全文获取类型
收费全文 | 1851篇 |
免费 | 65篇 |
国内免费 | 5篇 |
专业分类
林业 | 167篇 |
农学 | 45篇 |
基础科学 | 3篇 |
306篇 | |
综合类 | 82篇 |
农作物 | 92篇 |
水产渔业 | 194篇 |
畜牧兽医 | 888篇 |
园艺 | 21篇 |
植物保护 | 123篇 |
出版年
2022年 | 22篇 |
2021年 | 47篇 |
2020年 | 16篇 |
2019年 | 28篇 |
2018年 | 27篇 |
2017年 | 41篇 |
2016年 | 59篇 |
2015年 | 73篇 |
2014年 | 87篇 |
2013年 | 140篇 |
2012年 | 97篇 |
2011年 | 132篇 |
2010年 | 59篇 |
2009年 | 65篇 |
2008年 | 112篇 |
2007年 | 114篇 |
2006年 | 121篇 |
2005年 | 115篇 |
2004年 | 114篇 |
2003年 | 97篇 |
2002年 | 73篇 |
2001年 | 61篇 |
2000年 | 42篇 |
1999年 | 18篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 7篇 |
1991年 | 16篇 |
1990年 | 8篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1984年 | 13篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1963年 | 1篇 |
1961年 | 1篇 |
1927年 | 1篇 |
排序方式: 共有1921条查询结果,搜索用时 613 毫秒
81.
Muneto?HirobeEmail author John?Sabang Balram K.?Bhatta Hiroshi?Takeda 《Journal of Forest Research》2004,9(4):347-354
The effects of tree species on the dynamics of nutrient transformations during leaf-litter decomposition are not well understood
in tropical rain forests. To examine differences in the dynamics of C, nutrients, and organic constituents during decomposition
among tree species, the leaf-litter decomposition of 15 trees was assessed using a litter-bag method in a lowland tropical
rain forest in Sarawak. The dynamics of C was parallel to that of weight loss. The dynamics of nutrients were grouped into
three patterns. The dynamics of K was characterized by a high leaching loss in the initial stages, and that of Ca and Mg generally
showed a gradual decrease over the course of decomposition. The dynamics of N and P showed highly different patterns with
the weight loss, and was characterized by relatively higher remaining mass at the end of the experiment. The variations or
exceptions of nutrient dynamics among tree species were considered to be related to the initial concentration of each nutrient.
For the dynamics of organic constituents, water-soluble carbohydrates disappeared quickly at the initial stages, and acid-soluble
carbohydrates were the second fastest decomposing fraction; the decomposition of acid-insoluble residue (AIS) was the slowest.
The release of limiting nutrients (N and P) generally followed the disappearance of AIS, but was independent of the disappearance
of AIS when the initial concentrations of these nutrients were very low. 相似文献
82.
INTRODUCTION Wood is far from a stable material. One of the biggest challenges for woodworking is learning to work within the constraints of wood properties. Discoloration of wood directly influences the decorative performance of wood products. Therefore, the degree of color change is a critical factor that determines the utilization area of dyed wood (Sakuragawa Satoshi, 1996). Discoloration has occurred because the wood components and dye molecules are degraded by UV-ray (Kaneko Shin… 相似文献
83.
Makoto Kiguchi Yutaka Kataoka Hiroshi Matsunaga Koichi Yamamoto Philip D. Evans 《Journal of Wood Science》2007,53(3):234-238
The market for wood-fiber plastic composites (WPCs) is expanding rapidly in many countries including Japan, where WPCs are
mainly used for exterior products. In such applications, WPCs undergo undesirable color change, chalking, and shrinkage and
swelling, and accordingly there is a need to better understand the mechanisms responsible for the weathering of WPC and develop
methods of improving their weathering resistance. In this study, weatherability of WPC was assessed by natural and accelerated
weathering trials. Discoloration (whitening) of WPC during exposure was caused by degradation of both wood and plastic. Darker
color pigments as additives improved the color stability of WPC; however, chalking on the surfaces still occurred. The color
stability of WPC was improved by application of exterior coatings. Preweathering of WPC (before coatings were applied) increased
the absorption of coatings by the WPC and had a positive effect on the color stability and prevented chalking of the composites.
Parts of this study were presented at the IUFRO XXII World Congress Meeting, Brisbane, August 2005 and the IAWPS 2005, Yokohama,
November 2005 相似文献
84.
Alnus trabeculosa Hand.-Mazz. is classed as “near threatened,” and efforts should be made to conserve the species, but effective action would
require understanding of its genetic variation and structure. Therefore, the genetic variation at 12 isozyme loci was examined
in seven populations of the species in Japan. The expected heterozygosity within species (H
es=0.222) and the expected heterozygosity within populations (H
ep=0.199) were found to be slightly higher than in most other woody species. The coefficient of genetic differentiation (G
ST=0.146) was also high. The northernmost population had the lowest values for almost all measures of genetic variation, and
populations in southern Japan tended to show greater within-population variation than those in northern Japan. The level and
distribution of genetic variation in this species might be related to its life history and ecological traits, and distribution
history. 相似文献
85.
This paper presents an on-line method for detecting washboarding generated in bandsaws. It uses a parameter based on the shape of sawing force amplitude distributions. The curve of the probability density function of the parallel sawing force amplitude obeyed a normal distribution for the normal sawn surface, but it changed to an M-shaped distribution when washboarding appeared on the sawn surface of the workpiece. The curve of probability density function of the normal sawing force amplitude obeyed the normal distribution for any sawn surface investigated. The workpiece including a knot did not influence use of the parameter for detecting the appearance of washboarding. 相似文献
86.
Leaf-fall phenology was studied in a cool–temperate deciduous broad-leaved forest in central Japan in relation to the topographic environmental gradients that occur along a short mountain slope. Leaf-fall phenology was described quantitatively using data from leaf litter collected along the slope. In autumn, leaf fall at the study site tended to occur slightly earlier on the upper slope than on the lower slope. This pattern was found at both the stand and the species levels. Our results suggest that leaf-fall phenology may be affected by difference in microclimatic conditions, because environmental conditions are thought to be more severe on the upper slope than on the lower slope. The less intensive methods used in this study, the litter trap method, and Dixon’s model succeeded in quantifying the phenological patterns of leaf fall within stands and within species along the short mountain slope. 相似文献
87.
Yoshitaka Kubojima Hiroshi Yoshihara Hisashi Ohsaki Masamitsu Ohta 《Journal of Wood Science》2000,46(4):279-283
We examined the accuracy of the shear properties of wood by the Iosipescu shear test using specimens whose shape was simplified. Quartersawn boards of sitka spruce (Picea sitchensis Carr.) and shioji (Japanese ash,Fraxinus spaethiana Lingelsh.) were used. Two types of specimen for the Iosipescu shear test were compared: a standard specimen whose notch angle is 90° and a keyhole type specimen, which is more easily prepared than the standard type. The shear modulus, yield shear stress, and failure shear stress of the keyhole-type specimen were compared to those of the standard specimen. Shear stress analysis was conducted using the finite element method (FEM). The results obtained were as follows: (1) The failure pattern obtained by the simplified Iosipescu shear test was similar to that seen with the standard Iosipescu shear test. (2) The shear modulus, yield stress, and failure stress obtained by the simplified Iosipescu shear test coincided with those by the standard Iosipescu shear test. (3) The principal strain angle and principal stress angle of the simplified Iosipescu shear test were about 45°. (4) It is recognized that pure stress is applied to the strain-gauge regions in the simplified Iosipescu shear test, and it is expected that the shear properties are independent of the notch angle. 相似文献
88.
Takuyuki Yoshioka Kazuhiro Aruga Toshio Nitami Hiroshi Kobayashi Hideo Sakai 《Journal of Forest Research》2005,10(2):125-134
Using the method of a life cycle inventory (LCI) analysis, the energy balance and the carbon dioxide (CO2) emission of logging residues from Japanese conventional forestry as alternative energy resources were analyzed over the entire life cycle of the residues. The fuel consumption for forestry machines was measured in field experiments for harvesting and transporting logging residues at forestry operating sites in Japan. In addition, a total audit of energy consumption was undertaken. It involved an assessment of materials, construction, and the repair and maintenance of forestry machines as well as the costs associated with an energy-conversion plant. As a result, the ratio of energy output to input was calculated to be 5.69, indicating that the system examined in this study could be feasible as an energy production system. The CO2 emission per MWhe (e: electricity) of the biomass-fired power generation plant was calculated to be 61.8kgCO2/MWhe, while that of coal-fired power generation plants in Japan is 960kgCO2/MWhe. Therefore, the reduction in the amount of CO2 emission that would result from replacing coal with biomass for power generation by as much as 3.0 million dry-t/year of logging residues in Japan was estimated to be 1.66 million tCO2/year, corresponding to 0.142% of the national CO2 emission. This study provides evidence that Japan could reduce its domestic CO2 emission by using logging residues as alternative energy resources. 相似文献
89.
1,4-Linked β-d-galactooligosaccharides with a degree of polymerization (DP) between 1 and 7 and 1,5-linked α-l-arabinooligosaccharides with a DP between 1 and 8 were labeled at their reducing ends with 2-aminobenzamide (2AB) in the presence of sodium cyanoborohydride. The 2AB-labeled oligosaccharides were shown to be homogeneous using high-performance anion-exchange chromatography (HPAEC) and by electrospray ionization mass spectrometry (ESI-MS). The signals in the 1H and 13C nuclear magnetic resonance (NMR) spectra of the 2AB-labeled oligosaccharides were then assigned using one- and two-dimensional NMR spectroscopy. These NMR data will be useful for the structural analysis of enzymatically synthesized galactan and arabinan side chains derived from rhamnogalacturonan I. 相似文献
90.
Masaki Jinkawa Hirokazu Yamaguchi Kuniaki Furukawa Toshiaki Satake Hiroshi Kobayashi 《Journal of Forest Research》2006,11(2):77-88
For monorail systems, it is very important to ensure the safety of the ground structure. We developed a tram car for slopes
that utilizes the mechanism of the monorail and analyzed the stress of the ground structure that had double rails. First,
we divided the ground structure into seven components, and formulated a procedure for calculating the stress of the ground
structure. As a result, the stress that acts upon the main rail and the main rail connecting part was near the allowable stress,
and each calculated value was within the allowable stress. We measured the stress by running the vehicle, and compared the
measured values with the calculated values. As a result, some measured values were larger than the calculated values. However,
the ratio of measured value to allowable stress was 90% or less. Finally, we calculated the static loading coefficient for
each part, results of which were as follows: main and subrail: 1.1; rail connection part and prop foundation part: 1.0; rail
installation part: 1.3. In the recalculations, it became clear that the recalculated values exceeded the allowable stresses.
These results suggest that we need to review the ground structure materials. 相似文献