全文获取类型
收费全文 | 17791篇 |
免费 | 101篇 |
国内免费 | 1篇 |
专业分类
林业 | 3688篇 |
农学 | 1334篇 |
基础科学 | 140篇 |
3007篇 | |
综合类 | 850篇 |
农作物 | 2152篇 |
水产渔业 | 1898篇 |
畜牧兽医 | 1728篇 |
园艺 | 1130篇 |
植物保护 | 1966篇 |
出版年
2023年 | 9篇 |
2022年 | 12篇 |
2021年 | 28篇 |
2020年 | 52篇 |
2019年 | 69篇 |
2018年 | 2768篇 |
2017年 | 2722篇 |
2016年 | 1215篇 |
2015年 | 100篇 |
2014年 | 67篇 |
2013年 | 88篇 |
2012年 | 871篇 |
2011年 | 2234篇 |
2010年 | 2154篇 |
2009年 | 1292篇 |
2008年 | 1404篇 |
2007年 | 1668篇 |
2006年 | 133篇 |
2005年 | 188篇 |
2004年 | 191篇 |
2003年 | 239篇 |
2002年 | 128篇 |
2001年 | 18篇 |
2000年 | 53篇 |
1999年 | 14篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 12篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 19篇 |
1992年 | 11篇 |
1991年 | 4篇 |
1989年 | 10篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1973年 | 4篇 |
1970年 | 2篇 |
1969年 | 3篇 |
1968年 | 6篇 |
1966年 | 2篇 |
1960年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
Biodiversity and its fragility in Yunnan,China 总被引:1,自引:0,他引:1
PU Ying-shan ZHANG Zhi-yi PU Li-na HUI Chao-mao 《林业研究》2007,18(1):39-47
In Yunnan, 8 major aspects of biodiversity and fragility in landforms, ecosystems, distribution populations, alien invasion, segregation, pollution and maladministration with various menace factors causing biodiversity loss have been described. It is revealed that the facts that the biodiversity and fragility coexists in this paper. Accordingly, 6 major countermeasures for effective conservation and rational utilization of the provincial biodiversity were suggested on the basis of the scientific development concepts, principles of nature protection, conservation biology, resource management and ethnobotany and present status in Yunnan with rich intangible resources such as climatic, ethnical and cultural diversity, etc. 相似文献
52.
Within a forested watershed at the Uryu Experimental Forest of Hokkaido University in northern Hokkaido, overstory litterfall and related nutrient fluxes were measured at different landscape zones over two years. The wetland zone covered with Picea glehnii pure stand. The riparian zone was deciduous broad-leaved stand dominated by Alnus hirsuta and Salix spp., while the mixture of deciduous broadleaf and evergreen conifer dominated by Betula platyphylla, Quercus crispula and Abies sachalinensis distributed on the upland zone. Annual litterfall averaged 1444, 5122, and 4123 kg.hm^-2·a^-1 in the wetland, riparian and upland zones, respectively. Litterfall production peaked in September-October, and foliage litter contributed the greatest amount (73.4%-87.6 %) of the annual total litterfall. Concentrations of nutrients analyzed in foliage litter of the dominant species showed a similar seasonal variation over the year except for N in P glehnii and A. hirsuta. The nutrient fluxes for all elements analyzed were greatest on riparian zone and lowest in wetland zone. Nutrient fluxes via litterfall followed the decreasing sequence: N (11-129 kg.hm-2.aq) 〉 Ca (9-69) 〉 K (5-20) 〉 Mg (3-15) 〉 P (0.4-4.7) for all stands. Significant differences were found in litterfall production and nutrient fluxes among the different landscape components. There existed significant differences in soil chemistry between the different landscape zones. The consistently low soil C:N ratios at the riparian zone might be due to the higher-quality litter inputs (largely N-fixing alder). 相似文献
53.
林业生态工程效益补偿问题研究初探 总被引:1,自引:0,他引:1
生态效益补偿对于促进林业生态工程建设、保护森林生产者和经营者的切身利益具有重要的作用.本文在分析国内外生态效益补偿现状的基础上,通过对建立森林生态效益补偿机制的必要性、原则、途径以及补偿标准等问题进行深入探讨,为进一步完善我国森林生态效益补偿机制提供科学依据.森林生态效益补偿资金的建立,不仅为森林资源管护提供稳定的资金来源,更是对森林生态效益价值的认可,从根本上解决了林业生态工程建设的动力和机制问题,将对中国林业和生态建设产生广泛而深远的影响. 相似文献
54.
55.
In May 2006, a high intensity wildfire occurred in Songling forest region in Daxing'an Mountains, China. The concentration changes of eight ions (K^+, Na^+, Ca^2+, Mg^2+, Cl^-, Br^-, NO3^- and SO4^2-) were measured in burned and tmbumed streams after fire from May to Oct., 2006. Results show that the most ions flux were higher in burned stream than that in unburned stream during the sampling period, and the greatest concentrations of most ions transported from burned stream occurred in July. After fire, the most amplitude chemical ion was Ca^2+, whose average concentration was 5.50 mg·L^-1 higher than that in unburned stream, and the total concentration of every chemical ion presents a trend Ca^2+〉SO4^2- 〉Na^+〉Mg^2+〉NO3^- . The average concentrations of Ca^2+, SO4^2- , Na^+'Mg^2+,NO3^- showed an increase trend, but those of K^+, Cl^- , Br had a decreased trend. SO4^2- had the largest loss among these anions, followed by NO3^-. Overall, the increase degree of cation was greater than that of anion after burning. 相似文献
56.
Anne C. Arsenault Peter M. Foley Noel P. Clancey 《The Canadian veterinary journal. La revue veterinaire canadienne》2022,63(6):589
A 12-year-old neutered male American Staffordshire terrier dog was referred to the Atlantic Veterinary College, Prince Edward Island, Canada, for suspected immune-mediated hemolytic anemia. Babesiosis (Babesia vulpes) was confirmed using polymerase chain reaction testing. The dog was successfully treated with a 10-day protocol of atovaquone/proguanil (TEVA Pharmaceutical Industries, Toronto, Ontario), 13.5 mg/kg BW, PO, q8h and azithromycin (Pharmascience, Montreal, Quebec), 10 mg/kg BW, PO, q24h. To the authors’ knowledge, this report is the first documented case of babesiosis caused by Babesia vulpes in a dog from Canada. 相似文献
57.
58.
The Alstroemeria cultivars Diamond, King Cardinal and Libelle were grown for 18 months under five lighting regimes with, and without, soil cooling. The aim was to optimize the daily investment of light energy from artificial sources with respect to photoperiod and photosynthetic fluence rates and to elucidate possible links between reactions to photoperiod and root-zone temperature. The more photons (photosynthetically active radiation, PAR) that were supplied to the plants per day (8, 11 and 13 mol m−2), the higher was the total production of flowering stems. The total yield from regimes with 13 mol m−2 day−1 was higher when the light was spread over 20 and 16 h compared to 12 h. In treatments with soil cooling, the plants flowered continuously under all combinations of photoperiods and photosynthetic fluence rates, and the summer and autumn recession in flower production that occurred for non-cooled ‘King Cardinal' and ‘Diamond' was the same under all lighting regimes. It is concluded that it might be more cost-effective to spread the daily investment of light over 20 rather than 16 or 12 h when the total energy budget and CO2 costs are taken into consideration. 相似文献
59.
Consumer perception versus scientific evidence of farmed and wild fish: exploratory insights from Belgium 总被引:2,自引:2,他引:0
Wim Verbeke Isabelle Sioen Karen Brunsø Stefaan De Henauw John Van Camp 《Aquaculture International》2007,15(2):121-136
The increasing number of marketable fish being supplied from aquaculture is a response to the increasing demand for healthy
food and is filling the gap left by depleting natural fish stocks. Little is known about the awareness and perception of the
consumer in terms of farmed fish versus fish from capture fisheries. The consumer's subjective point of view is of overriding
importance for the production system and product acceptance as well as for future market success. In this paper consumer perception
in Belgium is explored and compared against scientific evidence of farmed versus wild fish. Primary data were collected through
a consumer survey (April 2003) and focus group discussions (May 2004) with Belgian consumers. The majority of the consumer
sample reported no perceived differences between farmed versus wild fish. However, mean perception scores were slightly in
favour of wild fish on the attributes taste, health and nutritious value, in particular among consumers aged 55 years and
older. The availability of farmed fish was perceived to be better than that of wild fish, while the consumer's perception
of safety did not differ between farmed and wild fish. The focus group discussions indicated that consumers’ opinions and
beliefs about farmed fish are mainly based on emotion and image transfer from intensive terrestrial livestock production rather
than on awareness and factual knowledge of aquaculture.
相似文献
John Van CampEmail: |
60.
Tsutomu MATSUMOTO Yuichiro NARA Hiromitsu FURUYA Harumi TAKAHASHI Kiichi TAIRAKO Hideki YAMAMOTO 《Journal of General Plant Pathology》2002,68(4):382-384
L11A-Fukushima (L11A-F) derived from attenuated isolate LuA of Tomato mosaic virus (ToMV) has the highest ability to cross protect against virulent ToMV among LuA and its derivatives and is stably inherited.
Growth, yield, fruit quality and symptom attenuation of inoculated tomato plants did not differ significantly between L11A-F and L11A. The infectivity of progeny viruses in tomato infected with LuA-F was less than 4% of that with virulent ToMV. From these
results, L11A-F appears to possess the properties necessary for practical use. To manage L11A-F strictly, a PCR-based assay to detect trace contamination of virulent ToMV in L11A-F preparations was established.
Received 10 June 2002/ Accepted in revised form 30 October 2002 相似文献