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991.
Directed Evolution of RebH for Site‐Selective Halogenation of Large Biologically Active Molecules
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James T. Payne Dr. Catherine B. Poor Prof. Jared C. Lewis 《Angewandte Chemie (International ed. in English)》2015,54(14):4226-4230
We recently characterized the substrate scope of wild‐type RebH and proceeded to evolve variants of this enzyme with improved stability for biocatalysis. The substrate scopes of both RebH and the stabilized variants, however, are limited primarily to compounds similar in size to tryptophan. A substrate walking approach was used to further evolve RebH variants with expanded substrate scope. Two particularly notable variants were identified: 3‐SS, which provides high conversion of tricyclic tryptoline derivatives; and 4‐V, which accepts a broad range of large indoles and carbazoles. This constitutes the first reported use of directed evolution to enable the functionalization of substrates not accepted by wild‐type RebH and demonstrates the utility of RebH variants for the site‐selective halogenation of biologically active compounds. 相似文献
992.
Self‐Immolative Poly(4,5‐dichlorophthalaldehyde) and its Applications in Multi‐Stimuli‐Responsive Macroscopic Plastics
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Anthony M. DiLauro Gregory G. Lewis Prof. Scott T. Phillips 《Angewandte Chemie (International ed. in English)》2015,54(21):6200-6205
End‐capped poly(4,5‐dichlorophthalaldehyde) (PCl2PA), which is a new self‐immolative CDr polymer with the unique capability of depolymerizing continuously and completely in the solid state when an end cap is cleaved from the polymer by reaction with a specific molecular signal, is described. End‐capped poly(4,5‐dichlorophthalaldehyde) is sufficiently stable to enable patterning of three‐dimensional macroscopic polymeric materials by selective laser sintering. These unique materials are capable of 1) autonomously amplifying macroscopic changes in the material in response to specific molecular inputs, and 2) altering their responses depending on the identity of the applied signal. Thus, not only does end‐capped PCl2PA provide new and unique capabilities compared to the small subset of existing CDr polymers, but it also provides access to a new class of stimuli‐responsive materials. 相似文献
993.
D. L. Damcott J. M. Cookson R. D. Carter JR. J. R. Martin M. Atzmon G. S. Was 《辐射效应与固体损伤》2013,168(4):383-392
Abstract A technique is developed which addresses the problem of irradiation assisted stress corrosion cracking of stainless steels in light water reactors using high energy protons to induce grain boundary segregation. These results represent the first grain boundary segregation measurements in bulk produced by proton irradiation of stainless steel. The technique allows the study of grain boundary composition with negligible sample activation, short irradiation time, rapid sample turnaround and at minimal cost. Scanning Auger electron microscopy is used to obtain grain boundary composition measurements of irradiated and unirradiated samples of ultra high purity (UHP) type 304L stainless steel and UHP type 304L steels with the additions of phosphorus (UHP + P) and sulphur (UHP + S). Results show that irradiation of all three alloys causes significant Ni segregation to the grain boundary and Cr and Fe away from it. Irradiation of the UHP + P alloy also results in segregation of P at the grain boundary from 5.3 to 8.7 at %, over 80 times the bulk value. No radiation-induced grain boundary segregation of S was measured in the UHP + S alloy. Results also indicate that the presence of P or S may enhance radiation-induced segregation of major alloying elements at the boundary. Comparison of irradiated and unirradiated regions of the UHP + P alloy indicate that while a prior thermal treatment segregates P to the grain boundary to 5.3 at %, the major element concentrations at the grain boundary are completely different from those under irradiation. 相似文献
994.
995.
Scott Lewis Jaime Maerten‐Rivera Karen Adamson Okhee Lee 《School science and mathematics》2011,111(4):156-163
The study examined relationships among key domains of science instruction with English language learning (ELL) students based on teachers' perceptions of their classroom practices (i.e., what they think they do) and actual classroom practices (i.e., what they are observed doing). The four domains under investigation included: (1) teachers' knowledge of science content; (2) teaching practices to support scientific understanding; (3) teaching practices to support scientific inquiry; and (4) teaching practices to support English language development during science instruction. The study involved 38 third‐grade teachers participating in the first‐year implementation of a professional development intervention aimed at improving science and literacy achievement of ELL students in urban elementary schools. Based on teachers' self‐reports, practices for understanding were related to practices for inquiry and practices for English language development. Based on classroom observations in the fall and spring, practices for understanding were related to practices for inquiry, practices for English language development, and teacher knowledge of science content. However, we found a weak to non‐existent relationship between teachers' self‐reports and observations of their practices. 相似文献
996.
R. Lewis X. Song K. Dowsland J. Thompson 《European Journal of Operational Research》2011,213(1):379-65
This paper considers variants of the one-dimensional bin packing (and stock cutting) problem in which both the ordering and orientation of items in a container influences the validity and quality of a solution. Two new real-world problems of this type are introduced, the first that involves the creation of wooden trapezoidal-shaped trusses for use in the roofing industry, the second that requires the cutting and scoring of rectangular pieces of cardboard in the construction of boxes. To tackle these problems, two variants of a local search-based approximation algorithm are proposed, the first that attempts to determine item ordering and orientation via simple heuristics, the second that employs more accurate but costly branch-and-bound procedures. We investigate the inevitable trade-off between speed and accuracy that occurs with these variants and highlight the circumstances under which each scheme is advantageous. 相似文献
997.
Tan C Yang S Champness NR Lin X Blake AJ Lewis W Schröder M 《Chemical communications (Cambridge, England)》2011,47(15):4487-4489
The polyhedral complex [Cu(4)L(H(2)O)(4)]solv (NOTT-140) shows a 4,8-connected structure of rare scu topology comprising octahedral and cuboctahedral cages; desolvated NOTT-140a shows a total CO(2) uptake of 314.6 cm(3) (STP) cm(-3) at 20 bar, 293 K, and a total H(2) uptake of 6.0 wt% at 20 bar, 77 K. 相似文献
998.
Anderson JC Stepney GJ Mills MR Horsfall LR Blake AJ Lewis W 《The Journal of organic chemistry》2011,76(7):1961-1971
We report an enantioselective conjugate addition nitro-Mannich reaction protocol which combines dialkylzinc, aromatic nitro alkene and imine to form two C-C bonds and three contiguous stereocenters in one reaction vessel. Absolute stereochemistry was controlled from the initial 1,4-addition of dialkylzinc to aromatic nitroalkenes by known copper-chiral ligand catalysts. The choice of solvent dictated the formation of either the syn,anti or syn,syn diastereoisomers, two of the four possible diastereoisomers. The syn,syn isomer is a rare example of a syn-selective nitro-Mannich reaction. The diastereoselectivity is dependent upon the presence or not of Zn(O(2)CCF(3))(2) in the reaction mixture and empirical transition state models are proposed to account for the observed stereochemical course of the two reaction conditions. The extent of enantioselectivity and structural diversity of the process is limited by current methodology for the catalytic asymmetric addition of dialkylzincs to nitrostyrenes. The synthetically versatile products are the most complex β-nitro amines prepared using the nitro-Mannich reaction and are formed in high yield and enantioselectivity. 相似文献
999.
Denton RM An J Adeniran B Blake AJ Lewis W Poulton AM 《The Journal of organic chemistry》2011,76(16):6749-6767
Catalytic phosphorus(V)-mediated chlorination and bromination reactions of alcohols have been developed. The new reactions constitute a catalytic version of the classical Appel halogenation reaction. In these new reactions oxalyl chloride is used as a consumable stoichiometric reagent to generate the halophosphonium salts responsible for halogenation from catalytic phosphine oxides. Thus, phosphine oxides have been transformed from stoichiometric waste products into catalysts and a new concept for catalytic phosphorus-based activation and nucleophilic substitution of alcohols has been validated. The present study has focused on a full exploration of the scope and limitations of phosphine oxide catalyzed chlorination reactions as well as the development of the analogous bromination reactions. Further mechanistic studies, including density functional theory calculations on proposed intermediates of the catalytic cycle, are consistent with a catalytic cycle involving halo- and alkoxyphosphonium salts as intermediates. 相似文献
1000.
A synthesis of the structure reported for the natural product crassiflorone, a furocoumarin naphthoquinone, is described. The key steps are a Diels-Alder reaction to form 2-bromo-8-hydroxy-6-methylnaphthoquinone, followed by O-protection and copper(II) mediated coupling to 4-hydroxy-5-methylcoumarin to establish the pentacyclic framework whose structure was unambiguously confirmed by X-ray crystallography. Since the spectroscopic data of the synthetic material did not match those reported for the natural product, three further regioisomeric furocoumarin naphthoquinones were prepared by copper(II) mediated coupling of 4-hydroxy-5- or 8-methyl coumarins with 5-benzyloxy-2-bromo-7-methyl- or 8-benzyloxy-2-bromo-6-methyl-1,4-naphthoquinone. Again the spectroscopic data did not match those of the natural material and therefore the true structure of crassiflorone remains unknown. 相似文献