全文获取类型
收费全文 | 1385篇 |
免费 | 75篇 |
国内免费 | 32篇 |
专业分类
林业 | 109篇 |
农学 | 19篇 |
基础科学 | 19篇 |
157篇 | |
综合类 | 288篇 |
农作物 | 39篇 |
水产渔业 | 56篇 |
畜牧兽医 | 689篇 |
园艺 | 44篇 |
植物保护 | 72篇 |
出版年
2023年 | 17篇 |
2022年 | 16篇 |
2021年 | 19篇 |
2020年 | 36篇 |
2019年 | 23篇 |
2018年 | 26篇 |
2017年 | 33篇 |
2016年 | 19篇 |
2015年 | 31篇 |
2014年 | 47篇 |
2013年 | 71篇 |
2012年 | 64篇 |
2011年 | 74篇 |
2010年 | 67篇 |
2009年 | 47篇 |
2008年 | 77篇 |
2007年 | 38篇 |
2006年 | 49篇 |
2005年 | 36篇 |
2004年 | 42篇 |
2003年 | 51篇 |
2002年 | 41篇 |
2001年 | 31篇 |
2000年 | 27篇 |
1999年 | 31篇 |
1998年 | 18篇 |
1997年 | 17篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1992年 | 27篇 |
1991年 | 24篇 |
1990年 | 22篇 |
1989年 | 29篇 |
1988年 | 25篇 |
1986年 | 21篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 14篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1974年 | 12篇 |
1973年 | 7篇 |
1972年 | 7篇 |
1971年 | 8篇 |
1970年 | 13篇 |
1968年 | 12篇 |
1967年 | 7篇 |
1966年 | 7篇 |
排序方式: 共有1492条查询结果,搜索用时 421 毫秒
11.
12.
13.
Rita M. Hanel DVM DACVIM DACVECC Lee Palmer DVM MS DACVECC NREMT‐T WEMT CCRP Janice Baker DVM DACVPM Jo‐Anne Brenner BA EMT‐I EMT‐T David Dorman DVM PhD DABVT John C. Gicking DVM DACVECC Brian Gilger DVM MS DACVO DABT Cynthia M. Otto DVM PhD DACVECC DACVSMR Elizabeth Rozanski DVM DACVECC DACVIM Brian Trumpatori DVM 《Journal of Veterinary Emergency and Critical Care》2016,26(2):166-233
14.
While agricultural production statistics are reported on a geopolitical – often national – basis we often need to know the status of production or productivity within specific sub-regions, watersheds, or agroecological zones. Such re-aggregations are typically made using expert judgments or simple area-weighting rules. We describe a new, entropy-based approach to making spatially disaggregated assessments of the distribution of crop production. Using this approach, tabular crop production statistics are blended judiciously with an array of other secondary data to assess the production of specific crops within individual ‘pixels’ – typically 25–100 square kilometers in size. The information utilized includes crop production statistics, farming system characteristics, satellite-derived land cover data, biophysical crop suitability assessments, and population density. An application is presented in which Brazilian state level production statistics are used to generate pixel level crop production data for eight crops. To validate the spatial allocation we aggregated the pixel estimates to obtain synthetic estimates of municipality level production in Brazil, and compared those estimates with actual municipality statistics. The approach produced extremely promising results. We then examined the robustness of these results compared to short-cut approaches to allocating crop production statistics and showed that, while computationally intensive, the cross-entropy method does provide more reliable estimates of crop production patterns. 相似文献
15.
我国西部地区水电开发问题探讨 总被引:1,自引:0,他引:1
水能资源是我国西部地区的优势资源,由于历史和政策的原因,开发利用程度相对较低,资源优势没有形成产业优势。在分析西部水能资源分布特点和开发现状的基础上,结合西部大开发和西电东送战略,提出目前水电产业存在的市场、政策和资金方面问题,探讨了加快西部水电开发的对策和建议。 相似文献
16.
17.
Christley RM Hodgson DR Rose RJ Hodgson JL Wood JL Reid SW 《The Veterinary record》2001,148(4):99-104
A matched case-control study was made of 100 thoroughbred horses which were coughing and 148 control horses which were free of clinical signs of respiratory tract disease. The variables identified by multivariable conditional logistic regression as being significantly associated with coughing included age (the risk decreased with age), the stage of training (horses in early training were at greatest risk), the time since the last race (horses that had never raced were at greatest risk) and the time since they were last transported (horses transported more than 14 days previously were more likely to cough than those transported within the last week). The coughing horses were significantly more likely to have high scores for upper and lower tracheal mucus and pharyngeal lymphoid hyperplasia. In addition, the tracheal aspirates of the coughing horses had increased odds of neutrophilia and were more likely to have intracellular bacteria than the control horses. However, a considerable proportion of the control horses had cytological and/or endoscopic evidence of airway inflammation. 相似文献
18.
Hoffmann KL Wood AK Griffiths KA Evans DL Gill RW Kirby AC 《Equine veterinary journal》2001,33(3):269-273
The effects of feeding on blood flow to the equine foot are poorly understood. In a temperature-controlled room, duplex Doppler ultrasonographic observations were made pre- and postprandially of the lateral proper palmar digital artery of 5 horses, randomly assigned to twice and 4 times daily feeding in an unbalanced 2 period crossover design. Arterial diameter and blood velocity were measured over 4 h and additional observations made of heart rate, blood pressure, total plasma protein, packed cell volume, plasma glucose and insulin. There was no effect of the feeding regimen on any variable. Postprandially, there were significant increases in arterial diameter, blood velocity, total plasma protein, plasma glucose and insulin; the other variables were unchanged. It appeared that the normal postprandial response was an increase in blood flow to the foot. The value of ultrasonography for noninvasive investigation of the peripheral vasculature of the conscious horse was established; and in the future it may have a role in the diagnosis of vascular diseases of the foot. 相似文献
19.
20.
Hoffmann KL Wood AK McCarthy PH Griffiths KA Evans DL Gill RW 《Anatomia, histologia, embryologia》1999,28(5-6):281-289
Investigations of the equine peripheral vascular system have been constrained by the lack of a non-invasive method of examining the arteries and veins of the limbs of the conscious horse. Precise correlations were established between the gross anatomical features of the peripheral vessels and their B-mode sonographic appearance in each thoracic limb of 35 horses. A sonographic imaging protocol was established. Additional Doppler sonographic recordings defined the arterial waveforms and demonstrated that blood flow to the foot could be evaluated in the lateral proper digital artery, distal to the level of the coronary band. Valves (with 2-4 cusps) were identified in the lumina of the medial and lateral palmar common digital veins and those of the medial and lateral palmar proper digital veins. Spontaneous echo contrast, a smoke-like haze of echoic blood, was seen in the lateral and medial palmar common digital veins, the distal deep palmar venous arch and communicating branches, and the palmar proper digital veins, and occasionally seen in the distal deep palmar arterial arch and distal proper palmar digital arteries. The value of duplex sonography (B-mode and Doppler) for anatomical and physiological studies of the peripheral vasculature of the horse was clearly established. Such data could be applied to the investigation of diseases affecting the peripheral circulation. 相似文献