全文获取类型
收费全文 | 2003篇 |
免费 | 181篇 |
国内免费 | 15篇 |
专业分类
耳鼻咽喉 | 14篇 |
儿科学 | 46篇 |
妇产科学 | 42篇 |
基础医学 | 322篇 |
口腔科学 | 21篇 |
临床医学 | 191篇 |
内科学 | 536篇 |
皮肤病学 | 97篇 |
神经病学 | 114篇 |
特种医学 | 53篇 |
外科学 | 391篇 |
综合类 | 8篇 |
一般理论 | 1篇 |
预防医学 | 57篇 |
眼科学 | 14篇 |
药学 | 122篇 |
中国医学 | 10篇 |
肿瘤学 | 160篇 |
出版年
2023年 | 16篇 |
2022年 | 103篇 |
2021年 | 131篇 |
2020年 | 56篇 |
2019年 | 71篇 |
2018年 | 93篇 |
2017年 | 66篇 |
2016年 | 86篇 |
2015年 | 69篇 |
2014年 | 104篇 |
2013年 | 91篇 |
2012年 | 126篇 |
2011年 | 147篇 |
2010年 | 77篇 |
2009年 | 66篇 |
2008年 | 113篇 |
2007年 | 124篇 |
2006年 | 112篇 |
2005年 | 116篇 |
2004年 | 85篇 |
2003年 | 67篇 |
2002年 | 60篇 |
2001年 | 17篇 |
2000年 | 9篇 |
1999年 | 13篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 4篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1991年 | 15篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 15篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1981年 | 3篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1973年 | 3篇 |
1971年 | 4篇 |
1970年 | 5篇 |
1969年 | 4篇 |
1968年 | 7篇 |
1967年 | 7篇 |
1934年 | 2篇 |
1933年 | 2篇 |
排序方式: 共有2199条查询结果,搜索用时 15 毫秒
21.
Jinhe Pan Xin Long Lei Zhang Andrei Shoppert Dmitry Valeev Changchun Zhou Xiao Liu 《Materials》2022,15(23)
Coal ash (CA) is not only one of the most solid wastes from combustion, easily resulting in a series of concerns, but it is also an artificial deposit with considerable metals, such as iron and rare earth. The variation in the coal ash characteristics due to the origins, combustion process, and even storage environment has been hindering the metal utilization from coal ash. In this study, three ash sample from lab muffle, circulating fluidized bed (CFB), and pulverized coal (PC) furnace was derived for the discrepancy study from the combustion furnace, including properties, iron, and rare earth recovery. The origins of the coal feed samples have more of an effect on their properties than combustion furnaces. Magnetic separation is suitable for coal ash from PC because of the magnetite product, and the iron content is 58% in the Mag-1 fraction, with a yield of 3%. The particles in CA from CFB appear irregular and fragmental, while those from PC appear spherical with a smooth surface. The results of sequential chemical extraction and observation both indicated that the aluminosilicate phase plays an essential role in rare earth occurrences. Rare earth in CA from muffling and CFB is facilely leached, with a recovery of approximately 50%, which is higher than that from PC ash. This paper aims to offer a reference to easily understand the difference in metal recovery from coal ash. 相似文献
22.
23.
Chunpeng Xu Bo Wang Torsten Wappler Jun Chen Dmitry Kopylov Yan Fang Edmund A. Jarzembowski Haichun Zhang Michael S. Engel 《Proceedings of the National Academy of Sciences of the United States of America》2022,119(51)
Acoustic communication has played a key role in the evolution of a wide variety of vertebrates and insects. However, the reconstruction of ancient acoustic signals is challenging due to the extreme rarity of fossilized organs. Here, we report the earliest tympanal ears and sound-producing system (stridulatory apparatus) found in exceptionally preserved Mesozoic katydids. We present a database of the stridulatory apparatus and wing morphology of Mesozoic katydids and further calculate their probable singing frequencies and analyze the evolution of their acoustic communication. Our suite of analyses demonstrates that katydids evolved complex acoustic communication including mating signals, intermale communication, and directional hearing, at least by the Middle Jurassic. Additionally, katydids evolved a high diversity of singing frequencies including high-frequency musical calls, accompanied by acoustic niche partitioning at least by the Late Triassic, suggesting that acoustic communication might have been an important driver in the early radiation of these insects. The Early—Middle Jurassic katydid transition from Haglidae- to Prophalangopsidae-dominated faunas coincided with the diversification of derived mammalian clades and improvement of hearing in early mammals, supporting the hypothesis of the acoustic coevolution of mammals and katydids. Our findings not only highlight the ecological significance of insects in the Mesozoic soundscape but also contribute to our understanding of how acoustic communication has influenced animal evolution.The production of acoustic signals is one of the most important behavioral adaptions in animal communication, and the sending and receiving messages using sound is essential for the survival and success of many animals. Acoustic communication can be defined as the transmission of messages via airborne sound waves and is enabled by specialized hearing and sound-producing organs (1–4). It is widespread in two disparate extant animal taxa: insects and vertebrates, the latter including frogs, reptiles, birds, and mammals. Animal acoustic communication serves many purposes, including mating rituals, warning calls, conveying the location of food sources, and social learning, and has led to an amazing diversity and complexity of recent soundscapes (1). Therefore, exploring the evolution of animal acoustics will provide robust evidence for addressing how our modern-day soundscapes came into existence. Moreover, understanding the evolutionary history of animal acoustic behavior is crucial to unveiling how acoustic communication affects large-scale patterns of diversification (1, 2), and knowing how animals have evolved in response to sound pressure (e.g., natural noise) is also a key to the future in predicting how animals will deal with anthropogenic noise stressors (3). Nevertheless, the reconstruction of deep-time acoustic behavior is a major challenge. Using phylogenetic methods based on data from living animals is the most prevalent approach for reconstructing past acoustic behavior (2), although the fossil record of morphological traits permitting the analysis of acoustic communication is rather poor (4).Insects were the first terrestrial animals to use air-borne sound signals for long-distance communication (5). They display an extremely high diversity of auditory systems and sound-producing organs. For example, tympanal ears have evolved at least 18 times independently in diverse taxa of seven extant insect orders (Orthoptera, Mantodea, Hemiptera, Diptera, Neuroptera, Coleoptera, and Lepidoptera), involving at least 15 body locations (6, 7). The ability to produce a sound that can travel over a long distance using specialized organs, such as a stridulatory (vibration-producing) apparatus or tymbals, has evolved at least in six insect orders, Blattodea, Orthoptera, Mantodea, Hemiptera, Coleoptera, and Lepidoptera (6). These insects provide important clues for understanding the evolutionary processes driving the diversity of acoustic signaling and behavior (1, 6, 8).Among acoustically signaling insects, katydids (Orthoptera: Tettigoniidae, Prophalangopsidae, and extinct Haglidae) stand out as an ideal model to investigate the evolution of acoustic organs and behavior (1, 8–10). Male katydids produce sounds through friction between specialized veins of the forewings (tegminal stridulation), and these sounds are received by males and females primarily through the ears (auditory tympana) on the protibiae (11) (Fig. 1A). Their sophisticated acoustic communication, an important innovation in sexual selection, has been intensively studied from behavioral, neurological, and evolutionary perspectives (1, 5, 6, 10, 12–22). Although katydids have a rich fossil record dating back to the Triassic, songs have been inferred from only three species: one from the Middle Jurassic (14) and the others from the Early Eocene (13, 15). Therefore, the early evolution of their acoustic communication remains unclear. More importantly, Mesozoic katydid high-frequency songs are thought to be related to hearing improvement in early mammals (5, 12, 23). However, only low-frequency pure-tone (musical) songs have been reported in extinct katydids (13–15), and the origin of high-frequency songs remains unknown (12, 13, 17).Open in a separate windowFig. 1.Prophalangopsidae and Haglidae from the Jurassic Daohugou Konservat-Lagerstätte. (A) Sigmaboilus sinensis, NND04329, male, with stridulatory files and tympanal ears. (B) Tympanal ears on forelegs (enlargement of boxed area in a). Note the right external (posterior) and left internal (inner) tympana are of similar size. (C) Sigmaboilus sinensis, NND04334, female, tympanal ears (SI Appendix, Fig. S1A). (D) Sigmaboilus sp., NND12z088, female, tympanal ear (SI Appendix, Fig. S1B). (E) Liassophyllum caii, NND12z186, male, stridulatory file (SI Appendix, Fig. S2C). (F) Allaboilus gigantus, NND12z171, male, stridulatory file, and harp (SI Appendix, Fig. S2D). ey, eye; ha, harp; hl, hind leg; sf, stridulatory file; te, tympanal ear. (Scale bars, 10 mm (A), 1 mm (B–F).)In this study, we describe the exceptionally preserved stridulatory and hearing organs of katydids from the Middle Jurassic Daohugou Konservat-Lagerstätte (approximately 160 Mya) in China. Furthermore, we reexamine some key fossils from the Triassic of South Africa and Kyrgyzstan and compile an updated database of Mesozoic katydids. Using this, we calculate the singing frequencies of Mesozoic katydids, reconstruct their potential acoustic behavior, and analyze the evolution of their acoustic communications. Our results demonstrate that Mesozoic katydids evolved a high diversity of singing frequencies, acoustic niche partitioning, complex acoustic communication, and high-frequency musical calls. 相似文献
24.
Dmitry Permin Olga Postnikova Stanislav Balabanov Alexander Belyaev Vitaliy Koshkin Oleg Timofeev Jiang Li 《Materials》2023,16(1)
This study looked at optimizing the composition of precursors for yttria nanopowder glycine–nitrate self-propagating high-temperature synthesis (SHS). Based on thermodynamic studies, six different precursor compositions were selected, including with excesses of either oxidant or fuel. The powders from the precursors of all selected compositions were highly dispersed and had specific surface areas ranging from 22 to 57 m2/g. They were consolidated by hot pressing (HP) with lithium–fluoride sintering additive and subsequent hot isostatic pressing (HIP). The 1 mm thick HPed ceramics had transmittance in the range of 74.5% to 80.1% @ 1μm, which was limited by optical inhomogeneity due to incomplete evaporation of the sintering additive. Two-stage HIP significantly improves optical homogeneity of the ceramics. It was shown that an excess of oxidizer in the precursor decreases the powders’ agglomeration degree, which forms large pore clusters in the ceramics. 相似文献
25.
Sergey V. Panin Alexey A. Bogdanov Alexander V. Eremin Dmitry G. Buslovich Vladislav O. Alexenko 《Materials》2022,15(13)
The fatigue properties of neat polyimide and the “polyimide + 10 wt.% milled carbon fibers + 10 wt.% polytetrafluoroethylene” composite were investigated under various cyclic loading conditions. In contrast to most of the reported studies, constructing of hysteresis loops was performed through the strain assessment using the non-contact 2D Digital Image Correlation method. The accumulation of cyclic damage was analyzed by calculating parameters of mechanical hysteresis loops. They were: (i) the energy losses (hysteresis loop area), (ii) the dynamic modulus (proportional to the compliance/stiffness of the material) and (iii) the damping capacity (calculated through the dissipated and total mechanical energies). On average, the reduction in energy losses reached 10–18% at the onset of fracture, whereas the modulus variation did not exceed 2.5% of the nominal value. The energy losses decreased from 20 down to 18 J/m3 (10%) for the composite, whereas they reduced from 30 down to 25 J/m3 (17%) for neat PI in the low-cycle fatigue mode. For high-cycle fatigue, energy losses decreased from 10 to 9 J/m3 (10%) and from 17 to 14 J/m3 (18%) for neat PI and composite, respectively. For this reason, the changes of the energy losses due to hysteresis are of prospects for the characterization of both neat PI and the reinforced PI-based composites. 相似文献
26.
Daria Matyushkina Varvara Shokina Polina Tikhonova Valentin Manuvera Dmitry Shirokov Daria Kharlampieva Vasily Lazarev Anna Varizhuk Tatiana Vedekhina Alexander Pavlenko Leonid Penkin Georgij Arapidi Konstantin Pavlov Dmitry Pushkar Konstantin Kolontarev Alexander Rumyantsev Sergey Rumyantsev Lyubov Rychkova Vadim Govorun 《Viruses》2022,14(6)
COVID-19 caused by SARS-CoV-2 is continuing to spread around the world and drastically affect our daily life. New strains appear, and the severity of the course of the disease itself seems to be decreasing, but even people who have been ill on an outpatient basis suffer post-COVID consequences. Partly, it is associated with the autoimmune reactions, so debates about the development of new vaccines and the need for vaccination/revaccination continue. In this study we performed an analysis of the antibody response of patients with COVID-19 to linear and conformational epitopes of viral proteins using ELISA, chip array and western blot with analysis of correlations between antibody titer, disease severity, and complications. We have shown that the presence of IgG antibodies to the nucleoprotein can deteriorate the course of the disease, induce multiple direct COVID-19 symptoms, and contribute to long-term post-covid symptoms. We analyzed the cross reactivity of antibodies to SARS-CoV-2 with own human proteins and showed that antibodies to the nucleocapsid protein can bind to human proteins. In accordance with the possibility of HLA presentation, the main possible targets of the autoantibodies were identified. People with HLA alleles A01:01; A26:01; B39:01; B15:01 are most susceptible to the development of autoimmune processes after COVID-19. 相似文献
27.
28.
29.
Rubens Caliento Dmitry José de Santana Sarmento Érika Mont’alverne Pereira Silva Tânia Regina Tozetto-Mendoza Priscila Lie Tobouti Vanda Benini 《Acta odontologica Scandinavica》2013,71(8):539-544
Objective: Previous research demonstrated that salivary shedding of HSV-1 and EBV occurs often in adult renal transplant recipients, but there is a lack of studies on the presence of them in the saliva of paediatric population. Therefore, the objective of this study is to describe oral characteristics and to compare the shedding profile of HSV-1 and EBV in the saliva of children with renal transplant to that of chronic kidney disease patients and controls.Methods: This is a cross-sectional study involving 100 children, being 25 renal transplant recipients, 25 chronic kidney disease patients and 50 healthy children. Demographic and oral clinical characteristics were assessed. Saliva samples were collected and submitted to screening for EBV and HSV-1 by using nested polymerase chain reaction technique. Fisher’s exact, Pearson’s chi-square and Kruskal–Wallis tests were used for statistical analysis at a significance level of 5%.Results: Oral shedding of HSV-1 (28%) and EBV (60%) were significantly higher in renal transplant recipients compared to the other groups. Single vesicles in the oral mucosa were statistically associated with the presence of HSV-1 (p?=?.035). In children with chronic kidney disease, there was a higher prevalence of pale oral mucosa (32%) and enamel hypoplasia (40%) compared to paediatric renal transplant recipients and controls. Dental calculus (36%), candidiasis (8%), drug-induced gingival overgrowth (16%), mouth blisters (8%), xerostomia (12%) and salivary gland enlargement (20%) were more common in paediatric renal transplant recipients.Conclusions: Therefore, it can be concluded that salivary shedding of HSV-1 and EBV in paediatric patients was more often found in renal transplant recipients than in the renal failure and control children. Transplanted recipients showed more oral manifestations than renal failure and control children did. 相似文献
30.