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991.
Sheng‐Xiong Huang Xun Liao Quan‐Jiang Nie Li‐Sheng Ding Shu‐Lin Peng 《Helvetica chimica acta》2004,87(3):598-604
Three new phenyl glycosides, scrophenoside A ( 1 ), B ( 2 ), and C ( 3 ), and two new phenylethyl glycosides, scroside D ( 4 ) and scroside E ( 5 ), were isolated from the stem of Picrorhiza scrophulariiflora Pennell (Scrophularlaceae), besides five known compounds. On the basis of spectroscopic evidence, the structures of the new compounds were elucidated as 4‐acetyl‐2‐methoxyphenyl 6‐O‐[4‐(β‐D ‐glucopyranosyloxy)vanilloyl]‐β‐D ‐glucopyranoside ( 1 ), 4‐acetylphenyl 6‐O‐[(E)‐p‐coumaroyl]‐β‐D ‐glucopyranoside ( 2 ), 4‐[(1R)‐ and (1S)‐1‐hydroxyethyl]‐2‐methoxyphenyl β‐D ‐glucopyranoside ( 3a and 3b , resp.), 2‐(3,4‐dihydroxyphenyl)ethyl O‐β‐D ‐glucopyranosyl‐(1→3)‐4‐O‐[(E)‐feruloyl]‐β‐D ‐glucopyranoside ( 4 ), and 2‐(3,4‐dihydroxyphenyl)ethyl O‐β‐D ‐glucopyranosyl‐(1→3)‐6‐O‐[(E)‐feruloyl]‐β‐D ‐glucopyranoside ( 5 ). 相似文献
992.
An accurate estimation of pKa values in methanol-water binary mixtures is very important for several separation techniques such as liquid chromatography and capillary electrophoresis that use these solvent mixtures. In this study, the pKa values of 11 polyphenolic acids have been determined in methanol-water binary mixtures (10%, 20% and 30% (v/v)) by potentiometry, liquid chromatography (LC) and LC-DAD methodology.The results show a similar trend for the pKa values of all the studied compounds, as they increase with increasing concentration of organic modifier, which allows a linear relationship between pKa values and mole fraction of methanol to be obtained. The pKa values obtained in aqueous medium have been compared with those given in the literature, and also with the values predicted by the SPARC on-line pKa calculator. The data obtained have been used to test the feasibility of an estimation of dissociation constants in a methanol-water medium from the relationship between pKa values and the organic cosolvent fraction in the mixtures. 相似文献
993.
Qiang Xu Prof. Dr. Nobuko Tsumori Prof. Dr. Ling Jiang Masanobu Kondo Ryuichi Arakawa Prof. Dr. 《化学:亚洲杂志》2007,2(5):599-608
Carbonyldinitrosyltris(fluorosulfato)tungstate(II) and ‐molybdate‐(II) anions, [fac‐M(CO)(NO)2(SO3F)3]? (M=W, Mo), which are novel weakly coordinating anions that contain a metal carbonyl/nitrosyl moiety, have been generated in fluorosulfonic acid and completely characterized by multinuclear NMR, IR, and Raman spectroscopy as well as ESI mass spectrometry. ESI MS measurements performed for the first time on a superacidic solution system unambiguously reveal the formation of the monoanionic, mononuclear W and Mo complexes formulated as [M(CO)(NO)2(SO3F)3]? (M=W, Mo). Multinuclear NMR spectroscopic studies at natural abundance and 13C and 15N enrichment clearly indicate the presence of one CO ligand, two equivalent NO ligands, and two types of nonequivalent SO3F? groups in a 2:1 ratio. The IR and Raman spectra reveal that the two equivalent NO ligands have a cis conformation, thus indicating a fac structure. Density functional calculations at the B3LYP level of theory predict that these anions have a singlet ground state (1A′) with a Cs symmetry along with C–O and N–O vibrational frequencies that are in agreement with the experimental observations. Mulliken population analysis shows that the monovalent negative charge is dispersed on the bulky sphere, the surface of which is covered by all the negatively charged O and F atoms with charge densities much lower than SO3F?, suggesting that [fac‐M(CO)(NO)2(SO3F)3]? (M=W, Mo) are weakly nucleophilic and poorly coordinating anions. 相似文献
994.
The structure of [(CF3N2NMe)Mo(CH2SiMe3)2] (in which (CF3N2NMe)2? is [(3‐CF3C6H4NCH2CH2)2NMe]2?) is approximately trigonal bipyramidal with one axial and one equatorial alkyl ligand. Heating of solutions of [(CF3N2NMe)Mo(CH2SiMe3)2] in [D6]benzene in the presence of five equivalents of 2‐butyne led to diamagnetic [(CF3N2NMe)Mo(CHSiMe3)(η2‐MeC?CMe)], whose structure is approximately square pyramidal with the alkyne occupying the axial site. Addition of one equivalent of cyclohexene sulfide to [(CF3N2NMe)Mo(CH2SiMe3)2] at room temperature produced the diamagnetic, dimeric molybdenum(IV) sulfido complex, [{(CF3N2NMe)MoS}2]. This complex is composed of two approximately trigonal bipyramidal centers, each containing one axial and one equatorial sulfur atom. Oxidation of [(CF3N2NMe)Mo(CH2SiMe3)2] with hexachloroethane resulted in formation of tetramethylsilane, HCl, and the sparingly soluble, red alkylidyne complex, [{(CF3N2NMe)Mo(CSiMe3)Cl}2]. This complex forms a dimer through bridging chlorides. The oxidation reactions of [(CF3N2NMe)Mo(CH2SiMe3)2] with 2‐butyne, cyclohexene sulfide, or C2Cl6 are all proposed to proceed by α‐hydrogen abstraction in the MoVI species to yield (initially) the Mo?CHSiMe3 species and tetramethylsilane. 相似文献
995.
Zhen‐Yu Li Ping Chen Hong‐Gui Xu Shu‐Ying Peng Yi‐Ming Yang Zhong‐Zhen Zhao Yue‐Wei Guo 《Helvetica chimica acta》2007,90(7):1353-1359
Five new polycyclic Daphniphyllum alkaloids, macropodumines F ( 1 ) and G ( 2 ), 17‐oxoyuzurimine ( 3 ), and macropodumines H ( 4 ) and I ( 5 ), were isolated from the leaves of D. macropodum Miq ., collected in Sichuan Province, China. The structures and relative configurations of the new compounds – as well as of four known, related alkaloids – were elucidated on the basis of in‐depth spectroscopic and mass‐spectrometric analyses, by chemical derivatization, and by comparison of spectroscopic data with those of known compounds. 相似文献
996.
New copper(II) complexes of the hydrazone ligands H2salhyhb, H2salhyhp, and H2salhyhh, derived from salicylaldehyde and ω‐hydroxy carbonic acid hydrazides, have been synthesized and physically characterized. Two fundamental structures were found in solid state depending on the pH‐value of the reaction solution. Acidic conditions lead to the formation of the di‐μ‐phenoxo‐bridged dicationic complex dimers [{Cu(Hsalhyhb)}2]2+ ( 1a ), [{Cu(Hsalhyhp)}2]2+ ( 2a ), and [{Cu(Hsalhyhh)}2]2+ ( 3a ), isolated as perchlorate salts. The dimeric complexes show strong antiferromagnetic coupling with J = ?399 ( 1a ), ?410 ( 2a ), and ?311 cm?1 ( 3a ). Higher pH‐values resulted in the aggregation of neutral copper ligand fragments to the one‐dimensional coordination polymers [{Cu(salhyhb)}n] ( 1b ), [{Cu(salhyhp)}n] ( 2b ), and [{Cu(salhyhh)}n] ( 3b ). 3b has been examined by means of X‐ray crystallography and represents the first example of a structurally characterized neutral copper(II) N‐salicylidenehydrazide complex without additional ligands. The magnetic interactions in the polymers are also antiferromagnetic with J = ?125 ( 1b ), ?136 ( 2b ), and ?148 cm?1 ( 3b ), but strongly reduced compared to the corresponding dimeric complexes. The two basic structure types can be reversibly interconverted simply by pH‐control. 相似文献
997.
The method developed in this work for the separation and preconcentration of Cr(III) is based on its retention by an Amberlite XAD-2 copolymer resin functionalized with 5-palmitoyl-8-hydroxyquinoline (oxine), abbreviated XAD-POx, with the ligand covalently bound to the copolymer. Cr(III) sorption was quantitative within the pH range 4.5–7.0 and Cr(VI) was not retained. The Cr(III) held by the resin column was eluted with a hot solution of H2O2 in pH9.0 aqueous NH3–NH4Cl buffer, and Cr oxidized to CrO42– was rejected by the chelating cation-exchanger column. Any Cr(VI) originally present with Cr(III) could be reduced with an acidic solution of H2O2, and retained by the column yielding total Cr results, Cr(VI) being determined from the difference. The resin showed a maximal preconcentration factor of 60 for Cr(III), the LOD and LOQ being 9.3 and 30.1 nmol L–1, respectively. The developed preconcentration-speciation analysis was finished with a diphenylcarbazide (DPC) spectrophotometric procedure suitable for conventional laboratories. The resin showed excellent salt tolerance, enabling Cr analysis in seawater, and was stable over extended use. All the interferents of this procedure that normally occur in an electroplating effluent, a blended coal CRM, and a standard steel sample could be removed by the recommended procedure, by use of partial and total selectivity at the adsorption and desorption stages, respectively, enabling preconcentration and colorimetric determination of chromium in various complex matrices. 相似文献
998.
IntroductionReversiblecolorchangesuponexternalorinternalstimulationshavebeenattractingmuchattentionduetotheirutilityasfunctionalmaterials .Forexample ,pho tochromismdescribesthecolorchangesinducedbypho toirradiationandcanbeusedasphoto recordingmateri als… 相似文献
999.
Ute Ch.?Rodewald Mar’yana?Lukachuk Rolf-Dieter?Hoffmann Rainer?P?ttgenEmail author 《Monatshefte für Chemie / Chemical Monthly》2005,136(12):1985-1991
Summary. The gadolinium–rhodium–indide Gd3Rh1.940(7)In4 was prepared by arc-melting of the elements and subsequent annealing in a corundum crucible in a sealed silica tube. Gd3Rh1.940(7)In4 adopts the hexagonal Lu3Co1.87In4 type, space group
, a = 781.4(5), c = 383.8(3) pm, wR2 = 0.0285, BASF = 0.375(1) (merohedric twinning via a twofold axis (xx0)), 648 F2 values, 22 variables. The structure is derived from the well known ZrNiAl type through an ordering of rhodium and indium
atoms on the Ni2 sites. The Rh/In ordering forces a reduction of the space group symmetry from
to
, leading to merohedric twinning for the investigated crystal. The Rh1 site has an occupancy of only 94.0(7)%. The investigated
crystal had a composition Gd3Rh1.940(7)In4. The main geometrical motif are three types of centered, tricapped trigonal prisms, i.e., [Rh1In26Gd3], [Rh2Gd6In23], and [In1Gd6In23]. The shortest interatomic distances occur for Rh–In (276–296 pm) followed by In–In (297 pm). Together, the rhodium and indium
atoms build up a three-dimensional [Rh1.940(7)In4] network, in which the gadolinium atoms fill slightly distorted pentagonal channels. The crystal chemistry of Gd3Rh1.940(7)In4 is discussed on the basis of a group-subgroup scheme. 相似文献
1000.
Self-assembly of amphiphilic hexapyridinium cations at the air/water interface and on HOPG surfaces.
Haofei Gong Dr. Björn Bredenkötter Dr. Christoph Meier Carola Hoffmann‐ Richter Dr. Ulrich Ziener Dr. Dirk G. Kurth Dr. Dirk Volkmer Prof. Dr. 《Chemphyschem》2007,8(16):2354-2362
Mono- and multilayers of a novel amphiphilic hexapyridinium cation with six eicosyl chains (3) are spread at the air/water interface as well as on highly ordered pyrolytic graphite (HOPG). On water, the monolayer of 3 is investigated by recording surface pressure/area and surface potential/area isotherms, and by Brewster angle microscopy (BAM). Self-organized tubular micelles with an internal edge-on orientation of molecules form at the air/water interface at low surface pressure whereas multilayers are present at high surface pressure, after a phase transition. Packing motifs suggesting a tubular arrangement of the constituting molecules were gleaned from atomic force microscopy (AFM) investigations of Langmuir-Blodgett (LB) monolayers being transferred on HOPG at different surface pressures. These LB film structures are compared to the self-assembled monolayer (SAM) of 3 formed via adsorption from a supersaturated solution, which is studied by scanning tunnelling microscopy (STM). On HOPG the SAM of 3 consists of nanorods with a highly ordered edge-on packing of the aromatic rings and an arrangement of alkyl chains which resembles the packing of molecules at the air/water interface at low surface pressure. Additional details of the molecular packing were gleaned from single-crystal X-ray structure analysis of the hexapyridinium model compound 2b, which possesses methyl instead of eicosyl residues. 相似文献