全文获取类型
收费全文 | 6953篇 |
免费 | 465篇 |
国内免费 | 268篇 |
专业分类
电工技术 | 414篇 |
技术理论 | 1篇 |
综合类 | 254篇 |
化学工业 | 666篇 |
金属工艺 | 315篇 |
机械仪表 | 220篇 |
建筑科学 | 187篇 |
矿业工程 | 101篇 |
能源动力 | 175篇 |
轻工业 | 238篇 |
水利工程 | 53篇 |
石油天然气 | 105篇 |
武器工业 | 52篇 |
无线电 | 766篇 |
一般工业技术 | 517篇 |
冶金工业 | 2872篇 |
原子能技术 | 41篇 |
自动化技术 | 709篇 |
出版年
2024年 | 28篇 |
2023年 | 93篇 |
2022年 | 206篇 |
2021年 | 280篇 |
2020年 | 163篇 |
2019年 | 134篇 |
2018年 | 135篇 |
2017年 | 155篇 |
2016年 | 135篇 |
2015年 | 172篇 |
2014年 | 210篇 |
2013年 | 303篇 |
2012年 | 332篇 |
2011年 | 302篇 |
2010年 | 219篇 |
2009年 | 267篇 |
2008年 | 280篇 |
2007年 | 246篇 |
2006年 | 184篇 |
2005年 | 143篇 |
2004年 | 125篇 |
2003年 | 115篇 |
2002年 | 124篇 |
2001年 | 95篇 |
2000年 | 72篇 |
1999年 | 129篇 |
1998年 | 964篇 |
1997年 | 565篇 |
1996年 | 299篇 |
1995年 | 205篇 |
1994年 | 182篇 |
1993年 | 189篇 |
1992年 | 32篇 |
1991年 | 49篇 |
1990年 | 35篇 |
1989年 | 44篇 |
1988年 | 41篇 |
1987年 | 37篇 |
1986年 | 33篇 |
1985年 | 35篇 |
1984年 | 8篇 |
1983年 | 17篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1980年 | 28篇 |
1978年 | 6篇 |
1977年 | 56篇 |
1976年 | 140篇 |
1975年 | 9篇 |
1973年 | 5篇 |
排序方式: 共有7686条查询结果,搜索用时 343 毫秒
61.
62.
63.
64.
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
65.
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
66.
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
67.
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
68.
工作流是近年来网络领域里研究的一个热点,对工作流模型的性能分析是工作流研究的一个重要内容.实际的模型往往规模大而复杂,这为分析其性能带来了很大的困难.但有一类模型可由工作流的四种基本模型(顺序、并行、选择、循环)嵌套组成,对于这类模型,本文给出了计算其性能乘积解的数学公式.文中给出了如何由这四种基本模型嵌套组成实际模型的方法,推导出了计算这四种基本模型的性能等价公式,并按建立实际模型相反的顺序,用由里到外逐层的分析方法,给出了计算实际模型的性能乘积解. 相似文献
69.
Hexagonal AlN films have been obtained by arc ion plating at different negative biases ,X-ray diffraction and scanning electron microscopy results show that AlN films with smooth surfaces and (002) preferred orientation are obtained at low biases ,whereas those with coarse surfaces and (100) preferred orientation are obtained at high biases,The formation mechanism of AlN is analyzed and the experiment results are discussed,The effect of bias on adhesion strength has also been examined. 相似文献
70.
Ching‐Nan Chuang Liang Chao Ying‐Jie Huang Tar‐Hwa Hsieh Hung‐Yi Chuang Shu‐Chi Lin Ko‐Shan Ho 《应用聚合物科学杂志》2008,107(6):3917-3924
The synthesis of a p‐toluidine/formaldehyde (PTF) resin was performed, and the effects of the molar ratio of the individual monomers and the polymerization conditions on the structure of the PTF resin were studied. Fourier transform infrared and 13C‐NMR spectra were used to characterize the PTF. Wide‐angle X‐ray diffraction patterns revealed the crystalline structures of various PTFs. Polarized optical microscopy revealed that the molar ratio of the monomers had a strong effect on the crystalline morphologies. A longer polymerization time turned out a polymer with a higher intrinsic viscosity and molecular weight, which led to differences in the proton conductivity. All of the PTFs showed a higher proton conductivity than a commercial Nafion membrane at 90–100°C and 0% relative humidity. The proton conductivity of the PTF series could be improved by sulfonation with sulfuric acid and could be maintained after blending with polyurethane. Pure methanol could be used as a fuel source because of the insolubility and nonwetting properties of PTF in methanol to increase the output current density for a PTF membrane electrode assembly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 相似文献