全文获取类型
| 收费全文 | 3684篇 |
| 免费 | 181篇 |
| 国内免费 | 3篇 |
专业分类
| 林业 | 242篇 |
| 农学 | 96篇 |
| 基础科学 | 27篇 |
| 647篇 | |
| 综合类 | 612篇 |
| 农作物 | 121篇 |
| 水产渔业 | 331篇 |
| 畜牧兽医 | 1496篇 |
| 园艺 | 101篇 |
| 植物保护 | 195篇 |
出版年
| 2023年 | 16篇 |
| 2022年 | 32篇 |
| 2021年 | 66篇 |
| 2020年 | 72篇 |
| 2019年 | 91篇 |
| 2018年 | 86篇 |
| 2017年 | 102篇 |
| 2016年 | 86篇 |
| 2015年 | 62篇 |
| 2014年 | 92篇 |
| 2013年 | 143篇 |
| 2012年 | 223篇 |
| 2011年 | 280篇 |
| 2010年 | 162篇 |
| 2009年 | 143篇 |
| 2008年 | 271篇 |
| 2007年 | 272篇 |
| 2006年 | 256篇 |
| 2005年 | 262篇 |
| 2004年 | 237篇 |
| 2003年 | 210篇 |
| 2002年 | 196篇 |
| 2001年 | 26篇 |
| 2000年 | 26篇 |
| 1999年 | 35篇 |
| 1998年 | 30篇 |
| 1997年 | 25篇 |
| 1996年 | 22篇 |
| 1995年 | 31篇 |
| 1994年 | 19篇 |
| 1993年 | 25篇 |
| 1992年 | 21篇 |
| 1991年 | 15篇 |
| 1990年 | 15篇 |
| 1989年 | 12篇 |
| 1988年 | 18篇 |
| 1987年 | 27篇 |
| 1986年 | 13篇 |
| 1985年 | 8篇 |
| 1984年 | 16篇 |
| 1983年 | 12篇 |
| 1982年 | 8篇 |
| 1978年 | 6篇 |
| 1977年 | 7篇 |
| 1976年 | 5篇 |
| 1973年 | 6篇 |
| 1972年 | 7篇 |
| 1970年 | 6篇 |
| 1969年 | 6篇 |
| 1898年 | 5篇 |
排序方式： 共有3868条查询结果，搜索用时 15 毫秒
991.
Mark D.G. Pinches Guy Liebenberg Mark F Stidworthy 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》2008,37(4):443-446
Abstract: A 7‐year‐old neutered male polecat‐type ferret (Mustela putorius furo) was presented for evaluation of a cutaneous mass close to the preputial orifice. Cytologic examination of a fine‐needle aspirate revealed numerous large clumps of amorphous pink mucinous material and numerous large clumps of slightly pleomorphic epithelial cells. The cells were arranged in papillary structures, palisades, and loosely cohesive sheets with a vaguely honeycomb appearance. Occasional acinar formations were also seen. The cells had moderate to large amounts of finely granular gray to gray–blue cytoplasm. The cells were round to wispy and elongated, with indistinct borders. Often, anuclear cytoplasmic clumps were seen free in the background or adjacent to intact cells. Nuclei were round to oval and usually off‐center. Chromatin was finely stippled and contained 1–3 indistinct nucleoli. Anisokaryosis and anisocytosis were moderate. Binucleated cells were noted occasionally. The cytologic features were consistent with a carcinoma of probable apocrine origin. Histopathologic examination supported a diagnosis of secretory apocrine adenocarcinoma of the preputial skin. Secretory apocrine adenocarcinomas of the prepuce are seen relatively frequently in ferrets, although their cytologic appearance has not been described widely. These neoplasms carry a poor prognosis although prompt surgical removal with wide and deep surgical margins and adjunctive radiotherapy may improve survival. 相似文献
992.
Patel H Mackintosh D Ayling RD Nicholas RA Fielder MD 《Veterinary microbiology》2008,127(3-4):309-314
Mycoplasma ovipneumoniae is considered an emerging veterinary pathogen causing pneumonia in sheep and goats worldwide. Currently it has not been possible to define a growth medium that yields the maximum growth of M. ovipneumoniae within a short incubation period. Growth yields of M. ovipneumoniae in Eaton's medium are variable and not as consistently high as those seen with other Mycoplasma spp. This study investigated the ability of different M. ovipneumoniae field strains to grow in various media formulations, where PPLO broth was replaced by a vegetable protein source, and comparisons were made in terms of strain viability in Eaton's medium. Studies were also conducted to determine the optimal carbohydrate source for use in the M. ovipneumoniae medium. Generally, it was found that different strains showed good growth in all media tested, with growth yields at 24h in TSB-1 medium higher than those observed with Eaton's medium. Growth yields reached 10(8) to 10(9)cfu ml(-1) within 24h for particular field strains, with all strains achieving this growth level within 48-72h. 相似文献
993.
- 1. The decline of large‐bodied predatory species in the oceans is a concern both from a sustainability perspective and because such species can have important ecological roles. Sharks are particularly vulnerable to fishing as their life histories are characterized by late age at maturity, large body size, and low fecundity.
- 2. Substantial shark population declines have been documented for a number of coastal and pelagic systems, with high population abundance limited to a few remote locations. The relative abundance and composition of reef shark populations are assessed from 1975 to 2006 at a remote, largely uninhabited, group of atolls in the central Indian Ocean; the Chagos Archipelago.
- 3. Number of sharks observed per scientific dive declined from a mean of 4.2 in the 1970s to 0.4 in 2006, representing a decline of over 90%. Silvertip sharks displayed an increase in abundance from 1996, whereas blacktip and whitetip reef sharks were rarely encountered in 2006.
- 4. Poaching in the archipelago, is the most likely cause of these declines, highlighted by a number of illegal vessels containing large numbers of sharks arrested since 1996. The data highlight that shark populations, even in remote, otherwise pristine, marine areas, are vulnerable to distant fishing fleets, and a range of strategies will need to be used in concert for their conservation. Copyright © 2010 John Wiley & Sons, Ltd.
994.
Tobacco anionic peroxidase often increases resistance to insects in different dicotyledonous species
Different species and strains of tobacco (Nicotiana spp), tomato (Lycopersicon esculentum) and sweetgum (Liquidambar styraciflua) that had total peroxidase activity enhanced by a few- to over 100-fold through the expression of a tobacco anionic peroxidase gene driven by a cauliflower mosaic promoter were compared with wild-type plants for resistance to relevant insects. Reduced levels of feeding were generally noticed for leaves, stems and fruit, but the age of tissues and insects influenced the response. Enhanced resistance to Helicoverpa zea and Manduca sexta were noted for tobacco and tomato, and resistance to Hyphantria cunea and Lymantria dispar were noted for sweetgum. In several cases increased mortality and/or reduced growth rates were noted for the high-peroxidase plants. Although many modes of action are possible, indirect comparisons and gravitational nutritional studies suggest peroxidase-enhanced rates of production of compounds toxic to the insects are the most important. 相似文献
995.
Antony M Hooper Jude A Bennison Mark C Luszniak John A Pickett Eleanor M Pow Lester J Wadhams 《Pest management science》1999,55(6):660-662
Western flower thrips (WFT) are attracted to three flowering verbena cultivars. The volatile components of these cultivars contain different enantiomers of linalool oxide which have been synthesised and one shown to be attractive to WFT. 相似文献
996.
Metalaxyl resistance has been identified in the Phytophthora porri population in the UK. In field experiments the presence of such resistant strains reduced the level of control of leek white tip given by applications of phenylamide-containing fungicides. The level of control achieved by fungicides with alternative modes of action to the phenylamides was not affected. ©1997 SCI 相似文献
997.
A method to accelerate and quantitate retrogradation of starch pastes using a freeze-thaw cycle (FTC) process and turbidometric analysis has been developed. Using this method and differential scanning calorimetry (DSC), it was determined that the rate of retrogradation in 2.5% waxy maize pastes was inversely correlated to the rate of freezing, and that the thawing temperature affected perfection of the crystallites in retrograded amylopectin. DSC and X-ray diffraction were used to determine whether the crystallites formed during the FTC process were the same as those formed in starch pastes held isothermally at 4°C. Analysis of retrogradation of pastes of starches from various botanical sources indicated that the method reflects retrogradation in higher concentration pastes. Retrogradation rates were reduced by the addition of sodium dodecyl sulfate. Microstructures of freeze-thaw processed waxy maize and common corn starch pastes were examined. 相似文献
998.
Impacts of the COVID-19 pandemic on the dairy industry: Lessons from China and the United States and policy implications 
下载免费PDF全文
下载免费PDF全文 Qingbin WANG LIU Chang-quan ZHAO Yuan-feng Anthony KITSOS Mark CANNELLA WANG Shu-kun HAN Lei 《农业科学学报》2020,19(12):2903-2915
The purposes of this study are to assess the COVID-19 pandemic's impacts on the dairy industries in China and the United States and to derive policy recommendations for enhancing the diary industries' resilience to pandemics and other market shocks. Specifically, data from the two nations are used to analyze and compare the mechanisms through which the pandemic has affected their dairy industries and to discuss potential lessons from their experiences. The findings suggest that this pandemic has heavily affected the dairy industries in both China and the United States through similar mechanisms, such as decreased farmgate milk prices, disruption and difficulties of moving milk within the supply chains, worker shortages, increased production costs, and lack of operating capital. There were also significant differences in the affecting mechanisms between the two nations, including transportation difficulties from widespread road closures and significant reduction in holiday sales of dairy products in China, and the shutdown of many dairy processors in the United States due to the closing of schools, restaurants, and hotels. While government financial reliefs are highly needed to help many dairy farms and processors survive this pandemic in the short term, the dairy industries and governments need to work together to develop long-term strategies and policies to balance the industries' efficiency and flexibility, product specialization and diversification, supply chain integration and local food systems, and market mechanisms and policy regulations and interventions. 相似文献
999.
Context
Land use changes have modified the extent and structure of native vegetation, resulting in fragmentation of native species habitat. Connectivity is increasingly seen as a requirement for effective conservation in these landscapes, but the question remains: ‘connectivity for which species?’.Objective
The aim of this study was to develop and then apply a rapid, expert-based, dispersal guild approach where species are grouped on similar fine-scale dispersal behaviour (such as between scattered trees) and habitat characteristics.Methods
Dispersal guilds were identified using clustering techniques to compare dispersal and habitat parameters elicited from experts. We modelled least-cost paths and corridors between patches and individual movement probabilities within these corridors for each of the dispersal guilds using Circuitscape. We demonstrate our approach with a case study in the Tasmanian Northern Midlands, Australia.Results
The dispersal guild approach grouped the 12 species into five dispersal guilds. The connectivity modelling of those five guilds found that broadly dispersing species in this landscape, such as medium-sized carnivorous mammals, were unaffected by fragmentation while from the perspective of the three dispersal guilds made up of smaller mammals, the landscape appeared highly fragmented.Conclusions
Our approach yields biologically defensible outputs that are broadly applicable, particularly for conservation planning where data and resources are limited. It is a useful first step in multi-species conservation planning which aims to identify those species most in need of conservation efforts.1000.