全文获取类型
收费全文 | 475篇 |
免费 | 43篇 |
专业分类
林业 | 37篇 |
农学 | 29篇 |
基础科学 | 1篇 |
70篇 | |
综合类 | 17篇 |
农作物 | 30篇 |
水产渔业 | 71篇 |
畜牧兽医 | 206篇 |
园艺 | 8篇 |
植物保护 | 49篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 20篇 |
2021年 | 20篇 |
2020年 | 35篇 |
2019年 | 35篇 |
2018年 | 28篇 |
2017年 | 22篇 |
2016年 | 38篇 |
2015年 | 27篇 |
2014年 | 23篇 |
2013年 | 24篇 |
2012年 | 37篇 |
2011年 | 36篇 |
2010年 | 16篇 |
2009年 | 14篇 |
2008年 | 28篇 |
2007年 | 17篇 |
2006年 | 17篇 |
2005年 | 22篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 7篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1980年 | 1篇 |
1974年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有518条查询结果,搜索用时 31 毫秒
511.
Eliane Marinho-Soriano Marcos Rogério Camara Thiago de Melo Cabral & Marcella Araíyo do Amaral Carneiro 《Aquaculture Research》2007,38(2):182-187
The aim of this study was to evaluate the use of Gracilaria cervicornis meal as a partial substitute for the industrial feeds used in shrimp (Litopenaeus vannamei) farming. A total of 90 L. vannamei juveniles (0.34 g) were assigned randomly into nine experimental units at a stocking density of 10 shrimp tank−1 and fed a commercial shrimp feed (CSF; 35% crude protein) as a control treatment, a feed made entirely of G. cervicornis (GCM), and a mixture of equal parts of the commercial shrimp feed and the Gracilaria meal (MIX) for 30 days. Over the first 2 weeks of the experiment, the survival was high (100%) in all dietary treatments. However, at the termination of the feeding trial survival decreased to 40% in shrimp fed GCM, significantly lower (P<0.05) than survival of shrimp fed the commercial diet control (CSF) or MIX treatments (100%). The highest growth performance was obtained in the CSF or MIX treatment groups. The absolute growth increase in these groups was significantly higher than for shrimp fed GCM. Similarly, the specific growth rates (SGRs) of shrimp given feeds containing CSF (5.11% day−1) and MIX (4.71% day−1) were significantly greater (P<0.05) than that of shrimp fed GCM pellets (0.44% day−1). The feed efficiency ratios (FERs) were 64 for CSF, 54.3 for MIX and 3.3 for GCM. The results obtained in this study indicated the effectiveness of using G. cervicornis as a partial substitute for shrimp feeds. To our knowledge, this is the first time that the concept that macroalgae can partially substitute for the industrial feeds used in shrimp (L. vannamei) farming has been demonstrated. 相似文献
512.
Andressa Reis Alitcia Moraes Kleinowski Fátima Rosane Schuquel Klein Renata Trevizan Telles Luciano do Amarante Eugenia Jacira Bolacel Braga 《Journal of Crop Science and Biotechnology》2015,18(5):349-357
In tissue culture, several chemical and physiological factors can influence the production of secondary metabolites. The growth response and increased secondary metabolite production generated by a high irradiance environment, can be used to determine a favorable habitat for the growth and conservation of medicinal plants. Thus, the present study aimed to evaluate the influence of light quality on growth and production of secondary metabolites in Alternanthera sessilis (L.) R. Br. ex DC. (sessile joyweed), Alternanthera philoxeroides (Mart.) Grisebach (alligatorweed), Alternanthera tenella Colla (joyweed), and Alternanthera brasiliana (L.) Kuntze (Brazilian joyweed) plants cultured in vitro. The species were grown in MS medium, for 45 days in different light qualities (blue, white, and red). Growth parameters and biochemical analysis were performed at the end of the study. The results show that the red light allowed a higher accumulation of biomass in most species; red and white light were great inductors for the production of betacyanin and the blue light favored the enhancement of flavonoids. In this manner, the quality of light can affect the betacyanin, betaxanthin, and flavonoid biosynthesis as well as growth patterns in the related Alternanthera species. Based on the data presented, we suggest that specific genes can encode the pigment production according to the light quality which exhibit distinct activation patterns in different plant species. 相似文献
513.
Francisco L. Nascimento Iola G. Boëchat Alexandre O. Teixeira Björn Gücker 《Water, air, and soil pollution》2012,223(1):389-398
This study examined patterns of stream sediment granulometry, organic matter (OM) and metal concentration, and surface water
characteristics in a catchment in the Brazilian Iron Quadrangle that is highly impacted by surface iron mining and gully erosion.
Sediment granulometry indicated fine sediment deposition at impacted stream sites, i.e., tendencies towards bimodal particle
size distributions with an additional peak in the sand fraction at impacted stream sites that did not occur at pristine reference
sites, as well as towards smaller mean sediment particle sizes at impacted sites than at reference sites. Impacted sites also
had significantly lower sediment OM contents than reference sites. Sediment heavy metal and arsenic concentrations did not
differ between impacted and reference sites and were generally below published target or threshold effect concentrations.
Impacts on surface water characteristics occurred only locally at a site that received tailings pond effluent from an iron
mine and had very low pH and conductivity values. Sediment characteristics exhibited substantial spatial variability in the
studied tropical catchment, showing that land use impacts can hardly be detected in routine monitoring and impact assessment
studies that adopt a before–after control-impact approach and do not consider pristine reference streams. These results underline
the importance of high-resolution and long-term sediment monitoring as well as integrated basin-scale sediment management
programs. 相似文献
514.
Abdo AA Ackermann M Ajello M Allafort A Baldini L Ballet J Barbiellini G Bastieri D Bechtol K Bellazzini R Berenji B Blandford RD Bloom ED Bonamente E Borgland AW Bouvier A Brandt TJ Bregeon J Brez A Brigida M Bruel P Buehler R Buson S Caliandro GA Cameron RA Cannon A Caraveo PA Casandjian JM Çelik Ö Charles E Chekhtman A Cheung CC Chiang J Ciprini S Claus R Cohen-Tanugi J Costamante L Cutini S D'Ammando F Dermer CD de Angelis A de Luca A de Palma F Digel SW do Couto e Silva E Drell PS 《Science (New York, N.Y.)》2011,331(6018):739-742
A young and energetic pulsar powers the well-known Crab Nebula. Here, we describe two separate gamma-ray (photon energy greater than 100 mega-electron volts) flares from this source detected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. The first flare occurred in February 2009 and lasted approximately 16 days. The second flare was detected in September 2010 and lasted approximately 4 days. During these outbursts, the gamma-ray flux from the nebula increased by factors of four and six, respectively. The brevity of the flares implies that the gamma rays were emitted via synchrotron radiation from peta-electron-volt (10(15) electron volts) electrons in a region smaller than 1.4 × 10(-2) parsecs. These are the highest-energy particles that can be associated with a discrete astronomical source, and they pose challenges to particle acceleration theory. 相似文献
515.
Carvalho Ddo C Brigagão MR dos Santos MH de Paula FB Giusti-Paiva A Azevedo L 《Plant foods for human nutrition (Dordrecht, Netherlands)》2011,66(2):114-121
Differentiation between organic and conventional coffee has increased due to the growing demand and high consumption of healthy
foods that contain compounds with antioxidant potential, which have been associated with the reduction of chronic diseases.
We used organic and conventional coffee in powder 4% (w/w) and infusions 5%, 10% and 20% (w/v) incorporated in a commercial
diet to test in vivo. The levels of chlorogenic acid, caffeine and trigonelline were determined by high performance liquid chromatography. The
body weight, weight gain, food consumption, aberrant foci crypt, mucin depleted foci, stress biomarkers protein carbonyl and
malondialdehyde, biochemical parameters and behavior of the rats were compared between the experimental and control groups
within a framework of colon carcinogenesis. The organic coffee showed higher levels of chlorogenic acid, caffeine and trigonelline
than conventional, however, this difference did not significantly affect behavior. The infusions had an antioxidant effect,
reducing the levels of malondialdehyde; however, the biochemical parameters of the serum were not altered, and there was neither
induction nor prevention of preneoplasic lesions. 相似文献
516.
517.
Anticancer activity evaluation of kuanoniamines A and C isolated from the marine sponge Oceanapia sagittaria, collected from the Gulf of Thailand 总被引:1,自引:0,他引:1 下载免费PDF全文
The pyridoacridine alkaloids kuanoniamines A and C were isolated together with 24 α-methylcholestanol, p-hydroxybenzaldehyde, p-hydroxybenzoic acid, phenylacetic acid and 3-formylindole from the ethyl acetate extract of the marine sponge Oceanapia sagittaria (Sollas), collected from the Gulf of Thailand. Kuanoniamines A and C were evaluated for their effect on the growth of five human tumour and a non-tumour cell lines, as well as on the proliferation of human lymphocytes. Kuanoniamine A was found to be a potent growth inhibitor of all the tumour and a non-tumour cell lines while kuanoniamine C was less potent but showed high selectivity toward the estrogen dependent (ER+) breast cancer cell line. Kuanoniamine A has shown to be a more potent inhibitor of DNA synthesis than kuanoniamine C. Kuanoniamine A was also found to cause an extensive reduction of the MCF-7 cells in G2/M phase as well as an increase in the apoptotic cells. 相似文献
518.