全文获取类型
收费全文 | 2473篇 |
免费 | 16篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 8篇 |
化学工业 | 52篇 |
金属工艺 | 15篇 |
机械仪表 | 2篇 |
建筑科学 | 7篇 |
能源动力 | 10篇 |
轻工业 | 47篇 |
水利工程 | 6篇 |
石油天然气 | 3篇 |
无线电 | 25篇 |
一般工业技术 | 45篇 |
冶金工业 | 2210篇 |
原子能技术 | 7篇 |
自动化技术 | 58篇 |
出版年
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 19篇 |
2020年 | 24篇 |
2019年 | 9篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 17篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 18篇 |
2012年 | 12篇 |
2011年 | 21篇 |
2010年 | 8篇 |
2009年 | 6篇 |
2008年 | 8篇 |
2007年 | 7篇 |
2005年 | 3篇 |
2003年 | 9篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 70篇 |
1998年 | 748篇 |
1997年 | 434篇 |
1996年 | 270篇 |
1995年 | 157篇 |
1994年 | 114篇 |
1993年 | 120篇 |
1992年 | 13篇 |
1991年 | 21篇 |
1990年 | 16篇 |
1989年 | 31篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 24篇 |
1985年 | 22篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 15篇 |
1980年 | 15篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 37篇 |
1976年 | 67篇 |
1975年 | 5篇 |
1971年 | 2篇 |
1959年 | 3篇 |
1948年 | 2篇 |
1890年 | 3篇 |
排序方式: 共有2495条查询结果,搜索用时 16 毫秒
91.
A simplified generalized finite difference solution using MATLAB has been developed for steady‐state heat transfer in a bar, slab, cylinder, and sphere. Solutions are given for all types of boundary conditions: temperature and flux boundary conditions. A generalized solution for 2D heat transfer in a slab is also developed. Solutions have been compared with analytical solutions and there is very good agreement between computed and analytical solutions. The solution can easily be extended to similar types of situations in fluid flow and mass transport operations. 相似文献
92.
B. S. Mann Vivek Arya B. K. Pant 《Journal of Materials Engineering and Performance》2012,21(6):849-853
Twin wire arc-sprayed (TWAS) coating of commercially available SHS 7170-cored wire was obtained on Ti6AL4V alloy, and to improve its properties, it was further surface treated with high-power diode laser (HPDL). The cavitation erosion (CE) resistance of TWAS-coated samples was evaluated as per ASTM G-32-2003 and it was compared with laser-treated and untreated Ti6Al4V alloys. The CE resistance of TWAS-coated SHS 7170 samples after HPDL treatment has improved significantly. The main reasons for its improvement are elimination of pores, increased fracture toughness, reduced hardness, and brittleness. The CE resistance of HPDL-treated TWAS coating is compared with water droplet erosion resistance. It is observed that there is a similarity in the both the phenomenon. 相似文献
93.
Saleem Khan Sandeep Arya Parveen Lehana Suresh Kumar 《Bulletin of Materials Science》2014,37(4):889-893
The special behaviour of nanowires with respect to electrical conductivity makes them suitable for sensing application. In this paper, we present a copper-ferrous (CuFe) nanowires based sensor for detection of chemicals. CuFe nanowires were synthesized by template-assisted electrochemical method. By optimizing the deposition parameters, continuous nanowires on a copper substrate were synthesized. The morphological and structural studies of the synthesized CuFe nanowires were carried out using scanning electron microscope (SEM) and X-ray diffraction (XRD). Substrates containing CuFe nanowires were moulded to form a capacitor. Different chemicals were used as dielectric in the capacitor which showed that the capacitance was a nonlinear function of the dielectric constant of fluid unlike the linear relation shown by conventional capacitors. This unique property of the nanowires based capacitors may be utilized for developing fluid sensors with improved sensitivity. 相似文献
94.
Ghanshyam Arya Ravinder K. Kotnala Nainjeet Singh Negi 《Journal of the American Ceramic Society》2014,97(5):1475-1480
In this study we report the synthesis of Bi1?xInxFe1?yTiyO3 (0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.05) nanoparticles by a simple cost effective solution combustion method. Pure BFO samples shows distorted rhombohedral perovskite structure with space group R3c which is also supported by Fourier transform infrared spectra study. The codoping of In and Ti at A–B sites of BFO (BIFTO) partially distorts the crystal structure, increases the lattice strain, reduces the average particle size (14 nm), and increases the Fe3+/Fe2+ ratio which significantly affect the observed results. The saturation magnetization increases significantly upon codoping (4.60 emu/gm) by about 12 times than that of pure BFO (0.4 emu/gm). The improved ferromagnetic properties upon codoping is further manifestated in large value of linear magnetoelectric coupling coefficient (4.8 mV/cmOe) which further provides an indirect evidence for the collapse of space modulated spin structure. The activation energy increases with codoping (0.68 eV), although less than 1 eV which indicates that the conduction is still dominated by charged defects. 相似文献
95.
S.M. Deshmukh C.K. Ghatak P.R. Arya A. Subhananda Rao 《Journal of Energetic Materials》2013,31(4):321-331
In an attempt to replace toxic ingredients like lead ferrocyanide (LFCN) in electrical squibs, experiments were conducted by using barium ferrocyanide (BFCN) as an ingredient of squib composition. Electrothermal response (ETR), functional characteristics such as no-fire current (NFC) and all-fire current (AFC), were studied and compared with lead ferrocyanide-based squibs. Threshold firing currents were determined using the Bruceton staircase method. The squibs were also subjected to accelerated ageing and performance was evaluated. The results indicate better performance of barium ferrocyanide squibs to electrothermal response and a higher threshold no fire current, making it comparatively safe to handle as compared to lead ferrocyanide–based squibs. The results of accelerated ageing indicate a reasonable shelf life. ETR technique is found to be a good diagnostic tool for quality control. 相似文献
96.
Babani Vikas Charulata Pragya Prateek Arya Rajeev Qamar Shamimul 《Wireless Personal Communications》2022,124(3):2699-2722
Wireless Personal Communications - Water Cycle Algorithm (WCA) is a nature-inspired metaheuristic algorithm. There is a lack of literature surrounding the use of WCA in modern cellular mobile... 相似文献
97.
98.
DN Maiorov ER Wilton E Badoer D Petrie GA Head SC Malpas 《Canadian Metallurgical Quarterly》1999,815(2):227-236
OBJECT: This study is a retrospective analysis of clinical data obtained in 28 patients affected by obstructive hydrocephalus who presented with signs of midbrain dysfunction during episodes of shunt malfunction. METHODS: All patients presented with an upward gaze palsy, sometimes associated with other signs of oculomotor dysfunction. In seven cases the ocular signs remained isolated and resolved rapidly after shunt revision. In 21 cases the ocular signs were variably associated with other clinical manifestations such as pyramidal and extrapyramidal deficits, memory disturbances, mutism, or alterations in consciousness. Resolution of these symptoms after shunt revision was usually slow. In four cases a transient paradoxical aggravation was observed at the time of shunt revision. In 11 cases ventriculocistemostomy allowed resolution of the symptoms and withdrawal of the shunt. Simultaneous supratentorial and infratentorial intracranial pressure recordings performed in seven of the patients showed a pressure gradient between the supratentorial and infratentorial compartments, with a higher supratentorial pressure before shunt revision. Inversion of this pressure gradient was observed after shunt revision and resolution of the gradient was observed in one case after third ventriculostomy. In six recent cases, a focal midbrain hyperintensity was evidenced on T2-weighted magnetic resonance imaging sequences at the time of shunt malfunction. This rapidly resolved after the patient underwent third ventriculostomy. CONCLUSIONS: It is probable that in obstructive hydrocephalus, at the time of shunt malfunction, the development of a transtentorial pressure gradient could initially induce a functional impairment of the upper midbrain, inducing upward gaze palsy. The persistence of the gradient could lead to a global dysfunction of the upper midbrain. Third ventriculostomy contributes to equalization of cerebrospinal fluid pressure across the tentorium by restoring free communication between the infratentorial and supratentorial compartments, resulting in resolution of the patient's clinical symptoms. 相似文献
99.
David A. Conner Ph.D. P.E. Gary J. Grimes Ph.D. Jay Goldman D.SC. P.E. 《Journal of Systems Integration》2000,10(1):81-94
For telemedicine to reach its potential in the Internet2 environment,significant progress must be made in a number of areas. The emergingtelecommunications will include the Internet2 between medicalinstitutions and emerging broadband loop and wireless technologiesfor interconnections to homes. Within the technical environment,problems that must be addressed include the development of robotic-controlled,remote-monitoring devices unique to the various medical specialties;the encoding, transmission, and decoding of raw data specificto the specialized needs of various medical application areas;and the reduction of data for storage and retrieval in patientrecords. Institutionally, human factor and information accessissues with respect to physicians, patients, and non-physicianhealthcare providers must be addressed; healthcare insuranceprovider policies, government regulation, and state licensinglaws must be adapted for a new paradigm of healthcare delivery;and the philosophy of capital investment for the delivery ofhealthcare must be revised.Many current practiceswill be supplanted by home healthcare alternatives, the use ofpatient-initiated preventive healthcare initiatives, and remote-clinicactivity. These applications will result in central record archivingsystems; the need for encryption schemes, virus protection, andvandalism protection; extensive, additional connectivity betweenhealthcare providers and professionals; and new commercial playersin the healthcare arena.The hot applicationareas will include women's health, children's health, healthcarefor senior citizens, home healthcare, well-patient monitoring,and early-detection of medical problems. 相似文献
100.
DK Jones D Lythgoe MA Horsfield A Simmons SC Williams HS Markus 《Canadian Metallurgical Quarterly》1999,30(2):393-397
BACKGROUND AND PURPOSE: Information on the neuropathological changes underlying ischemic leukoaraiosis is only available postmortem, and there are limited data on histological appearances early in the disease. Diffusion tensor imaging allows determination of the directionality of diffusion, which is greater in the direction of white matter bundles. Therefore, the technique might be expected to show loss of anisotropy (directional diffusion) in leukoaraiosis. METHODS: Nine patients with ischemic leukoaraiosis (radiological leukoaraiosis and clinical lacunar stroke) and 10 age-matched controls were studied. Diffusion tensor imaging was performed, and maps of diffusion trace and fractional anisotropy were constructed. Mean values of trace and fractional anisotropy were determined in standard regions of the anterior and posterior white matter in both hemispheres. RESULTS: In all patients with ischemic leukoaraiosis, a characteristic abnormal pattern was found, with loss of anisotropy and increased trace in the white matter. For example, in the right anterior white matter mean (SD) trace/3 was 1.12 (0.33) x10(-3) mm2 s-1 in patients and 0.75 (0.11) in controls (P=0.001). In the same region, fractional anisotropy was 0.53 (0.11) in patients and 0.78 (0.09) in controls (P<0.001). Within the white matter regions, there was a strong negative correlation between mean diffusivity and anisotropy (r=-0.92, P<0.0001). CONCLUSIONS: The characteristic pattern found on diffusion tensor imaging in this patient group is consistent with axonal loss and gliosis leading to impairment to and loss of directional diffusion. The "in vivo histological" information obtained may be useful in monitoring disease progression and in investigating the pathogenesis of the cognitive impairment that may be present. 相似文献