全文获取类型
收费全文 | 1047篇 |
免费 | 146篇 |
出版年
2021年 | 18篇 |
2019年 | 10篇 |
2017年 | 7篇 |
2016年 | 15篇 |
2015年 | 28篇 |
2014年 | 36篇 |
2013年 | 37篇 |
2012年 | 63篇 |
2011年 | 48篇 |
2010年 | 25篇 |
2009年 | 29篇 |
2008年 | 25篇 |
2007年 | 35篇 |
2006年 | 42篇 |
2005年 | 40篇 |
2004年 | 20篇 |
2003年 | 30篇 |
2002年 | 32篇 |
2001年 | 24篇 |
2000年 | 21篇 |
1999年 | 24篇 |
1998年 | 16篇 |
1997年 | 12篇 |
1996年 | 15篇 |
1995年 | 18篇 |
1994年 | 8篇 |
1992年 | 21篇 |
1991年 | 17篇 |
1990年 | 23篇 |
1989年 | 24篇 |
1988年 | 30篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 28篇 |
1984年 | 21篇 |
1983年 | 22篇 |
1982年 | 18篇 |
1981年 | 22篇 |
1980年 | 11篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1974年 | 12篇 |
1973年 | 19篇 |
1972年 | 12篇 |
1971年 | 15篇 |
1970年 | 11篇 |
1968年 | 8篇 |
1967年 | 9篇 |
排序方式: 共有1193条查询结果,搜索用时 31 毫秒
11.
Dr. Katsushi Owaribe Jürgen Kartenbeck Elisabeth Rungger-Brändle Werner W. Franke 《Cell and tissue research》1988,254(2):301-315
Summary In vertebrate tissue development a given cell differentiation pathway is usually associated with a pattern of expression of a specific set of cytoskeletal proteins, including different intermediate filament (IF) and junctional proteins, which is identical in diverse species. The retinal pigment epithelium (RPE) is a layer of polar cells that have very similar morphological features and practically identical functions in different vertebrate species. However, in biochemical and immunolocalization studies of the cytoskeletal proteins of these cells we have noted remarkable interspecies differences. While chicken RPE cells contain only IFs of the vimentin type and do not possess desmosomes and desmosomal proteins RPE cells of diverse amphibian (Rana ridibunda, Xenopus laevis) and mammalian (rat, guinea pig, rabbit, cow, human) species express cytokeratins 8 and 18 either as their sole IF proteins, or together with vimentin IFs as in guinea pig and a certain subpopulation of bovine RPE cells. Plakoglobin, a plaque protein common to desmosomes and the zonula adhaerens exists in RPE cells of all species, whereas desmoplakin and desmoglein have been identified only in RPE desmosomes of frogs and cows, including bovine RPE cell cultures in which cytokeratins have disappeared and vimentin IFs are the only IFs present. These challenging findings show that neither cytokeratin IFs nor desmosomes are necessary for the establishment and function of a polar epithelial cell layer and that the same basic cellular architecture can be achieved by different programs of expression of cytoskeletal proteins. The differences in the composition of the RPE cytoskeleton further indicate that, at least in this tissue, a specific program of expression of IF and desmosomal proteins is not related to the functions of the RPE cell, which are very similar in the various species. 相似文献
12.
The determination of the enantiomeric impurity, i.e., the percentage of (+) N?0437 (= N?0924) in several batches of (??) N-0437 (= N-0923) by chiral HPLC is described. Enantiomeric impurities were calculated based on the peak areas of the two baseline separated enantiomers in the chromatogram. The enantiomeric impurities found in different batches ranged from 0.02% to 0.11%. Calibration curves of the two isomers of N-0437 (Fig. 1,) were made twice to study the reproducibility and linearity of the method. The absorbance ratio, N-0923/N-0924, was found to be 1.02 with a relative standard deviation (RSD) of 9% over the whole concentration range used for the calibration curves. 相似文献
13.
14.
Characterization of dimer subunits of intermediate filament proteins 总被引:16,自引:0,他引:16
R A Quinlan M Hatzfeld W W Franke A Lustig T Schulthess J Engel 《Journal of molecular biology》1986,192(2):337-349
The fundamental subunit of the various types of intermediate-sized filaments (IF) has been shown to be a tetramer that is thought to represent a double dimer, i.e. an array of two laterally packed coiled-coils of alpha-helices. The two-chain state of intact IF proteins had up to this point not been isolated and characterized as has been done for other fibrous alpha-helical coiled-coil proteins. Using buffers containing 3 M-guanidinium hydrochloride we prepared dimers by depolymerization of IF or by reconstitution from fully denatured molecules. Dimers of desmin (from chicken gizzard), vimentin (from bovine lens tissue and cultured human fibroblasts) and the neurofilament protein NF-L (from bovine brain) as well as in vitro formed homodimers of human and rat cytokeratins numbers 8 (A), 18 (D) and 19 ("40K"), are characterized by ultracentrifugation techniques (sedimentation velocity and equilibrium), electron microscopy and chemical cross-linking. The results show that IF proteins from discrete complexes of two polypeptide chains in parallel orientation and probably in coiled-coil configuration, which apparently have a high tendency to further associate into double dimers. Implications of these results for concepts of IF organization and IF protein assembly are discussed. 相似文献
15.
16.
17.
Identification and localization of synaptophysin, an integral membrane glycoprotein of Mr 38,000 characteristic of presynaptic vesicles 总被引:111,自引:0,他引:111
A polypeptide of Mr 38,000 has been identified as a specific component of the membrane of presynaptic vesicles, using the monoclonal antibody SY38. This protein, which is acidic (isoelectric at approximately pH 4.8) and glycosylated, appears to be an integral membrane protein, as suggested by its solubilization with the nonionic detergent Triton X-100 and the finding that the epitope recognized by antibody SY38 is located on the cytoplasmic surface of those vesicles. It is found in presynaptic vesicles of neurons of the brain, spinal cord, and retina as well as at neuromuscular junctions. It is also found in the adrenal medulla. Its occurrence in diverse vertebrate species indicates its stability during evolution. This protein, for which we propose the name synaptophysin*, provides a molecular marker for the presynaptic vesicle membrane and may be involved in synaptic vesicle formation and exocytosis. 相似文献
18.
In vitro cultivation of Dipetalonema viteae third-stage larvae: evaluation of culture media, serum, and other supplements 总被引:1,自引:0,他引:1
Third-stage larvae of Dipetalonema viteae obtained from the tick vector developed to the fourth stage in several cell-free culture systems. Survival and development of larvae in a number of commercially available cell culture media, supplemented with serum and other defined and undefined components, were compared. All cultures were gassed with 5% carbon dioxide in nitrogen. Best survival, growth and development were obtained in stationary cultures containing 1:1 (v/v) mixtures of NCTC 135, either RPMI 1640 or Iscove's Modified Dulbecco's Medium, and a supplement of 20% non-heat-inactivated fetal bovine serum. The importance of the medium composition and physical environment of the culture system, for the survival, growth and development of D. viteae was demonstrated. 相似文献
19.
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
20.
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