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991.
[reaction: see text] Phenyl 4,6-di-O-benzyl-2,3-O-carbonyl-beta-D-glucothiopyranoside and the regiosiomeric phenyl 2,6-di-O-benzyl-3,4-O-carbonyl-beta-D-glucothiopyranoside were prepared and studied as glucosyl donors at -60 degrees C in dichloromethane with preactivation by 1-benzenesulfinyl piperidine before addition of the acceptor alcohol. The 2,3-O-carbonate protected donor showed moderate to excellent beta-selectivity under these conditions depending on the acceptor employed, thereby providing a means for 1,2-trans-equatorial glycosidic bonds without recourse to neighboring group participation and its associated problem of ortho ester formation. In contrast, the 3,4-O-carbonate protected donor showed moderate to no beta-selectivity under the conditions employed. The results obtained in this study with carbonate protected glucopyranosyl donors are contrasted with those obtained previously in the manno- and rhamnopyranosyl series when the 2,3-O-carbonate protected is alpha-selective and the 3,4-O-carbonate is beta-selective. 相似文献
992.
993.
Xu‐Cheng Fu Xiao‐Yan Wang Ming‐Tian Li Xiao‐Tao Deng Cheng‐Gang Wang 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):m343-m345
The title complex, {[Cu2(C8H4O4)2(C3H4N2)4(H2O)]·H2O}n, is a three‐dimensional polymer formed through bridging by phthalate dianions of two different CuII cations and a network of O(N)—H⋯O hydrogen bonds. The Cu—O and Cu—N interaction distances are in the ranges 2.0020 (16)–2.4835 (17) and 1.968 (2)–1.9855 (19) Å, respectively. The structure is composed of alternating polymer chains parallel to the c axis, with a shortest Cu⋯Cu distance of 6.3000 (5) Å. 相似文献
994.
Li Zhang Xin‐An Chang Xue‐An Chen He‐Gui Zang Wei‐Qiang Xiao 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(9):i76-i78
The title compound represents a new structure type, in which distorted VO6 octahedra are bridged by iodate groups to form infinite two‐dimensional [VO2(IO3)2]− layers that are separated by octahedrally coordinated Li+ cations. 相似文献
995.
Ohsuna T Slater B Gao F Yu J Sakamoto Y Zhu G Terasaki O Vaughan DE Qiu S Catlow CR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(20):5031-5040
High-resolution electron microscopy (HREM) has been used to image the surface structure of nano- and micrometer-sized synthetic crystals of zeolite-Linde-L (LTL). Columnar holes and rotational, nano-sized, wheel-like defects were observed within the crystals, where the hole has a minimum size equal to that of the rotational defect. Predictions of surface structure from atomistic computer simulation concur with the observations from HREM and provide insight into the crystal growth mechanism of perfect and defective LTL. Analysis of the energetics of the formation of rotational defect structures reveals that the driving force for defect creation is thermodynamic and furthermore, the rotational defects could be created in high concentrations. Formation of a columnar hole is found to be slightly energetically unfavourable and therefore we speculate that the incidence of both rotational and nano-sized vacancy defects is strongly dependent on kinetic factors and reaction conditions. The morphology of nano- and microcrystalline LTL is contradistinct and we use insights from simulation to propose an explanation of the disparity in crystal shape. 相似文献
996.
Mulligan A Lane I Rousseau GB Hecht L Johnston SM Lennon D Kadodwala M 《Chemical communications (Cambridge, England)》2004,(21):2492-2493
Using a novel non-linear optical technique enantiomeric excess within a translationally disordered overlayer on a metal surface has been monitored for the first time. 相似文献
997.
Using the mixture of cetyltrimethylammonium bromide (CTAB) and p‐Octyl polyethylene glycol phenyl ether (OP‐10) as templates, siliceous MCM‐48 materials can be synthesized with low molar ratio of CTAB to silica (0.139:1) and low concentration of mixed surfactants (ca.5%) and within a wide range of OP‐10/CTAB ratio (0.08?0.25). The materials were characterized by X‐ray powder diffraction, N2 adsorption/desorption isotherm, TEM, TG‐DSC and 29Si MAS NMR. Measurements indicated that the use of mixed surfactants allowed better condensation and higher ordering of the cubic mesostructure; at the same time, some properties of these materials were sensitive to the OP‐10/CTAB ratio. It was also found that the reduced pH of the gel which had been crystallized for a certain time gave a highly reproducible synthesis with a high silica yield (about 95%). Furthermore, the reaction mechanism of the synthesis is discussed in detail. 相似文献
998.
999.
Philippe Gerbier Daniel Ruiz-Molina Neus Domingo David B. Amabilino José Vidal-Gancedo Javier Tejada David N. Hendrickson Jaume Veciana 《Monatshefte für Chemie / Chemical Monthly》2003,134(2):265-276
Summary. A new modified approach for the synthesis of Mn12 clusters, based on the use of complex [Mn12O12(O2C
t
Bu)16(H2O)4] (2) as starting material to promote the acidic ligand replacement, is presented here. This new synthetic approach allowed us
to obtain complex [Mn12O12(O2CC6H4N(O•)
t
Bu)16(H2O)4] (3), whose preparation remained elusive by direct replacement of the acetate groups of Mn12Ac (1). Complex 3 bearing open-shell radical units, was prepared to increase the total spin number of its ground state, and consequently, to
increase T
B
, with the expectation that the radical ligands may couple ferromagnetically with the Mn12 core. Unfortunately, magnetic measurements of complex 3 revealed that the sixteen radical carboxylate ligands interact antiferromagnetically with the Mn12 core to yield a S = 2 magnetic ground state.
Corresponding author. E-mail: vecianaj@icmab.es
Received March 27, 2002; accepted May 2, 2002 相似文献
1000.
Young PM Price R Lewis D Edge S Traini D 《Journal of colloid and interface science》2003,262(1):298-302
Drug particulate interactions in pressurized metered dose inhalers (pMDI) may lead to a decrease in aerosolization efficiency and subsequent efficacy in patient treatment. The interactions between salbutamol sulfate (commonly used in Ventolin pMDIs) and a series of pMDI canister materials were investigated using the atomic force microscope (AFM) colloid probe technique. Approximately 4000 individual force-distance curves were determined for a drug probe and three surfaces (10 x 10 mum areas) in situ, in a model propellant. The area under each force-distance curve was integrated to obtain separation energy values. Median separation energy values followed the rank order borosilicate glass > aluminum > PTFE, suggesting PTFE to be the most suitable canister coating. 相似文献