全文获取类型
收费全文 | 6245篇 |
免费 | 452篇 |
国内免费 | 517篇 |
专业分类
林业 | 1260篇 |
农学 | 1259篇 |
基础科学 | 187篇 |
336篇 | |
综合类 | 2266篇 |
农作物 | 531篇 |
水产渔业 | 302篇 |
畜牧兽医 | 624篇 |
园艺 | 203篇 |
植物保护 | 246篇 |
出版年
2024年 | 23篇 |
2023年 | 84篇 |
2022年 | 126篇 |
2021年 | 157篇 |
2020年 | 169篇 |
2019年 | 198篇 |
2018年 | 125篇 |
2017年 | 181篇 |
2016年 | 200篇 |
2015年 | 189篇 |
2014年 | 265篇 |
2013年 | 298篇 |
2012年 | 372篇 |
2011年 | 424篇 |
2010年 | 387篇 |
2009年 | 367篇 |
2008年 | 362篇 |
2007年 | 392篇 |
2006年 | 353篇 |
2005年 | 290篇 |
2004年 | 276篇 |
2003年 | 223篇 |
2002年 | 179篇 |
2001年 | 157篇 |
2000年 | 144篇 |
1999年 | 125篇 |
1998年 | 109篇 |
1997年 | 125篇 |
1996年 | 112篇 |
1995年 | 104篇 |
1994年 | 98篇 |
1993年 | 92篇 |
1992年 | 92篇 |
1991年 | 94篇 |
1990年 | 84篇 |
1989年 | 46篇 |
1988年 | 45篇 |
1987年 | 31篇 |
1986年 | 28篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1983年 | 3篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1955年 | 2篇 |
排序方式: 共有7214条查询结果,搜索用时 15 毫秒
91.
Lemon (Citrus limon (L.) Burm. f.) is one of the most important Citrus fruit for Turkey because of its great amount of production and export. It has been cultivated for a long time in Turkey, and therefore variations for agronomical traits are likely among cultivated lemons due to bud mutations and, hybridizations. The objectives of this study were to determine variations for some selected agronomical traits and genetic markers among 12 new lemons derived from selections. Tree growth, yield, fruit quality, and molecular diversification of these clones were determined. After four years of evaluation, ‘Kutdiken’ M-51 indicated the highest canopy volume. For yield per tree, the best clone was ‘Kutdiken’ M-51. After five years of evaluation, ‘Kibris’ M-54 had the highest fruit weight and acidity. ‘Italian Memeli’ M-56 contained the lowest seed number and the highest total soluble solids. Molecular analysis, as assessed with 22 random amplification of polymorphic DNA (RAPD) and 11 inter simple sequence repeats (ISSR) primers, indicated that seven of twelve clones were separated with RAPD markers, whereas four were distinguished with ISSR markers. Combined analysis of RAPD and ISSR data detected that similarity values among the lemons clones were between 0.97 and 1.00. It can be concluded that variations in orchards are abundant and mainly due to mutations. 相似文献
92.
L.H. Wang X.H. Gu M.Y. Hua S.L. Mao Z.H. Zhang D.L. Peng X.F. Yun B.X. Zhang 《Scientia Horticulturae》2009
The root-knot nematodes (Meloidogyne spp.) are important nematode pests and cause serious diseases in pepper in the world. No molecular markers linked to the nematodes resistance N gene have been reported. In this paper, ‘Carolina Wonder’ (Capsicum annuum L.), a sweet pepper line resistant to root-knot nematode with N gene, ‘20080-5-29’ (C. annuum L.), an inbred line susceptible to root-knot nematode with good horticultural characteristics, and their F2 progeny with 320 individuals were used as materials. Evaluation of resistance and susceptibility of parental lines, F1 and F2 progeny inoculated with root-knot nematodes (Meloidogyne incognita) were carried out. ‘Bulked segregant analysis’ method was used to search for polymorphic markers from 512 pairs of AFLP primers. Based on the assessment of resistance and susceptibility and polymorphism of the AFLP marker in F2 population, the genetic linkage distance between the AFLP marker and the N gene was estimated. One AFLP marker E39/M41-339 was obtained and transferred to a SCAR marker amplifying a 315 bp DNA fragment linked to the N resistant allele and a 331 bp fragment linked to the N+ susceptible allele. The distance between the molecular marker and the nematodes resistance N gene is 6.3 cM. This research delivered a valuable tool for the marker assisted selection of nematodes resistance in pepper. 相似文献
93.
The conversion of forests and farmlands to human settlements has negative impacts on many native species, but also provides
resources that some species are able to exploit. American Crows (Corvus brachyrhynchos), one such exploiter, create concern due to their impact as nest predators, disease hosts, and cultural harbingers of evil.
We used various measures of crow abundance and resource use to determine crows’ response to features of anthropogenic landscapes
in the Puget Sound region of the United States. We examined land cover and land use composition at three spatial scales: study
sites (up to 208 ha), crow home ranges within sites (18.1 ha), and local land cover (400 m2). At the study site and within-site scales crow abundance was strongly correlated with land cover providing anthropogenic
resources. In particular, crows were associated with the amount of ‘maintained forest’ cover, and were more likely to use
grass and shrub cover than forest or bare soil cover. Although crows did not show a generalized response to an edge variable,
they exhibited greater use of patchy habitat created by human settlements than of native forests. Radio-tagged territorial
adults used resources within their home ranges relatively evenly, suggesting resource selection had occurred at a larger spatial
scale. The land conversion pattern of new suburban and exurban settlements creates the mix of impervious surfaces and maintained
vegetation that crows use, and in our study area crow populations are expected to continue to increase.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
94.
黄瓜根际促生菌的促生效应与防病作用 总被引:3,自引:0,他引:3
对黄瓜植物根际促生菌(PGPR)菌株的分离筛选、分类鉴定以及人们对其促生防病作用的应用和防病机制的研究现状进行了综述,以期为新型PGPR制剂的进一步研制、开发和应用提供参考. 相似文献
95.
Kullapapruk Piewthongngam Supachai Pathumnakul Kanchana Setthanan 《Agricultural Systems》2009,102(1-3):58-66
The poorly integrated cane supply planning between mills and cane growers in the Northeast of Thailand generates an excess of cane supplies that exceeds the mills’ capacity during the peak of harvest season. Each grower individually determines his/her cultivation plan by selecting planting dates and cultivars based on one’s own preference without taking into account the individual mill’s capacity and other growers’ plans. This situation causes most sugarcane grown in this area to reach its mature stage at the same period. In this study, we propose a framework of cultivation planning to cope with the problem. The focus of the cultivation plan is a long-term plan to determine the cultivation time, the cultivar selection and the corresponding prospective harvesting time window for each field such that overall sugar production is optimized.The crop growth model and a mathematical model are employed for yield simulation and optimization task. The crop growth model enables decision-makers to visualize cane production of each individual field at different dates with different cultivars and allow decision-makers to apply the mathematical programming to cultivation planning. The suggested framework has the potential to increase sugar production by 23% when compared to the traditional method. 相似文献
96.
97.
98.
粒重是影响小麦产量的主要因素之一。QGw.nau-5A是一个从我国小麦骨干亲本南大2419中鉴定的粒重主效QTL。为评价该QTL不同等位基因对粒重的效应及在育种中的应用潜力,利用分子标记辅助选择技术,分别将南大2419和早洋麦的QGw.nau-5A区段导入望水白和川麦42,构建了不同背景的近等基因系,并比较了不同背景下粒重QTL的效应。结果表明,QGw.nau-5A能在不同背景下显著提高小麦粒重,与轮回亲本相比,近等基因系的百粒重显著增加0.2~0.6g。QGw.nau-5A等位变异对粒重的贡献存在差异,与川麦42的等位变异相比,南大2419和早洋麦的等位变异均能增加粒重,但后者效应更大。 相似文献
99.
Comparing mating designs to restore seed production of interspecific hybrids between Trifolium repens (white clover) and Trifolium uniflorum
下载免费PDF全文
![点击此处可从《Plant Breeding》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Muhammad Naeem Isabelle Marjorie Verry Peter D. Kemp James P. Millner Warren Mervyn Williams 《Plant Breeding》2017,136(3):420-426
Interspecific hybrids between Trifolium uniflorum and cultivated white clover (Trifolium repens) have highly useful characteristics for temperate pastoral systems derived from both parent species. However, the early hybrids (F1 and BC1) also have unacceptably poor seed production for commerce. This study analysed the basis for the poor seed production and investigated breeding strategies for overcoming the problem. The BC1F1 generation produced lower‐than‐expected numbers of heads per plant and seeds per floret. Backcrossing of selected hybrids to white clover corrected these deficiencies and created new variation. Seed numbers were also returned to near target levels by recurrent selection within the BC1 generation. Thus, it was possible to retain a theoretical average of 25% of T. uniflorum genome and still achieve high seed production per plant. The BC1F2 and BC2F1 generations produced high seed numbers per plant, along with reasonable variation. Both of these second‐generation hybrid forms have high reproductive potential and should be the focus for the selection of the desired combinations of agronomic and seed production traits. 相似文献
100.
Simultaneous selection for seed and forage production in cocksfoot (Dactylis glomerata): application of drought tolerance and susceptibility indices
下载免费PDF全文
![点击此处可从《Grass and Forage Science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
An experiment was conducted to estimate drought tolerance of some cocksfoot genotypes based on seed and forage yield and related indices (including tolerance index, mean productivity, geometric mean productivity, reduction percentage index, stress tolerance index and stress susceptibility index) and to identify relationships between measured traits. Twenty‐five genotypes were evaluated in the field under control and drought‐stress environments over 2 years. The results revealed a high variation for seed yield and forage yield and the measured indices under both moisture conditions. No correlation was observed between seed yield and forage yield under the control treatment, but this correlation was positively significant under the water‐stress treatment. Drought‐tolerant and susceptible genotypes were identified based on seed and forage yield performance. Genotypes 2, 4 and 7 had high seed yield, while genotypes 7 and 10 had high forage yield under both stressed and non‐stressed conditions and were identified as the most tolerant genotypes in each category. The results also revealed that genotypes 1, 2, 4, 6, 7, 8 and 24 had relatively high seed and forage yield in both control and drought‐stressed conditions. These genotypes can be used for further studies to improve both seed and forage yields concurrently. 相似文献