全文获取类型
收费全文 | 1490篇 |
免费 | 129篇 |
国内免费 | 48篇 |
出版年
2024年 | 1篇 |
2023年 | 34篇 |
2022年 | 22篇 |
2021年 | 52篇 |
2020年 | 58篇 |
2019年 | 71篇 |
2018年 | 45篇 |
2017年 | 59篇 |
2016年 | 74篇 |
2015年 | 61篇 |
2014年 | 63篇 |
2013年 | 111篇 |
2012年 | 59篇 |
2011年 | 68篇 |
2010年 | 57篇 |
2009年 | 74篇 |
2008年 | 99篇 |
2007年 | 74篇 |
2006年 | 69篇 |
2005年 | 68篇 |
2004年 | 44篇 |
2003年 | 46篇 |
2002年 | 36篇 |
2001年 | 31篇 |
2000年 | 28篇 |
1999年 | 38篇 |
1998年 | 19篇 |
1997年 | 19篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 14篇 |
1992年 | 9篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1977年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 3篇 |
排序方式: 共有1667条查询结果,搜索用时 15 毫秒
991.
The aim of this study was to develop DNA probes that could identify the major fungal species associated with mountain pine beetles (MPB). The beetles are closely associated with fungal species that include ophiostomatoid fungi that can be difficult to differentiate morphologically. The most frequently isolated associates are the pine pathogens Grosmannia clavigera and Leptographium longiclavatum, the less pathogenic Ophiostoma montium, and an undescribed Ceratocystiopsis species (Cop. sp.). Because growing, isolating and extracting DNA from fungi vectored by MPB can be time and labour intensive, we designed three rDNA primer sets that specifically amplify short rDNA amplicons from O. montium, Cop. sp. and the pine Leptographium clade. We also designed two primer sets on a gene of unknown function that can differentiate G. clavigera and L. longiclavatum. We tested the primers on 76 fungal isolates that included MPB associates. The primers reliably identified their targets from DNA obtained from pure fungal cultures, pulverized beetles, beetle galleries, and tree phloem inoculated with G. clavigera. The primers will facilitate large-scale work on the ecology of the MPB-fungal-lodgepole pine ecosystem, as well as phytosanitary/quarantine sample screening. 相似文献
992.
Diet composition and foraging ecology of Asian elephants in Shangyong, Xishuangbanna, China
下载免费PDF全文
![点击此处可从《农业工程》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The composition of the diet and the foraging ecology of the Asian elephant in its natural habitat were studied from 1998 to 2000 in the Shangyong National Natural Reserve located at Xishuangbanna, China, using field observation and dung analysis. A total of 106 plant species were recorded as being eaten by Asian elephants, 83 of which were identified in the elephants' dung. The plant families that contributed to a major proportion of the elephants' diet in the study area were: Gramineae (8 spp., 10.0%), Moraceae (7 spp., 9.9%), Papilionaceae (4 spp., 8.4%), Araliaceae (3 spp., 6.6%), Vitaceae (3 spp., 5.7%), Apocynaceae (3 spp., 4.6%), Musaceae (1 spp., 4.2%), Zingiberaceae (3 spp., 3.7%), Myrsinaceae (3 spp., 3.6%), Rosaceae (3 spp., 3.6%), Euphorbiaceae (5 spp., 3.3%), Ulmaceae (2 spp., 3.0%) and Mimosaceae (4 spp., 2.9%). The most important plants in the elephants' diet were Ficus spp. (Moraceae, 9.0%), Dendrocalamus spp. (Gramineae, 4.5%), Musa acuminata (Musaceae, 4.2%), Microstegium ciliatum (Gramineae, 3.5%) and Amalocalyx yunnanensis (Apocynaceae, 3.1%). Asian elephants consumed a variety of plants in terms of life forms, including trees, vines, shrubs and herbs. Early successional plant species constitute a higher proportion of the diet than late successional plants (42 spp. taking 59% vs. 32 spp. taking 37%). Browsing species accounted for a larger proportion of the diet compared to grazing species (77 spp. taking 91% vs. 6 spp. taking 9%). The number of plant taxa (species, genus, family) in elephants' diet each month negatively correlated with monthly rainfall and mean temperature. The study may help to develop proper strategies for wildlife management especially with regard to the human-elephant conflict, which is now a serious issue in the conservation of Asian elephants in this area. 相似文献
993.
Diaz-Mendoza M Bideshi DK Ortego F Farinós GP Federici BA 《Letters in applied microbiology》2012,54(2):88-95
Aims: To determine whether the 20‐kDa chaperone‐like protein of Bacillus thuringiensis ssp. israelensis enhances synthesis, crystallization and solubility of the Cry3A coleopteran toxin and whether the crystalline inclusions produced are toxic to neonates of the Colorado potato beetle, Leptinotarsa decemlineata. Methods and Results: The cry3A gene was expressed in the 4Q7 strain of B. thuringiensis ssp. israelensis in the absence or presence of the 20‐kDa gene. The 20‐kDa protein enhanced Cry3A yield by 2·7‐fold per unit of fermentation medium. Crystal volumes averaged 2·123 and 0·964 μm3 when synthesized in, respectively, the presence or absence of the 20‐kDa protein. Both crystals were soluble at pH 5 and pH 6; however, the larger crystal was 1·7× and 1·5× more soluble at, respectively, pH 7 and pH 10. No significant difference in toxicity against L. decemlineata neonates was observed. Conclusions: This report demonstrated that the 20‐kDa chaperone‐like protein enhances yield, volume and solubility of the coleopteran Cry3A crystalline inclusions per unit crystal/spore mixture. Significance and Impact of the Study: This is the first report showing that an accessory protein (20‐kDa) could enhance synthesis and crystallization of Cry3A, a finding that could be beneficial for commercial production of this coleopteran‐specific insecticidal protein for microbial insecticides and possibly even for transgenic crops. 相似文献
994.
Shun‐ichiro TAKANO Keiji TAKASU Tsutomu FUSHIMI Ryoko T. ICHIKI Satoshi NAKAMURA 《Entomological Science》2012,15(2):238-245
The coconut hispine beetle Brontispa longissima has been causing serious damage to the coconut palm Cocos nucifera in the Pacific, and Southeast and East Asia. This beetle also attacks Satakentia liukiuensis, an endemic palm on Ishigaki and Iriomote Islands, Japan. To assess the potential impact of B. longissima on S. liukiuensis, we examined the development period, survival rate, egg production and body size of B. longissima on S. liukiuensis at 22–31°C and consumption of S. liukiuensis leaf at 28°C. We also examined these life history traits on C. nucifera at 28°C to compare with those on S. liukiuensis. Brontispa longissima completed their development and reproduced on S. liukiuensis at 22–30°C. Linear regression analysis was used to estimate the effective cumulative temperature (k) as 891.2 degree‐days, and the lower developmental threshold as 13.3°C. On the basis of these values and monthly average temperatures on Ishigaki Island, it was estimated that B. longissima has four generations per year on the island. Satakentia liukiuensis was less suitable for B. longissima than C. nucifera in terms of immature survival, development time, resultant adult size and reproduction. The low quality of S. liukiuensis as a host‐plant may prevent the outbreak of B. longissima, which has not occurred yet on Ishigaki and Iriomote Islands. 相似文献
995.
The mite Paramicrodispus scarabidophilus Hajiqanbar and Rahiminejad sp. nov. (Acari: Prostigmata: Microdispidae) is described and illustrated based on phoretic females recovered from Oryctes nasicornis L. (Col.: Scarabaeidae) hosts, which were collected from forests in northern Iran. It is the first record of the genus Paramicrodispus for the mite fauna of Iran. We also found Paramicrodispus crenulatus (Savulkina, 1978) associated with Lucanus ibericus Motschulsky (Col.: Lucanidae), the first report of association between beetles of the family Lucanidae and the mite family Microdispidae. Moreover, for the first time we report an association between beetles of the family Scarabaeidae and Paramicrodispus mites. 相似文献
996.
KATHARINE A. MARSKE RICHARD A. B. LESCHEN GARY M. BARKER THOMAS R. BUCKLEY 《Molecular ecology》2009,18(24):5126-5142
The Last Glacial Maximum (LGM) severely restricted forest ecosystems on New Zealand’s South Island, but the extent of LGM distribution for forest species is still poorly understood. We used mitochondrial DNA phylogeography (COI) and ecological niche modelling (ENM) to identify LGM refugia for the mycophagous beetle Agyrtodes labralis (Leiodidae), a forest edge species widely distributed in the South Island. Both the phylogenetic analyses and the ENM indicate that A. labralis refuged in Kaikoura, Nelson, and along much of the South Island’s west coast. Phylogeography of this species indicates that recolonization of the largely deforested east and southeast South Island occurred in a west–east direction, with populations moving through the Southern Alps, and that the northern refugia participated little in interglacial population expansion. This contradicts published studies of other New Zealand species, in which recolonization occurs in a north–south fashion from many of the same refugia. 相似文献
997.
998.
Chatchote Thitaram Saran Chansitthiwet Pornsawan Pongsopawijit Janine L. Brown Waroot Wongkalasin Prachayarat Daram Ronnachit Roongsri Anchalee Kalmapijit Sittidet Mahasawangkul Suvichai Rojanasthien Ben Colenbrander Gysbert C. van der Weijden Frank J.C.M. van Eerdenburg 《Animal reproduction science》2009,115(1-4):267-278
Captive Asian elephant (Elephas maximus) populations are decreasing due to low birth rates compared to wild elephants. Improving oestrous detection in female elephants is required to ensure successful mating in captive and semi-captive herds. Responsive behaviours of eight semi-captive bull elephants to the uro-genital area (genital inspection test) or urinary pheromones (urine test) of 14 female elephants throughout the oestrous cycle were evaluated. Weekly blood samples were collected for 27 consecutive months (14 months for the genital inspection test and 13 months for the urine test) from female elephants to characterize the patterns of circulating progestagen. Responsive behaviours of bulls were compared between females in the follicular versus the luteal phase of the cycle. The sensitivity and specificity of the genital inspection test were 65% and 68%, while those of the urine test were 52% and 61%, respectively. The bulls showed significantly higher “genital inspection”, “flehmen from genital area” and “trunk on back” behaviours during the genital inspection test, and “flehmen” behaviours during the urine test in oestrous than in non-oestrous females. In sum, this study showed that monitoring sexual behaviours of Asian elephant bulls towards females or their urine can be used to detect the oestrous period. Although the sensitivity and specificity of both tests were not as high as expected, still, these methods appear to be more efficient at detecting oestrous than traditional methods based on mahout estimations of female receptivity. The use of genital inspection and urine tests may lead to more successful matings and thus to creating self-sustaining populations of captive elephants in range countries. 相似文献
999.
1000.
We isolated ophiostomatoid fungi from bark beetles infesting Pinus densiflora and their galleries at 24 sites in Japan. Twenty-one ophiostomatoid fungi, including species of Ophiostoma, Grosmannia, Ceratocystiopsis, Leptographium, and Pesotum, were identified. Among these, 11 species were either newly recorded in Japan or were previously undescribed species. Some
of these fungal species were isolated from several bark beetles, but other species were isolated from only a particular beetle
species. Thus, it is suggested that some ophiostomatoid fungi have specific relationships with particular beetle species.
In addition, fungus-beetle biplots from redundancy analysis (RDA) summarizing the effects of beetle ecological characteristics
suggested that the association patterns between bark beetles and the associated fungi seemed to be related to the niches occupied
by the beetles. 相似文献