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151.
Because of the still increasing noise pollution the numerical simulation of acoustic problems becomes more and more important. One essential aspect is the numerical treatment of noise insulation of solid walls. The main noise source is the bending vibration of separating components. In general, they consist of porous material, e.g., concrete or bricks. To take into account the porous structure as well as the damping effect of the porosity of these components a poroelastic plate theory is developed. The Finite Element implementation of this plate theory shows the importance of taking porous materials into account. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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AnneSophie Droz Ulf Neidlein Sally Anderson Paul Seiler Franois Diederich 《Helvetica chimica acta》2001,84(8):2243-2289
A new family of optically active cyclophane receptors for the complexation of mono‐ and disaccharides in competitive protic solvent mixtures is described. Macrocycles (−)‐(R,R,R,R)‐ 1 – 4 feature preorganized binding cavities formed by four 1,1′‐binaphthalene‐2,2′‐diyl phosphate moieties bridged in the 3,3′‐positions by acetylenic or phenylacetylenic spacers. The four phosphodiester groups converge towards the binding cavity and provide efficient bidentate ionic H‐bond acceptor sites (Fig. 2). Benzyloxy groups in the 7,7′‐positions of the 1,1′‐binaphthalene moieties ensure solubility of the nanometer‐sized receptors and prevent undesirable aggregation. The construction of the macrocyclic framework of the four cyclophanes takes advantage of Pd0‐catalyzed aryl—acetylene cross‐coupling by the Sonogashira protocol, and oxidative acetylenic homo‐coupling methodology (Schemes 2 and 8 – 10). Several cleft‐type receptors featuring one 1,1′‐binaphthalene‐2,2′‐diyl phosphate moiety were also prepared (Schemes 1, 6, and 7). An undesired side reaction encountered during the synthesis of the target compounds was the formation of naptho[b]furan rings from 3‐ethynylnaphthalene‐2‐ol derivatives, proceeding via 5‐endo‐dig cyclization (Schemes 3 – 5). Computer‐assisted molecular modeling indicated that the macrocycles prefer nonplanar puckered, cyclobutane‐type conformations (Figs. 7 and 8). According to these calculations, receptor (−)‐(R,R,R,R)‐ 1 has, on average, a square binding site, which is complementary in size to one monosaccharide. The three other cyclophanes (−)‐(R,R,R,R)‐ 2 – 4 feature, on average, wider rectangular cavities, providing a good fit to one disaccharide, while being too large for the complexation of one monosaccharide. This substrate selectivity was fully confirmed in 1H‐NMR binding titrations. The chiroptical properties of the cyclophanes and their nonmacrocyclic precursors were investigated by circular dichroism (CD) spectroscopy. The CD spectra of the acyclic precursors showed a large dependence from the number of 1,1′‐binaphthalene moieties (Fig. 9), and those of the cyclophanes were remarkably influenced by the nature of the functional groups lining the macrocyclic cavity (Fig. 11). Profound differences were also observed between the CD spectra of linear and macrocyclic tetrakis(1,1′‐binaphthalene) scaffolds, which feature very different molecular shapes (Fig. 10). In 1H‐NMR binding titrations with mono‐ and disaccharides (Fig. 13), concentration ranges were chosen to favor 1 : 1 host−guest binding. This stoichiometry was experimentally established by the curve‐fitting analysis of the titration data and by Job plots. The titration data demonstrate conclusively that the strength of carbohydrate recognition is enhanced with an increasing number of bidentate ionic host−guest H‐bonds (Table 1) in the complex formed. As a result of the formation of these highly stable H‐bonds, carbohydrate complexation in competitive protic solvent mixtures becomes more favorable. Thus, cleft‐type receptors (−)‐(R)‐ 7 and (−)‐(R)‐ 38 with one phosphodiester moiety form weak 1 : 1 complexes only in CD3CN. In contrast, macrocycle (−)‐(R,R,R,R)‐ 1 with four phosphodiester groups undergoes stable inclusion complexation with monosaccharides in CD3CN containing 2% CD3OD. With their larger number of H‐bonding sites, disaccharide substrates bind even more strongly to the four phosphodiester groups lining the cavity of (−)‐(R,R,R,R)‐ 2 and complexation becomes efficient in CD3CN containing 12% CD3OD. Finally, the introduction of two additional methyl ester residues further enhances the receptor capacity of (−)‐(R,R,R,R)‐ 3 , and efficient disaccharide complexation occurs already in CD3CN containing 20% CD3OD. 相似文献
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Three bowl‐type cavitand receptors ( 1 – 3 ), consisting of a resorcin[4]arene core with four convergent phenylamidinium groups, were prepared in gram quantities by efficient synthetic routes (Schemes 1 and 2) for the recognition of organic anions in CD3OD and D2O. The key steps in the syntheses are the Suzuki cross‐coupling reactions between the tetraiodo cavitands 12 , 13 , and 23 , respectively, with the m‐cyanophenylboronic ester 14 and subsequent conversion of the nitrile to amidinium groups by the Garigipati reaction. Compounds 1 and 2 displayed limited solubility in protic solvents, and evidence for stoichiometric host‐guest association between 2 and AMP ( 28 ) could only be obtained by FAB‐MS analysis of a complex precipitated from MeOH (Fig. 2). In contrast, receptor 3 with four triethyleneglycol monomethyl ether side chains was readily soluble in the protic environments, and complexation of isophthalates and nucleotides 25 – 37 was extensively studied by 1H‐NMR titrations and Job's method of continuous variation. In CD3OD and pure D2O, isophthalates 25 and 26 formed stable 1 : 2 host‐guest complexes (Table 1 and Fig. 3), whereas upon addition of borate (pH 9.2) or Tris/HCl buffer (pH 8.3) to the D2O solution, the tendency for higher‐order complexation vanishes. Stable 1 : 1 complexes formed in the buffered solutions (Fig. 4) with 5‐methoxyisophthalate being selectively bound over the 5‐NO2 derivative. Complexation‐induced upfield shifts of specific isophthalate 1H‐NMR resonances (Fig. 5) suggest a preferred inclusion of the methoxyphenyl ring into the receptor cavity. Cavitand 3 forms stable 1 : 1 host‐guest complexes with nucleotides in Tris/HCl‐buffered D2O. Association constants increase strongly with increasing guest charge in the series cAMP<AMP<ADP<ATP (Table 2). Association strength is strongly reduced in the presence of high salt (NaCl) concentration (Table 3). Receptor 3 shows a slight preference for the complexation of AMP (Fig. 7) and analogs dAMP or ε‐AMP (Table 4) over nucleotides containing G (guanine), C (cytosine), T (thymine), or U (uracil) as bases. According to the 1H‐NMR analysis, only the nucleobase adenine and derivatives thereof possess the necessary stereoelectronic complementarity for inclusion into the bowl‐type cavity. The major forces stabilizing the complexes of 3 with isophthalates and nucleotides result from ion pairing and ionic H‐bonding between the charged groups of host and guest, and from the desolvation of these groups upon complexation. Apolar interactions and hydrophobic desolvation do not seem to make a large contribution to the measured binding free enthalpies. 相似文献
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159.
Anja Bhr AnneSophie Droz Martin Püntener Ulf Neidlein Sally Anderson Paul Seiler Franois Diederich 《Helvetica chimica acta》1998,81(11):1931-1963
The synthesis and carbohydrate-recognition properties of a new family of optically active cyclophane receptors, 1 – 3 , in which three 1,1′-binaphthalene-2,2′-diol spacers are interconnected by three buta-1,3-diynediyl linkers, are described. The macrocycles all contain highly preorganized cavities lined with six convergent OH groups for H-bonding and complementary in size and shape to monosaccharides. Compounds 1 – 3 differ by the functionality attached to the major groove of the 1,1′-binaphthalene-2,2′-diol spacers. The major grooves of the spacers in 2 are unsubstituted, whereas those in 1 bear benzyloxy (BnO) groups in the 7,7′-positions and those in 3 2-phenylethyl groups in the 6,6′-positions. The preparation of the more planar, D3-symmetrical receptors (R,R,R)- 1 (Schemes 1 and 2), (S,S,S)- 1 (Scheme 4), (S,S,S)- 2 (Scheme 5), and (S,S,S)- 3 (Scheme 8) involved as key step the Glaser-Hay cyclotrimerization of the corresponding OH-protected 3,3′-diethynyl-1,1′-binaphthalene-2,2′-diol precursors, which yielded tetrameric and pentameric macrocycles in addition to the desired trimeric compounds. The synthesis of the less planar, C2-symmetrical receptors (R,R,S)- 2 (Scheme 6) and (S,S,R)- 3 (Scheme 9) proceeded via two Glaser-Hay coupling steps. First, two monomeric precursors of identical configuration were oxidatively coupled to give a dimeric intermediate which was then subjected to macrocyclization with a third monomeric 1,1′-binaphthalene precursor of opposite configuration. The 3,3′-dialkynylation of the OH-protected 1,1′-binaphthalene-2,2′-diol precursors for the macrocyclizations was either performed by Stille (Scheme 1) or by Sonogashira (Schemes 4, 5, and 8) cross-coupling reactions. The flat D3-symmetrical receptors (R,R,R)- 1 and (S,S,S)- 1 formed 1 : 1 cavity inclusion complexes with octyl 1-O-pyranosides in CDCl3 (300 K) with moderate stability (ΔG0 ca. −3 kcal mol−1) as well as moderate diastereo- (Δ(ΔG0) up to 0.7 kcal mol−1) and enantioselectivity (Δ(ΔG0)=0.4 kcal mol−1) (Table 1). Stoichiometric 1 : 1 complexation by (S,S,S)- 2 and (S,S,S)- 3 could not be investigated by 1H-NMR binding titrations, due to very strong signal broadening. This broadening of the 1H-NMR resonances is presumably indicative of higher-order associations, in which the planar macrocycles sandwich the carbohydrate guests. The less planar C2-symmetrical receptor (S,S,R)- 3 formed stable 1 : 1 complexes with binding free enthalpies of up to ΔG0=−5.0 kcal mol−1 (Table 2). With diastereoselectivities up to Δ(ΔG0)=1.3 kcal mol−1 and enantioselectivities of Δ(ΔG0)=0.9 kcal mol−1, (S,S,R)- 3 is among the most selective artificial carbohydrate receptors known. 相似文献
160.
Jean-Pascal Bourgeois Luis Echegoyen Monia Fibbioli Ern Pretsch Franois Diederich 《Angewandte Chemie (International ed. in English)》1998,37(15):2118-2121
Regioselective Bingel macrocyclization of C60 with a bis-malonate containing a novel dibenzo[18] crown-6 tether provides a versatile access to trans-1 fullerene bis-adducts such as (±)- 1 . Complexation of a potassium ion by (±)- 1 has a pronounced effect on the redox properties of the carbon sphere as a result of the close proximity of the fullerene surface to the crown ether bound cation, which is enforced by the double bridging. 相似文献