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101.
Berezkin Victor G. Mardanov Robert G. Moiseew Aleksey A. Malinowska Irena Różyło Jan K. 《平面色谱法杂志一现代薄层色谱法》2002,15(5):377-379
JPC – Journal of Planar Chromatography – Modern TLC - 相似文献
102.
Studies on the photooxidation mechanism of polymers. I. Photolysis and photooxidation of polystyrene
A new mechanism has been proposed for the photooxidation of polystyrene as film and in benzene. The initial stage of the photooxidative degradation may involve reactions of singlet oxygen with polystyrene molecules. Singlet oxygen may be formed in the reaction between excited benzene ring in polystyrene molecule and molecular oxygen. The addition of singlet oxygen quenchers such as 1,3-cyclohexadiene or β-carotene reduces the rate of polymer degradation in benzene solution. The mechanisms of the photolysis of polystyrene as film and in benzene solution, in vacuo and in the presence of oxygen, are discussed and interpretations proposed. The pronounced yellowing of polystyrene during the photooxidation process is interpreted as a reaction involving benzene ring-opening photooxidation in polystyrene molecule. These results were obtained by comparing ultraviolet and infrared spectra in experiments of photooxidation of pure liquid benzene and polystyrene film. 相似文献
103.
Summary The calculation of vibrational states using a gradient extremal path is discussed. Gradient extremal paths are defined by local criteria, which lead to stable solutions. This has certain advantages in comparison with a steepest-descent path, which is often difficult to determine accurately. For cases where a reaction path formalism is applicable, a path based on the gradient extremal concept gives results in close agreement with those obtained using traditional steepest-descent methods. We present algorithms for carrying out such calculations and also give some numerical results. 相似文献
104.
105.
Crich D Mataka J Zakharov LN Rheingold AL Wink DJ 《Journal of the American Chemical Society》2002,124(21):6028-6036
A series of four S-allyl D-thiopyranosides, alpha- and beta-manno and xylo, were oxidized with MCPBA at low temperature to give seven of the eight possible sulfoxides, whose configuration at sulfur was determined either directly by X-ray crystallography or by correlation with closely related structures. For the axial thioglycosides oxidation leads very predominantly to the (R)(S)-diastereomer in the xylo series and exclusively so in the manno series; the configuration at C2 is of little importance in determining the stereoselectivity of oxidation of axial thioglycopyranosides. In the equatorial series the configuration at C2 has a significant effect on the outcome of the reaction as, although both series favored the (S)(S)-sulfoxide, selectivity was significantly higher in the case of the beta-mannoside than of the beta-xyloside. The two alpha-xylo sulfoxides have different conformations of the pyranoside ring with the (R)(S)-isomer adopting the (1)C(4) chair and the (S)(S)-diastereomer the (4)C(1). Each pair of diastereomeric sulfoxides was thermally equilibrated in C(6)D(6) and in CD(3)OD. In the mannose series the kinetic isomers are also thermodynamically preferred. In the xylose series, on the other hand, the nature of the thermodynamic isomer in both the alpha- and beta-anomers is a function of solvent with a switch observed on going from C(6)D(6) to CD(3)OD. The results are rationalized in terms of the exo-anomeric effect, steric shielding provided by H3 and H5 in the axial series, the interaction of the C2-O2 and sulfoxide dipoles, and increased steric interactions on hydrogen bonding of the sulfoxides to CD(3)OD. 相似文献
106.
Mona Wells Michael Gösch Hauke Harms Jan Roelof van der Meer 《Mikrochimica acta》2005,151(3-4):209-216
This paper describes the development of an analytical technique for arsenic analyses that is based on genetically-modified
bioreporter bacteria bearing a gene encoding for the production of a green fluorescent protein (gfp). Upon exposure to arsenic
(in the aqueous form of arsenite), the bioreporter production of the fluorescent reporter molecule is monitored spectroscopically.
We compared the response measured as a function of time and concentration by steady-state fluorimetry (SSF) to that measured
by epi-fluorescent microscopy (EFM). SSF is a bulk technique; as such it inherently yields less information, whereas EFM monitors
the response of many individual cells simultaneously and data can be processed in terms of population averages or subpopulations.
For the bioreporter strain used here, as well as for the literature we cite, the two techniques exhibit similar performance
characteristics. The results presented here show that the EFM technique can compete with SSF and shows substantially more
promise for future improvement; it is a matter of research interest to develop optimized methods of EFM image analysis and
statistical data treatment. EFM is a conduit for understanding the dynamics of individual cell response vs. population response, which is not only a matter of research interest, but is also promising in the practical terms of developing
micro-scale analysis. 相似文献
107.
The title compound 3g is obtained via two different routes, either in a multistep synthesis starting from 2-amino-2-methylpropionic acid (methylalanine) or by light-induced, oxidative dealkylation of the corresponding N-isopropyl derivative 3c . 相似文献
108.
We report on a novel ultrafast two-dimensional infrared laser experiment that correlates vibrational bands of reactant and product of a photoreaction. The possibilities of this technique are demonstrated for the metal-to-ligand charge transfer (MLCT) in [Re(CO)3Cl(dmbpy)] (dmbpy = 4,4'-dimethyl-2,2'bipyridine) where we correlated the CO vibrational modes of the ground state and the MLCT state. A distinct vibrational mode is excited in the electronic ground state by an infrared laser pulse. This vibrational label survives the subsequent electronic excitation and can be followed in the excited electronic state. It is shown that the order of the vibrational energy levels is not preserved when exciting the molecule as was commonly assumed in the literature. 相似文献
109.
Griffiths WJ Alvelius G Liu S Sjövall J 《European journal of mass spectrometry (Chichester, England)》2004,10(1):63-88
Neutral oxosteroids have been derivatised with Girard T and P hydrazine reagents to give the corresponding Girard hydrazone quaternary ammonium salts. Both Girard T (GT) and Girard P (GP) hydrazones of oxosteroids give very intense [M](+) ion signals in electrospray (ES) mass spectra and fragment within the ES interface and collision cell to give characteristic fragment ions. GT and GP derivatives give informative high-energy collision-induced dissociation spectra, from which the structure of the precursor oxosteroid can be determined. Both charge-remote and charge-mediated mechanisms are responsible for the formation of the fragment ions at high collision-energy. 相似文献
110.
Jan S. Jaworski 《Monatshefte für Chemie / Chemical Monthly》1984,115(4):415-418
A two parameter approach to solvent variations in the electroreduction rate constants of cobalt complexes and europium cations is presented and discussed in terms of solvent—solute and solvent—solvent interactions.
Ein Zwei-Parameter Donor-Acceptor-Ansatz für Lösungsmitteleffekte bei der Elektrodenkinetik von Kationen (Kurze Mitteilung)
Zusammenfassung Es wird eine Zwei-Parameter-Annäherung der Lösungsmitteleinflüsse auf die Geschwindigkeitskonstanten der Elektroreduktion von Kobalt-Komplexen und Europium-Kationen präsentiert und auf der Basis von Lösungsmittel—gelöster Stoff- und Lösungsmittel—Lösungsmittel-Wechselwirkung diskutiert.相似文献