全文获取类型
收费全文 | 41291篇 |
免费 | 5189篇 |
国内免费 | 3817篇 |
专业分类
电工技术 | 3589篇 |
技术理论 | 3篇 |
综合类 | 5493篇 |
化学工业 | 2881篇 |
金属工艺 | 2395篇 |
机械仪表 | 2703篇 |
建筑科学 | 2396篇 |
矿业工程 | 1153篇 |
能源动力 | 837篇 |
轻工业 | 1301篇 |
水利工程 | 1788篇 |
石油天然气 | 936篇 |
武器工业 | 492篇 |
无线电 | 4964篇 |
一般工业技术 | 5501篇 |
冶金工业 | 1284篇 |
原子能技术 | 576篇 |
自动化技术 | 12005篇 |
出版年
2024年 | 119篇 |
2023年 | 488篇 |
2022年 | 892篇 |
2021年 | 1178篇 |
2020年 | 1229篇 |
2019年 | 1210篇 |
2018年 | 1114篇 |
2017年 | 1498篇 |
2016年 | 1649篇 |
2015年 | 1873篇 |
2014年 | 2688篇 |
2013年 | 2961篇 |
2012年 | 3154篇 |
2011年 | 3247篇 |
2010年 | 2592篇 |
2009年 | 2763篇 |
2008年 | 2532篇 |
2007年 | 2958篇 |
2006年 | 2594篇 |
2005年 | 2214篇 |
2004年 | 1836篇 |
2003年 | 1571篇 |
2002年 | 1286篇 |
2001年 | 1134篇 |
2000年 | 954篇 |
1999年 | 792篇 |
1998年 | 588篇 |
1997年 | 493篇 |
1996年 | 440篇 |
1995年 | 420篇 |
1994年 | 373篇 |
1993年 | 290篇 |
1992年 | 246篇 |
1991年 | 184篇 |
1990年 | 141篇 |
1989年 | 123篇 |
1988年 | 90篇 |
1987年 | 53篇 |
1986年 | 41篇 |
1985年 | 36篇 |
1984年 | 32篇 |
1983年 | 28篇 |
1982年 | 19篇 |
1981年 | 16篇 |
1980年 | 14篇 |
1979年 | 14篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1966年 | 11篇 |
1964年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
The combination of the chemical aggressivity of water and lead piping, as is well known, can cause severe cases of lead poisoning in those who consume such water. After a great number of observations and epidemiological studies which have strongly incriminated this metal in a wide range of pathologic conditions, other materials have been gradually substituted for lead; however, the problem remains.In compliance with a European Directive to survey the risk of lead poisoning (Council Directive, 1977), a random sample of 321 residents was selected from the Vosgian Mountains of France. This region is noted for its high incidence of cases of lead poisoning: 150 reported during 8 months in 1983 (Barbier et al., 1983).During the course of a health evaluation, a blood sample was taken from each subject for lead analysis. At the same time, a sample of tap-water (after running for 5 s) was taken from each subject home. Both lead analyses (blood and water) were performed by electrothermal atomization-atomic absorption spectrophotometry. Because of the log-normality of the distributions of the blood lead levels and the concentrations of lead in the drinking water, a logarithmic transformation was performed so that the results are expressed as the geometric mean, which for the amount of lead in the drinking water of our sample was found to be 0.16 mg l?1.Among the subjects of this study, 28% are served by water containing more than 0.10 mg l?1 of lead (the standard for France) and 48% by water containing more than 0.05 mg l?1 (the European and WHO standard). In concurrence with numerous authors, our study indicates that, among our subjects, the blood lead level is much higher in men than in women (geometric means 22.9 and 15.0 μg dl?1 respectively); this difference is highly significant (t-test:P < 0.001). Table 1 summarizes the results, by sex, obtained in this region compared with those from a study (Huel, 1982) concerning an urban French population whose geometric mean blood lead levels were 15.9 μg dl?1 for men and 11.4 μg dl?1 for women. The irrespective of sex, is highly significant (P < 0.001). Table 2 shows the significance of the relation between these subjects, high blood lead levels and the concentration of lead in their drinking water, while Fig. 1 shows that for contamination levels up to 0.02 mg l?1 of lead in water, the blood lead level remains relatively stable, while above this apparent “threshold” value, the blood lead level begins to increase finally reaching quite high values in response to high contamination levels, suggesting a direct translation of increases in the water above the 0.02 mg l?1 level to increases in the blood. 相似文献
102.
本文提出二种算法分别标号和计数线性八元树表示的三维客体群的连通分量.这些操作典型地需要检查线性八元树中诸八分体在三个主方向上的面邻接对.根据这些邻接对,可以建造在计算机中用关联矩阵表示的邻接图.连通分量标号和计数是在关联矩阵上分别执行相应的操作而完成的.连通分量标号的执行时间是O(n+m·logm),而连通分量计数需要O(n)时间,其中m和n分别是线性八元树中八分体和邻接对的数目. 相似文献
103.
104.
获得了一种研究碲镉汞深能级的方法。通过分析迁移率 载子浓度与温度的关系,可以得到关于深能级的重要依据。 相似文献
105.
灰色关联分析在腐蚀非晶态镍基合金中的应用 总被引:4,自引:3,他引:1
用灰色关联分析方法取代传统的数理统计方法,对非晶态镍基合金在FeCl_3溶液中的腐蚀速率与影响因素之间的相互关系进行处理,确定各影响因子之间的主次关系。结果表明溶液流速是最关键因子,次关键因子为溶液pH值,其次为溶液温度和溶液浓度,并根据分析结果提出实际应用时的相应对策。 相似文献
106.
107.
利用美国SSI公司研制的COMPN模拟软件对双重孔隙介质油藏一种重要的开采机理 吸渗排油进行了模拟研究,考察了一个基质岩块为四周裂缝所包围时.在驱动压力和毛管压力的不同平衡(驱动压力和毛管压力的相对大小)关系下的水驱油采收率和水驱油效率的变化规律. 相似文献
108.
109.
110.
The effect of particle distribution on damage formation in particulate reinforced metal matrix composites deformed in compression 总被引:1,自引:0,他引:1
P.B. Prangnell S.J. Barnes S.M. Roberts P.J. Withers 《Materials Science and Engineering: A》1996,220(1-2):41-56
Image analysis results are reported on the generation of damage in particulate reinforced metal matrix composites during compressive deformation. The technique allows the automated collection of data on the incidence of particle fracture and void formation in the matrix as a function of important microstructural parameters such as local particle volume fraction and particle size. There is a strong relationship between damage and the local volume fraction of the reinforcement proving that damage formation is accentuated in regions of particle clustering. With the SiC reinforced materials examined, there was observed to be a change in dominance of damage mechanism from particle fracture at low local volume fractions to void formation in the matrix within strongly clustered regions. The results are compared with finite element (FE) modelling of the compressive deformation of clustered particles using a simple cluster of equi-spaced particles. The FE results suggest that plastic flow is generally inhibited in clustered regions. In certain highly clustered configurations shielding is such that flow does not occur in the heart of the cluster even at high levels of average plastic strain. The modelling suggests that the change in dominance of damage mechanism is related to the dramatic increase in tensile hydrostatic stresses in the matrix with higher levels of particle clustering. 相似文献