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排序方式: 共有111条查询结果,搜索用时 31 毫秒
1.
对中南地区10个钨矿1972—1974年入矿(工龄至少1年)的在册职工28453人进行了队列研究。队列成员追访至1989年,死亡2870人,比全国居民死亡率计算的期望值略高(SMR=1.15,95%CI=1.11—1.19);主要是非恶性呼吸道疾病,特别是尘肺(SMR=66.79,95%CI=59.65—73.68)以及与呼吸道疾病相关的肺心病明显超高(SMR=8.19,95%CI=7.42—9.02),比全国居民死亡率高5倍。癌症死亡数在全死因中虽占第一位,但仅鼻咽癌轻度超高(SMR=1.73,95%CI=1.23—2.37),而肺癌死亡率明显偏低(SMR=0.53)。研究结果不支持矽肺与肺癌病因学相关的假说。 相似文献
2.
Dariusz Bartkowski Aneta Bartkowska Pawe Popielarski Jakub Hajkowski Adam Piasecki 《Materials》2020,13(22)
The paper presents the study results of laser processing of precoat applied on C30 steel. The precoat consisted of powder mixtures with a binder in the form of water glass. Tungsten powder, chromium, and tungsten carbide (WC) were used to produce the precoat. The laser processing was carried out using a Yb:YAG disc laser with a rated power of 1 kW. Constant producing parameters (power of laser beam, 600 W; laser beam scanning rate, 400 mm/min) were applied. Chemical composition of the precoat was a variable parameter in coating production. A mixture consisting of 50% W and 50% Cr as a metal matrix was prepared. Subsequently, WC particles in weight ratios of 25%, 50%, and 75% were added to matrix. As a result, W–Cr metal matrix composite coatings reinforced with WC particles were formed. This study focused on investigation of microstructure, microhardness, phase, and chemical composition as well as corrosion and wear resistance, of the newly formed W–Cr/WC coatings. An instrumented nanoindentation test was also used in this study. As a result of laser beam action, the newly formed coatings had an interesting microstructure and good properties which were improved in comparison to substrate material. It is anticipated that the resulting coatings, depending on the treatment parameters (e.g., W–Cr/WC powder mixture) used, can be successfully applied to metal forming or foundry tools. 相似文献
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4.
Senthilnathan Natarajan Venkatachalam Gopalan Raja Annamalai Arunjunai Rajan Chun-Ping Jen 《Materials》2021,14(7)
Tungsten heavy alloys are two-phase metal matrix composites that include W–Ni–Fe and W–Ni–Cu. The significant feature of these alloys is their ability to acquire both strength and ductility. In order to improve the mechanical properties of the basic alloy and to limit or avoid the need for post-processing techniques, other elements are doped with the alloy and performance studies are carried out. This work focuses on the developments through the years in improving the performance of the classical tungsten heavy alloy of W–Ni–Fe through doping of other elements. The influence of the percentage addition of rare earth elements of yttrium, lanthanum, and their oxides and refractory metals such as rhenium, tantalum, and molybdenum on the mechanical properties of the heavy alloy is critically analyzed. Based on the microstructural and property evaluation, the effects of adding the elements at various proportions are discussed. The addition of molybdenum and rhenium to the heavy alloy gives good strength and ductility. The oxides of yttrium, when added in a small quantity, help to reduce the tungsten’s grain size and obtain good tensile and compressive strengths at high temperatures. 相似文献
5.
Dmitrij Morozow Marek Barlak Zbigniew Werner Marcin Pisarek Piotr Konarski Jerzy Zagrski Mirosaw Rucki Leszek Chako Marek agodziski Jakub Narojczyk Zbigniew Krzysiak Jacek Caban 《Materials》2021,14(2)
The paper is dedicated to the life prolongation of the tools designed for deep-hole drilling. Among available methods, an ion implantation process was used to improve the durability of tungsten carbide (WC)-Co guide pads. Nitrogen fluencies of 3 × 1017 cm−2, 4 × 1017 cm−2 and 5 × 1017 cm−2 were applied, and scanning electron microscope (SEM) observations, energy dispersive spectroscopy (EDS) analyses, X-ray photoelectron spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS) measurements were performed for both nonimplanted and implanted tools. The durability tests of nonimplanted and the modified tools were performed in industrial conditions. The durability of implanted guide pads was above 2.5 times greater than nonimplanted ones in the best case, presumably due to the presence of a carbon-rich layer and extremely hard tungsten nitrides. The achieved effect may be attributed to the dissociation of tungsten carbide phase and to the lubrication effect. The latter was due to the presence of pure carbon layer with a thickness of a few dozen nanometers. Notably, this layer was formed at a temperature of 200 °C, much smaller than in previously reported research, which makes the findings even more valuable from economic and environmental perspectives. 相似文献
6.
In vivo comparison of tantalum,tungsten, and bismuth enteric contrast agents to complement intravenous iodine for double‐contrast dual‐energy CT of the bowel 下载免费PDF全文
Samira Rathnayake John Mongan Andrew S. Torres Robert Colborn Dong‐Wei Gao Benjamin M. Yeh Yanjun Fu 《CONTRAST MEDIA & MOLECULAR IMAGING》2016,11(4):254-261
To assess the ability of dual‐energy CT (DECT) to separate intravenous contrast of bowel wall from intraluminal contrast, we scanned 16 rabbits on a clinical DECT scanner: n = 3 using only iodinated intravenous contrast, and n = 13 double‐contrast enhanced scans using iodinated intravenous contrast and experimental enteric non‐iodinated contrast agents in the bowel lumen (five bismuth, four tungsten, and four tantalum based). Representative image pairs from conventional CT images and DECT iodine density maps of small bowel (116 pairs from 232 images) were viewed by four abdominal imaging attending radiologists to independently score each comparison pair on a visual analog scale (?100 to +100%) for (1) preference in small bowel wall visualization and (2) preference in completeness of intraluminal enteric contrast subtraction. Median small bowel wall visualization was scored 39 and 42 percentage points (95% CI 30–44% and 36–45%, both p < 0.001) higher for double‐contrast DECT than for conventional CT with enteric tungsten and tantalum contrast, respectively. Median small bowel wall visualization for double‐contrast DECT was scored 29 and 35 percentage points (95% CI 20–35% and 33–39%, both p < 0.001) higher with enteric tungsten and tantalum, respectively, than with bismuth contrast. Median completeness of intraluminal enteric contrast subtraction in double‐contrast DECT iodine density maps was scored 28 and 29 percentage points (95% CI 15–31% and 28–33%, both p < 0.001) higher with enteric tungsten and tantalum, respectively, than with bismuth contrast. Results suggest that in vivo double‐contrast DECT with iodinated intravenous and either tantalum‐ or tungsten‐based enteric contrast provides better visualization of small bowel than conventional CT. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
7.
Frederic Moynier Qing-Zhu Yin Keita Irisawa Maud Boyet Benjamin Jacobsen Minik T. Rosing 《Proceedings of the National Academy of Sciences of the United States of America》2010,107(24):10810-10814
Recent high precision 142Nd isotope measurements showed that global silicate differentiation may have occurred as early as 30–75 Myr after the Solar System formation [Bennett V, et al. (2007) Science 318:1907–1910]. This time scale is almost contemporaneous with Earth’s core formation at ∼30 Myr [Yin Q, et al. (2002) Nature 418:949–952]. The 182Hf-182W system provides a powerful complement to the 142Nd results for early silicate differentiation, because both core formation and silicate differentiation fractionate Hf from W. Here we show that eleven terrestrial samples from diverse tectonic settings, including five early Archean samples from Isua, Greenland, of which three have been previously shown with 142Nd anomalies, all have a homogeneous W isotopic composition, which is ∼2ε-unit more radiogenic than the chondritic value. By using a 3-stage model calculation that describes the isotopic evolution in chondritic reservoir and core segregation, as well as silicate differentiation, we show that the W isotopic composition of terrestrial samples provides the most stringent time constraint for early core formation (27.5–38 Myr) followed by early terrestrial silicate differentiation (38–75 Myr) that is consistent with the terrestrial 142Nd anomalies. 相似文献
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9.
Aleksandr B. Stefaniak M. Abbas VirjiChristopher J. Harvey Deborah C. SbarraGregory A. Day Mark D. Hoover 《International journal of hygiene and environmental health》2010,213(2):107-115
The dissolution of metal-containing particles in the gastric compartment is poorly understood. The purpose of this study was to elucidate the influence of artificial gastric juice chemical composition on bioaccessibility of metals associated with ingestion-based health concerns. Dissolution rates were evaluated for well-characterized feedstock cobalt, tungsten metal, and tungsten carbide powders, chemically bonded pre-sintered (spray dryer material) and post-sintered (chamfer grinder) cemented tungsten carbide materials, and an admixture of pure cobalt and pure tungsten carbide, prepared by mechanically blending the two feedstock powders. Dissolution of each study material was evaluated in three different formulations of artificial gastric juice (from simplest to most chemically complex): American Society of Testing Materials (ASTM), U.S. Pharmacopoeia (USP), and National Institute for Occupational Safety and Health (NIOSH). Approximately 20% of cobalt dissolved in the first dissolution phase (t1/2 = 0.02 days) and the remaining 80% was released in the second long-term dissolution phase (t1/2 = 0.5 to 1 days). Artificial gastric juice chemical composition did not influence dissolution rate constant values (k, g/cm2 day) of cobalt powder, either alone or as an admixture. Approximately 100% of the tungsten and tungsten carbide that dissolved was released in a single dissolution phase; k-values of each material differed significantly in the solvents: NIOSH > ASTM > USP (p<0.05). The k-values of cobalt and tungsten carbide in pre- and post-sintered cemented tungsten carbide powders were significantly different from values for the pure feedstock powders. Solvent composition had little influence on oral bioaccessibility of highly soluble cobalt and our data support consideration of the oral exposure route as a contributing pathway to total-body exposure. Solvent composition appeared to influence bioaccessibility of the low soluble tungsten compounds, though differences may be due to variability in the data associated with the small masses of materials that dissolved. Nonetheless, ingestion exposure may not contribute appreciably to total body burden given the short residence time of material in the stomach and relatively long dissolution half-times of these materials (t1/2 = 60 to 380 days). 相似文献
10.
Toxicity of Tungsten Carbide and Cobalt-Doped Tungsten Carbide Nanoparticles in Mammalian Cells in Vitro 下载免费PDF全文
Susanne Bastian Wibke Busch Dana Kühnel Armin Springer Tobias Mei?ner Roland Holke Stefan Scholz Maria Iwe Wolfgang Pompe Michael Gelinsky Annegret Potthoff Volkmar Richter Chrysanthy Ikonomidou Kristin Schirmer 《Environmental health perspectives》2009,117(4):530-536