全文获取类型
收费全文 | 1143篇 |
免费 | 57篇 |
专业分类
林业 | 49篇 |
农学 | 20篇 |
基础科学 | 4篇 |
170篇 | |
综合类 | 113篇 |
农作物 | 25篇 |
水产渔业 | 49篇 |
畜牧兽医 | 716篇 |
园艺 | 23篇 |
植物保护 | 31篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 11篇 |
2021年 | 31篇 |
2020年 | 41篇 |
2019年 | 32篇 |
2018年 | 18篇 |
2017年 | 18篇 |
2016年 | 26篇 |
2015年 | 18篇 |
2014年 | 27篇 |
2013年 | 44篇 |
2012年 | 64篇 |
2011年 | 108篇 |
2010年 | 49篇 |
2009年 | 66篇 |
2008年 | 74篇 |
2007年 | 81篇 |
2006年 | 80篇 |
2005年 | 65篇 |
2004年 | 58篇 |
2003年 | 72篇 |
2002年 | 84篇 |
2001年 | 8篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1963年 | 1篇 |
排序方式: 共有1200条查询结果,搜索用时 359 毫秒
971.
Extracts of the mantle and viscera of the Indo-Pacific nudibranchs Goniobranchus aureopurpureus and Goniobranchus sp. 1 afforded 11 new diterpenoids (1–11), all of which possess a tetracyclic spongian-16-one scaffold with extensive oxidation at C-6, C-7, C-11, C-12, C-13, and/or C-20. The structures and relative configuration were investigated by NMR experiments, while X-ray crystallography provided the absolute configuration of 1, including a 2′S configuration for the 2-methylbutanoate substituent located at C-7. Dissection of animal tissue revealed that the mantle and viscera tissues differed in their metabolite composition with diterpenes 1–11 present in the mantle tissue of the two nudibranch species. 相似文献
972.
Armando García-Ortega Johan Verreth Karen Vermis Hans J. Nelis Patrick Sorgeloos Martin Verstegen 《Aquaculture International》2010,18(2):119-134
Temporary accumulation of ascorbic acid 2-sulfate (AAS) was measured to estimate food intake and gut evacuation in larvae
of African catfish. Fish larvae were fed decapsulated cysts of Artemia containing AAS. In a first experiment it was found that no biosynthesis of AAS occurs in the larvae of this species. In a
second experiment, the gut contents of the fish larvae fed were calculated as they changed during development. In a third
experiment, the gut evacuation rate of fish larvae was determined during continuous and discontinuous feeding regimes in the
first five days after the start of exogenous feeding. Food consumption by catfish larvae increased from 46.5% of their body
dry weight (BDW) on day 1 after the start of exogenous feeding to 53.8% BDW on day 3. Thereafter, food consumption decreased
to 27.8% BDW on day 5. A similar pattern was observed for gut evacuation, which increased during the first days of exogenous
feeding and decreased as fish growth continued. The rate of gut evacuation in a continuous feeding regime was significantly
higher (P < 0.05) than that under discontinuous feeding. On day 1 post-hatch and 7 h after first food ingestion the fish larvae evacuated
87% of the food in continuous feeding compared with 43% under discontinuous feeding. It was found that gut emptying differs
during larval development. Under continuous feeding, on days 1 and 3 post-hatch and 11 h after the first meal 90% of the food
was evacuated compared with 71% evacuated on day 5. The advantages and limitations of the AAS method for estimation of food
consumption by fish larvae are discussed. 相似文献
973.
Gas bubble disease and improper inflation of swim bladders in larval striped bass Morone saxatilis have been recently related in laboratory studies to very low levels of gas supersaturation. In other species, kills resulting from gas supersaturation have been reported in natural waters as large as Galveston Bay. We monitored warmwater ponds during spring to determine the extent of naturally occurring gas supersaturation and compared these levels with levels of gas saturation in ponds equipped with airlift pumps. Total gas pressure averaged 110% in the morning at the surface of non-aerated ponds and in the afternoon in ponds with airlift pumps. At other times of the day total gas pressure averaged 106–107% at the surface and bottom, morning and afternoon, in both aerated and non-aerated ponds. No evidence of gas bubble disease was found in 15-day-old striped bass fry cultured for 42 days in either aerated or non-aerated ponds. 相似文献
974.
Karen E. van de Wolfshaar P. Daniël van Denderen Tim Schellekens Tobias van Kooten 《Fish and Fisheries》2020,21(5):962-972
Bottom trawl fisheries have significant effects on benthic habitats and communities, and these effects have been studied intensively in the last decades. Most of these studies have related the changes in benthic community composition to direct effect of trawl gears on benthos, through imposed mortality. This line of argumentation ignores the fact that benthic organisms themselves form a complex food web and that bottom trawling may trigger secondary effects through this food web. We studied the potential consequences of such food web effects using a model of benthic predators, filter feeders, deposit feeders and fish. Our analysis shows how inclusion of ecological interactions complicates the relationship between bottom trawling intensity and the state of the benthic community and causes a non‐linear and non‐monotonic response of the benthic community to trawling. This shows that indirect food web effects can fundamentally alter the response of a benthic ecosystem to bottom trawling, compared to the direct effects of mortality. In light of our results, we argue that indicators of fishing impact on benthos need to account for positive as well as negative effects of bottom trawling, in order to accurately quantify the impact. Our findings highlight that understanding the food web ecology of the benthic ecosystem is crucial for understanding and predicting the effects of trawling on the seafloor. Work that promotes such understanding of the food web ecology seems a more productive research strategy than conducting ever more empirical trawling effect measurements. 相似文献
975.
976.
977.
Tien‐Tien Vicky Lau Suat‐Moi Puah Ching‐Kee Karen Hon Fui‐Fui Ching Jin‐Ai Mary Anne Tan Savithri Devi Ampalam Puthucheary Ping‐Chin Lee Kek‐Heng Chua 《Aquaculture Research》2020,51(10):3972-3982
Aeromonads are ubiquitous in aquatic environments and have been implicated in fish and human infections. In this study, we isolated, studied antimicrobial susceptibility patterns and screened the existence of 15 virulence genes in aeromonads from two famously consumed fish species—seven marine Tiger Grouper (Epinephelus fuscoguttatus) and eight freshwater Marble Goby (Oxyeleotris marmoratus) from the aquaculture hatchery in Sabah, Malaysia. A total of 30 aeromonads (17 A. caviae, 9 A. rivuli, 4 A. dhakensis) were identified using PCR targeting GCAT gene, rpoD‐restriction fragment length polymorphism and multi‐locus phylogenetic analysis. All 30 strains were resistant to amoxicillin and cephalothin and five strains were multidrug‐resistant. Nine virulence genes (lip, ela, eno, fla, aerA, hylA, dam, alt and ser) present in A. dhakensis, suggesting the virulence potential of this species as a fish pathogen. This study offers as a baseline for future studies in monitoring and managing these two fish in aquaculture industry. 相似文献
978.
An experiment is described that examined mowing with the return of excreta and mowing with the return of clippings as methods of simulating the return of nutrients by grazing animals in experiments where grazing is impracticable. These treatments were applied to a pure grass and to a grass/clover sward. Both methods gave herbage nearer in yield and composition to that resulting from natural grazing than did mowing with no return, but neither was suitable for use on sites outside experimental stations. Although the nitrogen returned in excreta was rather inefficiently used, it appeared to be the major factor in increasing yield on the grass sward and in changing the grass/clover balance on the mixed sward. The return-treatments had a marked effect on the potassium nutrition of both swards and the results suggest that omitting the grazing animal from trials assessing potassium fertilizer requirements may invalidate the results. 相似文献
979.
980.