全文获取类型
收费全文 | 737篇 |
免费 | 24篇 |
国内免费 | 3篇 |
专业分类
林业 | 64篇 |
农学 | 17篇 |
基础科学 | 5篇 |
133篇 | |
综合类 | 61篇 |
农作物 | 22篇 |
水产渔业 | 17篇 |
畜牧兽医 | 408篇 |
园艺 | 8篇 |
植物保护 | 29篇 |
出版年
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 7篇 |
2019年 | 13篇 |
2018年 | 12篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 12篇 |
2013年 | 36篇 |
2012年 | 37篇 |
2011年 | 46篇 |
2010年 | 19篇 |
2009年 | 32篇 |
2008年 | 43篇 |
2007年 | 44篇 |
2006年 | 40篇 |
2005年 | 38篇 |
2004年 | 34篇 |
2003年 | 42篇 |
2002年 | 28篇 |
2001年 | 24篇 |
2000年 | 16篇 |
1999年 | 18篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 11篇 |
1974年 | 6篇 |
1970年 | 6篇 |
1966年 | 3篇 |
1934年 | 2篇 |
1867年 | 2篇 |
1866年 | 7篇 |
1865年 | 2篇 |
排序方式: 共有764条查询结果,搜索用时 125 毫秒
151.
152.
H. J. Von Braun 《Forest Pathology》1977,7(2):76-93
Beech (Fagus sylvatica L.) bark disease, caused by Cryptococcus fagi Bär. II. The progress of the disease. The progress of the disease can be divided into 7 phases. The chances of recovery of diseased trees are poor if extensive areas of the tree have been attacked by Cryptococcus fagi Bär. and are moderate to good if the attacked areas are small and not numerous. 相似文献
153.
G. Braun 《Forest Pathology》1977,7(3):129-152
Causes and critcria of resistance to air pollution in Norway spruce. II. Reflexive resistance . The different reactions of stomata of resistant and “normal” spruce grafts were investigated. Resistant grafts were shown to have a more sensitive reaction by measuring water potentials and by analyzing S content in SO2 fumigated needles or F contents in grafts exposed to polluted air. Other tcsts involving gas permeability of stomata, clecrrical conductivity of needle cxtracts and watcr content of SO2 fumigated needles were less effective. 相似文献
154.
The effect of nitrogen fertilization on fungistatic phenolic compounds in fine roots of beech and Norway spruce growing in afforestation plots was analysed. The plots were situated at two sites in Switzerland on acidic soil with low base saturation. For 9 years, the trees have been treated with dry ammonium nitrate to give 0, 10, 20, 40, 80, 160 kg N ha?1 year?1, respectively. The phenolic compounds responded differently to fertilization. Fine roots of beech showed a significant decrease of (?)‐epicatechin and piceatannol with increasing nitrogen fertilization. The concentration of protocatechuic acid was increased with fertilization. Roots of fertilized Norway spruce showed significantly decreased concentrations of 4‐hydroxyacetophenone and piceatannol. The mycelial growth of three isolates each of Heterobasidion annosum s.l. and Cylindrocarpon destructans was tested on agar media containing various phenolic compounds in concentrations found in fine roots of Norway spruce (Picea abies) and beech (Fagus sylvatica). All three H. annosum isolates were inhibited by p‐coumaric acid and (?)‐epicatechin. Two isolates were inhibited by another four phenolic compounds (p‐hydroxybenzoic acid, 4‐hydroxyacetophenone, piceatannol and protocatechuic acid), one by (+)‐catechin. Two of three C. destructans isolates were inhibited by all phenolic compounds except for (+)‐catechin which affected only one isolate, one isolate did not respond at all. 相似文献
155.
156.
157.
Johannes?EichhornEmail author Regina?Icke Ansgar?Isenberg Uwe?Paar Egbert?Sch?nfelder 《European Journal of Forest Research》2005,124(4):335-347
The evaluation uses the longest available time series for beech and oak defoliation in Germany. The data from Hesse, starting
from 1984, show a typical pattern: for the first 12 years, a continuous increase in defoliation was observed ranging from
an average value of 14% in 1984 to a peak value of 30%. This was followed by a subsequent decrease in the loss of foliage
accompanied by a high variability, until the last monitoring in 2003, where an average value of 25% defoliation was observed.
For both tree species, the years of trend reversal were identical. The same pattern was observed in the German federal states:
Rhineland-Palatinate, North Rhine-Westphalia, and Bavaria. The year of trend reversal was identical in Hesse and Rhineland-Palatinate.
In North Rhine-Westphalia, it occurred 1 year earlier and in Bavaria 3 years earlier. Whereas defoliation trends were clearly
demonstrated, tree mortality did not appear on a large scale. The sample trees were grouped into four discrete clusters according
to their annual defoliation values from 1984 to 2003. In 1996, the clusters represent 15, 25, 35, and 50% defoliation values.
Regarding beech in Hesse, there was no overlap in the defoliation curves observed among the different clusters. These four
clusters having different degrees of defoliation over the whole time span of 20 years were used for a further detailed statistical
analysis. For discrete variables like crown spacing and—in the case of beech—fruit bearing, mosaic plots were applied in order
to visualize relations of low dimensional contingency tables, with defoliation trends being used as the response variable.
The data show for beech a very clear relation between defoliation and age, relative crown spacing, stand composition, and
fruit bearing. Regarding oak, besides age and relative crown spacing, the years with significant appearance of biotic stress
factors—leaf eating insects—show a clear relation to trends of defoliation. The statistical model used in this study—logistic
regression—allows applying a multinomial response variable and a number of continuous or categorical explanatory variables.
With this approach, an iterative optimized selection of effect variables was used to test the relevance of different variables
on the defoliation pattern of the same four clusters mentioned above. For this, the variables were grouped in an iterative
process with five steps, starting with a few basic variables of tree and site information, and ending with a total of more
than 20 variables in the fifth step. The process selects first the variables which are of significance on the defoliation,
and calculates the possible errors in the grouping of the different trees to the four clusters. In this analysis of beech,
the basic tree and stand variables: age, relative crown spacing, stand composition and fruit bearing proved to be the most
relevant group of parameters, with the other variables explaining the variation of defoliation only to a minor extent. More
complex model levels do not change any basic selected variables; however, Cation Exchange Capacity (CEC), C/N-ratio, Al- and
Ca-proportion of CEC are additionally selected and give a hint of the relevance of soil conditions. Regarding beech, the errors
of the statistical model are lower compared to oak. 相似文献
158.
159.
Ohne Zusammenfassung 相似文献
160.
Breme K Fernandez X Meierhenrich UJ Brevard H Joulain D 《Journal of agricultural and food chemistry》2007,55(5):1932-1938
New, odorant nitrogen- and sulfur-containing compounds are identified in cress extracts. Cress belongs to the botanical order Brassicales and produces glucosinolates, which are important precursors of nitrogen- and sulfur-containing compounds. Those compounds often present low perception thresholds and various olfactive notes and are thus of interest to the flavor and fragrance chemistry. When the study of organonitrogen and organosulfur compounds is undertaken, Brassicale extracts are one of the matrices of choice. Cress extracts were studied by analytical (GC-MS, GC-FPD) and chemical (fractionation) means to identify new interesting odorant compounds. Two compounds that have never been reported in cress extracts, containing both nitrogen and sulfur, were discovered: N-benzyl O-ethyl thiocarbamate and N-phenethyl O-ethyl thiocarbamate. These two molecules being of organoleptic interest, their homologues were synthesized and submitted to organoleptic tests (static and GC-sniffing). Their odors evolve from garlic and onion over green, mushroom- and cress-like to fresh, spearmint-like. This paper presents the origin, chemical synthesis, and organoleptic properties of a series of O-alkyl thiocarbamates. 相似文献