全文获取类型
收费全文 | 430篇 |
免费 | 36篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 13篇 |
2015年 | 20篇 |
2014年 | 24篇 |
2013年 | 51篇 |
2012年 | 32篇 |
2011年 | 30篇 |
2010年 | 28篇 |
2009年 | 30篇 |
2008年 | 22篇 |
2007年 | 18篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 6篇 |
2003年 | 8篇 |
2002年 | 2篇 |
2001年 | 11篇 |
2000年 | 12篇 |
1999年 | 5篇 |
1998年 | 14篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1984年 | 5篇 |
1982年 | 3篇 |
1976年 | 3篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1967年 | 2篇 |
1966年 | 1篇 |
1958年 | 5篇 |
1957年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
1952年 | 2篇 |
1949年 | 1篇 |
1948年 | 1篇 |
1938年 | 1篇 |
排序方式: 共有466条查询结果,搜索用时 15 毫秒
1.
Reiko Yu-Ito Kazuko Ôba Ikuzo Uritani 《Bioscience, biotechnology, and biochemistry》2013,77(8):2087-2091
In addition to HMG-CoA reductase, another HMG-CoA utilizing enzyme is present in the Mt fraction of sweet potato root tissue and its activity interferes with the assay to HMG-CoA reductase activity. 相似文献
2.
THE DEVELOPMENT OF CHLOROPLASTS IN ROOT MERISTEMATIC TISSUE OF SECALE CEREALE L. SEEDLINGS 总被引:1,自引:1,他引:0
LUIS OLIVEIRA 《The New phytologist》1982,91(2):263-275
3.
PAULO S. OLIVEIRA 《Zoological Journal of the Linnean Society》1985,83(4):371-384
Nymphs of Hyalymenus , unlike adults, have a highly differentiated ant-like morphology. Both H. tarsatus and H. limbativentris feed mainly on reproductive parts of composites and solanaceous plants, respectively. Mimetic nymphs were observed on plants, together with ants, both day and night; adult Hyalymenus , however, are predominantly nocturnal. Ant-resemblance in nymphs is achieved by several structural adaptations which, when coupled with the mimic's zig-zag locomotion and constantly agitated antennae, produces a striking visual deception. Experiments in captivity showed that mimetic nymphs, but not adult Hyalymenus , are somewhat protected against attacks from the praying mantid Oxyopsis media found on their host plant. Colour and size changes through different nymphal instars of Hyalymenus allow the immature bugs to resemble, during their development, differently sized and coloured ant models. Similar-looking ant species seem to act as Mullerian mimics toward insectivorous vertebrates and invertebrates that avoid ants. It is suggested that nymphs of Hyalymenus gain Batesian protection by resembling available ant models of different Mullerian complexes. Density-dependent selection is thought to be responsible for the observed differences in mimetic morph proportions between populations of mimics, as well as for the mimetic strategy itself employed by nymphs of Hyalymenus. 相似文献
4.
Effect of removal of snow cover in winter was investigated in an 80-year-old sugar maple (Acer saccharum Marsh.) stand in southern Quebec. We hypothesized that winter soil frost would induce some of the decline symptoms observed in sugar maple stands in southern Quebec in the early 1980's. Snow was continuously removed from around trees for a one week (partial removal) or for a four-month period (complete removal) during the 1990–1991 winter. Foliage and soils were sampled periodically during the summer of 1991. The complete snow removal treated trees showed decreased leaf water potential and increased peroxidase activity over most of the growing season. Foliar Ca was reduced in both snow removal treatments early in the growing season while foliar N was reduced in the complete snow removal trees late in the growing season. Soil NO
3
–
and K+ were elevated in both snow removal treatments at various times throughout the growing season. Prolonged soil frost in a sugar maple stand can induce lower leaf water potential, higher leaf peroxidase activity and early leaf senescence during the following growing season. Soil frost may have reduced nutrient uptake without affecting significantly the leaf nutrient status. 相似文献
5.
Pleural Fluid Adenosine Deaminase and Lymphocyte Proportion: Clinical Usefulness In the Diagnosis of Tuberculosis 总被引:1,自引:0,他引:1
Adenosine deaminase (ADA) and lymphocyte proportion are known to be independently elevated in tuberculous effusions, but are non-specific, and false positive results are frequent. to overcome this problem the combined use of both parameters was prospectively studied in 276 patients with pleural effusion seen at Porto Alegre, Brazil. Using a cut-off level of 40 U/l at 37°C (method of Giusti19 ) for ADA activity and lymphocyte proportion of more than 50%, the correct diagnosis of tuberculosis (sensitivity) was made in 90.7% (CI 87.3–94.1%) of 54 patients. A specificity of 97.7% (CI 95.9–99.5%) was recorded. Five false positive diagnoses of tuberculous effusion were made. Five false negative diagnoses were made: three cases with haematogenous tuberculous dissemination with low ADA levels, and two other patients with low lymphocyte proportion. the combined use of ADA activity determination and lymphocyte proportion is a highly efficient diagnostic strategy of low cost, that merits wider use. 相似文献
6.
Varilla González Jean David Macedo Alves Flávio Bagnatori Sartori Ângela Lúcia de Oliveira Arruda Rosani do Carmo 《Journal of plant research》2023,136(4):453-481
Journal of Plant Research - The Pterocarpus clade includes 23 genera previously attributed to different Fabaceae tribes. The recent rearrangements of many genera in the clade do not recognize... 相似文献
7.
8.
9.
10.
1. Biofilm biomass and metabolism were analysed in La Solana, a calcareous, undisturbed second-order stream. Measurements were carried out in two Mediterranean climatic extremes, summer and winter. Two on-site experimental channels were used to study changes following nutrient addition to one of them. 2. Algal biomass (chlorophyll a), NDPP (net daily primary production), GDPP (gross daily primary production) and R (respiration) increased in the enriched channel, and these increases were greater in summer. 3. Photosynthetic capacity (Pmaxchl) decreased during summer, possibly due to enhanced self-shading accompanying the increase in biomass. 4. In winter, Pmaxchl increased and reached values similar to those in the summer control channel. Because grazing was low, the higher values of Pmaxchl were attributed to partial substitution of the cyanobacterial assemblage by a green-algae dominated assemblage with higher photosynthetic capacity as well as the low increase in biomass preventing any significant self-shading. 相似文献