全文获取类型
收费全文 | 808篇 |
免费 | 72篇 |
专业分类
880篇 |
出版年
2021年 | 14篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 10篇 |
2016年 | 14篇 |
2015年 | 28篇 |
2014年 | 29篇 |
2013年 | 35篇 |
2012年 | 43篇 |
2011年 | 48篇 |
2010年 | 35篇 |
2009年 | 32篇 |
2008年 | 31篇 |
2007年 | 42篇 |
2006年 | 33篇 |
2005年 | 35篇 |
2004年 | 31篇 |
2003年 | 33篇 |
2002年 | 24篇 |
2001年 | 27篇 |
2000年 | 18篇 |
1999年 | 28篇 |
1998年 | 17篇 |
1997年 | 13篇 |
1996年 | 11篇 |
1995年 | 12篇 |
1994年 | 10篇 |
1993年 | 14篇 |
1992年 | 9篇 |
1991年 | 21篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1976年 | 7篇 |
1975年 | 6篇 |
1974年 | 8篇 |
1973年 | 9篇 |
1972年 | 5篇 |
1971年 | 6篇 |
1969年 | 4篇 |
1967年 | 4篇 |
排序方式: 共有880条查询结果,搜索用时 15 毫秒
831.
832.
833.
FACL4, a New Gene Encoding Long-Chain Acyl-CoA Synthetase 4, Is Deleted in a Family with Alport Syndrome, Elliptocytosis, and Mental Retardation 总被引:1,自引:0,他引:1
834.
Anna Godhe Jenny Egardt David Kleinhans Lisa Sundqvist Robinson Hordoir Per R. Jonsson 《Proceedings. Biological sciences / The Royal Society》2013,280(1773)
We investigated the gene flow of the common marine diatom, Skeletonema marinoi, in Scandinavian waters and tested the null hypothesis of panmixia. Sediment samples were collected from the Danish Straits, Kattegat and Skagerrak. Individual strains were established from germinated resting stages. A total of 350 individuals were genotyped by eight microsatellite markers. Conventional F-statistics showed significant differentiation between the samples. We therefore investigated whether the genetic structure could be explained using genetic models based on isolation by distance (IBD) or by oceanographic connectivity. Patterns of oceanographic circulation are seasonally dependent and therefore we estimated how well local oceanographic connectivity explains gene flow month by month. We found no significant relationship between genetic differentiation and geographical distance. Instead, the genetic structure of this dominant marine primary producer is best explained by local oceanographic connectivity promoting gene flow in a primarily south to north direction throughout the year. Oceanographic data were consistent with the significant FST values between several pairs of samples. Because even a small amount of genetic exchange prevents the accumulation of genetic differences in F-statistics, we hypothesize that local retention at each sample site, possibly as resting stages, is an important component in explaining the observed genetic structure. 相似文献
835.
NIR spectroscopy,mineral nitrogen analysis and soil incubations for the prediction of crop uptake of nitrogen during the growing season 总被引:2,自引:2,他引:0
To predict the amount of N taken up in above-ground plant parts during the growing season, initial mineral soil N, a soil
incubation method, soil organic matter and NIR data were compared as predictors. Soil samples were taken from 15 plots cropped
with winter wheat on a farm in south-western Sweden. The plots were not fertilized with N during the 1997 growing season.
N contents in above-ground plant parts were measured in mid-June and in mid-August. All methods were capable of predicting
the crop uptake of N reasonably well. NIR data gave at least as good predictions as the best traditional method, initial soil
NO3-N. The most important wavelengths, around 1400 and 1700 nm, and above 2000 nm, coincide with the wavelengths reported earlier
to be important for the prediction of soil organic matter. However, the data suggest that other soil components influencing
mineralization are also spectrally active. Since very few samples were taken, the studies need to be extended in order to
be able to use the method in practice. It is recommended that further studies be instigated for the possibility of using the
same NIR calibration over several years and to clarify the spatial regions that the calibrations can cover.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
836.
To identify thresholds in the relationship between the number of species in viable populations and habitat availability is useful for nature conservation. However, to obtain such empirical data may be extremely laborious. Many saproxylic (wood-living) species are under threat because there is little coarse woody debris (CWD) in managed forests. Based on computer simulations of CWD dynamics, and information about the substrate requirements of red-listed saproxylic species, we conclude that it is unlikely that any specific quantity of CWD can be defined as the extinction threshold for large numbers of species, since different species are specialists in utilising different types of CWD. In our analysis, we identified a curvilinear relationship between total CWD and the number of red-listed species in viable populations, even assuming that there were sharp extinction thresholds for individual species. Thus, it is highly unlikely that it will ever be possible to identify simple targets for maintenance of CWD based on extinction thresholds for the whole community of saproxylic species. Instead other strategies are necessary when formulating conservation targets. 相似文献
837.
838.
L. Anders Nilsson Lars Jonsson Lydia Rason Emile Randrianjohany 《Nordic Journal of Botany》1986,6(4):411-422
Interactions between the terrestrial endemic Cymbidiella flabellata (Thou.) Rolfe (Orchidaceae) and flower-visiting insects were observed in a marsh on the east coast of Madagascar. The plant acted by deceit. Two large sphecid wasp species, females of Sceliphron fuscum Klug and males of Sphex torridus Sm. (Hymenoptera, Sphecidae), made frequent visits to the showy, ca. 5 cm wide, nectarless and fragrant flowers. During a visit the wasps alighted on the large, hinged labellum which they depressed while forcing their heads towards the basal cavity below the column. When the wasps withdrew they pressed powerfully down on the labellum and brushed their heads backwards against the floral sexual organs removing the pollinarium with the frons or vertex – from which position pollination took place. The wasps on average visited only two flowers consecutively and about 55% of the flowers in the orchid population received visits. About six times more pollinaria were dispersed by pollen vectors than reached stigmas and a high proportion of the flowers were aborted due to lack of pollination. Data suggest that S. fuscum , a spider hunting and mud-daubing species, is a principal pollinator. C. flabellata is interpreted as playing the role of a generalized food-flower mimic which is specialized to moist habitats where females of S. fuscum collect mud for their nests. 相似文献
839.
Luca Mazzurana Paulo Czarnewski Viktor Jonsson Leif Wigge Markus Ringnr Teresa C. Williams Avinash Ravindran sa K. Bjrklund Jesper Sfholm Gunnar Nilsson Sven-Erik Dahln Ann-Charlotte Orre Mamdoh Al-Ameri Charlotte Hg Charlotte Hedin Sylwester Szczegielniak Sven Almer Jenny Mjsberg 《Cell research》2021,31(5):554
840.
Quantification of viral infectious units is traditionally measured by methods based on forming plaques in semisolid media (PFU) or endpoint dilution of a virus-containing solution (TCID50 ), methods that are laborious, time-consuming and take on average 3–7 days to carry out. Quantitative real-time PCR is an established method to quantify nucleic acids at high accuracy and reproducibility, routinely used for virus detection and identification. In the present study, a procedure was developed using a two-step real-time PCR and the SYBR Green detection method to study whether there are correlations between TCID50 /ml, PFU/ml and Ct values generated by real-time PCR enabling rapid and efficient calculation of titer equivalents when working with viruses in the research laboratory. In addition, an external standard with known concentrations was included using in vitro transcribed viral RNA, thus allowing the calculation of the amount of RNA copies needed for various applications (i.e. per plaque or TCID50 ).The results show that there is a correlation between the three quantification methods covering a wide range of concentration of viruses. Furthermore, a general regression line between TCID50 and Ct values was obtained for all viruses included in the study, which enabled recording titer equivalents using real-time PCR. Finally, by including an external standard, the amount of RNA genomes generating one TCID50 or PFU for each enterovirus serotype included was determined. 相似文献