全文获取类型
收费全文 | 571篇 |
免费 | 31篇 |
国内免费 | 4篇 |
专业分类
林业 | 38篇 |
农学 | 58篇 |
基础科学 | 8篇 |
170篇 | |
综合类 | 52篇 |
农作物 | 51篇 |
水产渔业 | 21篇 |
畜牧兽医 | 133篇 |
园艺 | 16篇 |
植物保护 | 59篇 |
出版年
2023年 | 5篇 |
2022年 | 20篇 |
2021年 | 21篇 |
2020年 | 26篇 |
2019年 | 28篇 |
2018年 | 48篇 |
2017年 | 28篇 |
2016年 | 29篇 |
2015年 | 18篇 |
2014年 | 28篇 |
2013年 | 70篇 |
2012年 | 34篇 |
2011年 | 28篇 |
2010年 | 24篇 |
2009年 | 17篇 |
2008年 | 22篇 |
2007年 | 14篇 |
2006年 | 15篇 |
2005年 | 14篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1978年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1971年 | 2篇 |
1970年 | 1篇 |
1967年 | 2篇 |
排序方式: 共有606条查询结果,搜索用时 193 毫秒
551.
Abdul Majid Ayatollahi Mustafa Ghanadian Suleiman Afsharypuor Muhammad Iqbal Choudhary Farzad Kobarfard Mohammad Rahmati 《Fitoterapia》2010
Euphorbia aellenii Rech. f. (Euphorbiaceae) afforded a cytotoxic chloroform fraction from which two new esters of 6(17)-epoxylathyrol were identified (1 and 2). The structure of these compounds was elucidated by spectroscopic methods. 相似文献
552.
Both hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) and balsam fir sawfly (Neodiprion abietis (Harris)) undergo periodic outbreaks in eastern Canada and cause significant growth and mortality losses to forests. Tree growth and mortality are closely related to cumulative defoliation estimates, which integrate annual defoliation over multiple years. Our objective was to determine a method to estimate cumulative defoliation of balsam fir (Abies balsamea [L.] Mill) due to these insects in western Newfoundland, using aerial defoliation survey data, as an essential input to modeling impacts for Decision Support Systems. Interpretation of aerial defoliation survey data for hemlock looper and balsam fir sawfly is problematic because both insects feed upon multiple age classes of foliage. Current-year (2008) aerial defoliation survey data were compared with ground estimates of defoliation by age class from 45 plots (450 trees and 395 mid-crown branch samples), representing a range of defoliation severity classes for each insect. Cumulative defoliation was calculated using defoliation per foliage age class, weighted by relative foliage mass for a given age of foliage. Three significantly different severity classes were defined based on cumulative defoliation values derived from aerial defoliation survey: (i) 1-year moderate (30–70%) defoliation, (ii) 1-year severe (71–100%) defoliation with calculated cumulative defoliation values of 19 and 39%, respectively, for balsam fir sawfly, 21 and 34% respectively for hemlock looper; and (iii) 2–3 years of moderate–severe defoliation, with cumulative defoliation ranging between 59 and 64% for balsam fir sawfly and 49% for hemlock looper. Defoliation severity from aerial defoliation survey alone hence can be misleading if defoliation measurements are not converted to cumulative defoliation values. 相似文献
553.
Structural root growth of young Veronese poplars on erodible slopes in the southern North Island,New Zealand 总被引:1,自引:0,他引:1
I. R. McIvor G. B. Douglas S. E. Hurst Z. Hussain A. G. Foote 《Agroforestry Systems》2008,72(1):75-86
In New Zealand poplars are commonly planted on moist, unstable pastoral hill country to prevent or reduce soil erosion, thereby
maintaining hillslope integrity and pasture production. Mechanical reinforcement by poplar root systems aids slope stabilisation.
Root mass and distribution were determined for three Populus deltoides × nigra ‘Veronese’ trees aged 5, 7 and 9.5 year planted as 3 m poles at 8 m × 8 m spacing on a hillslope near Palmerston North in
the southern North Island. Most of the structural roots (≥2 mm diameter) were distributed in the top 40 cm of soil. Vertical
roots penetrated to about 1.0 m, being the depth of the soil above a fragipan. Total structural root dry masses (excluding
root crown) were 0.57, 7.8 and 17.90 kg for the trees aged 5, 7 and 9.5 year, respectively. Total structural root length was
79.4 m for the 5 year tree and 663.5 m for the 9.5 year tree. Surrounding trees were estimated to increase root mass density
to 3 times and root length density to 4–5 times the contribution of the single tree at 9.5 year. The study indicated that
root development of wide-spaced poplar trees on hillslopes was minimal in the first 5 years but then increased rapidly. These
results suggest that poplar trees established from poles may take at least 5 years to develop a structural root network that
will effectively bind soil. 相似文献
554.
Sulaiman MR Hussain MK Zakaria ZA Somchit MN Moin S Mohamad AS Israf DA 《Fitoterapia》2008,79(7-8):557-561
The aqueous extract of Ficus deltoidea leaves was evaluated for possible antinociceptive activity in three models of nociception, namely, acetic acid-induced abdominal writhing, formalin and hot plate test. The results of the present study showed that intraperitoneal administration of the F. deltoidea leaves aqueous extract at the dose of 1, 50 and 100 mg/kg, 30 min prior to pain induction produced significant dose-dependent antinociceptive effect in all the models used, which indicating the presence of both central and peripherally mediated activities. Furthermore, the antinociceptive effect of the extract in the formalin and hot plate test was reversed by the non-selective opioid receptor antagonist naloxone suggesting that the endogenous opioid system is involved in its analgesic mechanism of action. Thus, the present results demonstrated that F. deltoidea leaves aqueous extract contains pharmacologically active constituents which possess antinociceptive activity justifying its popular therapeutic use in treating conditions associated with the painful conditions. 相似文献
555.
Aijaz Hussain Mir M.A. Khan Faculty of Forestry Sher-e-Kashmir University of Agricultural Sciences Technology of Kashmir Shalimar Srinagar- India 《林业研究》2008,(4)
2005.2006年间,在印度喀什米尔地区的克什米尔农业科学大学的试验地对农林兼作体系进行研究,柳树与农作物的间混种植包括柳树,羽衣甘蓝(Brassica oleracea Var.acephala)和球茎甘蓝(Brassica oleracea var.caularapa)。试验地分成几个小区,每个小区(8m×2m)种植4棵两年生的柳树,间距为2m×2m。采用被推荐的间混种植的植株间距和施用的肥料浓度。结果表明:羽衣甘蓝和球茎甘蓝与柳树间混种植得出这种的种植模式的预计效益成本率分别为2.78和2.79,单独的柳树种植效益率为2.66。本研究表明,可以促进蔬菜作物与柳树间混种植模式从而代替单独的柳树种植模式。图1表7参27。 相似文献
556.
557.
David N. Laband Anwar Hussain Armando Gonzlez-Cabn 《Forest Policy and Economics》2008,10(7-8):444-449
In this paper, we explore empirically whether the USDA Forest Service's litigation success rate in each Forest Service region helps explain the persistent regional effects noted by Laband et al. (Laband, D.N., González-Cabán, A., and Hussain, A. (2006). “Factors That Influence Administrative Appeals of Proposed USDA Forest Service Fuels Reduction Actions,” Forest Science, 52(5): 477–488.) with respect to the pattern of administrative appeals of proposed fuels reduction actions. We find strong evidence of an inverse relationship between the Forest Service's litigation success rate and the likelihood of administrative appeal of proposed fuels reduction actions on public lands. However, inclusion of this variable explains only about 20% of the region-specific impact noted in Laband et al. (Laband, D.N., González-Cabán, A., and Hussain, A. (2006). “Factors That Influence Administrative Appeals of Proposed USDA Forest Service Fuels Reduction Actions,” Forest Science, 52(5): 477–488.), which continues to command additional investigation. 相似文献
558.
Syed Mustafa Tauqeer Ahmad Abdul Naeem Khizar Hussain Shah Muhammad Waseem 《Water, air, and soil pollution》2010,210(1-4):43-50
A strong base anion exchange resin Amberlite IRA-400 Cl? and its hybrids with Mn(OH)2 and Cu(OH)2 are used for the removal of chromium from the synthetic spent tannery bath. The recovery is examined by varying the experimental conditions, viz., resin dosage, stirring speed, and temperature. The rate of chromium removal by Amberlite IRA-400 Cl? increased almost four times when the resin dosage was increased from 0.2 to 1.0 g. Furthermore, the rate of chromium sorption almost doubled when the stirring speed was increased from 100 to 1,000 rpm, suggesting that the sorption is a diffusionally controlled process. The chromium removal capacity also increased with the rise of temperature, showing the endothermic nature of the process. The results are explained with the help of film diffusion, particle diffusion, and Lagergren pseudo-first-order kinetic models. The kinetics results of the Amberlite IRA-400 Cl? are compared with its hybrid anion exchange resins IRA-400 Mn(OH)2 and IRA-400 Cu(OH)2. It is found that the hybrid ion exchangers have greater removal ability and fast kinetics as compared to the parent exchanger. 相似文献
559.
560.