全文获取类型
收费全文 | 6200篇 |
免费 | 360篇 |
国内免费 | 3篇 |
专业分类
林业 | 1092篇 |
农学 | 173篇 |
基础科学 | 18篇 |
1323篇 | |
综合类 | 562篇 |
农作物 | 181篇 |
水产渔业 | 237篇 |
畜牧兽医 | 2409篇 |
园艺 | 140篇 |
植物保护 | 428篇 |
出版年
2023年 | 37篇 |
2022年 | 43篇 |
2021年 | 90篇 |
2020年 | 87篇 |
2019年 | 64篇 |
2018年 | 199篇 |
2017年 | 192篇 |
2016年 | 172篇 |
2015年 | 146篇 |
2014年 | 176篇 |
2013年 | 398篇 |
2012年 | 339篇 |
2011年 | 375篇 |
2010年 | 186篇 |
2009年 | 184篇 |
2008年 | 313篇 |
2007年 | 347篇 |
2006年 | 325篇 |
2005年 | 303篇 |
2004年 | 276篇 |
2003年 | 293篇 |
2002年 | 235篇 |
2001年 | 197篇 |
2000年 | 183篇 |
1999年 | 110篇 |
1998年 | 41篇 |
1997年 | 40篇 |
1996年 | 48篇 |
1995年 | 85篇 |
1994年 | 52篇 |
1993年 | 30篇 |
1992年 | 36篇 |
1991年 | 26篇 |
1990年 | 30篇 |
1989年 | 31篇 |
1988年 | 35篇 |
1986年 | 36篇 |
1985年 | 34篇 |
1984年 | 25篇 |
1983年 | 24篇 |
1982年 | 16篇 |
1980年 | 30篇 |
1979年 | 16篇 |
1977年 | 25篇 |
1976年 | 17篇 |
1975年 | 15篇 |
1973年 | 15篇 |
1972年 | 16篇 |
1967年 | 20篇 |
1966年 | 19篇 |
排序方式: 共有6563条查询结果,搜索用时 15 毫秒
81.
Current silvicultural treatments in beech forests are aimed at achieving thick logs without discoloured hardwood. Therefore
intensive thinning is applied already in younger stands with the objective of large-sized trunks at an age of 100 years. However,
this approach bears the risk that dead wood structures and broken trees are completely removed from the forest. The impact
of three different silvicultural management intensity levels on wood-inhabiting fungi over decades was investigated in a large
beech forest (>10,000 ha) in southern Germany in 69 sampling plots: A Intensive Thinning and Logging with high-value trees,
B Conservation-Oriented Logging with integration of special structures such as dead wood and broken trees and C Strict Forest
Reserves with no logging for 30 years. The analysis of community showed marked differences in the fungus species composition
of the three treatments, independent of stand age. The relative frequencies of species between treatments were statistically
different. Indicator species for naturalness were more abundant at sites with low silvicultural management intensity. Fomes fomentarius, the most common fungus in virgin forests and strict forest reserves, is almost missing in forests with high-management intensity.
The species richness seemed to be lower where intensive thinning was applied (P = 0.051). Species characteristic for coarse woody debris were associated to low management intensity, whereas species with
a significant preference for stumps became more frequent with increasing management intensity. A total amount of dead wood
higher than 60 m3/ha was found to enable significantly higher numbers of species indicators of naturalness (P = 0.013). In conclusion, when applying intensive silvicultural treatment, the role of dead wood needs to be actively considered
in order to maintain the natural biocoenosis of beech forests. 相似文献
82.
Zusammenfassung Es wurden 79Rhizoctonia solani-Isolate von verschiedenen Orten in Baden-Württemberg isoliert. Es konnten Isolate gefunden werden, die gegenüber Gurken und Bohnen pathogen waren. Bei Bohnen kann das Sproßgewicht als leicht zu erfassender Parameter für die Quantifizierung der Schadwirkung benutzt werden. Eine trockene Lagerung von mitRhizoctonia solani durchwachsenen Haferkörnern erwies sich als besonders geeignet für eine Stammkulturhaltung.
Mit einer Abbildung und 6 Tabellen 相似文献
Isolation and pathogenicity ofRhizoctonia solani to cucumber and bean
79Rhizoctonia solani strains were isolated from different locations in Baden-Württemberg. Some of these strains were pathogenic against cucumber and bean. The sprout-weight of bean can be used as an easy-to-measure parameter for quantification of the damage caused by teh fungus. The dry storage of oat seeds, previously inoculated withRhizoctonia solani, has been shown to be the best method for long-term storage.
Mit einer Abbildung und 6 Tabellen 相似文献
83.
Sabine Augustin Jan Evers Hans-Peter Dietrich Johannes Eichhorn Thomas Haussmann Regina Icke Ansgar Isenberg Wolfgang Lux Monica Musio Hans Pretzsch Winfried Riek Thomas Rötzer Bernd Schultze Andreas Schulze Jörg Schröder Walter Seidling Nicole Wellbrock Klaus von Wilpert Barbara Wolff 《European Journal of Forest Research》2005,124(4):251-260
In the 1970s unexpected forest damages, called “new type of forest damage” or “forest decline”, were observed in Germany and
other European countries. The Federal Republic of Germany and the German Federal States implemented a forest monitoring system
in the early 1980s, in order to monitor and assess the forest condition. Due to the growing public awareness of possible adverse
effects of air pollution on forests, in 1985 the ICP Forests was launched under the convention on long-range transboundary
air pollution (CLRTAP) of the United Nations Economic Commission for Europe (UN-ECE). The German experience in forest monitoring
was a base for the implementation of the European monitoring system. In 2001 the interdisciplinary case study “concept and
feasibility study for the integrated evaluation of environmental monitoring data in forests”, funded by the German Federal
Ministry of Education and Research, concentrated on in-depths evaluations of the German data of forest monitoring. The objectives
of the study were: (a) a reliable assessment of the vitality and functioning of forest ecosystems, (b) the identification
and quantification of factors influencing forest vitality, and (c) the clarification of cause-effect-relationships leading
to leaf/needle loss. For these purposes additional data from external sources were acquired: climate and deposition, for selected
level I plots tree growth data, as well as data on groundwater quality. The results show that in particular time series analysis
(crown condition, tree growth, and tree ring analysis), in combination with climate and deposition are valuable and informative,
as well as integrated evaluation of soil, tree nutrition and crown condition data. Methods to combine information from the
extensive and the intensive monitoring, and to transfer process information to the large scale should be elaborated in future.
相似文献
Sabine AugustinEmail: |
84.
Christiansen E Krokene P Berryman AA Franceschi VR Krekling T Lieutier F Lönneborg A Solheim H 《Tree physiology》1999,19(6):399-403
Norway spruce trees (Picea abies (L.) Karst.) pretreated by wounding and fungal infection showed highly enhanced resistance to a subsequent challenge inoculation with the pathogenic bluestain fungus Ceratocystis polonica (Siem.) C. Moreau. This is the first time the effectiveness of the constitutive and inducible defenses has been shown to depend on prior wounding and infection in conifers, although such acquired resistance has previously been found in several angiosperms. Trees that were pretreated with a combination of 12 bark wounds (1.6 x 10 cm), four fungal inoculations and four sterile inoculations 1-15 days before mass inoculation with C. polonica at 400 inoculations per square meter over a 0.8 m stem section had significantly shorter necroses in the phloem, less bluestained sapwood, and less dead cambium than untreated control trees. Pretreatment with four fungal or sterile inoculations alone did not lead to enhanced resistance. Pretreatment by bark wounding alone seemed to provide an intermediate degree of resistance compared to bark wounding, fungal inoculations and sterile inoculations combined. All trees had a marked increase in the number of resin ducts in the year of inoculation compared with previous years, suggesting that formation of traumatic resin ducts play an important role in the development and maintainance of enhanced resistance. 相似文献
85.
Composition of the water-distilled oil of the aerial parts of Centaurea aladagensis, endemic in Turkey, was analysed by GC-MS. Hexadecanoic acid (39.3%), caryophyllene oxide (6.6%) and hexahydrofarnesyl acetone (4.3%) were found as main constituents in the oil. The oil was tested against 7 human pathogenic microorganisms. 相似文献
86.
87.
88.
89.
90.
Ohne Zusammenfassung 相似文献