全文获取类型
收费全文 | 438篇 |
免费 | 70篇 |
出版年
2021年 | 7篇 |
2016年 | 6篇 |
2015年 | 12篇 |
2014年 | 9篇 |
2013年 | 23篇 |
2012年 | 20篇 |
2011年 | 22篇 |
2010年 | 6篇 |
2009年 | 19篇 |
2008年 | 16篇 |
2007年 | 19篇 |
2006年 | 10篇 |
2005年 | 15篇 |
2004年 | 14篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 12篇 |
1984年 | 4篇 |
1983年 | 13篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1972年 | 6篇 |
1971年 | 3篇 |
1969年 | 5篇 |
1967年 | 5篇 |
1965年 | 4篇 |
1962年 | 5篇 |
1945年 | 3篇 |
排序方式: 共有508条查询结果,搜索用时 171 毫秒
71.
72.
Tolerance, the degree to which plant fitness is affected by herbivory, is associated with invasiveness and biological control of introduced plant species. It is important to know the evolutionary changes in tolerance of invasive species after introduction in order to understand the mechanisms of biological invasions and assess the feasibility of biological control. While many studies have explored the evolutionary changes in resistance of invasive species, little has been done to address tolerance. We hypothesized that compared with plants from native populations, plants from invasive populations may increase growth and decrease tolerance to herbivory in response to enemy release in introduced ranges. To test this hypothesis, we compared the differences in growth and tolerance to simulated herbivory between plants from invasive and native populations of Chromolaena odorata, a noxious invader of the tropics and subtropics, at two nutrient levels. Surprisingly, flower number, total biomass (except at high nutrient), and relative increase in height were not significantly different between ranges. Also, plants from invasive populations did not decrease tolerance to herbivory at both nutrient levels. The invader from both ranges compensated fully in reproduction after 50?% of total leaf area had been damaged, and achieved substantial regrowth after complete shoot damage. This strong tolerance to damage was associated with increased resource allocation to reproductive structures and with mobilization of storage reserves in roots. The innately strong tolerance may facilitate invasion success of C. odorata and decrease the efficacy of leaf-feeding biocontrol agents. Our study highlights the need for further research on biogeographical differences in tolerance and their role in the invasiveness of exotic plants and biological control. 相似文献
73.
VC Barclay D Sim BH Chan LA Nell MA Rabaa AS Bell RF Anders AF Read 《PLoS biology》2012,10(7):e1001368
Malaria vaccine developers are concerned that antigenic escape will erode vaccine efficacy. Evolutionary theorists have raised the possibility that some types of vaccine could also create conditions favoring the evolution of more virulent pathogens. Such evolution would put unvaccinated people at greater risk of severe disease. Here we test the impact of vaccination with a single highly purified antigen on the malaria parasite Plasmodium chabaudi evolving in laboratory mice. The antigen we used, AMA-1, is a component of several candidate malaria vaccines currently in various stages of trials in humans. We first found that a more virulent clone was less readily controlled by AMA-1-induced immunity than its less virulent progenitor. Replicated parasites were then serially passaged through control or AMA-1 vaccinated mice and evaluated after 10 and 21 rounds of selection. We found no evidence of evolution at the ama-1 locus. Instead, virulence evolved; AMA-1-selected parasites induced greater anemia in naïve mice than both control and ancestral parasites. Our data suggest that recombinant blood stage malaria vaccines can drive the evolution of more virulent malaria parasites. 相似文献
74.
H. J. Barclay 《Population Ecology》2001,43(3):197-206
Models were constructed for control of a pest species by the release of sterile insects and these models explored the consequences
of incomplete sterility. This feature was then coupled with the lack of competitive ability of released insects, the immigration
of insects from outside the control area, and the mode of population regulation (density independent vs. density dependent).
Using the density-independent models, it was seen that the limits on residual fertility of treated insects become much more
stringent when incomplete sterilization is combined with a lack of competitive ability and immigration of insects into the
control area. Strong density dependence in the system has a marked moderating effect on the requirements for sterility, competitive
ability, and immigration. However, if the density-independent limits on these factors are exceeded, then suppression is possible,
but collapse of the pest population is impossible using sterile releases alone. Even suppression might not be satisfactory
if these three detrimental factors are prominent. It is suggested that one remedy is the use of the sterile release method
in combination with other control methods.
Received: January 18, 2001 / Accepted: August 7, 2001 相似文献
75.
Scott S. Barclay John M. Woodley Malcolm D. Lilly Peter L. Spargo Alan J. Pettman 《Biotechnology letters》2001,23(5):385-388
Cyclohexanone monooxygenase was produced from Acinetobacter calcoaceticus grown on a medium containing both glutamate (30 g l–1) and cyclohexanol (1 g l–1). Productivity was increased to 650 U l–1, an order of magnitude greater than previous production methods, thereby enhancing the potential commercial utility of this enzyme. 相似文献
76.
The subunit structure of horse spleen apoferritin: the molecular weight of the oligomer and its stability to dissociation by dilution (Short Communication) 总被引:1,自引:0,他引:1 下载免费PDF全文
Robert R. Crichton Robert Eason Allan Barclay Charles F. A. Bryce 《The Biochemical journal》1973,131(4):855-857
The oligomer molecular weight of horse spleen apoferritin was determined by sedimentation-equilibrium techniques and a value of 443000 found. It is concluded that the apoferritin molecule consists of 24 subunits. At concentrations as low as 0.01mum there is no evidence of subunit dissociation. 相似文献
77.
78.
79.
80.