全文获取类型
收费全文 | 43287篇 |
免费 | 905篇 |
国内免费 | 178篇 |
专业分类
电工技术 | 533篇 |
综合类 | 634篇 |
化学工业 | 4647篇 |
金属工艺 | 589篇 |
机械仪表 | 869篇 |
建筑科学 | 873篇 |
矿业工程 | 419篇 |
能源动力 | 410篇 |
轻工业 | 2169篇 |
水利工程 | 615篇 |
石油天然气 | 48篇 |
武器工业 | 4篇 |
无线电 | 1849篇 |
一般工业技术 | 3399篇 |
冶金工业 | 21515篇 |
原子能技术 | 188篇 |
自动化技术 | 5609篇 |
出版年
2024年 | 55篇 |
2023年 | 188篇 |
2022年 | 114篇 |
2021年 | 109篇 |
2018年 | 449篇 |
2017年 | 671篇 |
2016年 | 1052篇 |
2015年 | 785篇 |
2014年 | 423篇 |
2013年 | 443篇 |
2012年 | 2136篇 |
2011年 | 2455篇 |
2010年 | 682篇 |
2009年 | 761篇 |
2008年 | 611篇 |
2007年 | 648篇 |
2006年 | 584篇 |
2005年 | 3359篇 |
2004年 | 2566篇 |
2003年 | 2049篇 |
2002年 | 856篇 |
2001年 | 739篇 |
2000年 | 277篇 |
1999年 | 621篇 |
1998年 | 6167篇 |
1997年 | 3817篇 |
1996年 | 2508篇 |
1995年 | 1459篇 |
1994年 | 1084篇 |
1993年 | 1106篇 |
1992年 | 250篇 |
1991年 | 309篇 |
1990年 | 308篇 |
1989年 | 283篇 |
1988年 | 300篇 |
1987年 | 228篇 |
1986年 | 206篇 |
1985年 | 188篇 |
1984年 | 83篇 |
1983年 | 90篇 |
1982年 | 134篇 |
1981年 | 179篇 |
1980年 | 198篇 |
1979年 | 63篇 |
1978年 | 100篇 |
1977年 | 632篇 |
1976年 | 1331篇 |
1975年 | 105篇 |
1973年 | 55篇 |
1971年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
152.
I Haulic? 《Canadian Metallurgical Quarterly》1995,99(1-2):27-34
153.
NMR束缚流体体积确定方法及其应用条件 总被引:4,自引:2,他引:2
NMR测井不能直接测定束缚流体饱和度(Swir)和束缚总流体(BVI)体积,而是根据T1分布和有效孔隙度(φe)间接确定。其精度取决于解释T2分布所选用的方法及其相关参数。NMR测井确定VBI方法有T21截止值方法,频谱BVI(简称SBVI)方法和BVI加权函数方法。 相似文献
154.
155.
对2003年上半年安全生产工作的进展作了论述,强调了学习实践“三个代表”重要思想,强化对安全生产的使命感、责任感和紧迫感,并要求在“三个代表”重要思想的指导下,推动安全生产的全面创新,提出了加大力度、狠抓落实、确保全年工作目标的完成。 相似文献
156.
Further evidence was delivered that certain impurities, which could be contained in MgO samples, might be responsible for observed variability in MgO basicity and catalytic performance in oxidative coupling of methane. The surface basicity/base strength distribution of a series of MgO samples containing or not containing Ca and Na impurities was determined by a temperature-programmed desorption of CO2. It was revealed that samples containing Ca and Na impurities have much more medium, strong and very strong basic sites. The surface basicity of MgO samples containing added alkali or alkaline earth compounds or water was characterized by a test reaction of transformation of 2-butanol. It was confirmed that the introduction of these compounds to a pure MgO enhanced both its basicity and activity in oxidative coupling of methane. 相似文献
157.
AK Ma?ek O Rowiński T Ostrowski L Hilgertner M Januszewicz M Szostek 《Canadian Metallurgical Quarterly》1995,50(40-44):19-22
Subclavian steal syndrome (SSS) appears when the origin of the subclavian artery (SA) is occluded or stenosed. Introduction of transcranial Doppler sonography (TCD) provided an opportunity to evaluate parameters of the blood flow in the vertebral (VA) and basilar artery (BA). Measurements of blood flow velocities performed at rest and after the brachial hyperemia test allow one to classify hemodynamic types of SSS. The aim of the study was to categorize types of steal and to compare the differences of flow patterns before and after percutaneous transluminal SA balloon angioplasty (SA-PTA). Fourty-eight patients with angiographically confirmed SSS (aged from 27 to 68 years, mean 53; 2/1 f/m ratio) were examined with 2 MHz range-gated, pulsed transcranial Doppler device (TC 2-64B EME). Both VA and BA were evaluated by the transoccipital approach at rest and during the brachial hyperemia. In 5 cases (10.4%) permanent reversal blood flow in the BA was observed (complete basilar steal). In flow in the BA blood flow was in the normal direction at rest and altered (reversed or decreased) when induced with brachial hyperemia test (transient basilar steal). In the next 14 patients (29.2%) permanently reversed VA blood flow was observed with only a slight or no alterations of the BA flow after the hyperemia test (complete vertebral steal). In the last 19 cases (39.6%) alterations of the VA blood flow without changes in BA flow were observed (latent vertebral steal). Between 1991 and 1994 twenty seven symptomatic patients with different hemodynamic types of SSS were treated with SA-PTA. TCD evaluation of VA's and BA using the hyperemia test was performed before, 3 to 7 days and 3 months after morphologically and hemodynamically successful subclavian artery balloon PTA. Normal results of vertebrobasilar examinations were obtained in 26 cases after this procedure. In one case the latent vertebral steal was detected. The 28 months mean follow-up revealed no significant changes in TCD flow patterns recorded from VA's and BA. After collecting data of about 60 patients with SSS we examined with TCD we conclude that: in patients with a hemodynamically significant SA stenosis the presence of reversed ipsilateral VA blood flow (a radiologic steal) its not a good determinant of either the presence or type of presenting symptoms and after successful PTA or recanalisation and PTA of SA in almost all cases we examined close to normal TCD recordings in BA and VA. 相似文献
158.
159.
160.
In the last decade the 'comet assay' or 'single cell gel electrophoresis assay' has been established as a sensitive method for the detection of DNA damage and the measurement of its recovery. The results published in the literature have often been obtained with different methods for comet structure measurement. In most cases these data are not comparable with each other. Even when using similar systems for the analysis, it is difficult to obtain matching data. This presentation will describe some technical aspects of our measurement equipment and evaluation software. It focuses on necessary experimental conditions to minimize errors in obtaining such data. The software developed here allows the rapid analysis of the microscopic samples (< 2 s per image). The image analysis was designed with respect to the morphological shapes of comet cells, which were investigated with a confocal laser microscope. The system is built with standard components which are commercially available. As a measure of the amount of DNA damage the ratio of fluorescence intensity was used inside the comet tail and the fluorescence intensity of the comet head. Other parameters such as DNA content, comet area, head radius, tail length and tail moment are also determined. The reproducibility of the system has been evaluated in several experiments over a period of 5 years. 相似文献