全文获取类型
收费全文 | 1801篇 |
免费 | 127篇 |
专业分类
林业 | 151篇 |
农学 | 56篇 |
基础科学 | 36篇 |
414篇 | |
综合类 | 79篇 |
农作物 | 108篇 |
水产渔业 | 229篇 |
畜牧兽医 | 698篇 |
园艺 | 33篇 |
植物保护 | 124篇 |
出版年
2024年 | 1篇 |
2023年 | 14篇 |
2022年 | 47篇 |
2021年 | 86篇 |
2020年 | 64篇 |
2019年 | 79篇 |
2018年 | 79篇 |
2017年 | 69篇 |
2016年 | 78篇 |
2015年 | 74篇 |
2014年 | 99篇 |
2013年 | 133篇 |
2012年 | 150篇 |
2011年 | 154篇 |
2010年 | 79篇 |
2009年 | 94篇 |
2008年 | 89篇 |
2007年 | 107篇 |
2006年 | 88篇 |
2005年 | 62篇 |
2004年 | 61篇 |
2003年 | 63篇 |
2002年 | 40篇 |
2001年 | 13篇 |
2000年 | 9篇 |
1999年 | 13篇 |
1998年 | 10篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1976年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1928条查询结果,搜索用时 109 毫秒
271.
Vicente Torres-Olivar Luis Alonso Valdez-Aguilar Antonio Cárdenas-Flores Hugo Lira-Saldivar Marcela Hernández-Suárez 《Journal of plant nutrition》2016,39(14):2144-2152
The aim of this study was to realize whether soil mulching, with different plastic mulch colors, is a suitable practice under shade house (SH) conditions for the culture of cucumber. To do so, cucumber was cultured mulched or not with black, blue, red or white-on-black plastic films under SH, and contrasted against mulched cucumber in open field (OF). Red mulch produced the highest shoot dry weight per plant and bare soil the lowest. However, it was the white mulch which produced the highest commercial yield per plant. Contrastingly, bare soil plants produced the lowest commercial yield. SH plants two folded photosynthetic rates compared to OF plants. Mulch color mainly impacted leaf phosphorus (P) and magnesium (Mg) content while the SH affected nitrogen (K), calcium (Ca) and magnesium (Mg). Our results confirm that soil mulching, and shading positively impact the cucumber yield and quality but also show that soil mulching under SH enhances cucumber crop. 相似文献
272.
Dongli She Yuanhang Fei Qian Chen Luis Carlos Timm 《Archives of Agronomy and Soil Science》2016,62(12):1625-1639
High spatial variability of soil salinity in coastal reclamation regions makes it difficult to obtain accurate scale-dependent information. The objectives of this study were to describe the spatial patterns of saline-sodic soil properties (using soil pH, electrical conductivity (EC1:5) and sodium ion content (SIC) as indicators) and to gain knowledge of the scaling relationships between those variables. The soil pH, EC1:5 and SIC data were measured at intervals of 285 m along a 13,965-m temporal transect in a coastal region of China. The spatial variability of soil pH was weak but it was strong for soil EC1:5 and SIC at the measurement scale. There was a significant positive correlation between soil EC1:5 and SIC, while correlations between soil pH and either EC1:5 or SIC were weak and negative. For each saline-sodic soil parameter, the variability changed with the decomposition scales. The high-variance area at the larger scales (≥570 m) occupied less than 10% of the total area in the local wavelet spectrum, which meant that the spatial variations of the salinity indicators were insignificant at these scales. For local wavelet coherency, at a scale of 1500–2800 m and a sampling distance of 0–4500 m, the covariance was statistically significant between any two of the saline-sodic soil parameters. 相似文献
273.
274.
Mona M Y Elghandour Abdelfattah Z M Salem Jose S Martínez Castaneda Luis M Camacho Ahmed E Kholif Juan C Vázquez Chagoyán 《农业科学学报》2015,14(3):526-533
For many years, ruminant nutritionists and microbiologists have been interested in manipulating the microbial ecosystem of the rumen to improve production efficiency of different ruminant species. Removal and restriction of antibiotics subtherapeutic uses from ruminant diets has amplified interest in improving nutrient utilization and animal performance and search for more safe alternatives. Some bacterial and fungal microorganisms as a direct-fed microbial(DFM) can be the most suitable solutions. Microorganisms that are commonly used in DFM for ruminants may be classified mainly as lactic acid producing bacteria(LAB), lactic acid utilizing bacteria(LUB), or other microorganism's species like Lactobacillus, Bifidobacterium, Enterococcus, Streptococcus, Bacillus, Propionibacterium, Megasphaera elsdenii and Prevotellabryantii, in addition to some fungal species of yeast such as Saccharomyces and Aspergillus. A definitive mode of action for bacterial or fungal DFM has not been established; although a variety of mechanisms have been suggested. Bacterial DFM potentially moderate rumen conditions, and improve weight gain and feed efficiency. Fungal DFM may reduce harmful oxygen from the rumen, prevent excess lactate production, increase feed digestibility, and alter rumen fermentation patterns. DFM may also compete with and inhibit the growth of pathogens, immune system modulation, and modulate microbial balance in the gastrointestinal tract. Improved dry matter intake, milk yield, fat corrected milk yield and milk fat content were obtained with DFM administration. However, the response to DFM is not constant; depending on dosages, feeding times and frequencies, and strains of DFM. Nonetheless, recent studies have supported the positive effects of DFM on ruminant performance. 相似文献
275.
276.
Diego Moreira de Souza Sabrina Medeiros Suita Luis Alberto Romano Wilson Wasielesky Jr Eduardo Luis Cupertino Ballester 《Aquaculture Research》2014,45(2):270-277
The present work evaluated the use of molasses as a carbon source during the nursery rearing of Farfantepenaeus brasiliensis in a Biofloc technology system. During a 30 days trial, three replicate tanks were randomly assigned to the following treatments: 1.) molasses (with molasses addition) and 2.) control (without molasses addition). Bacteriological analysis was used to quantify the abundance of presumptive Vibrio spp. between control and molasses treatment. The concentration of this microorganism was lower in molasses compared with control. For the immunological analysis, shrimp haemolymph was collected to determine the total haemocyte count and the total protein concentration. The immunological results were not different between treatments. The performance results of shrimp reared with molasses addition showed that the survival rate (88.87 ± 6.36), the mean final weight (1.22 ± 0.38) and the specific growth rate (0.0309 ± 1.06) were significantly higher compared with control (80.5 ± 2.42; 1.03 ± 0.13; 0.0256 ± 0.97 respectively). Moreover, the addition of molasses contributed to the maintenance of water quality and lower concentration of presumptive Vibrio spp. The control presented an unstable variation of Vibrio spp. reaching values of 80 × 102 CFU/ml, while the highest result of molasses was 20 × 102 CFU/ml, confirming the beneficial effects of molasses addition. 相似文献
277.
Helvécio Della Coletta-Filho Sérgio Alves Carvalho Luis Fernando Carvalho Silva Marcos Antonio Machado 《European journal of plant pathology / European Foundation for Plant Pathology》2014,139(3):593-596
Knowledge about the mechanism of transmission of systemic pathogens of citrus species is highly important for the safe movement of citrus germplasm, management of citrus mother trees, and also production of young plants. Among systemic pathogens of citrus, Xylella fastidiosa the causal agent of the citrus variegated chlorosis (CVC), is one the most important pathogens causing decline in tree vigour and productivity. Seven-year experiments were conducted to evaluate the hypothesis of seed-to-seedling transmission of X. fastidiosa. This bacterium was found colonizing the fruit (exocarp, central axis and mesocarp) and the seed parts (seed coat and endosperm plus embryo). After 7 years of PCR assay, no positive PCR detection of X. fastidiosa was confirmed in seedlings propagated from the seeds infected with X. fastidiosa. This result demonstrates the lack of seed-to-seedling transmission of this bacterium. 相似文献
278.
A Mediterranean japonica rice (Oryza sativa) cultivar improvement through anther culture 总被引:1,自引:0,他引:1
X. Serrat M. Cardona J. Gil A. M. Brito L. Moysset S. Nogués E. Lalanne 《Euphytica》2014,195(1):31-44
Certified seed producers systematically select and propagate registered varieties year after year in order to maintain their uniformity and the original registered cultivar traits. However, natural mutations, spontaneous breeding between varieties and alien grain contamination can introduce undesirable variability. NRVC 980385 is a temperate japonica rice cultivar (Oryza sativa ssp. japonica) first registered in Spain in 2002. In 2005 certification tests detected a plot differing from the original traits in terms of uniformity and height suggesting the presence of a certain heterozygosis. This material was therefore seen as an opportunity to obtain newly stabilized doubled haploid (DH) lines which could compete in the Spanish short grain seed market. In this study, an in vitro anther culture protocol is defined which also covers the field tests selection to obtain four new, improved and stabilized DH derived lines ready to be registered for commercial proposes. This took just 4 years from the initial anther collection until new lines were grown in large scale field trials. Consequently, this protocol reduces the time for obtaining field assessed DH lines thereby having considerable advantages over other techniques by both maintaining the original registered cultivars and/or generating new derived varieties. 相似文献
279.
In North Africa, and especially in the Sahara Desert, biodiversity is poorly known. Of the five widespread canid species present, one is Data Deficient, three are considered widespread although habitat selection could limit their area of occupancy, and distribution maps available are coarse for conservation planning. This study identifies biogeographic patterns in North-African canids through the combination of high resolution presence data with 16 environmental factors. Predictive models trained in north-west Africa are projected to all North Africa. canids exhibited distinct biogeographical affinities. GIS tools and Maximum Entropy models identify a mixture of climatic and habitat factors as main predictors of species occurrence. Suitable habitats for North-African canids are mostly fragmented: probable occurrence was identified for Canis aureus in Saharan peripheral regions and mountains, for Vulpes pallida in a narrow band along the Sahel and in southern Saharan mountains, for Vulpes rueppellii throughout the Sahara, for Vulpes vulpes in northern Africa until the Sahara northern limit, and for Vulpes zerda in almost all Sahara. Areas of potential sympatry between species with similar niches and parapatric ranges are identified along relatively narrow bands. The small pixel size of projections allows the identification of suitable refuges for species otherwise absent in the driest Saharan habitats, providing framework data for the definition of the global conservation status of V. pallida, and conservation strategies for the guild. The biological value of Saharan mountains is emphasised as they constitute isolated suitable areas. Ecological-niche based models should be developed for other endangered Saharan vertebrates. 相似文献
280.
Jos Miguel Reichert Luis Eduardo Akiyoshi Sanches Suzuki Dalvan Jos Reinert Rainer Horn Inge Hkansson 《Soil & Tillage Research》2009,102(2):242
The concept of degree of compactness (DC), referred to as field bulk density (BD) as a percentage of a reference bulk density (BDref), was developed to characterize compactness of soil frequently disturbed, but for undisturbed soil such as under no-tillage critical degree of compactness values have not been tested. The objective of this study was to compare methods to determine BDref and limits of DC and BD for plant growth under no-tillage in subtropical soils. Data from the literature and other databases were used to establish relationships between BD and clay or clay plus silt content, and between DC and macroporosity and yield of crops under no-tillage in subtropical Brazil. Data of BDref reached by the soil Proctor test on disturbed soil samples, by uniaxial compression with loads of 200 kPa on disturbed and undisturbed soil samples, and 400, 800 and 1600 kPa on undisturbed soil samples, were used. Also, comparisons were made with critical bulk density based on the least limiting water range (BDc LLWR) and on observed root and/or yield restriction in the field (BDc Rest). Using vertical uniaxial compression with a load of 200 kPa on disturbed or undisturbed samples generates low BDref and high DC-values. The standard Proctor test generates higher BDref-values, which are similar to those in a uniaxial test with a load of 1600 kPa for soils with low clay content but lower for soils with high clay content. The BDc LLWR does not necessarily restrict root growth or crop yield under no-tillage, since field investigations led to higher BDc Rest-values. A uniaxial load greater than 800 kPa is promising to determine BDref for no-tillage soils. The BDref is highly correlated to the clay content and thus pedotransfer functions may be established to estimate the former based on the latter. Soil ecological properties are affected before compaction restricts plant growth and yield. The DC is an efficient parameter to identify soil compaction affecting crops. The effect of compaction on ecological properties must also be further considered. 相似文献