全文获取类型
收费全文 | 2865篇 |
免费 | 165篇 |
国内免费 | 101篇 |
出版年
2024年 | 7篇 |
2023年 | 35篇 |
2022年 | 23篇 |
2021年 | 29篇 |
2020年 | 57篇 |
2019年 | 58篇 |
2018年 | 42篇 |
2017年 | 64篇 |
2016年 | 69篇 |
2015年 | 73篇 |
2014年 | 84篇 |
2013年 | 181篇 |
2012年 | 80篇 |
2011年 | 78篇 |
2010年 | 57篇 |
2009年 | 110篇 |
2008年 | 122篇 |
2007年 | 92篇 |
2006年 | 120篇 |
2005年 | 117篇 |
2004年 | 72篇 |
2003年 | 93篇 |
2002年 | 89篇 |
2001年 | 67篇 |
2000年 | 77篇 |
1999年 | 56篇 |
1998年 | 69篇 |
1997年 | 49篇 |
1996年 | 52篇 |
1995年 | 61篇 |
1994年 | 63篇 |
1993年 | 47篇 |
1992年 | 53篇 |
1991年 | 33篇 |
1990年 | 54篇 |
1989年 | 61篇 |
1988年 | 44篇 |
1987年 | 54篇 |
1986年 | 52篇 |
1985年 | 49篇 |
1984年 | 83篇 |
1983年 | 29篇 |
1982年 | 47篇 |
1981年 | 51篇 |
1980年 | 47篇 |
1979年 | 45篇 |
1978年 | 38篇 |
1977年 | 37篇 |
1976年 | 39篇 |
1975年 | 14篇 |
排序方式: 共有3131条查询结果,搜索用时 125 毫秒
1.
In a eutrophic lake, a crash of the algal population was followed by a significant increase in the number of virus-like particles (from ca. 1 106 ml–1 to ca. 26 106 ml–1), and soon thereafter by an increase of the amount of extracellular DNA (from ca. 20 µg l–1 to ca. 40 µg l–1). The same pattern of correlation between decrease of algae and increase of viruses and extracellular DNA could be demonstrated by an in vitro experiment with a Chlorella-virus-system. Lysis of algae by viruses increased both the number of viruses and the amount of DNA in the culture medium. Extracellular DNA mainly consisted of material with a molecular weight below 500 bp.The Chlorella-virus-system is discussed. It could be used as a model-system for studying the dynamics of interaction of viruses and algae in aquatic ecosystems. 相似文献
2.
Euglena gracilis and Chlamydomonas reinhardtii were used as model organisms to establish the best conditions for studying photosynthetic efficiency using the Light Pipette
– experimental system, which enables sensitive detection of changes in oxygen evolution/consumption and an easy collection
and digitalisation of data. Chlorophyll concentrations of 0.005, 0.025, 0.050 and 0.075 mgmL-1 were investigated using different light regimes. Cultures of E. gracilis at the same chlorophyll concentration absorbed more light(measured at 580 μmol m-2 s-1) than those of C. reinhardtii. Cell density had a considerable effect on the reliability of measurements. Chlorophyll concentrations between 0.025 mgChl ml-1 and 0.050 mgChlml-1 can be recommended when applying the Light Pipette system in bioassays using microalgae.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
The Bryopsidales contains some of the most species rich and ecologically dominant algae in tropical ecosystems. However, the evolutionary relationships among the 29 genera and several hundred species of this order remain poorly resolved. Because of a lack of known reproductive characters for many taxa, evolutionary hypotheses grouped genera by similarities in morphological characters. To apply standard cladistical analyses to further our understanding of this group, this study presents the first comprehensive compilation of reported morphological, reproductive, and subcellular characteristics for genera in the Bryopsidales. Computer-assisted cladistical analyses ultimately identified phylogenetically informative and uninformative characters. Although the topology of the trees generated in this study is expected to change as additional data are added to this matrix, many traditional groupings and recent groupings based on molecular data were supported. 相似文献
4.
Vanadate-sensitive proton efflux by filamentous cyanobacteria 总被引:1,自引:0,他引:1
Abstract Light-induced proton efflux has been investigated with intact cells of Anabaena, Nostoc, Anacystis , and Aphanocapsa . The proton efflux by filamentous blue-green algae is biphasic, strongly inhibited by ortho -vanadate and insensitive to cyanide. These data are taken as evidence for a proton-pumping ATP-hydrolase present on the cytoplasmic membrane of Anabaena and Nostoc . 相似文献
5.
Graciela De Lara-Isassi Sergio Álvarez-Hernández Ligia Collado-Vides 《Journal of applied phycology》2000,12(1):45-52
Seventy-three species of macroalgae from the Mexican Pacific, Atlantic and Caribbean coast were screened for ichtyotoxic activity.
Ethanolic, acetonic and aqueous extracts were prepared and tested against the fish Carassius auratus. The extracts were classified on the basis of their effects as: toxic if the fish died in two hours or less; moderately toxic,
if the organism behaved abnormally but death did notoccur, and non-toxic if the fish did not display any change. 79% species
were ichtyotoxic to some degree. Extracts of 39 species were toxic, with at least one extract with lethal effects, 19 were
moderately toxic and 15 species were non-toxic. Only the extracts ofDictyota bartayresiana, Dictyota cervicornis,Lobophora variegata, Bryothamnion triquetrum and Laurencia obtusa were toxic in all three solvents. The acetone and ethanol extracts were more active, and therefore are more suitable for
extraction of toxic substances.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
7.
Concentration factor and biological half-life of 54Mn were determined in three species representing an ecologically and economically important food chain. Green algae (Chlorella spp.), Daphnia magna and yellow perch (Perca flavescens) were exposed to 54Mn in water and assayed for 54Mn uptake. Steady state concentration factors computed from the laboratory data for algae, Daphnia and perch were 4230, 17 000 and 11, respectively. Respective biological half-lives were 1.6, 1.2 and 8.3 days. 相似文献
8.
MaoSen Hua E. Imre Friedmann Roseli Ocampo-Friedmann Susan B. Campbell 《Plant Systematics and Evolution》1989,164(1-4):17-26
Cyanocystis violacea isolated from a marine rock sample conforms with the diagnosis ofDermocarpa violacea
Crouan in all significant characteristics. The distinct heteropolarity of the cells and simultaneous cell divisions, are stable characters in culture. Development and growth of cells, simultaneous cell division and nanocyte formation have been documented by single-cell slide cultures and fine structural studies. The reddish violet color of the cytoplasm is due to the abundance of phycoerythrin.This paper is dedicated to Prof. DrLothar Geitler, whose monumental contribution to the knowledge of blue-green algae will remain the basis for future studies on these organisms for many years to come. One of us (EIF) was fortunate enough to have had Prof.Geitler as his major professor. All of us consider Prof.Geitler our teacher. 相似文献
9.
Fluctuation of algal alkaline phosphatase activity and the possible mechanisms of hydrolysis of dissolved organic phosphorus in Lake Barato 总被引:3,自引:3,他引:0
Shuji Hino 《Hydrobiologia》1988,157(1):77-84
For freshwater cyanobacteria, the autofluorescence of phycocyanin is quite high while the in vivo fluorescence (IVF) yield of chlorophyll-a is relatively low, apparently because of low chlorophyll concentrations associated with photosystem II. In eucaryotic phytoplankton, even those with phycobili-protein accessory pigments (e.g. some cryptophytes), the opposite is true. Thus, an IVF ratio which relates phycocyanin to chlorophyll-a signals could be a good index of relative cyanobacterial abundance in the field. Spectrofluorometric scans of whole cells from laboratory cultures indicated that the ratio Em660 @ Ex630/Em680 @ Ex430 could be a very sensitive cyanobacterial indicator. Tandem flowthrough fluorometers were then fitted with the appropriate interference filters and their discriminatory power was evaluated with mixtures of cyanobacterial and eucaryotic phytoplankton. Although subject to many of the constraints of other IVF assays, tandem fluorometry should be particularly appropriate for real-time mapping of the relative spatial and temporal distributions of broad phytoplankton taxa in continuous vertical of horizontal profiles in lakes. 相似文献
10.
Possible mechanisms for the inhibition of photosynthesis by ozone 总被引:20,自引:0,他引:20
Robert L. Heath 《Photosynthesis research》1994,39(3):439-451
Tropospheric ozone produced by industrial civilization is widespread. Although the levels are not clearly life threatening, they do have the potential to inhibit normal plant productivity, thought to be by an inhibition of photosynthesis. While the mechanism for this inhibition is not yet clear, there are several hypotheses for its cause. It is unlikely that ozone can penetrate the cell membrane unreacted; therefore, reactions at the plasma membrane either causing general ionic and metabolic disturbance within the cell or causing the production of unidentified toxic products must ultimately produce the alterations within the chloroplasts. While model systems, such as individual biochemicals, isolated chloroplasts, and algae, can give some understanding of possible reactions, they cannot provide the full story. One continuing controversy revolves about the role of stomata in the inhibition process-they play an important role, but the full interaction between stomatal closure and inhibition of photosynthesis has not yet emerged. In order to reach a political compromise on air quality standards, we need to have a good understanding of the fundamental mechanisms by which ozone causes any decline in plant productivity. 相似文献