全文获取类型
收费全文 | 1070篇 |
免费 | 70篇 |
国内免费 | 3篇 |
专业分类
林业 | 135篇 |
农学 | 24篇 |
基础科学 | 7篇 |
364篇 | |
综合类 | 52篇 |
农作物 | 64篇 |
水产渔业 | 152篇 |
畜牧兽医 | 267篇 |
园艺 | 21篇 |
植物保护 | 57篇 |
出版年
2023年 | 16篇 |
2022年 | 14篇 |
2021年 | 33篇 |
2020年 | 43篇 |
2019年 | 53篇 |
2018年 | 44篇 |
2017年 | 47篇 |
2016年 | 54篇 |
2015年 | 33篇 |
2014年 | 44篇 |
2013年 | 62篇 |
2012年 | 85篇 |
2011年 | 102篇 |
2010年 | 49篇 |
2009年 | 46篇 |
2008年 | 84篇 |
2007年 | 71篇 |
2006年 | 59篇 |
2005年 | 42篇 |
2004年 | 45篇 |
2003年 | 31篇 |
2002年 | 39篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1948年 | 1篇 |
1940年 | 1篇 |
1930年 | 1篇 |
排序方式: 共有1143条查询结果,搜索用时 369 毫秒
881.
de la Luz Cádiz-Gurrea María Fernández de las Nieves Ignacio Aguilera Saez Luis Manuel Fernández-Arroyo Salvador Legeai-Mallet Laurence Bouaziz Mohamed Segura-Carretero Antonio 《Plant foods for human nutrition (Dordrecht, Netherlands)》2019,74(1):40-46
Plant Foods for Human Nutrition - Plants, including most food and feed plants, produce a broad range of bioactive chemical compounds. Among these compounds, polyphenols are reported to provide... 相似文献
882.
Valria P. B. Euclides Denise B. Montagner Manuel Cludio M. Macedo Alexandre R. de Araújo Gelson S. Difante Rodrigo A. Barbosa 《Grass and Forage Science》2019,74(3):450-462
This 3‐year study evaluated the effects of grazing intensity on herbage and steer responses in continuously stocked Brachiaria brizantha cv. Marandu pasture in the Brazilian savanna. Treatments consisted of three grazing intensity levels, characterized by canopy heights of 15, 30 and 45 cm, measured twice per week. Responses variables included tiller population density (TPD), herbage accumulation rate (HAR) and body weight gain per area (WGA). A decline in TPD (1,237 vs. 767 tillers/m2) was observed from the first to the third grazing years, which influenced the HAR from the first to the third years (90.1 vs. 52.4 kg ha?1 day?1). A marked decline in body WGA (541 vs. 276 kg ha?1 year?1) was observed along the three years in pastures managed at a height of 15 cm, indicating that this is an unstable condition for Marandu palisadegrass pasture. HAR was similar for pastures managed at 30 or 45 cm and was relatively stable during the experimental period, averaging 91.8 and 99.1 kg ha?1 day?1 respectively. Body WGA was similar and constant throughout the experimental period for pastures managed at 30 (596 kg ha?1 year?1) and 45 cm (566 kg ha?1 year?1). Maintaining continuously stocked Marandu palisadegrass pastures at a 15 cm canopy height should be avoided due to long‐term decreases in plant persistence and animal body WGA, particularly when soil P is below critical levels at pasture establishment and during pasture utilization. 相似文献
883.
Cecilia Martínez Susana Manzano Zoraida Megías Dolores Garrido Belén Picó Manuel Jamilena 《Euphytica》2014,199(3):349-362
Cytoplasmic genic male sterility system based hybrids were synthesized by line × tester design and evaluated with check GTH 1 in RBD at Sardarkrushinagar, Jagudan and Khedbrahma during kharif 2007. Analysis of variance in individual and across environments revealed significant differences among genotypes and existence of overall heterosis for seed yield per plant and other thirteen traits. The top ranking on the basis of standard heterosis were CMSGT087A × GTR0525 (116.40 %) followed by CMSGT087A × AGTR0534 (108.93 %), CMSGT0307A × AGTR0538 (99.21 %) and CMSGT 0301A × AGTR 0534 (95.51 %) for seed yield per plant and for one or two of its contributing traits. Combining ability analysis revealed presence of both additive and non-additive gene effects. The specific combining ability variance was found more compaired to general combining ability variance for all the characters under studied. This favored a hybrid breeding programme. In stability analysis, linear portion was considerably high for all the traits except for days to flower and pod length. The best stable hybrids for seed yield per plant over environments were CMSGT 308A × AGTR 0534, CMSGT 307A × AGTR 0543, CMSGT 0308A × AGTR 0536 and CMSGT 0311A × GTR 0525 and also recorded stability in any one or more of its contributing traits viz. pods per plant, branches per plant, seed per pod, pod length and test weight. Top ranking hybrids had high mean performance, high heterosis and desirable sca effects and stability for seed yield per plant. Therefore, these hybrids could be valuable for commercial exploitation. 相似文献
884.
Manuel López-Gómez Soledad Verdejo-Lucas 《European journal of plant pathology / European Foundation for Plant Pathology》2014,138(4):863-871
Cucurbits are often cultivated in rotation with Solanaceae in double-cropping systems. Most cucurbits have been described as susceptible to root-knot nematodes (RKN) but little is known on their relative levels of susceptibility. Because RKN species differ in rates of root invasion and reproductive traits, isolates of M. arenaria, M. incognita and M. javanica were compared on five cucurbit hosts in experiments run in a climate growth chamber. They included zucchini squash cv Amalthee, cucumber cv Dasher II, melon cv Pistolero, pumpkin cv Totanera and watermelon cv Sugar Baby. All cucurbits were susceptible to the three RKN isolates although M. javanica showed higher invasion rates, faster development and higher egg production than M. arenaria on the selected cucurbits. Apparent differences among cucurbits were primarily due to root invasion rates and formation of egg masses. Both Cucumis species (cucumber and melon) were better hosts for nematode invasion and reproduction than zucchini squash, followed by watermelon. Large invasion rates followed by small reproduction traits were linked to M. incognita on zucchini squash. Reduced invasion rates and egg mass formation along with delayed early development were shown on watermelon. 相似文献
885.
886.
María Vanessa Lencinas Guillermo Martínez PasturEmilce Gallo Juan Manuel Cellini 《Forest Ecology and Management》2011,262(7):1236-1250
Understory plants could can act as indicators of temperate forest sustainability, health and conservation status due to their importance in ecosystem function. Harvesting impacts on understory plant diversity depends on their intensity. Variable retention has been proposed to mitigate the harmful effects of timber harvesting, but its effectiveness remains unknown in southern Patagonian Nothofagus pumilio forests. The objectives of this study were to: (i) define a baseline of understory plant diversity in old-growth forests along a site quality gradient and under canopy gaps; (ii) evaluate stands with three different variable retention treatments compared to old-growth forests; and (iii) assess temporal changes during 4 years after harvesting (YAH). A 61 ha N. pumilio forest was selected. Understory plant (Dicotyledonae, Monocotyledonae and Pteridophyta) richness, cover (including woody debris and bare forest floor) and aboveground dry biomass were characterized in summer for 5 years. Before harvesting, baseline samples were conducted along a site quality gradient and outside/inside canopy gaps. Analyzed treatments include a control of old-growth forest (OGF) and three different harvesting treatments with variable retention: (i) dispersed retention (DR) of 30 m2 ha−1 (20-30% retention); (ii) aggregated retention (AR) with one aggregate per hectare and clear-cuts (28% retention); and (iii) combined dispersed and aggregated retention (DAR) with one aggregate per hectare and dispersed retention of 10-15 m2 ha−1 (40-50% retention). Data analyses included parametric and permutational ANOVAs, multivariate classification and ordinations.Before harvesting, 31 plant species were found, where richness, cover and biomass were directly related to site quality. The presence of canopy gaps did not have a significant impact on the measured variables. After harvesting, 20 new species appeared from adjacent associated environments (two from N. antarctica forests and 18 from grasslands and peatlands). At the stand level, understory values were higher in AR > DR > DAR > OGF. Most (81-95%) plant richness at baseline conditions was conserved in all treatments, where inside the aggregates understory remained similar to OGF. Combination of aggregated and dispersed retention (DAR) better limited exotic species introduction and protected sensitive species, improving conservation in harvested stands. Changes in understory variables were observed after the first YAH in all treatments; greater changes were observed in the harvested areas than in aggregates. Changes stabilized at the fourth YAH. As a conclusion, the location of retention aggregates should be selected to preserve species understory diversity of more speciose and diverse habitats or particularly uncommon stands. Implementation of different kinds (patterns and levels) of retention for improvement of biodiversity conservation in harvested forests should be included in timber and forest management planning. 相似文献
887.
Tamara S. Vilches Manuel Norte Antonio Hern��ndez Daranas Jos�� J. Fern��ndez 《Marine drugs》2012,10(10):2234-2245
The dinoflagellate Prorocentrum belizeanum is responsible for the production of several toxins involved in the red tide phenomenon known as Diarrhetic Shellfish Poisoning (DSP). In this paper we report on the biosynthetic origin of an okadaic acid water-soluble ester derivative, DTX5c, on the basis of the spectroscopical analysis of 13C enriched samples obtained by addition of labelled sodium [l-13C], [2-13C] acetate to artificial cultures of this dinoflagellate. 相似文献
888.
889.
890.
Changing face of microglia 总被引:1,自引:0,他引:1
Graeber MB 《Science (New York, N.Y.)》2010,330(6005):783-788
Microglia are resident brain cells that sense pathological tissue alterations. They can develop into brain macrophages and perform immunological functions. However, expression of immune proteins by microglia is not synonymous with inflammation, because these molecules can have central nervous system (CNS)-specific roles. Through their involvement in pain mechanisms, microglia also respond to external threats. Experimental studies support the idea that microglia have a role in the maintenance of synaptic integrity. Analogous to electricians, they are capable of removing defunct axon terminals, thereby helping neuronal connections to stay intact. Microglia in healthy CNS tissue do not qualify as macrophages, and their specific functions are beginning to be explored. 相似文献