全文获取类型
收费全文 | 3048篇 |
免费 | 224篇 |
国内免费 | 321篇 |
专业分类
3593篇 |
出版年
2023年 | 55篇 |
2022年 | 56篇 |
2021年 | 103篇 |
2020年 | 115篇 |
2019年 | 132篇 |
2018年 | 107篇 |
2017年 | 104篇 |
2016年 | 104篇 |
2015年 | 113篇 |
2014年 | 154篇 |
2013年 | 188篇 |
2012年 | 133篇 |
2011年 | 135篇 |
2010年 | 102篇 |
2009年 | 130篇 |
2008年 | 145篇 |
2007年 | 146篇 |
2006年 | 132篇 |
2005年 | 91篇 |
2004年 | 114篇 |
2003年 | 118篇 |
2002年 | 98篇 |
2001年 | 99篇 |
2000年 | 79篇 |
1999年 | 57篇 |
1998年 | 73篇 |
1997年 | 72篇 |
1996年 | 62篇 |
1995年 | 56篇 |
1994年 | 54篇 |
1993年 | 56篇 |
1992年 | 33篇 |
1991年 | 37篇 |
1990年 | 33篇 |
1989年 | 37篇 |
1988年 | 23篇 |
1987年 | 30篇 |
1986年 | 22篇 |
1985年 | 27篇 |
1984年 | 37篇 |
1983年 | 16篇 |
1982年 | 13篇 |
1981年 | 20篇 |
1980年 | 11篇 |
1979年 | 16篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1974年 | 9篇 |
1973年 | 5篇 |
排序方式: 共有3593条查询结果,搜索用时 15 毫秒
1.
The association between the red macroalga Jania adhaerens J. V. Lamour. and the sponge Haliclona caerulea is the most successful life‐form between 2 and 4 m depth in Mazatlán Bay (Mexican Pacific). J. adhaerens colonizes the rocky intertidal area and penetrates into deeper areas only when it lives in association with H. caerulea. The aposymbiotic form of the sponge has not been reported in the bay. To understand the ecological success of this association, we examined the capacity of J. adhaerens to acclimate in Mazatlán Bay using transplant experiments. The transplanted aposymbiotic J. adhaerens did not survive the first 2 weeks; however, J. adhaerens when living in association with H. caerulea, acclimated easily to depth, showing no sign of mortality during the 103 d of the experiment. We conclude that the ability of J. adhaerens to colonize in deeper areas in this hydrodynamic environment may in part rely on the protection provided by the sponge to the algal canopy. Both species contribute to the shape of the associated form. Nevertheless, the morphological variation in the association appears to be dominated by the variation in J. adhaerens canopy to regulate pigment self‐shading under light‐limited conditions and/or tissue resistance under high hydrodynamics. Consequently, our results are consistent with light as the abiotic controlling factor, which regulates the lower depth distribution of the association in Mazatlán Bay, through limiting the growth rate of J. adhaerens. Hydrodynamics may determine the upper limit of the association by imposing high mass losses. 相似文献
2.
FRANÇOIS MUNOZ THIERRY PAILLER INGRID KOTTKE CÉDRIC GONNEAU MARC‐ANDRÉ SELOSSE 《Molecular ecology》2012,21(20):5098-5109
Characterizing the architecture of bipartite networks is increasingly used as a framework to study biotic interactions within their ecological context and to assess the extent to which evolutionary constraint shape them. Orchid mycorrhizal symbioses are particularly interesting as they are viewed as more beneficial for plants than for fungi, a situation expected to result in an asymmetry of biological constraint. This study addressed the architecture and phylogenetic constraint in these associations in tropical context. We identified a bipartite network including 73 orchid species and 95 taxonomic units of mycorrhizal fungi across the natural habitats of Reunion Island. Unlike some recent evidence for nestedness in mycorrhizal symbioses, we found a highly modular architecture that largely reflected an ecological barrier between epiphytic and terrestrial subnetworks. By testing for phylogenetic signal, the overall signal was stronger for both partners in the epiphytic subnetwork. Moreover, in the subnetwork of epiphytic angraecoid orchids, the signal in orchid phylogeny was stronger than the signal in fungal phylogeny. Epiphytic associations are therefore more conservative and may co‐evolve more than terrestrial ones. We suggest that such tighter phylogenetic specialization may have been driven by stressful life conditions in the epiphytic niches. In addition to paralleling recent insights into mycorrhizal networks, this study furthermore provides support for epiphytism as a major factor affecting ecological assemblage and evolutionary constraint in tropical mycorrhizal symbioses. 相似文献
3.
4.
The lipid composition of swimming spores, cysts and five hour germlings was established. Spores utilized triglycerides first, then phospholipids. Upon encystment all glycolipid components decreased, while in germlings the phospholipids, monoglycerides and sterol esters exhibited a marked increase. 相似文献
5.
6.
7.
Optimum growth conditions and inoculation regimes were determined for severalFrankia strains isolated from both Alnus and Casuarina host plants. Growth conditions were estabilished that allowed a reduction in generation time to less than 15 hours for certain Alnus derivedFrankia. Differences in plant growth response were observed with differing inoculum levels and soil mixtures. Elite strains of Alnus derivedFrankia were isolated that elicited similar growth reponses in allAlnus species tested; however, differences were observed betweenFrankia strains and plant growth response of variousCasuarina species tested. 相似文献
8.
Chlorella sorokiniana strain 211-40c, a symbiotic Chlorella isolated from a freshwater sponge, excreted between 3% and 5% of assimilated 14CO2 as glucose in the light, with a pH optimum around 5. This percentage increased when the illuminance was lowered (to 15% at 20 lx). Release of [14C]glucose continued in the dark and could be inhibited by the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP). Net efflux of glucose occurred even at a concentration ratio of extracellular/intracellular glucose of 4. This, together with the sensitivity to FCCP, is taken as evidence for active transport. Exogenous [14C]glucose was taken up by the cells under conditions of net glucose efflux, showing uptake and excretion to take place simultaneously.Abbreviations FCCP
carbonyl cyanide p-trifluoromethoxyphenylhydrazone
- p.c.
packed cells 相似文献
9.
Structures resembling Metallogenium spp. were observed in agar and in liquid cultures of a Mn-oxidizing basidiomycetous fungus only when Mn2+ was oxidized. Fungal viability was necessary for formation of the structures; Mn2+ concentration and the presence or absence of agar in the medium were important factors determining their morphology. Slide cultures revealed no identifiable cells in any stage of development. Fluorescent dyes that stained nucleic acids and polysaccharides in the fungal hyphae did not stain the Metallogenium-like structures. Likewise, Rhodamine 123, a fluorescent probe for membrane potential, stained fungal mitochondria, but did not stain the structures. Thin sections through the structures showed no biological membranes or other cellular features. Only the characteristic ultrastructure of biological Mn oxides were observed in serial thin sections. In agar, unfixed structures disappeared permanently during reduction of Mn oxides with hydroxylamine. Glutaraldehyde fixation stabilized these structures. Fixed structures lost most of their original phase density during reduction with hydroxylamine, but continuous microscopic observations showed that their phase density could be restored by staining with Coomassie blue. Structures that formed in liquid medium did not require stabilization with glutaraldehyde during reduction of Mn oxides. They, too, lost their original phase density during reduction with hydroxylamine; phase density could be restored by staining with cationic colloidal iron or Coomassie blue. The results suggest that the Metallogenium-like structures were formed as a result of Mn oxidation associated with exopolymers produced by the fungus.Non-standard abbreviations HEPES
(N-hydroxyethylpiperazine-N-2-ethane sulfonic acid)
- DAPI
(4,6-diamidino-2-phenylindole)
- PIPES
(piperazine-N,N-bis[2-ethane sulfonic acid]) 相似文献
10.
There are seven known species of Azolla, two of which have been used in cultivated systems, the tropical speciesA. pinnata, and the temperate speciesA. filiculoides. OnlyA. pinnata is indigenous in Thailand. In this study the two exotic species,A. caroliniana andA. microphylla, were evaluated under the various tropical field conditions in Thailand. When compared with seven selected strains ofA. pinnata under three field conditions,A. caroliniana andA. microphylla were similar to the indigenous species, in terms of growth performance, N2 fixation, and yield. This study suggests thatA. caroliniana andA. microphylla can be successfully cultivated as a nitrogen fixing green manure for rice production in the tropics. 相似文献