全文获取类型
收费全文 | 9237篇 |
免费 | 441篇 |
国内免费 | 14篇 |
专业分类
林业 | 588篇 |
农学 | 229篇 |
基础科学 | 84篇 |
1585篇 | |
综合类 | 1610篇 |
农作物 | 364篇 |
水产渔业 | 818篇 |
畜牧兽医 | 3368篇 |
园艺 | 278篇 |
植物保护 | 768篇 |
出版年
2023年 | 59篇 |
2022年 | 87篇 |
2021年 | 155篇 |
2020年 | 211篇 |
2019年 | 208篇 |
2018年 | 206篇 |
2017年 | 218篇 |
2016年 | 210篇 |
2015年 | 184篇 |
2014年 | 252篇 |
2013年 | 449篇 |
2012年 | 542篇 |
2011年 | 707篇 |
2010年 | 368篇 |
2009年 | 352篇 |
2008年 | 635篇 |
2007年 | 623篇 |
2006年 | 592篇 |
2005年 | 574篇 |
2004年 | 608篇 |
2003年 | 571篇 |
2002年 | 504篇 |
2001年 | 98篇 |
2000年 | 90篇 |
1999年 | 93篇 |
1998年 | 81篇 |
1997年 | 70篇 |
1996年 | 67篇 |
1995年 | 62篇 |
1994年 | 61篇 |
1993年 | 50篇 |
1992年 | 57篇 |
1991年 | 49篇 |
1990年 | 58篇 |
1989年 | 49篇 |
1988年 | 42篇 |
1987年 | 44篇 |
1986年 | 33篇 |
1985年 | 32篇 |
1984年 | 34篇 |
1983年 | 40篇 |
1982年 | 26篇 |
1981年 | 25篇 |
1980年 | 28篇 |
1979年 | 23篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1976年 | 20篇 |
1975年 | 22篇 |
1974年 | 15篇 |
排序方式: 共有9692条查询结果,搜索用时 15 毫秒
101.
Context
Playa wetlands are the primary habitat for numerous wetland-dependent species in the Southern Great Plains of North America. Plant and wildlife populations that inhabit these wetlands are reciprocally linked through the dispersal of individuals, propagules and ultimately genes among local populations.Objective
To develop and implement a framework using network models for conceptualizing, representing and analyzing potential biological flows among 48,981 spatially discrete playa wetlands in the Southern Great Plains.Methods
We examined changes in connectivity patterns and assessed the relative importance of wetlands to maintaining these patterns by targeting wetlands for removal based on network centrality metrics weighted by estimates of habitat quality and probability of inundation.Results
We identified several distinct, broad-scale sub networks and phase transitions among playa wetlands in the Southern Plains. In particular, for organisms that can disperse >2 km a dense and expansive wetland sub network emerges in the Southern High Plains. This network was characterized by localized, densely connected wetland clusters at link distances (h) >2 km but <5 km and was most sensitive to changes in wetland availability (p) and configuration when h = 4 km, and p = 0.2–0.4. It transitioned to a single, large connected wetland system at broader spatial scales even when the proportion of inundated wetland was relatively low (p = 0.2).Conclusions
Our findings suggest that redundancy in the potential for broad and fine-scale movements insulates this system from damage and facilitates system-wide connectivity among populations with different dispersal capacities.102.
Said Ennahli Sorkel Kadir Houchang Khatamian David Scurlock Hafida Hanine 《International Journal of Fruit Science》2017,17(1):1-19
Simultaneous responses of American (Concord), European (Pinot Noir), and American-European hybrid (Traminette) cultivars to seasonal and diurnal variation in field environmental conditions were assessed to propose suitable cultivars for potential use for selection and breeding in grapevines in dry areas. ‘Pinot Noir’ had higher gas exchange parameters, higher water potential, and chlorophyll fluorescence, while ‘Concord’ had the lowest values in all three seasons and experienced moderate stress by the end of each season. The dry conditions in 2005 caused water potential to decline sharply compared to values recorded in 2004 and 2006. ‘Pinot Noir’ and ‘Traminette’ exhibited a mild stress, while ‘Concord’ exhibited a moderate stress in 2006. Photosynthetic rate decreased slightly during the summer with a slight recovery at the beginning of September, and did not differ across the seasons among cultivars. Stomatal conductance followed the same pattern. However, in both 2004 and 2005, stomatal conductance dropped sharply late in the season because of frequently occurring high temperatures that were greater than 32 °C. Maximum morning values of Fv/Fm were within the optimal range. The study suggests the presence of marginal photoinhibition during mid-summer in Concord cultivars, because no full recovery of photochemical efficiency early in the evening was observed. The European cultivar (Pinot Noir) and the American-European hybrid (Traminette) are more adapted to field conditions in Kansas than Concord cultivars. However, high cold-mortality of Pinot Noir due to high sensitivity to cold winter temperature makes the hybrid cultivars the most suitable cultivar for Midwest regions with relatively cold winters. 相似文献
103.
Teresa Mosquera Vásquez Sara Del Castillo David Cuéllar Gálvez Luis Ernesto Rodríguez 《Potato Research》2017,60(3-4):361-381
Global challenges like sustainable development, climate change, malnutrition and gender inequality can be tackled from an agricultural perspective. Micronutrient deficiency is a major problem for the health and food security of the population. In Colombia, iron deficiencies affect 32% of the children under the age of five; and 43% of the Colombian population have zinc and vitamin A deficiencies. We designed and implemented a research-for-development programme that links agriculture and nutrition through a two-stage project. In the first stage, we selected three new yellow potato cultivars with better nutritional contents, higher yield and better resistance to late blight than the traditional yellow cultivars. We characterized the Colombian germplasm, Solanum tuberosum Group Phureja, for its nutritional attributes. During this stage, studies of the social and nutritional status of the communities were also conducted. In the second stage, we focused on scaling up new potato cultivars to reach potato producers and consumers by promoting the production and marketing of good quality seed potatoes, by establishing four Rural Entrepreneurs Nuclei. The programme promotes gender equity, good dietary habits, the consumption of more nutritious potatoes and empowers local leadership to strengthen governance. Field work was conducted in southern and central regions of Colombia by employing social strategies such as the Family Farming Community Schools. In 50% of the cultivated area, we are replacing the originally used traditional yellow potatoes by the new, more nutritious, potatoes to reach 6 million consumers. A good quality seed system for small-scale potato growers has been implemented. These achievements have been reached through a comprehensive approach in a period of two years. 相似文献
104.
Rocío Toraya-Avilés Maira Segura-Campos Luis Chel-Guerrero David Betancur-Ancona 《Plant foods for human nutrition (Dordrecht, Netherlands)》2017,72(2):149-155
Cassava (Manihot esculenta Crantz) native starch was treated with pyroconversion and enzymatic hydrolysis to produce a pyrodextrin and an enzyme-resistant maltodextrin. Some nutritional characteristics were quantified for both compounds. Pyroconversion was done using a 160:1 (p/v) starch:HCl ratio, 90 °C temperature and 3 h reaction time. The resulting pyrodextrin contained 46.21% indigestible starch and 78.86% dietary fiber. Thermostable α-amylase (0.01%) was used to hydrolyze the pyrodextrin at 95 °C for 5 min. The resulting resistant maltodextrin contained 24.45% dextrose equivalents, 56.06% indigestible starch and 86.62% dietary fiber. Compared to the cassava native starch, the pyrodextrin exhibited 56% solubility at room temperature and the resistant maltodextrin 100%. The glycemic index value for the resistant maltodextrin was 59% in healthy persons. Its high indigestible starch and dietary fiber contents, as well as its complete solubility, make the resistant maltodextrin a promising ingredient for raising dietary fiber content in a wide range of foods, especially in drinks, dairy products, creams and soups. 相似文献
105.
Christopher J. Smallwood Jason D. Gillman Arnold M. Saxton Hem S. Bhandari Phillip A. Wadl Benjamin D. Fallen David L. Hyten Qijian Song Vincent R. Pantalone 《Journal of Crop Science and Biotechnology》2017,20(4):243-253
Soybean [Glycine max (L.) Merrill] yield and seed fatty acids, protein, and oil content are important traits for which an improved understanding of significant genomic regions would be useful. To accomplish this, a soybean population consisting of 203 F5 derived recombinant inbred lines (RILs) was developed and genotyped with 11,633 polymorphic single nucleotide polymorphisms (SNPs). Each RIL was grown in a single plot at Knoxville, TN in 2010; followed by replicated, multi-location field trials in 2013 and 2014. The data from 2010, 2013, and 2014 were analyzed together in order to detect quantitative trait loci (QTL) for these traits, and 30 total QTLs were detected. Five QTLs are candidates for confirmed status and one QTL is a candidate for positional confirmation. Many of the genes with mutations in close proximity to the fatty acid QTLs are involved in biological processes for fatty acids and/or lipids and could be considered possible candidate genes. Similarly, genes with mutations in genomic regions near yield, protein, and oil QTLs were plentiful and may contribute to the variation observed in these traits. Except for yield and stearic acid, each trait displayed pleiotropic effects with other traits in this study. Notable are the pleiotropic effects for oleic and linolenic acid on chromosomes 9, 13, and 19. Overall, the findings from this research contribute new information to the genetic understanding of soybean yield and seed fatty acids, protein and oil content. This understanding will be useful in making trait improvements. 相似文献
106.
107.
Waseem Akbar Anilkumar Gowda Jeffrey E Ahrens Jason W Stelzer Robert S Brown Scott L Bollman John T Greenplate Jeffrey Gore Angus L Catchot Gus Lorenz Scott D Stewart David L Kerns Jeremy K Greene Michael D Toews David A Herbert Dominic D Reisig Gregory A Sword Peter C Ellsworth Larry D Godfrey Thomas L Clark 《Pest management science》2019,75(3):867-877
108.
109.
Since the discovery of penicillin in 1928 and throughout the ‘age of antibiotics’ from the 1940s until the 1980s, the detection of novel antibiotics was restricted by lack of knowledge about the distribution and ecology of antibiotic producers in nature. The discovery that a phenazine compound produced by Pseudomonas bacteria could suppress soilborne plant pathogens, and its recovery from rhizosphere soil in 1990, provided the first incontrovertible evidence that natural metabolites could control plant pathogens in the environment and opened a new era in biological control by root‐associated rhizobacteria. More recently, the advent of genomics, the availability of highly sensitive bioanalytical instrumentation, and the discovery of protective endophytes have accelerated progress toward overcoming many of the impediments that until now have limited the exploitation of beneficial plant‐associated microbes to enhance agricultural sustainability. Here, we present key developments that have established the importance of these microbes in the control of pathogens, discuss concepts resulting from the exploration of classical model systems, and highlight advances emerging from ongoing investigations. © 2019 Society of Chemical Industry 相似文献
110.
Adams Alison B. Pontius Jennifer Galford Gillian Gudex-Cross David 《Landscape Ecology》2019,34(10):2401-2419
Landscape Ecology - Understanding how the Northern Forest landscape has changed and is likely to change, both in terms of forest extent and forest configuration, has important implications for... 相似文献