首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   18378篇
  免费   209篇
  国内免费   1篇
林业   3751篇
农学   1386篇
基础科学   147篇
  3168篇
综合类   848篇
农作物   2173篇
水产渔业   2135篇
畜牧兽医   1827篇
园艺   1159篇
植物保护   1994篇
  2023年   17篇
  2022年   13篇
  2021年   22篇
  2020年   34篇
  2019年   28篇
  2018年   2825篇
  2017年   2783篇
  2016年   1267篇
  2015年   135篇
  2014年   91篇
  2013年   215篇
  2012年   925篇
  2011年   2256篇
  2010年   2168篇
  2009年   1298篇
  2008年   1392篇
  2007年   1670篇
  2006年   116篇
  2005年   202篇
  2004年   188篇
  2003年   244篇
  2002年   148篇
  2001年   76篇
  2000年   112篇
  1999年   38篇
  1998年   19篇
  1997年   16篇
  1996年   18篇
  1995年   27篇
  1994年   18篇
  1993年   28篇
  1992年   18篇
  1991年   7篇
  1990年   9篇
  1989年   15篇
  1988年   19篇
  1987年   4篇
  1986年   6篇
  1985年   5篇
  1984年   12篇
  1983年   13篇
  1980年   10篇
  1979年   7篇
  1978年   4篇
  1977年   12篇
  1976年   6篇
  1975年   6篇
  1972年   4篇
  1969年   5篇
  1968年   5篇
排序方式: 共有10000条查询结果,搜索用时 94 毫秒
51.
Umma Tamima 《林业研究》2016,27(4):853-861
The objective was to evaluate the performance of the co-management of Nishorgo Support Project at Chunati Wildlife Sanctuary in Bangladesh. I adopted the Focus Groups Discussion method for opinion survey and applied the SWOTAHP technique for data analysis. Local people did not participate in the decision-making process of forest management and they perceived co-management as a threat to their livelihoods. Moreover, mistrust and misunderstanding among different stakeholders, political and ethical conflicts, lack of property rights of tribal communities, and lack of accountability and transparency were identified as the drawbacks of co-management.  相似文献   
52.
53.
54.
55.
56.
Cañahua (Chenopodium pallidicaule Aellen) is a semi‐domesticated relative of quinoa (Chenopodium quinoa Willd.) with high nutritious quality. It is tolerant to frost, drought, saline soils and pests. One seed yield limitation is seed loss during the maturity stages. Two greenhouse experiments in Denmark and field experiments in Bolivia were carried out to determine seed shattering in landraces and cultivars with different growth habits. 15–21 % of the seed shattering in the fields took place whilst the plants still were flowering and 25–35 % during physiological maturity. Seed shattering varied between locations on the Bolivian Altiplano. Cañahua types with the semi‐prostrate growth (‘lasta’) had the highest seed shattering rate in the greenhouse experiments. The Umacutama landrace had lower seed shattering (1 %) than the cultivar Kullaca (7.2 %) both of the ‘lasta’ type. Under field conditions, the cultivar Illimani with the erect growth (‘saihua’) had the highest seed shattering rate (6.4–33.7 %) at both locations and at four different sowing dates. The Umacutama had the lowest rate (0.5–1.5 %). There were no significant differences between plants of the ‘lasta’ and the ‘saihua’ types. The landrace had significantly less seed loss than the cultivars. However, in the greenhouse, the landrace yield was approximately 25 % lower than the yields of the cultivars. In general, cañahua cultivars had higher yield compared to landraces, but also a higher seed shattering rate. Landraces may be used in breeding programmes to develop high‐yielding cultivars with reduced seed shattering.  相似文献   
57.
A new functional porous carbons (PC-WF) is prepared by activation-pyrolysis method use waste cotton fabrics (WF) as an abundant, cheap and available precursor for removal of Brilliant Crocein (BC-GR) and Cationic Red 2GL (CR-GL) from aqueous phase. The PC-WF was characterized by BET, FTIR, SEM, and XRD techniques, the surface area, total pore volume, average pore diameter was found as 1463.5 m2 g-1, 0.783 cm3 g-1 and 2.14 nm, respectively. The influences on BC-GR and CR-GL adsorption of various experimental factors such as initial concentration and temperature were investigated. Adsorption kinetics was found to be best represented by the pseudo-second order model. The adsorption capacity was 319.8 mg g-1 for BC-GR and 842.5 mg g-1 for CR-GL at 30 °C, respectively. The results indicate that for waste cotton fabrics in particular, the practical application of this process to the production of porous carbon would be possible.  相似文献   
58.
59.
60.
Contemporary genetic diversity is the product of both historical and contemporary forces, such as climatic and geological processes affecting range distribution and continuously moulded by evolutionary forces selection, gene flow and genetic drift. Predatory freshwater fishes, such as Northern Pike Esox lucius, commonly exhibit small population sizes, and several local populations are considered endangered. Pike inhabit diverse habitat types, including lakes, rivers and brackish marine waters, thus spanning from small isolated patches to large open marine systems. However, pike population structure from local to regional scales is relatively poorly described, in spite of its significance to developing conservation measures. We analysed microsatellite variation in a total of 1185 North European pike from 46 samples collected across both local and regional scales, as well as over time, to address two overarching questions: Is pike population structure associated with local and/or regional connectivity patterns, and which factors likely have the main influence on the contemporary distribution of genetic diversity? To answer this, we combined estimators of population diversity and structure to assess evidence of whether populations within (i) habitats, (ii) drainage systems and (iii) geographical regions are closer related than among these ranges, and whether patterns are temporally stable. Contrasting previous predictions that genetic drift obscures signals of postglacial colonisation history, we identified clear regional differences in population genetic signatures, suggesting a major effect of drainage divides on colonisation history and connectivity. However, several populations deviated from the general pattern, showing that local processes may be complex and need to be examined case‐by‐case.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号