全文获取类型
收费全文 | 4542篇 |
免费 | 386篇 |
国内免费 | 1篇 |
专业分类
4929篇 |
出版年
2023年 | 38篇 |
2022年 | 83篇 |
2021年 | 129篇 |
2020年 | 81篇 |
2019年 | 103篇 |
2018年 | 146篇 |
2017年 | 112篇 |
2016年 | 187篇 |
2015年 | 276篇 |
2014年 | 245篇 |
2013年 | 337篇 |
2012年 | 393篇 |
2011年 | 384篇 |
2010年 | 194篇 |
2009年 | 182篇 |
2008年 | 248篇 |
2007年 | 246篇 |
2006年 | 220篇 |
2005年 | 182篇 |
2004年 | 171篇 |
2003年 | 160篇 |
2002年 | 160篇 |
2001年 | 63篇 |
2000年 | 36篇 |
1999年 | 48篇 |
1998年 | 42篇 |
1997年 | 35篇 |
1996年 | 31篇 |
1995年 | 24篇 |
1994年 | 18篇 |
1993年 | 14篇 |
1992年 | 18篇 |
1991年 | 23篇 |
1990年 | 23篇 |
1989年 | 10篇 |
1988年 | 13篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 20篇 |
1984年 | 21篇 |
1983年 | 21篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1979年 | 13篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1974年 | 13篇 |
1973年 | 11篇 |
1968年 | 9篇 |
1966年 | 9篇 |
排序方式: 共有4929条查询结果,搜索用时 15 毫秒
991.
992.
993.
Dilva?TerzanoEmail author Ian?Kotzé Christo?Marais Silvio?Cianciullo Alessio?Farcomeni Paolo?Caroli Luca?Malatesta Fabio?AttorreView authors OrcID profile 《Plant Ecology》2018,219(3):277-297
Alien plants invasion has negative impacts on the structure and functionality of ecosystems. Understanding the determinants of this process is fundamental for addressing environmental issues, such as the water availability in South Africa’s catchments. Both environmental and anthropogenic factors determine the invasion of alien species; however, their relative importance has to be quantified. The aim of this paper was to estimate the importance of 32 explanatory variables in predicting the distribution of the major invasive alien plant species (IAPS) of South Africa, through the use of Species Distribution Models. We used data from the National Invasive Alien Plants Survey, delineated at a quaternary catchment level, coupled with climatic, land cover, edaphic, and anthropogenic variables. Using two-part generalized linear models, we compared the accuracy of two different sets of variables in predicting the spatial distribution of IAPS; the first included environmental correlates alone, and the second included both environmental and anthropogenic variables. Using Random Forest, we explored the relative importance of the variables in producing a map of potential distribution of IAPS. Results showed that the inclusion of anthropogenic variables did not significantly improve model predictions. The most important variables influencing the distribution of IAPS appeared to be the climatic ones. The modeled potential distribution was analyzed in relation to provinces, biomes, and species’ minimum residence time. 相似文献
994.
Marina Papaianni Felice Contaldi Andrea Fulgione Sheridan L. Woo Angela Casillo Maria Michela Corsaro Ermenegilda Parrilli Luca Marcolungo Marzia Rossato Massimo Delledonne Marianna Garonzi Domenico Iannelli Rosanna Capparelli 《BMC microbiology》2018,18(1):208
Background
The study describes the Salmonella Rissen phage ?1 isolated from the ?1-sensitive Salmonella Rissen strain RW. The same phage was then used to select the resistant strain RR?1+, which can harbour or not ?1.Results
Following this approach, we found that ?1, upon excision from RW cells with mitomycin, behaves as a temperate phage: lyses host cells and generates phage particles; instead, upon spontaneous excision from RR?1+ cells, it does not generate phage particles; causes loss of phage resistance; switches the O-antigen from the smooth to the rough phenotype, and favors the transition of Salmonella Rissen from the planktonic to the biofilm growth.The RW and RR?1+ strains differ by 10 genes; of these, only two (phosphomannomutase_1 and phosphomannomutase_2; both involved in the mannose synthesis pathway) display significant differences at the expression levels. This result suggests that phage resistance is associated with these two genes.Conclusions
Phage ?1 displays the unusual property of behaving as template as well as lytic phage. This feature was used by the phage to modulate several phases of Salmonella Rissen lifestyle.995.
Carlotta Biagi Luca Pierantoni Michelangelo Baldazzi Laura Greco Ada Dormi Arianna Dondi Giacomo Faldella Marcello Lanari 《BMC pulmonary medicine》2018,18(1):191
Background
Guidelines currently do not recommend the routine use of chest x-ray (CXR) in bronchiolitis. However, CXR is still performed in a high percentage of cases, mainly to diagnose or rule out pneumonia. The inappropriate use of CXR results in children exposure to ionizing radiations and increased medical costs. Lung Ultrasound (LUS) has become an emerging diagnostic tool for diagnosing pneumonia in the last decades. The purpose of this study was to assess the diagnostic accuracy and reliability of LUS for the detection of pneumonia in hospitalized children with bronchiolitis and to evaluate the agreement between LUS and CXR in diagnosing pneumonia in these patients.Methods
We enrolled children admitted to our hospital in 2016–2017 with a diagnosis of bronchiolitis and undergone CXR because of clinical suspicion of concomitant pneumonia. LUS was performed in each child by a pediatrician blinded to the patient’s clinical, laboratory and CXR findings. An exploratory analysis was done in the first 30 patients to evaluate the inter-observer agreement between a pediatrician and a radiologist who independently performed LUS. The diagnosis of pneumonia was established by an expert clinician based on the recommendations of the British Thoracic Society guidelines.Results
Eighty seven children with bronchiolitis were investigated. A final diagnosis of concomitant pneumonia was made in 25 patients. Sensitivity and specificity of LUS for the diagnosis of pneumonia were 100% and 83.9% respectively, with an area under-the-curve of 0.92, while CXR showed a sensitivity of 96% and specificity of 87.1%. When only consolidation >?1?cm was considered consistent with pneumonia, the specificity of LUS increased to 98.4% and the sensitivity decreased to 80.0%, with an area under-the-curve of 0.89. Cohen’s kappa between pediatrician and radiologist sonologists in the first 30 patients showed an almost perfect agreement in diagnosing pneumonia by LUS (K 0.93).Conclusions
This study shows the good accuracy of LUS in diagnosing pneumonia in children with clinical bronchiolitis. When including only consolidation size >?1?cm, specificity of LUS was higher than CXR, avoiding the need to perform CXR in these patients. Added benefit of LUS included high inter-observer agreement.Trial registration
Identifier: NCT03280732. Registered 12 September 2017 (retrospectively registered).996.
997.
998.
999.
Luca Espen Silvia Morgutti Chiara Alisi Livia Pirovano Enzio Ragg Sergio M. Cocucci 《Physiologia plantarum》1995,93(4):577-583
1000.