全文获取类型
收费全文 | 224篇 |
免费 | 26篇 |
专业分类
250篇 |
出版年
2021年 | 4篇 |
2020年 | 3篇 |
2018年 | 4篇 |
2016年 | 4篇 |
2015年 | 12篇 |
2014年 | 15篇 |
2013年 | 16篇 |
2012年 | 16篇 |
2011年 | 3篇 |
2010年 | 12篇 |
2009年 | 8篇 |
2008年 | 10篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2003年 | 11篇 |
2002年 | 10篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 11篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1963年 | 2篇 |
1958年 | 1篇 |
1944年 | 1篇 |
排序方式: 共有250条查询结果,搜索用时 0 毫秒
101.
Sensitive detection of RNA using strand-specific M13 probes 总被引:11,自引:0,他引:11
We have extended the method of Hu and Messing (Gene 17 (1982) 271-277) to prepare highly radioactive M13 probes suitable for use in RNA-DNA hybridization experiments. Single strands of M13 DNA carrying cloned sequences are rendered partially double-stranded by primed synthesis using a synthetic oligonucleotide primer complementary to a region 5' to the cloning site. The newly synthesized radioactive complementary strand is then covalently cross-linked to the M13 phage DNA by UV irradiation in the presence of 4,5,8-trimethylpsoralen (trioxsalen). Since the cross-linked probe is stable to heat denaturation, and the region of cloned sequence is kept single-stranded, these complexes may be used as strand-specific hybridization probes to detect RNA sequences under conditions which would denature DNA-DNA duplexes. 相似文献
102.
Water in the Avian Egg Overall Budget of Incubation 总被引:1,自引:0,他引:1
The loss of mass in eggs during incubation was examined andevidence is presented to show that this is essentially due toloss of water. The mean fraction of water lost by diffusionthroughout incubation is 0.150 ± 0.025 S D per gram ofegg and 0.162 ± 0.026 S D per gram of egg content for81 species. The water fraction of fresh eggs and of hatchingeggs was examined in 32 species divided according to maturityat hatching, and found to be very similar within each category(83% in altricial 83% in semi-altricial 78% in semi-precocial72% in precocial eggs). The 11% difference between the altricialand precocial categories is statistically significant. Duringincubation, dry matter is metabolized increasing the water fractionwhich is further increased by metabolic water production. Hence,water loss during incubation is mandatory if the relative watercontent of an egg at the end of incubation is to remain essentiallythe same as at the beginning. Equations are developed whichallow one to estimate the difference between diffusive waterloss and the total water loss in altricial and piecocial eggscaused by additional water loss during pipping and hatching. 相似文献
103.
Oscar Berlanga David Tulasne Teresa Bori Daniel C Snell Yoshiki Miura Stephanie Jung Masaaki Moroi Jonathan Frampton Steve P Watson 《European journal of biochemistry》2002,269(12):2951-2960
There is extensive evidence that FcR gamma-chain couples to the collagen receptor glycoprotein VI (GPVI) and becomes phosphorylated on tyrosines upon receptor cross-linking. However, it is not established whether this receptor complex is sufficient to initiate the signalling cascade. We transfected GPVI and the FcR gamma-chain into the human erythroleukaemia cell line K562, which lacks detectable expression of GPVI and the FcR gamma-chain. The results show that GPVI is unable to signal when expressed alone, despite its surface expression, upon stimulation with the snake C-type lectin, convulxin. Coexpression of the FcR gamma-chain confers signalling properties on the receptor. Furthermore, cotransfection of the FcR gamma-chain and two mutant versions of GPVI shows that the transmembrane arginine and cytoplasmic tail of GPVI are necessary for association with the FcR gamma-chain. These results demonstrate that reconstitution of the GPVI-FcR gamma-chain complex in cells expressing the necessary signalling network is sufficient to initiate signalling events in response to convulxin and collagen-related peptide. 相似文献
104.
S Jahan S Singh A Srivastava V Kumar D Kumar A Pandey CS Rajpurohit AR Purohit VK Khanna AB Pant 《Molecular neurobiology》2018,55(4):2828-2839
105.
Goldstein DB; Zhivotovsky LA; Nayar K; Linares AR; Cavalli-Sforza LL; Feldman MW 《Molecular biology and evolution》1996,13(9):1213-1218
It has recently been suggested that observed levels of variation at
microsatellite loci can be used to infer patterns of selection in genomes
and to assess demographic history. In order to evaluate the feasibility of
these suggestions it is necessary to know something about how levels of
variation at microsatellite loci are expected to fluctuate due simply to
stochasticity in the processes of mutation and inheritance (genetic
sampling). Here we use recently derived properties of the stepwise mutation
model to place confidence intervals around the variance in repeat score
that is expected at mutation-drift equilibrium and outline a statistical
test for whether an observed value differs significantly from expectation.
We also develop confidence intervals for the time course of the buildup of
variation following a complete elimination of variation, such as might be
caused by a selective sweep or an extreme population bottleneck. We apply
these methods to the variation observed at human Y-specific
microsatellites. Although a number of authors have suggested the
possibility of a very recent sweep, our analyses suggest that a sweep or
extreme bottleneck is unlikely to have occurred anytime during the last
approximately 74,000 years. To generate this result we use a recently
estimated mutation rate for microsatellite loci of 5.6 x 10(-4) along with
the variation observed at autosomal microsatellite loci to estimate the
human effective population size. This estimate is 18,000, implying an
effective number of 4,500 Y chromosomes. One important general conclusion
to emerge from this study is that in order to reject mutation-drift
equilibrium at a set of linked microsatellite loci it is necessary to have
an unreasonably large number of loci unless the observed variance is far
below that expected at mutation-drift equilibrium.
相似文献
106.
S J Rowland W G Allard S T Belt G Massé J M Robert S Blackburn D Frampton A T Revill J K Volkman 《Phytochemistry》2001,58(5):717-728
Polyunsaturated highly branched isoprenoid (HBI) hydrocarbon distributions of laboratory cultures of five strains of the planktonic diatom Rhizosolenia setigera (Brightwell) are shown herein to be highly variable. Some strains produced both haslenes with from three to five double bonds and rhizenes. The haslenes comprised not only Delta5 alkenes but also those with C7(20) unsaturation, including hasla-7(20),9E,Z, 23-trienes and hasla-7(20),9E,Z-13, 23-tetraenes. The rhizenes contained C7(25) unsaturation and the vinyl moiety common to all algal haslenes so far characterised. The effects of temperature and salinity on HBI composition, along with isotopic content, were determined in strain CS 389/A. Increase in growth temperature from 18 to 25 degrees C increased the degree of unsaturation in the haslenes and E to Z isomerisation in the triene. There was also an increase in unsaturation in the rhizenes at the highest growth temperature, with hexaenes dominant over the pentaenes but in the rhizenes, Z to E isomerisation increased. Increased salinity from 15 to 35 psu increased cell growth and rhizene production but decreased haslene production. Unsaturation in haslenes was not changed by increased salinity but unsaturation in the rhizenes decreased. These may reflect growth rate differences. The carbon isotopic compositions of the haslenes and rhizenes were similar to that of the major sterol at 18 degrees C, but the major HBI isomers were 3-4 per mil depleted relative to phytol released by saponification from chlorophyll a. This suggests biosynthesis of HBIs from a different isotopic pool of isopentenyl biphosphate to that from which phytol is biosynthesised. At 25 degrees C, further isotopic differences were observed. The variables controlling HBI distributions in R. setigera are still not fully understood and rationalisation of the environmental controls on the sedimentary distributions of the HBIs from R. setigera may only be possible once such factors are established. 相似文献
107.
108.
Mutations in v-myb alter the differentiation of myelomonocytic cells transformed by the oncogene 总被引:22,自引:0,他引:22
Chick myelomonocytic cells transformed by the v-myb oncogene-containing viruses E26 and AMV differ in that the former resemble myeloblasts and express the v-myb-regulated granulocyte-specific mim-1 gene, while the latter resemble monoblasts and are mim-1 negative. We constructed a series of AMV-E26 chimeras and localized the critical differences between these viruses to three point mutations within the second repeat of the v-myb DNA binding domain. These three positions are altered in the v-myb protein of AMV relative to the proteins encoded by c-myb or E26 v-myb. Back mutating AMV v-myb at any of these three sites restored the oncogene's ability to activate the mim-1 gene. Surprisingly, two of these changes led to the transformation, in vitro and in vivo, of cells having a promyelocyte-like phenotype. These results indicate that different forms of v-myb impose alternate phenotypes of differentiation on transformed myeloid cells, probably by regulating unique sets of differentiation-specific genes. 相似文献
109.
110.