全文获取类型
收费全文 | 28307篇 |
免费 | 842篇 |
国内免费 | 4篇 |
专业分类
林业 | 4438篇 |
农学 | 1746篇 |
基础科学 | 218篇 |
5783篇 | |
综合类 | 1208篇 |
农作物 | 2786篇 |
水产渔业 | 3066篇 |
畜牧兽医 | 5778篇 |
园艺 | 1334篇 |
植物保护 | 2796篇 |
出版年
2023年 | 106篇 |
2022年 | 194篇 |
2021年 | 370篇 |
2020年 | 363篇 |
2019年 | 408篇 |
2018年 | 3131篇 |
2017年 | 3072篇 |
2016年 | 1664篇 |
2015年 | 473篇 |
2014年 | 559篇 |
2013年 | 856篇 |
2012年 | 1701篇 |
2011年 | 2980篇 |
2010年 | 2558篇 |
2009年 | 1700篇 |
2008年 | 2059篇 |
2007年 | 2297篇 |
2006年 | 623篇 |
2005年 | 652篇 |
2004年 | 610篇 |
2003年 | 602篇 |
2002年 | 485篇 |
2001年 | 222篇 |
2000年 | 268篇 |
1999年 | 173篇 |
1998年 | 79篇 |
1997年 | 55篇 |
1996年 | 49篇 |
1995年 | 50篇 |
1994年 | 39篇 |
1993年 | 43篇 |
1992年 | 55篇 |
1991年 | 40篇 |
1990年 | 54篇 |
1989年 | 71篇 |
1988年 | 41篇 |
1987年 | 49篇 |
1986年 | 29篇 |
1985年 | 31篇 |
1984年 | 28篇 |
1983年 | 25篇 |
1980年 | 25篇 |
1979年 | 15篇 |
1977年 | 24篇 |
1976年 | 21篇 |
1972年 | 15篇 |
1969年 | 20篇 |
1968年 | 15篇 |
1967年 | 15篇 |
1966年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Inga Herrmann Amir Jourak Annelie Hedström Staffan Lundström Maria Viklander 《Water, air, and soil pollution》2014,225(1):1-11
The distribution of selected elements in individual fractions of organic matter from anthropogenically contaminated soils was investigated. The attention was paid especially at Hg. Furthermore, contents of S, Mg, Mn, Fe, Cu, Zn and Pb were also measured. The decomposition of organic matter to particular fractions was carried out by the resin DAX-8. Ten soil samples were collected, and the Advanced Mercury Analyzer (AMA-254) was used for the determination of the total Hg content. The two highest Hg values reached up to the concentration 10.5 mg kg?1, and in the highest one, it was almost 29 mg kg?1. In each extract, mercury was measured by inductively coupled plasma mass spectrometry (ICP-MS), for other elements, inductively coupled plasma optical emission spectrometry (ICP-OES) was applied. Results of the analysis show that the Hg content bound to the humic acids is inversely proportional to the content of Mg, Mn, Fe and Cu. However, this dependence was not confirmed by the samples with the mercury content above 10 mg kg?1. In the case of fulvic acids, the relationship between Hg and S was observed and has again an inverse character. 相似文献
52.
Compressed wooden plates and dowels were used to connect members in post-and-beam structures as a substitute for a steel fastener.
In order to take advantage of the characteristic properties of compressed wood and to achieve optimum joint performance, two
compressed wooden plates were used in each joint to give multiple shear planes for each compressed wooden dowel. Consequently,
this type of joint showed very good properties in pull-out and momen-trotation performance, and its engineering design could
be further optimized. This joint is expected to be introduced to many kinds of structural systems, including long-span frame
structures made of domestic timber found in Japanese residential houses. 相似文献
53.
Climate change spurs havoc on social-ecological system. People and places vulnerable to climate change have been the focus of many discussions. However, in the forestry sector, limited studies have been conducted that link human vulnerability to recent initiatives, such as reducing emissions from deforestation and forest degradation or REDD+, especially in highly vulnerable countries. Using case studies from the Philippines, this paper focuses on the vulnerability of two community-based forest management (CBFM) organizations, with and without REDD+ readiness intervention, to show the impacts of climate variability and extremes. Two balance-weighted approaches, the livelihood vulnerability index and the IPCC-framework, were used in the vulnerability assessments. Results revealed high vulnerability of both CBFM organizations, although Malitbog Upland Developers for Sustainable Association (MUDSA) livelihood vulnerability is largely aggravated by its exposure to disaster, climate variability and extremes, accessibility to health facilities and water supply. The long history of CBFM implementation in both organizations have minimal contribution in enhancing the adaptive capacity of members to cope with and adapt to climate change impacts. REDD+ (readiness), does not insure reduced vulnerability to climate change, unless sustainable livelihood is achieved. As the State controls forest resources, the rights of CBFM-organizations to commercially benefit from these resources are limited, a disincentive to the development of new and viable development programs in CBFM areas, such as REDD+. This also constrains the achievement of climate resiliency. 相似文献
54.
Xu Jun-liang Ma Lv-yi 《中国林学(英文版)》2007,9(4):251-255
In order to explore the relationship between the time processes of solar radiation and sap flow, sap flow velocity (SFV) of Platycladus orientalis and Pinus tabulaeformis, effective solar radiation (ESR) and other environmental factors were synchronously monitored for one year in the Beijing Western Mountains by using a thermal dissipation probe (TDP) system and an automatic weather station. Results showed significant differences between changes in diurnal characteristics of ESR and sap flow in sunny days during three seasons. Starting times of sap flow occurred generally 1.5–3 hours later than those of solar radiation and there were small differences between Platycladus orientalis and Pinus tabulaeformis. But peak times and stopping times of sap flow varied con-siderably with large contrasts in ESR. The duration of sap flow showed clear differences among the seasons owing to the variable rhythms of climate factors in Beijing. Fluctuation amplitude in the duration of sap flow remained relatively stable during the autumn but changed greatly during spring and summer. Changes in diurnal sap flow velocity of both Platycladus orientalis and Pinus tabu-laeformis were about 0–3 hours later than those of ESR but with the same configuration. The start of sap flow was mainly induced by the sudden intensification of ESR (sunrise effect). Seasonal models of SFV indicated that a cubic equation had the best fit. It was more practical to simulate seasonal water consumption models of trees with ESR. In further investigations, these models should be optimized. 相似文献
55.
Do multipurpose companion trees affect high value timber trees in a silvopastoral plantation system?
Establishment of native timber trees on deforested land may contribute to the livelihood of farmers, to improved ecosystem
services and to increased greenhouse gas uptake. Here, we present a new silvopastoral planting design to assess species performance
and interspecific competition or facilitation effects among native timber and multipurpose trees in Central America. Two timber
species, Tabebuia rosea and Cedrela odorata, were established in three low-density planting regimes allowing combined tree and future livestock production: (1) solitary
planting, (2) companion planting with Guazuma ulmifolia, and (3) companion planting with the nitrogen-fixing Gliricidia sepium. We quantified survival, growth and reforestation potential of the two timber species subjected to the different planting
regimes for the first 2 years after establishment. Nitrogen concentration as well as stable nitrogen and carbon isotope composition
(δ15N, δ13C) of leaves of the timber saplings were determined. T. rosea showed higher survival and better growth than C. odorata under varying environmental conditions (soil, concomitant vegetation). Performance of the timber saplings was unaffected
by either companion species. Planting regimes had no effect on foliar nitrogen concentration and δ15N of the two timber species, although δ15N values indicated nitrogen fixation activity in G. sepium trees. Planting regimes affected foliar δ13C values in T. rosea. δ13C values were significantly higher in solitarily growing individuals, suggesting lower exposition to water stress conditions
in saplings surrounded by companion species. As we found positively correlated growth traits among timber and multipurpose
trees, a combined planting may benefit farmers by providing additional goods and services. 相似文献
56.
This study investigates the optimal conditions for the vegetative propagation of the multipurpose leguminous shrub Colutea istria from leafy stem cuttings. The conditions examined included 1) the origin of the cutting (apical, medial or basal), 2) indole-3-butyric
acid (IBA) treatment (0, 50, 200 or 400 mg/l), 3) the relative humidity of the propagation environment (high or low), 4) wounding
base of cutting, and 5) the season in which the cutting was taken. The rooting ability of the cuttings was significantly influenced
by all these factors. Winter cuttings obtained from the middle and base of the branch showed a greater rooting capacity than
those harvested from the apical area, while autumn cuttings harvested from the middle and apical areas of the branch showed
a greater rooting capacity than those harvested from the base. Winter cuttings showed the best rooting capacity than autumn
cuttings. IBA treatment (200 mg/l), high humidity (98-100%), and wounding increased the rooting capacity of the cuttings. The sprout
of new leaves was higher in basal cuttings, while IBA and wounding also significantly enhanced the root number of rooted cuttings.
A method for vegetatively propagating C. istria plants is given. 相似文献
57.
58.
Giovanna Gilardi Stefano Demarchi Angelo Garibaldi Maria Lodovica Gullino 《Phytoparasitica》2013,41(1):59-72
To control downy mildew of sweet basil (Ocimum basilicum L.), incited by Peronospora belbahrii Thines, a number of compounds were tested in 2011 and 2012 under glasshouse conditions. These included copper-based fungicides, biocontrol agents, and compounds previously reported to induce resistance in plants to pathogens. Results were compared with those provided by fungicides registered for downy mildew control in Italy. The tested compounds were used alone or applied in rotation in spray programs. In all trials, the greatest reduction in disease incidence and severity was found with treatments that included metalaxyl-M?+?copper hydroxide, a mineral fertilizer ‘Alexin’, mandipropanid, and azoxystrobin. The glucohumates activator complex and acibenzolar-S-methyl also provided significant disease control (P?<?0.05). The mineral fertilizer Alexin, the glucohumates activator complex and acibenzolar-S significantly reduced disease incidence and severity 20 days after the last treatment compared with the untreated control (P?<?0.05). Among the copper-based products, the greatest reductions in disease incidence and severity were provided by copper hydroxide with terpenic alcohols and copper oxychloride?+?copper hydroxide. The mineral fertilizer Kendal and prohexadione-Ca, as well as mustard oil, partially reduced disease incidence and severity compared with the untreated control (P?<?0.05), whereas the biocontrol agent Bacillus subtilis QST 713 and thyme oil extract were not effective in two out of three trials. When different combinations of various products used in rotation were tested, effective control was found either using a rotation of fungicides with compounds that can induce resistance, as well as by using rotation with different resistance-inducing compounds on their own. 相似文献
59.
60.
Ojeda-Robertos Nadia Florencia Torres-Chablé Oswaldo Margarito Peralta-Torres Jorge Alonso Luna-Palomera Carlos Aguilar-Cabrales Aguilar Chay-Canul Alfonso Juventino González-Garduño Roberto Machain-Williams Carlos Cámara-Sarmiento Ramón 《Tropical animal health and production》2017,49(3):613-618
Tropical Animal Health and Production - The objective was to determine the frequency of gastrointestinal parasites (GP) genera affecting water buffalo (Bubalus bubalis) reared under humid tropical... 相似文献