首页 | 官方网站   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   324篇
  免费   25篇
  国内免费   1篇
工业技术   350篇
  2024年   1篇
  2023年   3篇
  2022年   14篇
  2021年   21篇
  2020年   14篇
  2019年   13篇
  2018年   22篇
  2017年   11篇
  2016年   21篇
  2015年   9篇
  2014年   10篇
  2013年   36篇
  2012年   15篇
  2011年   22篇
  2010年   14篇
  2009年   13篇
  2008年   14篇
  2007年   13篇
  2006年   14篇
  2005年   8篇
  2004年   6篇
  2003年   6篇
  2002年   3篇
  2001年   2篇
  2000年   7篇
  1999年   3篇
  1998年   2篇
  1997年   4篇
  1996年   5篇
  1995年   1篇
  1994年   4篇
  1993年   2篇
  1992年   3篇
  1991年   1篇
  1990年   1篇
  1985年   2篇
  1984年   1篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1979年   3篇
  1978年   1篇
  1975年   1篇
  1971年   1篇
排序方式: 共有350条查询结果,搜索用时 15 毫秒
101.
The objective was to study antiphospholipid antibody syndrome (APS or Hughes syndrome) in two major teaching hospitals in Kuwait. patients with suspected Hughes syndrome were investigated with tests for anticardiolipin antibodies (aCL) and lupus anticoagulants (LAC) over 1 yr. Diagnosis was considered confirmed if significant levels of either or both antibodies with no obvious cause (primary), or with systemic lupus erythematosus (SLE) or SLE-like illness (including SLE serology) (secondary) were present. Twelve (37.5%; seven females, 58%) primary and 20 (62.5%; 18 females, 90%) secondary Hughes syndrome patients were seen during this period. patients were Kuwaiti, Middle-Eastern and North-African Arabs (29). Filipinos (2) and White (1). None were from the Indian subcontinent. The main presentation was thrombosis in 75% (arterial in 25% and venous in 50%), and recurrent abortions in 50% of married women. Haematological and dermatological manifestations were limited entirely to the secondary variety, seen in 25% and 19%, respectively. Clinical manifestations were severe, leading to death in one, intensive-care management in 31% and with partial or complete warfarin resistance or brittleness in 25%. Neurological/eye and cardiac manifestations were not seen, as these patients may be attending separate speciality hospitals for these diseases in Kuwait. The approximate prevalence of this syndrome was 2.66/1000 admissions in medical wards. Projected to the total referral areas of the two hospitals, an approximate figure of 52 patients/million population/year was obtained. Hughes syndrome was a common problem among Arabs, Filipinos and possibly Whites in Kuwait. Its manifestations were severe, often requiring intensive-care management, and in one case it was fatal. Patients from the Indian subcontinent were conspicuous by their absence, despite the fact that they were well represented in all other rheumatic disease groups. Ethnic and/or geographical factors could be important in this syndrome. To the best of our knowledge, this is the first report of Hughes syndrome from the Middle East.  相似文献   
102.
This study was done to determine the role of cement liner as a reducing factor to the fluid movement in order to prevent tooth hypersensitivity according to the hydrodynamic theory during cementation of crowns. A total of fourty freshly extracted intact lower molar were selected for this study. After conventional tooth preparation the teeth were sub-divided into four equal groups to identify the role of cement liner in preventing the penetration of used cement into the dentinal tubules. Scanning electron microscopic study proved the efficiency of glass ionomer liner on preventing cement penetration into the dentinal tubules.  相似文献   
103.
The homogeneous degradation of benzene (B), toluene (T), ethylbenzene (E) and p‐xylene (X) (BTEX) was studied in aqueous solutions, at pH 3.0, of hydrogen peroxide (5.8 mM ) under UV irradiation in a photoreactor equipped with a 300 nm lamp of light intensity 3.5 × 10?5 Ein L?1 min?1. BTEX was substantially degraded by the H2O2/UV system, with >90% disappearing in 10 min of irradiation. The decomposition of BTEX was studied either as single or as multi‐component systems. The effects of irradiation time, amounts of H2O2 in molar ratios, rate of degradation and competition between components were thoroughly examined. It can be stated that the rate of BTEX degradation in mixture was higher than those for the individual components due to external effects of the absorption of UV light by the mixture, and their effects on enhancing the formation of OH? radicals. The appropriate figure of merit, the electrical energy per mass (EE/M), was estimated at various molar ratios and it was confirmed that the best value was the one depicted for p‐xylene (0.065 kWh kg?1). A theoretical model for the degradation pathway was proposed. Copyright © 2004 Society of Chemical Industry  相似文献   
104.
Crystals of KDyP4O12 have been grown by the flux technique and characterized by single-crystal X-ray diffraction. KDyP4O12 crystallizes in the monoclinic C2/c space group with lattice parameters: a=7.8158(3), b=12.3401(5), c=10.4382(3) Å, β=111.053°(2), V=939.6(4) Å3, Z=4. The crystal structure has been refined yielding a final R(F2)=0.034 and Rw(F2)=0.082 for 902 independent reflections (Fo2≥2σ(Fo2)). The structure of KDyP4O12 consists of DyO8 polyhedra and cyclotetraphosphate P4O12 groups sharing oxygen atoms to form a three-dimensional framework, delimiting intersecting tunnels in which the potassium ion is located. Each K+ ion is bonded to 10 oxygen atoms. The energies of the vibrational modes of the crystal were obtained from measurements of the infrared and Raman spectra.  相似文献   
105.
We demonstrate the application of a uniform Bragg grating as a dynamically reconfigurable phase encoder-decoder for optical systems. Precise discrete phase modulation between chips is obtained simply by heating segments along the grating with fine resistive wires. Its reliability to generate and recognize various phase code sequences is demonstrated in a 16-chip 20-Gchip/s quaternary phase-shift keying coherent optical code-division multiple access experiment. The bit-error-rate response is also included to highlight its performance.  相似文献   
106.
Crystals of thallium-holmium polyphosphate T1Ho(PO3)4 were grown by flux method technique and characterized by single crystal X-ray diffraction. Structure of T1Ho(PO3)4 was solved for the first time, and it crystallized in the monoclinic P21/n space group with the following unit-cell dimensions: a=1.02225(3) nm, b=0.88536(2) nm, c=1.09541(4) nm, β=105.888(1)°, V=0.95354(5) nm^3 and Z=4. The crystal structure was solved from 2174 independent reflections with final R1(F^2)=0.0442 and Rw(F^2)=0.0861 refined with 164 parameters. The atomic arrangement could be described as a long chain polyphosphate organization. Holmium atoms had eightfold coordination. The structure of T1Ho(PO3)4 consisted of HoO8 polyhedra sharing oxygen atoms with phosphoric group PO4. Infrared spectrum was investigated at room temperature in the frequencies range, 350--4000 cm^-1, showing some characteristic vibration bands of infinite chain structure of PO4 tetrahedra linked by bridging oxygen.  相似文献   
107.

Background  

Vitamin A and zinc are crucial for normal immune function, and may play a synergistic role for reducing the risk of infection including malaria caused by Plasmodium falciparum.  相似文献   
108.
Hydrothermally synthesized ZSM-5 zeolites using tetrapropyl-ammonium bromide (TPA-Br), Xylitol (Xy) and tetrapropyl-ammonium bromide + Xylitol templates; those compared with that of the parent having the same Si/Al molar ratio (64) and purchased from Mobil, were characterized with several physicochemical techniques including N2 adsorption, XRD, TG/DSC, FTIR and pyridine-FTIR. The effect of various templates on the crystallinity, crystallites size, surface properties and thermal stabilities of the produced ZSM-5 were investigated. ZSM-5 synthesized using TPA-Br + Xy; of S BET = 393 m2 g?1, exhibited a crystallinity percentage comprises of 142% when compared with that of the parent (taken at 100% crystallinity) and measured as well a crystallites size of 61 nm exceeding that derived from Xy (41 nm) that measured the lowest crystallinity percentages (71%), lowest S BET (303 m2 g?1) and highest yield (65%) between all samples. The former sample showed high thermal stability (till 1,000 °C) when compared with that derived from TPA-Br, as illustrated from TG/DSC thermograms that provided a criteria on decreasing the pore radius as a result of enclosing appreciable amounts of TPA+ and Xy inside narrow pores of ZSM-5. This sample also indicated a hydrophobic tendency when compared with that devoted from TPA-Br. Pyridine adsorption measurements showed that addition of Xy to TPA-Br stimulate the existence of basic sites in addition to acidic ones (mainly Brönsted ones) that was in the middle between that derived from Xy and TPA-Br templates. More infomations on the textural properties, morphologies, vibrational tetrahedral co-ordination T(Si or Al)–O modes and acidity were evaluated and discussed.  相似文献   
109.
The impact of the nanoparticles and ribs on the thermal performance of the rotating U-type cooling channel are investigated for turbulent forced convection flow of nanofluids. The nanofluids are provided by the inclusion of the nanoparticles of TiO2 and Al2O3 in water as the base fluid, namely, water/Al2O3 and water/TiO2 nanofluids mixtures. The simulations are performed for three-dimensional turbulent flow and heat transfer using an RNG k-? turbulence model for Reynolds number range of 5000 to 20,000. To show the effectiveness of the ribs and nanofluids, three criteria are employed: heat transfer enhancement, pressure drop or power consumed, and the thermal performance factor. It is found that the contribution of turbulence promotion in heat transfer enhancement of the ribbed channel is more effective than that of enlarging the heat surface area. The results show that using ribs at the lowest Reynolds number and utilizing nanofluids at the highest one provide high heat transfer rate and thermal performance. At the middle Reynolds numbers, the effects of these two methods on heat transfer enhancement are relatively close to each other. In this case, if the pumping power is the main concern, using nanofluids is recommended due to providing a smaller pressure drop penalty.  相似文献   
110.
A new multi-wavelength Brillouin erbium fiber laser (BEFL), which operates in the L-band region with double frequency Brillouin spacing, is demonstrated. This design uses a Raman pump (RP) and a piece of 2?km highly nonlinear fiber as a gain medium. The double frequency spacing is achieved by employing a dual ring configuration, which is formed by utilizing a four-port circulator that removes the odd-order Stoke signals. Twenty Stokes and seventeen anti-Stokes lines, which have optical signal to noise ratio (OSNR) greater than 15?dB, are generated simultaneously with a spacing of 0.16?nm when Brillouin pump and RP powers were fixed at the optimum values of 8 dBm and 40?mW, respectively. The BEFL can be tuned in the range between 1591?nm to 1618?nm. The proposed configuration increases the number of lines generated and the OSNR, and thus allows a compact multi-wavelength laser source to be realized.  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-23

京公网安备 11010802026262号