全文获取类型
收费全文 | 2715篇 |
免费 | 162篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 38篇 |
综合类 | 2篇 |
化学工业 | 750篇 |
金属工艺 | 45篇 |
机械仪表 | 67篇 |
建筑科学 | 109篇 |
矿业工程 | 1篇 |
能源动力 | 91篇 |
轻工业 | 272篇 |
水利工程 | 19篇 |
石油天然气 | 3篇 |
无线电 | 232篇 |
一般工业技术 | 406篇 |
冶金工业 | 150篇 |
原子能技术 | 20篇 |
自动化技术 | 676篇 |
出版年
2024年 | 6篇 |
2023年 | 48篇 |
2022年 | 147篇 |
2021年 | 178篇 |
2020年 | 80篇 |
2019年 | 76篇 |
2018年 | 117篇 |
2017年 | 69篇 |
2016年 | 134篇 |
2015年 | 88篇 |
2014年 | 128篇 |
2013年 | 205篇 |
2012年 | 180篇 |
2011年 | 234篇 |
2010年 | 145篇 |
2009年 | 150篇 |
2008年 | 150篇 |
2007年 | 125篇 |
2006年 | 106篇 |
2005年 | 81篇 |
2004年 | 62篇 |
2003年 | 55篇 |
2002年 | 42篇 |
2001年 | 23篇 |
2000年 | 26篇 |
1999年 | 29篇 |
1998年 | 41篇 |
1997年 | 33篇 |
1996年 | 34篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1990年 | 1篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1969年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有2881条查询结果,搜索用时 15 毫秒
211.
Jaward FM Di Guardo A Nizzetto L Cassani C Raffaele F Ferretti R Jones KC 《Environmental science & technology》2005,39(10):3455-3463
Passive air samplers (polyurethane foam disks) were deployed on an altitudinal transect in the rural Italian Alps to investigate the potential influence of forest cover on air concentrations. Samplers were exposed overtwo periods, each of several weeks, either in clearings or in forests. In the first period, there was high leaf coverage (high leaf area index, LAI); in the second, the LAI was low after the autumnal leaf fall. PCBs sequestered in the PUF generally declined with altitude, for example, in the clearings PCBs-28, 52, 90/101, 118, and 138, all showed statistically significant declines (p < 0.05). The mass of HCB sequestered increased with altitude, evidence of cold condensation. Ratios of the forest:clearing concentrations were calculated; this ratio expresses the filtering ability of forests to deplete air concentrations compared to the adjacent clearings. During the high LAI sampling period, these depletion factors ranged between 0.93 and 0.54 and were inversely correlated with temperature-corrected log K0A. This relationship was notobserved during the low LAI sampling period. The depletion factors were normalized using the LAI to give a density independent depletion factor (DIDF). The slopes of the correlations with K0A were comparable for broadleaf or coniferous forests at different altitudes, suggesting that leaf surfaces determine the exchanges with air. Broadleaf forests at 1000 and 1400 m showed similar behavior, while a conifer forest at 1800 m gave depletion factors which were higher by about a factor of 2. It is suggested that DIDF can be used in regional environmental fate models to estimate the contribution of forests to contaminant fate. 相似文献
212.
213.
Catalytic combustion of methane over perovskites 总被引:9,自引:0,他引:9
Perovskite-type oxides of the series La1− xAxMnO3 (A Sr, Eu and Ce) were prepared by the amorphous citrate process, leading to high surface area catalysts (up to 45 m2 g−1). They were tested in a flow reactor for the total combustion of methane. Complete conversion was obtained over all of the catalysts between 500 and 600°C and catalyst performance did not change significantly after 100 h on-stream. Specific activity was found to decrease monotonically with increasing the temperature of the O2 TPD desorption peak maximum. The rate of methane combustion was low below 500°C, then grew very fast, showing that two kinds of oxygen are active in these catalysts: an adsorbed oxygen species, that reacts at low temperature, and a lattice oxygen species, that becomes available at high temperature, boosting the catalytic activity. 相似文献
214.
Mauro Di Marco Mauro Forti Luca Pancioni 《International Journal of Circuit Theory and Applications》2016,44(11):1959-1981
The paper considers a feedback cellular neural network (CNN) obtained by interconnecting elementary cells with an ideal capacitor and an ideal flux‐controlled memristor. It is supposed that during the analogue computation of the CNN the memristors behave as dynamic elements, so that each dynamic memristor (DM)‐CNN cell is described by a second‐order differential system in the state variables given by the capacitor voltage and the memristor flux. The proposed networks are called DM‐CNNs, that is CNNs using a dynamic (D) memristor (M). After giving a foundation to the DM‐CNN model, the paper establishes a fundamental result on complete stability, that is convergence of solutions toward equilibrium points, when the DM‐CNN has symmetric interconnections. Because of the presence of dynamic memristors, a DM‐CNN displays peculiar and basically different dynamic properties with respect to standard CNNs. First of all a DM‐CNN computes during the time evolution of the memristor fluxes, instead of the capacitor voltages as for a standard CNN. Furthermore, when a steady state is reached, the memristors keep in memory the result of the computation, that is the limiting values of the fluxes, while all memristor currents and voltages, as well as all currents, voltages, and power in the DM‐CNN vanish. Instead, for standard CNNs, currents, voltages, and power do not drop off when a steady state is reached. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
215.
Hend Letaief Luca Rolle Giuseppe Zeppa Vincenzo Gerbi 《Journal of the science of food and agriculture》2008,88(9):1567-1575
BACKGROUND: The release of grape components during wine making might be related to the mechanical properties of the skin, in particular its hardness. Samples from three varieties collected during the 2005 vintage season in Piedmont, Italy, were tested for their skin hardness using a texture analyser. The goal was to understand the statistical interactions between three factors—variety, cluster position and puncture point—and their influence on the grape skin hardness. A discussion on the relationship between the size of the sample used and the confidence level is also provided. RESULTS: Results of the ANOVA test showed that there is an interaction between the variety and the puncture point when measuring the skin hardness with the break energy. The position of the berry on the cluster does not affect the berry skin break energy. We also show that a sample size depend on the variety tested. CONCLUSION: The break energy is more useful in understanding the effect of the three factors on the skin hardness. Other factors that might affect the puncture test applied to grapes need to be studied in the future and the usefulness of the test in winemaking will need to be further developed. Copyright © 2008 Society of Chemical Industry 相似文献
216.
Immacolata Ruggiero Monica Terracciano Nicola M Martucci Luca De Stefano Nunzia Migliaccio Rosarita Tatè Ivo Rendina Paolo Arcari Annalisa Lamberti Ilaria Rea 《Nanoscale research letters》2014,9(1):329
Diatomite is a natural fossil material of sedimentary origin, constituted by fragments of diatom siliceous skeletons. In this preliminary work, the properties of diatomite nanoparticles as potential system for the delivery of drugs in cancer cells were exploited. A purification procedure, based on thermal treatments in strong acid solutions, was used to remove inorganic and organic impurities from diatomite and to make them a safe material for medical applications. The micrometric diatomite powder was reduced in nanoparticles by mechanical crushing, sonication, and filtering. Morphological analysis performed by dynamic light scattering and transmission electron microscopy reveals a particles size included between 100 and 300 nm. Diatomite nanoparticles were functionalized by 3-aminopropyltriethoxysilane and labeled by tetramethylrhodamine isothiocyanate. Different concentrations of chemically modified nanoparticles were incubated with cancer cells and confocal microscopy was performed. Imaging analysis showed an efficient cellular uptake and homogeneous distribution of nanoparticles in cytoplasm and nucleus, thus suggesting their potentiality as nanocarriers for drug delivery.
PACS
87.85.J81.05.Rm; 61.46. + w 相似文献217.
218.
Marco Sanduzzi Zamparelli Debora Compare Pietro Coccoli Alba Rocco Olga Maria Nardone Giuseppe Marrone Antonio Gasbarrini Antonio Grieco Gerardo Nardone Luca Miele 《International journal of molecular sciences》2016,17(8)
The prevalence of metabolic disorders, such as type 2 diabetes (T2D), obesity, and non-alcoholic fatty liver disease (NAFLD), which are common risk factors for cardiovascular disease (CVD), has dramatically increased worldwide over the last decades. Although dietary habit is the main etiologic factor, there is an imperfect correlation between dietary habits and the development of metabolic disease. Recently, research has focused on the role of the microbiome in the development of these disorders. Indeed, gut microbiota is implicated in many metabolic functions and an altered gut microbiota is reported in metabolic disorders. Here we provide evidence linking gut microbiota and metabolic diseases, focusing on the pathogenetic mechanisms underlying this association. 相似文献
219.
The Impact of Nonalcoholic Fatty Liver Disease on Renal Function in Children with Overweight/Obesity
Lucia Pacifico Enea Bonci Gian Marco Andreoli Michele Di Martino Alessia Gallozzi Ester De Luca Claudio Chiesa 《International journal of molecular sciences》2016,17(8)
The association between nonalcoholic fatty liver disease (NAFLD) and chronic kidney disease has attracted interest and attention over recent years. However, no data are available in children. We determined whether children with NAFLD show signs of renal functional alterations, as determined by estimated glomerular filtration rate (eGFR) and urinary albumin excretion. We studied 596 children with overweight/obesity, 268 with NAFLD (hepatic fat fraction ≥5% on magnetic resonance imaging) and 328 without NAFLD, and 130 healthy normal-weight controls. Decreased GFR was defined as eGFR < 90 mL/min/1.73 m2. Abnormal albuminuria was defined as urinary excretion of ≥30 mg/24 h of albumin. A greater prevalence of eGFR < 90 mL/min/1.73 m2 was observed in patients with NAFLD compared to those without liver involvement and healthy subjects (17.5% vs. 6.7% vs. 0.77%; p < 0.0001). The proportion of children with abnormal albuminuria was also higher in the NAFLD group compared to those without NAFLD, and controls (9.3% vs. 4.0% vs. 0; p < 0.0001). Multivariate logistic regression analysis revealed that NAFLD was associated with decreased eGFR and/or microalbuminuria (odds ratio, 2.54 (confidence interval, 1.16–5.57); p < 0.05) independently of anthropometric and clinical variables. Children with NAFLD are at risk for early renal dysfunction. Recognition of this abnormality in the young may help to prevent the ongoing development of the disease. 相似文献
220.
Antonio Ieni Valeria Barresi Rosario Caltabiano Alessia Caleo Luca Reggiani Bonetti Salvatore Lanzafame Pio Zeppa Rosario Alberto Caruso Giovanni Tuccari 《International journal of molecular sciences》2014,15(12):22331-22341
Background: The assessment of human epidermal growth factor receptor 2 (HER2) gene amplification is essential in order to identify those patients affected by advanced gastric cancer who may benefit from Trastuzumab targeted therapy. Materials and Methods: With the aim to investigate the concordance rate in HER2 status between primary gastric carcinoma (GC) and synchronous lymphnode metastases, we investigated HER2 status in a cohort of 108 surgical formalin-fixed paraffin-embedded specimens of GC and matched synchronous metastatic lymph nodes collected from three different units of Anatomic Pathology in southern of Italy. Fleiss-Cohen weighted k statistics were used to assess the concordance rate of HER2 status. Results: HER2 amplification was observed in 17% of primary GCs and the overall concordance rate with corresponding nodal metastases was 90.74%. Changes in HER2 status between primary GC and matched synchronous metastases were evidenced in 10 (9.26%) cases. Of these, 6 cases were HER2 amplified in the primary GC and not amplified in the metastases, while 4 were HER2 not amplified in the primary tumour and amplified in the lymph node metastases. Conclusions: Although at present the simultaneous determination of HER2 in advanced gastric cancer and corresponding metastatic lymph nodes is not mandatory, the possibility that the synchronous metastases of GC have a different HER2 status from that of the primary tumour is of remarkable significance; Indeed this may have influence on the therapeutic management and prognosis of the patients. 相似文献