全文获取类型
收费全文 | 4848篇 |
免费 | 187篇 |
国内免费 | 16篇 |
专业分类
电工技术 | 49篇 |
综合类 | 3篇 |
化学工业 | 897篇 |
金属工艺 | 125篇 |
机械仪表 | 132篇 |
建筑科学 | 220篇 |
矿业工程 | 19篇 |
能源动力 | 153篇 |
轻工业 | 392篇 |
水利工程 | 53篇 |
石油天然气 | 15篇 |
无线电 | 327篇 |
一般工业技术 | 852篇 |
冶金工业 | 1155篇 |
原子能技术 | 53篇 |
自动化技术 | 606篇 |
出版年
2023年 | 61篇 |
2022年 | 87篇 |
2021年 | 114篇 |
2020年 | 119篇 |
2019年 | 114篇 |
2018年 | 121篇 |
2017年 | 108篇 |
2016年 | 121篇 |
2015年 | 87篇 |
2014年 | 117篇 |
2013年 | 246篇 |
2012年 | 181篇 |
2011年 | 244篇 |
2010年 | 178篇 |
2009年 | 190篇 |
2008年 | 238篇 |
2007年 | 192篇 |
2006年 | 145篇 |
2005年 | 142篇 |
2004年 | 104篇 |
2003年 | 103篇 |
2002年 | 67篇 |
2001年 | 86篇 |
2000年 | 86篇 |
1999年 | 99篇 |
1998年 | 222篇 |
1997年 | 147篇 |
1996年 | 135篇 |
1995年 | 99篇 |
1994年 | 78篇 |
1993年 | 69篇 |
1992年 | 37篇 |
1991年 | 39篇 |
1990年 | 50篇 |
1989年 | 46篇 |
1988年 | 36篇 |
1987年 | 41篇 |
1986年 | 50篇 |
1985年 | 54篇 |
1984年 | 37篇 |
1983年 | 31篇 |
1982年 | 44篇 |
1981年 | 39篇 |
1980年 | 50篇 |
1979年 | 32篇 |
1978年 | 33篇 |
1977年 | 36篇 |
1976年 | 52篇 |
1975年 | 29篇 |
1973年 | 28篇 |
排序方式: 共有5051条查询结果,搜索用时 15 毫秒
51.
Knapp Samuel; Gottlieb Michael; Berman Jason; Handelsman Mitchell M. 《Canadian Metallurgical Quarterly》2007,38(1):54
At times the laws under which psychologists function may appear to contradict generally recognized ethical values and/or good clinical care. When these circumstances arise, psychologists must determine if a conflict really exists and, if so, seek solutions that reconcile respect for the law with their ethical values. At times, psychologists may decide to follow the law despite their ethical concerns. At other times, they may determine that a conscientious objection is warranted. The authors recommend options to consider when these situations arise and offer a decision-making process. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
52.
Fabrice Martin Marc-Etienne Jan Samuel Rey-Mermet Brahim Belgacem Dong Su Marco Cantoni Paul Muralt 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2006,53(7):1339-1343
Polycrystalline A1N thin films were deposited by RF reactive magnetron sputtering on Pt(111)/Ti electrode films. The substrates were tilted by an angle ranging from 40 degrees to 70 degrees with respect to the target normal. A low deposition temperature and a high sputter gas pressure were found ideal for tilted growth. The resulting grain tilt angle amounts to about half the substrate tilt angle. For coupling evaluation, 5 GHz solidly mounted resonator structures have been realized. The tilted grain A1N films exhibited a permittivity in the 9.5-10.5 range and loss tangent of 0.3%. Two shear modes as well as the longitudinal mode could be clearly identified. The coupling coefficient k2(eff) of the fundamental thickness shear mode (TS0) was found to be about 0.5%, which is compatible with a c-axis tilt of about 6 degrees. 相似文献
53.
F. G. Johnson B. L. Olmsted Samuel Chen G. W. Wicks 《Journal of Electronic Materials》1993,22(3):331-334
The composition profile of an (AlAs)1/2(GaAs)1/2 tilted superlattice is characterized for the first time. The tilted superlattice sample is thermally disordered, and the
energy of the direct band gap photoluminescence peak is measured as a function of increasing layer interdiffusion. The shift
in the photoluminescence peak energy after completely disordering the tilted superlattice is 39 meV. A theoretical model is
used to simulate the change in band gap as a function of layer interdiffusion for several composition profiles. The profile
that gives the best fit to the experimental data is chosen. The tilted superlattice composition profile is found to be sinusoidal,
varying from Al0.40Ga0.60As to Al0.60Ga0.40As. 相似文献
54.
The effect of salt addition, in the form of a fluxing agent containing equivalent amounts of NaCl and KCl, on the microstructure and mechanical properties of 359/SiC/10p composite has been investigated. Both microstructure and properties are affected, with the removal of magnesium and strontium and the introduction of sodium and potassium being responsible for the degradation in properties. Thermodynamic calculations have been carried out to account for the effect of salt addition in terms of the surface adsorption of sodium and potassium impurities and the consequent changes in the surface-interface tension of their binary alloys. Mechanisms for the degradation of properties have been discussed. 相似文献
55.
56.
Isolation of porcine circovirus-like viruses from pigs with a wasting disease in the USA and Europe 总被引:3,自引:0,他引:3
GM Allan F McNeilly S Kennedy B Daft EG Clarke JA Ellis DM Haines BM Meehan BM Adair 《Canadian Metallurgical Quarterly》1998,10(1):3-10
Sinus pericranii is an anomalous extracranial vascular malformation that is in continuity with the intracranial dural venous sinuses. Five case reports, three congenital and two traumatic, are described. Clinical management, including evaluation, diagnosis, and treatment, is discussed. Awareness of this entity by plastic surgeons will allow for earlier diagnosis and appropriate surgical management, resulting in decreased risk of complications. 相似文献
57.
WJ Aspden A Rao K Rose PT Scott IJ Clarke TE Trigg J Walsh MJ D''Occhio 《Canadian Metallurgical Quarterly》1997,14(6):429-437
Tooth loss diminishes oral function and quality of life, and national health targets aim to reduce population levels of tooth loss. OBJECTIVES: The purpose of this study was to determine tooth loss incidence and predictors of tooth loss among older adults in South Australia. METHODS: Data were obtained from a cohort study of a stratified random sample of community-dwelling dentate people aged 60+ years. Interviews and oral examinations were conducted among 911 individuals at baseline and among 693 of them (76.1%) 2 years later. Incidence rates and relative risks were calculated for population subgroups and multivariate logistic regression was used to construct risk prediction models. A method was developed to calculate 95% confidence intervals (95% CI) for relative risks (RR) from logistic regression models using a Taylor series approximation. RESULTS: Some 19.5% (95% CI = 15.4-23.6%) of people lost one or more teeth during the 2 years. Men, people with a recent extraction, people who brushed their teeth infrequently, smokers and people born outside Australia had significantly (P < 0.05) greater risk of tooth loss. Baseline clinical predictors of tooth loss included more missing teeth, retained roots, decayed root surfaces, periodontal pockets and periodontal recession. In a multivariate model that controlled for baseline clinical predictors, former smokers (RR = 2.55, 95% CI = 1.48-4.40) and current smokers (RR = 2.06, 95% CI = 0.92-4.62) had similarly elevated risks of tooth loss compared with non-smokers. CONCLUSIONS: The findings from this population suggest that a history of smoking contributes to tooth loss through mechanisms in addition to clinical disease processes alone. 相似文献
58.
Eleven Spectralon1 (a sintered polytetrafluoroethylene-based material) and 16 BaSO4 reference reflectance panels were calibrated using a field calibration technique. The Spectralon panels differed both in their directional/hemispherical and directional/directional reflectance. However, the differences were sufficiently small that “general” calibration equations were developed. For panels constructed of the same material and with the same methods as those used in these experiments, the directional/directional reflectance may be within ± 0.020 at 10°, ± 0.015 at 45°, and ± 0.041 at 80° of that predicted by the “general” equations. For field measurements, these values are considerably better than those that would be obtained using a value of the directional/hemispherical reflectance. The directional/directional reflectance of the 16 BaSO4 panels varied considerably among panels, so much so that it was not feasible to develop “general” calibration equations. Apparently, the nonlambertian properties of BaSO4 panels are dependent upon the method of applying the barium sulfate coating. 相似文献
59.
The Roussy-Lévy syndrome (MIM #180800) was described in 1926 as a disorder presenting with pes cavus and tendon areflexia, distal limb weakness, tremor in the upper limbs, gait ataxia and distal sensory loss. We report a family with affected members in four generations, showing these clinical signs of Roussy-Lévy syndrome and a partial duplication at chromosome 17p11.2. This genetic defect is commonly found in patients with the hypertrophic form of the Charcot-Marie-Tooth syndrome. Our finding provides evidence against the Roussy-Lévy syndrome as a distinct entity but suggests a close relation with the Charcot-Marie-Tooth syndrome. What causes the additional features of gait ataxia and essential tremor needs further clarification. 相似文献
60.
Photovoltaic (PV) cells, when integrated within a building facade, offer the possibility of generating electric power and heat for local use or export. This paper reports on a project to investigate the practical operational efficiencies that might be delivered from such facades. The results from laboratory experiments and computer simulations are presented: the former were used to develop an empirical relationship between cell temperature and power output; the latter were undertaken to assess operational efficiencies under a range of climate conditions representative of the UK. 相似文献