首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   509篇
  免费   21篇
  国内免费   5篇
电工技术   7篇
综合类   2篇
化学工业   141篇
金属工艺   20篇
机械仪表   28篇
建筑科学   25篇
矿业工程   4篇
能源动力   26篇
轻工业   52篇
水利工程   2篇
无线电   31篇
一般工业技术   103篇
冶金工业   27篇
原子能技术   4篇
自动化技术   63篇
  2024年   1篇
  2023年   6篇
  2022年   19篇
  2021年   48篇
  2020年   13篇
  2019年   13篇
  2018年   19篇
  2017年   16篇
  2016年   12篇
  2015年   10篇
  2014年   26篇
  2013年   41篇
  2012年   35篇
  2011年   48篇
  2010年   31篇
  2009年   25篇
  2008年   26篇
  2007年   18篇
  2006年   18篇
  2005年   15篇
  2004年   8篇
  2003年   10篇
  2002年   7篇
  2001年   1篇
  2000年   4篇
  1999年   5篇
  1998年   6篇
  1997年   7篇
  1995年   3篇
  1994年   2篇
  1993年   2篇
  1992年   4篇
  1991年   4篇
  1989年   3篇
  1988年   1篇
  1987年   2篇
  1986年   4篇
  1985年   5篇
  1984年   2篇
  1983年   2篇
  1981年   2篇
  1980年   2篇
  1979年   1篇
  1976年   3篇
  1974年   2篇
  1973年   1篇
  1971年   1篇
  1945年   1篇
排序方式: 共有535条查询结果,搜索用时 15 毫秒
521.
522.
Pulsed Laser Deposition (PLD) was used to prepare thin films with the nominal composition La0.58Sr0.4Co0.2Fe0.8O3‐δ (LSCF). The thin film microstructure was investigated as a function of PLD deposition parameters such as: substrate temperature, ambient gas pressure, target‐to‐substrate distance, laser fluence and frequency. It was found that the ambient gas pressure and the substrate temperature are the key PLD process parameters determining the thin film micro‐ and nanostructure. A map of the LSCF film nanostructures is presented as a function of substrate temperature (25–700 °C) and oxygen background pressure (0.013–0.4 mbar), with film structures ranging from fully dense to highly porous. Fully crystalline, dense, and crack‐free LSCF films with a thickness of 300 nm were obtained at an oxygen pressure lower than 0.13 mbar at a temperature of 600 °C. The obtained knowledge on the structure allows for tailoring of perovskite thin film nanostructure, e.g., for solid oxide fuel cell cathodes. A simple geometrical model is proposed, allowing estimation of the catalytic active surface area of the prepared thin films. It is shown that voids at columnar grain boundaries can result in an increase of the surface area by approximately 25 times, when compared to dense flat films.  相似文献   
523.
Percutaneous coronary intervention (PCI) utilizing drug‐eluting stents is becoming a very common revascularization technique in the dialysis cohort; therefore, we sought to identify the impact of dialysis on outcomes in this group of patients. This is a multicenter registry comparing results of 290 patients (186 with normal kidney function, 104 on dialysis) who underwent PCI with exclusive use of paclitaxel‐eluting TAXUS stent. The primary endpoint was an assessment of major adverse cardiac events (MACE) at 1‐ and 2‐year observation. Mean follow‐up was 23.3 ± 6.1 months. Results at 12 months showed: MACE 11.8% vs. 7.7% (P = not significant [ns]), composite major adverse cardiac and cerebrovascular events (MACCE) 12.4% vs. 11.5% (P = ns), all‐cause death 2.7% vs. 8.6% (P < 0.05), cardiac death 2.7% vs. 1.9% (P = ns), target vessel revascularization (TVR) 9.1% vs. 6.7% (P = ns), acute myocardial infarction (AMI) 3.8% vs. 2.9% (P = ns), cerebrovascular events (CVA) 0.5% vs. 1.0% (P = ns); and results at 24 months showed: MACE 17.7% vs. 18.3% (P = ns), MACCE 21.5% vs. 26.0% (P = ns), all‐cause death 4.3% vs. 14.4% (P < 0.01), cardiac death 3.2% vs. 1.9% (P = ns), TVR 14.0% vs. 16.3% (P = ns), AMI 5.4% vs. 5.8% (P = ns), CVA 3.2% vs. 2.9% (P = ns) for non–end‐stage renal disease (ESRD) and dialysis group, respectively. Prior coronary artery bypass graft (CABG) was found to be single risk factor for MACE, TVR, and MACCE in patients with ESRD, while dialysis and prior CABG were found to be single risk factors for death in the entire population. PCI with TAXUS is a feasible procedure and presents promising results in dialysis‐dependent patients.  相似文献   
524.
The design and measurement results of a micro-power successive approximation charge redistribution ADC implemented in CMOS 180 nm technology are presented. The project has been optimized for very low area occupancy in order to utilize it in multichannel neural signal recording pixel systems for future application. The design has been fabricated, experimentally characterized and it exhibits good performance, especially from the silicon area occupation point of view. The presented converter achieves 500 kS/s sampling rate with ENOB of 6.54 at 4.45 μW and occupies only 90 μm×95 μm of silicon area.  相似文献   
525.
In this study, we investigated the effect of positively and negatively charged Fe3O4 and TiO2 nanoparticles (NPs) on the growth of soybean plants (Glycine max.) and their root associated soil microbes. Soybean plants were grown in a greenhouse for six weeks after application of different amounts of NPs, and plant growth and nutrient content were examined. Roots were analyzed for colonization by arbuscular mycorrhizal (AM) fungi and nodule-forming nitrogen fixing bacteria using DNA-based techniques. We found that plant growth was significantly lower with the application of TiO2 as compared to Fe3O4 NPs. The leaf carbon was also marginally significant lower in plants treated with TiO2 NPs; however, leaf phosphorus was reduced in plants treated with Fe3O4. We found no effects of NP type, concentration, or charge on the community structure of either rhizobia or AM fungi colonizing plant roots. However, the charge of the Fe3O4 NPs affected both colonization of the root system by rhizobia as well as leaf phosphorus content. Our results indicate that the type of NP can affect plant growth and nutrient content in an agriculturally important crop species, and that the charge of these particles influences the colonization of the root system by nitrogen-fixing bacteria.  相似文献   
526.
Starting from the classical centrifugal compressor, cone shaped in meridional cross section, two modifications are considered on the basis of results from 2D and 3D flow models. The first modification is the change of the meridional cross section to hyperbolically shaped channel. The second modification, proposed on the basis of 2D axisymmetric solution, concerns the shape of blading. On the strength of this solution the blades are formed as 3D shaped blades, coinciding with the recent tendency in 3D designs. Two aims were considered for the change of meridional compressor shape. The first was to remove the separation zone which appears as the flow turns from axial to radial direction. The second aim is to uniformize the flow at exit of impeller. These two goals were considered within the frame of 2D axisymmetric model. Replacing the cone shaped compressor by a hyperbolically shaped one, the separation at the corner was removed. The disc and shroud shape of the compressor was chosen in the way which sat  相似文献   
527.
In recent years, new cross-linkers from renewable resources have been sought to replace toxic synthetic compounds of this type. One of the most popular synthetic cross-linking agents used for biomedical applications is glutaraldehyde. However, the unreacted cross-linker can be released from the materials and cause cytotoxic effects. In the present work, dialdehyde starch nanocrystals (NDASs) were obtained from this polysaccharide nanocrystal form as an alternative to commonly used cross-linking agents. Then, 5–15% NDASs were used for chemical cross-linking of native chitosan (CS), gelatin (Gel), and a mixture of these two biopolymers (CS-Gel) via Schiff base reaction. The obtained materials, forming thin films, were characterized by ATR-FTIR, SEM, and XRD analysis. Thermal and mechanical properties were determined by TGA analysis and tensile testing. Moreover, all cross-linked biopolymers were also characterized by hydrophilic character, swelling ability, and protein absorption. The toxicity of obtained materials was tested using the Microtox test. Dialdehyde starch nanocrystals appear as a beneficial plant-derived cross-linking agent that allows obtaining cross-linked biopolymer materials with properties desirable for biomedical applications.  相似文献   
528.
Adverse early life experiences are associated with an enhanced risk for mental and physical health problems, including substance abuse. Despite clinical evidence, the mechanisms underlying these relationships are not fully understood. Maternal separation (MS) is a commonly used animal model of early neglect. The aim of the current study is to determine whether the N-methyl-D-aspartate receptor (NMDAR)/glycine sites are involved in vulnerability to alcohol consumption (two-bottle choice paradigm) and reversal learning deficits (Barnes maze task) in adolescent rats subjected to the MS procedure and whether these effects are sex dependent. By using ELISA, we evaluated MS-induced changes in the NMDAR subunits (GluN1, GluN2A, GluN2B) expression, especially in the glycine-binding subunit, GluN1, in the prefrontal cortex (PFC) and ventral striatum (vSTR) of male/female rats. Next, we investigated whether Org 24598, a glycine transporter 1 (GlyT1) inhibitor, was able to modify ethanol drinking in adolescent and adult male/female rats with prior MS experience and reversal learning in the Barnes maze task. Our findings revealed that adolescent MS female rats consumed more alcohol which may be associated with a substantial increase in GluN1 subunit of NMDAR in the PFC and vSTR. Org 24598 decreased ethanol intake in both sexes with a more pronounced decrease in ethanol consumption in adolescent female rats. Furthermore, MS showed deficits in reversal learning in both sexes. Org 24598 ameliorated reversal learning deficits, and this effect was reversed by the NMDAR/glycine site inhibitor, L-701,324. Collectively, our results suggest that NMDAR/glycine sites might be targeted in the treatment of alcohol abuse in adolescents with early MS, especially females.  相似文献   
529.
In this study, we evaluated the antiproliferative potential, DNA damage, crystal structures, and docking calculation of two spiropyrazoline derivatives. The main focus of the research was to evaluate the antiproliferative potential of synthesized compounds towards eight cancer cell lines. Compound I demonstrated promising antiproliferative properties, especially toward the HL60 cell line, for which IC50 was equal to 9.4 µM/L. The analysis of DNA damage by the comet assay showed that compound II caused DNA damage to tumor lineage cells to a greater extent than compound I. The level of damage to tumor cells of the HEC-1-A lineage was 23%. The determination of apoptotic and necrotic cell fractions by fluorescence microscopy indicated that cells treated with spiropyrazoline-based analogues were entering the early phase of programmed cell death. Compounds I and II depolarized the mitochondrial membranes of cancer cells. Furthermore, we performed simple docking calculations, which indicated that the obtained compounds are able to bind to the PARP1 active site, at least theoretically (the free energy of binding values for compound I and II were −9.7 and 8.7 kcal mol−1, respectively). In silico studies of the influence of the studied compounds on PARP1 were confirmed in vitro with the use of eight cancer cell lines. The degradation of the PARP1 enzyme was observed, with compound I characterized by a higher protein degradation activity.  相似文献   
530.
The paper concerns the phenomena of the fluid film that occurs in the bearing chamber of an aircraft engine.The geometry of the system includes two concentric cylinders,between which there is a mixture of oil and air.The fluid circulates in a closed circuit.The rotary movement of the inner cylinder causes creation of the fluid film on the walls of the chamber.The article proposes a measurement method that is allowing observation of this fluid film and,in particular,analysis of the movement of the air bubbles occurring in the film.An own model of the bearing chamber with transparent walls was constructed for the research.For the investigation,water was used instead of oil.Observation of the behaviour of the flow was possible thanks to video recordings made with the use of a fast-capture camera.The results presented in the paper include velocity magnitudes of the air bubbles in the fluid film in dependence on the rotational speed of the shaft and water volume fraction and with a range from 0.37 to 0.91 m/s.The results presented in this article can be used for the bearing chamber numerical models validation.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号