全文获取类型
收费全文 | 255篇 |
免费 | 13篇 |
专业分类
林业 | 6篇 |
农学 | 3篇 |
46篇 | |
综合类 | 31篇 |
农作物 | 1篇 |
水产渔业 | 3篇 |
畜牧兽医 | 161篇 |
园艺 | 4篇 |
植物保护 | 13篇 |
出版年
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 4篇 |
2015年 | 6篇 |
2014年 | 5篇 |
2013年 | 21篇 |
2012年 | 9篇 |
2011年 | 16篇 |
2010年 | 7篇 |
2009年 | 11篇 |
2008年 | 12篇 |
2007年 | 11篇 |
2006年 | 15篇 |
2005年 | 13篇 |
2004年 | 13篇 |
2003年 | 15篇 |
2002年 | 14篇 |
2001年 | 6篇 |
2000年 | 6篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1992年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1968年 | 1篇 |
1960年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有268条查询结果,搜索用时 31 毫秒
1.
2.
3.
4.
Concurrent measurements of net mineralization, nitrification, denitrification and leaching from field incubated soil cores 总被引:5,自引:0,他引:5
An improved method is described for incubating intact soil cores in the field, which permits concurrent measurement of net
mineralization, nitrification, denitrification and leaching. Cores were enclosed in PVC tubes with minimal disturbance to
the physical state or to the natural cycles of wetting/drying, soil temperature and aeration during an incubation lasting
4–5 days. An example of the application of the method is given in which soils with contrasting drainage characteristics were
compared. Over a 64-day experimental period, 58% of the mineralized nitrogen (N) in a freely drained soil was nitrified and
36% of the nitrate-N (NO3
–-N) was denitrified. In a poorly drained soil, 72% of the mineralized N was nitrified and 63% of the NO3
–-N was denitrified. In both soil types, 18% of the remaining NO3
–-N was leached. Rates of nitrification were significantly correlated with net mineralization (r
2=0.41 and 0.52) and also closely correlated with denitrification (r
2=0.67 and 0.68) in the freely and poorly drained soils, respectively. Independent measurements of these processes, using alternative
techniques (for the same period), compared favourably with measurements obtained with the improved incubation method. Adoption
of this method has a number of advantages with respect to field net N mineralization, and also allows interpretation of the
impact this may have on other N transformation processes.
Received: 18 June 1997 相似文献
5.
David G Ainley Nadav Nur Joseph T Eastman Grant Ballard Claire L Parkinson Clive W Evans Arthur L. DeVries 《Fish and Fisheries》2013,14(3):343-363
We report the analyses of a dataset spanning 39 years of near‐annual fishing for Dissostichus mawsoni in McMurdo Sound, Antarctica, 1972–2011. Data on total length, condition and catch per unit effort (CPUE) were derived from the > 5500 fish caught, the large majority of which were measured, tagged and released. Contrary to expectation, the length frequency of the McMurdo Sound catch was dominated by fish in the upper two‐thirds of the overall distribution exhibited in the industrial catch for the Ross Sea shelf. Fish length and condition increased from the early 1970s to the early 1990s and then decreased. Fish length positively correlated with Ross Sea ice extent in early spring, a relationship possibly caused by more ice encouraging larger fish to move farther south over the shelf and into the study area. Fish condition positively correlated with the amount of open water in the Ross Sea during the previous summer (Feb), perhaps reflecting greater availability of prey with the higher productivity that more open water brings. Decreasing fish size corresponds to the onset of the fishery, which targets the large individuals. CPUE was constant through 2001 and then decreased dramatically. We hypothesize that this decrease is related to the industrial fishery, which began in the 1996–97 austral summer, and concentrates effort over the ice‐free Ross Sea continental slope. As a result of limited prey choices and close coupling among mesopredators of the region, Antarctic toothfish included, the fishery appears to be dramatically altering the trophic structure of the Ross Sea. 相似文献
6.
7.
Khumsap S Lanovaz JL Rosenstein DS Byron C Clayton HM 《American journal of veterinary research》2003,64(12):1491-1495
OBJECTIVE: To study the effect of unilateral synovitis in the distal intertarsal and tarsometatarsal joints on locomotion, including the compensating effects within and between limbs. ANIMALS: 4 clinically normal horses. PROCEDURE: Gait analyses including kinematics, force plate, and inverse dynamic analysis were performed at the trot before lameness, after which synovitis was induced by injecting endotoxin into the right distal intertarsal and tarsometatarsal joints. Gait analyses were repeated 24 to 30 hours later during lameness. Differences between the stride variables during the 2 conditions (lame and sound) were identified. RESULTS: Tarsal joint range of motion, peak vertical force, and vertical impulse were decreased during lameness. Mechanical deficits included a decrease in negative work performed by the tarsal extensors during the early stance phase and a decrease in positive work by the tarsal extensors during push off. No compensatory changes in work were performed by other joints within the lame hind limb during the stance phase. Vertical impulse in the diagonal forelimb decreased, but there were no significant changes in forces or impulses in the ipsilateral forelimb or contralateral hind limb. CONCLUSION AND CLINICAL RELEVANCE: Results indicate that horses are able to manage mild, unilateral hind limb lameness by reducing the airborne phase of the stride rather than by increased loading of the compensating limbs. 相似文献
8.
9.
Julie Perkins Alfonso Clavijo Josue I Ortiz Timothy J Salo Hilary J Holland Benjamin J Hindson Mary T McBride 《Journal of veterinary diagnostic investigation》2007,19(2):180-184
Initial results demonstrating the feasibility of a multiplexed liquid array immunoassay for foot-and-mouth disease viral antigen detection and simultaneous serotype differentiation are presented. Serotype-specific antibodies from rabbit and guinea pig hyperimmunesera were isolated and prepared for use in a multiplexed, bead-based assay. The performance of all of the available antibodies as both capture and detector reagents was evaluated in the multiplexed system to establish a combination exhibiting the highest homotypic responses and lowest heterotypic reactions. The multiplexed assay was evaluated against inactivated cell culture supernatant samples of the same subtype as the virus used to raise the capture and detector antibodies. Distinct serotype differentiation was observed, except in the case of serotype SAT1. Subsequently, cell culture supernatant samples from a larger pool of viral subtypes were analyzed. Distinct serotype differentiation was obtained when analyzing cell culture supernatant samples from viral serotypes C, Asia, and SAT3, irrespective of the subtype. However, limitations of the current antibody pairs were realized in some inconclusive results obtained when analyzing samples from a broader range of O, A, and SAT2 subtypes. The results obtained in this initial study will be used to further optimize the assay using polyvalent or monoclonal antibodies and move toward the analysis of clinical samples. 相似文献
10.
Hilary Crusz 《Biological conservation》1973,5(3):199-208
Sri Lanka (Ceylon) was once part of an Indo-Malayan and Afro-Madgascan complex, and has three peneplains. These circumtances are reflected in her fauna and flora, of which 28·5 per cent of the vascular plants and 16 per cent of the land vertebrates are endemic, inhabiting mostly the central montane and southwestern regions. Such figures could provide indices or coefficients of insularity of islands of the nature of Sri Lanka and Madagascar. The parasites of the endemics and relicts could also point to the relationships of the hosts and the antiquity of the geographical regions. Nearly all the wildlife reserves are in the dry northern and eastern halves of the island, in areas of monsoon scrub-jungle, monsoon forest, or grassland. Further strict natural reserves are urgently needed in the montane and southwestern rain-forest and grassland areas. Significant conservation measures have been taken since 1885 by the Government and by what in 1971 was renamed the Wildlife and Nature Protection Society of Ceylon. Constitutional changes have also had their impact, while human population increase has affected land utilization and the extents of nature reserves. Twenty-seven mammal, 340 bird, 7 reptile, and 9 plant, species are absolutely protected. Despute such efforts, conservation science and practice, based on ecological studies, have lagged behind, but some progress is being made through the work of foreign and local scientists, and the new interest taken by Government and the universities. That Sri Lanka is well suited to effective nature conservation is shown also by the ethos of her people, as shaped by Buddhist teachings and by the concern of kings during her long history. 相似文献