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961.
962.
Volker Weinrich Kurt Polborn Christian Robl Karlheinz Sünkel Wolfgang Beck 《无机化学与普通化学杂志》2000,626(3):706-716
Hydrocarbon‐bridged Metal Complexes. L Dicarbonyl Cyclopentadienyl Pyridoyl Iron Complexes as Ligands Dicarbonyl‐cyclopentadienyl‐2‐ and 3‐pyridoyl‐iron (L1, L2) and 2,6‐dicarbonyl‐pyridine‐bis(dicarbonyl‐cyclopentadienyl‐iron) (L3) function as ligands in metal complexes and the N,O‐chelates [(OC)4M(L1)] (M = Mo, W, 8 a, b ) and [(Ph3P)2Cu(L1)]+BF4– ( 9 ) were prepared. Monodentate coordination of L1 and L2 through the pyridine N‐atom occurs in the palladium(II) complexes [Cl2Pd(PnBu3)(L1)] ( 10 ), [Cl2Pd(PnBu3)(L2)] ( 11 ) and [Cl2Pd(L2)2] ( 12 ). Ligand L3 forms the O,N,O‐bis(chelate) [Cl2Zn(L3)] ( 13 ). The crystal and molecular structures of L1, 8 b (M = W), 9–11 and 13 were determined by X‐ray diffraction. 相似文献
963.
MarkusF.H. Hoffmann ArndtM. Brückner Thomas Hupp Bernd Engels Ulf Diederichsen 《Helvetica chimica acta》2000,83(9):2580-2593
Purine‐purine base pairing with guanine, isoguanine, 2,6‐diaminopurine, and xanthine is investigated within the topology of alanyl‐PNA. Alanyl‐PNA is based on a regular peptide backbone with alternating configuration of the amino acids. The nucleobases are covalently linked as side chains. Their distance in peptides with β‐sheet conformation is similar to the favored base‐pair stacking distance. Therefore, alanyl‐PNA provides self‐pairing linear double‐strands. The linear double‐strand topology does not restrict base‐pair size and geometry. The favored base pairs are formed mostly dependent on recognition by H‐bonding. The synthesis of the nucleo‐amino acids with unnatural nucleobases and their oligomerization is described. Hexamers and a tetramer based on 2,6‐diaminopurine‐xanthine and guanine‐isoguanine base pairs were observed with very high stabilities. For xanthine‐xanthine self‐pairing, an unusual tridentate reverse Watson‐Crick pairing mode is indicated, that is only possible with xanthines pairing in different tautomeric forms. To investigate the nature of xanthine‐xanthine base pairs in more detail, quantum‐chemical calculations were performed. They establish the easier tautomerization of xanthine compared to uracil and indicate that, in the AO basis‐set limit, the tridentate pairing mode with mixed tautomers is favored. 相似文献
964.
Evgueni L. Piatnitski Kurt D. Deshayes 《Angewandte Chemie (International ed. in English)》1998,37(7):970-972
Cleavage of one of the four bridging units in the two new types of hemicarceplexes presented here is sufficient to effect immediate guest release into the chloroform solvent (shown schematically on the right). The thermal stability and photoactivity of these hemicarceplexes indicate that incarceration is potentially useful for the controlled delivery of drugs. 相似文献
965.
Nils Wiberg Harald Auer Heinrich Nth Jrg Knizek Kurt Polborn 《Angewandte Chemie (International ed. in English)》1998,37(20):2869-2872
The red-orange tetrasilacyclobutene 1 (R*=SitBu3) is formed quantitatively by the reaction of tetrasilatetrahedrane 2 and iodine. Surprisingly, water and methanol do not react with 1 with addition to the Si−Si double bond, but instead with replacement of the silicon-bound iodine atoms with oxygen or the methoxy group, respectively. The substitutions possibly proceed by dissociative activation via intermediate 3 . 相似文献
966.
Cyclothiazeno Complexes of Tungsten with Phosphoraneiminato and t-Butoxy Ligands The cyclothiazeno complex [WCl3(N3S2)]2 reacts with the silylated phosphaneimine Me3SiNPPh3 in THF solution forming the cyclothiazenophosphoraneiminato complex [Cl2W(N3S2)(NPPh3)]n which forms green crystals of [Cl2W(N3S2)(NPPh3)(Py)] ( 1 ) when pyridine is added. The corresponding reaction with Me3SiNPMe3 leads to the methyl derivative which is analogous to 1 and which is obtained as dark green crystals along with the tetrakis(phosphoraneiminato) complex of the crystal composition [W(NPMe3)4]Cl2 · 2 [Cl2W(N3S2)(NPMe3)(Py)] · 2 CH2Cl2 ( 2 ). According to the crystal structure analyses the phosphoraneiminato ligands NPR3– cause as a result of the short WN bonds of approximately 180 pm a strong trans influence on one of the WN bonds of the planar WN3S2 rings and alternatingly long SN bonds. With LiOCMe3 [WCl3(N3S2)]2 reacts forming the centrosymmetrically dimeric cyclothiazeno alkoxy complex [(Me3CO)4W(N3S2)Li2Cl]2 ( 3 ) the ion ensemble of which is linked via the lithium and the chlorine atoms. 相似文献
967.
968.
Three mushroom species from two old arsenic smelter sites in Austria were analyzed for arsenic compounds. The total arsenic concentrations were determined by ICP–MS. Collybia maculata contained 30.0 mg, Collybia butyracea 10.9 mg and Amanita muscaria 21.9 mg As kg−1 dry mass. The arsenic compounds extracted with methanol/water (9:1) from the dried mushroom powders were separated by HPLC on anion-exchange and reversed-phase columns and detected by ICP-MS using a hydraulic high-pressure nebulizer. In Collybia maculata almost all arsenic is present as arsenobetaine. Collybia butyracea contained mainly arsenobetaine (8.8 mg As kg−1 dry mass) and dimethylarsinic acid (1.9 mg As kg−1). Amanita muscaria contained arsenobetaine (15.1 mg As kg−1), traces of arsenite, dimethylarsinic acid and arsenate, and surprisingly arsenocholine (2.6 mg As kg−1) and a tetramethylarsonium salt (0.8 mg As kg−1). © 1997 by John Wiley & Sons, Ltd. 相似文献
969.
970.
1,2,3,4‐Tetrahydro‐1,2‐dimethylidenenaphthalene 11 has been derived in three steps from tetralone. In the condensed state and at −80°, it undergoes a highly chemo‐ and regioselective cyclodimerization to give 3,3′,4,4′‐tetrahydro‐2‐methylidenespiro[naphthalene‐1(2H),2′(1′H)‐phenanthrene] ( 14 ), the structure of which has been established by single‐crystal X‐ray‐diffraction analysis. Dimer 14 undergoes cycloreversion to diene 11 under flash‐pyrolysis conditions. The reaction of diene 11 with SO2 occurs without acid promoter at −80° and gives a mixture of (±)‐1,4,5,6‐tetrahydronaphth[1,2‐d][1,2]oxathiin 2‐oxide ( 23 ; a single sultine), 1,3,4,5‐tetrahydronaphtho[1,2‐c]thiophene 2,2‐dioxide ( 25 ), and dimer 14 . The high reactivity of diene 1 in its Diels‐Alder cyclodimerization and its highly regioselective hetero‐Diels‐Alder addition with SO2 can be interpreted in terms of the formation of relatively stable diradical intermediates or by concerted processes with transition states that can be represented as diradicaloids. 相似文献