全文获取类型
收费全文 | 2530篇 |
免费 | 126篇 |
国内免费 | 12篇 |
专业分类
耳鼻咽喉 | 38篇 |
儿科学 | 40篇 |
妇产科学 | 71篇 |
基础医学 | 358篇 |
口腔科学 | 214篇 |
临床医学 | 165篇 |
内科学 | 631篇 |
皮肤病学 | 58篇 |
神经病学 | 167篇 |
特种医学 | 77篇 |
外科学 | 363篇 |
综合类 | 4篇 |
预防医学 | 138篇 |
眼科学 | 35篇 |
药学 | 170篇 |
中国医学 | 19篇 |
肿瘤学 | 120篇 |
出版年
2023年 | 26篇 |
2022年 | 60篇 |
2021年 | 89篇 |
2020年 | 57篇 |
2019年 | 72篇 |
2018年 | 103篇 |
2017年 | 69篇 |
2016年 | 76篇 |
2015年 | 83篇 |
2014年 | 102篇 |
2013年 | 89篇 |
2012年 | 178篇 |
2011年 | 199篇 |
2010年 | 78篇 |
2009年 | 74篇 |
2008年 | 118篇 |
2007年 | 114篇 |
2006年 | 113篇 |
2005年 | 115篇 |
2004年 | 107篇 |
2003年 | 84篇 |
2002年 | 73篇 |
2001年 | 54篇 |
2000年 | 52篇 |
1999年 | 48篇 |
1998年 | 18篇 |
1997年 | 17篇 |
1996年 | 16篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 14篇 |
1992年 | 22篇 |
1991年 | 28篇 |
1990年 | 29篇 |
1989年 | 24篇 |
1988年 | 32篇 |
1987年 | 26篇 |
1986年 | 15篇 |
1985年 | 23篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1979年 | 12篇 |
1974年 | 8篇 |
1973年 | 8篇 |
1970年 | 6篇 |
1969年 | 6篇 |
1968年 | 9篇 |
1967年 | 8篇 |
1966年 | 8篇 |
1965年 | 10篇 |
排序方式: 共有2668条查询结果,搜索用时 15 毫秒
31.
Groppo FC Bergamaschi Cde C Cogo K Franz-Montan M Motta RH de Andrade ED 《Phytotherapy research : PTR》2008,22(8):993-998
Over the past decade, interest in drugs derived from medicinal plants has markedly increased. This study was aimed at a literature review focusing on studies investigating herbal drugs and other natural products, as well as their therapeutic application, side effects and possible drug interactions. Few studies were found to support their rational use in dentistry. Since there is an increasing use of phytotherapeutic agents in dentistry, further studies are needed to evaluate their safety and effectiveness for clinical use. 相似文献
32.
33.
Cecilia Padilla-Iglesias Lane M. Atmore Jesús Olivero Karen Lupo Andrea Manica Epifanía Arango Isaza Lucio Vinicius Andrea Bamberg Migliano 《Proceedings of the National Academy of Sciences of the United States of America》2022,119(21)
The evolutionary history of African hunter-gatherers holds key insights into modern human diversity. Here, we combine ethnographic and genetic data on Central African hunter-gatherers (CAHG) to show that their current distribution and density are explained by ecology rather than by a displacement to marginal habitats due to recent farming expansions, as commonly assumed. We also estimate the range of hunter-gatherer presence across Central Africa over the past 120,000 years using paleoclimatic reconstructions, which were statistically validated by our newly compiled dataset of dated archaeological sites. Finally, we show that genomic estimates of divergence times between CAHG groups match our ecological estimates of periods favoring population splits, and that recoveries of connectivity would have facilitated subsequent gene flow. Our results reveal that CAHG stem from a deep history of partially connected populations. This form of sociality allowed the coexistence of relatively large effective population sizes and local differentiation, with important implications for the evolution of genetic and cultural diversity in Homo sapiens.The evolutionary history of African hunter-gatherers may hold key insights into patterns and processes behind the evolution of modern human diversity. Recent genomic studies have revealed that these populations represent the oldest and most diverse human genetic lineages and have been genetically differentiated from one another since the origin of humans (1–3) (SI Appendix, Table S1). Therefore, a first question is whether their current ecological niches were also characteristic of early Homo sapiens populations. However, genetic data alone can neither determine the geographic distribution of hunter-gatherers in the past nor demonstrate a deep history of adaptation of hunter-gatherers to their current environments. In fact, various studies have proposed that farming expansions within the past 5,000 years (in particular by the ancestors of Bantu speakers) would have only recently displaced hunter-gatherers to marginalized regions less favorable to agriculture (such as rainforests and deserts) (4–7).For example, the central part of Africa, between latitudes 5°N and 5°S currently is inhabited by ∼20 scattered hunter-gatherer ethnic groups (8). These Central African hunter-gatherers (CAHG) form a genetic clade thought to have diverged from other African populations as far back as 120,000 to 200,000 years ago (2, 9). The lack of any major linguistic specificity between them is often implied to reflect extensive contacts with surrounding farmer populations (8, 10), and seen as evidence of recent displacement into marginal forest environments by expanding farming populations. However, anthropologists have remarked on the huge variability in lifestyle, habitat, techniques, and tools between CAHG (11), suggestive of long-term cultural diversification and adaptation to forest environments. Research on the drivers of demography and adaptation of CAHG populations remains extremely limited, which can be partially attributed to the lack of archaeological and osteological data resulting from a rapid disintegration of fossil remains in the rainforest’s acidic soils, in addition to social instability in the region (12). Therefore, we are still left with crucial questions regarding the time depth of occupation of Central Africa by hunter-gatherers, the breadth of the niche exploited by earlier populations in the region, and variations in levels of interconnectivity at different points in time.To address those questions, we first compiled ethnographic data on the distribution of 749 camps from 11 hunter-gatherer groups extending from West to East Central Africa. We used them as inputs for environmental niche models (ENMs) to determine the relative influence of several bioclimatic and ecological factors, as well as the presence of farming populations, on the distribution and abundance of CAHG (13, 14). Then, we used high-resolution paleoclimatic reconstructions and topographic maps to make continuous predictions about where CAHG could have lived over the past 120,000 years and the potential extension of their interaction networks. Next, we compiled all reliably dated archaeological assemblages ascribed to hunter-gatherer groups in the Congo Basin (n = 168) and confirmed the model’s ability to predict the location and date of the sites. We further contextualized genomic estimates of population divergences with changes in population densities and interpopulation connectivity predicted by our model. Last, we complemented these analyses with a detailed assessment of present and historical gene flow between nine CAHG populations (n = 265 individuals), which we used to assess recent interactions between previously diverged CAHG populations, after farming expansions. Our study therefore provides a causal link between past environmental changes and human population dynamics over evolutionary time, by predicting where and when populations across Central Africa could have exchanged genetic and/or cultural information throughout their evolutionary history. 相似文献
34.
Vinicius Rossa Luanne Ester Monteiro Ferreira Sancler da Costa Vasconcelos Eric Thomas Tai Shimabukuro Vinicius Gomes da Costa Madriaga Anna Paula Carvalho Sibele Berenice Castell Pergher Fernando de Carvalho da Silva Vitor Francisco Ferreira Carlos Adam Conte Junior Thiago de Melo Lima 《RSC advances》2022,12(22):14084
Nanotechnology experienced a great technological advance after the discovery of the graphene family (graphene – Gr, graphene oxide – GO, and reduced graphene oxide-rGO). Based on the excellent properties of these materials, it is possible to develop novel polymeric nanocomposites for several applications in our daily routine. One of the most prominent applications is for food packaging, offering nanocomposites with improved thermal, mechanical, anti-microbial, and barrier properties against gas and water vapor. This paper reviewed food packaging from its inception to the present day, with the development of more resistant and intelligent packaging. Herein, the most common combinations of polymeric matrices (derived from non-renewable and renewable sources) with Gr, GO, and rGO and their typical preparation methods are presented. Besides, the interactions present in these nanocomposites will be discussed in detail, and their final properties will be thoroughly analyzed as a function of the preparation technique and graphene family-matrix combinations.Food packaging based on nanotechnology of polymeric nanocomposites of graphene and graphene oxide results in packaging with better thermal, mechanical, antimicrobial, electrical packaging, moisture barrier and gas properties. 相似文献
35.
Alessandro Schuffner Ana Paula Lisboa Vinicius Bonato da Rosa Monica Maria Gomes da Silva 《The Brazilian journal of infectious diseases》2011,15(4):397-398
Due to HIV care improvement, discordant couples more frequently seek help in order to conceive their own biological child. Besides the advance of antiretroviral therapy, unprotected intercourse is not a complete safe option, carrying a low but still present risk of HIV transmission. We report 10 serodiscordant couples in whom the male partner is HIV positive, submitted to sperm washing and intrauterine insemination. The procedure resulted in four pregnancies and no HIV transmission to mother or child was observed. Techniques of assisted reproduction can help HIV discordant couples to conceive biological offspring and is a safer option than unprotected intercourse. 相似文献
36.
37.
38.
39.
Karina Azzolin Claudia Motta Mussi Karen Brasil Ruschel Emiliane Nogueira de Souza Amália de Fátima Lucena Eneida Rejane Rabelo-Silva 《Applied Nursing Research》2013,26(4):239-244
ObjectiveThe objective of the study is to evaluate the effectiveness of nursing interventions (NIC) using nursing outcomes (NOC) and based on NANDA-I nursing diagnoses in patients with heart failure in home care.MethodIn this longitudinal study, 23 patients with heart failure were followed for 6 months, in four home visits. During the visits, nursing diagnoses were established, outcomes assessed, and interventions implemented.ResultsOf the 11 NIC interventions implemented, eight proved effective, that is, showed significant improvement between the first and the fourth visit, according to scores obtained for six outcomes: knowledge: treatment regimen, knowledge: medication, compliance behavior, symptom control, activity tolerance, and energy conservation.ConclusionNIC interventions health education, self-modification assistance, behavior modification, teaching: prescribed medication, teaching: disease process, nutritional counseling, telephone consultation, and energy conservation showed effective outcomes based on NOC scores, suggesting that the NANDA-I, NIC, and NOC linkage is useful in patients with heart failure in home care. 相似文献
40.
Luz CR Mascarenhas JD Gabbay YB Motta AR Lima TV Soares Lda S Linhares AC 《Revista do Instituto de Medicina Tropical de S?o Paulo》2005,47(5):287-293
During June 1997-June 1999 rotavirus infection was screened in infants aged up to 2 years and hospitalised with acute diarrhoea in S?o Luís, Northeastern Brazil. Altogether, 128 stool samples were collected from diarrhoeic patients and additional 122 faecal specimens from age and temporal matched inpatients without diarrhoea were obtained; rotavirus positivity rates for these groups were 32.0% (41/128) and 9.8% (12/122), respectively (p < 0.001). Both electropherotyping and serotyping could be performed in 42 (79.2%) of the 53 rotavirus-positive stool samples. Long and short electropherotypes were detected at similar rates--38.1% and 40.5% of specimens, respectively. Overall, a G serotype could be assigned for 35 (83.3%) of specimens, the majority of them (66.7%) bearing G1-serotype specificity. Taking both electropherotypes and serotypes together, G1 rotavirus strains displaying long and short RNA patterns accounted for 30.9% and 19.0% of tested specimens, respectively; all G2 strains had short electropherotype. Rotavirus gastroenteritis was detected year-round and, in 1998, the incidence rates tended to be higher during the second semester than in the first semester: 45.2% and 26.1% (p = 0.13), respectively. Rotavirus infections peaked at the second semester of life with frequencies of 30.1% and 13.5% for diarrhoeic children and controls, respectively. While the six rotavirus strains bearing G2-type specificity were circulating throughout the whole study period, G1 serotypes (n = 27) emerged as from June 1998 onwards, 20 (74.1%) of which clustering in 1998. These data underscore the importance of rotaviruses in the aetiology of severe infantile gastroenteritis in Northeastern Brazil and sustain the concept that a future vaccine should confer protection against more than one serotype. 相似文献