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161.
This paper describes the synthesis of a bicyclic beta-amino acid scaffold in both pure enantiomeric forms and its application as chiral auxiliary in an intramolecular version of the Ugi multicomponent reaction (U-5C-4CR) to prepare alpha-amino acid derivatives of both D- and L-series in a straightforward and very stereoselective manner. The mild conditions required for the Ugi condensation and for the removal of the chiral auxiliary make this method very attractive to prepare a wide range of differently structured N-alkylated and unalkylated amino acid derivatives. 相似文献
162.
Bergman SD Gut D Kol M Sabatini C Barbieri A Barigelletti F 《Inorganic chemistry》2005,44(22):7943-7950
The synthesis and characterization of new Ru(II) and Os(II) complexes of the ligand eilatin (1) are described. The new complexes [Ru(bpy)(eil)(2)](2+) (2), [Ru(eil)(3)](2+) (3), and [Os(eil)(3)](2+) (4) (bpy = 2,2'-bipyridine; eil = eilatin) were synthesized and characterized by NMR, fast atom bombardment mass spectrometry, and elemental analysis. In the series of complexes [Ru(bpy)(x)(eil)(y)()](2+) (x + y = 3), the effect of sequential substitution of eil for bpy on the electrochemical and photophysical properties was examined. The absorption spectra of the complexes exhibit several bpy- and eil-associated pi-pi and metal-to-ligand charge-transfer (MLCT) transitions in the visible region (400-600 nm), whose energy and relative intensity depend on the number of ligands bound to the metal center (x and y). On going from [Ru(bpy)(2)(eil)](2+) (5) to 2 to 3, the d(pi)(Ru) --> pi(eil) MLCT transition undergoes a red shift from 583 to 591 to 599 nm, respectively. Electrochemical measurements performed in dimethyl sulfoxide reveal several ligand-based reduction processes, where each eil ligand can accept up to two electrons at potentials that are significantly anodically shifted (by ca. 1 V) with respect to the bpy ligands. The complexes exhibit near-IR emission (900-1100 nm) of typical (3)MLCT character, both at room temperature and at 77 K. Along the series 5, 2, and 3, upon substitution of eil for bpy, the emission maxima undergo a blue shift and the quantum yields and lifetimes increase. The radiative and nonradiative processes that contribute to deactivation of the excited level are discussed in detail. 相似文献
163.
Andrea Schfer Manfred Hesse Max Viscontini Henning Paul Berthold Fischer 《Helvetica chimica acta》1995,78(7):1763-1776
The experimental conditions developed for the detection of rather stable radical cations in solution by electrospray-ionization mass spectrometry (ESI-MS) of a FeII complex of 2-amino-5,6,7,8-tetrahydro-5-methylpteridin-4 (3H)-one ( 1c ) are used to observe the formation of the more unstable radical cations formed from 2-amino-5,6,7,8-tetrahydropteridin-4(3H)-one ( 1a ) and tris(pentane-2,4-dionato)iron(III) ([FeIII(acac)3]; 4 ) and to monitor their oxidation to the corresponding p-quinonoid dihydropterin complexes. These results contribute to the understanding of the important role played by 6β-5,6,7,8-tetrahydro-L -biopterin ( 1b ; a homologue of 1a ) together with iron as constituent of some cofactors. The complexes obtained from 1a and iron may be considered, e.g. as a model of the cofactor of the phenylalanine hydroxylase. Moreover, we describe an improved synthesis of 1c . 相似文献
164.
165.
Baldelli E Battaglia A Bombardelli E Carenzi G Fontana G Gelmi ML Guerrini A Pocar D 《The Journal of organic chemistry》2004,69(20):6610-6616
New taxanes 15 and 18, containing the unsaturated and saturated baccatin[14,1-d]furan-2-one nucleus, respectively, were prepared starting from the readily available 13-oxo-7-Tes-baccatin III (3). Sequential formation of the enolate of 3 and reaction with ethyl glyoxylate gave the 13-oxo-7-Tes-baccatin[14,1-d]-3,4-dehydrofuran-2-one 4. The reduction of 4 can result in the formation of a mixture of compounds corresponding to 13-hydroxy alcohol 5 and 13-enol derivative 6. Both 5 and 6 were transformed into 13-oxo-7-Tes-baccatin[14,1-d]furan-2-one 8 by treatment with a base. Further reduction of 8 gave 13-hydroxy compound 9. Esterification of 6 and 9 with N,O-protected norstatine 12, followed by deprotection, gave the new promising anticancer taxanes 15 and 18, respectively. 相似文献
166.
At pH 4.5 (citrate buffer), D -gluconhydroximo-lactone ( 2 ), the N-methylurethane 3 and the N-phenylurethane 4 inhibit competitively the hydrolysis of p-nitrophenyl β-D -glucopyranoside by emulsin. The IC50 values of 2, 3 , and 4 were 1.6 × 10?4, 1.0 × 10?4, and 5.8 × 10?6 M , respectively. The Ki values of 2 and 4 were 9.8 × 10?5 and 2.3 × 10?6 M , respectively, while D-glucono-1,5-lactone ( 1 ) showed IC50 = 1.1 × 10?4 M and Ki = 3.7 × 10?5 M . 相似文献
167.
168.
Amidoalkyl radicals, generated from amides by Mn(OAc)3 in acetic acid react with phenyl substituted alkenes to generate five-membered lactones or lactams. Ultrasound at ambient temperature significantly accelerates these single electron transfer reactions even when compared with conventional conditions under reflux or simple mechanical stirring. In some cases sonication leads to unusual products. 相似文献
169.
α-acyloxyaminoamides can be prepared, with yields ranging from fair to very good (up to 89%), through an Ugi four component reaction by mixing a carbonyl component, a carboxylic acid, an isocyanide and an N-alkylated hydroxylamine in methanol. Preformed nitrones furnish the same final compounds with comparable yields. 相似文献
170.
A numerical model for the adsorption kinetics of proteins on the walls of a microchannel has been developed using the finite element method (FEM) to address the coupling with diffusion phenomena in the restricted microchannel volume. Time evolutions of the concentration of one species are given, both in solution and on the microchannel walls. The model illustrates the adsorption limitation sometimes observed when the microdimensions of these systems induce a global depletion of the bulk solution. A new non-dimensional parameter is introduced to predict the final value of the coverage of any microsystem under static adsorption. A working curve and a criteria (h/K[Gamma](max) > 10) are provided in order to choose, for given adsorption characteristics, the value of the volume-to-surface ratio (i.e. the channel height h) avoiding depletion effects on the coverage (relative coverage greater than 90% of the theoretical one). Simulations were compared with confocal microscopy measurements of IgG antibody adsorption on the walls of a PET microchannel. The fit of the model to the experimental data show that the adsorption is under apparent kinetic control. 相似文献