全文获取类型
收费全文 | 828篇 |
免费 | 35篇 |
国内免费 | 157篇 |
专业分类
林业 | 40篇 |
农学 | 204篇 |
基础科学 | 52篇 |
88篇 | |
综合类 | 297篇 |
农作物 | 137篇 |
水产渔业 | 91篇 |
畜牧兽医 | 62篇 |
园艺 | 29篇 |
植物保护 | 20篇 |
出版年
2024年 | 4篇 |
2023年 | 9篇 |
2022年 | 13篇 |
2021年 | 12篇 |
2020年 | 30篇 |
2019年 | 17篇 |
2018年 | 14篇 |
2017年 | 29篇 |
2016年 | 23篇 |
2015年 | 22篇 |
2014年 | 34篇 |
2013年 | 60篇 |
2012年 | 62篇 |
2011年 | 59篇 |
2010年 | 45篇 |
2009年 | 58篇 |
2008年 | 62篇 |
2007年 | 81篇 |
2006年 | 59篇 |
2005年 | 56篇 |
2004年 | 44篇 |
2003年 | 26篇 |
2002年 | 24篇 |
2001年 | 15篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 17篇 |
1997年 | 19篇 |
1996年 | 13篇 |
1995年 | 18篇 |
1994年 | 10篇 |
1993年 | 12篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1977年 | 1篇 |
1963年 | 2篇 |
排序方式: 共有1020条查询结果,搜索用时 31 毫秒
61.
62.
63.
采用RT-PCR方法从小麦品种豫教2号发育的籽粒中克隆出淀粉合酶I基因(starch synthase I,SSI)部分cDNA片段(795 bp)(GenBank No.EF221762),同源性比较结果显示,它与GenBank上已报道的SSI基因有高度同源性。以p WM101质粒为基础,构建了由35S启动子调控的SS I基因的反义表达载体p WM101SSI;另外,还以pFGC5941质粒为基础,构建了SSI基因的RNAi载体pFGC5941SSIsa,这些载体的构建为研究此基因的功能奠定了基础。 相似文献
64.
Abstract – To address the dearth of information on tagging effects and long-term survivorship of tagged fish in native and introduced species, laboratory and field investigations were undertaken on three non-native fish species (pumpkinseed Lepomis gibbosus ; topmouth gudgeon Pseudorasbora parva ; pikeperch Sander lucioperca ) tagged with coded-wire (CW), passive integrated transponder (PIT), radio (RT) telemetry and/or acoustic tags (AT), with survivorship of native brown trout ( Salmo trutta ) examined in the field. Laboratory results revealed high survivorship following tag attachment/insertion and resumption of feeding within 24–48 h of tagging (all mortalities could be attributed to an unrelated outbreak of fungal infection), with retention rates being high in both pumpkinseed and pikeperch but low in topmouth gudgeon (excluded from field studies). In the field, short-term post-operation survival was high in pikeperch, pumpkinseed and brown trout. In pumpkinseed and trout, 100% of RT fish survived a 24–30 day tracking study, with 60% and 80%, respectively, recaptured alive at least 3 months post-tagging. Of PIT tagged pumpkinseed, 44% were recaptured (after 6–18 months), with small-sized, CW-tagged fish (0.38 g weight) captured up to 1 year after tagging. In pikeperch, all AT fish except one (the smallest specimen) survived their full expected tracking period (i.e. tag life) – the single lost specimen survived at least half of its expected tracking period (i.e. 6 month battery life). Overall, the tagging methods used were highly effective in pumpkinseed and pikeperch, showing good retention and survival, but PIT tagging of topmouth gudgeon was plagued by low survivorship and tag rejection. 相似文献
65.
66.
肖扬 《黑龙江八一农垦大学学报》1998,10(1):53-57
汽车起动机是用来起动机的装置,它主要由三部分组成,即电机、传动机构和起动开发、本文介绍了汽车起动机常见故障的检查诊断步骤,并提出了具体修理方法。 相似文献
67.
王述洋 《林业机械与木工设备》2001,29(12):11-15
以AutoCAD R14为开发平台,综合运用ObjectARX SDK、Visual C^ 6.0及CNC技术,在研究了AutoCAD R14的数据结构、平面图形CNC自动编程及加工过程仿真和虚拟现实算法基础上,开发出一种适用于CNC木工镂铣、CNC线切割和CNC激光平面轨迹加工的、集CAD/CNC APT/虚拟加工功能于一体的集成技术。该技术可直接将二维AutoCAD图形快速自动转换成二维CNC加工程序,并可对所编程序进行虚拟加工实验,以检验加工的正确性和可靠性;解决了实际二维平面图形加工CAD/CAM集成及其一体化的瓶颈问题。 相似文献
68.
Walter Seidling 《European Journal of Forest Research》2007,126(4):529-544
Crown transparency estimates of Scots pine, Norway spruce, common beech, pedunculate and sessile oak, annually surveyed between
1990 and 2004 within a grid over Germany, provide a suitable response variable to study drought effects on forest trees. Major
climatic factors, available on a monthly basis as plot-specifically interpolated values and parameters of site and stand conditions,
biotic and other relevant factors were used as predictors in different cross- and length-sectional, and longitudinal models.
Stand age is a considerable and most constant driver of crown transparency in all species. Pine, spruce and beech responded—mainly
with a delay of 1 year—with some foliar loss in areas where there was a surplus of temperature after the generally hot and
dry summer of 2003. Parallel time-series analyses delivered species-specific geographic large-scale patterns with delayed
or recent precipitation deficits or temperature surpluses. Even if beech is partly responding in current years with leaf loss
towards precipitation surpluses, defoliation is especially high 1 year after hot summers, partly a result of high seed sets
after such summers. Crown condition of oak responds in dry and warm areas according to the drought stress hypothesis, however,
in cool and wet mountainous ranges oak responds after wet summers with higher defoliation. Longitudinal approaches revealed
for all 4-tree species significant relationships between crown condition and deviations from the long-term means of temperature,
precipitation but also global radiation and wind speed. Results do not always match the drought stress hypothesis, however,
this is not to expect considering the heterogeneous site, stand and climatic conditions across Germany. Complex interactions
of climatic and biotic factors also impede simple relationships. Soil-related clusters reveal higher sensitivity of spruce
and beech towards climatic drought factors on more acid soils with thin humus layers. Also clusters constructed from plot-specific
courses of defoliation reveal groups with rather closer relationships like a group of pine plots in the Oberpfalz, which seems
to be especially sensitive to summer drought. 相似文献
69.
本文以单相漏电保护器为例,阐明其几种错误接线的原因,并针对其不同的错误安装接线方法,提出了具体的改进措施。 相似文献
70.
农业是引发温室气体增多、生物多样性下降以及水体污染等生态安全事件的主要产业之一。在种种生态安全事件的挑战下,农业应该朝着绿色生态的方向进行转型已经成为多数国家的共识。欧盟的共同农业政策是世界上较早提倡农业绿色发展的农业政策之一。从1992年开始的麦克萨里改革到已经达成的《2023—2027年共同农业政策》临时协议,欧盟共同农业政策绿色生态转型体现出政策支持更加明确、以农民利益保护为重点、自愿性与强制性措施相结合、以数字技术为支撑以及多政策配套实施等改革趋向。在强调绿色发展与转型的新时代,欧盟共同农业政策的改革历程及发展趋向可以为中国农业政策改革提供一定的经验及启示,通过优化顶层设计、健全补贴机制、坚持弹性原则、提高科技能力、增加政策协同等措施来推进农业的绿色生态转型。 相似文献