全文获取类型
收费全文 | 2839篇 |
免费 | 8篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 47篇 |
金属工艺 | 4篇 |
机械仪表 | 4篇 |
建筑科学 | 4篇 |
能源动力 | 5篇 |
轻工业 | 15篇 |
水利工程 | 4篇 |
石油天然气 | 3篇 |
无线电 | 43篇 |
一般工业技术 | 46篇 |
冶金工业 | 2634篇 |
原子能技术 | 6篇 |
自动化技术 | 32篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2019年 | 3篇 |
2018年 | 11篇 |
2017年 | 4篇 |
2016年 | 2篇 |
2014年 | 5篇 |
2013年 | 11篇 |
2012年 | 8篇 |
2011年 | 13篇 |
2010年 | 6篇 |
2009年 | 9篇 |
2008年 | 9篇 |
2007年 | 8篇 |
2006年 | 7篇 |
2005年 | 4篇 |
2004年 | 9篇 |
2003年 | 12篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 9篇 |
1999年 | 77篇 |
1998年 | 882篇 |
1997年 | 508篇 |
1996年 | 264篇 |
1995年 | 169篇 |
1994年 | 154篇 |
1993年 | 170篇 |
1992年 | 16篇 |
1991年 | 26篇 |
1990年 | 26篇 |
1989年 | 34篇 |
1988年 | 31篇 |
1987年 | 24篇 |
1986年 | 22篇 |
1985年 | 25篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 19篇 |
1980年 | 24篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 55篇 |
1976年 | 141篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1968年 | 2篇 |
1955年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有2848条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
RA Reinhardt MP Masada GK Johnson LM DuBois GJ Seymour AC Allison 《Canadian Metallurgical Quarterly》1993,20(7):514-519
Interleukin (IL)-1 alpha and beta are cytokines which can mediate inflammatory, bone resorbing, and reparative effects in the periodontium, but few longitudinal data exist exploring their role following periodontal therapy. This study examined gingival crevicular fluid (GCF) concentrations of IL-1 alpha and IL-1 beta at sites with shallow sulci (SS) or inflamed moderate/advanced pockets (M/AP) before and 6 months after treatment with closed scaling/root planing (SC/RP) or papillary flap debridement (PFD), all in the same subject (n = 14 patients). No significant differences were noted in IL-1 alpha or beta concentrations (determined with two-site enzyme-linked immunosorbent assays) between SS and M/AP sites at baseline. While both therapies improved clinical parameters of periodontal disease, IL-1 alpha concentration increased significantly (p < 0.05) in M/AP-PFD sites 6 months after treatment, but were unchanged in other groups. IL-1 beta concentrations were numerically lower after therapy, except for a significant increase (p < 0.05) in M/AP-PFD sites. These data suggest that surgical wound healing in an inflamed, plaque-infected site (M/AP-PFD) results in prolonged production of IL-1, which may be a reflection of the extent of tissue trauma and delayed wound healing. In spite of increased IL-1 levels, these sites demonstrated significant short-term improvement in clinical attachment level (+ 1.8 mm, p < or = 0.001) postoperatively. 相似文献
45.
TEE is an exciting and useful diagnostic tool that is rapidly gaining widespread acceptance in both teaching centers and community hospitals. Because of the semi-invasive nature of the procedure, nursing expertise is essential to ensure patient safety and comfort during the TEE examination. 相似文献
46.
Investigation of multicarrier modulation has demonstrated the feasibility of using this modulation format to deliver relatively high channel bit rates (24 kbps) to a low cost, pager-like personal communications service (PCS) terminal that enjoys long battery life (e.g., one month on a few pen-light cells). This is to be compared to the 1200 bps carried by typical current paging systems or the 6250 bps attained by the new ERMES paging system. While more complex modulation formats, such as PSK and QAM, might achieve higher bit rates in less (power, size, cost) constrained environments, amplitude keying of the component subcarriers allows simple noncoherent energy detection that is found to be robust in this short message delivery application 相似文献
47.
The contrasting agent Gd-DTPA (Magnevist, Schering AG, Germany) was tested when used in magnetic resonance tomography using extra-low (0.04 T) magnetic field intensity in 68 patients with various brain and spine tumors. The agent was injected intravenously in a dose of 0.1 mmol/kg. No complications were found. The tests showed its high efficiency in the diagnosis of brain neoplasms (particularly in malignant intracerebral disorders, meningiomas and neurinomas). Benign astrocytomas induced no noticeable signal intensification on post-contrasting T1-weighed tomograms. In all cases of spinal tumors, the application of Gd-DTPA could specify the extent of tumor invasions, the presence of cysts and identify accessory tumor nodes in one case. 相似文献
48.
As many as 3033 patients with myocardial infarction residing in rural areas were kept under observation. In this population, myocardial reinfarction (MRI) was diagnosed in 411 subjects, with 78.8% having had it for 4 years. Those MRI patients ranging between 51 to 60 years showed the greatest prevalence (44.3%). The ratio of micro- to macrofocal (through-and-through) MRI was 1:3, that of males to females 9:1. Microfocal MRI was commonly associated with a pain-free variant of the disease (23.5%) with low frequency of thromboembolic complications (3.1%). Every fifth patient with macrofocal (through-and-through) renecrosis presented with aneurysm of the heart. In a 10-year and longer follow-up, mortality from MRI was 43.6 percent among patients with macrofocal MRI, while deaths attributable to microfocal MRI were estimated to be 28.9 percent. High mortality rates suggest great severity of illness and low efficacy of the drug therapy adopted. 相似文献
49.
Review Mechanical properties of ice and snow 总被引:2,自引:0,他引:2
J. J. Petrovic 《Journal of Materials Science》2003,38(1):1-6
The mechanical properties of ice and snow are reviewed. The tensile strength of ice varies from 0.7–3.1 MPa and the compressive strength varies from 5–25 MPa over the temperature range –10°C to –20°C. The ice compressive strength increases with decreasing temperature and increasing strain rate, but ice tensile strength is relatively insensitive to these variables. The tensile strength of ice decreases with increasing ice grain size. The strength of ice decreases with increasing volume, and the estimated Weibull modulus is 5. The fracture toughness of ice is in the range of 50–150 kPa m1/2 and the fracture-initiating flaw size is similar to the grain size. Ice-soil composite mixtures are both stronger and tougher than ice alone. Snow is a open cellular form of ice. Both the strength and fracture toughness of snow are substantially lower than those of ice. Fracture-initiating flaw sizes in snow appear to correlate to the snow cell size. 相似文献
50.
A. Demoz C. Khulbe C. Fairbridge S. Petrovic 《Journal of Applied Electrochemistry》2008,38(6):845-851
Hydrogen is among the emerging energy vectors that are being developed to replace nonrenewable hydrocarbon energy sources.
The preferred method to produce hydrogen without generating greenhouse gases is the electrolysis of water using renewable
energy. The reduction of energy during the water electrolysis process is a desirable goal regardless of the source of electric
power. Similar to ferrous/ferric mediation, iodide can be used as a mediator in the electrolysis of an acidic suspension of
coke or coal. The iodide ion is oxidized at a far lower anodic potential than the alternative oxygen evolution reaction. This
reduces the cell electrolysis voltage and, consequently, reduces electricity use. The iodide consumed at the anode is continuously
regenerated by chemical reaction with the coke/coal in suspension. 相似文献