全文获取类型
收费全文 | 525篇 |
免费 | 51篇 |
出版年
2023年 | 2篇 |
2021年 | 8篇 |
2020年 | 3篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 9篇 |
2016年 | 21篇 |
2015年 | 30篇 |
2014年 | 32篇 |
2013年 | 32篇 |
2012年 | 35篇 |
2011年 | 38篇 |
2010年 | 39篇 |
2009年 | 18篇 |
2008年 | 25篇 |
2007年 | 21篇 |
2006年 | 36篇 |
2005年 | 17篇 |
2004年 | 25篇 |
2003年 | 27篇 |
2002年 | 21篇 |
2001年 | 7篇 |
2000年 | 15篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1979年 | 2篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1965年 | 2篇 |
1964年 | 2篇 |
1960年 | 2篇 |
1949年 | 1篇 |
1926年 | 1篇 |
排序方式: 共有576条查询结果,搜索用时 62 毫秒
11.
Acid atmospheric deposition can cause losses of metal nutrients from the organic layer of a soil. The size of these losses
depend on the sizes of the different pools in which the metals are present, as these pools differ in mobility. The metal pools
in an organic soil layer of a Douglas fir forest in the Netherlands subjected to acid deposition were determined by means
of extractions and percolations. Na was mainly dissolved and exchangeably adsorbed, K dissolved, exchangeably adsorbed and
present in the soil microbial biomass, Ca exchangeably adsorbed and present in organic precipitates, Mg exchangeably adsorbed
and present in the soil biomass, and Mn exchangeably adsorbed and present in inorganic precipitates. The main part of the
metals was exchangeably adsorbed. The adsorption affinity increased in the order Na < K < Mg < Mn ≈ Ca. The vertical distribution
of the metals in the organic layer showed that all metals were continuously lost from the organic layer. The differences between
the metals in retention and vertical distribution patterns were in agreement with their differences in deposition rate, pool
distribution, and exchange affinity. Since the metals were mainly exchangeably adsorbed, and the acidifying cations dominated
the atmospheric deposition, acid deposition and cation exchange must be processes that strongly affect the losses of metals
from this organic soil layer. R F Huettl Section editor 相似文献
12.
Black SJ Goding JW Gutman GA Herzenberg LA Loken MR Osborne BA van der Loo W Warner NL 《Immunogenetics》1978,7(1):213-230
Murine antisera raised against allogeneic lymphoid cells often contain antibodies to IgM allotypes. Rarely, allotypic antibodies to IgM have been found after immunization withB. pertussis anti-B. pertussis conjugates. Using both types of antibodies, we have defined a new constant-region locus for both secreted and membrane-bound chains. This locus,Ig-6, is closely linked to the previously described H-chain constant-region loci (Ig-1 throughIg-5) and is subject to allelic exclusion. We have identified three alleles and four antigenic specificities ofIg-6.Authors listed alphabetically 相似文献
13.
14.
15.
Sabrina Camargo Maik Riedl Celia Anteneodo Jürgen Kurths Thomas Penzel Niels Wessel 《PloS one》2014,9(9)
Sleep disorders are a major risk factor for cardiovascular diseases. Sleep apnea is the most common sleep disturbance and its detection relies on a polysomnography, i.e., a combination of several medical examinations performed during a monitored sleep night. In order to detect occurrences of sleep apnea without the need of combined recordings, we focus our efforts on extracting a quantifier related to the events of sleep apnea from a cardiovascular time series, namely systolic blood pressure (SBP). Physiologic time series are generally highly nonstationary and entrap the application of conventional tools that require a stationary condition. In our study, data nonstationarities are uncovered by a segmentation procedure which splits the signal into stationary patches, providing local quantities such as mean and variance of the SBP signal in each stationary patch, as well as its duration . We analysed the data of 26 apneic diagnosed individuals, divided into hypertensive and normotensive groups, and compared the results with those of a control group. From the segmentation procedure, we identified that the average duration , as well as the average variance , are correlated to the apnea-hypoapnea index (AHI), previously obtained by polysomnographic exams. Moreover, our results unveil an oscillatory pattern in apneic subjects, whose amplitude is also correlated with AHI. All these quantities allow to separate apneic individuals, with an accuracy of at least . Therefore, they provide alternative criteria to detect sleep apnea based on a single time series, the systolic blood pressure. 相似文献
16.
The ability of the carcinogen, N-acetoxy-2-acetylaminofluorene (N-AcO-AAF), to induce mutations to azaguanine resistance in diploid human cells was quantitatively investigated and shown to be dose-dependent. The 8-azaguanine (AG) resistance was shown to be heritable in the absence of mutagen or selective agent and the cells of the mutant clones were shown to retain normal sensitivity to N-AcO-AAF. 相似文献
17.
18.
Craig R. Jackson Thomas Maddox Franco P. Mbise Brd G. Stokke Jerrold L. Belant Kjetil Bevanger Sarah M. Durant Robert Fyumagwa Peter S. Ranke Eivin Rskaft Roel May Frode Fossy 《Ecology and evolution》2020,10(13):6769-6774
Carrion represents an unpredictable and widely distributed primary food source for vultures and other avian scavengers. Avian scavengers in African savanna ecosystems are reported to rely exclusively on visual stimuli to locate carcasses. However, carnivores’ predation of large mammalian herbivores and subsequent competition for access to the carcass can result in considerable noise, often audible over long distances and for prolonged periods. Vultures and other avian scavengers may therefore detect and respond to these auditory cues, as do the mammalian carnivores alongside which vultures have coevolved, but this has not been investigated to date. Working in the Serengeti ecosystem, Tanzania, we used diurnal auditory broadcasts to simulate predation and competitive carnivore feeding interactions. Based on the current understanding of avian scavenger ecology, we hypothesized that avian responses to call‐in stations would be evoked exclusively by visual, rather than auditory, cues. We therefore predicted that (a) the arrival of avian scavengers at call‐in stations should be preceded and facilitated by mammalian carnivores and that (b) the arrival of avian scavengers would be positively correlated with the number of mammalian scavengers present, which would increase detectability. We recorded 482 birds during 122 separate playback events. In 22% of these instances, avian scavengers arrived first, ruling out responses based exclusively on visual observations of mammalian carnivores, thereby contradicting our first prediction. Furthermore, the first avian arrivals at survey sessions were inversely related to the number of hyenas and jackals present, contradicting our second prediction. Since no bait or carcasses were used during the experiments, these responses are indicative of the birds’ ability to detect and respond to audio stimuli. Our findings challenge the current consensus of sensory perception and foraging in these species and provide evidence that avian scavengers have the ability to use sound to locate food resources. 相似文献
19.
Julien Cucherousset Line E. Sundt-Hansen Mathieu Buoro Libor Závorka Rémy Lassus Knut A. E. Bækkelie Ian A. Fleming Björn Thrandur Björnsson Jörgen I. Johnsson Kjetil Hindar 《Journal of fish biology》2021,99(6):1978-1989
Use of fast-growing domesticated and/or genetically modified strains of fish is becoming increasingly common in aquaculture, increasing the likelihood of deliberate or accidental introductions into the wild. To date, their ecological impacts on ecosystems remain to be quantified. Here, using a controlled phenotype manipulation by implanting growth hormone in juvenile Atlantic salmon (Salmo salar), we found that growth-enhanced fish display changes in several phenotypic traits known to be important for ecosystem functioning, such as habitat use, morphology and excretion rate. Furthermore, these phenotypic changes were associated with significant impacts on the invertebrate community and key stream ecosystem functions such as primary production and leaf-litter decomposition. These findings provide novel evidence that introductions of growth-enhanced fish into the wild can affect the functioning of natural ecosystems and represent a form of intraspecific invasion. Consequently, environmental impact assessments of growth-enhanced organisms need to explicitly consider ecosystem-level effects. 相似文献
20.
Diversity in the fertilization envelopes of echinoderms 总被引:1,自引:0,他引:1