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   365篇
  免费   12篇
林业   19篇
农学   17篇
基础科学   6篇
  97篇
综合类   33篇
农作物   33篇
水产渔业   24篇
畜牧兽医   107篇
园艺   17篇
植物保护   24篇
  2023年   3篇
  2022年   5篇
  2021年   7篇
  2020年   10篇
  2019年   12篇
  2018年   7篇
  2017年   10篇
  2016年   9篇
  2015年   9篇
  2014年   14篇
  2013年   33篇
  2012年   15篇
  2011年   25篇
  2010年   27篇
  2009年   12篇
  2008年   21篇
  2007年   18篇
  2006年   23篇
  2005年   19篇
  2004年   10篇
  2003年   14篇
  2002年   11篇
  2001年   3篇
  2000年   2篇
  1999年   4篇
  1998年   3篇
  1997年   1篇
  1996年   4篇
  1994年   1篇
  1992年   3篇
  1991年   1篇
  1990年   3篇
  1989年   3篇
  1988年   5篇
  1987年   1篇
  1986年   2篇
  1985年   5篇
  1984年   1篇
  1983年   1篇
  1981年   3篇
  1980年   1篇
  1979年   2篇
  1977年   1篇
  1975年   1篇
  1974年   2篇
  1971年   1篇
  1969年   4篇
  1968年   1篇
  1967年   3篇
  1964年   1篇
排序方式: 共有377条查询结果,搜索用时 31 毫秒
351.
352.
The moisture-dependent physical properties are important to design post harvest equipments of the product. The physical properties of Karanja kernel were evaluated as a function of moisture content in the range of 8.56–22.22% d.b. The average length, width, thickness and 1000 kernel mass were 25.29 mm, 15.58 mm, 7.88 mm and 1036.45 g, respectively, at moisture content of 8.56% d.b. The geometric mean diameter and sphericity increased from 14.55 to 15.97 mm and 0.57 to 0.6 as moisture content increased from 8.56 to 22.22% d.b., respectively. In the same moisture range, the bulk density decreased from 663 to 616 kg/m3, whereas the corresponding true density and porosity increased from 967 to 1081 kg/m3 and 31.44 to 43.02%, respectively. As the moisture content increased from 8.56 to 22.22% d.b., the angle of repose and surface areas were found to increase from 27.69 to 37.33° and 665.74 to 801.63 mm2, respectively. The static coefficient of friction of Karanja kernel increased linearly against the surfaces of three structural materials, namely plywood (28.72%), mild steel sheet (29.88%) and aluminium (18.86%) as the moisture content increased from 8.56 to 22.22% d.b.  相似文献   
353.
Caves are an important resource to a large proportion of temperate bat species, primarily as mating and hibernation sites. However, information on bat use exists for only a small fraction of caves in many parts of the temperate world, in part because current survey methods are inappropriate for many species. We surveyed the UK’s largest karst landscape, the Yorkshire Dales, by monitoring autumn swarming (mating) activity at 53 caves using automated echolocation call loggers, followed by trapping. Over 60% of caves surveyed were used by bats, but there was considerable variation in activity. Swarming activity was positively correlated with chamber development and negatively correlated with the amount of water the cave carried: together these two predictors explained 45% of the variance. Entrance orientation and shelter explained a further 10%. Activity was not correlated with entrance size, altitude or connectivity to the nearest summer habitat. All five resident swarming species were caught at most sites: Myotis brandtii, Myotis daubentonii, Myotis mystacinus, Myotis nattereri and Plecotus auritus. Behaviour, species composition and sex and age ratios were typical of swarming reported in other studies. Bat populations and catchment sizes were large and despite the proximity of other suitable caves, bats showed high fidelity to single sites. Our results show that the national importance of these caves has been overlooked. We suggest that survey for swarming activity is a quick and effective method of identifying underground bat sites and is likely to uncover many previously unknown and important sites throughout the temperate world.  相似文献   
354.
Due to analytical similarities with the mycorrhizal glycoprotein glomalin, ubiquitous citrate and heat-extractable soil protein fractions have been assumed to be predominantly glomalin-stabilised within soil. Often termed glomalin-related soil protein (GRSP), little however is actually known of the “glomalin-purity” of these soil fractions. We undertook western and lectin blots and crossed immuno/lectin affinity electrophoresis (CIE/CLAE) analysis of “easily extractible” GRSP fractions, as well as liquid chromatography-tandem mass spectrometry (LC–MS/MS) of “total” GRSP fractions. To further test whether soil saprobes contribute to GRSP production, we amended soil with 14C-sucrose and examined whether 14C could be traced in the GRSP pool over a 500-day incubation period.While only four of six bands on SDS–PAGE profiles of easily extracted GRSP reacted with anti-glomalin MAb32B11 and the lectin Con A under our blotting conditions, CIE/CLAE indicated the presence of a single protein moiety in the easily extractible GRSP pool. LC–MS/MS analysis of total GRSP pooled from various soils also showed that although traces of protein tentatively assignable to soil bacteria were present in GRSP, their concentrations were low. Additionally, specific activity of total GRSP in 14C-labelled soil was relatively depleted compared to the bulk soil and soil microbial biomass. This suggests that little GRSP of heterotrophic origin was laid down over the incubation period, although the potential presence of a pre-existing 14C-free GRSP background, as well as of low microbial dynamics in the absence of any further substrate inputs to the soil warrant caution with this inference.  相似文献   
355.
Bread loses crispness rapidly after baking because water originating from the wet crumb accumulates in the dry crust. This water accumulation might be increased by the dense and low permeable character of the bread crust. Our objective was to investigate the influence of permeability of the crust on water uptake in the crust and on crispness retention. To achieve this objective, we increased the permeability of the control bread crust by creating small channels through the crust. The water vapour permeability of the crust with and without channels was measured using a newly developed method for brittle materials. Two further properties were measured over time: crispness of bread by analysing acoustic properties and water content of the crust. Control bread crust had low water vapour permeability and functioned as a barrier, leading to increased uptake of water in the crust. Water uptake was halved, however, if the water vapour permeability of the crust was doubled. As a consequence, crispness retention increased eight-fold; breads stored for four hours were as crispy as control breads stored for 30 min. We can conclude, therefore, that permeability of crust is key to crispness retention.  相似文献   
356.
Bhatnagar I  Kim SK 《Marine drugs》2010,8(10):2673-2701
Oceans have borne most of the biological activities on our planet. A number of biologically active compounds with varying degrees of action, such as anti-tumor, anti-cancer, anti-microtubule, anti-proliferative, cytotoxic, photo protective, as well as antibiotic and antifouling properties, have been isolated to date from marine sources. The marine environment also represents a largely unexplored source for isolation of new microbes (bacteria, fungi, actinomycetes, microalgae-cyanobacteria and diatoms) that are potent producers of bioactive secondary metabolites. Extensive research has been done to unveil the bioactive potential of marine microbes (free living and symbiotic) and the results are amazingly diverse and productive. Some of these bioactive secondary metabolites of microbial origin with strong antibacterial and antifungal activities are being intensely used as antibiotics and may be effective against infectious diseases such as HIV, conditions of multiple bacterial infections (penicillin, cephalosporines, streptomycin, and vancomycin) or neuropsychiatric sequelae. Research is also being conducted on the general aspects of biophysical and biochemical properties, chemical structures and biotechnological applications of the bioactive substances derived from marine microorganisms, and their potential use as cosmeceuticals and nutraceuticals. This review is an attempt to consolidate the latest studies and critical research in this field, and to showcase the immense competence of marine microbial flora as bioactive metabolite producers. In addition, the present review addresses some effective and novel approaches of procuring marine microbial compounds utilizing the latest screening strategies of drug discovery.  相似文献   
357.
Cluster bean (Cymopsis tetragonoloba) belongs to tribe Indigoferae of family Leguminosae. India is the world-leader for cluster bean production as it contributes 80% shares of its total production. Cluster bean (guar) is a cash crop for its application in textile, paper, petroleum, mining, pharmaceuticals, explosives, and food industries. Owing to its immense wealth of variable morphophysiological and industrial qualities there is a strong need for appropriate addressing and well documentation of the germplasm. Efforts are to be made to organize research programs on germplasm characterization, utilization, and molecular characterization. Superior cluster bean varieties were selected on the basis of morphophysiological characters and subjected to DNA-based molecular marker analysis. Eighteen of the best genotypes were chosen for DNA extraction, optimization of PCR conditions, and genetic diversity studies using 37 random primers. A total of 381 random amplification fragments were obtained; number of amplifications ranging from 4 to 22 with an average of 10.29 amplified fragments per primer. Evaluation of RAPD data reveals a magnificent range (0.34–0.76) of genotypic similarity coefficients. The UPGMA dendrogram was constructed based on similarity indices which illustrated discrete clustering of different genotypes into groups. Results recorded a positive correlation amongst varieties vis-à-vis cluster analysis generated by NTSYSpc and morphophysiological characteristics. The degree and distribution of genetic diversity in cluster bean would facilitate an evolutionary relationship between numerous accessions that eventually catalogues genetic resources in a more concerted fashion.  相似文献   
358.
This study evaluated onset and incidence of palmar process fractures in foals and investigated corresponding changes in hoof conformation. Radiographs of 17 warmblood foals were taken at 1 week and at 2, 4, 6, 8, and 12 months of age and examined for evidence of palmar process fractures. Hoof parameters were measured from the radiographs, and comparisons were made between fractured and nonfractured feet. All foals suffered at least one fracture during the study period, with an average age of 3.68 ± 0.20 months at fracture occurrence. Hoof conformation and fracture occurrence were not significantly correlated. Foals consistently demonstrated higher lateral heights in the right foot and higher medial heights in the left foot. Hoof angle increased until 3 months of age and then gradually dropped. Hoof-pastern axis exhibited a broken forward conformation, but approached a more correct conformation by 12 months of age. There was a significant reduction in variation of variables for hoof and pastern angle in both feet, and hoof-pastern axis in the right foot. Hoof conformation does not appear to be a causative factor of palmar process fractures. It is possible that these fractures are a normal part of bone remodeling.  相似文献   
359.
360.
Between 1991 and 2001 a total of 12 cases of Mycobacterium tuberculosis infection in eight different species were recorded in the National Zoological Gardens of South Africa in Pretoria (Tshwane). The genetic relatedness between seven of the M. tuberculosis isolates was determined by IS6110 restriction fragment length polymorphism analysis. For the majority of isolates that were analyzed, a high degree of polymorphism suggested different sources of infection. Evidence of M. tuberculosis transmission between animals is reported in two chimpanzees (Pan troglodytes) housed together, from which samples were collected for analysis 29 mo apart.  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