全文获取类型
收费全文 | 7021篇 |
免费 | 349篇 |
国内免费 | 6篇 |
专业分类
林业 | 487篇 |
农学 | 148篇 |
基础科学 | 36篇 |
1314篇 | |
综合类 | 1224篇 |
农作物 | 225篇 |
水产渔业 | 558篇 |
畜牧兽医 | 2681篇 |
园艺 | 197篇 |
植物保护 | 506篇 |
出版年
2023年 | 58篇 |
2022年 | 73篇 |
2021年 | 147篇 |
2020年 | 151篇 |
2019年 | 178篇 |
2018年 | 180篇 |
2017年 | 150篇 |
2016年 | 177篇 |
2015年 | 162篇 |
2014年 | 185篇 |
2013年 | 264篇 |
2012年 | 476篇 |
2011年 | 599篇 |
2010年 | 296篇 |
2009年 | 240篇 |
2008年 | 493篇 |
2007年 | 521篇 |
2006年 | 462篇 |
2005年 | 431篇 |
2004年 | 407篇 |
2003年 | 378篇 |
2002年 | 387篇 |
2001年 | 68篇 |
2000年 | 50篇 |
1999年 | 63篇 |
1998年 | 50篇 |
1997年 | 50篇 |
1996年 | 42篇 |
1995年 | 47篇 |
1994年 | 43篇 |
1993年 | 43篇 |
1992年 | 30篇 |
1991年 | 34篇 |
1990年 | 32篇 |
1989年 | 34篇 |
1988年 | 28篇 |
1987年 | 26篇 |
1986年 | 24篇 |
1985年 | 35篇 |
1984年 | 26篇 |
1983年 | 27篇 |
1982年 | 20篇 |
1981年 | 15篇 |
1980年 | 23篇 |
1979年 | 23篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1975年 | 11篇 |
1974年 | 11篇 |
1973年 | 17篇 |
排序方式: 共有7376条查询结果,搜索用时 15 毫秒
21.
Yaxin Li Matthew R. Gronquist Guixia Hao Michele R. Holden Anatol Eberhard Russell A. Scott Michael A. Savka Erno Szegedi Sandor Sule Thomas J. Burr 《Physiological and Molecular Plant Pathology》2005,67(6):101
Agrobacterium vitis causes crown gall disease on grapevines. It also induces a specific necrosis on grape roots and a hypersensitive response (HR) on tobacco that are regulated by a complex quorum-sensing regulatory system. Strain F2/5 produces at least six N-acyl-homoserine lactones (AHLs) that function as signal molecules in quorum-sensing. The AHLs differ in acyl side chain length (8–16 carbons) as determined by gas chromatography/mass spectrometry and electrospray ionization tandem mass spectrometry. Mutant derivatives of F2/5 differ in ability to cause necrosis and the HR and show variable AHL profiles as determined by a thin-layer chromatography/biosensor assay. All wildtype A. vitis strains revealed the presence of long-chain AHLs regardless of tumorigenicity or ability to cause the HR. Whereas genes encoding long-chain AHLs are predicted to reside on the F2/5 chromosome, the determinants for short-chain AHLs were shown to be located on conjugal plasmids. 相似文献
22.
It is unlikely that human beings acquire a zoonotic infection from healthy cats without ectoparasites. The benefits of cat ownership to human mental health are well established. Veterinarians and physicians should work together closely to provide accurate information to cat owners so that logical decisions concerning cat ownership can be made by the owner. 相似文献
23.
24.
Michael E. Patterson Jessica M. Montag Daniel R. Williams 《Urban Forestry & Urban Greening》2003,1(3):171-183
Increasing urbanization of rural landscapes has created new challenges for wildlife management. In addition to changes in the physical landscape, urbanization has also produced changes in the socio-cultural landscape. The greater distancing from direct interaction with wildlife in urbanized societies has led to the emergence of a culture whose meanings for wildlife are less grounded in the utilitarian/instrumental orientation of rural agrarian systems. Urban perspectives on wildlife are comprised of more highly individualized emotional/symbolic values. This shift creates two problems with respect to managing wildlife in an urbanizing landscape. First the increased diversity in values and meanings increases the likelihood for social conflicts regarding wildlife management while at the same time making socially acceptable resolutions more intractable. This in turn requires fundamental changes in decision-making paradigms and the research approaches used to inform decision making. Second, as remaining rural communities feel the pressures of urbanization, wildlife conflicts become conflicts not just over wildlife but conflict over larger socio-political concepts such as equity, tradition, private property rights, government control, power, and acceptable forms of knowledge. This paper examines the wildlife management implications of changes associated with increasing urbanization and employs two case studies to illustrate these issues. First a study of a controversy over urban deer management provides insights into how to map conflicting values and search for common ground in an urban culture with increasingly individualistic values for wildlife. Specifically, the analysis illustrates that common ground may, at times, be found even among people with conflicting value systems. The second case study examined a ranching community faced with predator reintroduction. This case study illustrates tensions that occur when the community of interest (i.e. a national public) is broader than the community of place in which the problem occurs. In this latter situation, the debate centers around more than just different views about the rights of animals. It also entailed the rights of individuals and communities to decide their future. The conclusion discusses the need for wildlife institutions to adapt their underlying decision making philosophy including the way science is integrated into decision making processes in light of the changes in social context caused by urbanization. 相似文献
25.
26.
The liability United States (U.S.) tree owners face from hazardous trees on their private properties has and continues to undergo a transformation. The traditional common law legal test focused upon whether a tree owner had acted to create a hazardous condition on the property. The modern trend is towards a test that imposes greater responsibility and greater uncertainty on tree owners and arborists. Abandoning the natural/artificial distinction, the modern test, adopted in half the U.S. jurisdictions, imposes general principles of negligence on tree owners. This paper discusses the U.S. legal context for hazardous trees, particularly the impacts on individual tree owners. It closes by addressing various practical means to minimize the risks associated with the modern legal standards, both for susceptible tree owners, and for professionals assessing the subject property. 相似文献
27.
28.
Jorge F Soares Victoria J Chalker Kerstin Erles Sonya Holtby Michael Waters Stuart McArthur 《Journal of zoo and wildlife medicine》2004,35(1):25-33
During the months of April to August in 1999 and 2002, oral swabs were collected from 146 tortoises (Testudo sp.) in private collections in the United Kingdom and tested by polymerase chain reaction (PCR) for the presence of Mycoplasma agassizii and Chelonian herpesvirus (ChHV). The presence of M. agassizii was confirmed by restriction digestion of the PCR product. A 307-bp fragment of the ChHV UL5 homologue gene was sequenced and found to show most similarity to equine herpesvirus type 1. A prevalence of 15.8 and 8.2% was found for M. agassizii and ChHV, respectively. Comparison of the carriage of both M. agassizii and ChHV in different species of tortoises correlated the presence of M. agassizii with Testudo horsfieldii and ChHV with Testudo marginata and Testudo graeca iberia. An association of ChHV with stomatitis was also found. Mixed infections with both agents were detected. The findings further demonstrate this pathogen-tortoise association and the cross transmission of these infections if different tortoise species are housed together. 相似文献
29.
30.
Michael G Hoelzler David A Lidbetter 《Veterinary Clinics of North America: Small Animal Practice》2004,34(4):1057-73, viii
Urethral sphincter mechanism incompetence and ureteral ectopia are the two most common causes of urinary incontinence in dogs and cats. Surgical treatments for both disorders have been described.Once a diagnosis is made, surgical intervention may lead to improved outcomes with resolution of incontinence in many patients. Proper case selection and surgical technique are critical in achieving clinical success when managing these difficult cases. 相似文献