全文获取类型
收费全文 | 870篇 |
免费 | 53篇 |
国内免费 | 1篇 |
专业分类
林业 | 75篇 |
农学 | 37篇 |
基础科学 | 1篇 |
126篇 | |
综合类 | 74篇 |
农作物 | 43篇 |
水产渔业 | 104篇 |
畜牧兽医 | 412篇 |
园艺 | 11篇 |
植物保护 | 41篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 22篇 |
2018年 | 18篇 |
2017年 | 19篇 |
2016年 | 25篇 |
2015年 | 22篇 |
2014年 | 18篇 |
2013年 | 42篇 |
2012年 | 44篇 |
2011年 | 61篇 |
2010年 | 29篇 |
2009年 | 21篇 |
2008年 | 48篇 |
2007年 | 43篇 |
2006年 | 54篇 |
2005年 | 38篇 |
2004年 | 37篇 |
2003年 | 42篇 |
2002年 | 40篇 |
2001年 | 34篇 |
2000年 | 42篇 |
1999年 | 33篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 15篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1970年 | 5篇 |
排序方式: 共有924条查询结果,搜索用时 15 毫秒
31.
Seiichi Kanetani Mitsuteru Akiba Katsunori Nakamura Koichiro Gyokusen Akira Saito 《Journal of Forest Research》2001,6(4):307-310
The process of decline of an endangered tree species,Pinus armandii var.amamiana, was monitored on the southern slope of Mt. Hasa-dake in Yaku-shima Island from 1994 to 1998. There are 163 trees ofP. armandii var.amamiana over 1.3 m in height. They are distributed on steep ridges and rocks with a thin soil layer mostly consisting of friable
granite. During the monitoring period, 21 trees ofP. armandii var.amamiana died and the mortality rate was 12.9%. Dead trees were categorized into three types: standing, uprooted and landslide. The
uprooted- and landslide-typed dead trees were found only after a severe typhoon struck Yaku-shima Island. This suggests that
the combination of fragile site conditions and severe typhoons play an important role in the process of decline ofP. armandii var.amamiana. The standing-typed dead trees were presumed to have been killed by pine wilt disease, accounting for 71.4% of the dead trees.
However,Bursaphelenchus xylophilus, the cause of pine wilt disease, was not detected from any of the wood chips or branch samples from the standing-typed dead
trees ofP. armandii var.amamiana. This might indicate that some factor(s) other than pine wilt disease could be responsible for the standing-typed death ofP. armandii var.amamiana in natural habitats.
A part of this paper was presented at the 109th Meeting of the Japanese Forestry Society. 相似文献
32.
The nitrobenzene oxidation method was modified to obtain more reproducible data and more structural information about lignin, not only by gas chromatography (GC) but also by proton nuclear magnetic resonance (1H-NMR) spectroscopy for quantitative determination of the oxidation products and to simplify the procedures. The nitrobenzene oxidation mixture was directly extracted after acidification without preextraction of by-products. The direct extraction made the extractive step easy and gave reproducible data. 5-Iodovanillin was selected as a new internal standard. The reason for this selection was that 5-iodovanillin did not exist in the nitrobenzene oxidation products from any plant species and had an aldehyde group whose peak did not overlap with the other aldehyde peaks on an1H-NMR spectrum. Thus, the use of 5-iodovanillin enabled us to quantifyp-hydroxybenzaldehyde, vanillin, and syringaldehyde in oxidation products on the basis of1H-NMR analysis as well as GC. Furthermore, more information about the condensed structure of lignin was derived by comparing the1H-NMR and GC analyses.Part of this work was presented at the 42nd Annual Meeting of the Lignin Symposium, Sapporo, October 1997 相似文献
33.
Chikaya Sakai Atok Subiakto Hani Sitti Nuroniah Naoto Kamata Koji Nakamura 《Journal of Forest Research》2002,7(2):73-80
We developed a vegetative propagation system for mass-producing three dipterocarps species,Shorea selanica Bl.,Shorea leprosula Mig., andShorea platyclados Sloot. This system uses fog evaporative cooling inside a greenhouse to reduce the leaf-to-air vapor pressure deficit (leaf-to-air
VPD) inside the propagator, even under high irradiance conditions. This cooling method has no negative influence on medium
conditions such as overwetting. A plastic tent propagator combined with this cooling method was used for vegetative propagation
experiments. In mass-production experiments, the annual rooting percentages from the cuttings were low in the first 2 years
(1997–1998) due to operational problems of the tent propagator (S. selanica, 48–51%;S. leprosula, 56–59%;S. platyclados: 50–63%). A hard cover propagator improved the rooting percentages in the mass-production experiments in 1999 because it
made operations easier (S. selanica, 70%;S. leprosula, 77%;S. platyclados, 77%). This system, which uses a combination of fog evaporative cooling and a hard plastic propagator, should be useful for
the mass propagation of these dipterocarp planting stocks.
This study was carried out under a joint project of the Ministry of Forestry, Indonesia and Komatsu Ltd. The project was supported
by Research Association for Reforestation of Tropical Forest (RETROF) organized by Japanese Forestry Agency. 相似文献
34.
Riparian forests greatly influence aquatic ecosystems by providing shade cover, which controls water temperature and limits
primary production. We examined the relationship between forest cover and summer stream temperature in northernmost Japan.
Heat budget and statistical analyses were employed and the results were compared. Heat budget analysis revealed that the water
temperature would decrease almost linearly from 29°C to 25°C with an increase in forested reaches along a 3.2 km stretch of
the river. Multiple regression analysis by the stepwise method chose only open channel length as a variable to explain the
variation in maximum stream temperature. A sharp increase in stream temperature was noted when riparian forest cover was removed
in short lengths, of up to 1.0km; this increasing trend gradually flattened as the length of open stretch increased. Thus,
even small openings in the riparian canopy resulted in drastic rises in summer stream temperature. The maximum summer temperatures
estimated by the two methods were coincided, and can therefore be accurately estimated by regression analysis. Retrospective
analysis based on the regression equation showed that the maximum summer temperature in 1947 was 6°C lower than at present,
and that a sharp increase occurred from 1947 to 1960, a period of rapid expansion of agricultural land development in the
watershed. 相似文献
35.
Amin Setyo Leksono Kenta Takada Nobukazu Nakagoshi Koji Nakamura 《Journal of Forest Research》2006,11(1):61-64
A continuous sampling of canopy beetles was carried out to determine variations in the abundance, species diversity, richness,
and composition of the Mordellidae and Cerambycidae in a coppice woodland. Changes in the abundance and the species richness
were monitored at three heights in the forest throughout the season in 1999, using yellow and blue water pan traps. The results
showed significant variations in the abundance of Mordellidae among the canopy layers, while little variation was found for
Cerambycidae. The abundance, species diversity, and richness were generally greater in summer. The results showed distinct
species compositions in both families among layers. 相似文献
36.
Yasuyuki Tachiki Tetsuhiko Yoshimura Hisashi Hasegawa Tomonori Mita Tetsuro Sakai Futoshi Nakamura 《Journal of Forest Research》2005,10(6):419-427
The objectives of this study were to determine Global Positioning System (GPS) positional errors while moving under the forest
canopy and to clarify the effects of polyline simplification on area and perimeter estimations. We used the Pathfinder Pro
XR and GPSMAP 76S, which are categorized as “high-end mapping” and “general navigation” GPS receivers, respectively. The field
tests were conducted in both natural and plantation forests. The results showed that the Pathfinder Pro XR, which has better
multipath rejection technology, worked well, especially in the plantation forest under unfavorable conditions of higher stand
density. We used analysis of variance to clarify the effects of the receiver type, positioning mode, stand type, and polyline
simplification method on area and perimeter estimations. The receiver type and positioning mode were found to be significant
factors that affected area estimation. The Pathfinder Pro XR estimated the area more accurately than the GPSMAP 76S, and differential
GPS estimated the area more accurately than autonomous GPS. With respect to the perimeter, the receiver type, positioning
mode, and polyline simplification method were found to be significant factors. The results showed that perimeter estimation
was improved by using the velocity filter, and further improved by using the velocity filter and Douglas-Peucker algorithm,
especially when the Pathfinder Pro XR was used. The GPSMAP 76S estimated the perimeter accurately without any filtering because
its default speed filter worked well, even though the GPSMAP 76S is a general navigation GPS receiver. 相似文献
37.
Fumiaki Nakatsubo Kenichi Enokita Koji Murakami Keizo Yonemori Akira Sugiura Naoki Utsunomiya Suranant Subhadrabandhu 《Journal of Wood Science》2002,48(5):414-418
The structural variety of the condensed tannins (proanthocyanidins) in the fruits of 16Diospyros species are reported. Eleven species contained condensed tannins mostly consisting of a mixture of catechin (CA) and gallocatechin (GCA) repeating units; the other five species did not. The GCA content in the CA-GCA total varied from 0.3% to 84.6%. The number of esterified gallic acid per one flavan repeating unit (degree of galloylation, DG) ranged from 0.01 to 0.89. The GCA content was found to be proportional to the DG values. Thus, 16Diospyros species tested may be classified into five groups by the analytical data of their condensed tannins. It may be interesting to compare their structural characteristics with those of the condensed tannins in other fruits, leaves, woods, and barks from the viewpoint of their biosynthesis and function in the plants.Part of this paper was presented at the 46th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1995 相似文献
38.
A series of novel 4-O-alkoxytrityl chlorides (1) with different chain lengths was synthesized as a novel reagent for obtaining 6-O-alkylated cellulose with high regioselectivity via trityl groups in one reaction step without the use of any protective groups. These chlorides were reacted with methyl -d-glucoside, which was used as a model compound, to examine the reactivities toward the primary hydroxyl groups of cellulose to afford a series of 6-O-alkylated methyl -d-glucosides in high yields. The product compounds were found to have interesting solubilities and thermal properties. Thus, newly prepared trityl chloride derivatives were found to be useful regioselective derivatization reagents on the primary hydroxyl group in carbohydrates, especially in cellulose. 相似文献
39.
Surgical correction of gastro‐oesophageal intussusception with bilateral incisional gastropexy in three dogs 下载免费PDF全文
Three dogs presented for evaluation of acute onset tachypnoea and dyspnoea following episodes of vomiting and/or regurgitation. Thoracic radiographs were suggestive of a gastro‐oesophageal intussusception in all three dogs; one dog also showed evidence of aspiration pneumonia. All three dogs underwent surgical correction with a bilateral incisional gastropexy. All dogs recovered from anaesthesia uneventfully and were discharged from the hospital 3 days after presentation. Persistent megaoesophagus was evident in all three dogs, and they are being chronically managed with a strict feeding regime and pro‐motility agents. 相似文献
40.
Vitamin D Status in Different Stages of Disease Severity in Dogs with Chronic Valvular Heart Disease 下载免费PDF全文
T. Osuga K. Nakamura T. Morita S.Y. Lim K. Nisa N. Yokoyama N. Sasaki K. Morishita H. Ohta M. Takiguchi 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2015,29(6):1518-1523