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941.
In this paper an application of a reaction field theory of solvent effects has been made to study proton transfer mechanisms in hydrogen bonded systems coupled to an environment. The latter is simulated with reaction fields having variable strength and direction (defined with respect to the supermolecule's total dipole moment direction), together with superposed uniform external electric fields. Changes in proton potential curves and some other properties of a model water dimer and a water trimer are reported. The results are discussed in relation to relevant phenomena in biology and biochemistry, namely proton relay systems in enzymatic catalysis. 相似文献
942.
S. P. Kolesnikov A. I. Ioffe B. L. Perl'mutter O. M. Nefedov 《Russian Chemical Bulletin》1976,25(4):736-739
1. | We have used the extended Hückel method to examine the interaction of singlet methylene with water and found the existence of a molecular complex CH2·H2O with an energy of stabilization of 5.6 kcal/mole and a complex CH2·2H2O with an energy of stabilization of 2.1 kcal/mole, which tends to lose one water molecule during simultaneous approach of the other. |
2. | The structure of these complexes is determined by the interaction of the unoccupied methylene p orbital with the lone-pair orbitals of the water molecules. |
943.
Zusammenfassung Dambonit (1,3-Di-O-methyl-myo-inosit) entsteht inNerium oleander, wie durch Einbauversuche mit radioaktiv markiertemmyo-Inosit undd-Bornesit sowie durch Bestimmung der Zeitabhängigkeit der Bildung der Cyclite bei Assimilation von14CO2 nachgewiesen wurde, ausmyo-Inosit überd-Bornesit als Zwischenprodukt. Neben Dambonit finden sich in der Cyclitfraktion vonN. oleander auchd-Bornesit,myo-Inosit sowiel-Leucanthemit.myo-Inosit unterliegt in der Pflanze-besonders im Winter-einem sehr intensiven Stoffwechsel, der zu nichtzyklischen Verbindungen führt.
H. Kindl undO. Hoffmann-Ostenhof, Mh. Chem.97, 1771 (1966). 相似文献
InNerium oleander dambonitol (1,3-Di-O-methyl-myo-inositol) is formed frommyo-inositol withd-bornesitol as intermediate, as could be shown with the help of incorporation experiments with radioactively labelledmyo-inositol andd-bornesitol and also by the determination of the time dependence of the formation of the cyclitols from14CO2 in photoassimilation experiments. Besides dambonitol the cyclitol fraction ofN. oleander contains alsod-bornesitol,myo-inositol andl-leucanthemitol. Especially in wintermyo-inositol undergoes a very active catabolism in the plant which leads to the formation of non-cyclic compounds.
H. Kindl undO. Hoffmann-Ostenhof, Mh. Chem.97, 1771 (1966). 相似文献
944.
WO3 and WO3:P (5 mol% H3PO4) thin films were prepared using the sol-gel route and the electrochromic properties of the films were investigated using
in situ spectroelectrochemical methods. The measurements were performed in propylene carbonate solution with 0.1 M LiClO4 as electrolyte. During the cathodic polarization at –0.8 V a blue coloration is observed with a reversible variation between
14% and 84% of the transmittance at λ=633 nm. The kinetics for the bleaching process is faster for the WO3:P film than for the undoped WO3 film.
Electronic Publication 相似文献
945.
Nagornyi O. V. Kolyshkin A. S. Vol'khin V. V. 《Russian Journal of Applied Chemistry》2003,76(8):1238-1241
Fe(CN)6
3
- and Fe(CN)6
4
- anions are sorbed from aqueous solutions of their potassium and cesium salts on -Ni(OH)2 by the mechanism of anion exchange with hydroxy groups. Alkali metal cations (K+, Cs+) are also partly sorbed on nickel(II) hydroxide in the form of anionic complexes (K,Cs)
z
Fe(CN)6
(n - z)-, where n = 3 or 4 (0 < z < n). The chemical composition of the new phase appearing in contact of nickel(II) hydroxide with aqueous potassium and cesium hexacyanoferrates(II, III) was determined by X-ray phase analysis and IR spectroscopy. 相似文献
946.
V.A. Ozeryanskii A.F. Pozharskii D.A. Shevchuk A.N. Chekhlov O.A. Dyachenko 《Tetrahedron》2005,61(17):4221-4232
A simple procedure for the synthesis of N,N,N′-trialkyl-1,8-diaminonaphthalenes is described. It consists in partial demethylation (dealkylation) of commercially available proton sponge [1,8-bis(dimethylamino)naphthalene] and some of its derivatives at heating with HBr-KI-DMF system. Limitation, scope and a possible mechanistic pathway for the reaction are discussed. For isomeric 8-dimethylamino-1-methylamino- and 1-dimethylamino-8-methylamino-4-nitronaphthalenes, X-ray measurements have been conducted. The first examples of complete realkylation reactions in the naphthalene proton sponges are reported. 相似文献
947.
M. Ştefănescu M. Stoia O. Ştefănescu A. Popa M. Simon C. Ionescu 《Journal of Thermal Analysis and Calorimetry》2007,88(1):19-26
Hybrid organic-inorganic materials,
silica – polyols (ethylene-glycol – EG; 1,2 propane diol –
1,2PG; 1,3 propane diol – 1,3PG and glycerol – GL), were prepared
by a sol-gel process starting from tetraethylorthosilicate (TEOS) and polyols,
in acid catalysis. The resulting materials were studied by thermal analysis
(in air and nitrogen), FTIR and solid state 29Si-NMR
spectroscopy. These techniques evidenced the presence of polyols in the silica
matrix both hydrogen bounded and chemically bounded in the silica network.
The thermal analysis proves to be the most appropriate technique to evidence
the organic chains linked in the matrix network and to follow the thermal
evolution of the gels to the SiO2 matrix. 相似文献
948.
F. J. Molina A. O. Vila C. Llcer M. J. Martos J. E. Figueruelo 《Journal of separation science》1991,14(9):590-592
Internal calibration in modified hydrodynamic chromatography has been realized by the approach of Prieve and Hoysan, i.e. the use of polystyrene monodisperse latexes to evaluate the equivalent capillary radius, R. The value obtained has been used to estimate the average sizes of a variety of liposome samples from egg yolk lecithin. 相似文献
949.
A. P. Popov N. S. Shelekhov O. V. Bandyuk O. B. Ratner T. M. Vember A. O. Rebezov G. I. Lashkov 《Theoretical and Experimental Chemistry》1986,22(2):219-224
Sensitized photooxidation of a series of compounds with an anthracene structure in a block poly(methyl methacrylate) (PMMA) containing a tetrapyrrole pigment (TPP) or anthraquinone dyes as spectral sensitizers, was studied. The values of changes in the molar refraction at equal to 441 and 633 nm were determined experimentally. They satisfactorily agreed with the theoretical values calculated from dispersional relationships. The initial quantum yields of the photooxidation (0ox) of the anthracene compounds were measured both in solution and in PMMA blocks. The lack of correlation between the 0ox values in the solid polymers and in the liquid solution indicates the dominating role of the polymeric matrix in determining the effectiveness of photooxidation process taking place. In the selection of the optimal polymerization conditions for the synthesis of the polymeric blocks, the values of 0ox of certain anthracene compounds can be up to 1. In the series of the anthraquinone dyes used, 1,4-dihydroxy and 2-aminoanthraquinones, whose 0ox reaches the values of 0.2–0.25 have the highest sensitizing ability.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 2, pp. 235–240, March–April, 1986. 相似文献
950.
T P Davis C W Gehrke C W Gehrke T D Cunningham K C Kuo K O Gerhardt H D Johnson C H Williams 《Journal of chromatography. A》1979,162(3):293-310
A remarkably sensitive, simple and selective reversed-phase high-performance liquid chromatographic (HPLC) method has been developed, allowing, for the first time, the direct measurement of histamine, norepinephrine, octopamine, normetanephrine, dopamine, serotonin and tyramine in a single sample of plasma (2 ml), tissue (0.2 g), or urine. The biogenic amines were modified by pre-column derivatization with o-phthalaldehyde which stabilizes the molecules, aids in extraction, and improves HPLC detection at the nanogram level. To minimize losses during the sampling procedure a careful collection procedure was designed. We developed a simple sample cleanup in which the samples were thawed, neutralized with KOH, immediately derivatized, extracted into ethyl acetate (EtOAc) and then chromatographed by HPLC. The derivatives were stable in EtOAc for more then 24 h. Interfering amino acids were removed from the EtOAc by partitioning twice with Na2HPO4 buffer (pH 10.0). Complete separation was achieved in ca. 60--90 min on a muBondapak phenyl column using a stepwise gradient of acetonitrile and/or methanol-phosphate buffer (pH 5.1). A variable wavelength fluorometer with a 5-microliter flow-cell was used (excitation 340 nm; emission 480 nm). Linearity ranged from 200 pg to 50 ng onto the column. Precision (R.S.D.) for retention times was 1% and for derivatization and injection 2.5%. Recoveries of the seven biogenic amines from plasma spiked with 25 ng/ml averaged 70%, with a relative standard deviation of 6%. Separation studies were also done using a muBondapak C18 column. The effects of various eluents are presented. Gas-liquid chromatography was also investigated but lacked the sensitivity achieved by HPLC. The HPLC method is used routinely for the determination of biogenic amines in plasma from pigs with malignant hyperthemia and thermally stressed bovine. Significant differences in levels of biogenic amines were noted between stressed and non-stressed animals. Data on rat brain tissue samples were compared with the trihydroxyindole method and canine heart tissue was analyzed for ventricular norepinephrine and dopamine. Application of the method to urine from normal persons and a patient with a brain tumor has been demonstrated. 相似文献