全文获取类型
收费全文 | 442篇 |
免费 | 29篇 |
专业分类
林业 | 20篇 |
农学 | 14篇 |
106篇 | |
综合类 | 49篇 |
农作物 | 26篇 |
水产渔业 | 34篇 |
畜牧兽医 | 186篇 |
园艺 | 3篇 |
植物保护 | 33篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2020年 | 8篇 |
2019年 | 6篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 8篇 |
2015年 | 9篇 |
2014年 | 14篇 |
2013年 | 22篇 |
2012年 | 32篇 |
2011年 | 38篇 |
2010年 | 19篇 |
2009年 | 16篇 |
2008年 | 19篇 |
2007年 | 22篇 |
2006年 | 17篇 |
2005年 | 20篇 |
2004年 | 13篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 17篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1965年 | 3篇 |
1964年 | 5篇 |
1963年 | 4篇 |
排序方式: 共有471条查询结果,搜索用时 328 毫秒
81.
82.
ZF Ren ZP Huang JW Xu JH Wang P Bush MP Siegal PN Provencio 《Science (New York, N.Y.)》1998,282(5391):1105-1107
Free-standing aligned carbon nanotubes have previously been grown above 700 degreesC on mesoporous silica embedded with iron nanoparticles. Here, carbon nanotubes aligned over areas up to several square centimeters were grown on nickel-coated glass below 666 degreesC by plasma-enhanced hot filament chemical vapor deposition. Acetylene gas was used as the carbon source and ammonia gas was used as a catalyst and dilution gas. Nanotubes with controllable diameters from 20 to 400 nanometers and lengths from 0. 1 to 50 micrometers were obtained. Using this method, large panels of aligned carbon nanotubes can be made under conditions that are suitable for device fabrication. 相似文献
83.
KS Johnson JH Thywissen NH Dekker KK Berggren AP Chu R Younkin M Prentiss 《Science (New York, N.Y.)》1998,280(5369):1583-1586
The spatially dependent de-excitation of a beam of metastable argon atoms, traveling through an optical standing wave, produced a periodic array of localized metastable atoms with position and momentum spreads approaching the limit stated by the Heisenberg uncertainty principle. Silicon and silicon dioxide substrates placed in the path of the atom beam were patterned by the metastable atoms. The de-excitation of metastable atoms upon collision with the surface promoted the deposition of a carbonaceous film from a vapor-phase hydrocarbon precursor. The resulting patterns were imaged both directly and after chemical etching. Thus, quantum-mechanical steady-state atom distributions can be used for sub-0.1-micrometer lithography. 相似文献
84.
DT Rodbell GO Seltzer DM Anderson MB Abbott DB Enfield JH Newman 《Science (New York, N.Y.)》1999,283(5401):516-520
Debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the Pacific Ocean, in Ecuador. These storm-induced events were dated by radiocarbon, and the age of laminae that are less than 200 years old matches the historic record of El Nino events. From about 15,000 to about 7000 calendar years before the present, the periodicity of clastic deposition is greater than or equal to 15 years; thereafter, there is a progressive increase in frequency to periodicities of 2 to 8.5 years. This is the modern El Nino periodicity, which was established about 5000 calendar years before the present. This may reflect the onset of a steeper zonal sea surface temperature gradient, which was driven by enhanced trade winds. 相似文献
85.
Thuringiensin produced by Bacillus thuringiensis subsp. darmstadiensis was further subjected to a two-phase aqueous separation system. A modified HPLC method and a test for quantitative pathogenicity using the house fly Musca domestica were used for analysis of thuringiensin. Within a realistic range of dosages, more effect was observed in the pupal stage than in the larval stage. The percentage effective control rate (ECR) was calculated by (100-percentage emergence); malformed and non-reproductive adults were considered as emerged. Pupal mortality, pupal weight, and ECR after feeding the three-day-old larvae were the measured response criteria for bioassay. The EC50 of thuringiensin for pupae mortality was 1·64 μg ml-1 diet, and 0·83 μg ml-1 for mortality of adults. Insecticidal activity of the broth increased with fermentation time-course from 9th to 21st hour. The bioassay curve constructed with three-hour sampling interval during the fermentation course had good correlation to thuringiensin content as determined by the HPLC method. In the two-phase aqueous separation system, a maximum of 96·7% ECR was achieved with the bottom salt layer, compared to a value of 46·7% with the upper PEG layer. These results suggest that thuringiensin, prepared through a fermentation and recovery process, is suitable for pest control. © 1997 SCI. 相似文献
86.
Yi‐Jay Chang Kuo‐Wei Lan William A. Walsh Jhen Hsu Chih‐hao Hsieh 《Fisheries Oceanography》2019,28(3):291-304
We developed habitat suitability index (HSI) models for two size classes of Pacific saury Cololabis saira in the Northwestern Pacific Ocean. Environmental data, including sea surface temperature, sea surface height, salinity, and net primary production, and catch and effort data from Taiwanese distant‐water stick‐held dip net fisheries during the main fishing season (August–October) during 2002–2015 were used. Habitat preferences and suitable habitat area differed between size classes. The suitable habitat was located between 40–47.5°N and 145–165°E for large‐sized Pacific saury but encompassed a greater area (35–47°N and 140–165°E) for medium‐sized Pacific saury. Both size classes were affected by substantial interannual variation in the environmental variables, which in turn can be important in determining the potential fishing grounds. We found a significant negative relationship between the suitable habitat area and the Niño3.4 indices with a time‐lag of 6 months for the large‐sized (r = ?0.68) and medium‐sized (r = ?0.42) Pacific saury, respectively, as well as the total landings of Pacific saury by all fishing fleets (r = ?0.46). As remotely‐sensed environmental data become increasingly available, HSI models may prove useful for evaluation of possible changes in habitat suitability resulting from climate change or other environmental phenomena and in formulating scientific advice for management. 相似文献
87.
Travel and Activity Choices for Transit Travelers at Terminals with Dynamic Information Provision
下载免费PDF全文
![点击此处可从《Growth and change》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This study explores the impacts of providing dynamic information on travelers' behavior and the induced demand for terminal‐surrounding activities. A nested logit model was used to identify the important factors, and a questionnaire was designed to explore the preference of travelers regarding activities and travel choices. Adopting dynamic information was found to have a significant influence on travel decisions. The results show that an increased duration of activity participation may accompany an alteration of departure time or mode choice. The results also show that the use of dynamic information for travelers is related to induced activity participation and travelers' socioeconomic characteristics. The content of the dynamic information should be designed in accordance with the preference of travelers to encourage travelers participating in terminal‐surrounding activities. 相似文献
88.
Multiplex PCR genotyping for five bacterial blight resistance genes applied to marker‐assisted selection in rice (Oryza sativa)
下载免费PDF全文
![点击此处可从《Plant Breeding》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Bacterial blight (BB) is the most economically damaging disease of rice in Asia and other parts of the world. In this study, a multiplex PCR genotyping method was developed to simultaneously identify genotypes of five BB resistance genes, Xa4, xa5, Xa7, xa13 and Xa21. The resistance R alleles were amplified using five functional markers (FMs) to generate amplicons of 217, 103, 179, 381 and 595 bp in IRBB66. Amplicons of 198, 107, 87, 391 and 467 bp corresponded to susceptible alleles in Taiwanese japonica rice cultivars. In backcross breeding programmes, the multiplex PCR assay was integrated into selection from a population using BB resistance donor IRBB66 crossed to rice cultivar ‘Tainung82’. Two plants with homozygosity for Xa4, xa5, Xa7, xa13 and Xa21 were selected from 1100 BC2F2 plants. In addition, the five BB resistance genes were also accurately identified in F2 populations. This multiplex PCR method provides a rapid and efficient method for detecting various BB resistance genes, which will assist in pyramiding genes to improve durability of BB resistance in Taiwanese elite rice cultivars. 相似文献
89.
90.
南通棉花枯萎病菌对22个棉花品种致病性的田間和盆栽試驗说明:中棉品种如辽阳一号、鶯湖棉、长丰黑籽、常紫一号、南通白花鸡脚桠鈴果、云南布沼土棉等抗病性比較強,以中棉为母本的中印杂交棉的抗病性也較強;陆地棉和海島棉一般感病程度都較高,但四川选育的陆地棉品种52—128則具有一定的抗病性。将枯萎病菌接种到甘藷等27种作物上,均未感病。五个地区的棉花枯萎病菌致病性的盆栽試驗说明:四川、陝西、辽宁的病原菌致病力較強,江苏的其次,安徽的最弱。以葡萄糖、果糖、半乳糖、甘露糖、乳糖、蔗糖、菊糖、溶解淀粉、阿拉伯糖醇等九种糖和糖醇为碳素营养料时,除四川的病原菌在以半乳糖为碳素营养料时生长中等外,其他都生长旺盛。不同地区病原菌的色素形成、小型孢子、大型孢子和厚膜孢子的产生,随碳素营养料的不同而有所差異。 相似文献