全文获取类型
收费全文 | 7714篇 |
免费 | 470篇 |
国内免费 | 375篇 |
专业分类
电工技术 | 330篇 |
综合类 | 364篇 |
化学工业 | 1453篇 |
金属工艺 | 780篇 |
机械仪表 | 587篇 |
建筑科学 | 210篇 |
矿业工程 | 153篇 |
能源动力 | 178篇 |
轻工业 | 877篇 |
水利工程 | 28篇 |
石油天然气 | 199篇 |
武器工业 | 85篇 |
无线电 | 642篇 |
一般工业技术 | 766篇 |
冶金工业 | 326篇 |
原子能技术 | 176篇 |
自动化技术 | 1405篇 |
出版年
2024年 | 17篇 |
2023年 | 123篇 |
2022年 | 170篇 |
2021年 | 275篇 |
2020年 | 177篇 |
2019年 | 169篇 |
2018年 | 151篇 |
2017年 | 201篇 |
2016年 | 222篇 |
2015年 | 223篇 |
2014年 | 379篇 |
2013年 | 408篇 |
2012年 | 534篇 |
2011年 | 649篇 |
2010年 | 539篇 |
2009年 | 595篇 |
2008年 | 529篇 |
2007年 | 532篇 |
2006年 | 469篇 |
2005年 | 348篇 |
2004年 | 305篇 |
2003年 | 265篇 |
2002年 | 233篇 |
2001年 | 142篇 |
2000年 | 132篇 |
1999年 | 124篇 |
1998年 | 89篇 |
1997年 | 71篇 |
1996年 | 75篇 |
1995年 | 84篇 |
1994年 | 66篇 |
1993年 | 44篇 |
1992年 | 33篇 |
1991年 | 43篇 |
1990年 | 24篇 |
1989年 | 26篇 |
1988年 | 25篇 |
1987年 | 11篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1968年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有8559条查询结果,搜索用时 523 毫秒
31.
The dislocation structures of bulk textured and epitaxial thin film YBa2Cu3O7 superconductors are examined. Correlations between increases in flux pinning and dislocation densities are noted. A model
for flux pinning by individual dislocations is presented. This gives a treatment of strain induced effects and effects of
normal state region interactions. It is shown that the values of pinning predicted are in line with experimental observations. 相似文献
32.
通过对引信软件特性的分析,结合软件测试理论,建立了针对引信软件开发过程的简化螺旋模型和针对开发组织结构的七人模型,形成一个完整的软件开发模型.同时,结合有关标准,提出以McCabe指数作为引信软件逻辑复杂性测试的指标,并用该指标对某引信软件进行了分析. 相似文献
33.
The author explored the mathematics efficacy beliefs of 270 South Asian (Indo Canadian) immigrant and Anglo Canadian nonimmigrant Grade 7 students. Self-efficacy beliefs strongly predicted mathematics performance for both cultural groups, but there were differences between the 2 groups in the sources of self-efficacy, the predictiveness of the secondary motivation variables, and the vertical dimensions of individualism and collectivism. It is argued that the Indo Canadian students are more vertical or hierarchical than the Anglo Canadian students and that comparison with others strongly influences their motivation beliefs and the formation of their efficacy beliefs. Self-efficacy in some cultures may be more other-oriented than is typically seen in Western cultures. A caution against generalizing about Asian populations is given, and implications for school settings are explored. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
34.
Ln2B2O7 (Ln=Sm, Eu, Gd and Tb; B=Zr or Ti) with pyrochlore structure was prepared by sol–gel method for the high-temperature catalytic combustion. The crystal structure of Ln2B2O7 was identified by XRD and their surface area was about 4 m2/g after calcinations at 1200 °C. Catalytic activity of methane combustion was observed for Ln2Zr2O7 series and the best catalyst was Sm2Zr2O7. Its relative reaction rate per unit surface area at 600 °C was 2 cm3/m2 min, which was twice higher than that of Mn-substituted Sr hexaaluminate. From surface analysis by XPS, the low binding energy of each Ln element of Ln2Zr2O7 compared to that of Ln2Ti2O7, gave the catalytic activity of methane combustion. 相似文献
35.
介绍了单相负载一工频感应炉供电的S7-200CPU224改造实践方案.依托原有设备条件,三相功率分配同样设计采用电容、电抗进行调节,起、停及三相电流平衡控制由晶闸管 接触器形式替代原单纯采用接触器控制,有效值测量使用有别于FFT的检测算法.运行实践表明:节能降耗明显,设备故障率大幅降低,具有良好的推广应用价值. 相似文献
36.
In the present paper, a modified self-flux technique has been successfully employed for the growth of pure and praseodymium
substituted (partially) large single crystals of high temperature superconducting Y1−x
Pr
x
Ba2Cu3O7−δ
(x = 0·0,0·2,0·4). Typical sizes of the platy and bulky crystals of pure YBCO(123) material are ≈ 2 × 2 × 0·1 mm3 and 4 × 1 × 1 mm3, respectively. In case of Pr-substitution, the typical sizes of platy and bulky crystals of Y0·8Pr0·2Ba2Cu3O7−δ
and Y0·6Pr0·4Ba2Cu3O7−δ
materials are ≈ 2 × 3 × 0·1 mm3 and 5 × 1 × 1 mm3 and ≈ 1 × 1·5 × 0·1 mm3 and 7 × 0·2 × 0·1 mm3, respectively. The morphology and growth habit of the as-grown single crystals and the critical transition temperature (T
c) of the oxygenated crystals were found to depend on the Pr-content.
Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995 相似文献
37.
Mait Lang Tiit Nilson Andres Kuusk Andres Kiviste Maris Hordo 《Remote sensing of environment》2007,110(4):445-457
Several published foliage mass and crown radius regression models were tested on the preparation of the input for the reflectance model of Kuusk and Nilson [Kuusk, A. and Nilson, T. (2000), A directional multispectral forest reflectance model. Remote Sensing of Environment, 72(2):244–252.] for 246 forest growth sample plots in Estonia. In each test, foliage mass and crown radius for trees in the sample plots were predicted with a particular pair of allometric regression models. The forest reflectance model was then run using the estimated foliage mass and crown radius values. Reflectance factors were simulated and compared with the reflectance values obtained from three atmospherically corrected Landsat 7 Enhanced Thematic Mapper (ETM+) scenes. The statistics of linear regression between the simulated and measured reflectance factors were used to assess the performance of foliage and crown radius models. The hypothesis was that the best allometric regression models should provide the best fit in reflectance. The strongest correlation between the simulated and measured reflectance factors was found in the short-wave infrared band (ETM + 5) for all the images. The highest R2 = 0.71 was observed in Picea abies dominated stands. No excellent combination of foliage mass and crown radius functions was found, but the ranking based on determination coefficients showed that some linear crown radius models are not applicable to our data. Processing of raster images, reflectance measurement for small sample plots, usage of tree-species-specific fixed parameters (specific leaf area, etc.), and the ignored influence of phenology introduced additional variation into the relationships between simulated and measured reflectance factors. Further studies are needed, but these preliminary results demonstrate that the proposed method could serve as an effective way of testing the performance of foliage mass and canopy cover regressions. 相似文献
38.
39.
Wan Fokkink Rob van Glabbeek Paulien de Wind 《Electronic Notes in Theoretical Computer Science》2006,156(1):97
We present congruence formats for η- and rooted η-bisimulation equivalence. These formats are derived using a method for decomposing modal formulas in process algebra. To decide whether a process algebra term satisfies a modal formula, one can check whether its subterms satisfy formulas that are obtained by decomposing the original formula. The decomposition uses the structural operational semantics that underlies the process algebra. 相似文献
40.