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   317篇
  免费   13篇
  2024年   1篇
  2023年   8篇
  2022年   11篇
  2021年   22篇
  2020年   8篇
  2019年   13篇
  2018年   12篇
  2017年   19篇
  2016年   12篇
  2015年   19篇
  2014年   25篇
  2013年   29篇
  2012年   19篇
  2011年   21篇
  2010年   17篇
  2009年   8篇
  2008年   19篇
  2007年   10篇
  2006年   9篇
  2005年   14篇
  2004年   3篇
  2003年   1篇
  2002年   4篇
  2001年   3篇
  1999年   2篇
  1998年   3篇
  1997年   1篇
  1995年   1篇
  1994年   1篇
  1993年   1篇
  1992年   3篇
  1991年   1篇
  1990年   1篇
  1989年   3篇
  1988年   2篇
  1987年   1篇
  1984年   1篇
  1981年   1篇
  1976年   1篇
排序方式: 共有330条查询结果,搜索用时 15 毫秒
21.
The study aimed to investigate the soil-plant relationship by looking at knowledge levels of social media users. The study examined the relationship between the users’ characteristics and their knowledge on soil-plant relationship. Online survey was designed and distributed to gather the data. The number of response was received from 383 respondents where 375 participants provided completed information and the remaining eight responses were eliminated due to quality standards. The results show most of the participants (68.8%) are moderately depend on social media to acquire knowledge on soil-plant relationship and indicated “Twitter” as the highly utilized platform followed by the “Youtube”. Meanwhile, 48.8% of the participants indicated that social media have a high impact on their knowledge-based information on soil-plant relationship and agricultural contents. Inferential analysis shows there was a significant positive relationship (p < 0.01) between independent variables; Twitter, Youtube, Instagram, and Snapchat and the degree of trust on these platforms, and the level’s knowledge on soil-plant relationship (dependent variable). Only 13% of the variance accounted for the impact of social media on participants’ agricultural knowledge-base can be predicted from the combination of participants’ reliance on a set of social media platforms (Twitter, Instagram, Youtube, and Snapchat). The study revealed the trust and confidence of the users using social media on agricultural information/soil plant relationship had a medium effect in social and educational research.  相似文献   
22.
Factor VIIa (FVIIa), a serine protease enzyme, coupled with tissue factor (TF) plays an important role in a number of thrombosis-related disorders. Inhibition of TF·FVIIa occurs early in the coagulation cascade and might provide some safety advantages over other related enzymes. We report here a novel series of substituted biphenyl derivatives that are highly potent and selective TF·FVIIa inhibitors. Parallel synthesis coupled with structure-based drug design allowed us to explore the S2 pocket of the enzyme active site. A number of compounds with IC50 value of <10 nM were synthesized. The X-ray crystal structures of some of these compounds complexed with TF·FVIIa were determined and results were applied to design the next round of inhibitors. All the potent inhibitors were tested for inhibition against a panel of related enzymes and selectivity of 17,600 over thrombin, 450 over trypsin, 685 over FXa, and 76 over plasmin was achieved. Two groups, vinyl 36b and 2-furan 36ab, were identified as the optimum binding substituents on the phenyl ring in the S2 pocket. Compounds with these two substituents are the most potent compounds in this series with good selectivity over related serine proteases. These compounds will be further explored for structure–activity relationship.  相似文献   
23.
The diet and feeding behaviour of the kipunji (Rungwecebus kipunji) was studied over 45 months, the first dietary analysis for this species. During 9498 h of direct observation of 34 kipunji groups, a list of 122 identified foodplants was recorded. The list represents 60 families, including 64 trees, 30 herbs, 9 climbers, 7 shrubs, 6 lianas, 3 grasses and 3 ferns. Kipunji were observed eating bark, young and mature leaves, ripe and unripe fruits, flowers, pith, seed pods, rhizomes, tubers, shoots and stalks. Invertebrates, fungi, moss, lichen, and soil were also eaten. Macaranga capensis var. capensis, an early successional tree, was the most commonly consumed species, with leaves, leaf stalks, pith, flowers and bark all eaten. We demonstrate that the kipunji is an omnivorous dietary generalist, favouring mature and immature leaves, ripe and unripe fruits and bark in similar proportions, with an almost comparable fondness for leaf stalks and flowers. Kipunji appear to be adaptable foragers able to modify their diet seasonally, being more folivorous in the dry season and more frugivorous in the wet. Whereas more ripe fruit is eaten in the wet season, the proportion of unripe fruit remains similar across the year. The proportion of mature leaves and pith increases throughout the dry season at the expense of ripe fruits and bark, and this may compensate nutritionally for the lack of available dry-season ripe fruits. Relatively more pith is eaten in the dry season, more stalks at the end of the dry and beginning of the wet seasons, and bark consumption increases as the rainfall rises.  相似文献   
24.
The transboundary networks of Marine Protected Areas (MPAs) project, TRANSMAP, assessed local turnover and regional biodiversity across the East African Marine Ecoregion, where inter-governmental co-operation has been working to connect local MPAs. The benthic fauna in the three most dominant habitats on this coastline??beaches, mangroves and seagrasses??were studied in two Regions (Northern Region, 10?C13°S; Southern Region, 25?C28°S). Meiofaunal taxa were used as the model faunal group owing to their diversity and abundance across habitat types and environmental conditions. Meiofaunal abundance averaged 2,500 individuals 10 cm?2 and was generally higher in mangrove and seagrass sediments than on the beaches, and was significantly different between habitats × Regions. In total, 18 taxa were recorded with highest diversity in the beach samples. Diversity indices and assemblage structure were significantly different between habitats, but also Regions. Specific granulometric 1?? size classes, shore-height and number of rain days were the factors most significantly correlating with the observed assemblage patterns. Additionally, the size of a MPA and latitude (which correlated with MPA age, but not number of rain days), were the factors fitting best with meiofaunal assemblage patterns across the beaches, the habitat for which the most comprehensive data were generated. Sample diversity was higher in the Southern Region, and although within- and across-habitats diversity were similar across the Regions, the two Regions appeared to provide complementary habitats and supported different assemblages. Within the Regions, beaches (the only habitat for which more than one location was sampled) were significantly different between Locations, supporting the establishment of multiple protected locations of the same habitat within each transboundary MPA.  相似文献   
25.
The present study investigates the formation of aerobic granular sludge in sequencing batch reactor (SBR) fed with palm oil mill effluent (POME). Stable granules were observed in the reactor with diameters between 2.0 and 4.0 mm at a chemical oxygen demand (COD) loading rate of 2.5 kg COD m−3 d−1. The biomass concentration was 7600 mg L−1 while the sludge volume index (SVI) was 31.3 mL g SS−1 indicating good biomass accumulation in the reactor and good settling properties of granular sludge, respectively. COD and ammonia removals were achieved at a maximum of 91.1% and 97.6%, respectively while color removal averaged at only 38%. This study provides insights on the development and the capabilities of aerobic granular sludge in POME treatment.  相似文献   
26.

Background  

Migraine is a significant health problem, especially for the young people, due to its frequency and accompanying morbidity, causing disability and loss of performance. In this study, our aim was to determine the prevalence of migraine headaches among university students in Edirne, a Turkish city.  相似文献   
27.
Cyclopentane derivatives, designated as BCX-1812, BCX-1827, BCX-1898, and BCX-1923, were tested in parallel with oseltamivir carboxylate and zanamivir for the in vivo activity in mice infected with A/Turkey/Mas/76 X A/Beijing/32/92 (H6N2) influenza virus. The compounds were tested orally and intranasally at different dose levels. BCX-1812, BCX-1827, and BCX-1923 showed more than 50% protection at 1mg/kg/day dose level on oral treatment. The intranasal treatment was 100% effective even at 0.01 mg/kg/day for all four compounds. On comparison with oseltamivir carboxylate and zanamivir, these four cyclopentane derivatives have shown equal or better efficacies. The synthesis of two new compounds, BCX-1898 and BCX-1923, is also described.  相似文献   
28.
Various C-1'-substituted acyclic N9 adenine nucleosides were prepared from 9-[(1-hydroxymethyl)(3-monomethoxytrityloxy)propyl]-N6-monomethoxytrityladenine. The hydroxymethyl was modified to the phosphonomethoxy derivative, and the 3-monomethoxytrityloxy was converted to hydroxyl, methoxy, azido, and amino. Other substituents, such as ethyl and ea-hydroxyethyl were also prepared. The resulting phosphonomethoxy derivatives were converted to prodrugs.  相似文献   
29.
High-relief structures may influence the abundance and diversity of reef-associated fish. We conducted a field experiment to investigate whether the presence of vertical structures (PVC pipes) affects fish communities on artificial reefs. The effect of the height of the structures (1 and 3 m) was also tested. Furthermore, the effects on fish of placing artificial reefs on otherwise featureless bottoms were quantified. Algal and macro-invertebrate colonization of the reefs was also recorded. The experiment was carried out on the west coast of Sweden over a period of 1 year. The vertical structures had a positive effect on fish abundance but not on diversity. The height of the structures did not, however, influence the fish communities. Natural as well as urban vertical structures on the seafloor could have a positive effect on local fish abundance. The positive effects of artificial reefs on total fish abundance and diversity were immediate. Of the 10 species recorded, two, the black goby Gobius niger and the goldsinny wrasse Ctenolabrus rupestris, dominated over the whole survey period. There were significant temporal differences in fish abundance, and diversity increased with time.  相似文献   
30.
To determine whether PAX-2 and PAX-8 are involved in Wilms tumor (WT) pathogenesis, we sought mutations in these two genes in 99 Wilms tumors of favorable histology. We screened the entire protein coding sequences as well as the intronic regions adjacent to exons, using denaturing HPLC followed by sequencing of samples displaying abnormal chromatograms. In PAX-2, a silent polymorphism was found within exon 2 and exon 8 in 1% and 21% of cases, respectively. Three apparently silent polymorphisms were also found in PAX-8, two in exon 5 (2 of 99 cases or 2%) and one in exon 6 (22 of 99 cases or 22%), all of which were located 3' to the exons. In conclusion, no evidence for disease causing mutation was found using this technique, and so the direct involvement of either of these two genes in WT is unlikely.  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