全文获取类型
收费全文 | 1462篇 |
免费 | 73篇 |
国内免费 | 12篇 |
专业分类
林业 | 201篇 |
农学 | 38篇 |
基础科学 | 6篇 |
435篇 | |
综合类 | 182篇 |
农作物 | 40篇 |
水产渔业 | 63篇 |
畜牧兽医 | 461篇 |
园艺 | 26篇 |
植物保护 | 95篇 |
出版年
2023年 | 9篇 |
2022年 | 11篇 |
2021年 | 30篇 |
2020年 | 23篇 |
2019年 | 24篇 |
2018年 | 48篇 |
2017年 | 33篇 |
2016年 | 46篇 |
2015年 | 47篇 |
2014年 | 48篇 |
2013年 | 83篇 |
2012年 | 95篇 |
2011年 | 106篇 |
2010年 | 77篇 |
2009年 | 62篇 |
2008年 | 99篇 |
2007年 | 87篇 |
2006年 | 73篇 |
2005年 | 55篇 |
2004年 | 87篇 |
2003年 | 57篇 |
2002年 | 47篇 |
2001年 | 25篇 |
2000年 | 16篇 |
1999年 | 13篇 |
1998年 | 9篇 |
1997年 | 14篇 |
1996年 | 17篇 |
1995年 | 8篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1979年 | 4篇 |
1976年 | 4篇 |
1972年 | 6篇 |
1971年 | 8篇 |
1970年 | 5篇 |
1969年 | 5篇 |
1967年 | 4篇 |
1966年 | 5篇 |
1965年 | 8篇 |
1956年 | 3篇 |
1932年 | 4篇 |
1911年 | 6篇 |
排序方式: 共有1547条查询结果,搜索用时 15 毫秒
51.
52.
Otto Pesta 《Journal of pest science》1956,29(1):5-6
Ohne Zusammenfassung 相似文献
53.
54.
55.
Hans Jürgen Bestmann Beate Classen Uwe Kobold Otto Vostrowsky Fred Klingaup 《Journal of pest science》1987,60(2):31-34
The essential oil ofChrysanthemum balsamita L. revealed insecticidal properties when tested againstM. dirhodum aphids. The insecticidal activity was attributed to the presence of pyrethrine I in the oil. By an appropriate testing procedure, the dependence of the activity upon the time of harvesting of the plants was determined. Furthermore, the insecticidal effect of the oil was compared with that of a commercially available pyrethrum preparation. 相似文献
56.
Somatic embryos of Norway spruce (Picea abies (L.) Karst.) differentiate from proembryogenic masses (PEMs), which are subject to autodestruction through programmed cell death. In PEMs, somatic embryo formation and activation of programmed cell death are interrelated processes. We sought to determine if activation of programmed cell death in PEMs is caused by genetic aberrations during somatic embryogenesis. Based on the finding that withdrawal of auxin and cytokinin induces programmed cell death in PEMs, 1-week-old cell suspensions were cultured in medium either with or without auxin and cytokinin and then transferred to maturation medium containing abscisic acid. We analyzed the stability of three nuclear simple sequence repeat (SSR) microsatellite markers at successive stages of somatic embryogenesis in two cell lines. There were no mutations at the SSR loci at any of the successive developmental stages from PEMs to cotyledonary embryos, irrespective of whether or not the proliferation medium in which cell suspensions had been cultured contained auxin or cytokinin. The morphologies of plants regenerated from the cultures were similar, although withdrawal of auxin and cytokinin significantly stimulated the yield of both embryos and plants. We conclude, therefore, that the high genetic stability of somatic embryos in Norway spruce is unaffected by the induction of programmed cell death caused by withdrawal of auxin and cytokinin. 相似文献
57.
58.
Prof. Dr. D. Otto 《Journal of pest science》1997,70(2):30-33
The female sex pheromone ofL. decemlineata is an aphrodisiacum, switching on mating behaviour in contacting males. A biotest is described to estimate quantitatively the exciting power of a subject (female, isolated elytrae, glass dummy coated with extract) to males. The pheromone is present only in fertile females, also in freshly killed ones. It can be extracted by organic solvents. A dummy imitating a beetle's abdomen and contaminated with the residue of a female s wash solution is exciting to males too. Suitable solvents are ethylalcohol, acetonet, hexane. By this, the pheromone of 0,1 female is detectable. The residue can be taken up again with the same or an other solvent. The solution can be stored at ?18°C without significant losses, but at temperatures>+5°C their efficacy diminishes during 2 weeks. The exciting efficacy of the dry residue desreases to about 50% during nearly 4 weeks (at+22°C) or 9 weeks (at+5°C). The pheromone resists heating to about+160°C and is destroyed at higher temperatures. 相似文献
59.
通过在三种杨树无性系,I-214(Populus×euranericanacv.I-214)(ltalica)、中东杨(P.berolinensis)(Berolinensis)和群众杨(P.popularis35-44)(Popularis)一年生盆栽插条苗的木质部导入ABA和细胞分裂素,研究了这两类激素在气孔调控中的作用。尽管不同无性系的气孔在对ABA的敏感性上存在显著差异,但ABA仍可导致气孔的关闭,然而在蒸腾流中的细胞分裂素(与ABA共导入或分别导入)可以明显地抑制ABA的作用。并且玉米素还能推迟土壤干旱所诱导的气孔关闭,在水分胁迫条件下,内源细胞分裂素浓度下降而同时ABA上升.据此提出了复合胁迫信号的概念,即在根冠通讯中,是ABA和细胞分裂素共同调控气孔的运动。另外还研究了玉米素、激动素、6-BA等不同细胞分裂素与ABA的相互作用,结果发现6-BA与玉米素和激动素的作用相反,它不能抑制ABA的作用,反而促进其对气孔的关闭 相似文献
60.
Jürg Andreas Stückelberger Hans Rudolf Heinimann Edouard Charles Burlet 《European Journal of Forest Research》2006,125(4):377-390
Cost estimation is probably the most decisive factor in the process of computer-aided, preliminary planning for low-volume road networks. However, the cost of construction is normally assumed to be route-independent for a specific project area, resulting in sub-optimal layouts. This is especially true for mountainous terrain and in areas with unstable subsoil. Here, we present a model for more accurately estimating spatial variability in road life-cycle costs, based on terrain surface properties as well as geological properties of the subsoil. This parametric model incorporates four structural components: embankment, retaining structures, pavement, and drainage and stream-crossing structures. It is linked to a geo-database that allows users to derive location-specific parameter values as input. In applying this model, we have demonstrated that variability in costs ranges widely for mountainous areas, with the most expensive construction being approximately five times greater there than on more favorable sites. This variability strongly affects the optimal layout of a road network. First, when location-specific slope gradients are considered, costs are reduced by about 17% from those calculated via currently available engineering practices; when both slope gradient and geotechnical formations are included, those costs are decreased by about 20%. Second, the length of the road network is increased by about 4% and 10% respectively, compared with current practices. 相似文献