全文获取类型
收费全文 | 315篇 |
免费 | 48篇 |
国内免费 | 1篇 |
出版年
2022年 | 4篇 |
2021年 | 18篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 12篇 |
2015年 | 16篇 |
2014年 | 16篇 |
2013年 | 9篇 |
2012年 | 13篇 |
2011年 | 16篇 |
2010年 | 9篇 |
2009年 | 10篇 |
2008年 | 13篇 |
2007年 | 14篇 |
2006年 | 15篇 |
2005年 | 13篇 |
2004年 | 14篇 |
2003年 | 12篇 |
2002年 | 11篇 |
2001年 | 5篇 |
1999年 | 11篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1995年 | 4篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1974年 | 6篇 |
1973年 | 2篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1968年 | 2篇 |
1963年 | 2篇 |
1961年 | 2篇 |
1960年 | 3篇 |
1959年 | 3篇 |
1945年 | 2篇 |
1943年 | 2篇 |
1941年 | 3篇 |
排序方式: 共有364条查询结果,搜索用时 31 毫秒
1.
2.
Robert M. Scheller Alec M. Kretchun E. Louise Loudermilk Matthew D. Hurteau Peter J. Weisberg Carl Skinner 《Ecosystems》2018,21(4):643-656
Climate-driven increases in wildfires, drought conditions, and insect outbreaks are critical threats to forest carbon stores. In particular, bark beetles are important disturbance agents although their long-term interactions with future climate change are poorly understood. Droughts and the associated moisture deficit contribute to the onset of bark beetle outbreaks although outbreak extent and severity is dependent upon the density of host trees, wildfire, and forest management. Our objective was to estimate the effects of climate change and bark beetle outbreaks on ecosystem carbon dynamics over the next century in a western US forest. Specifically, we hypothesized that (a) bark beetle outbreaks under climate change would reduce net ecosystem carbon balance (NECB) and increase uncertainty and (b) these effects could be ameliorated by fuels management. We also examined the specific tree species dynamics—competition and release—that determined NECB response to bark beetle outbreaks. Our study area was the Lake Tahoe Basin (LTB), CA and NV, USA, an area of diverse forest types encompassing steep elevation and climatic gradients and representative of mixed-conifer forests throughout the western United States. We simulated climate change, bark beetles, wildfire, and fuels management using a landscape-scale stochastic model of disturbance and succession. We simulated the period 2010–2100 using downscaled climate projections. Recurring droughts generated conditions conducive to large-scale outbreaks; the resulting large and sustained outbreaks significantly increased the probability of LTB forests becoming C sources over decadal time scales, with slower-than-anticipated landscape-scale recovery. Tree species composition was substantially altered with a reduction in functional redundancy and productivity. Results indicate heightened uncertainty due to the synergistic influences of climate change and interacting disturbances. Our results further indicate that current fuel management practices will not be effective at reducing landscape-scale outbreak mortality. Our results provide critical insights into the interaction of drivers (bark beetles, wildfire, fuel management) that increase the risk of C loss and shifting community composition if bark beetle outbreaks become more frequent. 相似文献
3.
4.
Clustering of hypervariable minisatellites in the proterminal regions of human autosomes 总被引:42,自引:0,他引:42
Six of the human minisatellites detected by DNA fingerprint probes have been localized by in situ hybridization to human metaphase chromosomes. These hypervariable loci are not dispersed at random in the human genome, but show preferential, though not exclusive, localization to terminal G-bands of human autosomes. Two of the proterminal minisatellites are very closely linked to other variable loci. Sequence analysis of one of these additional minisatellites suggests that the two linked minisatellites arose by independent amplification of different repeat units. The proterminal regions of human autosomes may therefore be rich in minisatellites, analogous to the pseudoautosomal terminal pairing region of human sex chromosomes that is similarly abundant in hypervariable minisatellites. 相似文献
5.
6.
Alec Breen Alan F. Rope Denise Taylor John C. Loper P. R. Sferra 《Journal of industrial microbiology & biotechnology》1995,14(1):10-16
Summary The use of DNA amplification fingerprinting (DAF) as a tool for monitoring mixed microbial populations in bioreactors was evaluated. Short (8-mer or 10-mer) oligonucleotides were used to prime DNA extracts from various biological reactors during polymerase chain reaction (PCR) amplification. The reactors examined in this study included two sets of anaerobic stirred tank continuous flow bioreactors. One set of anaerobic reactors was operated under methanogenic conditions and one set was operated under sulfate-reducing conditions. The anaerobic reactor communities in the methanol-fed reactors showed extensive DAF homology. DAF was also applied to a fixed-film azo dye degrading reactor to examine the degree of uniformity of colonization of the substratum in representative regions of the reactor. This method is a quick and relatively inexpensive means of monitoring microbial community structure during biological processes. Since no cultivation of the sample is involved, the genetic profile of the community is not biased by outgrowth conditions. DAF profiles may be useful for comparisons of population changes over time or of bench-scale vs pilot-scale reactors but not adequate for assessing community diversity. 相似文献
7.
We studied the response of 31 migraine sufferers (20 women, 11 men) to intravenous tyramine (the tyraminedose)pressor response test). Patients were treated either with pacebo tablets or indoramin, and alpha-adrenergic blocking agent, in a double-blind crrossover trial. We found that patients with migraine required significantly less tyramine to increase their cystolic blod pressure by 30 mm Hg when compared with matched controls. Indoramin significantly increased the amount of tyramine needed to raise the systolic blood pressure among migraine suffers and reduced the incidence of posttyramine migraine for m 46% while patients were on placebo tablets to 8% when they were receiveing indoramin. There was no association between tyramine sensitivity and a history of premenstrual or dietary migraine, nor was there a significant difference in the indierenence in the incidence of post-tyramine migrain between men women. We conclude that the intravenous tyramine test may be valuable in assessing migraine suffers who will respond to an alpha-advenergic blocking agent such as indoramin. 相似文献
8.
9.
10.
Alec Walen 《Bioethics》2020,34(9):899-905
Subjects in studies on humans are used as a means of conducting the research and achieving whatever good would justify putting them at risk. Accordingly, consent must normally be obtained before subjects are exposed to any substantial risks to their welfare. Bystanders are also often put at risk, but they are not used as a means. Accordingly—or so I argue—consent is more often unnecessary before bystanders are exposed to similar substantial risks to their welfare. 相似文献