全文获取类型
收费全文 | 8947篇 |
免费 | 769篇 |
国内免费 | 1篇 |
出版年
2024年 | 12篇 |
2023年 | 39篇 |
2022年 | 109篇 |
2021年 | 228篇 |
2020年 | 113篇 |
2019年 | 152篇 |
2018年 | 188篇 |
2017年 | 161篇 |
2016年 | 291篇 |
2015年 | 469篇 |
2014年 | 508篇 |
2013年 | 546篇 |
2012年 | 775篇 |
2011年 | 736篇 |
2010年 | 460篇 |
2009年 | 423篇 |
2008年 | 569篇 |
2007年 | 570篇 |
2006年 | 531篇 |
2005年 | 535篇 |
2004年 | 491篇 |
2003年 | 457篇 |
2002年 | 429篇 |
2001年 | 73篇 |
2000年 | 50篇 |
1999年 | 104篇 |
1998年 | 111篇 |
1997年 | 71篇 |
1996年 | 57篇 |
1995年 | 58篇 |
1994年 | 47篇 |
1993年 | 51篇 |
1992年 | 40篇 |
1991年 | 31篇 |
1990年 | 38篇 |
1989年 | 26篇 |
1988年 | 28篇 |
1987年 | 18篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 18篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有9717条查询结果,搜索用时 31 毫秒
11.
12.
By enabling a tight control of cell excitation, optogenetics is a powerful approach to study the function of neurons and neural circuits. With its transparent body, a fully mapped nervous system, easily quantifiable behaviors and many available genetic tools, Caenorhabditis elegans is an extremely well-suited model to decipher the functioning logic of the nervous system with optogenetics. Our goal was to establish an efficient dual color optogenetic system for the independent excitation of different neurons in C. elegans. We combined two recently discovered channelrhodopsins: the red-light sensitive Chrimson from Chlamydomonas noctigama and the blue-light sensitive CoChR from Chloromonas oogama. Codon-optimized versions of Chrimson and CoChR were designed for C. elegans and expressed in different mechanosensory neurons. Freely moving animals produced robust behavioral responses to light stimuli of specific wavelengths. Since CoChR was five times more sensitive to blue light than the commonly used ChR2, we were able to use low blue light intensities producing no cross-activation of Chrimson. Thanks to these optogenetics tools, we revealed asymmetric cross-habituation effects between the gentle and harsh touch sensory motor pathways. Collectively, our results establish the Chrimson/CoChR pair as a potent tool for bimodal neural excitation in C. elegans and equip this genetic model organism for the next generation of in vivo optogenetic analyses. 相似文献
13.
Lisa Rizzetto Gloria Giovannini Michael Bromley Paul Bowyer Luigina Romani Duccio Cavalieri 《PloS one》2013,8(2)
For over a century microbiologists and immunologist have categorized microorganisms as pathogenic or non-pathogenic species or genera. This definition, clearly relevant at the strain and species level for most bacteria, where differences in virulence between strains of a particular species are well known, has never been probed at the strain level in fungal species. Here, we tested the immune reactivity and the pathogenic potential of a collection of strains from Aspergillus spp, a fungus that is generally considered pathogenic in immuno-compromised hosts. Our results show a wide strain-dependent variation of the immune response elicited indicating that different isolates possess diverse virulence and infectivity. Thus, the definition of markers of inflammation or pathogenicity cannot be generalized. The profound understanding of the molecular mechanisms subtending the different immune responses will result solely from the comparative study of strains with extremely diverse properties. 相似文献
14.
15.
Comparative phylogeography of two co‐distributed but ecologically distinct rainbowfishes of far‐northern Australia
下载免费PDF全文
![点击此处可从《Journal of Biogeography》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Andrew T. Mather Jeffrey O. Hanson Lisa C. Pope Cynthia Riginos 《Journal of Biogeography》2018,45(1):127-141
Aim
To test the influence of historical and contemporary environment in shaping the genetic diversity of freshwater fauna we contrast genetic structure in two co‐distributed, but ecologically distinct, rainbowfish; a habitat generalist (Melanotaenia splendida) and a habitat specialist (M. trifasciata).Location
Fishes were sampled from far northern Australia (Queensland and Northern Territory).Methods
We used sequence data from one mitochondrial gene and one nuclear gene to investigate patterns of genetic diversity in M. splendida and M. trifasciata to determine how differences in habitat preference and historical changes in drainage boundaries affected patterns of connectivity.Results
Melanotaenia splendida showed high levels of genetic diversity and little population structure across its range. In contrast, M. trifasciata showed high levels of population structure. Whereas phylogeographic patterns differed, both species showed a strong relationship between geographical distance and genetic differentiation between populations. Melanotaenia splendida showed a shallower relationship with geographical distance, and genetic differentiation was best explained by stream length and a lower scaled ocean distance (11.98 times coast length). For M. trifasciata, genetic differentiation was best explained by overwater distance between catchments and ocean distance scaled at 1.16 × 106 times coast length.Main conclusions
Connectivity of freshwater populations inhabiting regions periodically interconnected during glacial periods appears to have been affected by ecological differences between species. Species‐specific differences are epitomized here by the contrast between co‐distributed congeners with different habitat requirements: for the habitat generalist, M. splendida, there was evidence for greater historical genetic connectivity with oceans as a weaker barrier to gene exchange in contrast with the habitat specialist, M. trifasciata. 相似文献16.
17.
P. Mark Hogarth Margaret L. Hibbs Lisa Bonadonna Bernadette M. Scott Ewa Witort Geoffrey A. Pietersz Ian F. C. McKenzie 《Immunogenetics》1987,26(3):161-168
A cDNA clone encoding the mouse Ly-17+ Fc receptor for IgG, isolated from a myelomonocytic cell line, was sequenced and expression of mRNA and the functional FcR investigated. The receptor is a 301 amino acid transmembrane glycoprotein with two homologous extracellular domains that are also homologous to members of the Ig superfamily. The receptor has four sites of N-linked glycosylation and a long 94 amino acid cytoplasmic tail. Northern analysis, immune complex binding, and serological studies demonstrate that the receptor encoded by the cDNA clone binds mouse IgG1/2b and rabbit IgG complexes. 相似文献
18.
Characterization of phycoerythrin-containing Synechococcus spp. populations by immunofluorescence 总被引:1,自引:0,他引:1
Using an immunofluorescence assay developed to identify serogroups(i.e. clusters of strains labelled by one antiserum), the compositionof natural populations of phycoerythrin-containing Synechococcusspp. was examined. The 7803 (open ocean clone)-serogroup wasfound in most oceanic regions, but was most prevalent (up to85%) in tropical and subtropical waters during spring and summer.At coastal Long Island stations it was most abundant (up to65%) when water temperatures were >22°C. The seasonaland geographic distribution of the 7803-serogroup appeared tobe limited by water temperature. No consistent pattern was observedin the per cent composition with depth in the Sargasso Sea orat coastal to offshore stations in the North-west Atlantic Oceanor eastern tropical North Pacific Ocean. The 8016 (coastal clone)-serogroupwas abundant at coastal and estuarine stations off Long Island(up to 95 %) and its appearance was also correlated with warmwater temperature (> 15°C). However, this serogroup remaineda constant proportion of the population at the Long Island Soundstation during early winter months (through January) when abundanceof the 7803-serogroup was negligible. Owing to limited data,the oceanic distribution of the 8016-serogroup is not yet discernible.Lastly, antisera to the phycocyanin-dominant Synechococcus spp.clones failed to label any cells in samples collected from severaloceanic stations. Thus, these strains appear to be limited tocoastal and estuarine regions, which is consistent with predictionsfrom experiments comparing the photosynthetic performance ofthe phycoerythrin-dominant and phycocyanin-dominant clones.
1Present address: Department of Oceanography, University ofHawaii, Honolulu, HI 96822, USA 相似文献
19.
Mitochondrial DNA of the extinct quagga: Relatedness and extent of postmortem change 总被引:4,自引:0,他引:4
Russell G. Higuchi Lisa A. Wrischnik Elizabeth Oakes Matthew George Benton Tong Allan C. Wilson 《Journal of molecular evolution》1987,25(4):283-287
Sequences are reported for portions of two mitochondrial genes from a domestic horse and a plains zebra and compared to those published for a quagga and a mountain zebra. The extinct quagga and plains zebra sequences are identical at all silent sites, whereas the horse sequence differs from both of them by 11 silent substitutions. Postmortem changes in quagga DNA may account for the two coding substitutions between the quagga and plains zebra sequences. The hypothesis that the closest relative of the quagga is the domestic horse receives no support from these data. From the extent of sequence divergence between horse and zebra mitochondrial DNAs (mtDNAs), as well as from information about the fossil record, we estimate that the mean rate of mtDNA divergence in Equus is similar to that in other mammals, i.e., roughly 2% per million years. 相似文献
20.
George Harauz Lisa Borland Gunter F. Bahr Elmar Zeitler Marin van Heel 《Chromosoma》1987,95(5):366-374
A complete human metaphase chromosome has been reconstructed from a series of electron microscopical projections obtained by tilting the specimen stage at 3 degree intervals from –60 to +60 degrees. The reconstructed structure is about 3.0 m long, 1.6 m wide, and 0.8 m thick. The mass distribution was fairly homogeneous within the chromatids and neither a hollow nor a dense core was observed. The distribution and course of fibers observed are most consistent with a looping model of chromosome structure. 相似文献