全文获取类型
收费全文 | 6251篇 |
免费 | 523篇 |
国内免费 | 5篇 |
出版年
2023年 | 25篇 |
2022年 | 17篇 |
2021年 | 87篇 |
2020年 | 73篇 |
2019年 | 82篇 |
2018年 | 103篇 |
2017年 | 126篇 |
2016年 | 163篇 |
2015年 | 281篇 |
2014年 | 388篇 |
2013年 | 429篇 |
2012年 | 547篇 |
2011年 | 483篇 |
2010年 | 322篇 |
2009年 | 281篇 |
2008年 | 333篇 |
2007年 | 367篇 |
2006年 | 345篇 |
2005年 | 325篇 |
2004年 | 303篇 |
2003年 | 290篇 |
2002年 | 273篇 |
2001年 | 62篇 |
2000年 | 51篇 |
1999年 | 54篇 |
1998年 | 74篇 |
1997年 | 55篇 |
1996年 | 56篇 |
1995年 | 45篇 |
1994年 | 57篇 |
1993年 | 47篇 |
1992年 | 67篇 |
1991年 | 40篇 |
1990年 | 44篇 |
1989年 | 42篇 |
1988年 | 28篇 |
1987年 | 33篇 |
1986年 | 18篇 |
1985年 | 27篇 |
1984年 | 39篇 |
1983年 | 31篇 |
1982年 | 28篇 |
1981年 | 33篇 |
1980年 | 18篇 |
1978年 | 15篇 |
1977年 | 13篇 |
1976年 | 18篇 |
1975年 | 13篇 |
1974年 | 23篇 |
1972年 | 18篇 |
排序方式: 共有6779条查询结果,搜索用时 109 毫秒
1.
2.
The expression of the genes for two types of myrosinase (EC 3.2.3.1), designated MA and MB, during embryo and seedling development was investigated in Sinapis alba L. by in-situ and RNA slot-blot analyses. The expression of MA and MB genes followed similar temporal profiles during embryogenesis, but MB mRNA was present in considerably higher amounts than MA mRNA. In the embryo, both MA and MB genes are activated in cotyledons and axis. The MB genes are preferentially expressed in the cotyledons whereas MA genes are preferentially expressed in the axis. In the developing seedling, MA mRNA was not present in the organs investigated. By contrast, MB mRNA was found in appreciable amounts in hypocotyls, cotyledons and developing leaves. The MB genes seem to be activated preferentially in tissues undergoing rapid cell division and — or cell expansion.Abbreviations DAP
days after pollination
- MA, MB
A type, B type myrosinases in Sinapis alba
Anna-Stina Höglund (Uppsala Genetic Center) is gratefully acknowledged for valuable discussion, Anders Gobl (Department of Immunology, Uppsala University) for kindly advice with the labeling of probes and Qingzhu Zhai (Department of Pharmaceutical Biosciences, Uppsala University) for help with seed harvest. This work was supported by grants from the Swedish Research Council for Forestry and Agriculture. 相似文献
3.
Nanna Brink Scholz Lars Bolund Mette Nyegaard Louise Faaborg Mette Warming J?rgensen Helle Lund Isa Niemann Lone Sunde 《PloS one》2015,10(11)
Hydatidiform moles (HMs) are abnormal human pregnancies with vesicular chorionic villi, imposing two clinical challenges; miscarriage and a risk of gestational trophoblastic neoplasia (GTN). The parental type of most HMs are either diandric diploid (PP) or diandric triploid (PPM). We consecutively collected 154 triploid or near-triploid samples from conceptuses with vesicular chorionic villi. We used analysis of DNA markers and/or methylation sensitive-MLPA and collected data from registries and patients records. We performed whole genome SNP analysis of one case of twinning (PP+PM).In all 154 triploids or near-triploids we found two different paternal contributions to the genome (P1P2M). The ratios between the sex chromosomal constitutions XXX, XXY, and XYY were 5.7: 6.9: 1.0. No cases of GTN were observed. Our results corroborate that all triploid human conceptuses with vesicular chorionic villi have the parental type P1P2M. The sex chromosomal ratios suggest approximately equal frequencies of meiosis I and meiosis II errors with selection against the XYY conceptuses or a combination of dispermy, non-disjunction in meiosis I and meiosis II and selection against XYY conceptuses. Although single cases of GTN after a triploid HM have been reported, the results of this study combined with data from previous prospective studies estimate the risk of GTN after a triploid mole to 0% (95% CI: 0–1,4%). 相似文献
4.
Thomas Arn Hansen Helena Fridholm Tobias Guldberg Fr?slev Kristín Rós Kjartansdóttir Eske Willerslev Lars Peter Nielsen Anders Johannes Hansen 《PloS one》2015,10(11)
Rattus norvegicus (R. norvegicus) are ubiquitous and their presence has several effects on the human populations in our urban areas on a global scale. Both historically and presently, this close interaction has facilitated the dissemination of many pathogens to humans, making screening for potentially zoonotic and emerging viruses in rats highly relevant. We have investigated faecal samples from R. norvegicus collected from urban areas using a protocol based on metagenomic enrichment of circular DNA genomes and subsequent sequencing. We found a new type of papillomavirus, with a L1 region 82% identical to that of the known R. norvegicus Papillomavirus 2. Additionally, we found 20 different circular replication associated protein (Rep)-encoding single stranded DNA (CRESS-DNA) virus-like genomes, one of which has homology to the replication-associated gene of Beak and feather disease virus. Papillomaviruses are a group of viruses known for their carcinogenic potential, and although they are known to infect several different vertebrates, they are mainly studied and characterised in humans. CRESS-DNA viruses are found in many different environments and tissue types. Both papillomaviruses and CRESS-DNA viruses are known to have pathogenic potential and screening for novel and known viruses in R. norvegicus could help identify viruses with pathogenic potential. 相似文献
5.
Denise Risch Nicholas J. Gales Jason Gedamke Lars Kindermann Douglas P. Nowacek Andrew J. Read Ursula Siebert Ilse C. Van Opzeeland Sofie M. Van Parijs Ari S. Friedlaender 《Biology letters》2014,10(4)
For decades, the bio-duck sound has been recorded in the Southern Ocean, but the animal producing it has remained a mystery. Heard mainly during austral winter in the Southern Ocean, this ubiquitous sound has been recorded in Antarctic waters and contemporaneously off the Australian west coast. Here, we present conclusive evidence that the bio-duck sound is produced by Antarctic minke whales (Balaenoptera bonaerensis). We analysed data from multi-sensor acoustic recording tags that included intense bio-duck sounds as well as singular downsweeps that have previously been attributed to this species. This finding allows the interpretation of a wealth of long-term acoustic recordings for this previously acoustically concealed species, which will improve our understanding of the distribution, abundance and behaviour of Antarctic minke whales. This is critical information for a species that inhabits a difficult to access sea-ice environment that is changing rapidly in some regions and has been the subject of contentious lethal sampling efforts and ongoing international legal action. 相似文献
6.
The transthyretin-related protein family. 总被引:6,自引:0,他引:6
Therese Eneqvist Erik Lundberg Lars Nilsson Ruben Abagyan A Elisabeth Sauer-Eriksson 《European journal of biochemistry》2003,270(3):518-532
A number of proteins related to the homotetrameric transport protein transthyretin (TTR) forms a highly conserved protein family, which we present in an integrated analysis of data from different sources combined with an initial biochemical characterization. Homologues of the transthyretin-related protein (TRP) can be found in a wide range of species including bacteria, plants and animals, whereas transthyretins have so far only been identified in vertebrates. A multiple sequence alignment of 49 TRP sequences from 47 species to TTR suggests that the tertiary and quaternary features of the three-dimensional structure are most likely preserved. Interestingly, while some of the TRP orthologues show as little as 30% identity, the residues at the putative ligand-binding site are almost entirely conserved. RT/PCR analysis in Caenorhabditis elegans confirms that one TRP gene is transcribed, spliced and predominantly expressed in the worm, which suggests that at least one of the two C. elegans TRP genes encodes a functional protein. We used double-stranded RNA-mediated interference techniques in order to determine the loss-of-function phenotype for the two TRP genes in C. elegans but detected no apparent phenotype. The cloning and initial characterization of purified TRP from Escherichia coli reveals that, while still forming a homotetramer, this protein does not recognize thyroid hormones that are the natural ligands of TTR. The ligand for TRP is not known; however, genomic data support a functional role involving purine catabolism especially linked to urate oxidase (uricase) activity. 相似文献
7.
In the Okavango Delta 98–99% of the water from inflow and rainfall is lost to the atmosphere through evapotranspiration. As
a consequence 94% of inflowing solutes are retained within the Delta landscape. This process might be expected to result in
an entirely saline environment, but that is not the case: the surface waters have very low salinity, supporting a typical
freshwater biota. It has been deduced that the numerous islands in the Delta (about 150,000 within an area of 13,500 km2) have been formed through evapotransporative concentration in the groundwater, of infiltrating solutes, followed by precipitation
and volume increase. Evidence of this is the large amount of calcrete in island soils. These islands of 3–10 m thickness with
clayey soils are underlain by fine Kalahari sand to a depth of 200–300 m, which also indicates that they are formed through
surface processes. The infiltration rate of surface water from floodplains and streams into islands is very high, and is predominantly
a lateral process that is unidirectional. Evapotranspiration in the riparian woodland zone cause the ground-waters in the
central area of islands—with halophyte grasslands—to have very high salinities. By use of chloride as a conservative element
the concentration factor between central island groundwater and surface water is calculated to be 500–1,000. This groundwater
is depleted of calcium and magnesium supporting the early deductions that these elements have precipitated as calcrete. There
is also a large depletion of silicate and potassium that probably have precipitated as well forming the clayey soils typical
of the islands. The central island groundwater is dominated by sodium, bicarbonate and dissolved organic matter. The gradual
increase of salinity here causes a periodic let off of this water through a density-driven process to deeper layers. This
process together with island growth through precipitation of solutes are the two major sink processes of inflowing solutes
and explains why the Okavango Delta is at present a freshwater system. The whole island complex is calculated to be 100,000–400,000 years
old while some intensely studied islands may be younger: 80,000–240,000 years. The discrepancy is explained by a biassed selection
of islands currently in flooded areas with better growth conditions. The uniqueness of the Okavango Delta and ideas for future
research are discussed. 相似文献
8.
9.
Scytosiphon complanatus from Greenland was grown under long-day conditions on a temperature-gradient device with a temperature range from 5.4°C to 31.8°C. Growth was optimal between 16.0°C and 20.9°C. In a four week experimental period at 5.4°C and 7.5°C growth was slow and not measurable. The inoculated germlings died at temperatures between 24.0°C and 27.5°C. Under all temperatures the prostrate systems, knot filaments or ralfsioid thalli, as well as the parenchymatous macrothalli remained sterile during the experimental period. Prolongation of the growth period showed that formation of swarmers was prevented at temperatures above 18.6°C. The geographic distribution is discussed in relation to these results. 相似文献
10.
The occurrence of bikunin and ·1-microglobuli n was investigated in human ovary and Fallopian tubes. Bikunin and ·1-microglobulin are transcribed in the liver from a common gene. Bikunin immunoreactivity was detected in the zona pellucida.
A positive reaction for bikunin was also observed in connective tissue of the oviduct. In addition, mast cells showed a more
intense posi tive reaction than the surrounding connective tissue. Specific displaceable ·1-microglobulin immunoreactivity was revealed in the zona pellucida. The data suggest that bikunin and ·1- microglobulin are trapped in the zona pellucida.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献