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981.
Alvarez-Merino MA Joly JP Carrasco-Marín F Moreno-Castilla C 《Journal of colloid and interface science》2003,260(2):449-453
Intermittent temperature-programmed desorption of ammonia was used to study the strength and population of surface acid sites of tungsten oxide supported on activated carbon pretreated at 350 and 700 degrees C. Catalysts pretreated at 350 degrees C showed two types of surface acid sites and desorption occurred with free readsorption until a temperature of around 300 degrees C was reached. Pretreatment at 700 degrees C produced three different states of ammonia adsorbed on the catalysts and desorption occurred with free readsorption. 相似文献
982.
Capillary zone electrophoresis with UV detection was used for determination of dissociation constants of alkaloids sanguinarine and chelerythrine. Despite the limited solubility of the uncharged forms of the alkaloids resulting in insufficient analytical signal at higher pH the reliable dissociation constants were obtained when acidified samples containing low amount of the alkaloid were injected into the capillary. The precipitation of the alkaloid in the capillary induced by injecting sample of low pH into the background electrolyte of higher pH does not affect the mobility of the alkaloid if its concentration injected exceeds the solubility only to a small extent. Dissociation constants (pK(R+)) of sanguinarine and chelerythrine calculated to 8.3 +/- 0.1 and 9.2 +/- 0.1, respectively, are relevant to Good buffers of ionic strength of 30 mM. 相似文献
983.
Labuda J Bucková M Heilerová L Silhár S Stepánek I 《Analytical and bioanalytical chemistry》2003,376(2):168-173
Quercetin and rutin as well as catechin and epigallocatechin gallate were investigated, as widely distributed representatives of flavonols and flavanols, respectively, regarding their anti/pro-oxidant properties. The flavonoids are irreversibly oxidized at a dsDNA-modified screen-printed electrode within 0.368 to 0.449 V vs. SHE without binding to DNA. Using the DNA biosensor the detection scheme of a DNA prevention/degradation exploits the [Co(phen)(3)](3+) complex as an electrochemical DNA marker. Antioxidant activity of flavonoids was tested in a model cleavage mixture composed of 5 x 10(-7) mol L(-1) [Cu(phen)(2)](2+) as the catalyst, 1 x 10(-3) mol L(-1) ascorbic acid as the chemical reductant and atmospheric oxygen as the natural oxidant where reactive oxygen radicals are generated. The antioxidant activity increases with the concentration of flavonoids reaching a maximum where pro-oxidative behaviour becomes of importance. The pro-oxidant potency of flavonoids depends on the presence of atmospheric oxygen and follows the order quercetin>rutin>epigallocatechin gallate>catechin. 相似文献
984.
D. E. Damiani E. D. Pérez Millán A. J. Rouco 《Reaction Kinetics and Catalysis Letters》1988,36(1):15-20
A H2 chemisorption and TPR study of Ru–Ag/SiO2 catalysts reveals that after oxidation at 373 K this systems behaves like Ru–Cu/SiO2. High temperature oxidation, however, does not result in the separation of the metal like in the Ru–Cu case but in the redispersion of Ag on top of the Ru particles.
H2 Ru–Ag/SiO2 , 373 Ru–Cu/SiO2. , , , Ru–Cu, Ag Ru.相似文献
985.
The reductive electrochemistry of compounds of the type CpFe(CO)2L (Cp = η-C5H5, η-C5Me5; L = SP(S)(OEt)2, SP(S)(OiPr)2) has been examined by polarography, cylic voltammetry and coulometry. The first one-electron reduction step leads to a bond rupture process with formation of a mercury compound, [CpFe(CO)2]2Hg, at a mercury electrode and the corresponding dimer species at a platinum electrode. The second reduction step corresponds to the reduction of the dimer [CpFe(CO)2]2, except in the polarographic reduction of pentamethylcyclopentadienyl compounds. 相似文献
986.
It is demonstrated that relatively large geometrical changes make Emsley et al.'s assumption (J Am Chem Soc (1978) 100:3303)
on the counterpoise correction for the basis set superposition error including the fragment relaxation terms unacceptable.
Received: 23 September 1997 / Accepted: 31 October 1997 相似文献
987.
Miguel Clemente-León Eugenio Coronado Carlos J. Gómez-García Eugenia Martínez-Ferrero 《Journal of Cluster Science》2002,13(3):381-407
The use of polyoxometalates (pOM's) as inorganic component in the synthesis of new molecular hybrid materials is presented. Here we show that the combination of organic molecules of the tetrathiafulvalene (TTF) type or perylene (per) with POM's yields new radical salts with unprecedented structures that present interesting magnetic and/or electrical properties or coexistence of both. The first true metallic radical salt containing a POM has been prepared and characterized. We also describe the recent results obtained by combining magnetic POM's with the organometallic cation decamethylferrocene. 相似文献
988.
Chakraborty D Horchler S Krätzner R Varkey SP Pinkas J Roesky HW Usón I Noltemeyer M Schmidt HG 《Inorganic chemistry》2001,40(11):2620-2624
Reaction of t-BuP(O)(OSiMe(3))(OH) with Me(3)Al leads to the formation of [Me(2)Al(mu-O)(2)P(OSiMe(3))(t-Bu)](2) (1) whereas Me(2)AlCl reacts with Ph(2)P(O)(OH) to yield [(Cl)(Me)Al(mu-O)(2)PPh(2)](2) (2). These compounds represent the first examples of functionalized dimeric four-ring type aluminophosphonate systems. The double four-ring type gallophosphonate, namely, [t-BuPO(3)GaMe](4), reacts with n-Bu(4)NHF(2) under ambient conditions, resulting in the formation of a monomeric gallophosphonate [n-Bu(4)N][MeGa[t-BuPO(2)(OH)](3)] (3). These derivatives have been adequately characterized using various spectroscopic techniques and X-ray diffraction studies. 相似文献
989.
Lajos Simon S. Gizella Talpas Ferenc Fülp Gbor Bernth Gyula Argay Alajos Klmn PL Sohr 《Journal of heterocyclic chemistry》1995,32(1):161-167
trans-Perhydro-1,4-benzoxazepin-3-ones 2a-c were synthesized and transformed to condensed-skeleton perhydro-trans-1,4-benzoxazepines 3a,b , the thiones 4a,b , the urea derivatives 5a,b , and N-acylated compounds 6a-e . Compounds 6b,d were ring-opened by hydrochloric acid in ethanol to yield trans-2-(1-carbethoxyethoxy)-1-acylaminomethylcyclohexane derivatives 7b,d . The 1H- and 13C-nmr investigation and X-ray analysis of 5b and 6c,d proved that the expected N-acylated derivatives were formed and that both rings of the trans anellated compounds have a chair conformation. 相似文献
990.
The thermal treatment of N-(2-propenyl)-1-naphthylamines provided the expected aza-Claisen rearranged products, 2-(2-propenyl)-1-naphthylamines and benz[g]indoles, these last derived from an intramolecular hydroamination reaction on those primary products. The 2-(2-propenyl)-1-naphthylamines were converted into their triphenylphosphazene derivatives, which by aza-Wittig reaction with disubstituted ketenes yielded N-[2-(2-propenyl)-1-naphthyl] ketenimines. The heating of these ketenimines in boiling toluene induced their cyclization either via an intramolecular Diels-Alder reaction, to afford dibenz[b,h]acridines, or via [1,5] hydrogen migration from the sp3 carbon atom of the propenyl substituent to the central carbon atom of the ketenimine fragment, followed by a 6π electrocyclic ring closure, to give benzo[h]quinolines. 相似文献