全文获取类型
收费全文 | 2880篇 |
免费 | 177篇 |
国内免费 | 9篇 |
专业分类
林业 | 170篇 |
农学 | 61篇 |
基础科学 | 9篇 |
483篇 | |
综合类 | 471篇 |
农作物 | 130篇 |
水产渔业 | 221篇 |
畜牧兽医 | 1213篇 |
园艺 | 58篇 |
植物保护 | 250篇 |
出版年
2023年 | 13篇 |
2022年 | 15篇 |
2021年 | 42篇 |
2020年 | 75篇 |
2019年 | 81篇 |
2018年 | 52篇 |
2017年 | 74篇 |
2016年 | 83篇 |
2015年 | 62篇 |
2014年 | 72篇 |
2013年 | 137篇 |
2012年 | 188篇 |
2011年 | 212篇 |
2010年 | 122篇 |
2009年 | 91篇 |
2008年 | 190篇 |
2007年 | 180篇 |
2006年 | 186篇 |
2005年 | 180篇 |
2004年 | 150篇 |
2003年 | 156篇 |
2002年 | 156篇 |
2001年 | 37篇 |
2000年 | 30篇 |
1999年 | 33篇 |
1998年 | 25篇 |
1997年 | 34篇 |
1996年 | 21篇 |
1995年 | 35篇 |
1994年 | 28篇 |
1993年 | 18篇 |
1992年 | 17篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 22篇 |
1988年 | 24篇 |
1987年 | 19篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1979年 | 11篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1976年 | 6篇 |
1974年 | 7篇 |
1973年 | 5篇 |
1967年 | 5篇 |
排序方式: 共有3066条查询结果,搜索用时 15 毫秒
31.
INVITED REVIEW—IMAGE REGISTRATION IN VETERINARY RADIATION ONCOLOGY: INDICATIONS,IMPLICATIONS, AND FUTURE ADVANCES 下载免费PDF全文
Yang Feng Jessica Lawrence Kun Cheng Dean Montgomery Lisa Forrest Duncan B. Mclaren Stephen McLaughlin David J. Argyle William H. Nailon 《Veterinary radiology & ultrasound》2016,57(2):113-123
The field of veterinary radiation therapy (RT) has gained substantial momentum in recent decades with significant advances in conformal treatment planning, image‐guided radiation therapy (IGRT), and intensity‐modulated (IMRT) techniques. At the root of these advancements lie improvements in tumor imaging, image alignment (registration), target volume delineation, and identification of critical structures. Image registration has been widely used to combine information from multimodality images such as computerized tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) to improve the accuracy of radiation delivery and reliably identify tumor‐bearing areas. Many different techniques have been applied in image registration. This review provides an overview of medical image registration in RT and its applications in veterinary oncology. A summary of the most commonly used approaches in human and veterinary medicine is presented along with their current use in IGRT and adaptive radiation therapy (ART). It is important to realize that registration does not guarantee that target volumes, such as the gross tumor volume (GTV), are correctly identified on the image being registered, as limitations unique to registration algorithms exist. Research involving novel registration frameworks for automatic segmentation of tumor volumes is ongoing and comparative oncology programs offer a unique opportunity to test the efficacy of proposed algorithms. 相似文献
32.
Fabien Génin Ayabulela Yokwana Nokuthula Kom Sébastien Couette Thibault Dieuleveut Stephen D Nash 《African Zoology》2016,51(3):135-143
The primate fauna of South Africa has historically been viewed as comprising three diurnal cercopithecoid taxa – chacma baboons (Papio ursinus), vervet (Chlorocebus pygerythrus) and samango monkeys (Cercopithecus albogularis) – and two nocturnal lorisoid species – the thick-tailed greater galago (Otolemur crassicaudatus) and the southern lesser galago (Galago moholi). Here we report the positive identification of a third galago species within South Africa’s borders: the Mozambique dwarf galago or Grant’s galago, Galagoides granti (Thomas and Wroughton, 1907). The taxon was previously held to be restricted to Mozambique, eastern Zimbabwe, Malawi and Tanzania, but we have also observed it in the sand forest of Tembe Elephant Park and the Tshanini Community Reserve, near the Mozambique border. The species was formerly mistaken for Galago moholi, erroneously (we believe) extending the range of the latter species into northern KwaZulu-Natal. In South Africa the two small galagos are unlikely to have overlapping ranges: Galago moholi prefers dry savanna woodlands, whereas Galagoides granti is apparently confined to dry sand forest. However, both species may coexist with the larger and more widespread Otolemur crassicaudatus, an inhabitant of moist savanna, forest edge and thicket. The true South African ranges of both small galago species need to be ascertained. 相似文献
33.
Development and characterization of a technique for percutaneous radiologic gastrojejunostomy tube placement in the dog 下载免费PDF全文
34.
35.
36.
37.
Robert Jankowiak Piotr Bilański Julita Zając Adrianna Jobczyk Stephen J. Taerum 《Forest Pathology》2023,53(4):e12821
In Poland's pine forests, mistletoe (Viscum album subsp. austriacum) abundance has increased over the past 20 years. This mistletoe infestation has decreased the growth and vigour of Scots pine trees. In this study, we surveyed the culturable fungi from healthy and diseased V. album subsp. austriacum leaves from two stands in Poland. In total, 63 distinct species were identified, 99.8% of which belonged to the phylum Ascomycota. The community compositions of fungi in mistletoe leaves were similar in healthy and diseased leaves as Alternaria alternata, Aureobasidium pullulans, Botryosphaeria visci, Fusarium paeoniae and Microsphaeropsis olivacea were consistently found in leaves of all symptom types. The most frequently isolated fungus from asymptomatic leaves was M. olivacea, followed by A. alternata, A. pullulans and Hypoxylon rubiginosum. In comparison, the most frequently isolated fungi from leaves with rusty-brown necrotic spots were (in decreasing order) M. olivacea, B. visci, F. paeoniae and A. alternata, while the most frequently isolated fungi from leaves with black or dark brown spots were M. olivacea, A. alternata, A. pullulans, Epicoccum layuense and F. paeoniae. This study was the first comprehensive report showing that certain fungal species may be pathogens of V. album subsp. austriacum in Poland. This study was also the first report of F. paeoniae, F. juglandicola, Diaporthe vacuae and Heterotruncatella spartii from V. album, and the first report of D. vacuae and H. spartii in Poland. 相似文献
38.
Movement patterns of Brook Trout in a restored coastal stream system in southern Massachusetts 下载免费PDF全文
Erin L. Snook Benjamin H. Letcher Todd L. Dubreuil Joseph Zydlewski Matthew J. O'Donnell Andrew R. Whiteley Stephen T. Hurley Andy J. Danylchuk 《Ecology of Freshwater Fish》2016,25(3):360-375
Coastal Brook Trout (Salvelinus fontinalis) populations are found from northern Canada to New England. The extent of anadromy generally decreases with latitude, but the ecology and movements of more southern populations are poorly understood. We conducted a 33‐month acoustic telemetry study of Brook Trout in Red Brook, MA, and adjacent Buttermilk Bay (marine system) using 16 fixed acoustic receivers and surgically implanting acoustic transmitters in 84 individuals. Tagged Brook Trout used the stream, estuary (50% of individuals) and bay (10% of individuals). Movements into full sea water were brief when occurring. GAMM models revealed that transitions between habitat areas occurred most often in spring and fall. Environmental data suggest that use of the saline environment is limited by summer temperatures in the bay. Movements may also be related to moon phase. Compared to more northern coastal populations of Brook Trout, the Red Brook population appears to be less anadromous overall, yet the estuarine segment of the system may have considerable ecological importance as a food resource. 相似文献
39.
Stephen J. Dugdale Jan Franssen Emily Corey Normand E. Bergeron Michel Lapointe Richard A. Cunjak 《Ecology of Freshwater Fish》2016,25(3):429-445
Atlantic salmon become thermally stressed when water temperatures exceed 23 °C. To alleviate this stress, they behaviourally thermoregulate by moving to patches of cold water, often forming large aggregations. These patches are known as thermal refuges. Given the consensus that climate change will increase temperatures in Atlantic salmon catchments, thermal refuges will become increasingly important in minimising summer mortalities. While the behaviour of salmonids within thermal refuges is fairly well understood, less is known about their main stem movement in search of thermal refuges or its thermal and temporal cues. We detail the results of a PIT telemetry study to investigate the main stem movement behaviour of thermally stressed Atlantic salmon parr in a temperature‐impacted river. PIT antennas placed around two thermal refuges and at the upstream and downstream limits of their surrounding reach were used to record the movement of salmonids during a heatwave. We observed parr movement at the upstream and downstream antennas 135 min prior to the occurrence of the midpoint of aggregations in the thermal refuges, indicating that Atlantic salmon parr make reach‐scale movements in search of cool water prior to aggregating. Logistic regression showed that the number of degree hours >28 °C predicted the occurrence of main stem movement with a good degree of accuracy, indicating that this temperature represents a fundamental threshold causing Atlantic salmon parr to move towards cool water. Such data could be instrumental in allowing river managers to place limits on human activity within rivers, allowing salmon populations time to recover following heat stress events. 相似文献
40.
Jian Jin Xiaobing Liu Guanghua Wang Liang Mi Zhongbao Shen Xueli Chen Stephen J. Herbert 《Field Crops Research》2010,115(1):116-123
Increasing yield is a high priority in most breeding programs. Approximately 600 soybean cultivars had been released by the end of the last century in Northeast China. Understanding the agronomic and physiological changes is essential for planning further plant breeding strategies in soybean. In this study, 45 representative soybean cultivars, from maturity groups 00 and 0, released from 1950 to 2006 in Northeast China were compared in field conditions for 3 consecutive years. A positive correlation between seed yield and year of cultivar release was indicated with a 0.58% average annual increase. Seed number per plant was the most important contributor to yield gain, with a 0.41% increase per year. Pod number per plant and seed size varied slightly with the year of cultivar release. Although variation in protein was from 37.0% to 45.5%, and oil concentration was from 16.7% to 22.0%, their concentrations were not consistently related to year of cultivar release. A 33% increase in the photosynthetic rate, 10.6% increase in plant dry weight and 19.0% increase in harvest index (HI) were found, while leaf area index (LAI) decreased by 17.3%. Modern cultivars have higher photosynthetic rates than their predecessors. The reduced plant height gave increased resistance to lodging, with the lodging score dropping from 3.2 in 1951 to 1.0 in 2006. Seed resistances to disease and pest infestation were also improved. Yield stability was enhanced over years, which could be attributed to the stable pod production across different environments. A flow diagram to explain the contributors to genetic improvement of soybeans in Northeast China was developed. 相似文献