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481.
The c20-c21 α-ketol system of the 176 side chain of deoxycorti-costerone is in equilibrium with its c20-c21 enediol. The apparent dissociation constant of this enol was determined by a photometric method using crystal violet indicator; p Ka1 = 10.65 ± 044. Formation constants of the (1:1) deoxycorticosterone-cobalt (II) complex were determined by solvent extraction and in mixed solvent systems. The complex formation constant Kf in an aqueous medium was found by graphical extrapolation to be 2.5–3.0 × 10−1 1. mole−1 相似文献
482.
483.
The combined use in peptide synthesis of the Fmoc-group with methyl, benzyl or p-nitro benzyl esters is not practical because of the elimination of the Fmoc-group under basic conditions and by catalytic hydrogenation. Nevertheless the solution synthesis of peptides requires those combinations in some cases. For this purpose we have investigated enzymatic hydrolysis of some tri and tetrapeptide esters. The hydrolysis were carried out under pH-control. We measured deprotection of the carboxyl group by thermitase, porcine liver esterase, carboxypeptidase A and alpha-chymotrypsin. The main problems are to suppress proteolytic degradation of the peptide bond and to bring the protected peptides into solution. To solve both problems we used dimethylformamide and dimethylsulfoxide as cosolvents. The ratios between esterolytic and proteolytic activity were estimated under various cosolvent concentrations. Advantages of this method are to avoid side reactions of alkaline instable side chains (e.g. asparagine, glutamine), cleavage of base labile protecting groups and racemization by alkaline saponification. The enzymatic deprotection was followed by HPLC, HPTLC and titration. On a preparative scale this method gives good yields and sufficiently pure products. 相似文献
484.
485.
Hugo Greiner 《Palaeogeography, Palaeoclimatology, Palaeoecology》1973,13(2):129-141
Study reveals that 8 species of Cyrstospirifer: C. chemungensis, C. kennicotti, C. thalattodoxa, C. whitneyi, C. charitopes, C. hornellensis, C. alexandrae, C. inermis, 6 of Crytiopsis: C. mimetes, C. prepta, C. nahanniensis, C. normandvillana, “C”. hiraethlynae and C. kindlei, 4 of Tenticospirifer: T. sp. A, T. sp. B, T. kelecticus and T. standlyensis, 2 species of Eochoristies: E. protistus and E. glennfoxi and one species presumed to be a Spirifer: S. zantedeschii are present in the Canadian West, all with well-defined zones in the Frasnian and Famennian.Prelimanary comparison with similar groups in the classic Upper Devonian of the Appalachians shows that nine of these, or 45%, are identical species present in both provinces. 相似文献
486.
K Monory E Greiner N Sartania L Sallai Y Pouille H Schmidhammer J Hanoune A Borsodi 《Life sciences》1999,64(22):2011-2020
Several hydrazone, oxime, carbazone and semicarbazone derivatives of 14-alkoxycodeinones and 14-alkoxydihydrocodeinones were synthesised [1] and characterised in in vitro radioligand binding assays in rat brain membrane preparations. The tested compounds show the highest affinity for the mu opioid binding sites and most of them have agonist character. Subtype analysis of the binding shows mu2 specificity. However, some of these ligands are able to block partially (40-60%) the high affinity (putative mu1) opioid binding sites while all of them act as reversible ligands at the low affinity (putative mu2) sites. 相似文献
487.
488.
Interspecific variation in avian blood parasites and haematology associated with urbanization in a desert habitat 总被引:1,自引:0,他引:1
Many avian species are negatively impacted by urbanization, but other species survive and prosper in urbanized areas. One factor potentially contributing to the success of some species in urban areas is the reduced presence of predators or parasite vectors in urban compared to rural areas. In addition, urban areas may provide increased food and water resources, which can enhance immune capacity to resist infection and the ability to eliminate parasites. We determined patterns of blood parasitism, body condition, and immune cell profiles in urban and rural populations of five adult male songbird species that vary in their relative abundance within urban areas. Urban birds generally exhibited less blood parasitism than rural birds. This difference was particularly evident for the urban-adaptable Abert's towhee Pipilo aberti . In contrast, no difference in haemoparasitism was seen between urban and rural populations of the curve-billed thrasher Toxostoma curvirostre , a less-urban adaptable species. In two closely related species, the curve-billed thrasher and the northern mockingbird Mimus polyglottos , urban birds had a higher leukocyte count and a higher heterophil to lymphocyte ratio, which is often associated with chronic stress or current infection, than rural birds. Urban northern mockingbirds were in better condition than rural counterparts, but no habitat-related differences in condition were detected for other species. Parasitic infection was correlated with body condition in only one species, the canyon towhee Pipilo fuscus . Parasitic infection in most species was correlated with changes in leukocyte abundance and profile. The findings suggest that interspecific differences in parasitic infection cannot be attributed entirely to differences in vector abundance or body condition. Interactions between immune function, parasite infection risk, and resource availability may contribute to determining the relative ability of certain species to adapt to cities. 相似文献
489.
Lydia Seyfarth Georg Greiner Sebastian Kuenzel Wolfgang Poppitz Siegmund Reissmann 《Letters in Peptide Science》2001,8(1):13-20
Pseudotripeptide ligands with 4 different N-functionalized glycine residues were qualitatively, semiquantitatively and quantitatively tested for their complexation of the bivalent transition metal ions Zn2+, Cu2+, Co2+, Ni2+ and Mn2+. The functional side chains have different length and different groups available for complexation. MALDI-MS and ESI-MS were used for more qualitative or semiquantitative estimation of the complex formation tendencies. The found ranking differs by these two methods only for Zn2+ and Ni2+. For one of the pseudotripeptide ligands, the ligand L1, complex formation with certain transition metal was estimated quantitatively by potentiometric titration. The Zn-complex of that ligand polarizes bound water strongly, resulting in a low pKa-value. Complexes of pseudotripeptide ligand L1 with certain metal ions were tested for their hydrolytic activity. The pseudo first order rate constants of the hydrolysis of the substrates 4-nitrophenyl acetate and bis(4-nitrophenyl)phosphate were compared to complexes with the same metal ions formed with a very well studied ligand from the literature, the 1,4,7,10-tetraaza cyclododecane (cyclen). The hydrolysis of the phosphate ester occurs very slowly compared to the acetate ester. No correlation exists between the estimated pKa values of complexes formed from ligand L1 with different metal ions and the phosphate ester hydrolysis. The Ni ions give totally different hydrolytic activities for pseudotripeptide ligand L1 and cyclen. With one exception, the Ni-cyclen complex, all other complexes have only a low or moderate catalytic activity. 相似文献
490.
Uwe Rauwolf Hieronim Golczyk Stephan Greiner Reinhold G. Herrmann 《Molecular genetics and genomics : MGG》2010,283(1):35-47
Plastid genomes (plastomes) are part of the integrated compartmentalised genetic system of photoautotrophic eukaryotes. They
are highly redundant and generally dispersed in several regions (nucleoids) within organelles. DNA quantities and number of
DNA-containing regions per plastid vary and are developmentally regulated in a way not yet understood. Reliable quantitative
data describing these patterns are scarce. We present a protocol to isolate fractions of pure plastids with varying average
sizes from leaflets (≤1 mm) and leaves of different developmental stages continuously up to maturity (25 cm) from Beta vulgaris L. (sugar beet) to determine DNA amounts per organelle. The approach is based on plastid purification from homogenates of
moderately fixed tissue by differential and isopycnic gradient centrifugations and on application of two different DNA specific
colorimetric reactions after removing potentially interfering compounds. The sensitive fluorochrome DAPI (4′,6-diamidino-2-phenylindole)
was used to estimate numbers and emission intensity of nucleoids per plastid. The amounts determined ranged from 0.15 to 4.9 × 10−2 pg DNA for plastids of 1→8 μm average diameter, corresponding from approximately a dozen to 330 genome equivalents per organelle
and on average four to seven copies per nucleoid. The ratio of plastid/nuclear DNA changed continuously during leaf development
from as little as 0.4% to about 20% in fully developed leaves. On the other hand, mesophyll cells of mature leaves differing
in ploidy (di-, tri- and tetraploid) appeared to maintain a relatively constant nuclear genome/plastome ratio, equivalent
to about 1,700 copies per C-value. 相似文献