全文获取类型
收费全文 | 1096篇 |
免费 | 73篇 |
出版年
2023年 | 8篇 |
2022年 | 27篇 |
2021年 | 58篇 |
2020年 | 27篇 |
2019年 | 18篇 |
2018年 | 39篇 |
2017年 | 30篇 |
2016年 | 31篇 |
2015年 | 40篇 |
2014年 | 55篇 |
2013年 | 75篇 |
2012年 | 97篇 |
2011年 | 76篇 |
2010年 | 45篇 |
2009年 | 30篇 |
2008年 | 47篇 |
2007年 | 42篇 |
2006年 | 34篇 |
2005年 | 35篇 |
2004年 | 17篇 |
2003年 | 14篇 |
2002年 | 16篇 |
2001年 | 18篇 |
2000年 | 19篇 |
1999年 | 14篇 |
1995年 | 5篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 13篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1974年 | 6篇 |
1973年 | 11篇 |
1972年 | 11篇 |
1971年 | 8篇 |
1970年 | 6篇 |
1966年 | 6篇 |
排序方式: 共有1169条查询结果,搜索用时 15 毫秒
1.
2.
Jin Wei Mia Madel Alfajaro Peter C. DeWeirdt Ruth E. Hanna William J. Lu-Culligan Wesley L. Cai Madison S. Strine Shang-Min Zhang Vincent R. Graziano Cameron O. Schmitz Jennifer S. Chen Madeleine C. Mankowski Renata B. Filler Neal G. Ravindra Victor Gasque Fernando J. de Miguel Ajinkya Patil Huacui Chen Craig B. Wilen 《Cell》2021,184(1):76-91.e13
3.
T Faraggiana D Villari J Jagirdar J Patil 《The journal of histochemistry and cytochemistry》1986,34(6):811-816
Lung alveoli are coated by a thin layer of extracellular material rich in anionic charges. The nature of this acid layer and its relationship to the phospholipid surfactant are not known. We investigated the possible presence of sialic acid groups by light and electron microscopy in tissues from normal fetal and adult lungs, using neuraminidase treatment followed by staining with the galactose-binding lectin from peanut, labeled with peroxidase. Our results showed that adult lung does not bear peanut lectin-reactive sites but that a very thin and distinct reactive layer becomes evident after neuraminidase treatment, especially on type II pneumocytes. In fetal lung, the entire surface of the developing respiratory tree is outlined by a strongly peanut lectin-reactive layer even if neuraminidase digestion is not performed. We conclude that the acid coat of the alveolar lining is in part composed of sialic acid residues and that sialic acid is added to the fetal lung as the alveoli mature. 相似文献
4.
A child with normal growth and development and the abnormal karyotype 46,XY,17ps, was analyzed using molecular probes localized to 17p13. The results indicated the presence of two copies of the probes YNZ22.1 (D17S5) and YNH37.3 (D17S28), previously shown to be deleted in all Miller-Dieker (MDS) patients studied. However, the patient was hemizygous for probe p144D6 (D17S34), which is absent in approximately 75% of the MDS patients. As the patient is active at 9 months of age, with no clinical signs of MDS, the results confirm that the absence of locus D17S34 does not lead to the phenotypic expression of MDS. Furthermore, this deletion should assist in defining the distal limits of this contiguous gene syndrome. 相似文献
5.
Synthetic soluble (—)-dopa melanin was prepared in deuteriated buffer, pH 8, by autooxidation of the precursor. At 6 mM of the precursor, the incorporation was over 90%. The changes in the line width measurements of N-CH3 protons of enantiomers of ephedrine in the soluble melanin were quantified by NMR spectroscopy. The dissociation constants of (—)-1R,2S-ephedrine, (+)-1S,2R-ephedrine, (—)-1R,2R-ψ-ephedrine, and (+)-1S,2S-ψ-ephedrine were 11.7, 4.20, 3.60, and 4.80 mM, respectively. Since the concentration of (—)-dopa was known and since the conversion of (—)-dopa to indole units of melanin was considered as 1:1, the stoichiometry of the interaction between the drug and the indole unit was calculated. Based on the dissociation constants of the enantiomers, it appears that up to four molecules of (—)-ephedrine can interact with one indole unit of the melanin, while such a ratio for other isomers appear to be 2:1. The preference by indole units of melanin is stereoselective. © 1992 Wiley-Liss, Inc. 相似文献
6.
EPR-detectable redox centers of the periplasmic hydrogenase from Desulfovibrio vulgaris 总被引:1,自引:0,他引:1
D S Patil J J Moura S H He M Teixeira B C Prickril D V DerVartanian H D Peck J LeGall B H Huynh 《The Journal of biological chemistry》1988,263(35):18732-18738
The periplasmic hydrogenase of Desulfovibrio vulgaris (Hildenbourough NCIB 8303) belongs to the category of [Fe] hydrogenase which contains only iron-sulfur clusters as its prosthetic groups. Amino acid analyses were performed on the purified D. vulgaris hydrogenase. The amino acid composition obtained compared very well with the result derived from the nucleotide sequence of the structural gene (Voordouw, G., Brenner, S. (1985) Eur. J. Biochem. 148, 515-520). Detailed EPR reductive titration studies on the D. vulgaris hydrogenase were performed to characterize the metal centers in this hydrogenase. In addition to the three previously observed EPR signals (namely, the "isotropic" 2.02 signal, the rhombic 2.10 signal, and the complex signal of the reduced enzyme), a rhombic signal with resonances at the g-values of 2.06, 1.96, and 1.89 (the rhombic 2.06 signal) was detected when the samples were poised at potentials between 0 and -250 mV (with respect to normal hydrogen electrode). The midpoint redox potentials for each of the four EPR-active species were determined, and the characteristics of each EPR signal are described. Both the rhombic 2.10 and 2.06 signals exhibit spectral properties that are distinct from a ferredoxin-type [4Fe-4S] cluster and are proposed to originate from the same H2-binding center but in two different conformations. The complex signal of the reduced hydrogenase has been shown to represent two spin-spin interacting ferredoxin-type [4Fe-4S]1+ clusters (Grande, H. J., Dunham, W. R., Averill, B., Van Dijk, C., and Sands, R. H. (1983) Eur. J. Biochem. 136, 201-207). The titration data indicated a strong cooperative effect between these two clusters during their reduction. In an effort to accurately estimate the number of iron atoms/molecule of hydrogenase, plasma emission and chemical methods were used to determine the iron contents in the samples; and four different methods, including amino acid analysis, were used for protein determination. The resulting iron stoichiometries were found to be method-dependent and vary over a wide range (+/- 20%). The uncertainties involved in the determination of iron stoichiometry are discussed. 相似文献
7.
Redox titrations of the iron-sulphur clusters in fumarate reductase purified from Escherichia coli, monitored by ESR spectroscopy, identified three redox events, similar to those observed in other fumarate reductases and succinate dehydrogenases: Centre 1, a [2Fe-2S] cluster, at g = 2.03, 1.93, appeared on reduction with Em = -20 mV. Centre 3, probably a [3Fe-xS] cluster, at g = 2.02 appeared in the oxidized state with Em = -70 mV. Centre 2 has been observed as an increase in the electron-spin relaxation of Centre 1. It titrates as an n = 1 species with Em = -320 mV, but in our hands did not appear to contribute significant intensity to the g = 2.03, 1.93 signal. It therefore appears to be an additional centre which undergoes spin-spin interaction with Centre 1. The reduction of Centre 2 coincided with the appearance of an extremely broad ESR spectrum, observed at temperatures below 20 K, with features at g = 2.17, 1.9, 1.68. The broad signal was observed in both soluble and membrane-bound preparations. Its midpoint potential was -320 mV. Its integrated intensity was approximately equal to that of Centre 1, if its broad outer wings were taken into account. Consideration of the ESR properties of this signal, together with the amino acid sequence of the frdB subunit of the enzyme, indicates that Centre 2 is a [4Fe-4S] cluster which, in its reduced state, enhances the spin relaxation of the [2Fe-2S] Centre 1. 相似文献
8.
9.
Total sugars, reducing sugars, and phenols were estimated in internodes of tolerant and highly susceptible sovhum genotypes to charcoal, ln tolerant genotypes the sugar level was 2 to 3 times higher than in susceptible ones; phenol concentration also was higher in tolerant genotypes. In tolerant genotypes, sugar and phenol concentration was high in the lower most and in the upper most mternode. This may be used to identify sources of resistance. 相似文献
10.
A purification of ;malic' enzyme from potato is described. The purified enzyme is specific for NADP and requires a bivalent cation for activity. At pH values below 7 the plot of rate versus malate concentration approximates to normal Michaelis-Menten kinetics. At pH values above 7 the plot of rate versus malate concentration is sigmoid. A number of dicarboxylic acids activate the enzyme and remove the sigmoidicity. The enzyme is inhibited by phosphate, triose phosphates and AMP. In general, effectors of the oxidative decarboxylation of malate behave in the same manner in the reductive carboxylation of pyruvate. The response of the enzyme to energy charge is reported and the physiological significance of the response to metabolites is discussed in relation to the proposed role of the enzyme in the control of pH. 相似文献