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21.
Band broadening related to laminar flow and spray chamber dead volume is a potential problem in flow injection (FI)-inductively coupled plasma-mass spectrometry (ICP-MS). We studied these two dispersion effects with a sheath flow capillary electrophoresis (CE)-ICP-MS interface. A numerical model was used to simulate advection diffusion processes in the CE-capillary and dispersion in the spray chamber. Experimental results of FI with this CE-ICP-MS interface agree well with numerical modeling results. Dispersion due to laminar flow depends strongly on capillary diameter and analyte diffusion coefficient and to a lesser extent on laminar velocity and capillary length and typically amounts to one order of magnitude peak width increase. Three spray chambers of 5, 20 and 150 ml dead volume showed an increase in band broadening and peak tailing with increasing dead volume. The use of standard Scott-type spray chambers (>90 ml volume) increases peak widths by 5-10 s regardless of injection time. The use of a low dead volume spray chamber is recommended for experiments where resolution is critical. The modeling approach can be extended to the coupling of other flow injection techniques, like micro-LC and nano-LC with ICP-MS. 相似文献
22.
Synthetic erythropoietic proteins: tuning biological performance by site-specific polymer attachment
Chen SY Cressman S Mao F Shao H Low DW Beilan HS Cagle EN Carnevali M Gueriguian V Keogh PJ Porter H Stratton SM Wiedeke MC Savatski L Adamson JW Bozzini CE Kung A Kent SB Bradburne JA Kochendoerfer GG 《Chemistry & biology》2005,12(3):371-383
Chemical synthesis in combination with precision polymer modification allows the systematic exploration of the effect of protein properties, such as charge and hydrodynamic radius, on potency using defined, homogeneous conjugates. A series of polymer-modified synthetic erythropoiesis proteins were constructed that had a polypeptide chain similar to the amino acid sequence of human erythropoietin but differed significantly in the number and type of attached polymers. The analogs differed in charge from +5 to -26 at neutral pH and varied in molecular weight from 30 to 54 kDa. All were active in an in vitro cell proliferation assay. However, in vivo potency was found to be strongly dependent on overall charge and size. The trends observed in this study may serve as starting points for the construction of more potent synthetic EPO analogs in the future. 相似文献
23.
Sessler JL Roznyatovskiy V Pantos GD Borisova NE Reshetova MD Lynch VM Khrustalev VN Ustynyuk YA 《Organic letters》2005,7(23):5277-5280
[reaction: see text] Two easy-to-synthesize polypyrrolic 2,5-diamidothiophene Schiff base macrocycles are reported, along with their anion binding properties as determined via UV-vis spectroscopic titrations carried out in dichloroethane. There is a striking difference between the interactions with anions of the two macrocycles, a finding ascribed to differences in their rigidity. For example, the more flexible dipyrromethane-derived macrocycle displays a 1.2:1 hydrogen sulfate versus nitrate selectivity, while its more rigid bipyrrole-derived congener shows a 7.4:1 selectivity in favor to hydrogen sulfate. 相似文献
24.
Margaret C. Gerthoffer Sikai Wu Bo Chen Tao Wang Steven Huss Shalisa M. Oburn Vincent H. Crespi John V. Badding Elizabeth Elacqua 《Chemical science》2020,11(42):11419
Limited supramolecular strategies have been utilized to synthesize sequence-defined polymers, despite the prominence of noncovalent interactions in materials design. Herein, we illustrate the utility of ‘sacrificial’ aryl-perfluoroaryl supramolecular synthons to synthesize sp3-hybridized nanothreads from sp2-enriched reactants. Our strategy features A–B reactant pairs in the form of a phenol:pentafluorophenol co-crystal that is preorganized for an electronically-biased and sequence-defined polymerization. The polymerization, initiated at 12 GPa, affords an alternating copolymer featuring exogenous –OH functionalities. The external substitution is confirmed through IR spectroscopy. Importantly, the inclusion of the functional unit provides the first experimental glimpse at reaction mechanism: keto–enol tautomerization that can only occur during cycloaddition is observed through IR spectroscopy. Our approach realizes the first example of a functionalized nanothread and attains sequence definition through sacrificial supramolecular preorganization and presents a further approach for de novo design of complex nanothreads.Supramolecular synthons are exploited to synthesize –OH functionalized sp3-rich sequence-defined nanothreads using pressure-induced polymerization of a phenol:pentafluorophenol co-crystal. 相似文献
25.
A novel supramolecular strategy to prepare bidentate ligands via the assembly of functionalised monomeric ligands on a dimeric zinc(II) porphyrin template is presented; the assembled bidentate ligands show chelating behaviour and their rhodium complexes display enhanced selectivity in the hydroformylation compared to the non-template analogue. 相似文献
26.
In addition to halide oxidation, the vanadium haloperoxidases are capable of oxidizing sulfides to sulfoxides. Four vanadium complexes with tripodal amine ligands, K[VO(O(2))(heida)] (1), VO(2)(bpg) (2), K[VO(2)(ada)] (3), and K(2)[VO(O(2))(nta)] (4), previously shown to perform bromide oxidation (Colpas, G. J.; Hamstra, B. J.; Kampf, J. W.; Pecoraro, V. L. J. Am. Chem. Soc. 1996, 118, 3469-3477), have now been shown to oxidize aryl alkyl sulfides to the corresponding sulfoxides. The oxidation was observed by the disappearance of thioanisole's ultraviolet absorption at 290 nm, by the change in the aromatic region of the (1)H NMR spectrum of the sulfides, and by changes in the complexes' (51)V NMR spectra. The amount of methyl phenyl sulfide oxidized in 3 h was 1000 equiv (per metal complex). The oxidation product is almost exclusively sulfoxide, with very little sulfone (less than 3% over a 3 h experiment) formed. This is consistent with an electrophilic oxidation mechanism, as had been proposed for oxidation of bromide by 1-4. The rate was found to be first order in substrate concentration, similar to the rate law observed for bromide oxidation. Unlike the bromide oxidation, the equivalent of acid required for peroxovanadium complex activation is not consumed. The complexes 1-4 are not reactive with styrene or cyclooctene. The relevance of these reactions to the mechanism of the vanadium haloperoxidases and, more generally, peroxovanadium oxygenation of sulfides will be discussed. 相似文献
27.
Carlier J Arscott S Thomy V Camart JC Cren-Olivé C Le Gac S 《Journal of chromatography. A》2005,1071(1-2):213-222
We report here on an integrated microfabricated device dedicated to the preparation of biological samples prior to their on-line analysis by electrospray ionization-mass spectrometry (ESI-MS). This microfluidic device is fabricated using the negative photoresist SU-8 by microtechnology techniques. The device includes a chromatographic module plus an ESI interface for MS. The chromatographic module is dedicated to sample purification and is based on a polymer monolithic phase which includes hydrophobic moieties. The ESI interface is integrated onto the chip and is based on a capillary slot. We present here the integration of these different modules onto a single system that is fabricated via a SU-8-based microtechnology route. We present also their testing for the purification of peptide samples. This started with a partial integration step with the combination of at least two of the modules (microsystem + monolith; microsystem + nib) and their test before the fabrication and testing of fully integrated microsystems. 相似文献
28.
Humblot V Lorenzo MO Baddeley CJ Haq S Raval R 《Journal of the American Chemical Society》2004,126(20):6460-6469
A detailed comparison of tartaric acid (HOOC-CHOH-CHOH-COOH) and succinic acid (HOOC-CH(2)-CH(2)-COOH) molecules on a Cu(110) surface is presented with a view to elucidate how the two-dimensional chirality exhibited by such robust, chemisorbed systems is affected when both OH groups of the former molecule are replaced with H groups, a stereochemical change that leaves the metal-bonding functionalities of the molecule untouched but destroys both chiral centers. It is found that this change does not significantly affect the thermodynamically preferred chemical forms that are adopted, namely the doubly deprotonated bicarboxylate at low coverages (theta = (1)/(6) ML) and the singly deprotonated monocarboxylate at higher coverage. However, the kinetics of phase formation are significantly affected so that the conditions required for self-assembling pertinent two-dimensional chiral phases alter substantially. For both molecules, two-dimensional assembly is found to depend strongly on the nature of the local adsorption motif created, with each motif essentially acting as a "synthon" for the supramolecular assembly. In this respect, it seems that molecule-metal bonding interactions define the general self-assembly structure. The presence/absence of the OH groups, instead, cause a subtler, second-order effect on the finer details of the self-assembled structure. Finally, the creation of chirality in the achiral succinate system is shown to arise from adsorption-induced asymmetrization, inducing point chirality via molecular distortion and/or metal reconstruction of the local adsorption unit. This chiral adsorption unit is then responsible for creating chiral supramolecular through-space and through-metal interactions that propagate a chiral organization. However, the achirality of the succinate ensures that nucleation points of either chirality are equally created, producing a racemic conglomerate of coexisting mirror domains. It is in this aspect that the uniquely aligned OH groups of the rigid bitartrate system wield the greatest effect, by favoring one distortion/reconstruction for the (R,R)-bitartrate and its mirror image distortion/reconstruction for the (S,S)-enantiomer, creating surfaces that are globally chiral on the macroscopic scale. So overall, the OH groups do not dictate the general nature of the assembly but are critical as chiral propagators, breaking the degeneracy and thus promoting asymmetry to chirality. 相似文献
29.
Kim W McMillan RA Snyder JP Conticello VP 《Journal of the American Chemical Society》2005,127(51):18121-18132
Stereoelectronic effects have been identified as contributing factors to the conformational stability of collagen-mimetic peptide sequences. To assess the relevance of these factors within other protein structural contexts, three polypeptide sequences were prepared in which the sequences were derived from the canonical repeat unit (Val-Pro-Gly-Val-Gly) of the protein material elastin. These elastin-mimetic polypeptides, elastin-1, elastin-2, and elastin-3, incorporate (2S)-proline, (2S,4S)-4-fluoroproline, and (2S,4R)-4-fluoroproline, respectively, at the second position of the elastin repeat. Calorimetric and spectroscopic investigations of these three polypeptides indicate that the incorporation of the substituted proline residues had a dramatic effect upon the self-assembly of the corresponding elastin peptide. The presence of (2S,4R)-4-fluoroproline in elastin-3 lowered the temperature of the phase transition and increased the type II beta-turn population with respect to the parent polypeptide, while the presence of (2S,4S)-4-fluoroproline in elastin-2 had the opposite effect. These results suggest that stereoelectronic effects could either enhance or hinder the self-assembly of elastin-mimetic polypeptides, depending on the influence of the proline analogue on the energetics of the beta-turn conformation that develops within the pentapeptide structural repeats above the phase transition. Density functional theory (DFT) was employed to model three possible turn types (betaI-, betaII-, and inverse gamma-turns) derived from model peptide segments (MeCO-Xaa-Gly-NHMe) (Xaa = Pro, 4S-F-Pro, or 4R-F-Pro) corresponding to the turn-forming residues of the elastin repeat unit (Val-Pro-Gly-Val-Gly). The results of the these calculations suggested a similar outcome to the experimental data for the elastin-mimetic polypeptides, in that type II beta-turn structures were stabilized for peptide segments containing (2S,4R)-fluoroproline and destabilized for segments containing (2S,4S)-fluoroproline relative to the canonical proline residue. 相似文献
30.
We present an extensive investigation of the dependence of the scattering intensity difference of right and left circularly polarized light observed in vibrational Raman optical activity (VROA) on the choice of basis set and exchange-correlation functional. These dependencies are investigated for five molecules for which accurate experimental data are available: (S)-methyloxirane, (R)-epichlorhydrin, (S)-glycidol, (M)-spiro[2,2]pentane-1,4-diene, and (M)-sigma-[4]-helicene. Calculations are presented using the SVWN exchange-correlation functional (LDA), the BLYP exchange-correlation functional, and the B3LYP hybrid functional, using six different basis sets: the cc-pVDZ, cc-pVTZ, aug-cc-pVDZ, aug-cc-pVTZ, Sadlej's polarized basis set, and a minimal VROA basis set recently proposed by Zuber and Hug. It is demonstrated that results from pure gradient-corrected and hybrid functionals are comparable and that the aug-cc-pVDZ and aug-cc-pVTZ basis sets yield similar results. Furthermore, the combination of the small basis set by Zuber and Hug with an accurate force field represents the best compromise between computational accuracy and computational efficiency. 相似文献