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   1465篇
  免费   133篇
林业   136篇
农学   77篇
基础科学   8篇
  262篇
综合类   32篇
农作物   85篇
水产渔业   179篇
畜牧兽医   646篇
园艺   31篇
植物保护   142篇
  2024年   1篇
  2023年   17篇
  2022年   31篇
  2021年   73篇
  2020年   71篇
  2019年   82篇
  2018年   85篇
  2017年   102篇
  2016年   104篇
  2015年   46篇
  2014年   94篇
  2013年   101篇
  2012年   107篇
  2011年   121篇
  2010年   78篇
  2009年   60篇
  2008年   65篇
  2007年   67篇
  2006年   55篇
  2005年   39篇
  2004年   36篇
  2003年   29篇
  2002年   27篇
  2001年   21篇
  2000年   15篇
  1999年   8篇
  1998年   7篇
  1997年   11篇
  1996年   5篇
  1995年   5篇
  1994年   3篇
  1993年   2篇
  1992年   2篇
  1991年   2篇
  1990年   8篇
  1989年   2篇
  1988年   1篇
  1987年   2篇
  1985年   2篇
  1984年   3篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1976年   1篇
  1968年   1篇
  1967年   2篇
  1954年   1篇
排序方式: 共有1598条查询结果,搜索用时 453 毫秒
971.
The objective of this work was to describe the nutrition deficiencies symptoms in calla lily (Zantedeschia aethiopica). Seedlings were maintained in complete nutrition solution and with omission of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), boron (B), and manganese (Mn), totalizing 10 treatments. The first deficiencies symptoms appeared in plants cultivated in N omission, followed by treatments with omission of S, B, K, Fe, P, and Ca. Individual omissions of N and B prevented blooming, while S and K deficiencies resulted in production of small and greenish inflorescences with deformities. Reddish spots in leaves were observed in plants growing in solution with omission of P. Root development was affected either by omission of B or S. Death of the apical bud and formation of a “black center” in calla lily rhizome was caused by B deficiency. Nitrogen, B, and S are the most required nutrients for calla lily plants. The mineral composition of calla lily leaves is affected by nutritional deficiencies  相似文献   
972.
New Forests - The quality of forest seeds may be maintained in the course of storage for their use in the restoration of degraded areas and the conservation of genetic resources. In this sense,...  相似文献   
973.
New Forests - Mixed plantations composed of Eucalyptus intercropped with a high diversity of native tree species are a promising option for combining biodiversity recovery with wood production...  相似文献   
974.
Journal of Pest Science - The whiteflies of the Bemisia tabaci (Genn.) complex (Hemiptera: Aleyrodidae) are serious agricultural pests that cause severe losses to vegetable, ornamental and fiber...  相似文献   
975.

Background  

Confocal laser scanning microscopy (CLSM) is the method of choice to study interfacial biofilms and acquires time-resolved three-dimensional data of the biofilm structure. CLSM can be used in a multi-channel modus where the different channels map individual biofilm components. This communication presents a novel image quantification tool, PHLIP, for the quantitative analysis of large amounts of multichannel CLSM data in an automated way. PHLIP can be freely downloaded from .  相似文献   
976.
Natural marine products have shown an interesting array of diverse and novel chemical structures with potent biological activities. Our study reports the antiproliferative assays of crude extracts, fraction and pure compound (4R,9S,14S)-4α-acetoxy-9β,14α-dihydroxydolast-1(15),7-diene (1) obtained from brown alga Canistrocarpus cervicornis showing the antileishmanial activity. We showed that 1 had a dose-dependent activity during 72 h of treatment, exhibiting IC(50) of 2.0 μg/mL, 12.0 μg/mL, and 4.0 μg/mL for promastigote, axenic amastigote and intracellular amastigote forms of Leishmania amazonensis, respectively. A cytotoxicity assay showed that the action of the isolated compound 1 was 93.0 times less toxic to the macrophage than to the protozoan. Additionally, compound 1 induced ultrastructural changes, including extensive mitochondrial damage; decrease in Rh123 fluorescence, suggesting interference with the mitochondrial membrane potential; and lipid peroxidation in parasite cells. The use of 1 from C. cervicornis against L. amazonensis parasites might be of great interest as a future alternative to the development of new antileishmanial drugs.  相似文献   
977.
This work aimed at identifying plant compounds with insecticidal activity against Diaphania hyalinata (L.) (Lepidoptera: Pyralidae), Musca domestica (L.) (Diptera: Muscidae), Periplaneta americana (L.) (Blattodea: Blattidae) and Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae). The plant species used were: basil (Ocimum selloi Benth.), rue (Ruta graveolens L.), lion's ear (Leonotis nepetaefolia L.), Jimson weed (Datura stramonium L.), 'baleeira' herb (Cordia verbenaceae L.), mint (Mentha piperita L.), wild balsam apple (Mormodica charantia L.) and billy goat weed (Ageratum conyzoides L.). Firstly, the insecticidal activities of hexane and ethanol plant extracts were evaluated against adults of R. dominica. Among them, only the hexane extract of A. conyzoides showed insecticidal activity. The hexane extract of this plant species was therefore fractionated by silica gel column chromatography to isolate and purify its bioactive chemical constituents. Three compounds were identified using IR spectra, (1)H NMR, (13)C NMR, HMBC and NOE after gel chromatography: 5,6,7,8,3', 4', 5'-heptamethoxyflavone, 5,6,7,8,3'-pentamethoxy-4', 5'-methylenedioxyflavone and coumarin. The complete assignment of (13)C NMR to 5,6,7,8,3'-pentamethoxy-4', 5'-methylenedioxyflavone was successfully made for the first time. 5,6,7,8,3'-Pentamethoxy-4', 5'-methylenedioxyflavone did not show any insecticidal activity against the four insect species tested. 5,6,7,8,3', 4', 5'-Heptamethoxyflavone showed low activity against D. hyalinata and R. dominica and was not toxic to M. domestica or P. americana. In contrast, coumarin showed insecticidal activity against all four insect pest species tested, with the following order of susceptibility: R. dominica < P. americana < D. hyalinata < M. domestica after 24 h exposure.  相似文献   
978.
979.
New Forests - In order to better understand the physiological and technical aspects of yerba mate vegetative propagation, the present study sought to evaluate the rhizogenic capacity of apical and...  相似文献   
980.
Journal of Pest Science - Silicon (Si) has a physical barrier effect on plant tissues, decreasing nematode infection in different crops. Notwithstanding, research on lettuce is lacking, especially...  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