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71.
Dalvit C Hadden DT Sarver RW Ho AM Stockman BJ 《Combinatorial chemistry & high throughput screening》2003,6(5):445-453
High-throughput ligand-based proton NMR screening performed in the presence of a spy molecule and a control molecule is a valuable tool for identifying drug leads. A limitation of the technique is represented by the severe overlap encountered in the screening of large chemical mixtures. An approach for overcoming this overlap problem is the use of multi-selective R(1) filtered and COSY or TOCSY experiments. Application of this methodology to compounds binding to the Sudlow site I of human serum albumin is presented. The screening is performed by simply monitoring the intensity of two signals. The precise measurement of the relative intensity of the two resonances permits determination of the binding constant of the NMR-hit. For a simple competition binding mechanism, the rapidly-derived NMR binding constants are in good agreement with the values derived from full-titration ITC and fluorescence spectroscopy measurements. 相似文献
72.
The electrophilic iodocyclization reaction of (Z)- and (E)-5-n-alkylsubstituted 4-alken-1-ols followed by base-induced hydrodeiodination reaction stereoselectively gave, respectively, (Z)- and (E)-alkylidentetrahydrofurans in high yield. Completely different outcomes were observed with (Z)- and (E)-6,6-dimethylhept-4-en-1-ol: their iodocyclization furnished, respectively, threo- and erythro-2-(1-iodo-2,2-dimetylpropyl)tetrahydrofuran with high stereoselectivity. The threo isomer gave clean formation of 6-tert-butyl-3,4-dihydro-2H-pyran by base-induced ring expansion, while erythro isomer underwent a base-induced ring contraction to 1-cyclopropyl-3,3-dimethylbutan-1-one. Moreover, (Z)- and (E)-5-cyclopropylpent-4-en-1-ol underwent a 6-endo-iodocyclization to threo- and erythro-2-cyclopropyl-3-iodotetrahydro-2H-pyran, respectively, that under the same basic treatment, gave two isomeric 6-cyclopropyldihydro-2H-pyrans in a stereoselective fashion. 相似文献
73.
Methyl or silyl dissociation in the CH(2)=CHCH(2)-XH(3) (a-XH(3)(*)(+)) and CH(2)=CHCH=CHCH(2)-XH(3) (p-XH(3)(*) (+)) radical cations (X = C, Si) yields a(+) or p(+) and XH(3)(*). Similarly, the radical anions a-CH(3)(*) (-) and p-CH(3)(*) (-) give the pi-delocalized anion and CH(3)(*) preferentially. In contrast, a-SiH(3)(*) (-) and p-SiH(3)(*-) prefer to dissociate into the pi-delocalized radical and silide. All reactions are endoergic: by 43-50 kcal mol(-)(1) in the radical cations, and easier to some extent in the radical anions, that require 29-33 (X = C) and 13-14 kcal mol(-)(1) (X = Si). The fragmentation energy profiles do not present significant barriers for the backward process in the case of the radical cations. All radical anions exhibit an energy maximum along the dissociation pathway, but the barrier is lower than the dissociation limit. Fragmentation is "activated" more in the anions than in the cations with respect to homolysis in the corresponding neutrals (that requires 72-81 kcal mol(-)(1)). Wave function analysis indicates that the C-X bond cleavage in the hydrocarbon radical ions, although formally comparable to a homolytic process, is at variance with this model, due to the spin recoupling of one of the two C-X bond electrons with the originally unpaired electron. This is basically true also for the silyl-substituted radical anions, in which the initial more delocalized charge distribution might suggest some heterolytic character of the bond cleavage. 相似文献
74.
Julio Belmar Claudio Jimnez C. Ruiz‐Prez F. S. Delgado Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(10):o599-o601
In the title compound, C15H20N2O, the bond distances and angles are consistent with the presence of the hydroxy tautomer. This tautomer was unambiguously determined by the clear presence of a H atom bonded to oxygen, as well as the total absence of any residual electron density around the N atom in the heterocycle, thus precluding any possibility of desmotropism. 相似文献
75.
R. Friary J. H. Schwerdt V. Seidl F. J. Villani 《Journal of heterocyclic chemistry》1990,27(2):189-193
Arylmethylimidazolines and (3-chlorophenyl)methyl-1,4,5,6-tetrahydropyrimidine amidated 2-chloro-3-pyridinecarbonyl chloride, and potassium t-butoxide cyclized the products to linearly fused, tricyclic imidazo-and pyrimido[1,2-g][1,6]naphthyridinones. Condensation of ethyl 2-chloro-3-pyridinecarboxylate with 2-(phenylmethyl)imidazoline in the presence of sodium methoxide directly formed the isomeric, angularly fused 8,9-dihydro-6-phenylimidazo[1,2-a ] [1,8]naphthyridin-5(7H-one. 相似文献
76.
Lancelot N Elbayed K Raya J Piotto M Briand JP Formaggio F Toniolo C Bianco A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(6):1317-1323
A tetra- and a hepta-homopeptide from the C(alpha)-tetrasubstituted Aib (alpha-aminoisobutyric acid) residue were covalently linked to the POEPOP resin by the fragment-condensation approach. The conformational preferences of the two model peptides were determined for the first time on a solid support by means of high-resolution magic angle spinning NMR spectroscopy. The results obtained indicate that the Aib homopeptides adopt a regular 3(10)-helical structure even when they are covalently bound to a polymeric matrix, and thus confirm the remarkable conformational stability of the peptides rich in this amino acid. An ATR-FTIR spectroscopic investigation, performed in parallel, also confirmed that these polymer-bound peptides do indeed adopt a helical conformation. The results of this study open the possibility to exploit the peptide-resin conjugates based on C(alpha)-tetrasubstituted alpha-amino acids as helpful, structurally organized templates in molecular recognition studies or as catalysts in asymmetric synthesis. 相似文献
77.
Antonio L. Braga Helmoz R. Appelt Claudio C. Silveira Ludger A. Wessjohann Paulo H. Schneider 《Tetrahedron》2002,58(52):10413-10416
The enantioselective alkynylation reaction of aldehydes with alkynes and diethylzinc, catalyzed by chiral disulfide–oxazolidine ligands, provides a simple, practical and inexpensive method to access chiral propargylic alcohols in good yields and satisfactory ee's. 相似文献
78.
Lamellar crystalline calcium phenylphosphonate, as anhydrous Ca(HO3PC6H5)2 and hydrated Ca(HO3PC6H5)2·2H2O compounds, were used as hosts for intercalation of polar n-alkylmonoamine molecules of the general formula CH3(CH2)nNH2 (n=0–4, 7) in water or 1,2-dichloroethane. An increase in the interlayer distance was observed. The exothermic enthalpic values for intercalation increased with the number of carbon atoms and with increasing concentration of the amines. The intercalation followed by a titration procedure in the solid/liquid interface with Ca(HO3PC6H5)2·2H2O and Ca(HO3PC6H5)2 gave the enthalpy/number of carbons correlations: ΔintH=−(1.74±0.43)–(1.30±0.13)nc and ΔintH=−(4.15±0.15)–(1.07±0.03)nc, for water and 1,2-dichloroethane, respectively. A similar correlation ΔintH=−(4.27±0.80)–(1.85±0.21)nc was obtained in water by using the ampoule breaking procedure for Ca(HO3PC6H5)2·2H2O. The increase in exothermic enthalpic values with the increase in n-aliphatic carbon atoms is more pronounced for the anhydrous compound and also when using the ampoule breaking procedure. The Gibbs free energies are negative. Positive entropic values favor intercalation in these systems. 相似文献
79.
80.
Claudio Garola 《International Journal of Theoretical Physics》1992,31(9):1639-1652
We confute logical relativism and forward an alternative epistemological thesis according to which nonstandard truth-theories are considered theories of some metalinguistic concepts which do not coincide with truth, this latter concept being exhaustively described by Tarski's truth theory. We illustrate our viewpoint by showing that quantum logics can be interpreted as quantum physical theories of the metalinguistic concept of testability in the framework of a suitable classical language (with Tarskian semantics). 相似文献