全文获取类型
收费全文 | 2111篇 |
免费 | 148篇 |
国内免费 | 2篇 |
出版年
2022年 | 13篇 |
2021年 | 45篇 |
2020年 | 16篇 |
2019年 | 23篇 |
2018年 | 31篇 |
2017年 | 28篇 |
2016年 | 48篇 |
2015年 | 71篇 |
2014年 | 97篇 |
2013年 | 139篇 |
2012年 | 148篇 |
2011年 | 131篇 |
2010年 | 84篇 |
2009年 | 97篇 |
2008年 | 91篇 |
2007年 | 116篇 |
2006年 | 96篇 |
2005年 | 80篇 |
2004年 | 84篇 |
2003年 | 74篇 |
2002年 | 53篇 |
2001年 | 48篇 |
2000年 | 57篇 |
1999年 | 32篇 |
1998年 | 19篇 |
1997年 | 24篇 |
1996年 | 13篇 |
1995年 | 19篇 |
1994年 | 18篇 |
1993年 | 25篇 |
1992年 | 26篇 |
1991年 | 40篇 |
1990年 | 17篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1987年 | 23篇 |
1986年 | 13篇 |
1985年 | 22篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1979年 | 17篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 16篇 |
1974年 | 12篇 |
1973年 | 27篇 |
1972年 | 13篇 |
1971年 | 16篇 |
1967年 | 14篇 |
1966年 | 12篇 |
排序方式: 共有2261条查询结果,搜索用时 15 毫秒
981.
982.
-Aminolevulinic acid synthetase from cold-stored potatoes 总被引:6,自引:0,他引:6
983.
984.
985.
986.
K. Madhumathi P.T. Sudheesh Kumar K.C. Kavya T. Furuike H. Tamura S.V. Nair R. Jayakumar 《International journal of biological macromolecules》2009,45(3):289-292
Biopolymers like chitin are widely investigated as scaffolds in bone tissue engineering. Its properties like biocompatibility, biodegradability, non-toxicity, wound healing ability, antibacterial activity, hemostatic property, etc., are widely known. However, these materials are not much bioactive. Addition of material like silica can improve the bioactivity and biocompatibility of chitin. In this work, chitin composite scaffolds containing nanosilica were prepared using chitin hydrogel and their bioactivity, swelling ability and cytotoxicity was analyzed in vitro. These scaffolds were found to be bioactive in simulated body fluid (SBF) and biocompatible when tested with MG 63 cell line. These results suggest that chitin/nanosilica composite scaffolds can be useful for bone tissue engineering applications. 相似文献
987.
Seasonal distribution of Vibrio parahaemolyticus in freshwater environs and in association with freshwater fishes in Calcutta. 总被引:6,自引:4,他引:2
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The seasonal distribution of Vibrio parahaemolyticus in freshwater environs and in association with freshwater fishes was studied in 1982 and 1983. The occurrence of this organism in water and sediments at the three sites studied was very infrequent and was restricted to the summer months, although it was not always isolated during these months. The association of V. parahaemolyticus with plankton was chiefly confined to the summer months and progressively declined with the onset of monsoons, remaining below detectable levels during the postmonsoon and winter months. The incidence and counts of V. parahaemolyticus were consistently higher in association with plankton than with water and sediment samples. V. parahaemolyticus could be recovered throughout the period of investigation from freshly caught and market samples of freshwater fishes. The highest recovery rate of this halophile from fishes was invariably from fecal samples. Most of the strains isolated in this study were untypable, and those which could be typed were predominantly serotypes encountered in the environment. All the isolates were Kanagawa negative. From this study, it could be concluded that the survival of V. parahaemolyticus in freshwater ecosystems is transient and dependent on a biological host. 相似文献
988.
989.
Patrícia Ramos Agostinho Santos Nair Rosas Pinto Ricardo Mendes Teresa Magalhães Agostinho Almeida 《Biological trace element research》2014,161(2):190-201
Using inductively coupled plasma-mass spectrometry after samples microwave-assisted acid digestion, zinc (Zn), copper (Cu), and manganese (Mn) levels were measured in 14 different areas of the human brain of adult individuals (n?=?42; 71?±?12, range 50–101 years old) without a known history of neurodegenerative, neurological, or psychiatric disorder. The main goals of the work were to establish the “normal” (reference) values for those elements in the human brain and to evaluate the age-related changes, a prior and indispensable step in order to enlighten the role of trace element (TE) in human brain physiology and their involvement in aging and neurodegenerative processes. Considering the mean values for the 14 regions, Zn (mean ± sd; range 53?±?5; 43–61 μg/g) was found at higher levels, followed by Cu (22?±?5; 10–37 μg/g) and Mn (1.3?±?0.3; 0.5–2.7 μg/g). The TE distribution across the brain tissue showed to be quite heterogeneous: the highest levels of Zn were found in the hippocampus (70?±?10; 49–95 μg/g) and superior temporal gyrus (68?±?10; 44–88 μg/g) and the lowest in the pons (33?±?8; 19–51 μg/g); the highest levels of Cu and Mn were found in the putamen (36?±?13; 21–76 μg/g and 2.5?±?0.8; 0.7–4.5 μg/g, respectively) and the lowest in the medulla (11?±?6; 2–30 μg/g and 0.8?±?0.3; 0.2–1.8 μg/g, respectively). A tendency for an age-related increase in Zn and Mn levels was observed in most brain regions while Cu levels showed to be negatively correlated with age. 相似文献
990.
Andres Mansilla Juan Pablo Rodriguez Jonatas M. C. Souza Sebastián Rosenfeld Jaime Ojeda Nair S. Yokoya 《Journal of applied phycology》2014,26(2):1133-1139
Ahnfeltia plicata (Hudson) E.M. Fries (Rhodophyta, Ahnfeltiales) is one of the most commercially important agarophytes in the world for its production of agar that is high quality and low in sulfate content. In the Magellanic Region, A. plicata forms extensive beds with high biomass production, which could be commercially exploited for agar production. The purposes of this study were to determine the optimal conditions of temperature, salinity, and culture medium; to evaluate the effects of different types and concentrations of auxins and cytokinins on growth of red and yellow gametophytes; and to provide background information on ecological parameters of natural population of A. plicata. Temperatures of 5, 8, 15, and 23 °C were tested, and the interaction of salinity of 25 and 35 psu with Provasoli enriched medium in half (PES/2) and quarter strength (PES/4), and with von Stosch enriched medium in half (VSES/2) and quarter strength (VSES/4) was also conducted. Concentrations of 5.0 and 50.0 μM of two auxins (indole-3-acetic acid (IAA), 2,4-dichlorophenoxyacetic acid (2,4-D)), and two cytokinins (isopentenyladenine (iP) and benzylaminopurine) were added to VSES medium and gelled with 0.5 % agar. Each treatment was tested with three replicates. Red gametophytes of A. plicata tolerate a range of temperature variation, from 5 to 23 °C, and the optimum temperature for growth was 15 °C. The highest growth rate was observed in salinity of 35 psu with half strength of von Stosch culture medium. Red and yellow gametophytes showed different responses to plant growth regulators, and red gametophytes were more sensitive than yellow ones to the addition of IAA and high concentration of iP. However, growth of red gametophytes of A. plicata was stimulated by 2,4-D. The differential sensitivity of red and yellow gametophytes to plant growth regulators suggests the need to test other types and concentrations of auxins and cytokinins. 相似文献