全文获取类型
收费全文 | 7396篇 |
免费 | 544篇 |
国内免费 | 1篇 |
专业分类
7941篇 |
出版年
2023年 | 50篇 |
2022年 | 93篇 |
2021年 | 151篇 |
2020年 | 148篇 |
2019年 | 152篇 |
2018年 | 194篇 |
2017年 | 192篇 |
2016年 | 271篇 |
2015年 | 423篇 |
2014年 | 402篇 |
2013年 | 519篇 |
2012年 | 584篇 |
2011年 | 563篇 |
2010年 | 408篇 |
2009年 | 357篇 |
2008年 | 424篇 |
2007年 | 426篇 |
2006年 | 436篇 |
2005年 | 365篇 |
2004年 | 351篇 |
2003年 | 301篇 |
2002年 | 279篇 |
2001年 | 66篇 |
2000年 | 60篇 |
1999年 | 75篇 |
1998年 | 67篇 |
1997年 | 56篇 |
1996年 | 40篇 |
1995年 | 47篇 |
1994年 | 32篇 |
1993年 | 38篇 |
1992年 | 21篇 |
1991年 | 27篇 |
1990年 | 29篇 |
1989年 | 17篇 |
1988年 | 16篇 |
1987年 | 22篇 |
1986年 | 18篇 |
1985年 | 19篇 |
1984年 | 22篇 |
1983年 | 24篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1980年 | 11篇 |
1977年 | 15篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1973年 | 11篇 |
1971年 | 8篇 |
排序方式: 共有7941条查询结果,搜索用时 15 毫秒
951.
Emanuele Luciani Patrick L. S. van Dun Jorge Eduardo Esteves Christian Lunghi Marco Petracca Liria Papa Olivier Merdy Anne J?kel Francesco Cerritelli 《PloS one》2015,10(6)
Objective
1) to assess the preparedness to practice and satisfaction in learning environment amongst new graduates from European osteopathic institutions; 2) to compare the results of preparedness to practice and satisfaction in learning environment between and within countries where osteopathy is regulated and where regulation is still to be achieved; 3) to identify possible correlations between learning environment and preparedness to practice.Method
Osteopathic education providers of full-time education located in Europe were enrolled, and their final year students were contacted to complete a survey. Measures used were: Dundee Ready Educational Environment Measure (DREEM), the Association of American Medical Colleges (AAMC) and a demographic questionnaire. Scores were compared across institutions using one-way ANOVA and generalised linear model.Results
Nine European osteopathic education institutions participated in the study (4 located in Italy, 2 in the UK, 1 in France, 1 in Belgium and 1 in the Netherlands) and 243 (77%) of their final-year students completed the survey. The DREEM total score mean was 121.4 (SEM: 1.66) whilst the AAMC was 17.58 (SEM:0.35). A generalised linear model found a significant association between not-regulated countries and total score as well as subscales DREEM scores (p<0.001). Learning environment and preparedness to practice were significantly positively correlated (r=0.76; p<0.01).Discussion
A perceived higher level of preparedness and satisfaction was found amongst students from osteopathic institutions located in countries without regulation compared to those located in countries where osteopathy is regulated; however, all institutions obtained a ‘more positive than negative’ result. Moreover, in general, cohorts with fewer than 20 students scored significantly higher compared to larger student cohorts. Finally, an overall positive correlation between students’ preparedness and satisfaction were found across all institutions recruited. 相似文献952.
Road Traffic Injury Trends in the City of Valledupar,Colombia. A Time Series Study from 2008 to 2012
Objective
To analyze the behavior temporal of road-traffic injuries (RTI) in Valledupar, Colombia from January 2008 to December 2012.Methodology
An observational study was conducted based on records from the Colombian National Legal Medicine and Forensic Sciences Institute regional office in Valledupar. Different variables were analyzed, such as the injured person’s sex, age, education level, and type of road user; the timeframe, place and circumstances of crashes and the vehicles associated with the occurrence. Furthermore, a time series analysis was conducted using an auto-regressive integrated moving average.Results
There were 105 events per month on an average, 64.9% of RTI involved men; 82.3% of the persons injured were from 18 to 59 years of age; the average age was 35.4 years of age; the road users most involved in RTI were motorcyclists (69%), followed by pedestrians (12%). 70% had up to upper-secondary education. Sunday was the day with the most RTI occurrences; 93% of the RTI occurred in the urban area. The time series showed a seasonal pattern and a significant trend effect. The modeling process verified the existence of both memory and extrinsic variables related.Conclusions
An RTI occurrence pattern was identified, which showed an upward trend during the period analyzed. Motorcyclists were the main road users involved in RTI, which suggests the need to design and implement specific measures for that type of road user, from regulations for graduated licensing for young drivers to monitoring road user behavior for the promotion of road safety. 相似文献953.
954.
955.
Juan L. Torres-Pérez Liane S. Guild Roy A. Armstrong Jorge Corredor Anabella Zuluaga-Montero Ramón Polanco 《PloS one》2015,10(11)
Reef corals typically contain a number of pigments, mostly due to their symbiotic relationship with photosynthetic dinoflagellates. These pigments usually vary in presence and concentration and influence the spectral characteristics of corals. We studied the variations in pigment composition among seven Caribbean shallow-water Scleractinian corals by means of High Performance Liquid Chromatography (HPLC) analysis to further resolve the discrimination of corals. We found a total of 27 different pigments among the coral species, including some alteration products of the main pigments. Additionally, pigments typically found in endolithic algae were also identified. A Principal Components Analysis and a Hierarchical Cluster Analysis showed the separation of coral species based on pigment composition. All the corals were collected under the same physical environmental conditions. This suggests that pigment in the coral’s symbionts might be more genetically-determined than influenced by prevailing physical conditions of the reef. We further investigated the use of remote sensing reflectance (Rrs) as a tool for estimating the total pigment concentration of reef corals. Depending on the coral species, the Rrs and the total symbiont pigment concentration per coral tissue area correlation showed 79.5–98.5% confidence levels demonstrating its use as a non-invasive robust technique to estimate pigment concentration in studies of coral reef biodiversity and health. 相似文献
956.
Background
Trypanosoma cruzi is a parasitic protist that causes Chagas disease, which is prevalent in Latin America. Because of the unavailability of an effective drug or vaccine, and because about 8 million people are infected with the parasite worldwide, the development of novel drugs demands urgent attention. T. cruzi infects a wide variety of mammalian nucleated cells, with a preference for myocardial cells. Non-dividing trypomastigotes in the bloodstream infect host cells where they are transformed into replication-capable amastigotes. The amastigotes revert to trypomastigotes (trypomastigogenesis) before being shed out of the host cells. Although trypomastigote transformation is an essential process for the parasite, the molecular mechanisms underlying this process have not yet been clarified, mainly because of the lack of an assay system to induce trypomastigogenesis in vitro.Methodology/Principal Findings
Cultivation of amastigotes in a transformation medium composed of 80% RPMI-1640 and 20% Grace’s Insect Medium mediated their transformation into trypomastigotes. Grace’s Insect Medium alone also induced trypomastigogenesis. Furthermore, trypomastigogenesis was induced more efficiently in the presence of fetal bovine serum. Trypomastigotes derived from in vitro trypomastigogenesis were able to infect mammalian host cells as efficiently as tissue-culture-derived trypomastigotes (TCT) and expressed a marker protein for TCT. Using this assay system, we demonstrated that T. cruzi inositol 1,4,5-trisphosphate receptor (TcIP3R)—an intracellular Ca2+ channel and a key molecule involved in Ca2+ signaling in the parasite—is important for the transformation process.Conclusion/Significance
Our findings provide a new tool to identify the molecular mechanisms of the amastigote-to-trypomastigote transformation, leading to a new strategy for drug development against Chagas disease. 相似文献957.
Natalia María Arias-Palencia Monserrat Solera-Martínez Luis Gracia-Marco Pedro Silva Vicente Martínez-Vizcaíno Jorge Ca?ete-García-Prieto Mairena Sánchez-López 《PloS one》2015,10(11)
Background
Physical activity (PA) is associated with health enhancement. The aim of this study was to assess: 1) levels and patterns of PA in university students by using accelerometers; and 2) the percentage of fulfilment of PA recommendations for adults, according to different public health guidelines.Methods
Observational cross-sectional study (Cuenca’s Adults Study) involving 296 (206 women) healthy Spanish university students aged 18–25 years old. Participants wore the ActiGraph GT1M accelerometer for seven consecutive days. Total PA, steps and time spent in sedentary time, light, moderate, vigorous, and moderate to vigorous PA (MVPA) was assessed, and the prevalence of sufficient PA was calculated according to various public health guidelines.Results
No sex differences in total PA were found. University students were more sedentary during weekend days than weekdays (p<0.05). Only 30.3% of participants accumulated 30 min/day at least five days a week of MVPA. A total of 5.4% of students met the recommendation of 150 min/week of MVPA or 75 min/week of vigorous PA, in PA bouts of at least 10 min. using the same definition, but on five or more days a week, only 0.5% students were found to meet the recommendation. In addition, only 0.5% of students met the recommendation of 30 min/day of MVPA, at least five days a week and in bouts of at least 10 min. Finally, 28.1% of the students met the recommendation of 10,000 steps/day.Conclusions
Our study shows a high incidence of sedentary time in university students. The number of students meeting PA recommendations significantly differed depending on the recommendation proposed. Specific strategies to promote PA in this population are necessary as well as an agreement as to which PA guidelines should be used. 相似文献958.
Arlindo C. Motta-Silva Natanael A. Aleva Jorge K. Chavasco Mônica C. Armond Julieta P. França Luciano José Pereira 《Mycopathologia》2010,169(3):215-223
Diabetes mellitus (DM) is a systemic condition characterized by a deficient sugar metabolism, which affects the immune system
and favors the development of yeasts. The aim of the present study was to perform biochemical, morphological, exoenzyme analyses
of Candida species and the molecular identification (DNA) of C. albicans in patients with type II diabetes mellitus. The exoenzyme quantification was compared to non-diabetic patients as controls.
Two hundred and seventy-four patients who make use of complete dentures were evaluated, 28 of whom had diabetes and erythematous
oral candidiasis. Other thirty patients presented the same clinical feature but without diabetes. Samples were isolated for
biochemical identification (auxonogram), morphological identification (production of germ tubes) and PCR molecular identification
(DNA). The capability of the Candida samples in producing phospholipases and proteinases was also determined. The diabetic patients had a greater diversity of
Candida species (Fischer’s exact test, P = 0.04). The production of proteinases by C. albicans in patients with diabetes was greater than in the control group (unpaired “t” test P < 0.003). However, there was no difference between groups for phospholipase production (unpaired “t” test P > 0.05). It was concluded that patients with controlled DM exhibited systemic conditions predisposing C. albicans proteinase increased production. 相似文献
959.
Flavia Serpieri Andre Inocencio Jose Marcelino de Oliveira Alécio A. PimentaJr. Angélica Garbuio Jorge Kalil Marcelo M. Brigido Ana Maria Moro 《Molecular biotechnology》2010,45(3):218-225
Two humanized monoclonal antibody constructs bearing the same variable regions of an anti-CD3 monoclonal antibody, whole IgG
and FvFc, were expressed in CHO cells. Random and site-specific integration were used resulting in similar expression levels.
The transfectants were selected with appropriate selection agent, and the surviving cells were plated in semi-solid medium
for capture with FITC-conjugated anti-human IG antibody and picked with the robotic ClonePix FL. Conditioned media from selected
clones were purified by affinity chromatography and characterized by SDS-PAGE, Western-blot, SEC-HPLC, and isoelectric focusing.
Binding to the target present in healthy human mononuclear cells was assessed by flow cytometry, as well as by competition
between the two constructs and the original murine monoclonal antibody. The humanized constructs were not able to dislodge
the murine antibody while the murine anti-CD3 antibody could dislodge around 20% of the FvFc or IgG humanized versions. Further
in vitro and in vivo pre-clinical analyses will be carried out to verify the ability of the humanized versions to demonstrate
the immunoregulatory profile required for a humanized anti-CD3 monoclonal antibody. 相似文献
960.