全文获取类型
收费全文 | 821篇 |
免费 | 45篇 |
国内免费 | 1篇 |
专业分类
林业 | 79篇 |
农学 | 20篇 |
145篇 | |
综合类 | 138篇 |
农作物 | 48篇 |
水产渔业 | 100篇 |
畜牧兽医 | 255篇 |
园艺 | 10篇 |
植物保护 | 72篇 |
出版年
2023年 | 4篇 |
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 8篇 |
2018年 | 17篇 |
2017年 | 12篇 |
2016年 | 19篇 |
2015年 | 13篇 |
2014年 | 19篇 |
2013年 | 38篇 |
2012年 | 47篇 |
2011年 | 39篇 |
2010年 | 29篇 |
2009年 | 24篇 |
2008年 | 49篇 |
2007年 | 52篇 |
2006年 | 36篇 |
2005年 | 39篇 |
2004年 | 33篇 |
2003年 | 57篇 |
2002年 | 30篇 |
2001年 | 13篇 |
2000年 | 16篇 |
1999年 | 14篇 |
1998年 | 5篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1984年 | 5篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1980年 | 5篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 7篇 |
1972年 | 8篇 |
1971年 | 5篇 |
1959年 | 3篇 |
1945年 | 3篇 |
1925年 | 3篇 |
排序方式: 共有867条查询结果,搜索用时 125 毫秒
51.
We compared the amounts of learning achieved using two different instructional approaches under controlled conditions. We measured the learning of a specific set of topics and objectives when taught by 3 hours of traditional lecture given by an experienced highly rated instructor and 3 hours of instruction given by a trained but inexperienced instructor using instruction based on research in cognitive psychology and physics education. The comparison was made between two large sections (N = 267 and N = 271) of an introductory undergraduate physics course. We found increased student attendance, higher engagement, and more than twice the learning in the section taught using research-based instruction. 相似文献
52.
53.
54.
Darwin KH Ehrt S Gutierrez-Ramos JC Weich N Nathan CF 《Science (New York, N.Y.)》2003,302(5652):1963-1966
The production of nitric oxide and other reactive nitrogen intermediates (RNI) by macrophages helps to control infection by Mycobacterium tuberculosis (Mtb). However, the protection is imperfect and infection persists. To identify genes that Mtb requires to resist RNI, we screened 10,100 Mtb transposon mutants for hypersusceptibility to acidified nitrite. We found 12 mutants with insertions in seven genes representing six pathways, including the repair of DNA (uvrB) and the synthesis of a flavin cofactor (fbiC). Five mutants had insertions in proteasome-associated genes. An Mtb mutant deficient in a presumptive proteasomal adenosine triphosphatase was attenuated in mice, and exposure to proteasomal protease inhibitors markedly sensitized wild-type Mtb to RNI. Thus, the mycobacterial proteasome serves as a defense against oxidative or nitrosative stress. 相似文献
55.
Wunsch C 《Science (New York, N.Y.)》2002,298(5596):1179-1181
56.
57.
David A. Keith Tara G. Martin Eve McDonald-Madden Carl Walters 《Biological conservation》2011,(4):1175-1178
Adaptive management of natural resources is widely supported, but in biodiversity conservation there have been few practical applications of the approach in its entirety. Some of the contributions to this special publication examine progress in the implementation of adaptive approaches into conservation policy, while others explore novel theoretical and modeling approaches that seek to accommodate the complexities of real-world applications. Several of the papers address the treatment of uncertainty in adaptive management through innovative approaches to experimentation and monitoring, use and characterisation of expert knowledge and reconciliation of differences of opinion about parameters or systems. Drawing on these contributions, we discuss the major impediments to implementing adaptive management, why adaptive management has been slow to be implemented and how this can be redressed. 相似文献
58.
Nakamura RK Rishniw M King MK Sammarco CD 《Journal of Feline Medicine and Surgery》2011,13(4):266-271
The objective of this prospective study was to determine the prevalence of echocardiographic evidence of heart disease in apparently healthy cats with heart murmurs. Thirty-two privately owned domestic cats were examined. All cats were considered healthy on the basis of history and physical examination, except for the finding of a heart murmur on auscultation. Cats on any medications (besides regular flea, tick and heartworm preventative) or that were pregnant or lactating were excluded from this study. The prevalence of echocardiographic evidence of heart disease in this population of cats was 53%. Therefore, identification of a heart murmur on routine physical examination in apparently healthy cats warrants further investigation. 相似文献
59.
Balcer JL DeAmicis CV Johnson PL Klosin J Whiteker GT Rao CS Dai D 《Pest management science》2011,67(5):556-559
BACKGROUND: Tricyclazole is a commercial fungicide used to control rice blast. As part of re‐registration activities, samples of metabolites and process impurities are required. In addition, isotopically labeled tricyclazole samples are also required. RESULTS: Four new compounds related to tricyclazole are reported. An isotopically labeled sample of tricyclazole was prepared that contained two 15N atoms and one 13C atom. Radiolabeled tricyclazole with 14C at the triazole C3 position was also synthesized. A new process impurity in technical tricyclazole was identified and synthesized. A new metabolite of tricyclazole was identified, independently synthesized and characterized by X‐ray crystallography. CONCLUSION: A previously unreported metabolite of tricyclazole has been identified and structurally characterized. In addition, a new process impurity has been identified by independent synthesis. Identification of these new compounds has facilitated the continued registration of this important fungicide. Copyright © 2011 Society of Chemical Industry 相似文献