全文获取类型
收费全文 | 1076篇 |
免费 | 83篇 |
国内免费 | 121篇 |
专业分类
林业 | 22篇 |
农学 | 101篇 |
基础科学 | 136篇 |
92篇 | |
综合类 | 519篇 |
农作物 | 100篇 |
水产渔业 | 99篇 |
畜牧兽医 | 130篇 |
园艺 | 19篇 |
植物保护 | 62篇 |
出版年
2024年 | 4篇 |
2023年 | 26篇 |
2022年 | 28篇 |
2021年 | 32篇 |
2020年 | 44篇 |
2019年 | 43篇 |
2018年 | 23篇 |
2017年 | 49篇 |
2016年 | 48篇 |
2015年 | 50篇 |
2014年 | 68篇 |
2013年 | 58篇 |
2012年 | 98篇 |
2011年 | 86篇 |
2010年 | 82篇 |
2009年 | 63篇 |
2008年 | 78篇 |
2007年 | 78篇 |
2006年 | 44篇 |
2005年 | 38篇 |
2004年 | 36篇 |
2003年 | 24篇 |
2002年 | 20篇 |
2001年 | 18篇 |
2000年 | 21篇 |
1999年 | 14篇 |
1998年 | 16篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
排序方式: 共有1280条查询结果,搜索用时 15 毫秒
1.
2.
摘要:为研究同一品种不同发育阶段干旱胁迫对玉米植株高度、果穗性状以及产量的影响程度,设置全生育期供水充足、大田自然干旱、拔节期控水、抽雄期控水、拔节期控水-复水、抽雄期控水-复水6种处理的对比试验,用对比分析的方法比较不同处理下玉米的株高、果穗性状以及产量之间的差异。结果表明:干旱胁迫使玉米植株矮小,果穗长减小7.88%~54.55%,果穗粗减小14.58%~52.08%,秃尖长度增大66.67%~258.33%,百粒重减小0.99%~41.36%,单株产量减少15.03%~94.41%,最终导致减产23.57%~90.03%。不同发育阶段干旱胁迫对产量的影响差异显著,全生育期干旱最为严重,几乎无产量,拔节期次之,抽雄期干旱胁迫影响最小,复水后由于部分补偿了前期干旱胁迫所减少的生物量,果穗性状、百粒重均有好转,减产幅度减轻。 相似文献
3.
4.
电子商务专业人才培养研究 总被引:4,自引:0,他引:4
本文论述了我国与国外电子商务专业人才培养情况 ,以及当前国内电子商务人才的需求状况 ,从而确立我国电子商务人才培养方向。 相似文献
5.
本文运用SCM的基础理论,阐述了在当前信息技术环境下SCM模式的运用,探讨了目前我国森工企业在运用SCM模式中所存在的一些问题和误区。 相似文献
6.
Paul Joseph Dimitri Bakirtzis Audrey Vieille 《Wood material science & engineering》2015,10(1):130-144
AbstractSaving lives and properties are of primary importance in fire disasters. Unfortunately, current fire detectors are not fast enough to allow the detection of many fires, especially, at the smouldering stages. Some preliminary studies on laevoglucosan (LG), as an important product from cellulose degradation, have shown interesting properties and could be detected by devices classified as “electronic noses” (e-noses). In the present work, the mechanisms of pyrolysis of some ligno-cellulosic materials were investigated using thermo-gravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy and by a tube furnace with a view to determining the major degradation products from wood, white paper and cardboard samples. Additionally, an odour sensor, made of tin oxide semiconductor thin film, was employed to evaluate its sensitivity in detecting LG. It was found that LG can be readily found among the thermal degradation products of cellulosic materials in question, and that the metal oxide sensor employed was sufficiently sensitive in detecting its presence. Therefore, the work opens up the potential of using such a sensor as an “e-nose” for the early detection of fires stemming from forest product fire loads in storage places and in other enclosures. 相似文献
7.
采用不同母株年龄的穗条、不同类型的插条、不同基质配比及不同浓度生根剂进行巨尾桉扦插育苗试验。结果表明:巨尾桉插条随母株年龄增大其生根率和生长量下降;嫩枝扦插生根率高、平均根数多、生长快;用珍珠岩和红土等量均匀混合的基质扦插效果好;用质量分数为50×10-6~200×10-6浓度的IBA浸泡2 h,能较大幅度提高扦插成活率。 相似文献
8.
Charles N. Cathcart Keith B. Gido Mark C. McKinstry Peter D. MacKinnon 《Ecology of Freshwater Fish》2018,27(1):492-505
Quantifying fish movements in river networks helps identify critical habitat needs and how they change with environmental conditions. Some of the challenges in tracking fish movements can be overcome with the use of passive integrated transponder (PIT) tagging and antennas. We used PIT technology to test predictions of movement behaviour for four fish species at a mainstem–tributary confluence zone in an arid‐land river system. Specifically, we focused on the McElmo Creek tributary confluence with the San Juan River in south‐western Utah, USA. We quantified variation in species occurrences at this confluence zone from May 2012 to December 2015 relative to temporal and environmental conditions. We considered occurrences among species relative to tagging origins (tributary versus mainstem), season and time of day. Generally, fishes tagged in the focal tributary were more likely to be detected compared to fish tagged in the mainstem river or other tributaries. Additionally, adults were most likely to be detected across multiple years compared to subadults. Based on a Random Forests model, the best performing environmental variables for predicting seasonal detections included mainstem discharge during run‐off season (razorback sucker Xyrauchen texanus), tributary discharge during monsoon season (Colorado pikeminnow Ptychocheilus lucius) and mainstem water temperature (flannelmouth sucker Catostomus latipinnis and channel catfish Ictalurus punctatus). The variable responses by endemic and introduced fishes indicate tributary habitats provide several key functions within a fish community including spawning, rearing, foraging and refuge. 相似文献
9.
10.
Mapping and validation of the quantitative trait loci for leaf stay‐green‐associated parameters in maize 下载免费PDF全文
Zhen Yang Xin Li Ning Zhang Xiaolei Wang Yuna Zhang Yulong Ding Benke Kuai Xueqing Huang 《Plant Breeding》2017,136(2):188-196
Functional stay‐green is generally regarded as a desirable trait of varieties in major crops including maize. In this study, we used an F3:4 recombinant inbred line population with 165 lines from a cross between a stay‐green inbred line (Zheng58) and a model inbred line (B73) using 211 polymorphic simple sequence repeat markers to map quantitative trait loci for three stay‐green‐associated parameters, chlorophyll content, photosystem II photochemical efficiency and stay‐green area, at maturity stage, detected a total of 23 quantitative trait loci (QTL) on nine chromosomes. Single QTL explained 3.7–13.5% of the phenotypic variance. Additionally, we validated some important stay‐green QTL using a heterogeneous inbred family approach and found that the stay‐green‐associated parameters were significantly correlated with the plant yield. This study may contribute to a better insight into the regulatory mechanism behind leaf stay‐green in maize and a novel development of elite maize varieties with delayed leaf senescence through molecular marker‐assisted selection. 相似文献