全文获取类型
收费全文 | 325篇 |
免费 | 37篇 |
国内免费 | 1篇 |
出版年
2023年 | 1篇 |
2021年 | 6篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 11篇 |
2013年 | 12篇 |
2012年 | 19篇 |
2011年 | 18篇 |
2010年 | 19篇 |
2009年 | 16篇 |
2008年 | 19篇 |
2007年 | 26篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 9篇 |
2003年 | 12篇 |
2002年 | 16篇 |
2001年 | 11篇 |
2000年 | 11篇 |
1999年 | 10篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1968年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有363条查询结果,搜索用时 31 毫秒
1.
C Birchmeier D Birnbaum G Waitches O Fasano M Wigler 《Molecular and cellular biology》1986,6(9):3109-3116
A human oncogene, mcf3, previously detected by a combination of DNA-mediated gene transfer and a tumorigenicity assay, derives from a human homology of the avian v-ros oncogene. Both v-ros and mcf3 can encode a protein with homology to tyrosine-specific protein kinases, and both mcf3 and v-ros encode a potential transmembrane domain N terminal to the kinase domain. mcf3 probably arose during gene transfer from a normal human ros gene by the loss of a putative extracellular domain. There do not appear to be any other gross rearrangements in the structure of mcf3. 相似文献
2.
G Parlato R Pizzano D Picone J Guesnet O Fasano A Parmeggiani 《The Journal of biological chemistry》1983,258(2):995-1000
In this work we show that intact aminoacyl-tRNA (aa-tRNA) and its 3' half-molecule, but not its 3' C-C-A-aa fragment, require selective ionic conditions for stimulating the mRNA-independent GTPase of elongation factor Tu (EF-Tu) in the presence of ribosomes.l Stimulation by aa-tRNA and its 3' half-molecule is only observed at 20 and 30 mM Mg2+ and not at 10 mM, where they exert inhibitory activity; by contrast, C-C-A-aa enhances the GTPase activity at all three of these Mg2+ concentrations. Ammonium ion is needed for stimulation by C-C-A-aa, whereas it inhibits the stimulation by aa-tRNA and its 3' half-molecule. The concentration of aminoacylated fragments needed for half-maximum stimulation follows this order: A-Val much greater than C-A-Val greater than C-C-A-Val much greater than 3' Val-tRNA1Val half-molecule greater than Val-tRNA1Val. The extent of maximum stimulation of the EF-Tu GTPase in the presence of ribosomes varies moderately depending on the aa-tRNA species; a clear dependence on the nature of the aminoacyl side chain is observed in the effects of their respective C-C-A-aa fragments tested (C-C-A-Arg, C-C-A-Val, C-C-A-Phe, C-C-A-Met, C-C-A-Lys). In the absence of ribosomes and at low [Mg2+], the one-round GTP hydrolysis by EF-Tu is enhanced by C-C-A-aa fragments, whereas it is inhibited by the corresponding aa-tRNAs. Our results suggest that besides the 3' aminoacylated extremity another region(s) of the aa-tRNA molecule controls the GTPase of EF-Tu. The "unspecific" stimulation by C-C-A-aa and the "specific," aa-tRNA-like effect of the 3' aa-tRNA half-molecule point to the importance of the T chi C loop and stem, as well as of the adjacent regions for the regulation of this function. 相似文献
3.
We have broadly defined the DNA regions regulating esterase6 activity in
several life stages and tissue types of D. melanogaster using P-
element-mediated transformation of constructs that contain the esterase6
coding region and deletions or substitutions in 5' or 3' flanking DNA.
Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and
the primary sequences regulating its activity lie between -171 and -25 bp
relative to the translation initiation site: deletion of these sequences
decrease activity approximately 20-fold. Hemolymph activity is also
modulated by four other DNA regions, three of which lie 5' and one of which
lies 3' of the coding region. Of these, two have positive and two have
negative effects, each of approximately twofold. Esterase6 activity is
present also in two male reproductive tract tissues; the ejaculatory bulb,
which is another ancestral activity site, and the ejaculatory duct, which
is a recently acquired site within the melanogaster species subgroup.
Activities in these tissues are at least in part independently regulated:
activity in the ejaculatory bulb is conferred by sequences between -273 and
-172 bp (threefold decrease when deleted), while activity in the
ejaculatory duct is conferred by more distal sequences between -844 and
-614 bp (fourfold decrease when deleted). The reproductive tract activity
is further modulated by two additional DNA regions, one in 5' DNA (-613 to
-284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to
+2731 bp; threefold decrease when deleted) that probably overlaps the
adjacent esteraseP gene. Collating these data with previous studies
suggests that expression of EST6 in the ancestral sites is mainly regulated
by conserved proximal sequences while more variable distal sequences
regulate expression in the acquired ejaculatory duct site.
相似文献
4.
Riccardo Pierantoni Mauro D'Antonio Silvia Fasano 《Environmental Biology of Fishes》1993,38(1-3):187-196
Synopsis The tetrapod hypothalamus-pars distalis axis contains a blood portal system. Contrarily, elasmobranchs appear to lack a direct vascular supply from the hypothalamus to the ventral lobe of the pituitary where gonadotropic activity resides. The hypothalamus contains GnRH immunoreactivity and GnRH causes an increase in plasma gonadal steroids, perhaps via ventral lobe stimulation. Therefore, the question arises as to how GnRH reaches the pituitary. We suggest that the general circulation route might be practicable. Indeed, in the plasma of the electric ray,Torpedo marmorata, a major early eluting form has been detected using high performance liquid chromatography coupled with region specific radioimmunoassay. The presence of GnRH in the blood may allow the molecule to reach the gonads and to act there by direct mechanisms. Intragonadal levels of steroids may have a paracrine and/or autocrine role in the regulation of steroidogenesis in the testis and in the development f specific germinal cell stages. Particularly, the zonated morphology of the testis supports the concept of a diverse environment for different spermatogenic stages. Finally, gonadal steroids may feed back to affect pituitary activity. 相似文献
5.
Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
6.
J A King A A Steneveld R P Millar S Fasano G Romano A Spagnuolo L Zanetti R Pierantoni 《Peptides》1992,13(1):27-35
Gonadotropin-releasing hormone (GnRH) peptides in the brain, testis and plasma of an electric ray (Torpedo marmorata) were investigated by gel filtration chromatography, reverse phase high performance liquid chromatography and radioimmunoassay with region-specific antisera. In the brain, two major forms of GnRH were demonstrated. One form had identical chromatographic and immunological properties to chicken GnRH II, and the second, novel, molecular form had structural features in common with mammalian, chicken II and salmon GnRHs. A minor, early-eluting immunoreactive peak, possibly also a novel GnRH, was also evident. Immunoreactive GnRH was not detected in the testis. In the plasma, a single major early-eluting immunoreactive peak was demonstrated. This peak, identical to the minor peak observed in the brain, is likely to represent a novel form of GnRH which has immunological properties in common with mammalian, chicken II and salmon GnRHs. Immunoreactive GnRH was not detected in the plasma of species from other vertebrate classes, including rabbit, chicken, monitor lizard, clawed toad, frog, cichlid fish and lamprey. The finding of chicken GnRH II in a species of Chondrichthyes adds further support to our hypothesis that this widespread structural variant may represent an early-evolved and conserved form of GnRH. The presence of a GnRH molecular form in the plasma of the electric ray suggests that GnRH may reach target organs (pituitary and gonads) via the general circulation in some species of Chondrichthyes. 相似文献
7.
Genetic analysis of yeast RAS1 and RAS2 genes 总被引:59,自引:0,他引:59
We present a genetic analysis of RAS1 and RAS2 of S. cerevisiae, two genes that are highly homologous to mammalian ras genes. By constructing in vitro ras genes disrupted by selectable genes and introducing these by gene replacement into the respective ras loci, we have determined that neither RAS1 nor RAS2 are by themselves essential genes. However, ras1 - ras2 - spores of doubly heterozygous diploids are incapable of resuming vegetative growth. We have determined that RAS1 is located on chromosome XV, 7 cM from ade2 and 63 cM from his3; and RAS2 is located on chromosome XIV, 2 cM from met4 . We have also constructed by site-directed mutagenesis a missense mutant, RAS2val19 , which encodes valine in place of glycine at the nineteenth amino acid position, the same sort of missense mutation that is found in some transforming alleles of mammalian ras genes. Diploid yeast cells that contain this mutation are incapable of sporulating efficiently, even when they contain wild-type alleles. 相似文献
8.
We have developed a sensitive bioassay for transforming genes based on the tumorigenicity of cotransfected NIH3T3 cells in nude mice. The assay differs substantially from the NIH3T3 focus assay. Using it, we have detected the transfer of three transforming genes from the DNA of MCF-7, a human mammary carcinoma cell line. One of these is N-ras, which is amplified in MCF-7 DNA. The other two, which we have called mcf2 and mcf3, do not appear to be related to known oncogenes. We cannot detect their transfer by using the NIH3T3 focus assay. We do not yet know whether either mcf2 or mcf3 is associated with genetic abnormalities in MCF-7 cells. 相似文献
9.
10.