全文获取类型
收费全文 | 745篇 |
免费 | 119篇 |
国内免费 | 17篇 |
出版年
2021年 | 11篇 |
2020年 | 7篇 |
2016年 | 13篇 |
2015年 | 19篇 |
2014年 | 18篇 |
2013年 | 30篇 |
2012年 | 29篇 |
2011年 | 25篇 |
2010年 | 18篇 |
2009年 | 24篇 |
2008年 | 15篇 |
2007年 | 32篇 |
2006年 | 21篇 |
2005年 | 27篇 |
2004年 | 15篇 |
2003年 | 22篇 |
2002年 | 17篇 |
2001年 | 29篇 |
2000年 | 36篇 |
1999年 | 21篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 14篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 21篇 |
1985年 | 23篇 |
1984年 | 14篇 |
1983年 | 17篇 |
1982年 | 16篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 17篇 |
1976年 | 14篇 |
1975年 | 11篇 |
1974年 | 14篇 |
1973年 | 12篇 |
1971年 | 12篇 |
1968年 | 7篇 |
1966年 | 9篇 |
1965年 | 6篇 |
排序方式: 共有881条查询结果,搜索用时 15 毫秒
51.
A simple method with poliovirus as the model was developed for recovering human enteric viruses from aerosols. Filterite filters (pore size, 0.45 micron; Filterite Corp., Timonium, Md.) moistened with glycine buffer (pH 3.5) were used for adsorbing the aerosolized virus. No virus passed the filter, even with air flow rates of 100 liters/min. Virus recovery from the filter was achieved by rapid elution with 800 ml of glycine buffer, pH 10. The virus in the primary eluate was reconcentrated by adjusting the pH to 3.5, adding AlCl3 to 0.0005 M, collecting the virus on a 0.25-micron-pore Filerite disk (diameter, 25 mm) and and eluting with 6 ml of buffer, pH 10. With this method, virus could be detected regularly in aerosols produced by flushing when 3 X 10(8) PFU of poliovirus were present in the toilet bowl. Poliovirus-containing fecal material from two of four infants who had recently received oral polio vaccine also yielded virus in the aerosols when feces containing 2.4 X 10(7) to 4.5 X 10(7) PFU of virus had been added to the toilet bowl. Persons infected with a variety of natural enteric viruses are known to excrete this amount of virus in their daily stools. 相似文献
52.
53.
54.
55.
Ken Chen Nicholas E Navin Yong Wang Heather K Schmidt John W Wallis Beifang Niu Xian Fan Hao Zhao Michael D McLellan Katherine A Hoadley Elaine R Mardis Timothy J Ley Charles M Perou Richard K Wilson Li Ding 《Genome biology》2013,14(8):R87
Producing gene fusions through genomic structural rearrangements is a major mechanism for tumor evolution. Therefore, accurately detecting gene fusions and the originating rearrangements is of great importance for personalized cancer diagnosis and targeted therapy. We present a tool, BreakTrans, that systematically maps predicted gene fusions to structural rearrangements. Thus, BreakTrans not only validates both types of predictions, but also provides mechanistic interpretations. BreakTrans effectively validates known fusions and discovers novel events in a breast cancer cell line. Applying BreakTrans to 43 breast cancer samples in The Cancer Genome Atlas identifies 90 genomically validated gene fusions. BreakTrans is available at http://bioinformatics.mdanderson.org/main/BreakTrans 相似文献
56.
SA Carrasco 《New Zealand journal of zoology.》2013,40(1):32-45
This study combined morphological and morphometric information on egg clutches, egg capsules and paralarvae of two sympatric coastal octopuses from New Zealand waters, Octopus huttoni and Pinnoctopus cordiformis, to provide species-specific traits to identify their early life stages obtained from field surveys. Eggs of O. huttoni (2.5 mm length; 1 mm width) were entwined with one another forming strings that ranged from 11 to 25.8 mm in length. Eggs of P. cordiformis (6.4 mm length; 1.5 mm width) were significantly bigger than those of O. huttoni and were grouped in small clusters of about seven eggs. Paralarvae O. huttoni and P. cordiformis differed in hatching size (1.4 mm versus 3.1 mm mantle length), number of suckers per arm (four versus eight), number of lamellae per outer demibranch (five versus ten) and arrangements of chromatophores in the body surface (29 to 59 versus 91 to 179), respectively. The morphological traits described in hatchlings from the laboratory allowed comparisons with field-collected paralarvae, suggesting that such characters were reliable species-specific patterns to enable a consistent differentiation between the early life stages of these two sympatric species, even in the absence of the brooding female. 相似文献
57.
Hannah R. Windley Ian R. Wallis Jane L. DeGabriel Ben D. Moore Christopher N. Johnson William J. Foley 《Oecologia》2013,173(1):203-212
Estimating the nutritional value of a herbivore’s diet is difficult because it requires knowing what the animal eats, the relative quality of each component and how these components interact in relation to animal physiology. Current methods are cumbersome and rely on many assumptions that are hard to evaluate. We describe a new method for estimating relative diet quality directly from faeces that avoids the problems inherent in other methods. We combine this method with near infrared reflectance spectroscopy (NIRS) to analyse many samples and thus provide a technique with immense value in ecological studies. The method stems from the correlation between the concentrations of dietary and faecal nitrogen in herbivores eating a tannin-free diet, but a weaker relationship in browsers that ingest substantial amounts of tannins, which form complexes with proteins. These complexes reduce the availability of nitrogen and may increase faecal nitrogen concentrations. Using the tannin-binding compound, polyethylene glycol, we showed that tannin-bound nitrogen is a significant and variable part of faecal nitrogen in wild common brushtail possums (Trichosurus vulpecula). We developed a technique to measure faecal available nitrogen and found that it predicted the reproductive success of female brushtail possums in northern Australia. Faecal available nitrogen combined with NIRS provides a powerful tool for estimating the relative nutritional value of the diets of browsing herbivores in many ecological systems. It is a better indicator of diet quality than other commonly used single-nutrient measures such as faecal nitrogen and foliage analysis paired with observed feeding behaviour. 相似文献
58.
Camille Turlure Viktoriia Radchuk Michel Baguette Mark Meijrink Arnold van den Burg Michiel Wallis De Vries Gert‐Jan van Duinen 《Ecology and evolution》2013,3(2):244-254
The butterfly Boloria aquilonaris is a specialist of oligotrophic ecosystems. Population viability analysis predicted the species to be stable in Belgium and to collapse in the Netherlands with reduced host plant quality expected to drive species decline in the latter. We tested this hypothesis by rearing B. aquilonaris caterpillars from Belgian and Dutch sites on host plants (the cranberry, Vaccinium oxycoccos). Dutch plant quality was lower than Belgian one conferring lower caterpillar growth rate and survival. Reintroduction and/or supplementation may be necessary to ensure the viability of the species in the Netherlands, but some traits may have been selected solely in Dutch caterpillars to cope with gradual changes in host plant quality. To test this hypothesis, the performance of Belgian and Dutch caterpillars fed with plants from both countries were compared. Dutch caterpillars performed well on both plant qualities, whereas Belgian caterpillars could not switch to lower quality plants. This can be considered as an environmentally induced plastic response of caterpillars and/or a local adaptation to plant quality, which precludes the use of Belgian individuals as a unique solution for strengthening Dutch populations. More generally, these results stress that the relevance of local adaptation in selecting source populations for relocation may be as important as restoring habitat quality. 相似文献
59.
60.
Endothelial progenitor cells (EPC) participate in revascularization and angiogenesis. EPC can be cultured in vitro from mononuclear cells of peripheral blood, umbilical cord blood or bone marrow; they also can be transdifferentiated from mesenchymal stem cells (MSC). We isolated EPCs from Wharton's jelly (WJ) using two methods. The first method was by obtaining MSC from WJ and characterizing them by flow cytometry and their adipogenic and osteogenic differentiation, then applying endothelial growth differentiating media. The second method was by direct culture of cells derived from WJ into endothelial differentiating media. EPCs were characterized by morphology, Dil-LDL uptake/UEA-1 immunostaining and testing the expression of endothelial markers by flow cytometry and RT-PCR. We found that MSC derived from WJ differentiated into endothelial-like cells using simple culture conditions with endothelium induction agents in the medium. 相似文献