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991.
Challenges encountered in extending the sensitivity of US Environmental Protection Agency Method 314.0 for perchlorate in drinking water 总被引:1,自引:0,他引:1
Wagner HP Suarez FX Pepich BV Hautman DP Munch DJ 《Journal of chromatography. A》2004,1039(1-2):97-104
Concerns about the potential adverse health effects of perchlorate at concentrations below the minimum reporting level (MRL) of US Environmental Protection Agency (EPA) Method 314.0 (generally recognized as 4.0 microg/l) have led to an interest in increasing the sensitivity of the method. This work describes the use of 2 mm columns with a large-loop direct injection method, a column concentration technique and this concentration technique with a background reduction step, to increase the sensitivity for the analysis of trace levels of perchlorate in high ionic strength matrices. The concentrator columns studied were the Dionex TAC LP-1 and a new Dionex high capacity Cryptand concentrator column. The use of a surrogate to monitor trapping efficiency for the concentration technique and the use of confirmational columns to minimize the potential for false positives are also discussed. The large-loop direct injection method and the column concentration methods provided acceptable data when the samples were pre-treated with solid phase pretreatment cartridges. The background reduction technique did not provide acceptable data with either of the concentrator columns evaluated. 相似文献
992.
Irene Shim Karl A. Gingerich 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1990,16(2):141-148
All electron ab initio Hartree-Fock (HF), configuration interaction (CI) and multiconfiguration self-consistent field (CASSCF) calculations have been applied to investigate the low-lying electronic states of the NiSi molecule. The ground state of the NiSi molecule is predicted to be1Σ+. The chemical bond in the1Σ+ ground state is a double bond composed of one σ and one π bond. The σ bond is due to a delocalized molecular orbital formed by combining the Ni 4s and the Si 3pσ orbitals. The π bond is a partly delocalized valence bond, originating from the coupling of the 3dπ hole on Ni with the 3pπ electron on Si. Withing the energy range 1 eV 18 electronic states have been identified. The lowest lying electronic states have been characterized as having a hole in either the 3dπ or the 3dδ orbital of Ni, and the respective final states are formed when either of these holes are coupled to the 3pπ valence electron of Si. 相似文献
993.
Cámpora J Palma P del Río D López JA Valerga P 《Chemical communications (Cambridge, England)》2004,(13):1490-1491
Whereas the reaction of the anionic palladium metallacycle [K[Pd(CH2CMe2-o-C6H4)(kappa2-Tp)]] with CH2Cl2 leads to the isolation of the stable Pd(IV) chloromethyl complex [Pd(CH2CMe2-o-C6H4)(kappa3-Tp)(CH2Cl)], the analogous reactions with CH2Br2 and CH2I2 give rise to the six membered metallacycles [Pd(CH2CMe2-o-C6H4(CH2))(kappa3-Tp)X](X = Br or I), as a result of the formal insertion of CH2 into the Pd-C(aryl) bond. 相似文献
994.
Yolanda Pérez Isabel del Hierro Isabel Sierra Magda Monari Antonio Otero 《Journal of organometallic chemistry》2004,689(22):3492-3500
A variety of monocyclopentadienyl alkoxo titanium dichloride and bisalkoxo titanium dichloride complexes have been prepared and characterized by spectroscopic techniques. The titanium derivatives containing both cyclopentadienyl and various alkoxo ligands [Ti(η5-C5H5)(OR)Cl2] (1-5) have been synthesized from the reaction of [Ti(η5-C5H5)Cl3] with 1 equivalent of the corresponding alcohol in THF in the presence of triethylamine (ROH = Adamantanol, 1R,2S,5R-(−)-menthol, 1S-endo-(−)-borneol, cis-1,3-(−)-benzylideneglycerol, 1,2:3,4-di-O-isopropylidene-α-d-galactopyranose). The bisalkoxo titanium dichloride derivatives [TiCl2(OR)2] (6-10) have been prepared by a redistribution reaction between Ti(OR)4 and TiCl4 compounds 6-8 (OR = Adamantanoxy, (1R,2S,5R)-(−)menthoxy, (1S-endo)-(−)-borneoxy) and by reaction of [Ti(OR)2(OPri)2]2 with CH3COCl compounds 9 and 10 (OR = 1,2:3,4-di-O-isopropylidene-α-d-galactopyranoxy, and 1,2:5,6-di-O-isopropylidene-α-d-glucofuranoxy). The molecular structures of 2 and 3 have been determined by single crystal X-ray diffraction studies. 相似文献
995.
Margarita del Arco Cristina Martín Joao Rocha 《Journal of solid state chemistry》2004,177(11):3954-3962
Layered double hydroxides (LDHs) with the hydrotalcite type structure and a Mg:Al ratio of two have been prepared, with salicylate or naproxen in the interlayer. Two synthetic routes have been used: reconstruction from a mildly calcined hydrotalcite-CO3 precursor, and a coprecipitation method with chlorides of the metals. The solids have been characterized using several physicochemical techniques, i.e., powder X-ray diffraction, FTIR and 13C CP/MAS NMR spectroscopies and thermal analysis (thermogravimetric and differential thermal analyses). The gallery height determined is in all cases larger than the size of the drug, 11.5 Å for salicylate and 15.8 and 16.6 Å for naproxen, depending on the specific synthesis route followed. Experimental data suggest the anion molecules form a tilted bilayer, with the carboxylate groups pointing towards the brucite-like layers. The solids are stable up to 230 °C and their evolution from 350 °C upwards is very similar to that observed for a carbonate-containing hydrotalcite, forming mostly amorphous solids with a large specific surface area. 相似文献
996.
Wolf Peter Fehlhammer Thomas Bliss Ulrich Kernbach Irene Brüdgam 《Journal of organometallic chemistry》1995,490(1-2):149-153
1,1′-Methylene-3,3′-dialkyldiimidazolium salts have been deprotonated with n-butylithium in the presence of palladium(II) iodide to give the percarbene complexes 1 (alkyl=Me) and 2 (alkyl=Et), each containing two bidentate 1,1′-methylene-3,3′-dialkyldiimidazolin-2,2′-diylidene chelate ligands. The X-ray structure analysis of 1 reveals a stereochemistry in which the two spiro-linked six-membered metallacycles adopt boat-like conformations strongly bending out of the PdC4 coordination plane in opposite directions. The carbenoid imidazole rings, which are rotated by +42 and −43°, respectively, relative to this plane, break down into two tightly bound π-systems (N=4C=4N,= C=C) connected by long C---N bonds. 相似文献
997.
Toda F Yoshizawa K Hyoda S Toyota S Chatziefthimiou S Mavridis IM 《Organic & biomolecular chemistry》2004,2(4):449-451
The complete resolution of 2,2[prime or minute]-dihydroxy-1,1[prime or minute]-binaphthyl into its enantiomers by inclusion complexation with a commercially available derivative of choline, is reported. The two enantiomers are recovered in >99% ee from the inclusion complexes by simple dissolution in a diethyl ether-water medium and the resolving agent can be recycled. 相似文献
998.
Agustin A. Navarro del Cañizo Marcela Mazza Rodolfo Bellinzoni Osvaldo Cascone 《Applied biochemistry and biotechnology》1997,61(3):399-409
Foot and mouth disease virus, (FMDV) from a crude cell lysate was purified in a single step by affinity chromatography with
heparin as a ligand. The virus eluted from an Heparin-Ultrogel A4R column at 1M sodium chloride in 10 mM sodium phosphate buffer, pH 7.0, while most cell protein and albumin did so at lower
concentrations of sodium chloride in the same buffer. Purity of the eluted fraction containing the virus was assessed by SDS-PAGE,
HPLC, ultracentrifugation, and UV absorption spectrum. With this method, intact viral particles are recovered in high yield
(over 90%) and specific virus purity increases nearly 1000-fold. The capacity of the Chromatographic matrix for the virus
was found to be 1.1 mg viral mass per mL of hydrated gel. 相似文献
999.
The electrooxidation of mitoxantrone (MXT) on carbon paste electrodes was studied using voltammetric techniques in adsorption conditions. The analyte was accumulated at the working electrode (a carbon paste electrode) under precisely controlled mass-transport conditions and stripped electrochemically in the same solution. An electrode pretreatment is proposed which shows good reproducibility of the analytical signal (0.81%). The stripping step was studied with alternating current voltammetry providing a linear response in the concentration range 5 x 10(-11) to 7 x 10(-10)M in aqueous samples. Finally, a method using the medium exchange and AC phase-selective adsorptive stripping voltammetry technique was proposed for MXT analysis in urine samples. 相似文献
1000.
Synthesis and Crystal Structure of [N(Hex)4] [Cu2(CN)3] [N(Hex)4][Cu2(CN)3] has been prepared by solvothermal reaction of CuCN with Tetra‐n‐hexylammoniumiodide in acetone. The crystal structure is built up by condensed (CuCN)6 and (CuCN)7 rings, forming a zeolith type cyanocuprate(I) framework [Cu2(CN)3—]. Space group R3; α = 44.482(6), c = 21.283(4) Å, V = 36471(9) Å3; Z = 9. 相似文献