全文获取类型
收费全文 | 16704篇 |
免费 | 14篇 |
国内免费 | 3篇 |
专业分类
林业 | 3668篇 |
农学 | 1317篇 |
基础科学 | 141篇 |
2809篇 | |
综合类 | 720篇 |
农作物 | 2137篇 |
水产渔业 | 1805篇 |
畜牧兽医 | 1129篇 |
园艺 | 1116篇 |
植物保护 | 1879篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 13篇 |
2021年 | 10篇 |
2020年 | 18篇 |
2019年 | 17篇 |
2018年 | 2758篇 |
2017年 | 2706篇 |
2016年 | 1193篇 |
2015年 | 74篇 |
2014年 | 34篇 |
2013年 | 34篇 |
2012年 | 808篇 |
2011年 | 2139篇 |
2010年 | 2109篇 |
2009年 | 1264篇 |
2008年 | 1324篇 |
2007年 | 1591篇 |
2006年 | 36篇 |
2005年 | 108篇 |
2004年 | 108篇 |
2003年 | 159篇 |
2002年 | 68篇 |
2001年 | 9篇 |
2000年 | 45篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 14篇 |
1992年 | 10篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 6篇 |
1988年 | 12篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 5篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1969年 | 3篇 |
1968年 | 4篇 |
1967年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Laurel Bellante 《Agriculture and Human Values》2017,34(1):119-134
Alternative food networks (AFNs) have become a common response to the socio-ecological injustices generated by the industrialized food system. Using a political ecology framework, this paper evaluates the emergence of an AFN in Chiapas, Mexico. While the Mexican context presents a particular set of challenges, the case study also reveals the strength the alternative food movement derives from a diverse network of actors committed to building a “community economy” that reasserts the multifunctional values of organic agriculture and local commodity chains. Nonetheless, just as the AFN functions as an important livelihood strategy for otherwise disenfranchised producers it simultaneously encounters similar limitations as those observed in other market-driven approaches to sustainable food governance. 相似文献
52.
Investor ownership or social investment? Changing farmland ownership in Saskatchewan,Canada 总被引:1,自引:0,他引:1
Annette Aurélie Desmarais Darrin Qualman André Magnan Nettie Wiebe 《Agriculture and Human Values》2017,34(1):149-166
There is growing recognition that land grabbing is a global phenomenon. In Canada, investors are particularly interested in Saskatchewan farmland, the province where 40 % of country’s agricultural land is situated. This article examines how the changing political, economic, and legal context under neoliberalism has shaped patterns of farmland ownership in Saskatchewan, between 2002 and 2014. Our research indicates that over this time, the amount of farmland owned by investors increased 16-fold. Also, the concentration of farmland ownership is on the rise, with the share of farmland owned by the largest four private owners increasing six-fold. Our methodology addresses some of the criticisms raised in the land grabbing literature. By using land titles data, we identified farmland investors and determined very precisely their landholdings thus allowing us to provide a fine-grained analysis of the actual patterns of farmland ownership. Although the article analyzes changes to farmland ownership in a specific historical, cultural and legislative context, it serves as the basis for a broader discussion of the values and priorities that land ownership policies reflect. Namely, we contrast an ‘open for business’ approach that prioritizes financial investment to one based on a land sovereignty approach that prioritizes social investment. The latter has greater potential if the aim is ecological sustainability and food sovereignty. 相似文献
53.
The occurrence of genetic erosion in local maize varieties in Mexico is intensely debated. Recent publications from Mexico show contradicting results about the loss of local varieties. Genetic erosion is a complex process, and well-documented examples of actual genetic erosion are not common in the literature. We worked in a region in which adoption of improved varieties was negligible, but other factors affecting maize agriculture were at play. The objectives of the study were to describe changes in maize diversity in the last 10 years and to associate them with socio-economic and environmental changes in a region in Mexico’s Central Highlands. We used richness and abundance of local varieties and diversity indices of races as indicators of maize diversity changes over time. We analyzed statistics and based on interviews we evaluated maize diversity changes between 2005 and 2015. We interviewed 113 farmers on two occasions with intervals from 5 to 10 years. According to climate statistics, rain has declined and temperature has increased. We also found a decrease in the lake level during the past 35 years. The total population in the region has doubled since the 1960s. The indigenous population has not changed significantly. Number of people working in agriculture has decreased since the 1960s. Rain fed agriculture decreased 8.1 % from 1990 to 2007. In four villages studied, farmed land area had decreased between 1995 and 2015. This reduction varies between 22 and 39 % depending on the village. Maize planted area decreased from 9675 to 8115 ha from 2003 to 2014. In the same period, avocado plantations grew from 34 to 786 ha. In despite of these changes, we did not find significant changes in average landraces per farmer (2.13 ± 0.28 in 2015) nor per village (4.15 ± 1.26 in 2015). Significant changes in maize races were not found either (1.91 ± 0.26 per farmer, 2.85 ± 0.86 per village in 2015). These results show that maize landrace diversity in the region is resilient but dynamic. 相似文献
54.
Tamara J. Bergstra Henk Hogeveen Elsbeth N. Stassen 《Agriculture and Human Values》2017,34(2):393-405
The pig sector is struggling with negative attitudes of citizens. This may be the result of conflicting attitudes toward pig husbandry between citizens and other stakeholders. To obtain knowledge about these attitudes, the objectives of this study were (1) to determine and compare attitudes of various stakeholders toward animals, humans and the environment in the context of pig husbandry and (2) to determine and compare the acceptability of publically discussed issues related to pig husbandry of various stakeholders. A questionnaire was distributed to citizens, conventional pig farmers, organic pig farmers, pig husbandry advisors and pig veterinarians. Respondents could indicate their attitude toward aspects related to animals, humans and the environment in the context of pig husbandry and they could indicate their opinion about the acceptability of issues of pig husbandry, e.g. piglet mortality and inside pig housing. Based on measured attitudes and the acceptability of issues, the studied stakeholders could be divided into three distinctive groups. The group of citizens and organic pig farmers showed negative attitudes toward all aspects of pig husbandry, the group of conventional pig farmers and pig husbandry advisors only showed negative attitudes toward aspects related to economics and the group of pig veterinarians showed negative attitudes to specific aspects of pig husbandry. This indicates that stakeholders have different interests and different perspectives with regard to pig husbandry. The pig sector should learn to understand citizens’ perspectives and take these into account in their line of work, the implementation of animal welfare measures and in their communication. 相似文献
55.
56.
Trustworthy eco-labels provide consumers with valuable information on environmentally friendly products and thus promote green consumerism. But what makes an eco-label trustworthy and what can government do to increase consumer confidence? The scant existing literature indicates that low governmental involvement increases confidence. This suggests that government should just provide the basic legal framework for eco-labeling and leave the rest to non-governmental organizations. However, the empirical underpinning of this conclusion is insufficient. This paper analyses consumer confidence in different organic food labeling regimes with varying degrees of governmental involvement. Using unique and detailed survey data from the US, United Kingdom, Denmark, and Sweden, the analysis shows that confidence is highest in countries with substantial state involvement. This suggests that governments can increase green consumerism through active and substantial involvement in eco-labeling. 相似文献
57.
Jennifer A. Kimball Tan D. Tuong Consuelo Arellano David P. Livingston III Susana R. Milla-Lewis 《Euphytica》2017,213(5):110
Winter hardiness is a major-limiting factor for St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] grown in the transitional climatic region of the United States. Lab-based freeze tests that mimic the range of field winter survivability in St. Augustinegrass can contribute to the selection of cold hardy genotypes. This study used a whole container method, four freezing temperatures, and two data collection systems to evaluate the freezing response of nine St. Augustinegrass genotypes ranging in their winter hardiness. Results indicated ?3 and ?4 °C with average regrowth ratings of 33.6 and 17.8% respectively, were more suitable temperatures for evaluating freeze survival in St. Augustinegrass than ?5 and ?6 °C with average regrowth ratings of 0.4 and 0%, respectively. Visual ratings of surviving green tissue and regrowth were generally well correlated when evaluated over a six week period post-freeze with Pearson correlation coefficients ranging of 0.17–0.62 for ?3 °C freeze tests and 0.79–0.93 for ?4 °C freeze tests. Additionally, measurement of percent green cover using digital imaging techniques commonly utilized in turfgrass field studies were significantly correlated (0.66) with visual ratings averaged across weekly post-freeze evaluation measurements for both ?3 and ?4 °C freezing temperatures. These results provide evidence that digital imaging analyses are useful in estimating surviving green tissue and regrowth in lab-based freeze tests. This study provides additional information regarding freezing temperatures, genotype responses, and data collection methods in St. Augustinegrass, which should aid breeders in the improvement of freeze tolerance in the species. 相似文献
58.
The selection of cross-compatible cultivars is essential to ensure fruit set in self-incompatible species like Japanese plum and thus the S-genotype must be determined in order to establish incompatibility groups. In this study an improved Japanese plum S-genotyping method, based in polymerase chain reaction and capillary electrophoresis detection of intron polymorphisms of S-locus genes, S-RNase and SFB, has been assayed and validated in a wide sample of cultivars. This method allows a more precise determination of amplified fragment sizes and therefore a better differentiation of self-incompatibility alleles. The assayed methodology was proven effective in the detection of 13 different S-alleles of S-RNases and SFBs and was used to S-genotype 105 Japanese plum cultivars, 32 of which are described by first time in this work. Analysed cultivars were assigned into 11 incompatibility groups and two new incompatibility groups (XX and XXI) were identified, increasing to 21 the number of incompatibility groups described in this crop. 相似文献
59.
Robert F. Park Henriette Goyeau Friedrich G. Felsenstein Pavel Bartoš Friedrich J. Zeller 《Euphytica》2001,122(1):113-127
Pathogenicity data from surveys of Puccinia triticina (formerly P. recondita f. sp. tritici) conducted in western Europe in 1995 were analysed to compare the structure of regional populations of the pathogen. Many
of the populations differed in phenotypic diversity and pathotypic composition, even though they occurred within a single
epidemiological unit, suggesting that local factors may influence the establishment and propagation of individual pathotypes
in the regional populations. Neighbouring regions were more similar than distant regions, and all regions shared at least
one pathotype, except populations in northern Italy and Scotland. A high degree of similarity was found between populations
in northern France and Great Britain, providing strong evidence of free movement of inoculum between these regions. Resistance
genes were postulated for a selection of 91 wheat cultivars, representing those most commonly grown in western Europe in 1995.
Thirteen cultivars lacked detectable seedling resistance genes and the remaining 78 possessed from one to three resistance
genes; those detected were Lr1, Lr3a, Lr10, Lr13, Lr14a, Lr17b, Lr20, Lr26 and Lr37. The most commonly detected resistance gene was Lr13, which was present singly or in combination with other resistance genes in 48 cultivars (53%). The gene Lr14a was detected in 18 cultivars, Lr26 was present in 16 cultivars. The role of host selection in the composition of the regional populations of P. triticina in western Europe in 1995 was difficult to assess on the basis of the results obtained, since virulence data were not available
for Lr13 and Lr14a.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
60.
Kamal Fouad Abdellatif Yehia Abdallah Khidr Yasser Mohammad El-Mansy Mohammad Mohammad El-Lawendey Yasser Abdelraouf Soliman 《Journal of Crop Science and Biotechnology》2012,15(2):93-99
Twenty-eight Egyptian cotton (Gossypium barbadense L.) genotypes (varieties and hybrids) were used for analysis of genetic diversity using DNA based markers (ISSR, SSR, and
EST) and to study varietal development of cotton. The ISSR markers gave the highest percentage of polymorphic bands as well
as polymorphic information content compared with the other molecular markers (i.e. EST and SSR markers). Using clustering
analysis, no general clustering according to the pedigree history of the genotypes was observed. Using principal coordinate
analysis (PCOORDA), cotton genotypes were separated by the first three principal coordinates (PC1, PC2, and PC3) accounting
for 11.5, 8.6, and 7.2% of the total genetic variance, respectively. The cotton genotypes were distributed into three parts
based on the first PC, each part containing a group of varieties having a common ancestor. ‘Giza 12’ variety was the common
ancestor for the varieties included in the first part and ‘Ashmouni’ variety was the common ancestor for the varieties included
in the second part, while both ‘Sakha 3’ and ‘Sakha 4’ varieties were common ancestors for the varieties included in the third
part. The results of the PCOORDA also showed better resolution of the genetic diversity than cluster analysis especially in
the illustration of the varietal development of cotton. That means that principal coordinate analysis can be strongly used
either alone or in combination with cluster analysis to discuss both genetic diversity and varietal development in the cotton
genotypes. 相似文献