首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   707篇
  免费   36篇
林业   92篇
农学   19篇
基础科学   5篇
  277篇
综合类   51篇
农作物   16篇
水产渔业   30篇
畜牧兽医   180篇
园艺   14篇
植物保护   59篇
  2023年   6篇
  2022年   4篇
  2021年   12篇
  2020年   13篇
  2019年   16篇
  2018年   17篇
  2017年   15篇
  2016年   16篇
  2015年   15篇
  2014年   20篇
  2013年   48篇
  2012年   34篇
  2011年   45篇
  2010年   26篇
  2009年   22篇
  2008年   39篇
  2007年   45篇
  2006年   34篇
  2005年   32篇
  2004年   34篇
  2003年   35篇
  2002年   30篇
  2001年   12篇
  2000年   13篇
  1999年   9篇
  1998年   15篇
  1997年   10篇
  1996年   4篇
  1993年   7篇
  1992年   3篇
  1991年   6篇
  1989年   7篇
  1988年   4篇
  1987年   6篇
  1986年   4篇
  1985年   5篇
  1984年   7篇
  1982年   4篇
  1981年   3篇
  1980年   3篇
  1975年   3篇
  1974年   4篇
  1972年   7篇
  1971年   3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743条查询结果,搜索用时 46 毫秒
591.
Zusammenfassung Das während der Reise in ein Gebirgsgebiet der westlichen Slowakei 1981 (vgl.Kühn et al. 1982) gesammelte Kulturpflanzenmaterial wird botanisch charakterisiert. Es handelt sich überwiegend um Landsorten, alte Sortentypen und Kultursippen von oft sehr hoher Variabilität, deren Anbau meist in raschem Rückgang begriffen ist. Charakteristische indigene Formen konnten u. a. noch beiTriticum aestivum, Avena sativa, Papaver somniferum, Pisum sativum undPhaseolus vulgaris nachgewiesen werden. Bemerkenswert ist das Vorkommen ausgesprochener Reliktkulturen (z. B.Triticum dicoccon, Secale cereale var.multicaule, Panicum miliaceum, Cicer arietinum, Lathyrus sativus undFagopyrum esculentum). Die Gebirgsregion gehört zum Erhaltungsgebiet autochthoner Kulturpflanzen-Sippen in den Westkarpaten. Das rasche Fortschreiten der Generosion läßt eine baldige Fortführung der Sammeltätigkeit notwendig erscheinen.
Catalogue of indigenous taxa of cultivated plants collected 1981 in the SSR
Summary The material of cultivated plants collected during a mission to western Slovakia in 1981 (cf.Kühn et al. 1982) has been characterized botanically. It is represented mainly by land-races and old varieties which are often rather variable; their cultivation is mostly decreasing rapidly. Typical indigenous types could be discovered e.g. forTriticum aestivum, Avena sativa, Papaver somniferum, Pisum sativum andPhaseolus vulgaris. Remarkable is the occurrence if indigenous relic crops (e.g.Triticum dicoccon, Secale cereale var.multicaule, Panicum miliaceum, Cicer arietinum, Lathyrus sativus andFagopyrum esculentum). The mountainous region belongs to the Western Carpathian refugial area of autochthonous taxa of cultivated plants. Because of rapidly acting genetic erosion a continuation of the collecting work seems to be necessary now.

, 1981 .
, 1981 . (. ., 1982). , , ; . , ., , , , . (.:Triticum dicoccon, Secale cereale var.multicaule, Panicum miliaceum, Cicer arietinum, Lathyrus sativus, Fagopyrum esculentum). . ¶rt; 7qo .
  相似文献   
592.
The distribution and natural abundance isotopic (δ15N) content of whole tissue and individual amino acids in plants in a temperate grassland were determined using ion chromatography (IC), continuous flow‐isotope ratio mass spectrometry (CF‐IRMS), and gas chromatography‐combustion‐isotope ratio mass spectrometry (GC‐C‐IRMS). The results showed that the selected plants (Lolium perenne, Juncus effusus, and Brachythecium rutabulum) differed in their amino acid content and distribution from the parent grassland soil. Bulk and individual amino acid δ15N isotope signatures were different between the plants, which concurred with their functional strategy in relation to the relative acquisition of available N sources. The individual amino acid δ15N values of histidine and phenylalanine could be used to differentiate between the three plant species.  相似文献   
593.
594.
Effect of the heavy metals chromium, nickel, copper, zinc, cadmium, mercury and lead on uptake and translocation of K and P by young barley plants The uptake of potassium and phosphate into the roots and shoots of 7 days old barley plants from double-labelled (42K, 32P) nutrient solutions containing chromium, nickel, copper, zinc, cadmium, mercury or lead (10?6 - 10?4 moles/1) was measured in a constant environment after 5 hours, in order to compare early stages of toxicity. K and P uptake and translocation were inhibited by the 7 heavy metals to a different extent; K was more affected than P, and translocation of both nutrients into the shoots was more inhibited than uptake into the roots. Plants showed no visible injuries. Mercury had by far the greatest effect, zinc was almost ineffective: K uptake e.g. was reduced to 21% of the control by 10?4 moles Hg/l, but only to 97% by the same amount of Zn, and P translocation was reduced to 8% by Hg, but was not affected by Zn. The least significant effect of Hg was detectable at a concentration of 4.10?7 moles Hg/l ( = 0,08 ppm) in the nutrient solution, the effect of Zn only above 10?4 moles Zn/l ( = 6,5 ppm). Arranging the tested heavy metals according to their effects leads to the sequence Hg > Pb > Cu > Cd > Cr > Ni > Zn which corresponds – apart from two deviations – to the electrochemical series of the elements.  相似文献   
595.
3,4-Dimethylpyrazole phosphate (DMPP) is a new nitrification inhibitor with highly favourable properties. It has undergone thorough toxicology and ecotoxicology tests and application-technology experiments, and has been shown to have several distinct advantages compared to the currently used nitrification inhibitors. Application rates of 0.5-1.5 kg ha-1 are sufficient to achieve optimal nitrification inhibition. DMPP can significantly reduce NO3- leaching, without being liable to leaching itself. DMPP may reduce N2O emission, apparently without a negative effect on CH4 oxidation of the soil. The use of DMPP-containing fertilizers can improve yield. This offers the possibility of saving mineral fertilizer N, reducing the number of N-application rounds, and obtaining higher crop yields with current fertilizer-N rates.  相似文献   
596.
Summary Important papers on taxonomy and evolution of cultivated plants published in 1979 and 1980 were put together and briefly discussed.
Taxonomie und Evolution der Kulturpflanzen: Literaturübersicht 1979/1980
Zusammenfassung Wichtige Arbeiten über Taxonomie und Evolution der Kulturpflanzen aus den Jahren 1979 und 1980 wurden zusammengestellt und kurz kommentiert.

: 1979–1980
, 1979–1980 . .
  相似文献   
597.
Providing the Parameters of Unsaturated Soil Hydraulic Functions on the Basis of Soil Texture, Bulk Density and Type of Horizon The hydraulic conductivity function can be described by the van Genuchten equation, whereby its parameters are estimated from typical water retention data of soil types and textural classes. The value of saturated hydraulic conductivity can be derived from tables (e.g. Kartieranleitung, 1982) in case measured data are lacking. Especially in well structured or sandy soils saturated conductivity may differ by 1…2 orders of magnitude. This will lead to a shift of the conductivity function. But nevertheless for the first approximation of fluxes in soils such parameters can be used. Thus, soil dependent values of groundwater recharge and pollution can be roughly quantified.  相似文献   
598.
599.
Biochar application has the potential to improve soil fertility and increase soil carbon stock, especially in tropical regions. Information on the temperature sensitivity of carbon dioxide(CO_2) evolution from biochar-amended soils at very high temperatures, as observed for tropical surface soils, is limited but urgently needed for the development of region-specific biochar management targeted to optimize biochar effects on soil functions. Here, we investigated the temperature sensitivity of soil respiration to the addition of different rates of Miscanthus biochar(0, 6.25, 12.5, and 25 Mg ha~(-1)) in two types of soils with contrasting textures. Biochar-amended soil treatments and their controls were incubated at constant temperatures of 20, 30, and 40℃. Overall, our results show that: i) considering data from all treatments and temperatures, the addition of biochar decreased soil CO_2 emissions when compared to untreated soils;ii) CO_2 emissions from biochar-amended soils had a higher temperature sensitivity than those from biochar-free soils; iii) the temperature sensitivity of soil respiration in sandy soils was higher than that in clay soils; and iv) for clay soils, relative increases in soil CO_2 emissions from biochar-amended soils were higher when the temperature increased from 30 to 40℃, while for sandy soils, the highest temperature responses of soil respiration were observed when increasing the temperature from 20 to 30℃. Together, these findings suggest a significantly reduced potential to increase soil organic carbon stocks when Miscanthus biochar is applied to tropical soils at high surface temperatures, which could be counteracted by the soil-and weather-specific timing of biochar application.  相似文献   
600.
The core-shell structure of lycopene micronizates can be verified by employing a combination of solid-state and suspended-state NMR spectroscopy. The type of molecular aggregation of carotenoid nanoparticles can be clearly determined from their characteristic fingerprint pattern in the solid-state NMR spectra.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号