全文获取类型
收费全文 | 2292篇 |
免费 | 194篇 |
国内免费 | 6篇 |
专业分类
林业 | 177篇 |
农学 | 74篇 |
基础科学 | 18篇 |
488篇 | |
综合类 | 206篇 |
农作物 | 127篇 |
水产渔业 | 261篇 |
畜牧兽医 | 847篇 |
园艺 | 64篇 |
植物保护 | 230篇 |
出版年
2023年 | 16篇 |
2022年 | 27篇 |
2021年 | 59篇 |
2020年 | 70篇 |
2019年 | 123篇 |
2018年 | 84篇 |
2017年 | 97篇 |
2016年 | 82篇 |
2015年 | 73篇 |
2014年 | 80篇 |
2013年 | 131篇 |
2012年 | 157篇 |
2011年 | 172篇 |
2010年 | 110篇 |
2009年 | 97篇 |
2008年 | 148篇 |
2007年 | 135篇 |
2006年 | 94篇 |
2005年 | 107篇 |
2004年 | 102篇 |
2003年 | 100篇 |
2002年 | 104篇 |
2001年 | 32篇 |
2000年 | 24篇 |
1999年 | 20篇 |
1998年 | 9篇 |
1997年 | 19篇 |
1996年 | 12篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 13篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 6篇 |
1974年 | 4篇 |
1958年 | 3篇 |
1954年 | 3篇 |
排序方式: 共有2492条查询结果,搜索用时 15 毫秒
21.
Lina Maria Correa E Ricardo D. Moreno José Luis Riveros 《Anatomia, histologia, embryologia》2023,52(2):336-340
This is the first morpho-histological comparison of guanaco ovaries between reproductive (long-days) and non-reproductive (short-days) seasons, and oestrogen receptor-alpha (ERα) and beta (ERβ) detection. Different stages of follicle development were found in the cortical area, but no corpus luteum was detected. The size and frequency of antral follicles and large atretic follicles were higher in long-day ovaries than short-days, consistent with ovarian activity in this season. Differential expression of ERα and ERβ was observed in follicles at different stages of development between short and long days. These data reveal histological and molecular differences between reproductive and non-reproductive seasons of guanaco ovaries. 相似文献
22.
Can carbon sequestration markets benefit low-income producers in semi-arid Africa? Potentials and challenges 总被引:1,自引:0,他引:1
The Clean Development Mechanism (CDM) of the Kyoto Protocol of the United Nations Framework Convention on Climate Change allows a country that emits C above agreed-upon limits to purchase C offsets from an entity that uses biological means to absorb or reduce greenhouse emissions. The CDM is currently offered for afforestation and reforestation projects, but may apply subsequently to sequestration in agricultural soils. Additionally, markets outside of the Protocol are developing for soil C sequestration. 相似文献
23.
Lasmar Chaim J. Queiroz Antônio C. M. Rosa Clarissa Carvalho Nathália S. Schmidt Fernando A. Solar Ricardo R. C. Paolucci Lucas N. Cuissi Rafael G. Ribas Carla R. 《Landscape Ecology》2021,36(9):2583-2597
Landscape Ecology - Harmful effects of habitat loss and fragmentation can be detected across multiple spatial scales, yet most studies that aim to characterize these effects take place at a single... 相似文献
24.
In field and laboratory experiments, enhanced degradation of the dicarboximide fungicides, iprodione and vinclozolin, was stimulated by only one application of the fungicides in a soil with no previous history of any pesticide input. Field and laboratory studies demonstrated the ease of stimulation by pre-treatment with even very low concentrations of the fungicides (0·5 μg g−1 soil) and at a range of temperatures and soil moisture conditions. Soils that had acquired full enhanced degradation could rapidly degrade fungicide applied at 30 times the recommended field rate. Cross-enhancement of degradation was noted with both fungicides, but not with their common metabolite, 3,5-dichloroaniline. Application of the antibiotics chloramphenicol or rifampicin to soil reduced enhanced degradation to control levels; cycloheximide had no effect. This, together with the inhibitory action of azide, mercuric chloride and repetitive microwaving, indicated that the agent(s) of enhanced degradation was probably bacterial. 相似文献
25.
Robson RV Alves Tatiana Soares Elinaldo FL Bento Ricardo S Roldan‐Filho Brbara SS Souza Marcele KN Lima Jssica S Nascimento Luana CBB Coelho Roberto A S Thmarah A Lima Gabriel GA Gonalves Fbio A Brayner Luiz C Alves Daniela MAF Navarro Thiago H Napoleo Patrícia MG Paiva 《Pest management science》2020,76(2):730-736
26.
27.
Wardatou Boukari Denis Filloux Jean Heinrich Daugrois Emmanuel Fernandez Dimitre Mollov Claudia Kaye Martha Hincapie Alexander Sanchez Jianping Wang Philippe Roumagnac Philippe Rott 《Plant pathology》2020,69(6):1060-1069
Viruses in the genus Mastrevirus (family Geminiviridae), including those infecting sugarcane, have natural geographical ranges almost exclusively restricted to Africa and the Indian Ocean islands off the African coast. Only sugarcane white streak virus (SWSV) in Barbados and sugarcane striate virus (SStrV) in Florida and Guadeloupe are known to infect a few sugarcane varieties in the Western Hemisphere. In this study, PCR assays were developed to detect these two viruses in sugarcane. Five hundred and seventy-one DNA samples from Saccharum species and interspecific hybrids from the Miami World Collection of sugarcane and related grasses were tested for the presence of SStrV and SWSV by PCR. No variety was found infected by SWSV but SStrV was detected in 19 varieties. PCR data were confirmed by sequencing amplified fragments (248 bp). These fragments shared 93%–100% nucleotide identity with SStrV sequences from the GenBank database. SStrV isolates were distributed in six phylogenetic groups, including the four strains of the virus. Most varieties infected by SStrV originated from Asia, thus confirming a previous hypothesis stating that this virus originated from this continent. Absence of SStrV in commercial sugarcane in Florida also suggested that this virus has not been spread in this location, while infected plants have been present for several decades. 相似文献
28.
Genetic parameters for spawning and growth traits in the Pacific white shrimp (Penaeus (Litopenaeus) vannamei)
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)
Alejandra Caballero‐Zamora Eugenia Guadalupe Cienfuegos‐Rivas Hugo H Montaldo Gabriel Ricardo Campos‐Montes Alfonso Martínez‐Ortega Héctor Castillo‐Juárez 《Aquaculture Research》2015,46(4):833-839
The aim of this study was to estimate genetic parameters for spawning traits and growth traits in a breeding line of Pacific white shrimp, Penaeus (Litopenaeus) vannamei, selected for growth and survival. Traits studied were number of eggs (NE) and number of nauplii (NN) and female body weight at insemination (FWI) and body weight at 130 days of age (BW130). Genetic parameters were estimated using a multivariate animal model. Heritability for NE and NN were estimated as 0.13 ± 0.04 and 0.03 ± 0.04 respectively. The contribution to NN total variation due to ‘factors associated with male’ effect was estimated as 0.47 ± 0.07. In the cases of FWI and BW130, heritability was estimated as 0.44 ± 0.08 and 0.19 ± 0.03 respectively. Genetic correlation between FWI and NE was estimated as 0.49 ± 0.15, between FWI and NN as 0.54 ± 0.39 and between NE and NN as 0.27 ± 0.41, whereas the genetic correlations of FWI, NE and NN with BW130 were 0.30 ± 0.13, ?0.21 ± 0.19 and ?0.25 ± 0.38 respectively. Although it is important to perform more studies on this issue, our results found no evidence of a genetic antagonistic effect between female reproductive traits and body weight at harvesting (130 days of age) in P. vannamei. 相似文献
29.
Jean‐Pierre Cuif Yannicke Dauphin Gilles Luquet Oulfa Belhadj Stphan Rouzire Murielle Salom Marine Cotte Andrea Somogyi Kadda Medjoubi Cedrik Lo Denis Saulnier 《Aquaculture Research》2020,51(2):506-522
Cultivated pearls frequently exhibit morphological irregularities making obvious that mineral deposition was irregularly distributed onto nucleus surface. Taking advantage of experimental cultivations with short durations (from 10 days to few months), these irregular deposits predating occurrence of the nacre were investigated in Polynesian pearls by biochemical characterizations and a series of physical methods. Diversity in the resulting data suggests that various in‐depth alterations of the biomineralization mechanism may have occurred during the grafting process, leading to diversity in the biochemical pathways to nacreous deposition. This allows a precise discussion of current views about pearl formation. The “reversed shell theory” is formally disproved through point to point comparison with development of the shell growing edge. Similarity of pearl formation with “regeneration” or “shell repair” is also discussed, emphasizing the differences between these concepts. 相似文献
30.
Frederic Vandeperre Ruth M. Higgins Julio Sánchez‐Meca Francesc Maynou Raquel Goñi Pablo Martín‐Sosa Angel Pérez‐Ruzafa Pedro Afonso Iacopo Bertocci Romain Crec’hriou Giovanni D’Anna Mark Dimech Carmelo Dorta Oscar Esparza Jesús M. Falcón Aitor Forcada Ivan Guala Laurence Le Direach Concepción Marcos Celia Ojeda‐Martínez Carlo Pipitone Patrick J. Schembri Vanessa Stelzenmüller Ben Stobart Ricardo S. Santos 《Fish and Fisheries》2011,12(4):412-426
Marine protected areas (MPAs) are often promoted as tools for biodiversity conservation as well as for fisheries management. Despite increasing evidence of their usefulness, questions remain regarding the optimal design of MPAs, in particular concerning their function as fisheries management tools, for which empirical studies are still lacking. Using 28 data sets from seven MPAs in Southern Europe, we developed a meta‐analytical approach to investigate the effects of protection on adjacent fisheries and asking how these effects are influenced by MPA size and age. Southern European MPAs showed clear effects on the surrounding fisheries, on the ‘catch per unit effort’ (CPUE) of target species, but especially on the CPUE of the marketable catch. These effects depended on the time of protection and on the size of the no‐take area. CPUE of both target species and the marketable catch increased gradually by 2–4% per year over a long time period (at least 30 years). The influence of the size of the no‐take area appeared to be more complex. The catch rates of the entire fishery in and around the MPA were higher when the no‐take areas were smaller. Conversely, catch rates of selected fisheries that were expected to benefit most from protection increased when the no‐take area was larger. Our results emphasize the importance of MPA size on its export functions and suggest that an adequate, often extended, time frame be used for the management and the evaluation of effectiveness of MPAs. 相似文献