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   62篇
  免费   0篇
电工技术   5篇
化学工业   7篇
机械仪表   5篇
轻工业   2篇
水利工程   2篇
无线电   14篇
一般工业技术   8篇
冶金工业   10篇
自动化技术   9篇
  2024年   1篇
  2023年   1篇
  2021年   2篇
  2020年   2篇
  2019年   1篇
  2018年   3篇
  2017年   1篇
  2016年   1篇
  2014年   5篇
  2013年   2篇
  2012年   1篇
  2011年   4篇
  2010年   2篇
  2009年   1篇
  2008年   3篇
  2007年   3篇
  2005年   2篇
  2004年   1篇
  2002年   2篇
  2001年   1篇
  2000年   2篇
  1999年   3篇
  1998年   2篇
  1997年   5篇
  1996年   4篇
  1995年   3篇
  1992年   1篇
  1991年   1篇
  1980年   1篇
  1973年   1篇
排序方式: 共有62条查询结果,搜索用时 0 毫秒
41.
The authors report two cases (in brothers) of the persistence of Muller's ducts (uterus and uterine tubes), whilst both individuals led a normal though infertile sex life. They presented with a bilateral inguinal hernia and a cryptorchidism. The precise diagnosis was made at surgery in the first, whilst the family history led to the diagnosis in the second. Both underwent bilateral orchidopexy, and hysterectomy with excision of the uterine tubes. The caryotypes were normal. Of anatomical interest was the fact that both had vas deferens included within the uterine wall but the there was no continuity between the epididymes and the testes. The latter contained seminiferous ducts, Sertoli cells and spermatogonia but no spermatocyte nor spermatozoa. On the basis of these cases, the authors emphasise their demonstrative nature: the presence of testes resulted by the secretion of testosterone in the induction of normal external genitalia whilst the absence of factor inhibiting Mullers ducts (or tissue resistance to this factor) resulted in the development of the uterine tubes and uterus.  相似文献   
42.
In order to differentiate benign from malignant pulmonary masses by means of observing blood flow signal, with coloured Doppler sonography, the authors examined 67 in-patients who had been found having masses in the lungs by X-ray or CT. For comparison 43 benign cases showing blood signals in the lung was also examined. The results showed that the blood flow signals of all lung cancers were of relatively low blood flow resistance or arteriovenous shunting, while those of benign lesions were of high blood flow resistance. The pulsatility index in lung cancer was 1.02 +/- 0.30, the restance index was 0.52 +/- 0.13, the peak systolic velocity was 0.19 +/- 0.11 m/s, the end diastolic velocity was 0.06 +/- 0.02 m/s. The pulsatility index in benign pulmonary lesions was 1.53 +/- 0.30, the resitance index was 0.86 +/- 0.05, the peak systolic velocity was 0.28 +/- 0.05 m/s and the end diastolic velocity was 0.04 +/- 0.01 m/s. There were significant differences between the benign and malignant pulmonary lesions in the four indices (P < 0.01) by t test and t' test. Lower pulsatility index, lower resistance index, lower peak systolic velocity and higher end diastolic velocity were characteristics of malignancy.  相似文献   
43.
Hole trapping is often considered a parasitic component clouding the real degradation mechanism that is responsible for the negative bias temperature instability (NBTI). As such, it is often dealt with in a rather sketchy way that lacks physical rigor. We review hole trapping mechanisms that go beyond the conventional elastic tunneling mechanism by including structural relaxation and field effects. Contrary to some previous studies, it is shown that the rich spectrum of experimentally observed features of the most commonly observed defect in amorphous oxides, the E′ center, is consistent with experimental data available for NBTI. In particular, we show that a full model that includes the creation of E′ centers from their neutral oxygen vacancy precursors and their ability to be repeatedly charged and discharged prior to total annealing is consistent with a first stage of degradation. In a second stage, positively charged E′ centers can trigger the depassivation of Pb centers at the Si/ SiO2 interface or KN centers in oxynitrides to create an unpassivated silicon dangling bond. We formulate a complete model and evaluate it against experimental data.  相似文献   
44.
    
This paper presents sixth-order fully differential active low pass RC and switched-capacitor (SC) filters using N-type IGZO thin-film transistors for flexible wearable continuous health monitoring systems. As a first step, a low-gain amplifier using a diode-connected load and a fully differential amplifier is designed with positive feedback based on capacitor bootstrapping. These amplifiers present a gain around 5.03 and 40 dB, respectively, whereas their respective GBW product are around 450 and 200 kHz. Then these amplifiers are employed to realize biquads, with which a sixth-order Sallen-Key low-pass RC and SC filters are implemented. The SC filter realized with low-gain DDA has shown a simulated THD of −30.9 dB, SFDR of 30.1 dB, and a power consumption of 456 μW. On the other hand, the SC filter presents a THD of −31.4 dB, SFDR of 32.2 dB, and a power consumption of 573 μW with high-gain differential difference amplifier (DDA) when a power supply of 10 V is used. Circuit simulations have been carried out in Cadence Virtuoso using in-house IGZO TFT models.  相似文献   
45.
    
Acrylonitrile-butadiene rubber (NBR) and ethylene-propylene-diene monomer (EPDM) gaskets are used as seals in plates heat exchangers due to their elasticity and resilience. However, contact with fluids, oxygen, ozone, and heat lead to permanent deformation. This study investigates the degradation of gaskets submitted to similar service conditions: compressed in a groove for up to 360 h at 100 and 120°C. The analysis was carried through compression set (CS), compression stress relaxation, surface morphology, Shore A hardness, indentation modulus profile, crosslink density, and Fourier transform infrared region with attenuated total reflection analysis. For EPDM, in thermo-oxidative aging there is a counterbalance between chain scission and crosslinking, which increases CS while hardness and crosslink density remain low. For NBR, diffusion-limited oxidation causes heterogeneous oxidation, creating a crosslinking network near the surface. The values for CS, Shore A hardness, and crosslink density raised to 50%, 10%, and 75%, respectively. Furthermore, the side thermo-oxidation was reduced due to the presence of the groove, which reduces oxygen access. Using FITR analysis, a thermo-oxidative interaction mechanism was proposed for the EPDM and NBR gaskets. It was concluded that EPDM presented a more reliable behavior for the gasket and seal applications under the analyzed conditions.  相似文献   
46.
The present work developed a biomaterial (HA/SBA-16) based on the growth of calcium phosphate (HA) particles within an organized silica structure (SBA-16) to evaluate its application as a drug delivery system. The samples were charged with ciprofloxacin as a model drug and in vitro release assays were carried out. The samples were characterized by elemental analysis (CHN), Fourier transform infrared spectroscopy, nitrogen adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), small angle X-ray scattering (SAXS) and X-ray diffraction. The results obtained by TEM, SEM and SAXS reveal a well-defined cubic arrangement of a uniform spherical mesoporous structure, an intrinsic characteristic of these materials, which indicated that SBA-16 and HA/SBA-16 could potentially encapsulate bioactive molecules by means of ordered mesopores. It was found that both surface interaction and pore volume affect the rate and amount of ciprofloxacin released from the mesoporous materials. In vitro assays were performed to evaluate the adhesion, viability, and growth behavior of human adipose tissue-derived stem cells (hADSC) on SBA-16 and HA/SBA-16 nanocomposites to verify their potential as a scaffold for application in bone–tissue engineering using MTT assay and alkaline phosphatase activity tests. The results showed that the materials are promising systems for bone repair, providing a good environment for the adhesion and proliferation of rat mesenchymal stem cells and hADSC in vitro.  相似文献   
47.
Premium quality synthetic passenger vehicle engine oils have been marketed by the authors' company since the early 1970s. During this time, the performance benefits of synthetic-based engine oils have been documented in a wide variety of engine and vehicle tests. The purpose of this paper is to demonstrate that, with the use of synthetic base oils and advanced additive technology, low viscosity oils can be formulated that have high fuel efficiency but which retain superior engine protection and performance reserves. Specifically, two synthetic engine oils, an SAE OW–40 and an SAE OW–30, have been developed that exceed the highest industry standards in both US (AP1)and European (ACEA) fuel economy and durability engine tests. The high quality of this technology is demonstrated in industry-standard engine and laboratory performance tests, as well as non-standard tests, such as extended-length engine tests, vehicle fuel economy tests, high mileage chassis rolls tests, and extended oil drain ‘over-the-road’ vehicle tests.  相似文献   
48.
We propose a modular framework for robust 3D reconstruction from unorganized, unoriented, noisy, and outlierridden geometric data. We gain robustness and scalability over previous methods through an unsigned distance approximation to the input data followed by a global stochastic signing of the function. An isosurface reconstruction is finally deduced via a sparse linear solve. We show with experiments on large, raw, geometric datasets that this approach is scalable while robust to noise, outliers, and holes. The modularity of our approach facilitates customization of the pipeline components to exploit specific idiosyncracies of datasets, while the simplicity of each component leads to a straightforward implementation.  相似文献   
49.
Chitosan is a biopolymer derived from chitin deacetylation, present in the exoskeleton of crustaceans and insects. Chitosan has been evaluated as rumen modulator and silage additive due to its antimicrobial properties. The objective of this study was to determine the effects of both chitosan and a bacterial additive on microbiological quality, chemical composition, nutrient in vitro degradation, fermentative profile, and total losses of whole-soybean plant silage (SS) harvested at R6 stage. Four treatments in a factorial arrangement were randomly assigned to 40 experimental minisilos as no additives (CON), 8 g/t fresh forage of microbial inoculant (INO; Kera SIL, Kera Nutrição Animal, Bento Gonçalves, Brazil); 5 g/kg of fresh forage chitosan (CHI); and CHI + INO. Microbial inoculant was composed of Lactobacillus plantarum (4.0 × 1010 cfu/g) and Propionibacterium acidipropionici (2.6 × 1010 cfu/g). The CHI and INO alone increased counts of lactic bacteria and anaerobic bacteria and decreased counts of mold and yeast in SS. The CHI or INO alone increased in vitro degradation of dry matter, crude protein, and neutral detergent fiber, and decreased nonfiber carbohydrate content of SS. Chitosan increased NH3-N and lactate concentrations and decreased ethanol concentration in SS. The CHI increased dry matter recovery from SS; INO increased silage aerobic stability. The combination of CHI+INO showed the lowest value of gas losses. In general, the combination of CHI and INO had small positive effects on gas losses of SS; however, both CHI or INO alone improved nutrient in vitro degradation and decreased mold and yeast in SS. Chitosan or INO utilization improves SS quality.  相似文献   
50.
    
This study investigates the effects of aging on the physical and mechanical properties of commercially available acrylonitrile-butadiene rubber (NBR) gaskets while maintaining their original geometry. Thermo-oxidative cycles with 10 and 70 mm in length specimens were conducted from 80 to 170°C up to 180 days. The samples were analyzed employing compression set (CS), hardness, indentation modulus, cross-link density, total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and thermogravimetry. The results showed that longer specimens presented better resistance to thermo-oxidative aging. Indentation results indicated regular oxygen permeability into the entire samples up to 110°C, while at higher temperatures, limited diffusion oxidation (DLO) effects promoted non-uniform aging. Time–temperature superposition (TTS) and Arrhenius methods were applied to predict the specimens' lifetime using CS as a failure criterion. Activation energies for 10 and 70 mm samples were 68.74 and 43.63 kJ mol−1, respectively. Thus, the 70 mm specimen's lifetime was greater than 10 mm. For temperatures below ≈38°C, the response to the thermo-oxidative aging is independent of specimen length. Therefore, in determining the lifetime of gaskets with complex geometry, longer specimens are recommended to provide more reliable results than those suggested by the standards.  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