全文获取类型
收费全文 | 890篇 |
免费 | 33篇 |
国内免费 | 31篇 |
专业分类
林业 | 25篇 |
农学 | 26篇 |
基础科学 | 200篇 |
16篇 | |
综合类 | 314篇 |
农作物 | 14篇 |
水产渔业 | 14篇 |
畜牧兽医 | 332篇 |
园艺 | 12篇 |
植物保护 | 1篇 |
出版年
2023年 | 3篇 |
2022年 | 16篇 |
2021年 | 16篇 |
2020年 | 16篇 |
2019年 | 9篇 |
2018年 | 7篇 |
2017年 | 15篇 |
2016年 | 24篇 |
2015年 | 33篇 |
2014年 | 56篇 |
2013年 | 59篇 |
2012年 | 65篇 |
2011年 | 69篇 |
2010年 | 63篇 |
2009年 | 77篇 |
2008年 | 50篇 |
2007年 | 84篇 |
2006年 | 62篇 |
2005年 | 32篇 |
2004年 | 28篇 |
2003年 | 18篇 |
2002年 | 23篇 |
2001年 | 22篇 |
2000年 | 23篇 |
1999年 | 16篇 |
1998年 | 14篇 |
1997年 | 13篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1988年 | 1篇 |
1987年 | 2篇 |
排序方式: 共有954条查询结果,搜索用时 15 毫秒
1.
2.
2012年以来水产类上市公司经营面临困局.该研究根据11家水产类上市公司2012~2014年的面板数据,首先运用DEA模型进行生产效率的评价,研究发现水产类上市公司的技术效率、纯技术效率和规模效率3年平均值都较高,但2014年整体绩效有走低的趋势;然后运用Tobit模型,分析经营绩效的影响因素,发现公司总资产周转率和高等教育人员比例与技术效率正相关,而研发人员比例与技术效率不相关.最后,从资产整合、加强营销、重视人才和发展休闲渔业等方面提出了提高水产类上市公司经营绩效的对策建议. 相似文献
3.
The multiple new challenges facing agriculture require the development of innovative cropping systems with high environmental, economic and social performances. Many research programmes are currently focusing on the design of such cropping systems. Some include the multicriteria assessment of cropping systems by diverse methods and approaches. Some of these research programmes are supported by experimental or farmers’ networks, generating new opportunities for data analysis and raising new research and methodological questions. In this article, we provide an overview based on a review of 56 articles, comparing the various methods for sustainability assessment in single- and multi-site studies. Articles were classified according to three characteristics: (i) their objectives, (ii) the study design (single- vs. multi-site), (iii) the type of system assessed (fictitious vs. real). Our analysis was structured around four items: (i) the variables used to describe cropping systems and production situations and the use of these variables in the assessment process, (ii) the criteria and associated indicators assessed, (iii) the methods used to explore multiple aspects of the performance of cropping systems, (iv) the use of reference values. We identified key points to be taken into account in multi-site studies. The application of the proposed guidelines to experimental networks should facilitate the identification of high-performance cropping systems and the identification of the drivers of cropping system performance. 相似文献
4.
Hereditary equine regional derma asthenia (HERDA), an autosomal-recessive trait, found in Quarter Horses, causes abnormal collagen structure. Owing to current breeding practices, 3.5% of registered quarter horses and 28.3% of the cow horse population are heterozygote carriers. Research demonstrated homozygote horses develop hyperextensible skin susceptible to injury and other abnormal tissues containing high fibrillar collagen content. No research exists determining the effects of the disease in heterozygote carriers. Currently, 30% of cutting sires are HERDA carriers, potentially increasing the number of heterozygous individuals when bred. The objective of the present study is to gauge knowledge of the disease, perception, and concerns of the diseases’ impact on horse performance and perceived value and breeding decisions. A Qualtrics link was distributed to horse owners via extension specialists and was available online on equine-related Facebook pages. Overall group means and standard deviations for constructs were reported. A total of 228 responses were collected. Most participants were involved in reining and cutting and 34.6% reported they were very familiar with the disease. Participants (78.5%) reported that HERDA status affects value of a breeding animal. Owners of HERDA carriers (62.5%) noticed no difference in performance or injury compared with noncarriers. Respondents (95.2%) believed that all breeding animals should have HERDA status available. Respondents are attempting to make informed breeding decisions based on HERDA status by pairing carriers with noncarriers; however, it remains to be seen if that is adequate to control the disease. Education regarding breeding practices and its impact on the genetic pool are warranted. 相似文献
5.
为了研究酸化剂、微生态制剂和寡糖单独和联合添加对‘麒麟鸡’生长性能和消化道酶活力的影响,选择健康1日龄‘麒麟鸡’192只,随机分成8个处理组,每个处理组3个重复,每个重复8只鸡,采用L8(23)完全正交试验设计进行试验,酸化剂水平为0、0.15%,微生态制剂水平为0、0.15%,寡糖水平为0、0.10%,试验期28天。结果表明:单独添加0.15%酸化剂可提高‘麒麟鸡’生长性能、消化酶活力;单独添加0.15%微生态制剂对‘麒麟鸡’生长性能无显著影响,可提高胃蛋白酶活力;单独添加0.10%寡糖可降低‘麒麟鸡’生长性能和胃蛋白酶活力;0.15%酸化剂、0.15%微生态制剂和0.10%寡糖2种或3种联合添加对提高‘麒麟鸡’生长性能和消化酶活力的互作效应不明显。 相似文献
6.
7.
8.
横流式风机气动和噪声特性相似定律的研究 总被引:3,自引:1,他引:3
通过对两台几何相似但大小不同的横流式的试验,研究了该种风机的相似定律。证实了临界雷诺数的存在,超过该值后,气动和噪声特性的相似定律均成立,且临界值随风机尺寸的增大而增加,同时,风机尺寸以及叶轮与隔舌间的间隙对风机的相似定律也有影响。 相似文献
9.
10.