全文获取类型
收费全文 | 1103篇 |
免费 | 106篇 |
国内免费 | 113篇 |
出版年
2024年 | 1篇 |
2023年 | 20篇 |
2022年 | 42篇 |
2021年 | 49篇 |
2020年 | 32篇 |
2019年 | 67篇 |
2018年 | 51篇 |
2017年 | 59篇 |
2016年 | 64篇 |
2015年 | 53篇 |
2014年 | 65篇 |
2013年 | 74篇 |
2012年 | 42篇 |
2011年 | 67篇 |
2010年 | 39篇 |
2009年 | 53篇 |
2008年 | 68篇 |
2007年 | 50篇 |
2006年 | 44篇 |
2005年 | 41篇 |
2004年 | 42篇 |
2003年 | 42篇 |
2002年 | 36篇 |
2001年 | 26篇 |
2000年 | 29篇 |
1999年 | 26篇 |
1998年 | 19篇 |
1997年 | 13篇 |
1996年 | 16篇 |
1995年 | 12篇 |
1994年 | 18篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1322条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Mirza Barjees Baig Irena Gorski Roni A. Neff 《Saudi Journal of Biological Sciences》2019,26(7):1633-1648
IntroductionMultiple estimates suggest the Kingdom of Saudi Arabia (KSA) may have one of the highest rates of wasted food globally. The KSA has limited arable lands and scarce water and thus relies on extensive imports and food subsidies to meet food demand. Accordingly, waste and loss of food are a significant concern for food security.Materials and methodsA narrative literature review was performed to identify the available information relevant to characterizing the context, magnitude of food wasted in the KSA, key contributing factors, and existing interventions and recommendations.ResultsEstimates of annual per capita waste of food ranged from 165 kg to 511 kg. Given the country's relatively limited agricultural production, the consumer and retail levels are primary targets for intervention. Key contributors to waste include culture, food valuation, policy and industry factors, and awareness and concern. The country is at an early stage of developing responses. We build upon existing approaches and recommendations, with particular emphasis on the potential role of agricultural extension staff in addressing the issue, and highlight research needs.ConclusionsGiven the potentially exceptional levels of wasted food in the KSA and the extensive evidence gaps, there is a great need for further research and action. Our review and synthesis presents numerous opportunities to advance innovative waste reduction approaches in the country, with particular relevance for other parts of the Middle East and other areas early in their efforts to address waste of food. 相似文献
995.
《Critical reviews in biotechnology》2012,32(1):99-118
AbstractThe importance of highly efficient wastewater treatment is evident from aggravated water crises. With the development of green technology, wastewater treatment is required in an eco-friendly manner. Biotechnology is a promising solution to address this problem, including treatment and monitoring processes. The main directions and differences in biotreatment process are related to the surrounding environmental conditions, biological processes, and the type of microorganisms. It is significant to find suitable biotreatment methods to meet the specific requirements for practical situations. In this review, we first provide a comprehensive overview of optimized biotreatment processes for treating wastewater during different conditions. Both the advantages and disadvantages of these biotechnologies are discussed at length, along with their application scope. Then, we elaborated on recent developments of advanced biosensors (i.e. optical, electrochemical, and other biosensors) for monitoring processes. Finally, we discuss the limitations and perspectives of biological methods and biosensors applied in wastewater treatment. Overall, this review aims to project a rapid developmental path showing a broad vision of recent biotechnologies, applications, challenges, and opportunities for scholars in biotechnological fields for “green” wastewater treatment. 相似文献
996.
1. Agricultural intensification generally leads to large‐scale habitat changes marked by decreasing availability of nesting sites and flower resources for pollinators. However, little is known about how such changes impact wild bee maternal body size and foraging effort and, more importantly, whether there is a subsequent effect on their offspring. 2. Nests were collected from the common eastern North American stem nesting bee, Ceratina calcarata, across three land management types: (i) intensely managed conventional farms; (ii) moderately disturbed organic farmland; and (iii) least managed roadsides. The study assessed the effects of land use types on body size and wing wear (a proxy for foraging effort) of maternal bees, and on their offspring in terms of clutch size, survival, sex ratio and body size. 3. Findings revealed that more brood reached pupal stages from nests collected in conventional farmlands. This was due to the total lack of parasites, possibly because the host density is below the threshold that can support a brood parasite population in intensively farmed landscapes. A positive association between maternal bee size and clutch size was only found in least managed roadsides, while, in both farm types, body sizes for daughters and sons were smaller, barely reaching the predicted overwintering threshold. 4. The results suggest that the effects of intensified agricultural land use will be more pronounced in bee offspring, potentially leading to decreased fitness for subsequent generations. This implies far‐reaching consequences for agricultural pollination services and declines in wild bee populations. 相似文献
997.
The fragmentation of agricultural landscapes has a major impact on biodiversity. In addition to habitat loss, dispersal limitation increasingly appears as a significant driver of biodiversity decline. Landscape linear elements, like ditches, may reduce the negative impacts of fragmentation by enhancing connectivity for many organisms, in addition to providing refuge habitats. To characterize these effects, we investigated the respective roles of propagule source composition and connectivity at the landscape scale on hydrochorous and non-hydrochorous ditch bank plant metacommunities. Twenty-seven square sites (0.5 km2 each) were selected in an agricultural lowland of northern France. At each site, plant communities were sampled on nine ditch banks (totaling 243 ditches). Variables characterizing propagule sources composition and connectivity were calculated for landscape mosaic and ditch network models. The landscape mosaic influenced only non-hydrochorous species, while the ditch network impacted both hydrochorous and non-hydrochorous species. Non-hydrochorous metacommunities were dependent on a large set of land-use elements, either within the landscape mosaic or adjacent to the ditch network, whereas hydrochorous plant metacommunities were only impacted by the presence of ditches adjacent to crops and roads. Ditch network connectivity also influenced both hydrochorous and non-hydrochorous ditch bank plant metacommunity structure, suggesting that beyond favoring hydrochory, ditches may also enhance plant dispersal by acting on other dispersal vectors. Increasing propagule sources heterogeneity and connectivity appeared to decrease within-metacommunity similarity within landscapes. Altogether, our results suggest that the ditch network's composition and configuration impacts plant metacommunity structure by affecting propagule dispersal possibilities, with contrasted consequences depending on species' dispersal vectors. 相似文献
998.
Chromosomal editing constitutes the direct and specific modification of the genetic information present in the chromosome.
In the bacterium Escherichia coli, strategies were originally developed for the production of specific proteins, the genotypic improvement of strains, and
the analysis of regulation of gene expression. However, with the emerging field of metabolic engineering and genomics, efficient
means of targeting specific genetic mutations into the chromosome are most useful. In this review, a summary of the systems
currently available to generate insertions and deletions in the chromosome of E. coli are presented, as well as the current knowledge about the genetic mechanisms responsible for these processes. 相似文献
999.
1000.
Production and characterization of xylanase from a Streptomyces species grown on agricultural wastes
Alkali-treated corn stalk gave maximum xylanase production at supporting growth of Streptomyces HM-15. Xylanase was stable for 24 h over a pH range of 5.0 to 7.0, had optimal activity between 50 and 60°C and a halflife of 5 h at 60°C. Xylanase production and activity were inhibited by xylose.The authors are with Department of Biosciences, Sardar Patel University. Vallabh Vidyanagar-388120, Gujarat, India. 相似文献