全文获取类型
收费全文 | 685篇 |
免费 | 33篇 |
国内免费 | 35篇 |
专业分类
林业 | 95篇 |
农学 | 69篇 |
基础科学 | 27篇 |
41篇 | |
综合类 | 354篇 |
农作物 | 27篇 |
水产渔业 | 5篇 |
畜牧兽医 | 28篇 |
园艺 | 97篇 |
植物保护 | 10篇 |
出版年
2024年 | 3篇 |
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 16篇 |
2020年 | 12篇 |
2019年 | 14篇 |
2018年 | 13篇 |
2017年 | 22篇 |
2016年 | 24篇 |
2015年 | 30篇 |
2014年 | 46篇 |
2013年 | 36篇 |
2012年 | 54篇 |
2011年 | 68篇 |
2010年 | 54篇 |
2009年 | 38篇 |
2008年 | 40篇 |
2007年 | 34篇 |
2006年 | 36篇 |
2005年 | 31篇 |
2004年 | 21篇 |
2003年 | 34篇 |
2002年 | 19篇 |
2001年 | 21篇 |
2000年 | 12篇 |
1999年 | 11篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 11篇 |
1994年 | 5篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
排序方式: 共有753条查询结果,搜索用时 15 毫秒
21.
22.
The colored patterns on arbitrary cut plane is an important method in 3D data-field visualization of finite element.By using the technology of the Object-Oriented Programming and the method of scan-line,the colored patterns on arbitrary cut plane are given.The example by the OPENGL of Visual C++ R6 can support the theory satisfactorily. 相似文献
23.
The discretization of real values is always one of the key problems to be solved in the domain of machine learning for its great contribution to speeding up the followed learning algorithms, cutting down the real demand of algorithms on running space and time, and improving the clustering capability of the ultimate learning results. The basic characteristics and framework of discretization approaches based on rough set model are analyzed at first, then the different measurements of the importance of candidate cuts are discussed and researched. Two new heuristic algorithms are put forward to finally select the useful cuts from a candidate set. The selected cuts of the two algorithms will adequately maintain the discernible relation of information systems for their full considering the specialty of rough set, which perfectly embodies the advantages of this theory. Moreover, excellent discretization results may be expected through these heuristic algorithms. 相似文献
24.
New aspects of soybean somatic embryogenesis 总被引:4,自引:0,他引:4
Somatic embryo formation from immature cotyledons was improved in the following ways: by cutting into sections, supplementing culture media with spermine and using solid/liquid/solid type of culture. Cut cotyledons of the eight genotypes examined expressed a higher ability for somatic embryogenesis than whole cotyledons. Of the three polyamines tested, spermine considerably stimulated and putrescine slightly inhibited induction of somatic embryos. The ability of embryoid formation on medium with spermidine depended on the genotype. The solid/liquid/solid type of culture was better than the continuous solid culture. The best nitrogen ion content for the subculture of somatic embryos was 10 mM NH4NO3 and 30 mM KNO3. The possibility of using these modifications in Agrobacterium transformation is discussed. 相似文献
25.
Summary Thirty, one-season-old Rosa canina Inermis seedlings (8–12 mm in diameter) were grown in the greenhouse. After 5 months, single-node softwood cuttings were made of each plant. Analysis of variance demonstrated marked differences between the internode length, number of leaflets per leaf and the leaf area of the original seedling, and between the time of axillary bud-break, axillary sprout length and weight of adventitious roots of their 23-day-old cuttings. Clonal root weight of cuttings was highly significantly correlated with: number of leaflets per leaf (r=–0.65), leaf area (r=+0.65), and days to axillary bud-break (r=+0.62). The origin of heterogeneity among Inermis seedling rootstocks, its probable effect on the flower production of cut roses and its possible use in the selection for clonal rootstocks are discussed. 相似文献
26.
壳聚糖保鲜液对唐菖蒲切花保鲜的影响 总被引:9,自引:0,他引:9
试验采用0.25‰,0.5‰,0.75‰,1‰,1.25‰的壳聚糖保鲜液处理唐菖蒲切花,观察切花寿命和开花率,旨在探索壳聚糖保鲜液处理切花的效果。试验结果表明,1‰壳聚糖保鲜液处理后的鲜切花,寿命最长,开花率最高。 相似文献
27.
The South African Ornithogalum L. species are divided into three subgenera; Aspasia, Urophyllon and Osmyne. The species of horticultural importance, such as O. thyrsoides, are found in the subgenus Aspasia, and all have pure coloured flowers ranging from white to yellow to deep orange. Accessions numbering 299 were collected and grown under comparative conditions. Characteristics of use in discriminating superior parents for hybridization were measured, such as: leaf position and colour; stem length; shape, size and density of the inflorescence; size, shape and colour of the flower; the presence of visual virus symptoms and the reaction of leaf cuttings to tissue culture propagation. The aim was to quantify the variation according to the characteristics deemed of importance for selecting genotypes for cut or pot flower breeding. Variation for each of the traits measured was observed in each of the species. The evaluation of the Ornithogalum improved the process of selecting accessions as parents in hybridization by providing an indication of the variation present in the natural populations. Thus specific accessions could be selected to combine either at interspecific or intraspecific level to breed for distinct types. 相似文献
28.
坡林地间种红豆草技术措施试验研究 总被引:1,自引:0,他引:1
林地间种红豆草能促进幼树生长,充分利用土地潜力,增加经济收入。坡地采用人工“立体”法种植红豆草比一般单一深度“平播”法种植红豆草越冬率提高65%。冬前复土措施是红豆草播后田间管理的重要环节。红豆草适宜的平茬高度为5~10cm。 相似文献
29.
通过妃子笑荔枝未老熟末次梢进行剪截处理后,结果表明:剪截处理能有效地促进成花、挂果,全部剪截处理的末次梢成花率、平均穗坐果率显著高于其他处理;剪截末次梢2/3处理次之;不剪截的几乎不成花、不坐果。 相似文献
30.
研究了苏丹原油加剂时的处理温度、处理中的温升、原油含水量、处理过程听轻组分的挥发等因素对加剂处理效果的影响。研究结果表明,对于高凝点、高粘度的苏丹混合原油,随着处理温度的升高,原油粘度降低幅度增大;在原油处理过程中,温度回升将抑制化学剂的改性效果;原油中水含量减小,加剂生效果明显;在非密闭处理装置中,原油轻质组分的挥发是影响加剂改性效果的重要因素之一,特别在慢降温处理过程中影响更大。 相似文献