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891.
Detecting recombinant human growth hormone (rhGH) abuse in sport remains one of the major challenges in doping control. We have compared two different approaches to detect the hGH (human growth hormone) abuse. The first measures the concentrations of the 22 kDa hGH isoform (rec assay) and pituitary derived isoforms (pit assay) and a ratio rec/pit is obtained. The second measures the concentrations of 22 and 20 kDa hGH isoforms and also a ratio 22/20 kDa is derived. 相似文献
892.
Lluís Bosch Ionela Cialîcu Joaquim Caner Xavier Ariza Anna M. Costa Montserrat Terrazas Jaume Vilarrasa 《Tetrahedron letters》2012,53(11):1358-1362
Pd-catalysed reactions of 2-Cl, 2-Br and 2-I derivatives of a 6-chloropurine nucleoside with benzamide have been compared, using Pd2dba3, Xantphos and Cs2CO3 in toluene, between 20 and 80 °C. The reactivity order was 2-I > 2-Br > 6-Cl ? 2-Cl. The 2-I substituent could be replaced even at 0 °C, under conditions disclosed here for the first time. On the other hand, the replacement of the chlorine atom at position 2 (2-Cl) required 110 °C. 相似文献
893.
Bosch J Bachs J Gómez AM Griera R Écija M Amat M 《The Journal of organic chemistry》2012,77(14):6340-6344
Practical stereoselective synthetic routes to the antihistaminic drug olopatadine and its E-isomer have been developed, the key steps being a trans stereoselective Wittig olefination using a nonstabilized phosphorus ylide and a stereoselective Heck cyclization. The stereoselectivity of the Wittig reaction depends on both the phosphonium salt anion and the cation present in the base used to generate the ylide. 相似文献
894.
Isaac Garcia‐Bosch Dr. Xavi Ribas Dr. Miquel Costas 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(7):2113-2122
Reactions of the unsymmetric dicopper(II) peroxide complex [CuII2(μ‐η1:η1‐O2)(m‐XYLN3N4)]2+ ( 1 O2 , where m‐XYL is a heptadentate N‐based ligand), with phenolates and phenols are described. Complex 1 O2 reacts with p‐X‐PhONa (X=MeO, Cl, H, or Me) at ?90 °C performing tyrosinase‐like ortho‐hydroxylation of the aromatic ring to afford the corresponding catechol products. Mechanistic studies demonstrate that reactions occur through initial reversible formation of metastable association complexes [CuII2(μ‐η1:η1‐O2)(p‐X‐PhO)(m‐XYLN3N4)]+ ( 1 O2 ?X‐PhO) that then undergo ortho‐hydroxylation of the aromatic ring by the peroxide moiety. Complex 1 O2 also reacts with 4‐X‐substituted phenols p‐X‐PhOH (X=MeO, Me, F, H, or Cl) and with 2,4‐di‐tert‐butylphenol at ?90 °C causing rapid decay of 1 O2 and affording biphenol coupling products, which is indicative that reactions occur through formation of phenoxyl radicals that then undergo radical C? C coupling. Spectroscopic UV/Vis monitoring and kinetic analysis show that reactions take place through reversible formation of ground‐state association complexes [CuII2(μ‐η1:η1‐O2)(X‐PhOH)(m‐XYLN3N4)]2+ ( 1 O2 ?X‐PhOH) that then evolve through an irreversible rate‐determining step. Mechanistic studies indicate that 1 O2 reacts with phenols through initial phenol binding to the Cu2O2 core, followed by a proton‐coupled electron transfer (PCET) at the rate‐determining step. Results disclosed in this work provide experimental evidence that the unsymmetric 1 O2 complex can mediate electrophilic arene hydroxylation and PCET reactions commonly associated with electrophilic Cu2O2 cores, and strongly suggest that the ability to form substrate?Cu2O2 association complexes may provide paths to overcome the inherent reactivity of the O2‐binding mode. This work provides experimental evidence that the presence of a H+ completely determines the fate of the association complex [CuII2(μ‐η1:η1‐O2)(X‐PhO(H))(m‐XYLN3N4)]n+ between a PCET and an arene hydroxylation reaction, and may provide clues to help understand enzymatic reactions at dicopper sites. 相似文献
895.
Datcu A Roques N Jubera V Maspoch D Fontrodona X Wurst K Imaz I Mouchaham G Sutter JP Rovira C Veciana J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(1):152-162
Lanthanide coordination polymers {[Ln(PTMTC)(EtOH)2H2O] ? x H2O, y EtOH} [Ln=Tb ( 1 ), Gd ( 2 ), and Eu ( 3 )] and {[Ln(αH? PTMTC)(EtOH)2H2O] ? x H2O, y EtOH} [Ln=Tb ( 1′ ), Gd ( 2′ ), and Eu ( 3′ )] have been prepared by reacting LnIII ions with tricarboxylate‐perchlorotriphenylmethyl/methane ligands that have a radical (PTMTC3?) or closed‐shell (αH? PTMTC3?) character, respectively. X‐ray diffraction analyses reveal 3D architectures that combine helical 1D channels and a fairly rare (6,3) connectivity described with the (42.8)?(44.62.85.104) Schäfli symbol. Such 3D architectures make these polymers porous solids upon departure of the non‐coordinated guest‐solvent molecules as confirmed by the XRD structure of the guest‐free [Tb(PTMTC)(EtOH)2H2O] and [Tb(αH? PTMTC)(EtOH)2H2O] materials. Accessible voids represent 40 % of the cell volume. Metal‐centered luminescence was observed in TbIII and EuIII coordination polymers 1′ and 3′ , although the LnIII‐ion luminescence was quenched when radical ligands were involved. The magnetic properties of all these compounds were investigated, and the nature of the {Ln–radical} (in 1 and 2 ) and the {radical–radical} exchange interactions (in 3 ) were assessed by comparing the behaviors for the radical‐based coordination polymers 1 – 3 with those of the compounds with the diamagnetic ligand set. Whilst antiferromagnetic {radical–radical} interactions were found in 3 , ferromagnetic {Ln–radical} interactions propagated in the 3D architectures of 1 and 2 . 相似文献
896.
A practical enantioselective protecting group-free four-step route to the key quinolizidinone 6 from phenylglycinol-derived bicyclic lactam 1 is reported. The Grignard addition reaction to 6 takes place stereoselectively to give 1-ethyl-4-substituted quinolizidines 4-epi-207I and 7-9. Following a similar synthetic sequence, 9a-epi-6 is also accessed. However, the addition of Grignard reagents to 9a-epi-6 proceeds in a non-stereoselective manner. In order to gain insight into the different stereochemical outcome in the two series, theoretical calculations on the iminium salts A and B have been performed. The study concludes that the addition of the hydride, which is the step that determines the configuration of the final products, occurs in a stereoelectronic controlled manner. The theoretical study is in agreement with the experimental results. 相似文献
897.
In this paper we study the analytic integrability of degenerate vector fields of the form (y3+2ax3y+?,−x5−3ax2y2+?) around the origin. For these vector fields it is proved that integrability does not imply formal orbital equivalence to the Hamiltonian leading part. Moreover, it is shown the existence of a system in this class which has a center but is neither analytically integrable nor formal orbital reversible. 相似文献
898.
Maurício Firmino Silva Lima Jaume Llibre 《Annali di Matematica Pura ed Applicata》2014,193(4):1103-1122
In this paper, we work with a two-degree polynomial differential system in \(\mathbb R ^3\) related with the canard phenomena. We show that this system is completely integrable, and we provide its global phase portrait in the Poincaré ball using the Poincaré–Lyapunov compactification. 相似文献
899.
900.
Eimear Byrne Marcus Greferath Jaume Pernas Jens Zumbrägel 《Designs, Codes and Cryptography》2013,66(1-3):3-16
In this article we investigate Berlekamp’s negacyclic codes and discover that these codes, when considered over the integers modulo 4, do not suffer any of the restrictions on the minimum distance observed in Berlekamp’s original papers: our codes have minimum Lee distance at least 2t + 1, where the generator polynomial of the code has roots α, α 3, . . . , α 2t-1 for a primitive 2nth root α of unity in a Galois extension of ${\mathbb {Z}_4}$ ; no restriction on t is imposed. We present an algebraic decoding algorithm for this class of codes that corrects any error pattern of Lee weight ≤ t. Our treatment uses Gröbner bases, the decoding complexity is quadratic in t. 相似文献