全文获取类型
收费全文 | 57306篇 |
免费 | 3747篇 |
国内免费 | 4748篇 |
专业分类
林业 | 4062篇 |
农学 | 3850篇 |
基础科学 | 2753篇 |
23886篇 | |
综合类 | 20307篇 |
农作物 | 2526篇 |
水产渔业 | 854篇 |
畜牧兽医 | 3163篇 |
园艺 | 1017篇 |
植物保护 | 3383篇 |
出版年
2024年 | 249篇 |
2023年 | 1347篇 |
2022年 | 1883篇 |
2021年 | 2025篇 |
2020年 | 2064篇 |
2019年 | 2331篇 |
2018年 | 1906篇 |
2017年 | 2926篇 |
2016年 | 3458篇 |
2015年 | 2425篇 |
2014年 | 2841篇 |
2013年 | 4046篇 |
2012年 | 4971篇 |
2011年 | 3938篇 |
2010年 | 3065篇 |
2009年 | 3188篇 |
2008年 | 2826篇 |
2007年 | 3080篇 |
2006年 | 2707篇 |
2005年 | 2264篇 |
2004年 | 1724篇 |
2003年 | 1463篇 |
2002年 | 1180篇 |
2001年 | 1110篇 |
2000年 | 943篇 |
1999年 | 759篇 |
1998年 | 671篇 |
1997年 | 644篇 |
1996年 | 548篇 |
1995年 | 595篇 |
1994年 | 540篇 |
1993年 | 427篇 |
1992年 | 350篇 |
1991年 | 340篇 |
1990年 | 264篇 |
1989年 | 235篇 |
1988年 | 149篇 |
1987年 | 124篇 |
1986年 | 70篇 |
1985年 | 30篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1962年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
碧峰峡森林土壤性状研究 总被引:1,自引:0,他引:1
碧峰峡不仅是旅游景点,还是多学科研究的天然“实验室”,地处雅安亚热带区,原始森林植被保护完好,土壤垂直分布明显,地质现象复杂,也是大熊猫、金丝猴出没之地。经研究结果:土壤呈酸性,自然肥力高.经相关分析结果:土壤有机质含量和CEC等有关理化特性的相关性,较物理性粘粒与CEC间更加显著。 相似文献
132.
133.
梯田基线设计,多采用经验法,等高等宽不好兼顾,“大弯就势,小弯取直”往往只能定性,不能量化,由此设计出的梯田埂线,难以得出最佳梯田断面。如根据地形图等高线走向趋势,选择代表地面走向的等高线,通过概化分析,以数学函数式表达等高线,使其横贯坡面切割等高线为最少,以此作为梯田地埂基线,由其函数对应值,在实地进行坐标放线,即可做到等高布设、等宽兼顾和“大弯就势,小弯取直”定量化,既满足机械作业对曲率半径的要求,也避免了施工时的大切大垫。 相似文献
134.
J. Guan J. C. Kapteyn A. Kerkenaar M. A. De Waard 《European journal of plant pathology / European Foundation for Plant Pathology》1992,98(5):313-324
Differential accumulation of [14C]imazalil and [14C]fenarimol by germlings of wild-type and DMI-resistant isolates ofPenicillium italicum was studied at various pH values. At pH 7 and 8 the low-resistant isolate E300–3 accumulated 22% and 35%, respectively, less imazalil than the wild-type isolate W5. Imazalil accumulation at pH 5 and 6 was similar. Isolate E300–3 also accumulated less fenarimol as compared with the wild-type isolate. This difference was much more obvious than for imazalil and was observed at all pH values tested. Differences in accumulation of both imazalil and fenarimol between low (E300–3), medium (H17) and high resistant (I33) isolates were not observed. These results suggest that decreased accumulation of DMIs is responsible for a low level of resistance only and that additional mechanisms of resistance might operate in isolates with a medium and high degree of resistance. With all isolates fenarimol accumulation was energy-dependent. This was not obvious for imazalil.The wild-type and DMI-resistant isolates had a similar plasma membrane potential as determined with the probe [14C]tetraphenylphosphonium bromide ([14C]TPP+). Various test compounds, among which ATPase inhibitors, ionophoric antibiotics and calmodulin antagonists, affected the accumulation of [14C]TPP+, [14C]imazalil and [14C]fenarimol. No obvious correlation between the effects of the test compounds on accumulation levels of the fungicides and [14C]TPP+ could be observed. These results indicate that the plasma membrane potential does not mediate the efflux of DMI fungicides byP. italicum. 相似文献
135.
136.
The fate of fluroxypyr in the soil in an oil palm agroecosystem 总被引:1,自引:0,他引:1
A study on the fate of fluroxypyr in Malaysian agricultural soils was carried out under natural conditions in an oil palm plantation. Three experimental plots in the oil palm estate were selected and three types of treatments were administered, namely fluroxypyr at the recommended dosage, double the recommended rate, and the untreated control. Residues of fluroxypyr in the soil, water, and oil palm leaf were monitored at regular intervals up to 90 days after treatment (DAT). The recovery of fluroxypyr in the water and soil samples ranged from 91–102% when fortified at 1–25 p.p.b. and 91–98% when fortified at 4–50 p.p.b. The recovery from the oil palm leaf ranged from 76–114% when the oil palm leaf sample was fortified at 0.05–1.0 p.p.m. The results showed that fluroxypyr leached down to 50 cm depth at 1 DAT when the plots were treated with either dosage. However, fluroxypyr was not detected in the soil residue at 14 and 21 DAT. Fluroxypyr was not detected in the oil palm leaf samples irrespective of the rates of herbicide application or sampling intervals. The residue of fluroxypyr was detected in water from a nearby stream up to 5 DAT at levels ranging from 0.06–0.21 µg L−1 . This result suggests that fluroxypyr persists for a short period in the soil and water ecosystems, but not in the oil palm leaf. 相似文献
137.
新鲜蔬菜硝酸盐含量测定的改进试粉法 总被引:11,自引:0,他引:11
为适应新鲜蔬菜硝酸盐快速检测的需要, 在现有试粉法的基础上对硝酸盐测定的试粉法进行了改良研究。结果表明, 本研究建立的直接以去离子水浸提蔬菜匀浆, 混合试粉配方为柠檬酸∶一水硫酸锰∶无水对氨基苯磺酸∶N - 1 - 萘乙二胺盐酸盐∶细锌粉= 30∶4∶1.6∶0.8∶1, 其加入量为0.1 g的改进试粉法, 对于溶液中硝酸盐含量在0~20 mg/L范围时, 显色吸光值与硝酸盐含量呈现良好的线性关系, 相关系数达0.9999, 方法回收率在97.7%~104.5%之间, 相对标准偏差2.71%。用本改进试粉法测定11种蔬菜的硝酸盐含量与国标法测定结果的t检验具有一致性。 相似文献
138.
139.
本文综述了反刍动物肽的吸收特点及影响因素,肽的吸收代谢机制,肽对瘤胃微生物的调控及对反刍动物生产性能发挥的作用,以及饲料蛋白源活性肽的开发应用。 相似文献
140.