全文获取类型
收费全文 | 446篇 |
免费 | 72篇 |
专业分类
林业 | 20篇 |
农学 | 15篇 |
基础科学 | 6篇 |
55篇 | |
综合类 | 33篇 |
农作物 | 16篇 |
水产渔业 | 40篇 |
畜牧兽医 | 306篇 |
园艺 | 4篇 |
植物保护 | 23篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 10篇 |
2020年 | 21篇 |
2019年 | 18篇 |
2018年 | 17篇 |
2017年 | 27篇 |
2016年 | 22篇 |
2015年 | 24篇 |
2014年 | 22篇 |
2013年 | 29篇 |
2012年 | 10篇 |
2011年 | 27篇 |
2010年 | 22篇 |
2009年 | 16篇 |
2008年 | 26篇 |
2007年 | 21篇 |
2006年 | 23篇 |
2005年 | 30篇 |
2004年 | 17篇 |
2003年 | 10篇 |
2002年 | 17篇 |
2001年 | 10篇 |
2000年 | 5篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 3篇 |
1996年 | 11篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1966年 | 3篇 |
排序方式: 共有518条查询结果,搜索用时 15 毫秒
21.
22.
Anne-Sophie Sergent Nathalie Bréda Léopoldo Sanchez Jean-Charles Bastein Philippe Rozenberg 《Annals of Forest Science》2014,71(6):709-720
Context
Since the 2003 drought and heat wave, Douglas-fir dieback has been reported in France in trees older than 30 years. Consequently, it is questioned whether selected Douglas-fir provenances are suited to the frequent and severe drought events which are forecast due to climate change.Aims
Our objective was to contribute to the screening of variability in productivity and growth response to soil-water deficit of mature trees from provenances not currently used for plantation in France.Methods
We sampled 22 provenances, including coastal and interior Douglas-fir, covering a wide part of its natural distribution, from Oregon to California for coastal provenances and from British Columbia to New Mexico for interior provenances. These provenances were planted at the mid 1970s in two provenance trials located in the south-west area of France. Variability of productivity, of wood density, and of radial growth in response to drought episodes among provenances was quantified and related to soil-water deficit computed by daily water balance calculations.Results
Whatever the provenance, annual radial growth is highly dependent on local soil-water deficit (Felines R 2 = 0.57, Le Treps R2 = 0.49). Radial growth and wood properties exhibit large differences between provenances at 30 years old. Variability between provenances for all wood characteristics studied is mainly structured geographically. Coastal provenances perform best for productivity at 30 years old (619 cm2?±?59), and exhibit a small growth reduction in 2004, the second successive year of drought (?10.7 %?±?3.8). Surprisingly, the southern interior provenances from the driest environments in the natural range show a large growth reduction in 2004 (?30.5 %?±?5.2).Conclusions
The provenances tested exhibited significant differences in growth performance and growth reduction induced by the soil-water deficit. The approach coupling retrospective analysis of radial growth on mature trees and water balance modelling is relevant for evaluating provenance adaptation to more frequent or severe drought episodes. 相似文献23.
Effect of pH and Decapsulation on the Toxicity of Ammonia to the Brine Shrimp Artemia franciscana 总被引:1,自引:0,他引:1
Artemia franciscana were hatched and tested for tolerance to ammonia at pH 6.5 and 8.5 in artificial seawater with a salinity of 17 ‰. Nauplii seemed to be less tolerant of ammonia at pH 6.5 despite the fact that more of the ammonia is in the ionized form (NH4 + ). It is suggested that this greater sensitivity is a result of the NH4 + competing with the Na+ during gut transfer. Nauplii hatched from decapulated cysts were more tolerant of ammonia than those hatched from whole cysts, probably because of a greater energy reserve. 相似文献
24.
John M David Sandra Duarte Vogel Kimberly Longo Daniel Sanchez Gregory Lawson 《Veterinary anaesthesia and analgesia》2014,41(6):654-659
ObjectiveTo investigate a topical local anesthesia technique as a means to prevent and/or diminish pain in mice in a laboratory setting associated with tail vein injections performed by personnel in training.Study designProspective, randomized experimental trial.AnimalsThirty six adult female, 23–28 g CD-1 mice from an in-house training colony. They were acclimated to routine training and handling classes.MethodsEutectic mixture of local anesthetics (EMLA) cream (2.5% lidocaine/2.5% prilocaine) or a bland ointment control (n = 18) was applied on the tail prior to intravenous injection. The injections were performed by novices, who had never attempted the procedure, and experienced personnel. All participants were blinded to treatment groups. Three injection attempts were allowed per animal. The mice were observed and scored by blinded evaluators for behavioral and physiological changes, including respiratory rate, vocalization, tail flick, and escape behaviors, during and after the injection.ResultsThis study demonstrates that aversive behaviors induced by lateral tail vein injection were not changed by the preemptive application of EMLA cream. The aversive behaviors associated with lateral tail vein injection were significantly affected by the number of injection attempts and the individual's experience level.Conclusions and clinical relevanceTopical EMLA cream did not reduce signs of aversive reaction to tail vein injection and thus we did not find support for its use in mouse training programs for tail vein injections. 相似文献
25.
26.
S. Zia G. Romano W. Spreer C. Sanchez J. Cairns J. L. Araus J. Müller 《Journal of Agronomy and Crop Science》2013,199(2):75-84
The main task of this research was to evaluate canopy temperature and Crop Water Stress Index (CWSI) by assessing genotype variability of maize performance for different water regimes. To that end, three hundred tropical and subtropical maize hybrids with different phenology in terms of date of anthesis were evaluated. The influence of phenology on the change in canopy temperatures and CWSI was not equal during the three dates of measurement. At the end of vegetative growth (82 days after sowing, DAS) and at the blister stage (DAS 97), a high significant difference in temperatures and CWSI (P < 0.001) were obtained between the early‐ and late‐maturity genotypes. During anthesis (DAS 89), phenology had a significant effect (P < 0.01) only for the well‐watered genotypes, while under water‐stress conditions, no differences were found between early and late genotypes in terms of canopy temperature and CWSI. High significant differences (P < 0.001) in stomatal conductance (gs) between early and late genotypes for different treatments were observed. A relationship (R2 = 0.62) between gs and canopy temperature was obtained. Under a water‐stress canopy, temperature was measured at anthesis, which was negatively correlated with grain yield of the early (r = ?0.55)‐ and late (r = ?0.46)‐maturity genotypes in the water‐stressed condition. 相似文献
27.
DJ STEWART JA VAUGHAN TC ELLEMAN† PA HOYNE† KJ BURNS JH DUFTY 《Australian veterinary journal》1991,68(2):50-53
The relationship between the serological classification system for serogroup B and for serogroup H of Bacteroides nodosus and cross-protection between subgroups within these serogroups was examined. Protection against ovine footrot following vaccination was achieved against other subgroup strains provided sufficient cross-reactive antibody was induced by shared pilus antigens. Within serogroup B, better cross-protection against one subgroup was obtained with a pili vaccine than a whole cell vaccine which correlated with higher pilus antibody titres induced by the former. For serogroup H, a lack of cross-protection and serological reactivity between subgroups was demonstrated, which indicates that the prototype strain of subgroup H2 should be designated a new serogroup. 相似文献
28.
Sanchez CA Krieger RI Khandaker N Moore RC Holts KC Neidel LL 《Journal of agricultural and food chemistry》2005,53(13):5479-5486
The Colorado River is contaminated with perchlorate concentrations of 1.5-8 microg/L, an anion linked to thyroid dysfunction. Over 90% of the lettuce (Lactuca sativa L.) consumed during the winter months in the United States is produced in the Lower Colorado River region. Studies were conducted in this region to survey the potential for lettuce perchlorate accumulation and estimate potential human exposure to perchlorate from lettuce. Total uptake of perchlorate in the above-ground plant of iceberg lettuce was approximately 5 g/ha. Exposure estimates ranged from 0.45 to 1.8 microg/day depending on lettuce types and trimming. For all lettuce types, hypothetical exposures were less than 4% of the reference dose recommended by the National Academy of Sciences. Results show the relative iodide uptake inhibition potential because of lettuce nitrate was 2 orders of magnitude greater than that associated with the corresponding trace levels of perchlorate. These data support the conclusion that potential perchlorate exposures from lettuce irrigated with Colorado River water are negligible relative to acute or long-term harmful amounts. 相似文献
29.
Jose A Morales Ligbel Sanchez Harvi Velasquez Beatriz De Borrego Marlene De Nava Denis Portillo Yulixis Cano Angel Morillo Ana Albornoz Elsa Socorro 《Water, air, and soil pollution》2001,130(1-4):511-516
Nutrient content and pH of rain samples collected at nine sites during 1988-1996 were studied to determine the amounts of N, P and S added by precipitation over Maracaibo Lake basin. The basin is a wide depression occupied by Lake Maracaibo and extensive alluvial plains and delimited by a mountainous zone of variable physiolgraphic characteristics with different cattle ranching and industrial activities. Rain pHs averaged ≈ 4 to 6, individual samples occasionally reached as low as pH 3 in the south basin. NH4 + levels were significantly higher (up to 2.6 mg/l NH4-N) than NO3 ? plus NO2 ?. Phosphorus levels were low, ranging from undetectable to 1.5 mg/l. The amounts of inorganic N/ha/yr added ranged from ≈ 5.4 Kg in the north to ≈ 8 Kg in the south basin; around the lakeshore, it was estimated that ≈ 9.8–16.8 Kg TN/ha (≈ 55 % as organic-N) are annually deposited. The annual amounts of SO4-S/ha added range from ≈ 10 to 13 Kg. The contribution of precipitation to P in the ecosystem is very small; ≈ 0.02 – 0.8 Kg of PO4-P/ha/yr was added in basin. The results of this study show that precipitation represents a significant factor for the total nitrogen and sulfur loading to Maracaibo Lake Basin. 相似文献
30.
Maria Margarida Ribeiro Leopoldo Sanchez Carla Ribeiro Fátima Cunha José Araújo Nuno M. G. Borralho Cristina Marques 《Annals of Forest Science》2011,68(4):701-714