全文获取类型
收费全文 | 427篇 |
免费 | 17篇 |
专业分类
林业 | 43篇 |
农学 | 51篇 |
基础科学 | 8篇 |
106篇 | |
综合类 | 21篇 |
农作物 | 37篇 |
水产渔业 | 47篇 |
畜牧兽医 | 83篇 |
园艺 | 4篇 |
植物保护 | 44篇 |
出版年
2023年 | 11篇 |
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 18篇 |
2018年 | 17篇 |
2017年 | 17篇 |
2016年 | 20篇 |
2015年 | 5篇 |
2014年 | 16篇 |
2013年 | 45篇 |
2012年 | 22篇 |
2011年 | 21篇 |
2010年 | 20篇 |
2009年 | 20篇 |
2008年 | 22篇 |
2007年 | 16篇 |
2006年 | 15篇 |
2005年 | 11篇 |
2004年 | 14篇 |
2003年 | 5篇 |
2002年 | 7篇 |
2001年 | 12篇 |
2000年 | 3篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1971年 | 1篇 |
1967年 | 1篇 |
1966年 | 3篇 |
排序方式: 共有444条查询结果,搜索用时 0 毫秒
381.
AbstractThe German cockroach, Blattella germanica L. (Dictyoptera: Blattellidae), an invasive pest of human habitats, is distributed throughout the world, except in Antarctica. They have developed resistance against chemical pesticides used for the management of their populations. Numerous essential oils and their constituents have been tested; however, the insecticidal activities of clove bud powder, oil, and their constituents have not yet been tested against the German cockroaches. Thus, in this study, clove bud powder, oil, and their major constituents, eugenol and eugenol acetate, were evaluated for their contact toxicity and repellancy against adult German cockroaches under laboratory conditions. The clove bud powder applied at 30?mg/cm2 killed 92% of German cockroaches at 6?hours after treatment (HAT). Similarly, clove bud oil, eugenol and eugenol acetate applied at 4.00?ml/cm2 provided 95%, 85%, and 87% German cockroach mortality at 24, 6, and 24 HAT, respectively. At 2.0?ml/cm2, clove bud oil repelled 80% of German cockroaches within 30?min. In contrast, eugenol and eugenol acetate repelled 85% at 1.0?ml/cm2 and 2.5?ml/cm2, respectively, at 0.5 HAT. Based on this study, clove bud powder, oil, eugenol, and eugenol acetate could be environmentally friendly tools for the management of German cockroaches. 相似文献
382.
383.
384.
We used the water relations model, WINWAT, to model winter water relations of three conifer species-eastern hemlock (Tsuga canadensis (L.) Carr.), eastern white pine (Pinus strobus L.) and red pine (P. resinosa Ait.)-growing at their upper elevational limits on Mt. Ascutney, Vermont, USA, in the winters of 1997 and 1999. Modeled relative water contents remained above 60% in the two youngest foliar age classes of all three species during both winters, indicating that desiccation stress in winter is not responsible for setting the upper elevational limits of these species at this site under present climatic conditions. WINWAT indicated that winter water relations of these low-elevational species were sensitive to low relative humidity, which increased transpiration rates, and low temperatures, which inhibited recharge, but are much less sensitive to summer climate than in the case of subalpine conifers in Colorado. Our results indicate that summer and winter temperatures and relative humidities (or precipitation/potential evapotranspiration ratios) should be incorporated into climate change models designed to simulate future tree distributions. 相似文献
385.
Summary Simple sequence repeat (SSR) markers linked to quantitative trait loci (QTL) associated with resistance to sorghum shoot fly, Atherigona soccata resistance were used to characterize the genetic and phenotypic diversity of 12 cytoplasmic male-sterile (CMS) and maintainers, 12 restorer lines, and 144 F1 hybrids. The genetic diversity was quite high among the shoot fly-susceptible parents and the hybrids based on them, as indicated by high polymorphic information content (PIC) values, while limited genetic diversity was observed among shoot fly-resistant lines. The phenotypic and genotypic dissimilarity analysis indicated that the shoot fly-resistant and -susceptible parents were 73.2 and 38.5% distinct from each other, and the morphological and genetic distances of certain resistant and susceptible cross combinations was more than their resistant or susceptible parents. Genetic variability among the groups was low (10.8%), but high within groups (89.2%). The genetic and morphological distances suggested that the F1 hybrids were closer to CMS (5 to 12% dissimilar) than the restorer (11 to 87% dissimilar), suggesting that CMS influences the expression of resistance to sorghum shoot fly. The SSR markers can be used to characterize the homologous traits in sorghum germplasm. 相似文献
386.
A series of half-diallel crosses involving early, medium and late maturity desi and kabuli type chickpea (Cicer arietinum L.) genotypes with stable resistance to Helicoverpa pod borer, along with the parents, were evaluated at two locations in India to understand the inheritance of pod borer resistance
and grain yield. Inheritance of resistance to pod borer and grain yield was different in desi and kabuli types. In desi type chickpea, the additive component of genetic variance was important in early maturity and dominance component was predominant
in medium maturity group, while in the late maturity group, additive as well as dominance components were equally important
in the inheritance of pod borer resistance. Both dominant and recessive genes conferring pod borer resistance seemed equally
frequent in the desi type parental lines of medium maturity group. However, dominant genes were in overall excess in the parents of early and
late maturity groups. In the kabuli medium maturity group, parents appeared to be genetically similar, possibly due to dispersion of genes conferring pod borer
resistance and susceptibility, while their F1s were significantly different for pod borer damage. The association of genes conferring pod borer resistance and susceptibility
in the parents could be attributed to the similarity of parents as well as their F1s for pod borer damage in kabuli early and late maturity groups. Grain yield was predominantly under the control of dominant gene action irrespective of the
maturity groups in desi chickpea. In all the maturity groups, dominant and recessive genes were in equal frequency among the desi parental lines. Dominant genes, which tend to increase or decrease grain yield are more or less present in equal frequency
in parents of the early maturity group, while in medium and late maturity groups, they were comparatively in unequal frequency
in desi type. Unlike in desi chickpea, differential patterns of genetic components were observed in kabuli chickpea. While the dominant genetic component was important in early and late maturity group, additive gene action was involved
in the inheritance of grain yield in medium duration group in kabuli chickpea. The dominant and recessive genes controlling grain yield are asymmetrically distributed in early and medium maturity
groups in kabuli chickpea. The implications of the inheritance pattern of pod borer resistance and grain yield are discussed in the context
of strategies to enhance pod borer resistance and grain yield in desi and kabuli chickpea cultivars. 相似文献
387.
The growth and development of seven soybean cultivars were studied under shade in a coconut garden. Higher shoot height, internodal elongation and lower leaf area index were the most significant growth changes noticed under shade. Leaf net photosynthesis, crop growth rate and seed yield were also reduced under shade. The cultivars CO 1, UGM 30 and UGM 37 recorded higher yield under shade when compared to other cultivars tested. 相似文献
388.
De Ankan Das Tapan Kumar Chand Karam Debnath Bikas Chandra Dey Saikat Hemadri Divakar Barman Nagendra Nath Chaudhary Jitendra Kumar Muthuchelvan Dhanavelu Saxena Arpit Tewari Neha Chauhan Ankita Lohumi Ankita Biswas Sanchay Kumar 《Tropical animal health and production》2019,51(1):261-265
Tropical Animal Health and Production - Bluetongue (BT) is a notifiable multiple species transboundary viral disease of domestic and wild ruminants. Though the disease is enzootic in India, little... 相似文献
389.
B. Kalyana Babu N. Senthil S. Michael Gomez K. R. Biji N. S. Rajendraprasad S. Satheesh Kumar R. Chandra Babu 《Genetic Resources and Crop Evolution》2007,54(2):399-404
Finger millet (Eleusine coracana), an allotetraploid cereal, is widely cultivated in the arid and semiarid regions of the world. Being rich in protein and
calcium, finger millet serves as an important staple food for rural populations in developing tropical countries where calcium
deficiency and anemia are wide spread. Thirty-two finger millet genotypes were fingerprinted using 50 random amplified polymorphic
DNA (RAPD) markers. Out of the total 529 loci generated using the 50 RAPD primers, 479 loci (91%) were polymorphic and informative
to differentiate the accessions. Cluster analysis grouped the 32 finger millet accessions into two major clusters. Among the
32 finger millet genotypes, GEC 182 and CO 12 were distantly related with a low similarity index of 0.315. These two accessions
also differed considerably in days to flowering and grain weight; GEC 182 is early flowering and has bold grains, while CO
12 is late flowering and has smaller grains. These two accessions with higher diversity at molecular level, phenology and
grain weight will be ideal as parents in hybridization programme, to develop improved finger millet varieties suitable for
peninsular region of India. 相似文献
390.
Both engineering and evolution are constrained by trade-offs between efficiency and robustness, but theory that formalizes this fact is limited. For a simple two-state model of glycolysis, we explicitly derive analytic equations for hard trade-offs between robustness and efficiency with oscillations as an inevitable side effect. The model describes how the trade-offs arise from individual parameters, including the interplay of feedback control with autocatalysis of network products necessary to power and catalyze intermediate reactions. We then use control theory to prove that the essential features of these hard trade-off "laws" are universal and fundamental, in that they depend minimally on the details of this system and generalize to the robust efficiency of any autocatalytic network. The theory also suggests worst-case conditions that are consistent with initial experiments. 相似文献