent yields and moderate Z/E diastereoisomeric ratios. This method broadens the current toolbox to access 3-trifluoromethylated 1,3-dienes. 相似文献
947.
H2 Oxidation Electrocatalysis Enabled by Metal‐to‐Metal Hydrogen Atom Transfer: A Homolytic Approach to a Heterolytic Reaction 下载免费PDF全文
Dr. Geoffrey M. Chambers Dr. Eric S. Wiedner Dr. R. Morris Bullock 《Angewandte Chemie (International ed. in English)》2018,57(41):13523-13527
Oxidation of H2 in a fuel cell converts the chemical energy of the H?H bond into electricity. Electrocatalytic oxidation of H2 by molecular catalysts typically requires one metal to perform multiple chemical steps: bind H2, heterolytically cleave H2, and then undergo two oxidation and two deprotonation steps. The electrocatalytic oxidation of H2 by a cooperative system using Cp*Cr(CO)3H and [Fe(diphosphine)(CO)3]+ has now been invetigated. A key step of the proposed mechanism is a rarely observed metal‐to‐metal hydrogen atom transfer from the Cr?H complex to the Fe, forming an Fe?H complex that is deprotonated and then oxidized electrochemically. This “division of chemical labor” features Cr interacting with H2 to cleave the H?H bond, while Fe interfaces with the electrode. Neither metal is required to heterolytically cleave H2, so this system provides a very unusual example of a homolytic reaction being a key step in a molecular electrocatalytic process. 相似文献
948.
《Chemical record (New York, N.Y.)》2018,18(1):20-44
Radical‐mediated dissociations of peptide radical cations have intriguing unimolecular gas phase chemistry, with cleavages of almost every bond of the peptide backbone and amino acid side chains in a competitive and apparently “stochastic” manner. Challenges of unraveling mechanistic details are related to complex tautomerizations prior to dissociations. Recent conjunctions of experimental and theoretical investigations have revealed the existence of non‐interconvertible isobaric tautomers with a variety of radical‐site‐specific initial structures, generated from dissociative electron transfer of ternary metal‐ligand‐peptide complexes. Their reactivity is influenced by the tautomerization barriers, perturbing the nature, location, or number of radical and charge site(s), which also determine the energetics and dynamics of the subsequent radical‐mediated dissociatons. The competitive radical‐ and charge‐induced dissociations are extremely dependent on charge density. Charge sequesting can reduce the charge densities on the peptide backbone and hence enhance the flexibility of structural rearrangement. Analysing the structures of precursors, intermediates and products has led to the discovery of many novel radical migration prior to peptide backbone and/or side chain fragmentations. Upon these successes, scientists will be able to build peptide cationic analogues/tautomers having a variety of well‐defined radical sites. 相似文献
949.
Ligand‐Unsupported Cuprophilicity in the Preparation of Dodecacopper(I) Complexes and Raman Studies 下载免费PDF全文
N. V. Satyachand Harisomayajula Bo‐Han Wu Dr. Duan‐Yen Lu Ting‐Shen Kuo Prof. Dr. I‐Chia Chen Prof. Dr. Yi‐Chou Tsai 《Angewandte Chemie (International ed. in English)》2018,57(31):9925-9929
Synthesis and characterization of two dodecacopper(I) extended metal atom chains (EMAC) assembled by two hexadentate bis(pyridylamido)amidinate‐supported hexacopper(I) string complexes (monomers) via the ligand‐unsupported cuprophilicity are described. In addition to short unsupported Cu?Cu contacts, two hexacopper fragments in these two dodecacopper EMACs show a bent conformation based on X‐ray crystallography. Compared with their THF‐bound hexacopper(I) monomers and protonated ligands, these ligand‐unsupported cuprophilic interactions are shown to be weak by Raman spectroscopy. DFT calculations suggest the ligand‐unsupported cuprophilicity originate from weak attractive orbital interactions, and the strength is estimated to be 2.4 kcal mol?1. 相似文献
950.
Reversing Conventional Reactivity of Mixed Oxo/Alkyl Rare‐Earth Complexes: Non‐Redox Oxygen Atom Transfer 下载免费PDF全文
Dr. Jianquan Hong Haiwen Tian Prof. Lixin Zhang Prof. Xigeng Zhou Dr. Iker del Rosal Prof. Linhong Weng Prof. Laurent Maron 《Angewandte Chemie (International ed. in English)》2018,57(4):1062-1067
The preferential substitution of oxo ligands over alkyl ones of rare‐earth complexes is commonly considered as “impossible” due to the high oxophilicity of metal centers. Now, it has been shown that simply assembling mixed methyl/oxo rare‐earth complexes to a rigid trinuclear cluster framework cannot only enhance the activity of the Ln‐oxo bond, but also protect the highly reactive Ln‐alkyl bond, thus providing a previously unrecognized opportunity to selectively manipulate the oxo ligand in the presence of numerous reactive functionalities. Such trimetallic cluster has proved to be a suitable platform for developing the unprecedented non‐redox rare‐earth‐mediated oxygen atom transfer from ketones to CS2 and PhNCS. Controlled experiments and computational studies shed light on the driving force for these reactions, emphasizing the importance of the sterical accessibility and multimetallic effect of the cluster framework in promoting reversal of reactivity of rare‐earth oxo complexes. 相似文献