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941.
Arrigo Forni Irene Moretti Adele Mucci Fabio Prati Luisa Schenetti 《Chemistry of Heterocyclic Compounds》1995,31(9):1071-1078
A confrgurational and conformational study of NH, N-acetyl- and N-sulfonylaziridine carboxylates is performed by1H ,13C,17O, and15N NMR spectroscopy. The presence of acetyl and su fonyl groups on the ring nitrogen atom seems to reduce greatly the configurational stability at nitrogen.Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1226–1234, September, 1995. 相似文献
942.
Starting from the natural neo-clerodane diterpenoid teubotrin (1) several neo-clerodane derivatives (3-7,9-11) have been obtained. The naturally occurring diterpenoid teuscordinon (12) has also been synthesized from teubotrin (1), showing thereby how some of these transformations can be useful for the synthesis of other natural neo-clerodane diterpenes. The latter are of interest due to their activity as insect antifeedants and other important biological properties. 相似文献
943.
Isolation and structure elucidation of a C11 mono-carboxylic acid, apparently a nor-sesquiterpene, and, a sesquiterpene diosphenol from the essential oil of Cedrus deodara Loud. are described. 相似文献
944.
W. Jaegermann T. Sakata E. Janata H. Tributsch 《Journal of Electroanalytical Chemistry》1985,189(1):65-84
Laser-pulse transient measurements have been performed at single crystalline n-PtS2 electrodes with the aim of understanding light-induced hydroxide, oxide and oxygen formation. Different detected time constants permit the identification of distinct reaction products. They form surface states which function both as centers for recombination and charge accumulation in the interface. The rate constants determined are influenced by the RC-constant of the measuring circuit and can be interpreted only qualitatively. In the presence of recombination processes time constants faster than RLCSC are found. Evidence is given that the reaction step leading to oxygen evolution is dependent on the building-up of an electric field in the Helmholtz layer. This result may be of importance for the development of materials for the photoelectrolysis of water. 相似文献
945.
Yang Jie Wu Shou Quan Huo Li Yang Chen Xia Du 《Journal of organometallic chemistry》1995,490(1-2):249-254
Three series of cyclomercurated ferrocenylimines (2-chloromercurio-ferrocenylimines) have been studied using 13C NMR spectroscopy. Good to excellent linear relationships have been found to exist between the chemical shifts of the carbon atoms in the ferrocenyl moiety and normal Hammett substituent constants σm and σp. The δ values of the iminyl carbon atoms show excellent linear correlations with the σ values. In three series of the ferrocenes, the sensitivity of the carbon atoms to the substituent effect is different, which is discussed in terms of the twist angle between the N-phenyl ring and the C---C=N---C plane. The relative sensitivity of the chemical shifts on different positions in ferrocenyl moiety to the substituent effect has also been presented. 相似文献
946.
Akinori Ohshita Masaaki Okuhara Chiharu Matsuya Koichi Hata Kazuo Iida 《Mikrochimica acta》2006,155(1-2):225-228
A new electron holographic method is presented to directly visualize pure phase objects such as electromagnetic microfields,
which is achieved by superposition of two kinds of electron holograms. The method is very simple and is twice as sensitive
as the conventional double-exposure electron holography and the four-electron-wave interference. Using this technique, an
electric field around a charged latex sphere and a magnetic field around a barium ferrite particle have been directly observed. 相似文献
947.
Gejihu De Weiping Qin Jisen Zhang Yan Wang Chunyan Cao Yang Cui 《Journal of solid state chemistry》2006,179(3):955-958
In this work, we used the hydrothermal method to synthesize Eu3+ ion-doped cubic BaF2 nanorods, which is a luminescent material. The clubbed structures were well crystallized and exhibited face-centred cubic structures, as indicated by powder X-ray diffraction, scanning electron microscopy, electron diffraction, and transmission electron microscopy. The luminescent properties were studied, and local symmetry surrounding Eu3+ ions and electronic transition processes included. The results indicated that Eu3+ occupied only one C4ν site in nanorods. 相似文献
948.
D. Van Dyck 《Mikrochimica acta》2002,138(3-4):153-180
With the resolution becoming sufficient to reveal individual atoms, HREM is now entering the stage where it can compete with
X-ray methods to quantitatively determine atomic structures of materials without much prior knowledge, but with the advantage
of being applicable to aperiodic objects such as crystal defects. In our view the future electron microscope will be characterised
by a large versatility in experimental settings under computer control such as the illumination conditions (TEM-STEM), CBED,
detecting conditions (diffraction, image, ptychography) and many other tunable parameters such as focus (g), voltage, spherical aberration (C
s
), beam tilt, etc. Since modern detectors can detect single electrons, also the counting statistics is known. The only limiting
factor in the experiment will be the total number of electrons that interact with the object during the experiment due to
the limitations in the exposure time or in the object damage. However, instrumental potentialities will never be exploited
fully if not guided by an experimental strategy. Here intuitive guidelines can be very deceptive. For instance an image made
with the best electron microscope (C
s
= 0) at the best focus (g = 0) from the best object (phase object) would show no contrast at all. Hence, questions such as what is the best C
s
, focus, object thickness, etc. can only be answered properly if done using a method of experiment design. 相似文献
949.
The metalation of allyl benzyl thioether involves the benzylic or the allylic hydrogens. The benzylic carbanion undergoes a rapid[2,3] sigmatropic shift whereas the allylic carbanion gives rise to various rearrangements, among them migration of the allylic unit to the para position with allylic inversion. The temperature dependence of the ratio of products arising from the benzylic carbanion vs those from the allylic carbanion shows that the allylic-to-benzylic carbanion transformation occurs only under special conditions: (a) with slow addition of the base; (b) with thioether in excess relative to the base, and (c) on raising the temperature of the reaction medium from ?78° to ?15°. In the last instance, the proton transfer is intramolecular as shown with labeled thioethers. The extent of the different rearrangements depends on the temperature and solvent. A choice of mechanism cannot be made at this time for the para migration 5→9a. A leaving group effect on the reaction regioselectivity of the carbanion from allyl methyl thioether with benzyl halides has been noticed. The presence of dibenzyl indicates that, in addition to SN2 reactions, some electron transfer process is occurring. 相似文献
950.
David Ajó Maurizio Casarin Gaetano Granozzi Ignazio Fragalá 《Chemical physics letters》1981,80(1):188-191
The He(I) photoelectron spectra of 5-azauracil (1,3,5-triazine-2,4(1H,3H)-dione) and 6-azauracil (1,2,4-triazine-3, 5(2H,4H)-dione) are presented. The spectra are assigned by using INDO/S calculations and comparison arguments with uracil. The first ionization energy in the title compounds is higher than in the usual nucleic acid bases. 相似文献