全文获取类型
收费全文 | 680篇 |
免费 | 90篇 |
出版年
2021年 | 8篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 9篇 |
2015年 | 23篇 |
2014年 | 26篇 |
2013年 | 42篇 |
2012年 | 47篇 |
2011年 | 43篇 |
2010年 | 27篇 |
2009年 | 20篇 |
2008年 | 36篇 |
2007年 | 32篇 |
2006年 | 31篇 |
2005年 | 30篇 |
2004年 | 22篇 |
2003年 | 32篇 |
2002年 | 27篇 |
2001年 | 11篇 |
2000年 | 14篇 |
1999年 | 9篇 |
1997年 | 7篇 |
1995年 | 8篇 |
1993年 | 5篇 |
1992年 | 18篇 |
1991年 | 20篇 |
1990年 | 11篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1987年 | 9篇 |
1986年 | 18篇 |
1985年 | 10篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1970年 | 5篇 |
1969年 | 4篇 |
1964年 | 3篇 |
排序方式: 共有770条查询结果,搜索用时 15 毫秒
101.
Effects of scarcity and excess of larval food on life history traits of Aedes aegypti (Diptera: Culicidae) 下载免费PDF全文
Victoria Romeo Aznar Iris Alem María Sol De Majo Barbara Byttebier Hernán G. Solari Sylvia Fischer 《Journal of vector ecology》2018,43(1):117-124
Few studies have assessed the effects of food scarcity or excess on the life history traits of Aedes aegypti (L.) (Diptera: Culicidae) independently from larval density. We assessed immature survival, development time, and adult size in relation to food availability. We reared cohorts of 30 Ae. aegypti larvae from newly hatched to adult emergence with different food availability. Food conditions were kept constant by transferring larvae each day to a new food solution. Immature development was completed by some individuals in all treatments. The shortest development time, the largest adults, and the highest survival were observed at intermediate food levels. The most important effects of food scarcity were an extension in development time, a decrease in the size of adults, and a slight decrease in survival, while the most important effects of food excess were an important decrease in survival and a slight decrease in the size of adults. The variability in development time and adult size within sex and treatment increased at decreasing food availability. The results suggest that although the studied population has adapted to a wide range of food availabilities, both scarcity and excess of food have important negative impacts on fitness. 相似文献
102.
Questions
What are the syntaxonomic and synchorological patterns of the xerothermic chasmophytic vegetation in the central part of the Mediterranean Basin? What are the diagnostic species of the high‐rank syntaxa of Asplenietalia glandulosi, Onosmetalia frutescentis and Centaureo dalmaticae‐Campanuletalia pyramidalis?Location
Mediterranean coastal and subcoastal areas of southern France, Italy, Malta, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Albania and of mainland Greece.Methods
The data set of 1,261 published relevés was analysed using hierarchical clustering (Flexible Beta method), involving a series of data transformations. Indicator species analysis was used to select the best dendrogram solution and identify diagnostic taxa of the main clusters. The dendrogram was interpreted from a syntaxonomic point of view, using nomenclatural type relevés as a basis. The NMDS ordination was performed in order to visualize the floristic relationships among associations and high‐rank syntaxa. MRPP was used to test for differences among alliances.Results
The classification revealed four main clusters of relevés representing the chasmophytic vegetation of southern France, Sardinia and the northwestern part of Italy (Asplenienalia glandulosi/Asplenietalia glandulosi), the southwestern part of Italy and Malta (Tinguarrenalia siculae/Asplenietalia glandulosi), the Adriatic Basin area (Centaureo dalmaticae‐Campanuletalia pyramidalis) and the southern Balkans (Onosmetalia frutescentis). The NMDS ordination confirmed the overall pattern, while MRPP showed significant differences among the alliances of the above‐mentioned orders and suborders. The lists of diagnostic taxa of the high‐rank syntaxa were revised according to a supra‐national perspective.Conclusions
The new syntaxonomic scheme provides a comprehensive overview of the chasmophytic vegetation of the central part of the Mediterranean Basin. This scheme mostly matches the recently published EuroVegChecklist, but also exhibits important novelties concerning the syntaxonomic position of some alliances (Dianthion rupicolae, Centaureion pentadactyli, Arenarion bertolonii and Caro‐Aurinion), and the floristic and chorological relationships among high‐rank syntaxa, with new revised sets of diagnostic taxa. This revision might be useful for further small‐scale phytosociological studies.103.
104.
Influence of supplemental ultraviolet-B on indoleacetic acid and calmodulin in the leaves of rice (Oryza sativa L.) 总被引:9,自引:0,他引:9
Shaobai Huang Qiujie Dai Shaobing Peng Arlene Q. Chavez Ma. Lourdes L. Miranda Romeo M. Visperas Benito S. Vergara 《Plant Growth Regulation》1997,21(1):59-64
IR68 and Dular rice cultivars were grown under ambient, 13.0 (simulating 20% ozone depletion) and 19.1 (simulating 40% ozone depletion) kJ m-2 day-1 of biologically effective ultraviolet-B (UV-BBE) for 4 weeks. Plant height and leaf area were significantly reduced by supplemental UV-BBE radiation. Greater reduction in leaf area than of plant height was observed. A decrease in indole-3-acetic acid (IAA) content and increase in peroxidase and IAA oxidase activities of UV-B treated plants in both cultivars were observed compared with ambient control. Calmodulin content also decreased after plants were treated with high supplemental UV-B for two weeks and medium UV-B treatment for four weeks. The results indicated that peroxidase and IAA oxidase activities in rice leaves were stimulated by supplemental UV-B, resulting in the destruction of IAA which in turn may cause inhibition of rice leaf growth. Although the mechanism is unclear, calmodulin is most likely involved in leaf growth. 相似文献
105.
Eva Veronesi Roberto Pilani Marco Carrieri Romeo Bellini 《Journal of vector ecology》2007,32(2):313-318
The efficiency and practicality of two trapping methods for adult Phlebotomine sand flies in two areas of the Emilia-Romagna region (Italy) were evaluated. Suction traps (CO2) and sticky traps (ST) were used to collect sand flies every two weeks, from June to September, 1999, from 16:00 to 07:00. Two CO2 traps were activated at the same time for each area (one with light and one without light), whereas 38 (four with light and 34 without lights) and 48 (four with light and 44 without) sticky traps were activated in Borghi and Longiano, respectively. An Index of Apparent Abundance (IAA) was calculated for each trap type and area. A total of 2,253 sand flies was trapped over the four-month period, with 1,765 collected from Borghi and 488 from Longiano. Phlebotomus perfiliewi was the most abundant species collected, comprising 99.6% and 84.6% of the total flies trapped in Borghi and Longiano, respectively. Other species were also collected within the two areas (Phlebotomus perniciosus and Phlebotomus mascittii) but were not considered for further analyses due to low catches. Significantly more specimens were caught using CO2 than sticky traps and the addition of a light source also improved the catches, however, a significantly greater number of female specimens were collected by a CO2 trap without a light source. Phlebotomus perfiliewi thus appears to show a photophobic reaction in the case of females when trapped using CO2/light attractants. 相似文献
106.
107.
Kinetic and enzymatic features of metabolic stimulation of alveolar and peritoneal macrophages challenged with bacteria 总被引:3,自引:0,他引:3
The rate of oxygen uptake and of 14C-1-glucose oxidation by peritoneal and alveolar macrophages has been simultaneously recorded before and after the exposure of the cells to B. mycoides. A stimulation of both processes was detected within seconds after the addition of bacteria. A comparison of 14C-1-glucose with 14C-6-glucose oxidation has indicated that the stimulation of the 14CO2 production from 14C-1-glucose is substantially to be ascribed to an increased activity of the HMP pathway. On approaching anaerobiosis, the rate of the HMP pathway fell to zero, showing a direct link between cell respiration and production of NADP+ for the pathway. The assay of an enzyme, catalysing the reaction: NADPH + H+ + O2 → NADP+ + H2O2, in 20 000 g pellets has shown that this oxidase has a higher activity in subcellular fractions derived from macrophages previously exposed to bacteria. The activation of this enzyme may be the most important event in the metabolic stimulation of macrophages challenged with bacteria. On the basis of experiments carried out with KCN, an inhibitor of both NADPH oxidase and catalase, it has been concluded that, under particular conditions, also the concerted action of GSH peroxidase and GSSG reductase might contribute to supporting the HMP pathway activity. 相似文献
108.
J Romeo V Pinphanichakarn Y Iwamoto K Folkers 《Biochemical and biophysical research communications》1974,59(4):1286-1291
Many investigators have purified an aldehyde oxidase from mammalian livers, and described reactions of this enzyme with diverse substrates. Coenzyme Q10 was unambiguously identified and found present in some of these enzyme preparations. It was considered that coenzyme Q10 might participate in the functionality of this enzyme, but the validity of the intrinsic association of coenzyme Q10 was questioned. We have similarly purified aldehyde oxidase from rabbit livers. No coenzyme Q10 could be detected under controlled conditions for detecting the presence of coenzyme Q10. It is concluded that coenzyme Q10 may be a contaminant of some aldehyde oxidase preparations, and that it is not intrinsic for the functionality of this enzyme. 相似文献
109.
Anna Sannino PhD Stefania Romeo PhD Maria Rosaria Scarfì Daniele Pinchera PhD Fulvio Schettino PhD Mario Alonzo PhD Mariateresa Allocca PhD Olga Zeni PhD 《Bioelectromagnetics》2024,45(3):97-109
This study aims to investigate the cellular effects of radiofrequency exposure, 1950 MHz, long-term evolution (LTE) signal, administered alone and in combination with mitomycin-C (MMC), a well-known cytotoxic agent. Chinese hamster lung fibroblast (V79) cells were exposed/sham exposed in a waveguide-based system under strictly controlled conditions of both electromagnetic and environmental parameters, at specific absorption rate (SAR) of 0.3 and 1.25 W/kg. Chromosomal damage (micronuclei formation), oxidative stress (reactive oxygen species [ROS] formation), and cell cycle progression were analyzed after exposure and coexposure. No differences between exposed samples and sham-controls were detected following radiofrequency exposure alone, for all the experimental conditions tested and biological endpoints investigated. When radiofrequency exposure was followed by MMC treatment, 3 h pre-exposure did not modify MMC-induced micronuclei. Pre-exposure of 20 h at 0.3 W/kg did not modify the number of micronuclei induced by MMC, while 1.25 W/kg resulted in a significant reduction of MMC-induced damage. Absence of effects was also detected when CW was used, at both SAR levels. MMC-induced ROS formation resulted significantly decreased at both SAR levels investigated, while cell proliferation and cell cycle progression were not affected by coexposures. The results here reported provide no evidence of direct effects of 1950 MHz, LTE signal. Moreover, they further support our previous findings on the capability of radiofrequency pre-exposure to induce protection from a subsequent toxic treatment, and the key role of the modulated signals and the experimental conditions adopted in eliciting the effect. 相似文献
110.