全文获取类型
收费全文 | 474篇 |
免费 | 15篇 |
专业分类
林业 | 135篇 |
农学 | 12篇 |
103篇 | |
综合类 | 36篇 |
农作物 | 16篇 |
水产渔业 | 37篇 |
畜牧兽医 | 123篇 |
园艺 | 7篇 |
植物保护 | 20篇 |
出版年
2020年 | 7篇 |
2019年 | 6篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 12篇 |
2013年 | 11篇 |
2012年 | 18篇 |
2011年 | 30篇 |
2010年 | 10篇 |
2009年 | 15篇 |
2008年 | 28篇 |
2007年 | 20篇 |
2006年 | 22篇 |
2005年 | 17篇 |
2004年 | 19篇 |
2003年 | 22篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1997年 | 4篇 |
1992年 | 4篇 |
1989年 | 4篇 |
1986年 | 3篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1972年 | 6篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1967年 | 5篇 |
1966年 | 3篇 |
1965年 | 4篇 |
1962年 | 3篇 |
1956年 | 4篇 |
1948年 | 7篇 |
1941年 | 3篇 |
1934年 | 3篇 |
1933年 | 3篇 |
1932年 | 12篇 |
1927年 | 7篇 |
1919年 | 6篇 |
1918年 | 5篇 |
1915年 | 4篇 |
1904年 | 5篇 |
1902年 | 3篇 |
排序方式: 共有489条查询结果,搜索用时 31 毫秒
441.
442.
443.
Franz -Erich Eidmann 《Forstwissenschaftliches Centralblatt》1927,49(17):604-623
Ohne Zusammenfassung 相似文献
444.
445.
D. Franz 《Forstwissenschaftliches Centralblatt》1927,49(1):15-19
Ohne Zusammenfassung 相似文献
446.
F. Franz 《Forstwissenschaftliches Centralblatt》1966,85(5-6):134-147
Ohne ZusammenfassungÜberarbeitete Fassung eines auf der Jahrestagung 1965 des Bayerischen Forstvereins am 9. September 1965 in Bayreuth gehaltenen Vortrages. 相似文献
447.
Herbage yield trials are necessary to test if candidate varieties are well suited for organic conditions. In order to elucidate
a particular suitability for organic conditions, we run such trials in parallel under both organic and conventional conditions.
Here, we report on second and third year results of the sowings 2004 and 2005. These trials are part of a targeted breeding
programme for organic conditions. Irregular colonisation of pure grass plots with adventitious plants, in particular white
clover, was recognized as a major constraint to the quality of the results obtained under organic conditions. The coefficients
of variance in dry matter yield almost doubled when compared to conventional trials, and significant differences in annual
yield among varieties were rare. However, when herbage yield was corrected for the estimated fraction of adventitious plant
colonization at each cut, the number of instances with statistically significant differences for annual yield among varieties
increased more than fourfold. Dry matter yields under organic and conventional conditions were significantly and positively
correlated. However, analysis of variance showed a significant culture type by variety interaction for annual dry matter yield
in 12 out of 24 trials. When diploid and tetraploid varieties of the same Lolium species were tested in one common trial, only tetraploid varieties were identified as being particularly well suited for organic
conditions, while in these trials, the great majority of apparently poorly suited varieties were diploid. This suggests that
breeding tetraploid Lolium varieties is promising when aiming at a favourable response to organic agriculture. 相似文献
448.
To investigate the effect of water temperature on gamete maturation and gamete quality, European grayling (Thymalus thymallus) were held under different temperature regimes prior to spawning. Maturation of males and females and their gamete quality
depended strongly on temperature regime. The highest percentages of maturing fish and highest gamete quality were obtained
under a creek water temperature regime with natural seasonal fluctuations. In warmed creek water (3–4°C), at a constant temperature
of 8–9°C, and under an abruptly increasing temperature, regime maturation rates and gamete quality were reduced. The effect
was more pronounced in females than in males. The spawning dates of different wild Austrian grayling populations were also
correlated with water temperature data collected during the last 10–15 years. The mean spawning date expressed as the number
of days from 21 December until spawning ranged from 98 to 111 days for lower elevation populations, while it was considerably
delayed for an alpine population. All populations spawned at water temperatures of 5.5–7.2°C. Regression analysis indicated
that spawning date correlated with (1) the overall mean water temperature from 21 December until spawning, (2) the mean water
temperature during both the last 10 days and 15 days before spawning, and (3) the difference between mean January temperature
and that of the last 15 days before spawning. The regression functions indicate that an increase in water temperature from
21 December to spawning of 1°C advances spawning by 5? days, and an increase of 1°C in the last 10–15 days advances spawning
by 3? days. 相似文献
449.
Junbao Yu Franz X. Meixner Weidong Sun Guoping Wang Chuanhai Xia 《Soil biology & biochemistry》2010,42(10):1784-1792
Nitric oxide (NO) is an important component of biogeochemical cycling of nitrogen, produced via biologically mediated processes of nitrification and denitrification in soils. The production and consumption processes of NO in black soils are not fully understood. We established how moisture and temperature affect NO dynamics for black soil samples of maize land in the temperate zone of northeastern China. The optimum soil moisture for the maximum NO production and emission was determined to be 41% water-filled pore space (WFPS), based on laboratory experiments and modeling. For a given moisture, NO fluxes increased exponentially with soil temperature at any given soil moisture. The optimum soil moisture for the maximum NO emission was constant and independent of soil temperature. The NO consumption rate constant (k) in the studied soil (range 9.31 × 10−6-15.1 × 10−6 m3 kg−1 s−1) was in the middle of the range of similar k values published to date. The maximum NO emission potential for black soils at 25 °C and 15 °C were about 18.6 and 9.0 ng N m−2 s−1, respectively. Based on laboratory results and field monitoring data of soil water content and soil temperature, the average NO fluxes from black soils in the region were estimated to be 10.7 ng N m−2 s−1 for an entire plant growth period. NO emissions likely occur principally in July, associated with optimum soil moisture. The present study suggests that NO fluxes from black soil are much lower than the previous reports from cropland in southern parts of China. 相似文献
450.
Peter J. Lavrentyev Gayantonia Franzè James J. Pierson Diane K. Stoecker 《Marine drugs》2015,13(5):2834-2856
Allelopathy is wide spread among marine phytoplankton, including diatoms, which can produce cytotoxic secondary metabolites such as polyunsaturated aldehydes (PUA). Most studies on diatom-produced PUA have been dedicated to their inhibitory effects on reproduction and development of marine invertebrates. However, little information exists on their impact on key herbivores in the ocean, microzooplankton. This study examined the effects of dissolved 2E,4E-octadienal and 2E,4E-heptadienal on the growth rates of natural ciliate and dinoflagellate populations in the Chesapeake Bay and the coastal Atlantic waters. The overall effect of PUA on microzooplankton growth was negative, especially at the higher concentrations, but there were pronounced differences in response among common planktonic species. For example, the growth of Codonella sp., Leegaardiella sol, Prorodon sp., and Gyrodinium spirale was impaired at 2 nM, whereas Strombidium conicum, Cyclotrichium gigas, and Gymnodinium sp. were not affected even at 20 nM. These results indicate that PUA can induce changes in microzooplankton dynamics and species composition. 相似文献