全文获取类型
收费全文 | 965篇 |
免费 | 80篇 |
专业分类
林业 | 73篇 |
农学 | 16篇 |
基础科学 | 5篇 |
266篇 | |
综合类 | 69篇 |
农作物 | 52篇 |
水产渔业 | 201篇 |
畜牧兽医 | 282篇 |
园艺 | 28篇 |
植物保护 | 53篇 |
出版年
2024年 | 3篇 |
2023年 | 8篇 |
2022年 | 10篇 |
2021年 | 33篇 |
2020年 | 28篇 |
2019年 | 47篇 |
2018年 | 40篇 |
2017年 | 42篇 |
2016年 | 49篇 |
2015年 | 43篇 |
2014年 | 55篇 |
2013年 | 69篇 |
2012年 | 69篇 |
2011年 | 92篇 |
2010年 | 42篇 |
2009年 | 41篇 |
2008年 | 61篇 |
2007年 | 52篇 |
2006年 | 48篇 |
2005年 | 54篇 |
2004年 | 39篇 |
2003年 | 35篇 |
2002年 | 26篇 |
2001年 | 5篇 |
2000年 | 10篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1045条查询结果,搜索用时 140 毫秒
941.
Miguel Cid Sonia Pereira Cristina Cabaleiro Franco Faoro Antonio Segura 《European journal of plant pathology / European Foundation for Plant Pathology》2007,118(1):23-30
Grapevine leafroll-associated virus 3 (GLRaV-3) is a mealybug-transmissible ampelovirus. Though the transmission mechanism has been described as semipersistent
on the basis of temporal parameters, definitive proof of this mechanism has never been provided. In the present study, we
carried out preliminary assays to establish the location of the virus in its vector, Planococcus citri. After dissecting the insects, GLRaV-3 was detected by means of IC-RT-PCR in the salivary glands, intestine and Malpighian
tubes, but not in the sucking apparatus. Immunogold labelling of the capsid protein revealed the presence of the virus in
some cells of the primary salivary glands, but not in the alimentary channel of the stylet, or in the accessory salivary glands.
The strong labelling of the electron-dense secretion vesicles in some cells of the primary salivary glands, together with
the non-detection of the virus in the sucking apparatus suggests that the transmission mechanism may be different from that
previously described. We propose a circulative transmission mechanism based on a specific transportation route for the viral
particles from the midgut or hindgut to the salivary glands. As the transmission mechanism is generally a common feature of
a viral genus, the existence of a circulative transmission mechanism for other mealybug-transmitted ampeloviruses is expected.
Organ by organ analysis of GLRaV-1, another ampelovirus not transmissible by P. citri, showed the absence of the virus in the salivary glands, thus providing further, though indirect, evidence in favour of circulative
transmission for this virus genus. 相似文献
942.
Carlos Ovalle Alejandro Del Pozo Miguel A. Casado Belén Acosta José M. de Miguel 《Landscape Ecology》2006,21(4):585-594
The current land use system in the anthropogenic savannas (Espinales) of the Mediterranean climate region of Chile, has resulted in considerable heterogeneity at the landscape level which is
associated with different covers of the legume tree, Acacia caven. The effects of landscape heterogeneity on the diversity and productivity of herbaceous plant communities were studied in
29 plots of 1000 m2, with a wide range of woody cover. A detrended correspondence analysis of the species × plots matrix explained 73% of the
total variation and revealed the existence of two trends of variation in floristic composition: one associated with physiographic
position (hillsides and flatlands) and the other related to the number of years since the last cutting, or coppicing, of A. caven. Despite the great majority of the original herbaceous species having disappeared as a result of the prevailing land use
system, some native species have been able to survive especially on hillside areas with low grazing intensity. Woody cover
was a good indicator of spatial heterogeneity and land use history. It was also correlated with stocking rate, above-ground
biomass of herbaceous vegetation, and soil fertility (organic matter, nitrogen and phosphorus concentration), both on hillsides
and flatlands. The relationship between woody cover and herbaceous plant species richness was significant and unimodal in
flat land areas, and linear, and marginally significant, on hillsides. The consequences of land use changes on the conservation
of the ecological and productive values of grasslands are analyzed. 相似文献
943.
Figuerola J Jiménez-Clavero MA López G Rubio C Soriguer R Gómez-Tejedor C Tenorio A 《Veterinary microbiology》2008,132(1-2):39-46
The rapid range expansion of West Nile Virus has raised interest in understanding the population dynamics and dispersal patterns of emerging infectious diseases by wildlife. We analyzed different ecological and evolutionary factors related to West Nile Virus neutralizing antibody prevalence in 72 bird species sampled in southern Spain. Prevalence of antibodies reached its maximum during the autumn and winter in comparison to summer months. Prevalence of antibodies was directly related to body mass and migratory behaviour. The greater prevalence of antibodies observed in summer migrants can be explained, among other factors, by the diversity of localities involved in their life cycles or the geographic areas visited during their migrations. Greater prevalence in larger species was explained by their longevity because the relationship was already significant when analyzing only first year birds, and probably also involved a high attraction to vectors by larger hosts. Coloniality and winter gregarism were unrelated to the prevalence of antibodies against this highly host generalist pathogen. Evolutionary relationships between species were unrelated to differences in the prevalence of antibodies. Our results suggest larger species as good candidates for easy, faster and cheaper monitoring of local, seasonal and annual changes in WN virus serology. 相似文献
944.
Alvarez J de Juan L Bezos J Romero B Sáez JL Reviriego Gordejo FJ Briones V Moreno MA Mateos A Domínguez L Aranaz A 《Veterinary microbiology》2008,128(1-2):72-80
Detection of infected animals is a key step in eradication programs of tuberculosis. Paratuberculosis infection has been demonstrated to compromise the specificity of the diagnostic tests. However, its effect on their sensitivity has not been clarified. In the present study, skin tests and the interferon-gamma (IFN-gamma) assay were evaluated in a goat flock (n=177) with a mixed tuberculosis-paratuberculosis infection in order to assess the possible effect of paratuberculosis on their sensitivity. Culture of mycobacteria was performed as the gold standard to determine the true infection status. All techniques showed lower sensitivities than previously described; the single intradermal tuberculin (SIT) test and the IFN-gamma assay detected 71% (62.4-78.6, 95% C.I.) of the infected animals; the single intradermal cervical comparative tuberculin (SICCT) test detected only 42.7% (34.1-51.7, 95% C.I.) of infected animals. The highest level of sensitivity was obtained when SIT test and IFN-gamma assay were combined in parallel (90.8%, 84.5-95.2, 95% C.I.). Sensitivities of the tests were also assessed by comparing animals suffering tuberculosis and animals with a mixed infection; tests were found to be more effective in the former group. Paratuberculosis seems to have a major effect in the sensitivity of the diagnostic tests under study, and therefore must be taken into account; in particular, the use of the SICCT test should be questioned when both tuberculosis and paratuberculosis are present. 相似文献
945.
946.
947.
Javier A. García-Vilas Beatriz Martínez-Poveda Ana R. Quesada Miguel ángel Medina 《Marine drugs》2016,14(1)
Organisms lacking external defense mechanisms have developed chemical defense strategies, particularly through the production of secondary metabolites with antibiotic or repellent effects. Secondary metabolites from marine organisms have proven to be an exceptionally rich source of small molecules with pharmacological activities potentially beneficial to human health. (+)-Aeroplysinin-1 is a secondary metabolite isolated from marine sponges with a wide spectrum of bio-activities. (+)-Aeroplysinin-1 has potent antibiotic effects on Gram-positive bacteria and several dinoflagellate microalgae causing toxic blooms. In preclinical studies, (+)-aeroplysinin-1 has been shown to have promising anti-inflammatory, anti-angiogenic and anti-tumor effects. Due to its versatility, (+)-aeroplysinin-1 might have a pharmaceutical interest for the treatment of different pathologies. 相似文献
948.
Miguel Costa Leal Marcela Carraro Melo Vaz João Puga Rui Jorge Miranda Rocha Chris Brown Rui Rosa Ricardo Calado 《Fish and Fisheries》2016,17(2):459-468
The marine ornamental fish trade (MOFT) is a worldwide industry that targets a remarkable quantity and diversity of reef fish species and provides an important source of revenue for exporting countries, particularly developing nations in Southeast Asia. Here we provide, for the first time, an economic assessment of the MOFT to the European Union (EU), one of the key players of the marine aquarium trade, along with the USA and Japan. Data from EUROSTAT (the European Statistical System) was analysed for the MOFT between 2000 and 2011. Results show that this industry was not affected by the economic crisis and accounted for a total of 135 million Euros during the study period. Both the UK and Indonesia have been reinforcing their importance as leading importer and exporter countries, respectively. The long‐term temporal pattern of the MOFT by EU and non‐EU countries is described, as well as its diversity and evenness between importing and exporting countries. The present economic assessment also identifies the key players of this industry, and ultimately contributes to management and conservation practices that may enhance the sustainable use of world's coral reefs. 相似文献
949.
Study of liver and gut alterations in sea bream,Sparus aurata L., fed a mixture of vegetable protein concentrates
下载免费PDF全文
![点击此处可从《Aquaculture Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Rosa Baeza‐Ariño Silvia Martínez‐Llorens Silvia Nogales‐Mérida Miguel Jover‐Cerda Ana Tomás‐Vidal 《Aquaculture Research》2016,47(2):460-471
This study evaluated liver and gut alterations of gilthead sea bream, Sparus aurata L., fed diets in which fish meal was substituted by a mixture (M) of pea protein concentrate (PPC) and rice protein concentrate (RPC). Histological studies were conducted to evaluate the possible changes produced by four experimental isolipidic (18%) and isoproteic (48%CP) diets with 30%, 60% and 90% of fish meal substitution by a pea and rice mixture and compared with a control diet (0%). The results obtained in the present histological study showed significant changes especially in the case of the 90% substitution in parameters such as thickness of the layers, goblet cells and villi measurements. Structural integrity of the gut would not be significantly affected by a diet of up to 60% substitution. The alterations observed in the liver could not only be attributed to diet but also to possible individual variations. 相似文献
950.
The effect of density in larval rearing of the pullet carpet shell Venerupis corrugata (Gmelin, 1791) in a recirculating aquaculture system
下载免费PDF全文
![点击此处可从《Aquaculture Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Sandra Joaquim Domitília Matias Ana Margarete Matias Alexandra Leitão Florbela Soares Marina Cabral Luís Chícharo Miguel B Gaspar 《Aquaculture Research》2016,47(4):1055-1066
The pullet carpet shell Venerupis corrugata is an economically valuable species in several European countries, however, nowadays stocks are under high fishing pressure. Hatchery production of juveniles for release is a major contributor to strengthen the stock and consequently improve the sustainability of the natural stocks. This study aimed to determine the feasibility of rearing V. corrugata larvae with different larval densities (10, 40 and 200 larvae per mL) in a recirculating aquaculture system (RAS), compared with the traditional larval rearing methodology (Batch). The mean survival, growth and metamorphic rate of V. corrugata larvae in RAS was higher (11.1%; 71.3 μm; 21.6% respectively) than in the Batch system, in all tested densities. The larval growth was not affected by the initial density until 40 larvae per mL, however, 200 larvae per mL decreased the larval growth in length nearly 54 μm. The larval rearing time was shortened in 2 days in the RAS system. The physical, chemical and microbiologic parameters suggested that the tested densities were not excessive to disturb the biofilter stability of RAS. The V. corrugata larval rearing performed at high larval stocking densities in RAS system present a reduction in the operating costs to produce this species. 相似文献