全文获取类型
收费全文 | 39952篇 |
免费 | 2037篇 |
国内免费 | 4032篇 |
专业分类
林业 | 3093篇 |
农学 | 4773篇 |
基础科学 | 1847篇 |
7544篇 | |
综合类 | 17659篇 |
农作物 | 3721篇 |
水产渔业 | 857篇 |
畜牧兽医 | 3000篇 |
园艺 | 1175篇 |
植物保护 | 2352篇 |
出版年
2024年 | 305篇 |
2023年 | 830篇 |
2022年 | 1426篇 |
2021年 | 1627篇 |
2020年 | 1672篇 |
2019年 | 1771篇 |
2018年 | 1315篇 |
2017年 | 1985篇 |
2016年 | 2236篇 |
2015年 | 1885篇 |
2014年 | 2322篇 |
2013年 | 2601篇 |
2012年 | 3125篇 |
2011年 | 2947篇 |
2010年 | 2338篇 |
2009年 | 2228篇 |
2008年 | 1877篇 |
2007年 | 2081篇 |
2006年 | 1690篇 |
2005年 | 1468篇 |
2004年 | 1131篇 |
2003年 | 978篇 |
2002年 | 715篇 |
2001年 | 777篇 |
2000年 | 631篇 |
1999年 | 564篇 |
1998年 | 491篇 |
1997年 | 417篇 |
1996年 | 366篇 |
1995年 | 383篇 |
1994年 | 297篇 |
1993年 | 282篇 |
1992年 | 267篇 |
1991年 | 220篇 |
1990年 | 188篇 |
1989年 | 145篇 |
1988年 | 121篇 |
1987年 | 105篇 |
1986年 | 64篇 |
1985年 | 22篇 |
1984年 | 20篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 20篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 13篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1962年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
乌梁素海生态恢复机理与工程技术的研究 总被引:2,自引:1,他引:2
在我国干旱区典型草型湖泊—乌梁素海设立试验基地 ,进行生态恢复工程试验研究。研究表明 :乌梁素海受富营养化影响 ,正在向芦苇沼泽—碱蓬盐化草甸—白刺荒漠方向演化。生态恢复机理是 :( 1 )减少大型水生植物有机氮、磷向底质的沉降 ,削弱内源性营养物负荷的积累与储备 ;( 2 )减少大型水生植物死亡后矿化成氨态氮 ;( 3)控制底质中有机氮向水体释放生成氨态氮。采用机械化方式收割大型水生植物转移营养盐 ,抑制生物促淤效应以及对芦苇区进行园田化生态管理是乌梁素海生态恢复的关键技术 ,也是乌梁素海环境与资源持续发展的核心问题 相似文献
102.
AIM:To study the changes of excretive amount of albumin(ALB), N-acetyl-beta-D-glucosaminidase(NAG) in patients with high altitude polycythemia(HAPC) at different altitude and its mechanism.METHODS:Urinary ALB, NAG, activity of red blood cell superoxide dismutase(RBC-SOD), malonyldialdehyde(MDA) and erythrocyte filtration index(EFI) of 231 healthy subjects and 86 patients with HAPC at different altitude were detected.RESULTS:Excretive amount of urinary ALB, NAG, and plasma MDA, EFI were higher, and RBC-SOD was lower in patients with HAPC than those in healthy subjects, the changes were significantly obvious, with increasing altitude. Urinary ALB and NAG were negatively correlates to EFI, and no correlated to the content of MDA and RBC-SOD.CONCLUSIONS:EFI exertes an independent influence on urinary ALB and NAG. The decrease in erythrocyte deformability caused by the increase of peroxidation of lipids might participate in the pathogenesis and progress of the increase of excretive amount of ALB and NAG in HAPC. 相似文献
103.
关中平原小麦产量对气候变化区域响应的评价模型研究 总被引:4,自引:0,他引:4
根据关中地区宝鸡、西安、渭南与咸阳 4地 (市 )的 1 949~ 1 999年的逐年小麦单产记录序列以及 4地 (市 )的气象观测站点自建站以来至 2 0 0 0年近 5 0年的气象记录序列 ,对关中地区小麦产量与年均温、年降水作相关分析 ;探讨了关中地区小麦单产对气候变化区域响应的评价模型。结果发现 :关中平原气候具有暖干化趋势 ;随着气温变暖 ,小麦产量增加幅度减小 ;小麦产量对降水波动的响应比对气温波动的响应显著。 相似文献
104.
Z. Ngoko K.F. Cardwell W.F.O. Marasas M.J. Wingfield R. Ndemah F. Schulthess 《European journal of plant pathology / European Foundation for Plant Pathology》2002,108(9):893-902
The aim was to identify biological and physical factors responsible for reducing maize yield in Cameroon. Two surveys were conducted in 137 fields in two agroecological zones in 1995–1997. In the Humid Forest (HF), Bipolaris maydis, Stenocarpella macrospora, Puccinia polysora, Rhizoctonia solani and soil fertility were factors that reduced maize production in 1995 and 1996. In the Western Highlands (WHL), Cercospora zeae-maydis, and the interaction between soil fertility and maize variety were the most important constraints to maize production in 1996. In 1997, C. zeae-maydis, S. macrospora, physiological spot and stem borer damage (Busseola fusca) were negatively related to ear weight. The combination of these biological factors (diseases and insects), and the physical parameter of soil fertility were responsible for reducing maize yield in these selected benchmarks of Cameroon. Maximum potential yield reductions were estimated at 68% due to B. maydis and 46% due to S. macrospora, respectively, in the HF in 1995. In 1996, maximum potential yield reductions in the HF were estimated at 34%, 41% and 30% due to S. macrospora, P. polysora and R. solani, respectively. In the WHL, C. zeae-maydis had the potential to cause a yield reduction of 79% in 1996. In the WHL in 1997, the interaction between C. zeae-maydis and B. fusca, stem diseases and the physiological spot caused potential reductions of 52%, 34% and 39%, respectively. 相似文献
105.
20%多效唑·甲哌 FEE7 微乳剂防止小麦倒伏和增产机理研究 总被引:1,自引:0,他引:1
冬小麦二棱期喷施植物生长调节剂20%多效唑·甲哌鎓微乳剂375 mL/hm2,可以显著抑制茎秆基部节间伸长,增加各节间充实度,其中赤霉素(Gas)和生长素(IAA)降低,可显著增强小麦抗倒伏能力和降低田间倒伏率.处理还协调了穗数、穗粒数和粒重的关系,增产幅度6.2%~28.6%.增产原因可能在于促进籽粒灌浆强,增加籽粒中内源Gas、IAA、细胞分裂素(CTKs)的水平,增强了籽粒库活性,同时促进茎叶中干物质向籽粒运转. 相似文献
106.
107.
108.
氟虫腈(锐劲特)对水稻害虫防治效果及增产效应 总被引:6,自引:0,他引:6
为了阐明新一代杀虫剂氟虫腈(锐劲特)对二化螟、三化螟、稻纵卷叶螟的防治效果及应用前景,进行了水稻盆栽试验、田间防效试验,并对施用锐劲特后水稻叶绿素含量、功能叶叶面积和产量进行了测定。结果表明,锐劲特施药后13天接虫的三化螟幼虫死亡率仍高达94.44%。在田间防效试验中,每公顷施用锐劲特80%WG有效成分24g防治二化螟,防止枯心效果达97.62%,防止白穗效果达94.44%,害虫死亡率达96.15%;每公顷施用锐劲特5%SC有效成分22.5g防治晚稻三化螟,保苗效果可达95.91%,害虫死亡率达99.04%;每公顷施用锐劲特5%SC有效成分30g防治稻纵卷叶螟,保叶效果达97.88%。叶绿素含量比对照增加32.4%;每公顷施用锐劲特80%WG有效成分36g时,功能叶叶面积增加16%~27.5%,并且杂交稻博优湛19比常规稻早糯3321和早熟早籼815对锐劲特更敏感。每公顷施用锐劲特5%SC有效成分22.5~37.5g时,水稻株高增加4.0~6.1cm,每稻丛穗数增加2.6%~31.18%,结实率提高19.43%~33.97%,水稻产量增加21.58%~28.19%。 相似文献
109.
110.
Associations among Hop latent virus (HpLV), Hop mosaic virus (HpMV), and Apple mosaic virus (ApMV) were assessed in five hop cultivars at four commercial hop-growing regions in Victoria and Tasmania, Australia. The presence or absence of each virus was confirmed by double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). Spatial patterns of virus-infected plants were characterized using the Spatial Analysis by Distance IndicEs ( sadie ) system of pattern analysis. The association among viruses (occurrence and covariation) was assessed using the Jaccard similarity index, Spearman's rank correlation coefficient, and sadie . The spatial pattern of plants infected by HpLV and HpMV ranged from random to highly aggregated depending upon the cultivar infected and the mean disease incidence. The spatial pattern of plants infected by ApMV was aggregated in six of the seven plots where ApMV was present. A strong positive association between HpLV and HpMV was found in all cultivars at all locations. This association may be the result of the viruses sharing a common aphid vector species, the presence of one virus enhancing the ability of the aphid vector to acquire the other virus either through transencapsidation or influences on virus titre, or mixed infections within source plants. Significant associations, positive or negative, were found less frequently between HpLV and ApMV, and HpMV and ApMV. 相似文献