全文获取类型
收费全文 | 442篇 |
免费 | 21篇 |
专业分类
463篇 |
出版年
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 7篇 |
2016年 | 15篇 |
2015年 | 17篇 |
2014年 | 12篇 |
2013年 | 30篇 |
2012年 | 24篇 |
2011年 | 27篇 |
2010年 | 23篇 |
2009年 | 10篇 |
2008年 | 17篇 |
2007年 | 26篇 |
2006年 | 32篇 |
2005年 | 22篇 |
2004年 | 18篇 |
2003年 | 24篇 |
2002年 | 18篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 13篇 |
1980年 | 4篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1971年 | 2篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1914年 | 1篇 |
排序方式: 共有463条查询结果,搜索用时 0 毫秒
41.
Witas HW Jatczak I Jedrychowska-Dańska K Zadzińska E Wrzesińska A Wrzesiński J Nadolski J 《Anthropologischer Anzeiger; Bericht über die biologisch-anthropologische Literatur》2006,64(1):41-49
deltaF508 is the most common (70%) among over 1000 mutations of the gene encoding ATP-regulated chloride channel, namely CFTR--cystic fibrosis transmembrane regulator. The time which passed from the calculated mutation event was anticipated on the basis of the frequency of contemporary haplotypes, but not on its direct identification. The presence of three base pairs deletion in the ancient DNA (aDNA) isolated from skeletal remains of the Middle Ages origin was investigated. Teeth excavated in the area of three sites located in Central Poland were processed for a DNA. 6 out of 82 samples did not produce amplificable fragments of DNA. Although the number of specimens analyzed was sufficient to confirm the presence of the rare mutation, the deltaF508 CFTR sequence was not found in the remains of individuals living back 35 - 45 generations. The absence of the mutated allele in the particular geographic region cannot state for the status of mutated allele throughout the country, especially at times when migrations were limited and movements of people were more area restricted than at present days. 相似文献
42.
Kepa M Kozłowski T Szostek K Drozd A Walas S Mrowiec H Stepańczak B Głab H Grupa M 《Anthropologischer Anzeiger; Bericht über die biologisch-anthropologische Literatur》2012,69(3):367-377
The aim of the present work is to study the remains of seven individuals with typical symptoms of tertiary syphilis in terms of mercury content in bones, thereby verifying whether they were subjected to treatment and, if they were, how long their organisms were exposed to toxic mercury fumes. Mercury was used, mainly in the Middle Ages and in the early modern period, as a preventive measure in case of individuals suffering from syphilis, a venereal disease, and also leprosy. Syphilitic patients treated this way should demonstrate increased concentration of mercury in their bones. The skeletons studied in the present work originate from various archaeological sites in southern and north-central Poland. The analyses concerned individuals with diagnosed syphilis as well as healthy individuals who constituted the control group. The analyses were performed by the LA-ICP-MS technique, with the use of laser Nd: YAG, Macro, 266 nm, New Wave, USA, coupled with Spectrometer Elan DRC-e Perkin Elmer, USA. The content analysis of the studied bone material revealed with high probability that the contact method of mercurial treatment was used only in the case of two women from north-central Poland, deceased at the turn of the 15th century at the earliest. 相似文献
43.
Plants have developed a range of strategies for resisting environmental stresses. One of the most common is the synthesis
and deposition of callose, which functions as a barrier against stress factor penetration. The aim of our study was to examine
whether callose forms an efficient barrier against Pb penetration in the roots of Lemna minor L. exposed to this metal. The obtained results showed that Pb induced callose synthesis in L. minor roots, but it was not deposited regularly in all tissues and cells. Callose occurred mainly in the protoderm and in the centre
of the root tip (procambial central cylinder). Moreover, continuous callose bands, which could form an efficient barrier for
Pb penetration, were formed only in the newly formed and anticlinal cell walls (CWs); while in other CWs, callose formed only
small clusters or incomplete bands. Such an arrangement of callose within root CWs inefficiently protected the protoplast
from Pb penetration. As a result, Pb was commonly present inside the root cells. In the light of the results, the barrier
role of callose against metal ion penetration appears to be less obvious than previously believed. It was indicated that induction
of callose synthesis is not enough for a successful blockade of the stress factor penetration. Furthermore, it would appear
that the pattern of callose distribution has an important role in this defence strategy. 相似文献
44.
Henryk Brzeskwiniewicz 《Biometrical journal. Biometrische Zeitschrift》1995,37(2):191-198
We present the idea of using multiresponse incomplete block designs when not all responses can be observed in all experimental units. For a special class of such designs, in which partial designs are PBB designs, a method for estimating natural treatment contrast is given. We also consider the problem of testing the hypotheses concerning the natural and any estimable treatment contrasts. For testing this hypothesis the Wald statistics, being asymptotically chi-square distributed, is proposed. 相似文献
45.
In the preceding paper are described the isolation and physical characterization of seven narrowly disperse fractions of calf thymus DNA in the molecular weight range 0.3 to 1.3 × 106 daltons. Herein, we have determined by light scattering the molecular weights and root mean square radii of these fractions in a solvent comprising 0.2 M NaCl, 2 mM EDTA, 2m MNa-PO4, pH 7. Measurements were made in a modified Wippler—Scheibling photometer to a 20° lower limit of scattering angle on solutions rendered virtually dust-free by procedures described. The optical aniso tropics of the DNA fractions were measured permitting the experimental molecular weights and root mean square radii to be corrected to their true values. From these values, with appropriate polydispersity corrections, we calculate a Kratky—Porod persistence length, a, of 54.0 ± 5.6 nm which is invariant over the molecular weight range examined. From the sedimentation coefficients (preceding paper) and the theory of Yamakawa and Fujii, we calculate a to be 66 nm, a value found to apply equally well to several DNA samples of various origins whose sedimentation rates are known in the molecular weight range from about 4 × 104 to 108 daltons. Similarly, from the intrinsic viscosities and the theory of Yamakawa and Fujii, we calculate a to be 59 nm, which again adequately applies to a number of DNA samples whose viscosities have been measured by other workers in the molecular weight range 3 × 105 to 108 daltons. The Flory—Mandelkern parameter, β, was found to vary with molecular weight in the manner predicted by the theory of Yamakawa and Fujii. The average value of a from the three sets of measurements is 60 ± 6 nm, which we believe applies to double-stranded DNA molecules, independent of chain length, over the whole range of molecular weights for which reliable data exist. 相似文献
46.
47.
Henryk Brzeskwiniewicz 《Biometrical journal. Biometrische Zeitschrift》1989,31(5):631-635
In this paper an inequality for the smallest positive eigenvalues of the C-matrix of a block design are derived. This inequality is a generalization of a result by Constantine (1982) to the case of unequal block sizes. On the basis of the above result a certain E-optimality criterium of block designs is given. Furthermore coefficient ed has been introduced which permits to assess how close the block design is from the optimal one. 相似文献
48.
Commonly observed chemical modifications that occur in proteins during their in vitro purification, storage, and handling
are discussed. Covalent modifications described include deamidation and isoaspartate formation, cleavage of peptide bonds
at aspartic acid residues, cystine destruction and thioldisulfide interchange, oxidation of cysteine and methionine residues,
and the glycation and carbamylation of amino groups. 相似文献
49.
The prion protein is a membrane attached glycoprotein that is involved in binding of divalent copper ions. In vivo human and chicken PrPs exhibit SOD-like activity associated with octarepeat and hexarepeat regions, respectively, when bind Cu(II) ions. However, the species of Cu(II)-PrP involved in the Cu(II) center which determines the highest SOD-like activity is still unknown. The data presented here clearly show that the single Cu(II) ion bound to PrP octapeptide repeat region of mammalian prion and hexapeptide repeat region of avian prion via 4 His side-chain imidazoles reveals the highest SOD activity. 相似文献
50.
Ganadu ML Aru M Mura GM Coi A Mlynarz P Kozlowski H 《Journal of inorganic biochemistry》2004,98(6):1103-1109
AlphaB-crystallin is a small heat shock protein, showing chaperone-like activity, that is expressed in the lens and in several other tissues. The role of some metal ions in the alphaB-crystallin biology starts to be well documented. In some neuro-degenerative pathologies, like Parkinson and Alzheimer's diseases, alphaB-crystallin is expressed at high levels. In the same pathologies an accumulation of divalent metal cations is observed. In order to investigate the interactions between human alphaB-crystallin and divalent metal ions, the effect of copper, zinc and calcium on the chaperone-like activity of the protein has been studied. Copper and zinc at concentrations 0.1 and 1 mM significantly increase the chaperone-like activity, whereas calcium 1 mM completely inhibits activity. Electron paramagnetic resonance (EPR) and circular dichroism (CD) spectra indicate the possible complex formation between Cu(II) and protein at physiological pH. Molecular modeling calculations, carried out for the probable Cu(II) binding site, suggest that a complex with three histidine residues is possible. 相似文献