全文获取类型
收费全文 | 873篇 |
免费 | 39篇 |
专业分类
林业 | 132篇 |
农学 | 24篇 |
基础科学 | 5篇 |
302篇 | |
综合类 | 78篇 |
农作物 | 23篇 |
水产渔业 | 31篇 |
畜牧兽医 | 222篇 |
园艺 | 27篇 |
植物保护 | 68篇 |
出版年
2023年 | 7篇 |
2022年 | 5篇 |
2021年 | 13篇 |
2020年 | 15篇 |
2019年 | 23篇 |
2018年 | 23篇 |
2017年 | 15篇 |
2016年 | 23篇 |
2015年 | 20篇 |
2014年 | 24篇 |
2013年 | 54篇 |
2012年 | 39篇 |
2011年 | 60篇 |
2010年 | 33篇 |
2009年 | 28篇 |
2008年 | 51篇 |
2007年 | 54篇 |
2006年 | 36篇 |
2005年 | 40篇 |
2004年 | 44篇 |
2003年 | 42篇 |
2002年 | 33篇 |
2001年 | 17篇 |
2000年 | 16篇 |
1999年 | 11篇 |
1998年 | 16篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1982年 | 8篇 |
1978年 | 4篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1972年 | 8篇 |
1970年 | 4篇 |
1969年 | 4篇 |
1967年 | 5篇 |
1966年 | 5篇 |
1965年 | 6篇 |
1963年 | 3篇 |
排序方式: 共有912条查询结果,搜索用时 46 毫秒
251.
252.
Zusammenfassung Von 51 überprüften stickstoffhaltigen Steroiden mit bzw ohne 5-Doppelbindung (Solanum-Steroidalkaloide, N-haltige Cholestan- und Pregnan-Derivate) gaben lediglich 3 eine positive Liebermann-Burchard-Reaktion: N-Acetyltomatidadien, N-Acetyl-solasodien und Dihydrosolasodin A. Auch eine Anzahl 5-ungesättigter Steroidsapogenine und stickstofffreier Pregnan-Derivate zeigte eine nur schwache Farbreaktion.
XXXVII. Mitteil.: Schreiber, K., 1964. — Liebigs Ann. Chem.674, 168–175. 相似文献
Summary To obtain information about the value and limitations of the Liebermann-Burchard reaction 51 nitrogenous steroids with or without 5 double bond have been tested. Only 3 of them show a positive colour reaction: the N-acetyl derivatives of tomatidadiene and solasodiene as well as the dihydrosolasodine A. Also some 5-unsaturated steroidal sapogenins and nitrogen-free pregnane derivatives produce colours of only slight intensity.
am ¶rt;u 51 5- ( Solanum, ) 3 -: N--, N-- . 5 - .
XXXVII. Mitteil.: Schreiber, K., 1964. — Liebigs Ann. Chem.674, 168–175. 相似文献
253.
254.
Klaus Schreiber 《Genetic Resources and Crop Evolution》1963,11(1):502-506
Zusammenfassung Aus getrockneten Blättern derLycopersicon-esculentum-Mutantenexilis (Ausgangssorte Condine Red) undprunoidea (Lukullus) wurden 0,40 bzw. 0,81%
1-Tomatin isoliert. Die Identifizierung des xylosefreien Alkaloidglykosids erfolgte durch Papierchromatographie und Untersuchung der bei Säurehydrolyse entstandenen Spaltprodukte. Blätter nicht mutierter Kontroll-pflanzen enthielten 0,64% bzw. 0,82% Tomatin.
XXVIII. Mitteilung: Schreiber, K., Kulturpflanze11, 451–501 (1963); voranstehend. 相似文献
Summary From dried leaves of two mutants ofLycopersicon esculentum Mill., namelyexilis (mutant of the variety Condine Red) andprunoidea (Lukullus), t-tomatine has been isolated in an amount of 0,40% and 0,81%, respectively. The identification of the xylose-free alkaloid glycoside was carried out by paper chromatography and investigation of the products formed by acid hydrolysis. Leaves of the non-mutated controls contained 0,64% and 0,82% tomatine, respectively.
exilis ( ) prunoidea () 0,40% 0,81% 1-. , . 0,64% 0,82% .
XXVIII. Mitteilung: Schreiber, K., Kulturpflanze11, 451–501 (1963); voranstehend. 相似文献
255.
A simple method for estimating potential relative radiation (PRR) for landscape-scale vegetation analysis 总被引:3,自引:3,他引:0
Radiation is one of the primary influences on vegetation composition and spatial pattern. Topographic orientation is often used as a proxy for relative radiation load due to its effects on evaporative demand and local temperature. Common methods for incorporating this information (i.e., site measures of slope and aspect) fail to include daily or annual changes in solar orientation and shading effects from local topography. As a result, these static measures do not incorporate the level of spatial and temporal heterogeneity required to examine vegetation patterns at the landscape level. We developed a widely applicable method for estimating potential relative radiation (PRR) using digital elevation data and a widely used geographic information system (Arc/Info). We found significant differences among four increasingly comprehensive radiation proxies. Our GIS-based proxy compared well with estimates from more data-intensive and computationally rigorous radiation models. We note that several recent studies have not found strong correlations between vegetation pattern and landscape-scale differences in radiation. We suggest that these findings may be due to the use of proxies that were not accurately capturing variability in radiation, and we recommend PRR or similar measures for use in future vegetation analyses. 相似文献
256.
Khalid A. Hussein Klaus von Gadow Matthias Albert 《European Journal of Forest Research》2000,119(1-6):43-50
The paper presents a new method for assessing crown radii at different tree heights, using a simple mechanical device, the crown window. The accuracy of the crown window measuring device is evaluated using measurement data from different objects. The device is easy to manufacture and proved to be more useful than other more sophisticated techniques, such as digital photo analysis or laser based instruments in estimating crown radii and their corresponding heights with acceptable accuracy. 相似文献
257.
Von Klaus Hellrigl und Paolo Ambrosi 《Anzeiger für Sch?dlingskunde》2000,73(2):25-32
A survey on the present distribution of the horse chestnut leafmining moth, Cameraria ohridella Desch. & Dimic 1986, in Europe and in Italy is given: In Europe, within a period of 15 years, the leafminer – recently introduced into Central Europe – has settled in an area that spreads over 13 latitudinal and about 20 longitudinal degrees; in Northern Italy, an area of approximately 50,000 km2 has been afflicted in the 5 years since the leafminer's introduction in South Tyrol and Julian Venetia in 1993.The development of the distribution in the region of South Tyrol and Trentino is shown: In the province of Bozen-South Tyrol, between 1995 and 1999 the moth has spread in all the three principal valleys (Eisacktal, Pustertal, Etschtal); in the Trentino province, first local attacks began only in 1998, near Trento and Riva, but spread over the entire Etschtal/Adige Valley in 1999. While in South Tyrol C. ohridella was introduced from the North (North Tyrol), the introduction into the Trentino occured from the South (Verona).At present the attacks in Trentino province are preponderantly low (resulting heavy only in the city of Trento and in Riva del Garda) and limited to altitudes ranging from 70 to 700 in. In South Tyrol, attacks are mainly heavy in altitudes ranging from 250 to 900/950 m, while they are low in the increasingly affected higher altitudes of 1,000 to 1,230 m. Numeric attack parameters are given to show attack intensities.The number of generations per year depends on the respective climatic conditions: in lower-altitudes, usually three generations develop in a year, but in higher altitudes (800 to 1,100 m) only two generations; in the climatically favoured area around the Lake Garda a (partial) fourth generation appears possible.The question of host plants (Aesculus sp., Acer sp.) and the larval parasitism of C. ohridella is discussed. The parasitism of the larvae, principally by Eulophidae (Hym., Chalcidoidea), was ascertained already in the first years of attack: In South Tyrol, 16 species of parasitoids appeared, and 8 in the Trentino province, but only two species were dominant: Minotetrastichus sp. and Pnigalio sp. The level of parasitism reached was low, comparable to other Central European countries. 相似文献
258.
Sabina turm Tanja vara Ellinor Sprndly-Nees Vesna Cerkvenik-Flajs Mitja Gomba
Anna-Luisa Weber Klaus Weber 《Journal of toxicologic pathology》2021,34(4):331
Testicular histopathology is considered the most sensitive and reliable method to detect the effects of chemicals on sperm production. To carry out a sensitive examination of testicular histopathology and interpret the changes require knowledge of spermatogenic stages. Spermatogenic staging based on acrosome development during spermiogenesis is conventionally performed in animal species routinely used for research and toxicity testing. In contrast, small ruminants, such as sheep and goats, are rarely used as animal models to evaluate toxicity in male reproductive organs. To the best of our knowledge, a comparable spermatogenic staging system in rams has not yet been fully characterised. Hence, this study aimed to adapt the existing spermatogenic staging based on acrosome development in bull testes to fit the seminiferous epithelium cycle of ram testes. The results show that spermatogenic staging based on acrosome development in bull testes can, with slight modifications, be efficiently used for the staging of ram testes. 相似文献
259.
260.
Tree survival and maximum density of planted forests–Observations from South African spacing studies
Background:Among the most important aspects of risk and hazard studies relating to forest ecosystems are maximum forest density and density-dependent tree survival.Methods:Long-term observations about the maximum density of unthinned Pinus patula and P.elliottii field plots based on the Correlated Curve Trend(CCT)spacing studies which were established almost 8 decades ago by O’Connor(Forest Research with Special Reference to Planting Distances and Thinning,1935)in South Africa.Three specific approaches were introduced for analysing maximum density and tree survival,namely the‘limiting line’,Nilson’s sparsity and tree survival with the Weibull function.Results:The main results are:a)Maximum densities differ greatly among the two species grown on the same site and within the same species grown on different sites;it is possible to relate these differences to site index in both species.b)The relationship between the quadratic mean diameter and the minimum average spacing of surviving trees(known as Nilson’s Sparsity)appears to be surprisingly similar in both species.c)An analysis of tree survival in response to different initial planting espacements shows that the Weibull survival function parameters can be estimated if the initial planting density is known.This result is presented for each of the eight large experiments used in this study.Conclusions:This study contributes to a better understanding of tree survival and maximum density which are the key factors required for estimating risk and uncertainty.The risk of tree mortality is not constant,but varies with tree species,planting density,tree age and growing site.For estimating that risk,therefore,continuous long-term observation on different sites and with varying planting densities,as provided by the unthinned CCT series,are essential. 相似文献