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181.
Summary The mechanism of the catalyst formation in hept-2-ene metathesis was investigated by gas chromatographic analysis of the products from reactions of tungsten hexachloride with R4Sn(R = Ph, n-Bu), RLi, RMgl (R = n-Bu) or R3Al(R = Et) as cocatalyst. The products are chiefly RH, RCl and RR species, and the highest catalytic activity is observed for an equimolar ratio of products to tungsten hexachloride. The facts suggested that the active catalyst, a WCl4 species, is formed by the elimination of two R groups from R2WCl4 and/or one R group and chlorine from RWCl5. The total quantity and composition of the products varies with the cocatalyst:WCl6 ratio, and the difference between the behavior of tetra-n-butylstannane and n-butyllithium in the catalyst formation is explainable on the basis of their relative nucleophilicities. Gas chromatographic analysis of the organotin compounds resulting from the WCl6:: Bu4Sn system shows that tetra-n-butylstannane provides only one butyl group per mole of WCl6. 相似文献
182.
Okamoto Y Kataoka H Konishi C Fujiwara T Ito K 《Rapid communications in mass spectrometry : RCM》2004,18(19):2351-2353
183.
Efficient preparation of glycoclusters from silsesquioxanes 总被引:1,自引:0,他引:1
[structure: see text] A new type of glycocluster based on polyhedral oligosilsesquioxanes (POSS) has been efficiently prepared from unprotected mannoside and lactoside employing a convergent approach of thiol-radical addition reaction. The versatility of this approach was demonstrated by functionalization of mannosides and lactosides of different-length spacers. 相似文献
184.
We have clearly demonstrated reversible cyclic voltammograms for the redox reaction between the Rh(II) and Rh(III) states in rhodium octaethylporphyrin [Rh(OEP)] adsorbed on carbon black in an acidic aqueous solution. The emergence of the reversible wave can be ascribed to the suppression of the undesirable reactions between two molecules of [Rh(II)(OEP)] because of its strong interaction with the carbon black. The generated [Rh(II)(OEP)] exhibits a potent catalytic O(2) reduction activity. 相似文献
185.
Nonradiative deactivation processes of excited aniline and its derivatives in aqueous solution were investigated by steady-state and time-resolved fluorescence measurements to reveal characteristic solvent effects of water on the relaxation processes of excited organic molecules. The magnitude of nonradiative rate (knr) of excited aniline derivatives increased significantly in water compared to that in organic solvents (cyclohexane, ethanol, and acetonitrile). The fluorescence lifetime measurements in organic solvent/H2O mixed solvents suggested that the fluorescence quenching in water was not due to exciplex formation but due to interactions with a water cluster. From temperature effect experiments on the fluorescence lifetime and quantum yield of aniline, N-methylaniline, and N,N-dimethylaniline, the apparent activation energies for the nonradiative deactivation rate in water were determined as 21, 30, and 41 kJ mol-1, respectively. Upon substitution of hydrogen atoms in the aromatic ring of aniline derivatives for deuterium atoms resulted in normal deuterium isotope effect in cyclohexane, i.e. knr decreased by deuterium substitution, while in water the same deuterium substitution led to an increase in knr (the inverse isotope effect). The inverse isotope effects implied that a direct internal conversion to vibrationally higher excited states in the electronically ground state is not a dominant mechanism but the transition to a close-lying energy level, e.g. the relaxation to charge transfer to solvent (ctts) state, would be associated with the quenching mechanism in water. 相似文献
186.
If a vector-valued function space with a Hausdorff locally convex topology has a property such that every closed strongly bounded subset is compact, then we name this property Helly's property. In this paper, we show a class of vector-valued function spaces with Helly's property and consider convegence of vector measures and best approximations in function spaces in this class. 相似文献
187.
Hiroyasu Kondo Kazuaki Inohara Yuki Taniguchi Junko Nakahata Tetsuya Homma Hideo Takahashi 《Optical Review》2001,8(5):323-325
A thermo-optic switch in a thin-film optical waveguide was investigated. Fluorinated silicon oxide (SiOF) and organic spin-on-glass (SOG) films were used as core-layer and clad-layer, respectively, in the waveguide structure. The SiOF films were formed at 23#x00B0;C by a liquid-phase deposition (LPD) technique using a supersaturated hydrofluosilicic acid (H2SiF6) aqueous solution. Thermal coefficients of the refractive indices for LPD-SiOF and organic SOG films formed on silicon (Si) substrates were #x2212;4.0 #x00D7; 10#x2212;6/#x00B0;C, #x2212;60 #x00D7; 10#x2212;6/#x00B0;C at the wavelength of 632.8 nm, respectively. A high extinction ratio of 15 dB was obtained for this switch at the applied voltage of 12.8 V. 相似文献
188.
Hiroaki Yamaguchi Asuka Fujikawa Hajime Ito Nobuaki Tanaka Ayako Furugen Kazuaki Miyamori Natsuko Takahashi Jiro Ogura Masaki Kobayashi Takehiro Yamada Nariyasu Mano Ken Iseki 《Biomedical chromatography : BMC》2013,27(4):539-544
A column‐switching liquid chromatography/electrospray ionization tandem mass spectrometry to determine paclitaxel and its metabolites, 6α‐hydroxypaclitaxel and p‐3′‐hydroxypaclitaxel, in human plasma was developed. The analytical system had a Shim‐Pack MAYI‐ODS (10 × 4.6 mm i.d.) trapping column with deproteinization ability that concentrates analytes and removes water‐soluble components. This method covered a linearity range of 5–5000 ng/mL of concentrations in plasma for paclitaxel, a range of 0.87–870 ng/mL for 6α‐hydroxypaclitaxel and a range of 0.87–435 ng/mL for p‐3′‐hydroxypaclitaxel. The intra‐day precision and inter‐day precision of analysis were less than 11.1%, and the accuracy was within ±14.4% at concentrations of 5, 50, 500 and 5000 ng/mL for paclitaxel, 0.87, 8.7, 87 and 870 ng/mL for 6α‐hydroxypaclitaxel, and 0.87, 8.7, 87 and 435 ng/mL for p‐3′‐hydroxypaclitaxel. The total run time was 30 min. Our method was successfully applied to clinical pharmacokinetic investigation. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
189.
190.