全文获取类型
收费全文 | 681篇 |
免费 | 33篇 |
国内免费 | 3篇 |
专业分类
林业 | 61篇 |
农学 | 35篇 |
基础科学 | 4篇 |
122篇 | |
综合类 | 109篇 |
农作物 | 31篇 |
水产渔业 | 47篇 |
畜牧兽医 | 243篇 |
园艺 | 8篇 |
植物保护 | 57篇 |
出版年
2023年 | 7篇 |
2022年 | 5篇 |
2021年 | 15篇 |
2020年 | 8篇 |
2019年 | 16篇 |
2018年 | 17篇 |
2017年 | 26篇 |
2016年 | 25篇 |
2015年 | 12篇 |
2014年 | 13篇 |
2013年 | 25篇 |
2012年 | 46篇 |
2011年 | 43篇 |
2010年 | 27篇 |
2009年 | 29篇 |
2008年 | 50篇 |
2007年 | 42篇 |
2006年 | 22篇 |
2005年 | 26篇 |
2004年 | 26篇 |
2003年 | 31篇 |
2002年 | 25篇 |
2001年 | 9篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1969年 | 6篇 |
1967年 | 4篇 |
1964年 | 3篇 |
1939年 | 2篇 |
排序方式: 共有717条查询结果,搜索用时 0 毫秒
711.
Md. Ahasanul Hoque Mohammad Mahmudul Hassan Enamul Haque Amir Hossan Shaikat Shahneaz Ali Khan Abdul Alim Lee Francis Skerratt Ariful Islam Hein Min Tun Ravi Dissanayake Tapan Kumar Day Nitish Chandra Debnath Mat Yamage 《Preventive veterinary medicine》2014
A survey of gastrointestinal parasitic infection as determined by faecal examination was conducted among domestic and wild birds in Bangladesh. Birds were sampled from households, wet markets and wetlands in Chittagong and Greater Sylhet districts during April 2012 to February 2013. Mist nets were used to catch resident wild and migratory birds. The overall prevalence of parasitic infection ranged among locations from 25 to 55% in indigenous domestic ducks (live bird samples = 304), 20% in resident wild birds (environmental faecal samples = 40) and 40% in migratory birds (live bird samples = 35). The prevalence of parasitic infection was significantly higher in indigenous domestic ducks collected during summer (39%) than winter (22%) (p = 0.04). In domestic indigenous ducks and Muscovy ducks, both single and multiple types of parasitic infections were found. However, other domestic birds and wild birds often had a single type of parasitic infection. Ascaridia spp. with an average egg load of 50–900, was commonly detected in faecal samples of domestic and wild birds in this study. Other identified parasites were Capillaria spp. and Heterakis spp. both in domestic and wild birds. Improvement of biosecurity measures for household duck farms through educating and motivating household farmers could help mitigate the effects of parasitic infection on production. 相似文献
712.
Kevin J. Collier Michael A. Pingram Laura Francis Jeremy Garrett‐Walker Michele Melchior 《Ecology of Freshwater Fish》2018,27(4):888-897
We quantified trophic overlap between the invasive, non‐native catfish brown bullhead (Ameiurus nebulosus) and the New Zealand native shortfin eel (Anguilla australis) in four peat and riverine lakes using stable isotope (δ13C and δ15N) and gut content analyses. Across all lakes and fish sizes over the austral spring–summer period, shortfin eel guts were dominated numerically by fish prey (57% occurrence cf 42% in brown bullhead), while Diptera larvae were most commonly encountered in guts of brown bullhead (45% cf 14% in eels). Significant differences in % composition of animal contents in guts were detected between fish species and sampling occasions (n = 4) but not between lakes. In contrast, stable isotope signatures of brown bullhead and shortfin eel did differ significantly between lakes but not between sampling occasions, indicating enduring sources of nutrition despite apparently differing ingestion patterns over time. The R mixing model MixSIAR indicated that shortfins likely assimilated higher proportions of fish prey carbon compared to brown bullheads, which appeared to show greater assimilation of invertebrates, consistent with the results of gut content analyses. Isotopic niche regions, calculated in nicheROVER using probabilistic ellipses, indicated that shortfin eels occupied at least c.60% of brown bullhead trophic niche, which occupied less than 30% of eel trophic niche in all but one lake. These estimates suggest that brown bullhead has higher potential to influence shortfin eel nutrition than vice versa, or that a broad trophic niche occupied by eels provides resilience to the effects of overlapping consumption patterns with invasive omnivores. 相似文献
713.
Genotype × environment interactions for tea yields 总被引:1,自引:0,他引:1
Several methods were used to evaluate phenotypic stability in 20 tea (Camellia sinensis) genotypes, many of which are cultivated widely in East Africa. The genotypes were evaluated for annual yields at two sites
over a six year period. Data obtained were used to compare methods of analysis of G × E interactions and yield stability in
tea. A standard multi-factor analysis of variance test revealed that all first order interactions (genotypes × sites; genotypes
× years; sites × years) as well as second order interactions (sites × genotype × years) were significant. Regression analysis
was used to assess genotype response to environments. Regression coefficients (bi) obtained ranged from 0.78 to 1.25. Deviations from regression (S2d) were significant (p < 0.05) from 0.0 for all the test genotypes. Analysis for sensitivity to environment change (SE2
i) revealed that the test genotypes differed in their level of sensitivity. The hierarchical cluster analysis method was used
to assemble the test genotypes into groups with similar regression coefficients (bi) and mean yield, which proved useful for the identification of high yielding genotypes for breeding purposes as well as for
commercial exploitation. Rank correlation between yield and some stability parameters were significant. Mean yield was significantly
correlated to bi (r = 0.80***) and SE2
i(0.74***) which is an indication that selection for increased yield in tea would change yield stability by increasing bi and SE2
i leading to development of genotypes that are specifically adapted to environments with optimal growing conditions. Genotypes
differed in response to years and sites. As stand age increased, genotype yields generally increased though annual yield fluctuations
were more pronounced in some genotypes than others. This response was not consistent across the sites for all genotypes indicating
the need to test clones at multiple sites over longer periods of time.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
714.
Chidiebere Ofoegbu Paxie W Chirwa Joseph Francis Folarannmi D Babalola 《Southern Forests》2017,79(2):109-116
In most African countries, forest-based climate change intervention initiatives such as nationally appropriate mitigation actions (NAMAs) and national adaptation programmes of action (NAPAs) are widely accepted. This is mainly due to the fact that they are relevant in addressing multiple challenges associated with rural development, mitigation and adaptation to climate change, and sustainable forest management. However, there are concerns about the implications of strategic and practical steps taken in this context on forest-dependent communities. Thus, there is need to reconcile local socio-economic vulnerabilities and forest-based climate change intervention initiatives. In the current study, socio-economic factors influencing households’ dependence on forest resources and associated implications on climate change interventions were investigated. Proportionate stratified random sampling was used to select 366 households from forest-based rural communities in Vhembe District of South Africa. A structured questionnaire was administered to household heads in 21 villages. The Pearson’s chi-square test was used to analyse the factors that influence household dependence on forest. The effects of household socio-economic characteristics on households’ forest dependence influencing factor were determined using the binary logit model. Up to 97% of the respondents depended on the forest resources predominantly because of low costs associated with using them. It was observed that socio-economic characteristics of households such as farm husbandry skills, years of residence (53–65) in the community and age of respondents (≤38–65) significantly (P < 0.05) influenced use of the forest resources. Thus, effectiveness and sustainability of forest-based climate change intervention initiatives can be promoted if the socio-economic conditions prevailing within households in areas next to forests are improved. 相似文献
715.
Francis AJ Johnson MJ Culshaw GC Corcoran BM Martin MW French AT 《The Journal of small animal practice》2011,52(6):282-288
Objective : To determine the outcome, independent predictors of cardiac death, and the Doppler‐derived pressure gradient cut‐off for predicting cardiac death in dogs with pulmonic stenosis, with or without tricuspid regurgitation, that do not undergo balloon valvuloplasty or valve surgery. Methods : Review of medical records of two UK referral centres between July 1997 and October 2008 for all cases of pulmonic stenosis that had no balloon valvuloplasty or valve surgery. Inclusion criteria included a diagnosis of pulmonic stenosis; spectral Doppler pulmonic velocity greater than 1·6 m/s; characteristic valve leaflet morphological abnormalities. Exclusion criteria included concurrent significant cardiac defects, including tricuspid dysplasia. Dogs with tricuspid regurgitation were included. Dogs were classified according to Doppler‐derived pressure gradients into mild, moderate or severe pulmonic stenosis categories. Results : Presence of tricuspid regurgitation and severe stenosis were independent predictors of cardiac death. A pulmonic pressure gradient of more than 60 mmHg was associated with 86% sensitivity, and 71% specificity of predicting cardiac death. Clinical Significance : There is an increased probability of cardiac death in those cases which have a pulmonary pressure gradient greater than 60 mmHg and tricuspid regurgitation, though the effect of severity of tricuspid regurgitation on outcome was not measurable because of small sample sizes. These animals might benefit from intervention. 相似文献
716.
Francis Saiti Daniel M Jamu Busiso Chisala & Patrick Kambewa 《Aquaculture Research》2007,38(4):340-350
A cohort‐based bio‐economic biomass growth and economic model, validated with data from experiments conducted in Malawi, was used to identify an optimal harvesting strategy for mixed‐sex tilapia ponds. Three harvesting scenarios (baseline, economic optimum time +10 days and economic optimum time) were used. In each harvesting scenario four options were explored: (i) no further harvest, harvest every (ii) 60 days, (iii) 90 days and (iv) 120 days after initial harvest. The lowest simulated yield (487 kg ha−1 year−1) was obtained when no partial harvesting was carried out and fish were harvested after 365 days. Maximum yield (4416 kg ha−1 year−1) was obtained when partial harvests were carried out every 90 days starting with a first harvest of fish weighing 60 g or more at day 90. Maximum financial returns (US$2561 ha−1 year−1) were obtained when partial harvests were carried out every 120 days starting with the first harvest at day 90 and removing all fish ≥60 g. The model simulations indicate that mixed‐sex tilapia culture may be profitable for tilapia farmers in Africa where markets accept small (60–150 g)‐sized fish. The study further shows that a cohort‐based population growth model can be reliably incorporated in tilapia production models to simulate fish yields in mixed‐sex tilapia production systems. However, incorporation of intergenerational competition effects could improve the model's utility as a decision support tool for managing mixed‐sex tilapia production. 相似文献
717.
Mangroves are among the most productive ecosystems in tropical and subtropical regions. Historically, mangroves are assumed to support artisanal fisheries, leading decision‐makers to protect mangroves based on this premise. However, this relationship remains unclear, despite positive correlations obtained in different geographical regions. Here, we provide the first meta‐analysis of the mangroves–fisheries linkage at a global level. After conducting a systematic review, 23 publications containing 51 studies estimating the mangrove–fishery linkage were obtained. A random effect model was used to estimate the effect size (Pearson's correlation coefficient) of each individual study as well as the overall effect size. We found strong evidence for the mangrove–fishery linkage with an overall effect size of r = 0.72 (95% CI: 0.61–0.81), and substantial heterogeneity was observed (Q = 143.88, df = 50, P < 0.01). The countries where the studies were carried out were the only significant moderator (QM = 26.07, P < 0.01), while fisheries types (i.e. crab, fish, shellfish, prawn and total) and global regions were not good predictors of the relationship. Our results show that mangrove area is a good predictor of fishery catches overall, confirming the importance of conserving such habitats. 相似文献