全文获取类型
收费全文 | 1310篇 |
免费 | 90篇 |
国内免费 | 4篇 |
专业分类
耳鼻咽喉 | 3篇 |
儿科学 | 8篇 |
妇产科学 | 8篇 |
基础医学 | 262篇 |
口腔科学 | 42篇 |
临床医学 | 111篇 |
内科学 | 267篇 |
皮肤病学 | 46篇 |
神经病学 | 164篇 |
特种医学 | 44篇 |
外科学 | 162篇 |
综合类 | 6篇 |
预防医学 | 50篇 |
眼科学 | 27篇 |
药学 | 114篇 |
2篇 | |
肿瘤学 | 88篇 |
出版年
2023年 | 11篇 |
2022年 | 76篇 |
2021年 | 71篇 |
2020年 | 34篇 |
2019年 | 35篇 |
2018年 | 43篇 |
2017年 | 22篇 |
2016年 | 29篇 |
2015年 | 33篇 |
2014年 | 52篇 |
2013年 | 44篇 |
2012年 | 81篇 |
2011年 | 67篇 |
2010年 | 50篇 |
2009年 | 42篇 |
2008年 | 83篇 |
2007年 | 80篇 |
2006年 | 66篇 |
2005年 | 86篇 |
2004年 | 69篇 |
2003年 | 74篇 |
2002年 | 60篇 |
2001年 | 13篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 15篇 |
1997年 | 15篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1980年 | 7篇 |
1976年 | 2篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1961年 | 3篇 |
1944年 | 2篇 |
1943年 | 4篇 |
1942年 | 5篇 |
1941年 | 2篇 |
1915年 | 2篇 |
1914年 | 2篇 |
排序方式: 共有1404条查询结果,搜索用时 15 毫秒
41.
42.
Jawad Ahmad Zhiguang Zhou Rebeca Martínez-García Nikolai Ivanovich Vatin Jesús de-Prado-Gil Mohammed A. El-Shorbagy 《Materials》2022,15(7)
The by-product of the foundry industry is waste foundry sand (WFS). The use of WFS in building materials will safeguard the ecosystem and environmental assets while also durable construction. The use of industrial waste in concrete offsets a shortage of environmental sources, solves the waste dumping trouble and provides another method of protecting the environment. Several researchers have investigated the suitability of WFS in concrete production instead of natural river sand in the last few decades to discover a way out of the trouble of WFS in the foundry region and accomplish its recycling in concrete production. However, a lack of knowledge about the progress of WFS in concrete production is observed and compressive review is required. The current paper examines several properties, such as the physical and chemical composition of WFS, fresh properties, mechanical and durability performance of concrete with partially substituting WFS. The findings from various studies show that replacing WFS up to 30% enhanced the durability and mechanical strength of concrete to some extent, but at the same time reduced the workability of fresh concrete as the replacement level of WFS increased. In addition, this review recommended pozzolanic material or fibre reinforcement in combination with WFS for future research. 相似文献
43.
Jawad Ahmad Zhiguang Zhou Kseniia Iurevna Usanova Nikolai Ivanovich Vatin Mohammed A. El-Shorbagy 《Materials》2022,15(7)
The annual worldwide production rate of waste glass is a million tons; the waste glass is non-biodegradable, resulting in environmental pollution. However, the chemical composition of waste glass (WG) is promoted to be used as a partial substitution of binding or filler (aggregate) material in concrete production. Although significant research has been conducted in this area, the results of these studies are scattered, and it is difficult to judge the suitability of waste glass in concrete. This review looks at the effects of waste glass on concrete’s fresh, mechanical, and durability properties. It concludes that waste glass decreased the flowability of concrete. Furthermore, waste glass can be used as pozzolanic material, creating secondary cementitious compound (CSH) gel. CSH gel increased the cement paste’s binding properties, leading to increased mechanical performance. Moreover, this study reveals that the optimum dose of waste glass is important to minimize the possibility of an alkali–silica reactions. Based on this review, most researchers conclude that 20% substitution of waste glass as binding material is the optimum dose. The wide range of discussion provides the necessary guideline for the best research practice in the future. 相似文献
44.
Meera R. Chappidi Heather J. Chalfin Daniel J. Johnson Max Kates Nikolai A. Sopko Michael H. Johnson Jen-Jane Liu Steven M. Frank Trinity J. Bivalacqua 《Urologic oncology》2017,35(2):38.e17-38.e24
Background
Patients with bladder cancer undergoing radical cystectomy (RC) experience high rates of perioperative blood transfusions (PBTs) and morbidity. The aim of this study was to evaluate the effect of blood storage duration on the risk of adverse perioperative outcomes in this high-risk patient population.Materials and methods
In a retrospective review of RC patients from 2010 to 2014 who received PBTs, the average storage duration for all units transfused was used to classify patients as receiving older blood using 3 different definitions (≥21 days,≥28 days, and≥35 days). Multivariable Poisson regression models were used to determine the adjusted relative risk of perioperative infections and overall morbidity in those given older blood compared to fresher blood.Results
Of the 451 patients undergoing RC, 205 (45%) received nonirradiated PBTs. In multivariable modeling, increasing average blood storage duration, as a continuous variable, was associated with an increased risk of infections (risk ratio [RR] = 1.08 per day, 95% CI: 1.01–1.17) and overall morbidity (RR = 1.08 per day, 95% CI: 1.01–1.15). Furthermore, ≥28-day blood storage (vs.<28) was associated with increased infections (RR = 2.69, 95% CI: 1.18–6.14) and morbidity (RR = 2.54, 95% CI: 1.31–4.95), and ≥35-day blood storage (vs.<35) was also associated with increased infections (RR = 2.83, 95% CI: 1.42–5.66) and morbidity (RR = 3.35, 95% CI: 1.95–5.77).Conclusions
Although blood is stored up to 42 days, storage≥28 days may expose RC patients to increased perioperative infections and overall morbidity compared with storage<28 days. Prospective cohort studies are warranted in cystectomy and other high-risk surgical oncology patients to better determine the effect of blood storage duration. 相似文献45.
Wei Quan Chin Yeong Huei Lee Mugahed Amran Roman Fediuk Nikolai Vatin Ahmad Beng Hong Kueh Yee Yong Lee 《Materials》2022,15(5)
The fabrication of bricks commonly consumes relatively high natural resources. To reduce the carbon footprint in the brick production industry, repurposing industrial wastes in the making of sustainable bricks is a recent trend in research and application. Local wastes, such as oil palm shell (OPS), palm oil fuel ash (POFA), and quarry dust (QD), are massively produced annually in the palm oil-exporting countries. Moreover, QD from mining industries is hazardous to both water and air quality. For better waste management in marching towards sustainability, these wastes should be given their second life as construction materials. Therefore, this paper investigates the possibility of incorporating agro-industrial wastes into the brick mixture by examining their properties by means of several standardized tests. For the mix design, a 100% replacement of coarse aggregate with OPS, 20% replacement of cement with POFA, 20% cement weight of limestone as admixture, and 0 to 50% replacements of fine aggregate with QD are experimentally considered. The optimum mix of these wastes is preliminarily determined by focusing on high compressive strength as an indicator. Other examinations include splitting tensile, flexural strength, water absorption, and efflorescence tests. Although the agro-industrial waste cement brick is 18% lower in the strength to weight ratio compared to that of conventional, it is observed that it has better late strength development due to its POFA pozzolanic properties. Moreover, the proposed green cement brick is further checked for compliance with several standards for feasible use in the construction industry. Financially, the cost for the brick with the new mix design is almost equivalent to that of conventional. Hence, this green cement brick is reasonable to be employed in the construction industry to promote material sustainability for better waste management. 相似文献
46.
Long-term treatment outcomes in edentulous patients with implant-fixed prostheses: the Toronto study
PURPOSE: The aim of this prospective study was to report long-term treatment outcomes (prosthetic and implant related) of edentulous patients treated with implant-supported fixed prostheses who participated in the first clinical implant study in North America. MATERIALS AND METHODS: Forty-five patients were treated with Br?nemark implants supporting a total of 47 fixed prostheses (42 mandibular and 5 maxillary) between 1979 and 1984. All patients were recalled regularly for comprehensive prospective clinical and radiographic assessments. RESULTS: Thirty-one patients (33 prostheses) attended a final recall visit in 2002; 71% of patients had been followed for 20 years (range 18 to 23 years), with overall prosthetic plan and implant outcome success rates of 84% and 87%, respectively. Mean marginal bone loss around the implants after the first year of loading was small (0.05 mm/year), with high individual variations. Poor oral hygiene, smoking history, and implant position appeared to be predictors of marginal bone loss. Prosthetic maintenance was ongoing and included fractured components and replacement of prostheses; the longevity of a fixed prosthesis for this group of patients was 8.39+/-5.30 years. CONCLUSION: This study confirmed the overall long-term treatment outcome success of patients treated with fixed prostheses supported by Br?nemark implants. Successful osseointegration with a small mean bone loss was maintained as study patients aged, although prosthetic maintenance was required. The latter consideration should be discussed with all patients seeking such treatment. 相似文献
47.
Bo Chang Tanja Grau Susann Dangel Ron Hurd Bernhard Jurklies E. Cumhur Sener Sten Andreasson Helene Dollfus Britta Baumann Sylvia Bolz Nikolai Artemyev Susanne Kohl John Heckenlively Bernd Wissinger 《Proceedings of the National Academy of Sciences of the United States of America》2009,106(46):19581-19586
Retinal cone photoreceptors mediate fine visual acuity, daylight vision, and color vision. Congenital hereditary conditions in which there is a lack of cone function in humans cause achromatopsia, an autosomal recessive trait, characterized by low vision, photophobia, and lack of color discrimination. Herein we report the identification of mutations in the PDE6C gene encoding the catalytic subunit of the cone photoreceptor phosphodiesterase as a cause of autosomal recessive achromatopsia. Moreover, we show that the spontaneous mouse mutant cpfl1 that features a lack of cone function and rapid degeneration of the cone photoreceptors represents a homologous mouse model for PDE6C associated achromatopsia. 相似文献
48.
Margit Fröhlich Nikolai Mühlberger Hartmut Hanke Armin Imhof Angela Döring Mark B Pepys 《Annals of medicine》2013,45(5):353-361
BACKGROUND AND AIM. To measure inflammatory markers in postmenopausal women on different forms of hormone replacement therapy (HRT). METHOD. C-reactive protein (CRP), fibrinogen, plasma viscosity (PV), albumin and white blood cell (WBC) count were determined in 749 postmenopausal women. RESULTS. CRP concentration was significantly higher in women on estrogen monotherapy (difference of the median (d) 0.96 r mg/l, P r = r 0.013), compared to those without HRT, but there was no difference in women on combined HRT. Fibrinogen concentration was significantly lower in women on estrogen monotherapy (d 0.25 r g/l, P r = r 0.004) and combined HRT (d 0.4 r g/l, P r < r 0.001), compared to women without HRT. Similarly, PV was significantly lower in women on estrogen monotherapy (d 0.017 r mPa·s, P r = r 0.007) and women on combined HRT (d 0.039 r mPa·s, P r < r 0.001), compared to those without HRT. No differences were found for WBC count and the negative acute phase marker albumin in the various treatment groups. In contrast to oral estrogen administration, levels of CRP, fibrinogen and PV in women on transdermal estrogen therapy did not differ from the no-HRT group. There was no association between these markers of inflammation and plasma estrogen levels. CONCLUSION. Oral estrogen monotherapy was associated with highest concentrations of CRP. In contrast, other markers of inflammation were either similar or lower in the oral HRT group, compared to the group of women without HRT, suggesting that higher CRP concentrations reflect estrogen effects on CRP expression rather than a systemic pro-inflammatory effect. 相似文献
49.
Brian Walls Oisín Murtagh Sergey I. Bozhko Andrei Ionov Andrey A. Mazilkin Daragh Mullarkey Ainur Zhussupbekova Dmitry A. Shulyatev Kuanysh Zhussupbekov Nikolai Andreev Nataliya Tabachkova Igor V. Shvets 《Materials》2022,15(21)
The strongly correlated electron material, vanadium dioxide (VO), has seen considerable attention and research application in metal-oxide electronics due to its metal-to-insulator transition close to room temperature. Vacuum annealing a VO(010) single crystal results in Wadsley phases (VO, n > 1) and VO. The resistance changes by a factor of 20 at 342 K, corresponding to the metal-to-insulator phase transition of VO. Macroscopic voltage-current measurements with a probe separation on the millimetre scale result in Joule heating-induced resistive switching at extremely low voltages of under a volt. This can reduce the hysteresis and facilitate low temperature operation of VO devices, of potential benefit for switching speed and device stability. This is correlated to the low resistance of the system at temperatures below the transition. High-resolution transmission electron microscopy measurements reveal a complex structural relationship between VO, VO and VO crystallites. Percolation paths incorporating both VO and metallic VO are revealed, which can reduce the resistance below the transition and result in exceptionally low voltage resistive switching. 相似文献
50.
There is increasing evidence that glial cell line-derived neurotrophic factor (GDNF) plays a role as a limiting, striatal target-derived neurotrophic factor for dopamine neurons of the substantia nigra pars compacta (SNpc) by regulating the magnitude of the first phase of postnatal natural cell death which occurs in these neurons. While it has been shown that GDNF mRNA is relatively abundant in postnatal striatum, the cellular basis of its expression has been unknown. We therefore used nonradioactive in situ hybridization and immunohistochemistry to examine the cellular basis of GDNF mRNA and protein expression, respectively, in postnatal striatum and related structures. We found that GDNF mRNA is expressed within medium-sized striatal neurons. Expression in glia was not observed. At the protein level, regionally, GDNF expression in striatum was observed in striosomal patches, as previously described. At a cellular level a few neurons were observed, but they do not account for the striosomal pattern. This pattern is predominantly due to GDNF-positive neuropil. Some of this neuropil arises from tyrosine hydroxylase-positive nigro-striatal dopaminergic afferents. Astrocytic processes do not appear to contribute to the striosomal pattern. GDNF-positive fibers are identified not only within intrinsic striatal neuropil, but also in fibers within the major striatal efferent targets: the globus pallidus, the entopeduncular nucleus, and the SN pars reticulata. We conclude that during normal postnatal development, medium-sized neurons are the principal source of GDNF within the striatum. 相似文献