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141.
Heather L. Cuthbert John E. Greedan Lachlan Cranswick 《Journal of solid state chemistry》2006,179(7):1938-1947
La5Re3CoO16 and La5Re3NiO16 were synthesized by solid-state reaction and studied by SQUID magnetometry, heat capacity and powder neutron diffraction measurements. These two compounds belong to a series of isostructural Re-based pillared perovskites [Chi et al. J. Solid State Chem. 170 (2003) 165]. Magnetic susceptibility measurements indicate apparent short-range ferri or ferromagnetic correlations and possible long-range antiferromagnetic order for La5Re3CoO16 at 35 K, and at 38 and 14 K for La5Re3NiO16. Heat capacity measurements of the Co compound show a lambda anomaly, typical of long-range magnetic order, at 32 K. In contrast, the Ni compound displays a broader, more symmetric feature at 12 K in the heat capacity data, indicative of short-range magnetic order. Low-temperature powder neutron diffraction revealed contrasting magnetic structures. While both show an ordering wave vector, k=(0,0,1/2), in La5Re3CoO16, the Co2+ and Re5+ moments are ordered ferrimagnetically within the corner-shared octahedral layers, while the layers themselves are coupled antiferromagnetically along the c-axis, as also found in La5Re3MnO16 and La5Re3FeO16. In the case of the Ni material, the Re5+ and Ni2+ moments in the perovskite layers couple ferromagnetically and are canted 30° away from the c-axis, angled 45° in the ab-plane. The layers then couple antiferromagnetically at low temperature, a unique magnetic structure for this series. The properties of the La5Re3MO16 series, with M=Mn, Fe, Co, Ni and Mg are also reviewed. 相似文献
142.
Stuart Clough John Gupton Adepeju Ligali Matthew Roberts David Driscoll Scott Annett Alisa Hewitt Matthew Hudson Edward Jackson Robert Miller Bradley Norwood Rene Kanters Hadley Wyre Heather Petruzzi 《Tetrahedron》2005,61(31):7554-7561
The highly stereoselective conversions of (Z)-3-aryl-3-chloropropenals to (E)-3-alkoxy-3-arylpropenals, to (E)-3-aryl-3-morphorlinopropenals, and to vinamidinium salts are reported. The stereochemical assignments were based on 2D-NMR experiments. 相似文献
143.
Bontempo D Heredia KL Fish BA Maynard HD 《Journal of the American Chemical Society》2004,126(47):15372-15373
In this communication we report a strategy for the synthesis of semitelechelic polymers reactive to cysteines. An initiator modified with a pyridyl disulfide was prepared and used for the CuBr/2,2'-bipyridine-mediated atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate. Polydispersity indices (M(w)/M(n)) of the polymers with different molecular weights were 1.25 or less. The pyridyl disulfide end group was preserved during the polymerization and allowed direct conjugation of the polymer to cysteine residues of bovine serum albumin. The described method provides a general way for the preparation of protein-polymer conjugates through a reversible disulfide bond without the need for postsynthesis modification of the polymers. 相似文献
144.
Heather Davis Walter Skrzypek Arshad Khan 《Journal of polymer science. Part A, Polymer chemistry》1994,32(12):2267-2274
The iodine binding capacity (IBC) of amylopectin (AP, from potatoes) is determined to be around 0.38% (w/w) of the total AP in the solution. The mass of iodine bound comprises about 13.6% of the mass of AP involved with the complex, suggesting that with every four iodine atoms bound there are 23 anhydroglucose residues (AGU). Since our previous study indicates that four iodine atoms within the helix of 11 AGUs form a chromophore unit in the API complex, only 48% of the AGUs (11 out of 23) in the AP molecule are directly involved with the iodine. The heat of reaction for the API complex formation is determined to be around ?47 kJ/mol of I–I units bound and is significantly lower in magnitude than that of the amylose-iodine (AI) complex [Biopolymers, 31 , 57 (1991)]. A possible mechanism has been proposed for the formation of AI and API complexes with fixed compositions. © 1994 John Wiley & Sons, Inc. 相似文献
145.
Bacha PA Gruver HS Den Hartog BK Tamura SY Nutt RF 《Journal of chemical information and computer sciences》2002,42(5):1104-1111
A public bacterial mutagenicity database was classified into 2-D structural families using a set of specific algorithms and clustering techniques that find overlapping classes of compounds based upon chemical substructures. Structure-activity relationships were learned from the biological activity of the compounds within each class and used to identify rules that define substructures potentially responsible for mutagenic activity. In addition, this method of analysis was used to compare the pharmacologically relevant substructure of test compounds with their potential toxic substructures making this a potentially valuable in silico profiling tool for lead selection and optimization. 相似文献
146.
The π contribution to the electron localization function (ELF) is used to compare 4nπ‐ and (4n+2)π‐electron annulenes, with particular focus on the aromaticity of 4nπ‐electron annulenes in their lowest triplet state. The analysis is performed on the electron density obtained at the level of OLYP density functional theory, as well as at the CCSD and CASSCF ab initio levels. Two criteria for aromaticity of all‐carbon annulenes are set up: the span in the bifurcation values ΔBV(ELFπ) should be small, ideally zero, and the bifurcation value for ring closure of the π basin RCBV(ELFπ) should be high (≥ 0.7). On the basis of these criteria, nearly all 4nπ‐electron annulenes are aromatic in their lowest triplet states, similar to (4n+2)π‐electron annulenes in their singlet ground states. For singlet biradical cyclobutadiene and cyclooctatetraene constrained to D4h and D8h symmetry, respectively, the RCBV(ELFπ) at the CASSCF level is lower (0.531 and 0.745) than for benzene (0.853), even though they have equal proportions of α‐ and β‐electrons. 相似文献
147.
PC‐Activated Bimetallic Rhodium Xantphos Complexes: Formation and Catalytic Dehydrocoupling of Amine–Boranes 下载免费PDF全文
Dr. Heather C. Johnson Prof. Andrew S. Weller 《Angewandte Chemie (International ed. in English)》2015,54(35):10173-10177
{Rh(xantphos)}‐based phosphido dimers form by P? C activation of xantphos (4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene) in the presence of amine–boranes. These dimers are active dehydrocoupling catalysts, forming polymeric [H2BNMeH]n from H3B?NMeH2 and dimeric [H2BNMe2]2 from H3B?NMe2H at low catalyst loadings (0.1 mol %). Mechanistic investigations support a dimeric active species, suggesting that bimetallic catalysis may be possible in amine–borane dehydropolymerization. 相似文献
148.
Heather D. Booth Rajeev Govindan Michael A. Langston Siddharthan Ramachandramurthi 《Journal of Algorithms in Cognition, Informatics and Logic》1999,30(2):344
Many useful classes of graphs can in principle be recognized with finite batteries of obstruction tests. One of the most fundamental tests is to determine whether an arbitrary input graph containsK4in the immersion order. In this paper, we present for the first time a fast, practical algorithm to accomplish this task. We also extend our method so that, should an immersedK4be present, aK4model is isolated. 相似文献
149.
Noelia Rubio Heather Au Gabriel O. Coulter Laure Guetaz Gerard Gebel Cecilia Mattevi Milo S. P. Shaffer 《Chemical science》2021,12(44):14907
Here, the locus of functionalisation on graphene-related materials and the progress of the reaction is shown to depend strongly on the starting feedstock. Five characteristically different graphite sources were exfoliated and functionalized using a non-destructive chemical reduction method. These archetypical examples were compared via a model reaction, grafting dodecyl addends, evaluated with TGA-MS, XPS and Raman data. A general increase in grafting ratio (ranging from 1.1 wt% up to 25 wt%) and an improvement in grafting stoichiometry (C/R) were observed as flake radius decreased. Raman spectrum imaging of the functionalised natural flake graphite identified that grafting is directed towards flake edges. This behaviour was further corroborated, at atomistic resolution, by functionalising the graphene layers with bipyridine groups able to complex single platinum atoms. The distribution of these groups was then directly imaged using aberration-corrected HAADF-STEM. Platinum atoms were found to be homogeneously distributed across smaller graphenes; in contrast, a more heterogeneous distribution, with a predominance of edge grafting was observed for larger graphites. These observations show that grafting is directed towards flake edges, but not necessary at edge sites; the mechanism is attributed to the relative inaccessibility of the inner basal plane to reactive moieties, resulting in kinetically driven grafting nearer flake edges. This phenomenology may be relevant to a wide range of reactions on graphenes and other 2d materials. The flake size and morphology of the starting material strongly effect the degree and location of grafting when using reductive functionalisation. 相似文献
150.