全文获取类型
收费全文 | 4658篇 |
免费 | 238篇 |
国内免费 | 5篇 |
专业分类
林业 | 280篇 |
农学 | 108篇 |
基础科学 | 29篇 |
736篇 | |
综合类 | 741篇 |
农作物 | 143篇 |
水产渔业 | 456篇 |
畜牧兽医 | 2059篇 |
园艺 | 119篇 |
植物保护 | 230篇 |
出版年
2023年 | 18篇 |
2022年 | 36篇 |
2021年 | 77篇 |
2020年 | 80篇 |
2019年 | 108篇 |
2018年 | 102篇 |
2017年 | 112篇 |
2016年 | 99篇 |
2015年 | 72篇 |
2014年 | 103篇 |
2013年 | 192篇 |
2012年 | 251篇 |
2011年 | 325篇 |
2010年 | 183篇 |
2009年 | 170篇 |
2008年 | 313篇 |
2007年 | 310篇 |
2006年 | 300篇 |
2005年 | 284篇 |
2004年 | 269篇 |
2003年 | 238篇 |
2002年 | 244篇 |
2001年 | 53篇 |
2000年 | 65篇 |
1999年 | 66篇 |
1998年 | 42篇 |
1997年 | 39篇 |
1996年 | 31篇 |
1995年 | 32篇 |
1994年 | 21篇 |
1993年 | 31篇 |
1992年 | 39篇 |
1991年 | 36篇 |
1990年 | 48篇 |
1989年 | 24篇 |
1988年 | 41篇 |
1987年 | 42篇 |
1986年 | 30篇 |
1985年 | 26篇 |
1984年 | 30篇 |
1983年 | 26篇 |
1982年 | 17篇 |
1981年 | 14篇 |
1979年 | 21篇 |
1978年 | 15篇 |
1977年 | 17篇 |
1975年 | 18篇 |
1973年 | 19篇 |
1972年 | 16篇 |
1970年 | 17篇 |
排序方式: 共有4901条查询结果,搜索用时 31 毫秒
21.
22.
Johnson Chris J. Boyce Mark S. Mulders Robert Gunn Anne Gau Rob J. Cluff H. Dean Case Ray L. 《Landscape Ecology》2004,19(8):869-882
Multiscale analyses are widely employed for wildlife-habitat studies. In most cases, however, each scale is considered discrete and little emphasis is placed on incorporating or measuring the responses of wildlife to resources across multiple scales. We modeled the responses of three Arctic wildlife species to vegetative resources distributed at two spatial scales: patches and collections of patches aggregated across a regional area. We defined a patch as a single or homogeneous collection of pixels representing 1 of 10 unique vegetation types. We employed a spatial pattern technique, three-term local quadrat variance, to quantify the distribution of patches at a larger regional scale. We used the distance at which the variance for each of 10 vegetation types peaked to define a moving window for calculating the density of patches. When measures of vegetation patch and density were applied to resource selection functions, the most parsimonious models for wolves and grizzly bears included covariates recorded at both scales. Seasonal resource selection by caribou was best described using a model consisting of only regional scale covariates. Our results suggest that for some species and environments simple patch-scale models may not capture the full range of spatial variation in resources to which wildlife may respond. For mobile animals that range across heterogeneous areas we recommend selection models that integrate resources occurring at a number of spatial scales. Patch density is a simple technique for representing such higher-order spatial patterns. 相似文献
23.
Mark A Oyama 《Veterinary Clinics of North America: Small Animal Practice》2004,34(5):1083-104, v
Echocardiography is an exceptionally useful technique for diagnosing cardiovascular disease in small animals. It is noninvasive and provides a wealth of data concerning cardiac morphology and function. For many patients, echocardiography is the definitive diagnostic tool. A well-performed study coalesces the findings of the physical examination, electrocardiogram, and radiographs into a clearly defined diagnosis on which treatment decisions can be based. More so than other diagnostic techniques, echocardiography is highly operator dependent and relies on the proper acquisition and interpretation of results by an examiner who is familiar with the principles, capabilities, and limitations of ultrasound imaging.This article reviews the basics of echocardiography, measurement of cardiac dimensions, and assessment of cardiac function. Within these sections, emerging technologies that expand the capabilities of the echocardiographic examination are introduced. 相似文献
24.
Benjamin Young DVM Lisa Klopp DVM PhD Mark Albrecht DVM DACVS Susan Kraft DVM PhD 《Veterinary radiology & ultrasound》2004,45(6):538-541
This article describes the discovery of a chronic cervical wooden foreign body ventral to the left transverse processes of the cranial cervical spine using magnetic resonance imaging (MRI) in a dog that presented with chronic neck pain and lameness. The dog did not exhibit dysphagia or chronic draining tracts, the most common signs of the presumed cause, that of a penetrating oropharyngeal foreign body. The foreign body itself was represented on MR images as an oval straight-edged core within an inflammatory tissue reaction. The wood was slightly hyperintense on T2- and isointense on T1-weighted images relative to muscle. Surrounding this was a more conspicuous contrast-enhancing reactive tissue rim that was hyperintense on all pulse sequences. Adjacent musculature also exhibited diffuse edema and contrast enhancement that extended around the left cervical vertebral transverse processes and local intervertebral nerve roots. The foreign body was found to be a wooden stick upon surgical removal. MRI is an excellent method for visualizing the inflammatory tissue reactions associated with soft-tissue foreign bodies because of its contrast resolution and depiction of anatomy in multiple imaging planes. 相似文献
25.
Mark Thornley 《Australian veterinary journal》2004,82(12):722-722
26.
Serologic and fecal markers to predict response to induction therapy in dogs with idiopathic inflammatory bowel disease 下载免费PDF全文
27.
28.
29.
Kelsey T. Young Kevin K. Lahmers Holly S. Sellers David E. Stallknecht Rebecca L. Poulson Jerry T. Saliki Stephen Mark Tompkins Ian Padykula Chris Siepker Elizabeth W. Howerth Michelle Todd James B. Stanton 《Journal of veterinary diagnostic investigation》2021,33(2):202
RNA viruses rapidly mutate, which can result in increased virulence, increased escape from vaccine protection, and false-negative detection results. Targeted detection methods have a limited ability to detect unknown viruses and often provide insufficient data to detect coinfections or identify antigenic variants. Random, deep sequencing is a method that can more fully detect and characterize RNA viruses and is often coupled with molecular techniques or culture methods for viral enrichment. We tested viral culture coupled with third-generation sequencing for the ability to detect and characterize RNA viruses. Cultures of bovine viral diarrhea virus, canine distemper virus (CDV), epizootic hemorrhagic disease virus, infectious bronchitis virus, 2 influenza A viruses, and porcine respiratory and reproductive syndrome virus were sequenced on the MinION platform using a random, reverse primer in a strand-switching reaction, coupled with PCR-based barcoding. Reads were taxonomically classified and used for reference-based sequence building using a stock personal computer. This method accurately detected and identified complete coding sequence genomes with a minimum of 20× coverage depth for all 7 viruses, including a sample containing 2 viruses. Each lineage-typing region had at least 26× coverage depth for all viruses. Furthermore, analyzing the CDV sample through a pipeline devoid of CDV reference sequences modeled the ability of this protocol to detect unknown viruses. Our results show the ability of this technique to detect and characterize dsRNA, negative- and positive-sense ssRNA, and nonsegmented and segmented RNA viruses. 相似文献
30.
Mariano Carossino Rudy Bauer Mark A. Mitchell Charles O. Cummings Anke C. Sthr Nobuko Wakamatsu Kimberly Harper Ingeborg M. Langohr Kendra Schultz Maria S. Mitchell Daniel K. Howe Udeni B. R. Balasuriya 《Journal of veterinary diagnostic investigation》2021,33(3):554
Toxoplasma gondii is a zoonotic protozoan pathogen that infects many endothermic vertebrates, including humans; the domestic cat and other felids serve as the definitive host. Macropodids are considered highly susceptible to toxoplasmosis. Here, we describe the clinical, pathologic, and immunohistochemical findings of an outbreak of systemic toxoplasmosis in a mob of 11 red kangaroos (Macropus rufus), with high morbidity (73%) and mortality (100%) rates. Affected animals had either severe and rapidly deteriorating clinical conditions or sudden death, which was correlated with widespread necrotizing lesions in multiple organs and intralesional T. gondii organisms identified via MIC3-specific immunohistochemistry and confirmed by REP529-specific rtPCR. Quantification of parasites demonstrated the highest parasite density in pulmonary parenchyma compared with other tissues. Our study highlights the continued importance of this severe condition in Australian marsupials. 相似文献