全文获取类型
收费全文 | 1381篇 |
免费 | 81篇 |
国内免费 | 221篇 |
专业分类
林业 | 74篇 |
农学 | 48篇 |
基础科学 | 189篇 |
112篇 | |
综合类 | 450篇 |
农作物 | 23篇 |
水产渔业 | 68篇 |
畜牧兽医 | 638篇 |
园艺 | 38篇 |
植物保护 | 43篇 |
出版年
2024年 | 11篇 |
2023年 | 19篇 |
2022年 | 27篇 |
2021年 | 33篇 |
2020年 | 54篇 |
2019年 | 57篇 |
2018年 | 29篇 |
2017年 | 66篇 |
2016年 | 58篇 |
2015年 | 54篇 |
2014年 | 84篇 |
2013年 | 80篇 |
2012年 | 123篇 |
2011年 | 100篇 |
2010年 | 90篇 |
2009年 | 82篇 |
2008年 | 65篇 |
2007年 | 96篇 |
2006年 | 84篇 |
2005年 | 61篇 |
2004年 | 55篇 |
2003年 | 68篇 |
2002年 | 54篇 |
2001年 | 33篇 |
2000年 | 38篇 |
1999年 | 30篇 |
1998年 | 22篇 |
1997年 | 23篇 |
1996年 | 17篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 11篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1683条查询结果,搜索用时 15 毫秒
11.
柴油机喷油系统偶件间隙燃油泄漏量的试验与计算分析 总被引:1,自引:0,他引:1
柴油机喷油压力不断提高,承压偶件间的燃油泄漏对喷油过程的影响引起人们的关注,本文在已建立的恒压条件下偶件间燃油泄漏分析模型的基础上,得出传统喷油系统承压偶件间的燃油泄漏量的计算方法,阐述了在高喷射压力下泄漏量增加的影响因素和泄漏量的变化规律,分析了柱塞偶件泄漏量较大的原因和对喷油过程的影响,提出了采用较大的柱塞升程直径比能减少喷油泵不同运行工况的间隙泄漏量和压力变化,优化柴油机的性能。 相似文献
12.
13.
针对自然吸气直喷式柴油机,试验研究了喷油嘴压力室容积、喷油压力、喷孔直径、喷孔锥角、喷油提前角和空燃比等对HC排放的影响。试验结果表明,减少喷油嘴压力室容积,提高喷油压力,减小喷孔直径,适当加大喷孔锥我和小负荷时喷油提前角域可大幅度降低柴油机HC排放。 相似文献
14.
Selecting beneficial DNA variants is the main goal of animal breeding. However, this process is inherently inefficient because each animal only carries a fraction of all desirable variants. Genome editing technology with its ability to directly introduce beneficial sequence variants offers new opportunities to modernize animal breeding by overcoming this biological limitation and accelerating genetic gains. To realize rapid genetic gain, precise edits need to be introduced into genomically-selected embryos, which minimizes the genetic lag. However, embryo-mediated precision editing by homology-directed repair (HDR) mechanisms is currently an inefficient process that often produces mosaic embryos and greatly limits the numbers of available edited embryos. This review provides a summary of genome editing in bovine embryos and proposes an embryo-mediated accelerated breeding scheme that overcomes the present efficiency limitations of HDR editing in bovine embryos. It integrates embryo-based genomic selection with precise multi-editing and uses embryonic cloning with elite edited blastomeres or embryonic pluripotent stem cells to resolve mosaicism, enable multiplex editing and multiply rare elite genotypes. Such a breeding strategy would enable a more targeted, accelerated approach for livestock improvement that allows stacking of beneficial variants, even including novel traits from outside the breeding population, in the most recent elite genetic background, essentially within a single generation. 相似文献
15.
为有效防控柑橘黄龙病,于2017年在佛罗里达大学柑橘研究与教育中心的奥本代尔市柑橘试验场进行田间试验筛选黄龙病的防治药剂及其浓度,测定注射土霉素后叶片中柑橘黄龙病菌亚洲种Cadidatus Liberibacter asiaticus、土霉素、淀粉含量、柑橘产量、出汁率、可溶性固形物含量和酸度,显微镜下观察注射土霉素后淀粉粒的分布。结果表明,浓度为1.6g/株土霉素处理180 d后柑橘叶片中黄龙病菌亚洲种含量减少幅度最大,为91.78%;注射浓度为1.6g/株土霉素后7d,叶片中土霉素含量达142.2 μg/kg,注射后11 d叶片中土霉素含量达到最大,为239.8 μg/kg,注射后45 d叶片中土霉素含量低至99.6 μg/kg以下;注射后7~90d,叶片中黄龙病菌亚洲种含量呈波浪形变化,注射90 d后叶片中黄龙病菌亚洲种含量一直处于增长趋势,叶片中黄龙病菌亚洲种含量总体随着土霉素含量的升高而降低;注射浓度为1.6g/株土霉素后,叶片中淀粉含量大幅度下降,60d时达到最低值,为3.3 μg/mm2,90d时达到峰值,为14.5 μg/mm2;单株产量为16.7 kg,与注射浓度为0.8 g/株土霉素处理差异不显著,但均显著高于其它2个处理;柑橘出汁率、可溶性固形物和酸度均与清水对照差异不显著。表明土霉素可有效抑制黄龙病菌亚洲种,减少柑橘叶片内淀粉含量,增加柑橘产量,但对果实品质未产生显著影响。 相似文献
16.
17.
小反刍兽疫(PPR)是一种由小反刍兽疫病毒引起的疾病,主要感染山羊和绵羊。2021年为加快推进小反刍兽疫无疫区建设,实现小反刍兽疫非免疫无疫区建设标准,长沙市某县拟在本地开展小反刍兽疫退出强制免疫风险评估。通过对小反刍兽疫监测流调、危害识别、风险路径的确定和风险因素层级评估等方法进行的定性风险评估初步显示,在该地取消小反刍兽疫强制免疫后可能会发生小反刍兽疫的风险等级为中。在风险管理措施上,提出该地退出强制免疫应推迟一年,重点完善政策支持、加强监测排查、加强检疫监管、强化培训宣传等建议。 相似文献
18.
19.
Gene expression in black tiger prawns (Penaeus monodon) was studied following intra-muscular injection of CMVGal plasmid into the second abdominal segment. We used an in situ staining technique to detect -gal expression in one- and three-month-old injected prawns. We found that only one of the three-month-old prawns expressed the marker gene (2 days after injection), and the site of expression was confined to the sixth abdominal segment away from the injection site. We repeated the experiment on a new batch of three-month-old prawns, but using fluorometric determination technique. This time we found that -gal expression was detected (6/42) at the site of injection after 2, 7, and 14 days. In two other test samples, transgene expression was detected in the sixth abdominal segment only, further confirming the possibility of injected DNA dispersal. The results of the study also suggest that direct gene transfer is a feasible technique in black tiger prawns. 相似文献
20.
The Effects of Light Salting on Physicochemical Characteristics of Frozen Cod (Gadus morhua) Fillets
《Journal Of Aquatic Food Product Technology》2013,22(3-4):287-301
Abstract The effects of light salting by brine injection and brine immersion on physicochemical and textural properties of cod fillets were evaluated. Light salting significantly increased yield and water holding capacity. Adding brine injection to the process can be used to shorten the process time needed to obtain the desired salt content and increase yield. The effects on chemical composition were most significant in salt content, but water and protein content were also affected. Water content decreased from the tail to head direction of the fillets, both in unsalted and light salted fillets. Changes in protein content were in opposite proportion to changes in water content. This could be seen in the fresh fish and also after freezing, both in unsalted and light salted fillets. Texture of the fish was not significantly affected by salting and freezing. 相似文献