全文获取类型
收费全文 | 5647篇 |
免费 | 431篇 |
国内免费 | 2篇 |
出版年
2021年 | 42篇 |
2019年 | 44篇 |
2018年 | 57篇 |
2017年 | 59篇 |
2016年 | 83篇 |
2015年 | 131篇 |
2014年 | 140篇 |
2013年 | 209篇 |
2012年 | 244篇 |
2011年 | 252篇 |
2010年 | 168篇 |
2009年 | 141篇 |
2008年 | 229篇 |
2007年 | 280篇 |
2006年 | 276篇 |
2005年 | 265篇 |
2004年 | 290篇 |
2003年 | 230篇 |
2002年 | 271篇 |
2001年 | 116篇 |
2000年 | 96篇 |
1999年 | 93篇 |
1998年 | 87篇 |
1997年 | 80篇 |
1996年 | 78篇 |
1995年 | 70篇 |
1994年 | 71篇 |
1993年 | 78篇 |
1992年 | 99篇 |
1991年 | 75篇 |
1990年 | 76篇 |
1989年 | 73篇 |
1988年 | 65篇 |
1987年 | 66篇 |
1986年 | 47篇 |
1985年 | 67篇 |
1984年 | 81篇 |
1983年 | 58篇 |
1982年 | 72篇 |
1981年 | 58篇 |
1980年 | 72篇 |
1979年 | 54篇 |
1978年 | 60篇 |
1977年 | 54篇 |
1976年 | 51篇 |
1975年 | 46篇 |
1974年 | 50篇 |
1972年 | 49篇 |
1970年 | 45篇 |
1969年 | 41篇 |
排序方式: 共有6080条查询结果,搜索用时 15 毫秒
71.
Bluelight-induced,flavin-mediated transport of redox equivalents across artificial bilayer membranes
Werner Schmidt 《The Journal of membrane biology》1984,82(2):113-122
Summary This paper continues our studies of physico-chemical properties of vesicle-bound flavins. Based on previous results, an advanced model system was designed in order to study the mechanisms underlying bluelight-induced redox transport across artificial membranes. The lumen of single-shelled vesicles was charged with cytochromec, and amphiphilic flavin (AF1 3, AF1 10) was bound to the membrane. Upon bluelight irradiation redox equivalents are translocated from exogeneous 1e
–(EDTA)-and 2e
–(BH3CN–) donors across the membrane finally reducing the trapped cytochromec both under aerobic and anaerobic conditions. The mechanisms involved are explored and evidence for the involvement of various redox states of oxygen, dihydroflavin and flavosemiquinone is presented. 相似文献
72.
JoséL. Jorcano Michael Rieger Juergen K. Franz Dorothea L. Schiller Roland Moll Werner W. Franke 《Journal of molecular biology》1984,179(2):257-281
Cytoskeletal filaments of the α-keratin type (cytokeratins) are a characteristic of epithelial cells. In diverse mammals (man, cow and rodents) these cytokeratins consist of a family of approximately 20 polypeptides, which may be divided into the more acidic (I) and the more basic (II) subfamilies. These two subfamilies show only limited amino acid sequence homology. In contrast, nucleic acid hybridization experiments and peptide maps have been interpreted to show that polypeptides of the same subfamily share extended sequence homology.We compare two polypeptides of the acidic cytokeratin subfamily, VIb (Mr 54,000) and VII (Mr 50,000), which are co-expressed in large amounts in bovine epidermal keratinocytes. These two epidermal keratins can be distinguished by specific antibodies and show different patterns of expression among several bovine tissues and cultured cells. In addition, they differ in the stability of their complexes with basic keratin polypeptides and in their tryptic peptide maps. The amino acid sequences deduced from the nucleotide sequences of complementary DNA clones containing the 3′ ends of the messenger RNAs for these keratins are compared with each other and with available amino acid sequences of human, murine and amphibian epidermal keratins. Bovine keratins VIb and VII share considerable sequence homology in the α-helical portion (68% residues identical) but lack significant homology in the extrahelical portion. Bovine keratin VIb shows, in its α-helical region, a pronounced sequence homology (88% identity) to the murine epidermal keratin of Mr 59,000. In addition, the non-helical carboxy-terminal regions of both proteins are glycinerich and contain a canonic sequence GGGSGYGG, which may be repeated several times. Moreover, their mRNAs present a highly conserved stretch of 236 nucleotides containing, in the murine sequence, the end of the coding and all of the non-coding region (81% identical nucleotides). Bovine keratin VII is considerably different from the murine Mr 59,000 keratin but is almost identical to the human cytokeratin number 14 of Mr 50,000, both in the α-helical and in the non-α-helical regions of the proteins, and the mRNAs of the human and the bovine keratins also display a high homology in their 3′ non-coding ends.The results show that in the same species keratins of the same subfamily can differ considerably, whereas equivalent keratin polypeptides of different species are readily identified by characteristic sequence homologies in the α-helical and the non-helical regions as well as in the 3′ non-coding portions of their mRNAs. Among the members of the acidic subfamily I of cytokeratin polypeptides that are co-expressed in bovine epidermis, at least two types can be distinguished by their carboxy-terminal sequences. One type is characterized by its abundance of glycine residues, a consensus GGGSGYGG heptapeptide sequence, which may be repeated several times, and an extended stretch of high RNA sequence homology in the 3′ non-coding part. The other type shows a predominance of serine and valine residues, a subterminal GGGSGYGG sequence (which has been maintained in Xenopus, cow and man) and also a high level of homology in the 3′ non-coding part of the mRNA. The data indicate that individual keratin type specificity overrides species diversity, both at the protein and the mRNA level. We discuss the evolutionary conservation and the tissue distribution of these two types of acidic keratin polypeptides as well as their possible biological functions. 相似文献
73.
74.
Cytokeratin expression in simple epithelia 总被引:10,自引:0,他引:10
Valentino Romano Mechthild Hatzfeld Thomas M. Magin Ralf Zimbelmann Werner W. Franke Gernot Maier Herwig Ponstingl 《Differentiation; research in biological diversity》1986,30(3):244-253
To study the regulation of the expression of cytokeratins characteristic of simple epithelia, i.e., human cytokeratins nos. 7, 8, 18, and 19, we prepared several cDNA clones coding for these proteins and their bovine counterparts. In the present study, we describe a cDNA clone of the mRNA coding for human cytokeratin no. 18, which was isolated from an expression library using the monoclonal antibody, KG 8.13. This clone (756 nucleotides, excluding the polyA portion), encodes approximately one-half of the mRNA (approximately 1.4 kb), identifies one mRNA band in Northern-hybridization blots, and specifically selects one mRNA species coding for cytokeratin no. 18, as demonstrated by translation in vitro. Comparison of the deduced amino acid sequence--confirmed by direct amino-acid-sequence analyses of some polypeptide fragments produced by cleavage with cyanogen bromide--indicated that cytokeratin no. 18 is a member of the acidic (type I) subfamily of cytokeratins. It has only limited sequence homologies in common with other intermediate-sized filament proteins, and these are essentially restricted to certain domains of the alpha-helical rod portion. The carboxyterminal tail sequence does not contain glycine-rich elements, thus distinguishing this cytokeratin from those acidic (type I) cytokeratins that are characterized by this feature. The similarities and differences between cytokeratin no. 18 and previously described epidermal cytokeratins are discussed in relation to the differences in the stability of the complexes which this cytokeratin forms with basic (type II) cytokeratins, as well as in relation to possible functional differences of cytokeratins in simple and stratified epithelia. 相似文献
75.
Jörg Hacker Manfred Ott Günter Schmidt Richard Hull Werner Goebel 《FEMS microbiology letters》1986,36(2-3):139-144
Abstract The genetic determinant coding for the P-specific F8 fimbriae was cloned from the chromosome of the Escherichia coli wild-type strain 2980 (O18:K5:H5:F1C, F8). The F8 determinant was further subcloned into the Pst I site of pBR322 and a restriction map was established. In a Southern hybridization experiment identity between the chromosomally encoded F8 determinant of 2980 and its cloned counterpart was demonstrated. The cloned F8 fimbriae and those of the wild type strain consist of a protein subunit of nearly 20 kDa. F8 fimbriated strains were agglutinated by an F8 polyclonal antiserum, caused mannose-resistant hemagglutination and attached to human uroepithelial cells. The cloned F8 determinant was well expressed in a variety of host strains. 相似文献
76.
Sanjib Das Robindra N. Baruah Ram P. Sharma Jogendra N. Baruah Palaniappan Kulanthaivel Werner Herz 《Phytochemistry》1983,22(9):1989-1991
Cynaropicrin, 11βH-11,13-dihydrodesacylcynaropicrin, aguerins A and B, isoamberboin and the new guaianolides saussureolide and 11βH-11,13-dihydrodesacylcynaropicrin 8-β-d-glucoside were isolated from Saussurea affinis. 相似文献
77.
Summary Substitution of extracellular Na+ by Li+ causes depression of junctional membrane permeability inChironomus salivary gland cells; within 3 hr, permeability falls to so low a level that neither fluorescein nor the smaller inorganic ions any longer traverse the junctional membrane in detectable amounts (uncoupling). The effect is Li-specific: if choline+ is the Na+ substitute, coupling is unchanged. The Li-produced uncoupling is not reversed by restitution of Na+. Long-term exposure (>1 hr) of the cells to Ca, Mg-free medium leads also to uncoupling. This uncoupling is fully reversible by early restitution of Ca++ or Mg++. Coupling is maintained in the presence of either Ca++ or Mg++, so long as the total divalent concentration is about 12mm. The uncoupling in Ca, Mg-free medium ensues regardless of whether the main monovalent cation is Na, Li or choline.The uncouplings are accompanied by cell depolarization. Repolarization of the cells by inward current causes restoration of coupling; the junctional conductance rises again to its normal level. The effect was shown for Li-produced uncoupling, for uncoupling by prolonged absence of external Ca++ and Mg++, and for uncoupling produced by dinitrophenol. In all cases, the recoupling has the same features: (1) it develops rapidly upon application of the polarizing current; (2) it is cumulative; (3) it is transient, but outlasts the current; and (4) it appears not to depend on the particular ions carrying the current from the electrodes to the cell. The recoupling is due to repolarization of nonjunctional cell membrane; recoupling can be produced at zero net currernt through the junctional membrane. Recoupling takes place also as a result of chemically produced repolarization; restoration of theK gradients in uncoupled cells causes partial recoupling during the repolarization phase.An explanation of the results on coupling is proposed in terms of known mechanisms of regulation of Ca++ flux in cells. The uncouplings are explained by actions raising the Ca++ level in the cytoplasmic environment of the junctional membranes; the recoupling is explained by actions lowering this Ca++ level. 相似文献
78.
79.
80.