全文获取类型
收费全文 | 20188篇 |
免费 | 1311篇 |
国内免费 | 800篇 |
专业分类
林业 | 4660篇 |
农学 | 681篇 |
基础科学 | 1344篇 |
2416篇 | |
综合类 | 7682篇 |
农作物 | 822篇 |
水产渔业 | 1056篇 |
畜牧兽医 | 1369篇 |
园艺 | 382篇 |
植物保护 | 1887篇 |
出版年
2024年 | 108篇 |
2023年 | 352篇 |
2022年 | 395篇 |
2021年 | 571篇 |
2020年 | 660篇 |
2019年 | 768篇 |
2018年 | 476篇 |
2017年 | 581篇 |
2016年 | 749篇 |
2015年 | 632篇 |
2014年 | 1100篇 |
2013年 | 1264篇 |
2012年 | 1648篇 |
2011年 | 1648篇 |
2010年 | 1239篇 |
2009年 | 1307篇 |
2008年 | 1188篇 |
2007年 | 1212篇 |
2006年 | 1016篇 |
2005年 | 1025篇 |
2004年 | 788篇 |
2003年 | 685篇 |
2002年 | 509篇 |
2001年 | 469篇 |
2000年 | 395篇 |
1999年 | 265篇 |
1998年 | 200篇 |
1997年 | 194篇 |
1996年 | 156篇 |
1995年 | 136篇 |
1994年 | 98篇 |
1993年 | 81篇 |
1992年 | 95篇 |
1991年 | 81篇 |
1990年 | 54篇 |
1989年 | 66篇 |
1988年 | 49篇 |
1987年 | 23篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1982年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
961.
近10年来甘肃省在全省48个县、区对农田害鼠进行了较系统的调查研究,明确了本省农田的主要害鼠有27种,隶属2目6科14属。根据动物地理区划原则,可将本省农田害鼠分布划分为4个生态区域。①陇东旱塬区,农田害鼠有15种,优势鼠种为中华鼢鼠和大仓鼠;②陇南阴湿山区,有12种,优势鼠种为中华鼢鼠、黑线仓鼠和黑线姬鼠;③中部干旱区,有10种,优势鼠种为达乌尔黄鼠、中华鼢鼠和褐家鼠;④河西走廊区,有10种,优势鼠种为黑线仓鼠、长爪沙鼠和五趾跳鼠。 相似文献
963.
Francisco J. Escobedo David J. Nowak John E. Wagner Carmen Luz De la Maza Manuel Rodríguez Daniel E. Crane Jaime Hernndez 《Urban Forestry & Urban Greening》2006,4(3-4):105-114
Santiago, Chile's semi-arid climate and urbanized environment poses a severe limitation for the establishment and maintenance of urban forests. Municipalities, or comunas, are the main stakeholders in the management of Santiago's public urban forests. A tenable hypothesis would be that as the socioeconomic level of a comuna increases, the better the condition of a comuna's urban forest. Unfortunately, there is little comprehensive information on management, public expenditure, and structure of Santiago's public and private urban forests. To examine this hypothesis, Santiago was divided into socioeconomic strata, then using air photo interpretation and stratified field sampling, urban forest structures were quantified by socioeconomic strata. In addition, interview surveys were used to determine municipal urban forest management and expenditures for different public urban forests based on socioeconomic strata. Urban forests in the high socioeconomic strata had fewer public trees, greater tree cover, tree and leaf area density, and leaf area index than lower socioeconomic strata. The percentage of total municipal budget allocated to public urban forest management was consistent among strata, but the total public urban forest budgets were greater in the high socioeconomic strata. Public urban forest structure is related to the socioeconomic strata of Santiago's different comunas. 相似文献
964.
R. Patricia Penilla Janet Hemingway Alma D. López 《Pesticide biochemistry and physiology》2007,89(2):111-117
The relative rates of cytochrome P450 selection in southern Mexican Anopheles albimanus populations were investigated during a 3 years indoor residual house spraying intervention with a pyrethroid (PYR) or DDT, a mosaic of organophosphate (OP)-PYR, and the annual rotation of OP-PYR-carbamate (CARB). This insecticide resistance mechanism, initially evenly spread in the mosquito population, correlated with PYR resistance during the second treated year, when cytochrome P450 contents increased in most villages of the PYR, rotation and mosaic schemes. However, by the third year, mean cytochrome P450 contents declined to susceptible levels in mosquitoes of the rotation and one mosaic group but not in the PYR-treated villages. In DDT-treated villages, a continuous decrement of cytochrome P450 levels occurred since the first treatment year, and susceptible levels were observed at the end of the intervention. Most correlations of cytochrome P450 levels and PYR resistance were lost during the third year, indicating that another mechanism evolved in resistant mosquito populations. 相似文献
965.
Urban forests are unique and highly valued resources. However, trees in urban forests are often under greater stress than those in rural or undeveloped areas due to soil compaction, restricted growing spaces, high temperatures, and exposure to air and water pollution. In addition, conditions change more quickly in urban as opposed to rural and undeveloped settings. Subsequently, proactive management of urban forests can be challenging and requires the availability of current and comprehensive information. Geospatial tools, such as, geographic information systems (GIS), global positioning systems (GPS) and remote sensing, work extremely well together for gathering, analyzing, and reporting information. Many urban forest management questions could be quickly and effectively addressed using geospatial methods and tools. The geospatial tools can provide timely and extensive spatial data from which urban forest attributes can be derived, such as land cover, forest structure, species composition and condition, heat island effects, and carbon storage. Emerging geospatial tools that could be adapted for urban forest applications include data fusion, virtual reality, three-dimensional visualization, Internet delivery, modeling, and emergency response. 相似文献
966.
Simulating the cumulative effects of multiple forest management strategies on landscape measures of forest sustainability 总被引:1,自引:2,他引:1
While the cumulative effects of the actions of multiple owners have long been recognized as critically relevant to efforts
to maintain sustainable forests at the landscape scale, few studies have addressed these effects. We used the HARVEST timber
harvest simulator to predict the cumulative effects of four owner groups (two paper companies, a state forest and non-industrial
private owners) with different management objectives on landscape pattern in an upper Michigan landscape managed primarily
for timber production. We quantified trends in landscape pattern metrics that were linked to Montreal Process indicators of
forest sustainability, and used a simple wildlife habitat model to project habitat trends. Our results showed that most trends
were considered favorable for forest sustainability, but that some were not. The proportion of all age classes and some forest
types moved closer to presettlement conditions. The trend for the size of uneven-aged patches was essentially flat while the
average size of patches of the oldest and youngest age classes increased and the size of patches of the remaining age classes
decreased. Forest fragmentation generally declined, but edge density of age classes increased. Late seral forest habitat increased
while early successional habitat declined. The owners use different management systems that cumulatively produce a diversity
of habitats. Our approach provides a tool to evaluate such cumulative effects on other landscapes owned by multiple owners.
The approach holds promise for helping landowner groups develop and evaluate cooperative strategies to improve landscape patterns
for forest sustainability. 相似文献
967.
针对浑善达克沙地东段的自然经济条件和沙漠化危害特点,因地制宜地营建农防林与牧防林相结合,防护林与经济林相结合,沙漠化治理与沙产业开发相结合的综合防护体系6667hm2。防护体系建立后,区域内生态环境明显改善,维护了首都的生态安全。 相似文献
968.
Julie M. Steed Andreas Baierl Bruce D. L. Fitt 《European journal of plant pathology / European Foundation for Plant Pathology》2007,118(4):359-373
In winter oilseed rape experiments at Rothamsted in 2000/01 to 2002/03 growing seasons, the severity of phoma stem canker
epidemics in summer depended on the timing of phoma leaf spot epidemics in the previous autumn, and hence on the timing of
Leptosphaeria maculans ascospore release. The first major release of L. maculans ascospores was earlier in 2000 (26 September) and 2001 (18 September) than in 2002 (21 October). Consequently, the autumn
phoma leaf spot epidemic was also earlier in 2000 and 2001 than in 2002. The resulting stem canker epidemics were severe by
harvest (July) in 2001 and 2002 but not in 2003. No correlation was found between the severity or duration of phoma leaf spotting
(lesion days or lesion °C-days) and the subsequent severity of phoma stem canker epidemics. Rates of leaf production and loss
were similar in the three growing seasons. Out of ca. 25 leaves produced on plants during each season, leaf numbers 10–14 generally remained on plants for the longest. Treatment
with flusilazole + carbendazim in autumn decreased the severity of phoma leaf spotting for several weeks after treatment,
decreased the severity of stem canker the following summer and increased yield significantly in 2001 and 2002 but not in 2003.
The most effective timings for flusilazole + carbendazim application were when leaves 7–11 were present on most plants and
at least 10% of plants were affected by phoma leaf spot. Two half-dose applications of fungicide reduced phoma stem canker
and increased yield more than a single full dose application when phoma leaf spot epidemics were early (<800 °C-days after
sowing). 相似文献
969.
970.
N. A. S. Messiha A. D. van Diepeningen N. S. Farag S. A. Abdallah J. D. Janse A. H. C. van Bruggen 《European journal of plant pathology / European Foundation for Plant Pathology》2007,118(3):211-225
Stenotrophomonas maltophilia was isolated from the rhizosphere of eggplant in the Nile Delta of Egypt, and its antagonistic potential against Ralstonia solanacearum race 3 biovar 2, the causal agent of potato brown rot, was in vitro evaluated on KB agar medium and in vivo on potato plants.
In vitro, four isolates of S. maltophilia (PD3531, PD3532, PD3533, and PD3534) appeared antagonistic. The isolate (PD3533) was screened as the most promising antagonist
for the in vivo tests. In the greenhouse, the antagonist was applied directly to soil or by bacterization of potato eyepieces.
Stenotrophomonas maltophilia significantly suppressed potato brown rot in Egyptian clay soil but not in Dutch clay soil. Survival of a rifampicin and
chloramphenicol-resistant S. maltophilia strain PD4560 was investigated in two pairs of clay soils, conventionally and organically managed, from Egypt and the Netherlands.
The survival of S. maltophilia was significantly less in Dutch than in Egyptian soils, while the converse occurred for R. solanacearum. These results are in agreement with those obtained in the in vivo biocontrol tests. In conclusion, S. maltophilia may be useful for control of brown rot in the area where it was originally isolated, the Nile Delta in Egypt. 相似文献