全文获取类型
收费全文 | 1170篇 |
免费 | 183篇 |
出版年
2022年 | 10篇 |
2021年 | 21篇 |
2020年 | 14篇 |
2019年 | 19篇 |
2018年 | 21篇 |
2017年 | 25篇 |
2016年 | 27篇 |
2015年 | 41篇 |
2014年 | 38篇 |
2013年 | 55篇 |
2012年 | 62篇 |
2011年 | 54篇 |
2010年 | 31篇 |
2009年 | 33篇 |
2008年 | 51篇 |
2007年 | 40篇 |
2006年 | 44篇 |
2005年 | 41篇 |
2004年 | 45篇 |
2003年 | 41篇 |
2002年 | 33篇 |
2001年 | 31篇 |
2000年 | 46篇 |
1999年 | 29篇 |
1998年 | 14篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1992年 | 11篇 |
1991年 | 26篇 |
1990年 | 19篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1987年 | 24篇 |
1986年 | 16篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 14篇 |
1982年 | 10篇 |
1980年 | 11篇 |
1979年 | 13篇 |
1975年 | 9篇 |
1974年 | 12篇 |
1973年 | 13篇 |
1972年 | 11篇 |
1971年 | 19篇 |
1970年 | 8篇 |
1969年 | 8篇 |
1968年 | 8篇 |
1967年 | 9篇 |
1966年 | 8篇 |
排序方式: 共有1353条查询结果,搜索用时 31 毫秒
51.
52.
53.
C. J. Bond 《BMJ (Clinical research ed.)》1911,1(2629):1157-1164
54.
Erythrocytic cell kinetics were studied in normal dog bone marrow, at the transition between younger cells that are able to synthesize DNA, and more mature nucleated normoblasts which have lost this ability. the rate of progression out of the first group was compared to that into the second, after necessary adjustments of group sizes. No significant discrepancy was detected within the limits of resolution of autoradiographic cytokinetic analysis.
It is concluded that 'ineffective' red cell production in the normal dog, if it occurs at all, can only be very small in quantity. 相似文献
It is concluded that 'ineffective' red cell production in the normal dog, if it occurs at all, can only be very small in quantity. 相似文献
55.
Monica L. Bond Barbara König Arpat Ozgul Damien R. Farine Derek E. Lee 《The Journal of wildlife management》2021,85(5):920-931
Populations are typically defined as spatially contiguous sets of individuals, but large populations of social species can be composed of discrete social communities that often overlap in space. Masai giraffes (Giraffa camelopardalis tippelskirchi) of Tanzania live in distinct social subpopulations that overlap spatially, enabling us to simultaneously explore environmental and social factors correlated with demographic variation in a metapopulation of >1,400 adult females and calves. We considered statistically distinct communities in the social network as subpopulations and tested for variation among the 10 subpopulations in adult female survival, calf survival, and reproductive rate (calf-to-adult female ratio). We then related variation in demographic rates among subpopulations to differences in vegetation, soil type, proximity to 2 types of human settlements, local giraffe population density, and social metrics of relationship strength and exclusivity among adult females. We did not find any among-subpopulation effects on adult female survival, suggesting adult female survival is buffered against environmental heterogeneity among subpopulations. Variation in calf demographic rates among subpopulations were correlated with vegetation, soils, anthropogenic factors, and giraffe population density but not with adult female relationship metrics, despite substantial spatial overlap. Subpopulations with more dense bushlands in their ranges had lower calf survival probabilities, and those closer to human settlements had higher reproductive rates, possibly because of spatial gradients in natural predation. Reproductive rates were higher in subpopulations with more volcanic soils, and calf survival probabilities were greater in subpopulations with higher local adult female densities, possibly related to higher-quality habitat associated with fertile soils or lower predation risk, or to greater competitive ability. The variation in fitness among subpopulations suggests that giraffes do not move unhindered among resource patches to equalize reproductive success, as expected according to an ideal free distribution. The differences in calf survival and reproductive rates could rather indicate intercommunity differences in competitive ability, perception, learning, or experience. Our approach of comparing demography among spatially overlapping yet distinct socially defined subpopulations provides a biologically meaningful way to quantify environmental and social factors influencing fine-scale demographic variation for social species. © 2021 The Wildlife Society. 相似文献
56.
Rohan Bythell-Douglas Mark T. Waters Adrian Scaffidi Gavin R. Flematti Steven M. Smith Charles S. Bond 《PloS one》2013,8(1)
KARRIKIN INSENSITIVE 2 (KAI2) is an α/β hydrolase involved in seed germination and seedling development. It is essential for plant responses to karrikins, a class of butenolide compounds derived from burnt plant material that are structurally similar to strigolactone plant hormones. The mechanistic basis for the function of KAI2 in plant development remains unclear. We have determined the crystal structure of Arabidopsis thaliana KAI2 in space groups P21 21 21 (a = 63.57 Å, b = 66.26 Å, c = 78.25 Å) and P21 (a = 50.20 Å, b = 56.04 Å, c = 52.43 Å, β = 116.12°) to 1.55 and 2.11 Å respectively. The catalytic residues are positioned within a large hydrophobic pocket similar to that of DAD2, a protein required for strigolactone response in Petunia hybrida. KAI2 possesses a second solvent-accessible pocket, adjacent to the active site cavity, which offers the possibility of allosteric regulation. The structure of KAI2 is consistent with its designation as a serine hydrolase, as well as previous data implicating the protein in karrikin and strigolactone signalling. 相似文献
57.
Turner Alexandria Bond Danielle R. Vuong Quan V. Chalmers Anita Beckett Emma L. Weidenhofer Judith Scarlett Christopher J. 《Molecular biology reports》2020,47(3):2073-2084
Molecular Biology Reports - Treatment options for pancreatic cancer (PC) are severely limited due to late diagnosis, early metastasis and the inadequacy of chemotherapy and radiotherapy to combat... 相似文献
58.
Background and aims
Below-ground grass competition limits woody establishment in savannas. N2-fixing legumes may, however, have a nutritional advantage over broad-leaved species. We hypothesised that broad-leaved non-legume savanna thicket species would be more severely constrained by grass competition for N and consequently respond more to N-fertilization than the legume, Acacia karroo.Methods
A. karroo and five non-legume thicket species (Maytenus senegalensis, M. heterophylla, Euclea divinorum, Ziziphus mucronata, Schotia brachypetala) were grown together in an irrigated competition experiment with clipped-, unclipped-grass and without grass with/without N-fertilizer. The biomass, foliar nutrient, δ13C and δ15N of grasses and woody species were determined.Results
Growth of both A. karroo and the non-legume species was equally sensitive (c. 90 % reduction) to both clipped- and unclipped-grass competition, regardless of N-fertilization. With grass competition, however, foliar [N] increased and δ15N decreased in response to N-fertilization. Grass biomass accumulation was also unchanged by fertilisation, despite increases in foliar [N] and decreases in δ15N.Conclusions
The N2-fixation capacity of A. karroo provided no growth advantage over non-legumes. The lack of responsiveness of biomass accumulation by both the woody species and the grasses to N-fertilization, despite evidence that plants accessed the N-fertilizer, indicates limitation by other nutrients. 相似文献59.
60.