全文获取类型
收费全文 | 6437篇 |
免费 | 391篇 |
国内免费 | 485篇 |
专业分类
林业 | 825篇 |
农学 | 557篇 |
基础科学 | 305篇 |
794篇 | |
综合类 | 2918篇 |
农作物 | 420篇 |
水产渔业 | 201篇 |
畜牧兽医 | 689篇 |
园艺 | 271篇 |
植物保护 | 333篇 |
出版年
2024年 | 32篇 |
2023年 | 86篇 |
2022年 | 148篇 |
2021年 | 175篇 |
2020年 | 160篇 |
2019年 | 201篇 |
2018年 | 125篇 |
2017年 | 204篇 |
2016年 | 253篇 |
2015年 | 225篇 |
2014年 | 315篇 |
2013年 | 297篇 |
2012年 | 443篇 |
2011年 | 468篇 |
2010年 | 404篇 |
2009年 | 416篇 |
2008年 | 324篇 |
2007年 | 414篇 |
2006年 | 430篇 |
2005年 | 355篇 |
2004年 | 294篇 |
2003年 | 232篇 |
2002年 | 193篇 |
2001年 | 155篇 |
2000年 | 137篇 |
1999年 | 110篇 |
1998年 | 70篇 |
1997年 | 72篇 |
1996年 | 67篇 |
1995年 | 67篇 |
1994年 | 67篇 |
1993年 | 54篇 |
1992年 | 55篇 |
1991年 | 41篇 |
1990年 | 31篇 |
1989年 | 32篇 |
1988年 | 23篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 17篇 |
1984年 | 25篇 |
1983年 | 27篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1963年 | 1篇 |
排序方式: 共有7313条查询结果,搜索用时 15 毫秒
51.
为探明延边地区烟草病毒病的发病规律,为生产优质高产烟叶提供科学有效的病毒病预防措施,简要分析了延边地区2010和2011年病毒病与气象因子的关系.结果表明,延边地区进入6月份,当日平均温度高于16.0℃,烟草病毒病就可以发生.病毒病发病前10d的日平均温度高,日照时数大于6h的天数多,降雨量少的情况下,病毒病发生严重. 相似文献
52.
53.
Tea Bai J. Robert Britton Stephen P. Rice Andrew G. Pledger 《Ecology of Freshwater Fish》2019,28(1):110-122
The spawning success of lithophilic salmonids is strongly influenced by the fine sediment content (“fines”) of spawning substrates, yet knowledge on the impacts of fines on the spawning of non‐salmonid lithophiles remains limited, despite their ecological and socio‐economic importance in European rivers. Consequently, the aim here was to use an ex‐situ experiment to investigate the impact of sand content on egg survival and timing of larval emergence of the surface‐spawning cyprinid European barbel Barbus barbus. Thirty incubator boxes within a recirculating system were filled with one of five experimental sediment mixtures (0%–40% sand by mass) that each contained 300 fertilised eggs at a depth of 50 mm. Emerged, free‐swimming larvae were captured and counted daily to assess grain‐size effects on larval survival and emergence. Specifically, total proportion of emerged larvae, cumulative daily proportion of emerged larvae and time required to reach 50% emergence were measured during the study. Whilst the proportion of sand in the sediments did not have a significant impact on egg‐to‐emergence survival (mean survival per treatment 75%–79%), it significantly affected the timing of larval emergence to the water column; early emergence was detected in treatments with elevated sand content (on average, 50% emergence after 12–13 days versus 19 days in the control). Similar to findings from salmonid studies, these results suggest high sand content in spawning gravels can influence timing of larval emergence and potentially cyprinid lithophilic fish survival. 相似文献
54.
55.
为对秸秆覆盖混埋还田耕整地技术模式进行深入研究,需要研发配套圆盘耙联合整地机具,机具研发过程中首先要解决受秸秆影响的堵塞问题。通过进行影响因素的单因素试验和3因素3水平正交试验,探索独立连接圆盘耙单体排列参数对秸秆堵塞问题的影响规律。通过单因素试验确定对应机具通过性评分为3分的三个因素临界值:耙片间距为275 mm,横梁间距为900 mm,错位间距取值全部满足试验要求。正交试验极差分析结果表明:耙片排列参数对机具堵塞影响主次顺序为耙片间距B,横梁间距L,错位间距S;机具通过性的较优组合为耙片间距325 mm,横梁间距1 100 mm,错位间距0 mm。正交试验方差分析结果表明机具排列参数耙片间距和横梁间距对机具堵塞影响显著,错位间距对机具堵塞影响不显著。正交试验回归分析结果得到拟合度较高的机具通过性回归方程:T=0.833B+0.667L。本文试验结果为圆盘耙联合整地机的开发与设计提供数据参考。 相似文献
56.
《畜牧兽医杂志》2012,39(3)
进行了4个钢筋混凝土(RC)超短柱、4个型钢混凝土(SRC)超短柱和6个RC分体柱的滞回性能试验研究.8个超短柱的剪跨比为1;6个分体柱的剪跨比为2.4.试验结果表明,RC超短柱的变形能力不满足现行抗震规范要求.不设剪力连接件的SRC超短柱的破坏模式为黏结破坏,与RC超短柱相比,其抗剪承载力和变形能力并无明显提高;设置剪力连接件的SRC超短柱的破坏模式为斜压破坏,其抗剪承载力和变形能力显著提高,但构件的变形能力仍然难以满足现行抗震规范要求.试验结果还表明,在RC超短柱中开缝,形成剪跨比大于2的RC分体柱,可有效提高柱子的延性和变形能力.对于RC分体柱,随轴压比的提高,构件的抗弯承载力提高,但延性和变形能力下降;当设计轴压比大于0.7时,RC分体柱的变形能力不满足现行抗震规范要求.根据试验结果,提出了SRC超短柱的剪力连接件设计方法和RC分体柱的设计建议. 相似文献
57.
58.
Urinary Neutrophil Gelatinase‐associated Lipocalin as a Marker for Identification of Acute Kidney Injury and Recovery in Dogs with Gentamicin‐induced Nephrotoxicity 下载免费PDF全文
59.
Effects of different dl‐selenomethionine and sodium selenite levels on growth performance,immune functions and serum thyroid hormones concentrations in broilers 下载免费PDF全文
This trial was conducted in a 2 × 3 + 1 factorial arrangement based on a completely randomized design to evaluate the effects of different dl ‐selenomethionine (dl ‐Se‐Met) and sodium selenite (SS) levels on growth performance, immune functions and serum thyroid hormones concentrations in broilers. A total of 840 Ross 308 broilers (7 days old) were allocated by body weight to seven treatments (three replicates of 40 birds each treatment) including (1) basal diet (containing 0.04 mg of selenium (Se)/kg; control) without supplementary Se; (2, 3 and 4) basal diet + 0.05, 0.15 or 0.25 mg/kg Se as SS; (5, 6 and 7) basal diet + 0.05, 0.15 or 0.25 mg/kg Se as dl ‐Se‐Met. The experiment lasted 42 days. The results revealed that dietary Se supplementation improved (p < 0.05) average daily gain, feed efficiency, immune organ index, serum immunoglobulin A (IgA), immunoglobulin G (IgG), immunoglobulin M (IgM) and triiodothyronine (T3) concentrations and decreased (p < 0.01) thyroxine (T4)/T3 ratio in serum compared with the control. Broilers receiving the dl ‐Se‐Met‐supplemented diets had higher (p < 0.05) feed efficiency, thymus index, the amounts of IgA, IgG, IgM and T3 as well as lower (p < 0.05) serum T4 concentrations and T4/T3 ratio than those consuming the SS‐supplemented diets. Serum IgA and IgM levels of broilers fed 0.15 mg Se/kg were significantly higher (p < 0.05) than those of broilers fed 0.05 or 0.25 mg Se/kg. In summary, we concluded that dl ‐Se‐Met is more effective than SS in increasing immunity and promoting conversion of T4 to T3, thus providing an effective way to improve the growth performance of broilers. Besides, based on a consideration of all experiment indices, 0.15 mg Se/kg was suggested to be the optimal level of Se supplementation under the conditions of this study. 相似文献
60.
张文修 《湖南农业大学学报(自然科学版)》2007,(2)
陆九渊提出:“六经注我,我注六经。”又说:“学苟知道,六经皆我注脚。”在他看来,六经乃圣人的“写心之书”。圣人之心与我之本心不异,如能照自己的本心天德去做,便是真能发挥六经者。堂堂正正地做人,是人生第一等的学问。因此人应致力于道德实践,成就完美人格。果能如此,六经便成为自己的注脚。陆九渊无一部经学注疏之作,他以生命实践为经典诠释的形式,相比之下,儒者注经成了等而次之的学问了。 相似文献