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   4437篇
  免费   272篇
  国内免费   12篇
林业   213篇
农学   236篇
基础科学   48篇
  724篇
综合类   332篇
农作物   177篇
水产渔业   197篇
畜牧兽医   2253篇
园艺   110篇
植物保护   431篇
  2021年   37篇
  2020年   78篇
  2019年   61篇
  2018年   84篇
  2017年   98篇
  2016年   80篇
  2015年   64篇
  2014年   83篇
  2013年   204篇
  2012年   169篇
  2011年   222篇
  2010年   180篇
  2009年   167篇
  2008年   205篇
  2007年   174篇
  2006年   170篇
  2005年   167篇
  2004年   145篇
  2003年   145篇
  2002年   165篇
  2001年   131篇
  2000年   115篇
  1999年   106篇
  1998年   62篇
  1997年   37篇
  1996年   47篇
  1995年   36篇
  1994年   50篇
  1993年   51篇
  1992年   83篇
  1991年   77篇
  1990年   81篇
  1989年   74篇
  1988年   42篇
  1987年   58篇
  1986年   47篇
  1985年   56篇
  1984年   61篇
  1983年   51篇
  1982年   53篇
  1980年   34篇
  1979年   39篇
  1978年   45篇
  1977年   44篇
  1976年   43篇
  1975年   34篇
  1974年   41篇
  1972年   34篇
  1971年   34篇
  1969年   42篇
排序方式: 共有4721条查询结果,搜索用时 31 毫秒
91.
The efficacy of a subunit vaccine containing the Apx toxins of Actinobacillus pleuropneumoniae and transferrin-binding proteins was determined. Ten pigs were vaccinated twice with the vaccine. Eight control animals were injected twice with a saline solution. Three weeks after the second vaccination, all pigs were endobronchially inoculated with 10(6.5) colony-forming units (CFU) of an A. pleuropneumoniae serotype 9 strain. In the vaccine group, none of the pigs died after inoculation. Only one pig of the control group survived challenge. Surviving pigs were killed at 7 days after challenge. The mean percentage of affected lung tissue was 64% in the control group and 17% in the vaccine group. Actinobacillus pleuropneumoniae was isolated from the lungs of all animals. The mean bacterial titres of the caudal lung lobes were 5.0 x 10(8) CFU/g in the control group and 3.0 x 10(6) CFU/g in the vaccine group. It was concluded that the vaccine induced partial protection against severe challenge.  相似文献   
92.
Cet article présente les premières listes de nématodes parasites des plantes (Tylenchida et Dorylaimida) des départements français d'Amérique: Guadeloupe, Martinique et Guyane. Ces listes ont étéétablies suite aux nombreuses enquêtes faunistiques en nématologie conduites dans ces départements depuis les premiers résultats d'analyses nématologiques de Scotto La Massèse en 1968. L'inventaire général comporte 171 entrées taxinomiques, réparties en 42 genres et 18 nouvelles espèces. Ainsi, à la Guadeloupe, 82 espèces ont été inventoriées dont 3 espèces nouvelles; à la Martinique, 87 espèces ont été inventoriées dont 7 espèces nouvelles; et en Guyane, 97 espèces ont été inventoriées dont 8 espèces nouvelles. Quelques-unes de ces espèces sont sur les listes A1 et A2 de l'OEPP ( Aphelenchoides besseyi A2/122, Radopholus similis A2/126, Xiphinema americanum sensu lato A1/150 et Xiphinema rivesi A2/262). L'intérêt de telles études en nématologie est discuté ainsi que les dispositions réglementaires quant à la présence d'espèces économiquement importantes ou réglementées, au regard de l'accroissement des échanges inter-îles ou intercontinentaux et des risques phytosanitaires encourus, que ce soit dans les départements français d'outre-mer (DOM) ou les pays et territoires d'outre-mer (PTOM).  相似文献   
93.
94.
A field experiment with three potato cultivars, where plants were inoculated withPhytophthora infestans, was used to parameterize a model of potato growth and blight population dynamics. The model was validated by accurately simulating a field experiment conducted in another year. Sensitivity analysis with the model showed that late cultivars are longer able to maintain a green canopy in the presence of disease, but still suffer more yield loss than early cultivars. The level of partial resistance of a cultivar was more important than its level of tolerance, and other plant characteristics. The model calculations showed that only between 4 and 15% of the yield loss in the experiments was due to accelerated leaf senescence caused by the disease; the major part of the loss was caused by lesion coverage of leaves.  相似文献   
95.
A greenhouse screening method for resistance to ringspot (Mycosphaerella brassicicola) inBrassica oleracea is described. High infection levels were achieved by spraying young plants by mycelial inoculum enriched with 3% sucrose. The screening method was tested on three Brussels sprouts, three cabbage and three cauliflower cultivars, with known reactions to ringspot in the field. Resistance was expressed both in cotyledons and true leaves by a lower number of lesions than the susceptible control and/or by hypersensitive reactions. Results of the seedling tests reflected differences in resistance in the field. Under controlled conditions the new test can be applied year-round to young plants, thus accelerating selection procedures.  相似文献   
96.
To engineer resistance against potato virus X (PVX), the viral coat protein (CP) gene has been introduced into two potato cultivars. Stable expression of the gene in transgenic clones throughout the growing season has been obtained and resulted in considerably increased virus resistance. With varying frequencies depending on the original cultivar used, true-to-type PVX resistant transgenic clones have been obtained. Since deviant light sprout characteristics were invariably associated with aberrations in plant phenotype, they can be used in procedures to early screen for deviations. Furthermore, it has been possible to unequivocally discriminate between the original untransformed and independent transgenic cultivars. Although no relation has been found between the presence, if any, of the CP of potato virus Y (PVY) or potato leafroll virus (PLRV) in CP gene transgenic potato, appreciable levels of resistance to these viruses has been obtained. This suggests that the mechanism by which a viral CP gene in the potato genome evokes resistance, differs amongst various viruses.  相似文献   
97.
Progeny from reciprocal F1 crosses and F1 backcrosses between fenvalerate-resistant and fenvalerate-susceptible Colorado beetles, Leptinotarsa decemlineata (Say), and between carbofuran-resistant and carbofuran-susceptible Colorado beetles were bioassayed to investigate the mode of inheritance of resistance to these chemicals. Bioassays of progeny from these crosses indicate that resistance to fenvalerate is inherited in a semi-recessive, sex-linked manner and carbofuran resistance is inherited in a partially dominant autosomal fashion. Log concentration/probit mortality lines and chi-square tests, however, indicate that multiple genes may be involved in resistance to both insecticides.  相似文献   
98.
The Dutch government has a coherent, long-term policy regarding attainment of a sustainable development affecting agriculture and horticulture, the requirements of which are very strict and will be difficult to satisfy. The growers of protected crops try to meet these requirements by developing so-called closed growing systems. Two other approaches in the policy are a substantial reduction of the volume of pesticides used and a very critical evaluation of the pesticides permitted. In this governmental policy, Integrated Pest Management has shown prospects in horticulture; it will play a very important role in the near future but is now considered as part of the broader concept of Integrated Production Systems. The glasshouse industry is very actively developing its own strategy to satisfy government targets and market demands for high-quality products produced by environmentally safe methods. The vegetable auctions have developed a policy of environmentally conscious production which should put the vegetable industry into a strong marketing position for its produce.  相似文献   
99.
By means of standardized procedures, the metabolism of [ring-2,6-14C]-parathion was investigated in carrot (Daucus carota L.), purple foxglove (Digitalis purpurea L.), soybean (Glycine max Merrill cv. ?Mandarin’?, and Glycine max Merrill cv. ?Harosoy 63’? cultivated on B5 and Miller media, respectively), thorn apple (Datura stramonium L.), and wheat (Triticum aestivum L.) cell suspension cultures. In the wheat and soybean (Mandarin) cells only 2.9 and 8.9%, respectively, of the applied parthion remained unmetabolized after 48 h of incubation, while 51.2, 57.9, 60.3, and 62.4% of the unchanged parent were detected in the D. purpurea, D. Stramonium, carrot and soybean (Harosoy) cultures, respectively. In all suspensions, paraoxon and 4-nitrophenol were found as phase I metabolites, thus demonstrating that plant tissues can catalyse oxidative desulfuration and dearylation of parathion. 4-Nitrophenol was also glycosylated with glucose and possibly galactose. Further, as yet unidentified, metabolites indicated that bio-transformations had also occurred at the aromatic moiety. Large amounts of non-extractable residues were detected in the wheat suspension (38.3%), while the other cultures showed a lower incorporation of 14C into insoluble cell material (0.9-9.4%). For a prospective ecotoxicological evaluation of the metabolic fate of pesticides and xenobiotics in plants in general, the differential metabolic capacity of plant cell cultures and plants should be taken into account.  相似文献   
100.
In 1991 serious losses caused byVerticillium wilt were found on two holdings in the Westland glasshouse district in the Netherlands in which theVerticillium resistant tomato cultivars Calypso and Criterium were grown in soilless systems. Isolates from diseased plants were identified asVerticillium albo-atrum.In inoculation experimentsVerticillium resistant tomato cultivars were seriously affected by the new isolates but not by a control isolate. Moneydor, a susceptible cultivar without the Ve gene, was the most seriously diseased by all isolates. The isolates from theVerticillium resistant tomato cultivars were less virulent on the susceptible cultivar than the control isolate.  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