全文获取类型
收费全文 | 737篇 |
免费 | 63篇 |
专业分类
林业 | 8篇 |
农学 | 4篇 |
基础科学 | 4篇 |
56篇 | |
综合类 | 107篇 |
农作物 | 22篇 |
水产渔业 | 23篇 |
畜牧兽医 | 514篇 |
园艺 | 8篇 |
植物保护 | 54篇 |
出版年
2022年 | 6篇 |
2021年 | 10篇 |
2020年 | 13篇 |
2019年 | 15篇 |
2018年 | 13篇 |
2017年 | 22篇 |
2016年 | 15篇 |
2015年 | 17篇 |
2014年 | 11篇 |
2013年 | 34篇 |
2012年 | 32篇 |
2011年 | 30篇 |
2010年 | 26篇 |
2009年 | 21篇 |
2008年 | 35篇 |
2007年 | 29篇 |
2006年 | 27篇 |
2005年 | 22篇 |
2004年 | 24篇 |
2003年 | 32篇 |
2002年 | 27篇 |
2001年 | 22篇 |
2000年 | 19篇 |
1999年 | 19篇 |
1998年 | 18篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1991年 | 12篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1976年 | 10篇 |
1975年 | 7篇 |
1974年 | 7篇 |
1973年 | 8篇 |
1972年 | 9篇 |
1971年 | 11篇 |
1970年 | 6篇 |
1969年 | 7篇 |
1968年 | 5篇 |
1966年 | 7篇 |
1924年 | 5篇 |
排序方式: 共有800条查询结果,搜索用时 0 毫秒
81.
82.
A survey of Iowa farmers was conducted to assess the farmers' perceptions and beliefs regarding auger safety and how these perceptions are put into practice. A questionnaire was designed to obtain information on the following auger-related topics: recognition of safe practices and appropriate shielding, personal practices and behaviors, risk perception, and personal beliefs. A random sample of 400 Iowa farmers (arrayed by county) was selected to be representative of Iowa farms. The response to the mailed survey was 23%. Some returned surveys were eliminated because the respondent was retired or did not own/operate augers, resulting in 57 usable questionnaires. Survey responses indicate that the majority of Iowa farmers who participated in this study can correctly identify appropriate shielding for auger intake that meet or exceed ASAE standards. Survey responses suggest that it is common practice in Iowa for youth (age 13 to 19) to operate augers. Iowa farmers in this study perceive the most important contributing factors to auger-related injuries to be operating an auger without shielding, failure to pay attention on the job, moving augers in a raised position, and using hand or feet to redirect the flow of grain. Survey results also indicate that carelessness is perceived to be the leading cause of auger-related injuries, and that auger related injuries can be avoided by having respect for the equipment, being careful, and using common sense. The results also show that the Iowa farmers who participated in this study commonly perform auger-related practices (e.g., moving an auger in a raised position) that they identify as being unsafe. 相似文献
83.
84.
Abstract. Demand for water from catchments dominated by upland peat as a source of drinking water supplies in the UK is likely to increase in the future as demand per capita continues to rise (Thomsen 1990) and/or summer droughts increase in frequency (Arnell 1992). Concern has been expressed in recent years over rising colour levels (related to dissolved organic carbon (DOC) and iron (Fe)) from such catchments (e.g. Kay et al. 1989) causing reduced drinking water quality. One of the major causes of increased DOC concentrations is rewetting following periods of relative drought (Mitchell & McDonald 1992). Experimental rewetting of a naturally drained wetland in Mid‐Wales over four years was found to substantially increase the concentrations of DOC, and Fe in the pore‐water, with peak values of >60 mg dm–3 (Fe) and >300 mg dm–3 (DOC) after rewetting, compared with typical values of <1 mgdm–3 (Fe) and <15 mg dm–3 (DOC) under the drained conditions. Seasonal peak concentrations of Fe and DOC have since remained at these higher levels. Rewetting produced a selective enrichment of the >5000 to <90 000 apparent molecular weight (AMW) material and this fraction was found to yield peak Fe concentrations. Two additional peaks of DOC were also found in the experimental wetland (not present in the control wetland), of >90 000 to <200 000 AMW and >200 000 AMW material. The AMW spectrum of DOC in the experimental wetland changed with season, and the >90 000 to <200 000 AMW fraction could only be seen in spring, representing a transient pool of carbon that is rapidly transformed in or transported from the wetland. These findings suggest that rewetting of peatland following drought (e.g. due to climate change) has the potential to reduce water quality. Moreover, recent interest in restoration (rewetting) of drained peatlands (Wheeler & Shaw 1995) could create an additional source of DOC rich water. 相似文献
85.
86.
87.
REASONS FOR PERFORMING STUDY: Epiploic foramen entrapment (EFE) is one of the more common causes of colic in horses, but recent reports suggest a poor prognosis after surgical treatment. HYPOTHESIS: That EFE has a good prognosis compared with other small intestinal strangulating lesions. METHODS: Surgical findings, surgical procedures and short-term outcome were recorded for 157 horses that underwent surgery for strangulating lesions of the small intestine at the University of Illinois from 1994 to 2003. Horses were assigned to 3 groups for comparison; those with EFE, strangulation by lipoma and miscellaneous strangulating lesions. A logistic regression model and Monte Carlo tests of the binomial proportions were used to examine survival rates. The Kruskal-Wallis test was used to determine differences in usage of surgical treatments. Measurements of length and viability indices were analysed using a one-way analysis of variance followed by Tukey's HSD test, and viability scores were analysed using an exact Kruskal-Wallis test. Significance was set at P < 0.05. RESULTS: Horses with EFE were significantly more likely to be discharged (95%) than those with the other conditions (P < 0.05). The proportion of horses with ileal involvement was greater in horses with EFE than in the other 2 groups (P < 0.05), although this did not affect outcome. The distributions of viability grades for EFE and lipoma differed significantly (P < 0.05). CONCLUSIONS: The prognosis for horses that had surgery at this hospital for EFE was better than for those with the other conditions, although the greater proportion of horses with EFE with ileal involvement could influence outcome. Therefore, surgeons must consider ways of improving jejunocaecostomy and determining when bowel is viable, the latter to avoid jejunocaecostomy. 相似文献
88.
89.
Puglia GD Freeman LM Rush JE King RG Crawford SL 《American journal of veterinary research》2006,67(9):1533-1540
OBJECTIVE: To develop and assess the reproducibility of a protocol to noninvasively test endothelial function in dogs on the basis of the flow-mediated vasodilation (FMD) procedure used in humans. ANIMALS: 5 healthy spayed female dogs. PROCEDURES: Luminal arterial diameter and blood flow velocity in the brachial and femoral arteries were measured with ultrasonography. The within-dog reproducibility of these ultrasonographic measurements was tested. An occlusion period of 1, 3, or 5 minutes with an inflatable cuff was used to create the FMD response. Measurements made at 15, 30, and 60 seconds following release of the occlusion were compared with measurements made immediately prior to each occlusion to assess the FMD response. RESULTS: Within-dog reproducibility of measurements revealed moderate to high correlations. Change from baseline in luminal arterial diameter was most substantial when measured at 30 seconds following release of occlusion, whereas blood flow velocity changes were maximal when measured at 15 seconds following release. The brachial imaging site provided a larger number of significant FMD responses than the femoral site. The 3-minute occlusion period provided equal or better responses than the 5-minute occlusion period. CONCLUSIONS AND CLINICAL RELEVANCE: Ultrasonographic measurement of the FMD responses was a feasible and reproducible technique and significant changes from baseline were detected. The FMD responses in dogs were most substantial when performed at the brachial artery with blood flow velocity and luminal arterial diameter changes from baseline measured at 15 and 30 seconds, respectively, following release of a 3-minute occlusion period. 相似文献
90.