全文获取类型
收费全文 | 1279篇 |
免费 | 41篇 |
专业分类
林业 | 45篇 |
农学 | 23篇 |
基础科学 | 17篇 |
145篇 | |
综合类 | 376篇 |
农作物 | 36篇 |
水产渔业 | 21篇 |
畜牧兽医 | 581篇 |
园艺 | 21篇 |
植物保护 | 55篇 |
出版年
2020年 | 13篇 |
2019年 | 12篇 |
2018年 | 8篇 |
2017年 | 23篇 |
2016年 | 22篇 |
2015年 | 22篇 |
2014年 | 23篇 |
2013年 | 35篇 |
2012年 | 65篇 |
2011年 | 82篇 |
2010年 | 27篇 |
2009年 | 18篇 |
2008年 | 80篇 |
2007年 | 76篇 |
2006年 | 104篇 |
2005年 | 93篇 |
2004年 | 82篇 |
2003年 | 94篇 |
2002年 | 94篇 |
2001年 | 15篇 |
2000年 | 21篇 |
1999年 | 20篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 14篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1972年 | 20篇 |
1970年 | 5篇 |
1969年 | 8篇 |
1965年 | 6篇 |
排序方式: 共有1320条查询结果,搜索用时 15 毫秒
1.
This study investigated how urban cultural and economic tolerance affects urban innovative capacities based on China's prefecture‐level cities. Several tolerance indices, including ratios of migrants, rental housing, gay people, and private economies were introduced and the cities’ tolerance scores were measured using factor analysis. The results show that cities with higher cultural and economical tolerant scores were agglomerated in three metropolitan areas in China's southeastern coastal region. The spatial regression model demonstrates that urban cultural and economic tolerance increases urban innovation output and promotes innovation capacities. We also introduced the crime rate as an instrumental variable and found that the effect of tolerance on innovation remains robust. Our study suggests it is important for the Chinese government to establish an open and tolerant environment to attract migrants, creative artists, and entrepreneurs to foster urban vitality and improve urban innovative capacities. 相似文献
2.
角质蜡质是植物在长期的生态适应过程中进化形成的一类次生代谢产物,广泛参与了植物抗逆、抵御病虫害侵染等诸多抗性生理过程。角质蜡质在植物-病原互作中发挥了重要作用,是植物抗病机制的重要组成部分。随着分子生物学的发展,人们对植物角质蜡质代谢及其抗病机理的认知不断深入。本研究综述了植物角质蜡质生物合成与其抗病机理的最新研究进展并对未来研究提出展望。目前,植物角质蜡质的抗性机理研究主要集中于组成型抗性和诱导型抗性2类。角质蜡质作为角质层主要成分,一方面可作为组成型抗性成分发挥物理抗性(物理屏障)和化学抗性(抑菌)作用;另一方面,也可作为诱导型抗性成分发挥作用,诱导产生的角质蜡质单体除了作为角质层主要成分发挥物理抗性外,也可作为信号分子或者诱导子激活下游的抗性反应进而发挥其化学抗性功能。未来可侧重于对角质蜡质诱导抗性机理的深入阐释,进一步丰富植物化学生态学研究理论体系。此外,基于角质蜡质的诱导抗性作用,可开发角质蜡质类生物农药(植物免疫诱导剂),为植物病害防控提供新思路。图1参71 相似文献
3.
Cecilia Rohdin Douglas Gilliam Caroline A. O’Leary Dennis P. O’Brien Joan R. Coates Gary S. Johnson Karin Hultin J?derlund 《Acta veterinaria Scandinavica》2015,57(1)
Background
Hereditary ataxias with similar phenotypes were reported in the Smooth-Haired Fox Terrier, the Jack Russell Terrier and the Parson Russell Terrier. However, segregation analyses showed differing inheritance modes in these breeds. Recently, molecular genetic studies on the Russell group of terriers found independent mutations in KCNJ10 and CAPN1, each associated with a specific clinical subtype of inherited ataxia. The aim of this study was to clarify whether or not Smooth-Haired Fox Terriers with hereditary ataxia and dogs of other related breeds harbor either of the same mutations. A sub goal was to update the results of KCNJ10 genotyping in Russell group terriers.Findings
Three Smooth-Haired Fox Terriers with hereditary ataxia and two Toy Fox Terriers with a similar phenotype were all homozygous for the KCNJ10 mutation. The same mutation was also found in a heterozygous state in clinically unaffected Tenterfield Terriers (n = 5) and, in agreement with previous studies, in Jack Russell Terriers, Parson Russell Terriers, and Russell Terriers.Conclusions
A KCNJ10 mutation, previously associated with an autosomal recessive spinocerebellar ataxia in Jack Russell Terriers, Parson Russell Terriers, and Russell Terriers segregates in at least three more breeds descended from British hunting terriers. Ataxic members of two of these breeds, the Smooth-Haired Fox Terrier and the Toy Fox Terrier, were homozygous for the mutation, strengthening the likelihood that this genetic defect is indeed the causative mutation for the disease known as “hereditary ataxia” in Fox Terriers and “spinocerebellar ataxia with myokymia, seizures or both” in the Russell group of terriers. 相似文献4.
5.
A VALENTINE‐SHAPED CARDIAC SILHOUETTE IN FELINE THORACIC RADIOGRAPHS IS PRIMARILY DUE TO LEFT ATRIAL ENLARGEMENT 下载免费PDF全文
Trisha J. Oura Aisha N. Young Bruce W. Keene Ian D. Robertson Dennis E. Jennings Donald E. Thrall 《Veterinary radiology & ultrasound》2015,56(3):245-250
Conflicting information has been published regarding the cause of a valentine‐shaped cardiac silhouette in dorsoventral or ventrodorsal thoracic radiographs in cats. The purpose of this retrospective, cross‐sectional study was to test the hypothesis that the valentine shape is primarily due to left atrial enlargement. Images for cats with a radiographic valentine‐shaped cardiac silhouette and full echocardiography examination were retrieved and independently reviewed. A subjective scoring system was used to record severity of radiographic valentine shape. Subjective radiographic evidence of left atrial enlargement in a radiographic lateral projection and a final diagnosis based on medical records were also recorded. A total of 81 cats met inclusion criteria. There was a strong positive correlation (P < 0.001) between echocardiographic left atrial size and severity of radiographic valentine shape. There was no effect of echocardiographic right atrial size on the severity of valentine shape, except when concurrent with severe left atrial enlargement. In this situation, right atrial enlargement increased the likelihood of observing a severe valentine shape. There was no effect of right atrial enlargement on the shape of the cardiac silhouette when left atrial enlargement was absent or only mild to moderate. There was no correlation between the category of final diagnosis of cardiac disease and the severity of valentine shape. Findings from this study supported the hypothesis that a valentine‐shaped cardiac silhouette in radiographs is due primarily to left atrial enlargement in cats, with right atrial enlargement only impacting the shape if concurrent with severe left atrial enlargement. 相似文献
6.
Stephen J. Adolphson Michael L. Dunn Sarah Nielsen‐Barrows Dennis L. Eggett Frost M. Steele 《Cereal Chemistry》2016,93(5):508-512
Many Mexican women are deficient in folic acid. Fortification of the corn tortilla could be an effective way to help increase the folic acid levels among the Mexican population. Previous studies have shown significant folic acid losses in the masa dough as it is held before baking. This loss in folic acid could be owing to utilization by lactic acid bacteria naturally present in the masa. The objective of this study was to determine the effect of bacteria native to corn masa on the folic acid content in masa. Bacteria in dough samples from six mills in Guadalajara, Mexico, were isolated and identified. Bacterial isolates were inoculated into sterile fortified corn masa flour, which was converted to masa and held at 56°C for 0, 3, and 6 h, replicating the conditions of freshly milled masa as held before baking. All samples, including the control, showed losses of folic acid between 66 and 79% w/w in the first 3 h of incubation. Because folic acid degradation in the sterile control sample was not different than the inoculated sample results, the decline in folic acid was not owing to bacteria (mainly Streptococcus spp.) present in the masa flour but appeared to be a chemical degradation related to time and temperature. 相似文献
7.
Paige E. Axelrood Melody Neumann David Trotter Reed Radley Gwen Shrimpton John Dennis 《New Forests》1995,9(1):35-51
Twelve Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlots from coastal British Columbia were assayed for seedborne Fusarium. All of the seedlots were contaminated with Fusarium. Percent of nonstratified seeds from individual seedlots harboring Fusarium ranged from 0.3% to 95.4%. Sixty-seven percent of the seedlots had Fusarium on less than 2% of the seeds. Post-stratification seedborne Fusarium levels were significantly less for running water imbibition compared to standing water imbibition. However, seedling growth at a container nursery was not consistently different for stratified seed imbibed initially in standing or running water. Fusarium disease symptoms were not observed in the nursery environment. The species of Fusarium isolated from seed were F. acuminatum, F. avenaceum, F. lateritium, F. moniliforme, F. oxysporum, F. poae and F. sambucinum. Twelve Fusarium isolates, comprising six species, were assessed for pathogenicity. Disease symptoms were observed after four weeks incubation and Fusarium isolates ranged in virulence from low to high. Fusarium oxysporum isolates were the most pathogenic. 相似文献
8.
In a growth chamber experiment, 70-day-old seedlings of 10 conifer species were inoculated with Colletotrichum gloeosporioides conidia to determine the host range of the fungus. Based on the percentage of seedlings affected and the disease severity on individual seedlings, the order of most to least susceptibility was: western hemlock (WH), mountain hemlock, western larch, Sitka spruce, Engelmann spruce, Douglas-fir (coastal form, then interior form), white spruce and ponderosa pine; lodgepole pine and western red cedar remained unaffected. Inoculation of WH needles showed that within 24 h C. gloeosporioides conidia germinate and appressoria (penetration structures) form. A growth chamber study demonstrated that the pathogen can infect WH at needle wetness periods as short as 15 min; number of needles affected was higher at 0.5 h, but did not increase further even when wetness was extended up to 8 h. The results are discussed in relation to blight management of greenhouse-grown conifer seedlings.Portion of a Bachelor of Science (Honors) thesis, Department of Biology, University of Victoria, Victoria, British Columbia. 相似文献
9.
Dennis N. Lozada R. Esten Mason Md Ali Babar Brett F. Carver Gina-Brown Guedira Keith Merrill Maria Nelly Arguello Andrea Acuna Lucas Vieira Amanda Holder Christopher Addison David E. Moon Randal G. Miller Susanne Dreisigacker 《Euphytica》2017,213(9):222
Genome-wide association studies (GWAS) are useful to facilitate crop improvement via enhanced knowledge of marker-trait associations (MTA). A GWAS for grain yield (GY), yield components, and agronomic traits was conducted using a diverse panel of 239 soft red winter wheat (Triticum aestivum) genotypes evaluated across two growing seasons and eight site-years. Analysis of variance showed significant environment, genotype, and genotype-by-environment effects for GY and yield components. Narrow sense heritability of GY (h 2 = 0.48) was moderate compared to other traits including plant height (h 2 = 0.81) and kernel weight (h 2 = 0.77). There were 112 significant MTA (p < 0.0005) detected for eight measured traits using compressed mixed linear models and 5715 single nucleotide polymorphism markers. MTA for GY and agronomic traits coincided with previously reported QTL for winter and spring wheat. Highly significant MTA for GY showed an overall negative allelic effect for the minor allele, indicating selection against these alleles by breeders. Markers associated with multiple traits observed on chromosomes 1A, 2D, 3B, and 4B with positive minor effects serve as potential targets for marker assisted breeding to select for improvement of GY and related traits. Following marker validation, these multi-trait loci have the potential to be utilized for MAS to improve GY and adaptation of soft red winter wheat. 相似文献
10.
Evaluating the Impact of Irrigation and Drainage Policies on Agricultural Sustainability 总被引:3,自引:0,他引:3
Farmers in the Broadview Water District in central Californiahave been improving irrigation practices in response to risingirrigation water prices and reductions in water supply since1989, when incentive policies were first implemented to reducethe volume of subsurface drain water generated in theDistrict. The average salinity of water deliveries hasincreased, over time, as the District has recycled largeamounts of drainage water to achieve regional restrictions ondrainage water discharge. We review irrigation and drainageactivities in Broadview since 1986 with an emphasis on thesustainability of crop production when drainage discharge islimited. Average cotton yields in Broadview have declined inrecent years, both nominally and in comparison with averageyields reported for the large county in which Broadview islocated. Average tomato yields in Broadview have increased inrecent years, but county-wide yields have exceeded Broadviewyields with greater frequency than in the late 1980s. Theseobservations suggest that average crop yields in Broadview maybe starting to reflect the increasing salinity of soil andwater resources, which may be due in part to persistentrestrictions on drainage water discharge. 相似文献