全文获取类型
收费全文 | 619篇 |
免费 | 82篇 |
出版年
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 15篇 |
2017年 | 12篇 |
2016年 | 18篇 |
2015年 | 27篇 |
2014年 | 16篇 |
2013年 | 33篇 |
2012年 | 26篇 |
2011年 | 26篇 |
2010年 | 12篇 |
2009年 | 20篇 |
2008年 | 18篇 |
2007年 | 22篇 |
2006年 | 22篇 |
2005年 | 19篇 |
2004年 | 17篇 |
2003年 | 18篇 |
2002年 | 24篇 |
2001年 | 18篇 |
2000年 | 26篇 |
1999年 | 24篇 |
1998年 | 14篇 |
1997年 | 11篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1993年 | 5篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 21篇 |
1989年 | 12篇 |
1988年 | 17篇 |
1987年 | 7篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 11篇 |
1975年 | 6篇 |
1973年 | 6篇 |
1972年 | 4篇 |
1917年 | 3篇 |
1910年 | 3篇 |
排序方式: 共有701条查询结果,搜索用时 31 毫秒
81.
Peri E. Bolton Lee A. Rollins James Brazill-Boast Kimberley L. Maute Sarah Legge Jeremy J. Austin Simon C. Griffith 《Conservation Genetics》2018,19(3):737-754
Declines in population size can compromise the viability of populations by reducing the effective population size (Ne), which may result in loss of genetic diversity and inbreeding. Temporal population genetic data can be a powerful tool for testing the presence and severity of reductions in Ne. The Gouldian finch (Erythrura gouldiae) is a flagship for conservation of Australian monsoonal savanna species. This species underwent severe population declines in the twentieth century due to land use changes associated with European colonization. Microsatellite and mitochondrial genetic data from Gouldian finch samples sourced from natural history collections prior to land use changes were compared with contemporary samples to estimate the severity of decline in effective population size and to detect changes in gene flow. These data show that Gouldian finch decline was not as severe as some sources suggest, and that population genetic connectivity has not changed following land use changes in the twentieth century. Multiple estimators of current Ne using genetic data from consecutive years suggest the Gouldian finch Ne is likely between a few hundred and a few thousand individuals, with some estimates within the range considered of conservation concern. This work has identified the need to genetically characterize populations in Queensland, and to understand critical demographic parameters (e.g. lifespan) in the Gouldian finch. Understanding these factors is vital to further improve genetic estimates of population size, key to the formation of appropriate conservation management of this species. 相似文献
82.
Nicholas C. Coops Gregory J. M. Rickbeil Douglas K. Bolton Margaret E. Andrew Niels C. Brouwers 《Ecography》2018,41(7):1147-1160
Determining drivers of species richness is recognised as highly complex, involving many synergies and interactions. We examine the utility of newly available remote sensing representations of vegetation productivity and vegetation structure to examine drivers of species richness at continental and regional scales. We related richness estimates derived from stacked species distribution models for birds, mammals, amphibians, and reptiles to estimates of actual and potential evapotranspiration (AET and PET), forest structure, and forest productivity across Australia as a whole as well as by bioclimatic zones. We used structural equation modeling to partition correlations between climate energy and vegetation attributes and their subsequent associations with species richness. Continentally, vertebrate richness patterns were strongly related to patterns of energy availability. Richness of amphibians, mammals, and birds were positively associated with AET. However, reptile richness was most strongly associated with PET. Regionally, forest structure and productivity associations with bird, mammal, and amphibian richness were strongest. Again, reptile richness associated most strongly with PET. Our results suggest that a hierarchy of drivers of broad‐scale vertebrate richness patterns exist (reptiles excluded): 1) climate energy is most important at the continental scale; next, 2) vegetation productivity and vegetation structure are most important at the regional scale; except 3) at low extremes of climate energy when energy becomes limiting. 相似文献
83.
Mina?AryaEmail authorView authors OrcID profile Ali?Akbar?Mirzaei Abdol?Mahmood?Davarpanah Seyed?Masoud?Barakati Hossein?Atashi Abas?Mohsenzadeh Kim?Bolton 《Journal of molecular modeling》2018,24(2):47
Catalytic combustion of hydrocarbons is an important technology to produce energy. Compared to conventional flame combustion, the catalyst enables this process to operate at lower temperatures; hence, reducing the energy required for efficient combustion. The reaction and activation energies of direct combustion of hydrocarbons (CH?→?C?+?H) on a series of metal surfaces were investigated using density functional theory (DFT). The data obtained for the Ag, Au, Al, Cu, Rh, Pt, and Pd surfaces were used to investigate the validity of the Brønsted-Evans-Polanyi (BEP) and transition state scaling (TSS) relations for this reaction on these surfaces. These relations were found to be valid (R2?=?0.94 for the BEP correlation and R2?=?1.0 for the TSS correlation) and were therefore used to estimate the energetics of the combustion reaction on Ni, Co, and Fe surfaces. It was found that the estimated transition state and activation energies (ETS?=??69.70 eV and Ea?=?1.20 eV for Ni, ETS?=??87.93 eV and Ea?=?1.08 eV for Co and ETS?=??92.45 eV and Ea?=?0.83 eV for Fe) are in agreement with those obtained by DFT calculations (ETS?=??69.98 eV and Ea?=?1.23 eV for Ni, ETS?=??87.88 eV and Ea?=?1.08 eV for Co and ETS?=??92.57 eV and Ea?=?0.79 eV for Fe). Therefore, these relations can be used to predict energetics of this reaction on these surfaces without doing the time consuming transition state calculations. Also, the calculations show that the activation barrier for CH dissociation decreases in the order Ag ? Au ? Al ? Cu ? Pt ? Pd ? Ni?>?Co?>?Rh?>?Fe. 相似文献
84.
85.
Detection of Campylobacter jejuni and Campylobacter coli in Environmental Waters by PCR Enzyme-Linked Immunosorbent Assay 下载免费PDF全文
A. D. Sails F. J. Bolton A. J. Fox D. R. A. Wareing D. L. A. Greenway 《Applied microbiology》2002,68(3):1319-1324
A PCR enzyme-linked immunosorbent assay (ELISA) assay was applied to the detection of Campylobacter jejuni and Campylobacter coli in environmental water samples after enrichment culture. Bacterial cells were concentrated from 69 environmental water samples by using filtration, and the filtrates were cultured in Campylobacter blood-free broth. After enrichment culture, DNA was extracted from the samples by using a rapid-boiling method, and the DNA extracts were used as a template in a PCR ELISA assay. A total of 51 samples were positive by either PCR ELISA or culture; of these, 43 were found to be positive by PCR ELISA and 43 were found to be positive by culture. Overall, including positive and negative results, 59 samples were concordant in both methods. Several samples were positive in the PCR ELISA assay but were culture negative; therefore, this assay may be able to detect sublethally damaged or viable nonculturable forms of campylobacters. The method is rapid and sensitive, and it significantly reduces the time needed for the detection of these important pathogens by 2 to 3 days. 相似文献
86.
P. J. Ainsworth C. F. Bolton B. C. Murphy J. A. Stuart A. F. Hahn 《Human genetics》1998,103(2):242-244
X-linked Charcot-Marie-Tooth disease (CMTX) is a peripheral nerve disorder that has been linked to mutations in the connexin
32 gene (Cx32). These mutations have been shown to be genetically heterogeneous, though recurrences of specific mutations
in apparently unrelated families have been seen. The majority of mutations have been shown to be missense, resulting in non-conservative
amino acid changes. A few mutations resulting in a premature termination of protein translation, including both nonsense mutations
as well as frameshifting microdeletions, have been documented. We would like to report a deletion mutation that appears to
eliminate the entire coding sequence of the Cx32 gene, but which has been shown to segregate with a clinical phenotype not
unlike that seen in individuals with a less severe alteration of the Cx32 gene. The causes at a cellular level of the CMTX
phenotype are still not fully clear, though there has been speculation that these may involve a dominant negative effect where
the mutant connexin 32 suppresses the function of other connexins. Studies of kindreds such as this, where in CMTX-affected
males the Cx32 gene product is totally absent, will help us to better understand the molecular mechanisms underlying the clinical
phenotype associated with this disorder.
Received: 22 December 1997 / Accepted: 8 May 1998 相似文献
87.
88.
The available world literature (since Friedman''s and Levy''s comprehensive report in 1937) regarding actinomycosis of the central nervous system is reviewed. Only cases proved by culture were included in this analysis. A total of 17 cases was collected and an additional patient with this entity is described.The important differences between actinomycosis and nocardiosis are discussed. A definite diagnosis of actinomycosis was possible only when anaerobic cultures of cerebrospinal fluid or material obtained from a brain abscess yielded colonies of typical Actinomyces organisms. The characteristic result of infection of the brain by this fungus was abscess formation, and this occurred in all except one of the cases reviewed. Penicillin appears to be the drug of choice in treatment and, where possible, surgical excision of the cerebral abscess should be undertaken. 相似文献
89.
Assessing the effects of repeated handling on the physiology and condition of semi‐precocial nestlings 下载免费PDF全文
Repeated exposure to elevated levels of glucocorticoids during development can have long‐term detrimental effects on survival and fitness, potentially associated with increased telomere attrition. Nestling birds are regularly handled for ecological research, yet few authors have considered the potential for handling‐induced stress to influence hormonally mediated phenotypic development or bias interpretations of subsequent focal measurements. We experimentally manipulated the handling experience of the semi‐precocial nestlings of European Storm Petrel Hydrobates pelagicus to simulate handling in a typical field study and examined cumulative effects on physiology and condition in late postnatal development. Neither baseline corticosterone (the primary glucocorticoid in birds), telomere length nor body condition varied with the number of handling episodes. The absence of a response could be explained if Storm Petrels did not perceive handling to be stressful or if there is dissociation of the hypothalamic–pituitary–adrenal axis from stressful stimuli in early life. Eliciting a response to a stressor may be maladaptive for cavity‐dwelling young that are unable to escape or defend themselves. Furthermore, avoiding elevated overall glucocorticoid exposure may be particularly important in a long‐lived species, in which accelerated early‐life telomere erosion could impact negatively upon longevity. We propose that the level of colony‐wide disturbance induced by investigator handling of young could be important in underlining species‐specific responses. Storm Petrel nestlings appear unresponsive to investigator handling within the limits of handling in a typical field study and handling at this level should not bias physiological and morphological measurements. 相似文献
90.