全文获取类型
收费全文 | 94502篇 |
免费 | 382篇 |
国内免费 | 812篇 |
专业分类
95696篇 |
出版年
2021年 | 17篇 |
2018年 | 11845篇 |
2017年 | 10678篇 |
2016年 | 7469篇 |
2015年 | 625篇 |
2014年 | 308篇 |
2013年 | 338篇 |
2012年 | 4256篇 |
2011年 | 12852篇 |
2010年 | 12032篇 |
2009年 | 8268篇 |
2008年 | 9826篇 |
2007年 | 11434篇 |
2006年 | 318篇 |
2005年 | 576篇 |
2004年 | 1035篇 |
2003年 | 1084篇 |
2002年 | 836篇 |
2001年 | 286篇 |
2000年 | 209篇 |
1999年 | 67篇 |
1998年 | 21篇 |
1997年 | 41篇 |
1996年 | 26篇 |
1995年 | 14篇 |
1994年 | 17篇 |
1993年 | 42篇 |
1992年 | 47篇 |
1991年 | 71篇 |
1990年 | 41篇 |
1989年 | 35篇 |
1988年 | 38篇 |
1987年 | 42篇 |
1986年 | 25篇 |
1985年 | 24篇 |
1984年 | 35篇 |
1983年 | 31篇 |
1982年 | 14篇 |
1981年 | 11篇 |
1979年 | 25篇 |
1977年 | 14篇 |
1975年 | 15篇 |
1974年 | 14篇 |
1973年 | 11篇 |
1972年 | 252篇 |
1971年 | 280篇 |
1970年 | 18篇 |
1965年 | 15篇 |
1962年 | 24篇 |
1944年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Piotr Cysewski Maciej Przybyłek Dorota Ziółkowska Karina Mroczyńska 《Journal of molecular modeling》2016,22(5):103
The cocrystallization landscape of benzamide and urea interacting with aliphatic and aromatic carboxylic acids was studied both experimentally and theoretically. Ten new cocrystals of benzamide were synthesized using an oriented samples approach via a fast dropped evaporation technique. Information about types of known bi-component cocrystals augmented with knowledge of simple binary eutectic mixtures was used for the analysis of virtual screening efficiency among 514 potential pairs involving aromatic carboxylic acids interacting with urea or benzamide. Quantification of intermolecular interaction was achieved by estimating the excess thermodynamic functions of binary liquid mixtures under supercooled conditions within a COSMO-RS framework. The smoothed histograms suggest that slightly more potential pairs of benzamide are characterized in the attractive region compared to urea. Finally, it is emphasized that prediction of cocrystals of urea is fairly direct, while it remains ambiguous for benzamide paired with carboxylic acids. The two known simple eutectics of urea are found within the first two quartiles defined by excess thermodynamic functions, and all known cocrystals are outside of this range belonging to the third or fourth quartile. On the contrary, such a simple separation of positive and negative cases of benzamide miscibility in the solid state is not observed. The difference in properties between urea and benzamide R2,2(8) heterosynthons is also documented by alterations of substituent effects. Intermolecular interactions of urea with para substituted benzoic acid analogues are stronger compared to those of benzamide. Also, the amount of charge transfer from amide to aromatic carboxylic acid and vice versa is more pronounced for urea. However, in both cases, the greater the electron withdrawing character of the substituent, the higher the binding energy, and the stronger the supermolecule polarization via the charge transfer mechanism. 相似文献
992.
As human populations in Africa expand, humans encroach and modify wildlife habitats for farming, fishing, tourism, or settlement. Anthropogenic activities in shared environments may promote transmission of zoonotic pathogens between humans, domestic animals, and wildlife. Between July 2012 and February 2014, we evaluated Salmonella prevalence, serovars, genotypes, and antibiotic resistant phenotypes in resident and migratory birds utilizing human-impacted habitats in northwestern Lake Victoria and protected habitats in Queen Elisabeth National Park. Salmonella occurrence in the urban environment was assessed by sampling storm-water and wastewater from a channel that drains Kampala City into Lake Victoria. Salmonella was detected in 4.3% pooled bird fecal samples, and 57.1% of environmental samples. While birds in impacted and protected areas shared serovars, the genotypes were distinct. We found distinct strains in birds and the environment suggesting some strains in birds are host adapted, and strains circulating in the environment may not necessarily disseminate to birds. Conversely, birds in both impacted and protected areas shared strains with the urban environment, suggesting Salmonella disseminates between impacted environments and birds across sites. Overall, more strains were observed in the urban environment compared to birds, and poses risk of Salmonella reemergence in birds and transmission across species and space. 相似文献
993.
John J. Openshaw Sonia Hegde Hossain M. S. Sazzad Salah Uddin Khan M. Jahangir Hossain Jonathan H. Epstein Peter Daszak Emily S. Gurley Stephen P. Luby 《EcoHealth》2016,13(1):39-48
We used data on feeding practices and domestic animal health gathered from 207 Bangladeshi villages to identify any association between grazing dropped fruit found on the ground or owners directly feeding bat- or bird-bitten fruit and animal health. We compared mortality and morbidity in domestic animals using a mixed effects model controlling for village clustering, herd size, and proxy measures of household wealth. Thirty percent of household heads reported that their animals grazed on dropped fruit and 20% reported that they actively fed bitten fruit to their domestic herds. Household heads allowing their cattle to graze on dropped fruit were more likely to report an illness within their herd (adjusted prevalence ratio 1.17, 95% CI 1.02–1.31). Household heads directly feeding goats bitten fruit were more likely to report illness (adjusted prevalence ratio 1.35, 95% CI 1.16–1.57) and deaths (adjusted prevalence ratio 1.64, 95% CI 1.13–2.4). Reporting of illnesses and deaths among goats rose as the frequency of feeding bitten fruit increased. One possible explanation for this finding is the transmission of bat pathogens to domestic animals via bitten fruit consumption. 相似文献
994.
Patrick Lambert Jose Antonio Campoy Igor Pacheco Jehan-Baptiste Mauroux Cassia Da Silva Linge Diego Micheletti Daniele Bassi Laura Rossini Elisabeth Dirlewanger Thierry Pascal Michela Troggio Maria Jose Aranzana Andrea Patocchi Pere Arús 《Tree Genetics & Genomes》2016,12(6):121
One of the applications of genomics is to identify genetic markers linked to loci responsible for variation in phenotypic traits, which could be used in breeding programs to select individuals with favorable alleles, particularly at the seedling stage. With this aim, in the framework of the European project FruitBreedomics, we selected five main peach fruit characters and a resistance trait, controlled by major genes with Mendelian inheritance: fruit flesh color Y, fruit skin pubescence G, fruit shape S, sub-acid fruit D, stone adhesion-flesh texture F-M, and resistance to green peach aphid Rm2. They were all previously mapped in Prunus. We then selected three F1 and three F2 progenies segregating for these characters and developed genetic maps of the linkage groups including the major genes, using the single nucleotide polymorphism (SNP) genome-wide scans obtained with the International Peach SNP Consortium (IPSC) 9K SNP array v1. We identified SNPs co-segregating with the characters in all cases. Their positions were in agreement with the known positions of the major genes. The number of SNPs linked to each of these, as well as the size of the physical regions encompassing them, varied depending on the maps. As a result, the number of useful SNPs for marker-assisted selection varied accordingly. As a whole, this study establishes a sound basis for further development of MAS on these characters. Additionally, we also discussed some limitations that were observed regarding the SNP array efficiency. 相似文献
995.
Chunyan Liu Qiong Zhang Xiaohong Yao Caihong Zhong Chunlin Yan Hongwen Huang 《Tree Genetics & Genomes》2016,12(2):21
Simple sequence repeats (SSRs) have been widely used in the construction of linkage maps, quantitative trait loci (QTLs) mapping, and marker-assisted selection (MAS). The availability of the sequenced Actinidia chinensis (kiwifruit) genome allows for the inexpensive and efficient development of microsatellite markers. In this study, a total of 49,067 SSRs were identified and characterized in the genome sequences of kiwifruit. Dinucleotide repeats are the most abundant SSRs, with the AG/TC motif accounting for 44.2 % of all SSRs in the genome. Fifty-five newly derived SSRs, together with 46 previously available SSRs, were integrated into linkage maps of an interspecific kiwifruit population. In addition, eight sex-linked SSR markers (including one previously published SSR) were mapped in the sex-related region on the LG25, suggesting that recombination is partially suppressed to maintain dioecy in kiwifruit. The SSRs developed from this study are a valuable resource for kiwifruit genetics and will contribute to the use of MAS in early sex determination of dioecious plant breeding. 相似文献
996.
Lee McMichael Daniel Edson David Mayer Amanda McLaughlin Lauren Goldspink Miranda E. Vidgen Steven Kopp Joanne Meers Hume Field 《EcoHealth》2016,13(1):49-59
Bats of the genus Pteropus (Pteropodidae) are recognised as the natural host of multiple emerging pathogenic viruses of animal and human health significance, including henipaviruses, lyssaviruses and ebolaviruses. Some studies have suggested that physiological and ecological factors may be associated with Hendra virus infection in flying-foxes in Australia; however, it is essential to understand the normal range and seasonal variability of physiological biomarkers before seeking physiological associations with infection status. We aimed to measure a suite of physiological biomarkers in P. alecto over time to identify any seasonal fluctuations and to examine possible associations with life-cycle and environmental stressors. We sampled 839 adult P. alecto in the Australian state of Queensland over a 12-month period. The adjusted population means of every assessed hematologic and biochemical parameter were within the reported reference range on every sampling occasion. However, within this range, we identified significant temporal variation in these parameters, in urinary parameters and body condition, which primarily reflected the normal annual life cycle. We found no evident effect of remarkable physiological demands or nutritional stress, and no indication of clinical disease driving any parameter values outside the normal species reference range. Our findings identify underlying temporal physiological changes at the population level that inform epidemiological studies and assessment of putative physiological risk factors driving Hendra virus infection in P. alecto. More broadly, the findings add to the knowledge of Pteropus populations in terms of their relative resistance and resilience to emerging infectious disease. 相似文献
997.
Uthpala A. Jayawardena Jason R. Rohr Ayanthi N. Navaratne Priyanie H. Amerasinghe Rupika S. Rajakaruna 《EcoHealth》2016,13(1):111-122
The impact of widespread and common environmental factors, such as chemical contaminants, on infectious disease risk in amphibians is particularly important because both chemical contaminants and infectious disease have been implicated in worldwide amphibian declines. Here we report on the lone and combined effects of exposure to parasitic cercariae (larval stage) of the digenetic trematode, Acanthostomum burminis, and four commonly used pesticides (insecticides: chlorpyrifos, dimethoate; herbicides: glyphosate, propanil) at ecologically relevant concentrations on the survival, growth, and development of the common hourglass tree frog, Polypedates cruciger Blyth 1852. There was no evidence of any pesticide-induced mortality on cercariae because all the cercariae successfully penetrated each tadpole host regardless of pesticide treatment. In isolation, both cercarial and pesticide exposure significantly decreased frog survival, development, and growth, and increased developmental malformations, such as scoliosis, kyphosis, and also edema and skin ulcers. The combination of cercariae and pesticides generally posed greater risk to frogs than either factor alone by decreasing survival or growth or increasing time to metamorphosis or malformations. The exception was that lone exposure to chlorpyrifos had higher mortality without than with cercariae. Consistent with mathematical models that suggest that stress should increase the impact of generalist parasites, the weight of the evidence from the field and laboratory suggests that ecologically relevant concentrations of agrochemicals generally increase the threat that trematodes pose to amphibians, highlighting the importance of elucidating interactions between anthropogenic activities and infectious disease in taxa of conservation concern. 相似文献
998.
Lisa Shender Michael Niemela Patricia Conrad Tracey Goldstein Jonna Mazet 《EcoHealth》2016,13(3):525-534
Chagas disease, which manifests as cardiomyopathy and severe gastrointestinal dysfunction, is caused by Trypanosoma cruzi, a vector-borne parasite. In California, the vector Triatoma protracta frequently colonizes woodrat (Neotoma spp.) lodges, but may also invade nearby residences, feeding upon humans and creating the dual risk of bite-induced anaphylaxis and T. cruzi transmission. Our research aimed to assess T. cruzi presence in woodrats in a previously unstudied northern California area, statistically evaluate woodrat microhabitat use with respect to vegetation parameters, and provide guidance for habitat modifications to mitigate public health risks associated with Tr. protracta exposure. Blood samples from big-eared woodrats (N. macrotis) trapped on rural private properties yielded a T. cruzi prevalence of 14.3%. Microhabitat analyses suggest that modifying vegetation to reduce understory density within a 40 meter radius of human residences might minimize woodrat lodge construction within this buffer area, potentially decreasing human exposure to Tr. protracta. 相似文献
999.
1000.
Craig M. Hardner Kate Evans Chris Brien Fred Bliss Cameron Peace 《Tree Genetics & Genomes》2016,12(2):20
Accurate prediction of genetic potential and response to selection in breeding requires knowledge of genetic parameters for important selection traits. Data from breeding trials can be used to obtain estimates of these parameters so that predictions are directly relevant to the improvement program. Here, a factor allocation diagram was developed to describe the sampling design used to assess the quality of fresh and post-storage (2 months) fruit from advanced selection trial in an apple breeding program from which models for analyses were developed. Genetic variation was the largest source of variation for the fruit size, red colour type, proportion of red skin colour and lenticels, and instrumentally assessed fruit diameter, mass, puncture force and titratable acidity. In contrast, residual variation was the largest for fruit shape, juiciness, sweetness, aromatic flavour, eating and overall quality, and instrumental crispness. Genetic effects for traits were generally stable over fixed effects, except for a significant interaction with storage duration for firmness. Genetic correlations among traits were generally weak except between fruit mass (and diameter) and sensory size (0.98), titratable acidity and sensory acidity (0.97), puncture force and sensory firmness (0.96–0.90), crispness and juiciness (0.87), sweetness and aromatic flavour (0.84) and instrumental and sensory crispness (0.75). Predictions of the performance for seven commercial cultivars are presented. This study suggests that the Washington State apple production area can be treated as a single target environment and sufficient diversity exists to generate new elite cultivars. In addition, options for evaluating the efficiency of apple breeding are discussed. 相似文献