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991.
Dhar RS Verma V Suri KA Sangwan RS Satti NK Kumar A Tuli R Qazi GN 《Phytochemistry》2006,67(20):2269-2276
The main active components and genetic profile of 15 selected accessions of Withania somnifera Dunal. were analysed. Ethanolic extract of the dried roots/leaves of the plant was concentrated under pressure at 50+/-5 degrees C and was analysed for main compounds (withanolides and withaferin A) by HPLC. All the main components were found to be present in accessions (AGB 002, AGB 009, RSS 009, RSS 033). Correlation of these main components with their genetic factors, was undertaken using AFLP (amplified fragment length polymorphism) markers. Among 64 primers 7 yielded optimum polymorphism. A total of 913 polymorphic peaks were generated using these primers. Jaccard's similarity coefficient indicated that accessions having almost the same active compounds clustered together. The present study demonstrates that AFLP can be successfully used to resolve the correlation of AFLP data with the presence of secondary metabolites. 相似文献
992.
Using a phosphorus based Mannich condensation reaction the new pyridylphosphines {5-Ph2PCH2N(H)}C5H3(2-Cl)N (1-Cl) and {2-Ph2PCH2N(H)}C5H3(5-Br)N (1-Br) have been synthesised in good yields (60% and 88%, respectively) from Ph2PCH2OH and the appropriate aminopyridine. The ligands 1-Cl and 1-Br display variable coordination modes depending on the choice of late transition-metal complex used. Hence P-monodentate coordination has been observed for the mononuclear complexes AuCl(1-Cl) (2), AuCl(1-Br) (3), RuCl2(p-cymene)(1-Cl) (4), RuCl2(p-cymene)(1-Br) (5), RhCl2(Cp∗)(1-Cl) (6), RhCl2(Cp∗)(1-Br) (7), IrCl2(Cp∗)(1-Cl) (8), IrCl2(Cp∗)(1′-Cl) (8′), IrCl2(Cp∗)(1-Br) (9), cis-/trans-PdCl2(1-Cl)2 (10), cis-/trans-PdCl2(1-Br)2 (11), cis-PtCl2(1-Cl)2 (12) and cis-PtCl2(1-Br)2 (13). Reaction of Pd(Me)Cl(cod) (cod = cycloocta-1,5-diene) with either 1 equiv. of 1-Br or the known pyridylphosphines 1′-Cl, 1-OH or 1-H gave the P/N-chelate complexes Pd(Me)Cl(1-Br-1-H) (14)-(17). All new compounds have been fully characterised by spectroscopic and analytical methods. Furthermore the structures of 4, 5, 10 and 16 · (CH3)2SO have been elucidated by single crystal X-ray crystallography. A crystal structure of the dinuclear metallocycle trans,trans-[PdCl2{μ-P/N-{Ph2PCH2N(H)}C5H4N}]2 · CHCl3, 18 · CHCl3, has also been determined. Here 1-H bridges, using both P and pyridyl N donors, two dichloropalladium centres affording a 12-membered ring with the PdCl2 units adopting a head-to-tail arrangement. 相似文献
993.
Pascal V. Grundler 《Inorganica chimica acta》2006,359(6):1795-1806
The ruthenium(II) hexaaqua complex [Ru(H2O)6]2+ reacts with dihydrogen under pressure to give the η2-dihydrogen ruthenium(II) pentaaqua complex [Ru(H2)(H2O)5]2+.The complex was characterized by 1H, 2H and 17O NMR: δH = −7.65 ppm, JHD = 31.2 Hz, δO = −80.4 ppm (trans to H2) and δO = −177.4 ppm (cis to H2).The H-H distance in coordinated dihydrogen was estimated to 0.889 Å from JHD, which is close to the value obtained from DFT calculations (0.940 Å).Kinetic studies were performed by 1H and 2H NMR as well as by UV-Vis spectroscopy, yielding the complex formation rate and equilibrium constants: kf = (1.7 ± 0.2) × 10−3 kg mol−1 s−1 and Keq = 4.0 ± 0.5 mol kg−1.The complex formation rate with dihydrogen is close to values reported for other ligands and thus it is assumed that the reaction with dihydrogen follows the same mechanisn (Id).In deuterated water, one can observe that [Ru(H2)(H2O)5]2+ catalyses the hydrogen exchange between the solvent and the dissolved dihydrogen.A hydride is proposed as the intermediate for this exchange.Using isotope labeling, the rate constant for the hydrogen exchange on the η2-dihydrogen ligand was determined as k1 = (0.24 ± 0.04) × 10−3 s−1.The upper and lower limits of the pKa of the coordinated dihydrogen ligand have been estimated:3 < pKa < 14. 相似文献
994.
Robert J. Baker 《Inorganica chimica acta》2006,359(15):4797-4801
The reaction of [(η7-C7H7)Zr(η5-C5H5)] with two Lewis bases, tetramethylimidazolin-2-ylidene and PMe3, is reported and their stability probed via spectroscopic and theoretical methods. The strongly σ-basic N-heterocyclic carbene forms a stable adduct which has been structurally characterised, whilst the PMe3 ligand coordinates weakly to the metal centre. Variable temperature 31P NMR spectroscopy has been used to determine the activation energy for this process (ΔG‡ = 40.5 ± 1.9 kJ mol−1). DFT calculations have been performed on both complexes and the structures discussed. In addition, the enthalpies for the formation of these compounds have been calculated [ΔH0(Zr-IMe) = −56.3 kJ mol−1; ΔH0(Zr-PMe3) = −2.3 kJ mol−1] and show that the N-heterocyclic carbene forms a thermodynamically much more stable adduct than that with PMe3. 相似文献
995.
996.
Covalent linkages between wall polysaccharides and lignin, especially linkage between cellulose and lignin were discussed by carboxymethylation technique of whole cell walls of coniferous and nonconiferous woods. Hydroxyl groups of plant cell walls polysaccharides were highly substituted, but not those of lignin by carboxymethyl groups under the used conditions, and separated into water-soluble and insoluble fractions by water extraction. Carboxymethylated wall polysaccharides linked covalently with lignin were distributed into the water-insoluble fractions. Composition of carboxymethylated sugar residues in the both fractions was analyzed quantitatively by 1H NMR spectroscopy after hydrolyzation with D2SO4 in D2O. More than half of cellulose linked covalently with lignin in coniferous wood, but only one-sixth of cellulose was involved in the linkage in nonconiferous wood. The major noncellulosic wall polysaccharides of coniferous wood also linked significantly with lignin. On the other hand, noncellulosic wall polysaccharides of nonconiferous wood were involved slightly in the covalent linkage with lignin. The situation of linkage between wall polysaccharides containing cellulose and lignin was visualized by scanning electron micrographs. 相似文献
997.
Simulations of various beta-peptides have in the last years clarified several issues concerning peptide folding equilibria and interpretation of experimental data, especially from NMR and CD spectroscopy. These simulations involved different temperatures, pH-values, ionic strengths, solvents, and force-field parameters, but a variation of these factors for one beta-peptide has not yet been done. To investigate the influence of varying these factors, we analyze the helix stability of an all-beta3-icosapeptide bearing all 20 proteinogenic amino acid side chains, which is experimentally observed to fold into a 3(14)-helix in methanol but not in water. Structural aspects, such as hydrogen-bonded rings and salt bridges, are discussed and a comparison with NMR primary (NOE distance bounds and 3J-values) and secondary (NMR derived model structures) data is made. We further investigate the reasons for the 3(14)-helix stability/instability in methanol/water. Of all factors studied, the presence of counterions seems to be the one inducing most significant effects in the simulations. 相似文献
998.
We have explored the effect of gramicidin A (gA) on bicelle (Bic) orientation in the absence and presence of Eu(3+) by (31)P and (2)H NMR at different DMPC/gA ratios. FT-IR spectroscopy was used to assess the lipid chain ordering and verify the transmembrane peptide conformation. Our results show a time-dependent flipping of the bilayer normal alignment at high temperatures and high proportion of gA. The results are explained by both the diamagnetic susceptibility anisotropy of the beta(6.3) helical peptides and viscosity of the lipid mixture. The concentration effect of gramicidin on Bic/Eu(3+) is compared to that on Eu(3+)-doped DMPC liposomes. The Bic/Eu(3+) system is no longer oriented in the presence of gA and adopts a vesicular morphology while the peptide incorporation induces the formation of ellipsoidal DMPC/Eu(3+) assemblies aligned with their normal parallel to the magnetic field. The difference is explained in terms of lipid chain disorder and size of the bilayers. 相似文献
999.
Fa N Ronkart S Schanck A Deleu M Gaigneaux A Goormaghtigh E Mingeot-Leclercq MP 《Chemistry and physics of lipids》2006,144(1):108-116
Azithromycin is a macrolide antibiotic known to bind to lipids and to affect endocytosis probably by interacting with lipid membranes [Tyteca, D., Schanck, A., Dufrene, Y.F., Deleu, M., Courtoy, P.J., Tulkens, P.M., Mingeot-Leclercq, M.P., 2003. The macrolide antibiotic azithromycin interacts with lipids and affects membrane organization and fluidity: studies on Langmuir-Blodgett monolayers, liposomes and J774 macrophages. J. Membr. Biol. 192, 203-215]. In this work, we investigate the effect of azithromycin on lipid model membranes made of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) or 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). Thermal transitions of both lipids in contact with azithromycin are studied by (31)P NMR and DSC on multilamellar vesicles. Concerning the DPPC, azithromycin induces a suppression of the pretransition whereas a phase separation between the DOPC and the antibiotic is observed. For both lipids, the enthalpy associated with the phase transition is strongly decreased with azithromycin. Such effects may be due to an increase of the available space between hydrophobic chains after insertion of azithromycin in lipids. The findings provide a molecular insight of the phase merging of DPPC gel in DOPC fluid matrix induced by azithromycin [Berquand, A., Mingeot-Leclercq, M.P., Dufrene, Y.F., 2004. Real-time imaging of drug-membrane interactions by atomic force microscopy. Biochim. Biophys. Acta 1664, 198-205] and could help to a better understanding of azithromycin-cell interaction. 相似文献
1000.
The rapid cold-hardening (RCH) response not only confers dramatic protection against cold-shock (non-freezing) injury, but also "instantaneously" enhances organismal performance. Since cold-shock injury is associated with damage to the cell membrane, we investigated the relationship between RCH and changes in cold tolerance and membrane fluidity at the cellular level. None of the adult flies (Sarcophaga bullata) in the cold-shocked treatment group survived direct transfer to -8 degrees C for 2 h; in contrast, 64.5% of flies in the RCH group survived exposure to -8 degrees C. Differences between the treatment groups also were reflected at the cellular level; only 21.3% of fat body cells in the cold-shocked group survived compared to 68.5% in the RCH group. Using 31P solid-state NMR spectroscopy, we determined that membrane fluidity increased concurrently with rapid cold-hardening of fat body cells. This result suggests that membrane characteristics may be modified very rapidly to protect cells against cold-shock injury. 相似文献