全文获取类型
收费全文 | 115329篇 |
免费 | 13684篇 |
国内免费 | 9003篇 |
专业分类
电工技术 | 9968篇 |
技术理论 | 2篇 |
综合类 | 12394篇 |
化学工业 | 15400篇 |
金属工艺 | 7957篇 |
机械仪表 | 8160篇 |
建筑科学 | 8395篇 |
矿业工程 | 3936篇 |
能源动力 | 3280篇 |
轻工业 | 12315篇 |
水利工程 | 3399篇 |
石油天然气 | 4146篇 |
武器工业 | 1519篇 |
无线电 | 12328篇 |
一般工业技术 | 10461篇 |
冶金工业 | 4405篇 |
原子能技术 | 2103篇 |
自动化技术 | 17848篇 |
出版年
2024年 | 353篇 |
2023年 | 1876篇 |
2022年 | 4238篇 |
2021年 | 5487篇 |
2020年 | 3994篇 |
2019年 | 2891篇 |
2018年 | 3200篇 |
2017年 | 3453篇 |
2016年 | 3280篇 |
2015年 | 4791篇 |
2014年 | 6175篇 |
2013年 | 7473篇 |
2012年 | 8929篇 |
2011年 | 9508篇 |
2010年 | 9036篇 |
2009年 | 8661篇 |
2008年 | 9277篇 |
2007年 | 8890篇 |
2006年 | 7849篇 |
2005年 | 6558篇 |
2004年 | 4719篇 |
2003年 | 3488篇 |
2002年 | 3485篇 |
2001年 | 3269篇 |
2000年 | 2468篇 |
1999年 | 1242篇 |
1998年 | 565篇 |
1997年 | 485篇 |
1996年 | 455篇 |
1995年 | 371篇 |
1994年 | 241篇 |
1993年 | 226篇 |
1992年 | 198篇 |
1991年 | 146篇 |
1990年 | 125篇 |
1989年 | 112篇 |
1988年 | 89篇 |
1987年 | 68篇 |
1986年 | 55篇 |
1985年 | 35篇 |
1984年 | 32篇 |
1983年 | 26篇 |
1982年 | 25篇 |
1981年 | 26篇 |
1980年 | 36篇 |
1979年 | 23篇 |
1976年 | 5篇 |
1974年 | 6篇 |
1959年 | 27篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
1.
Haiyue Xu Ji Zou Weimin Wang Hao Wang Wei Ji Zhengyi Fu 《Journal of the European Ceramic Society》2021,41(1):635-645
Fully dense ceramics with retarded grain growth can be attained effectively at relatively low temperatures using a high-pressure sintering method. However, there is a paucity of in-depth research on the densification mechanism, grain growth process, grain boundary characterization, and residual stress. Using a strong, reliable die made from a carbon-fiber-reinforced carbon (Cf/C) composite for spark plasma sintering, two kinds of commercially pure α-Al2O3 powders, with average particle sizes of 220 nm and 3 μm, were sintered at relatively low temperatures and under high pressures of up to 200 MPa. The sintering densification temperature and the starting threshold temperature of grain growth (Tsg) were determined by the applied pressure and the surface energy relative to grain size, as they were both observed to increase with grain size and to decrease with applied pressure. Densification with limited grain coarsening occurred under an applied pressure of 200 MPa at 1050 °C for the 220 nm Al2O3 powder and 1400 °C for the 3 μm Al2O3 powder. The grain boundary energy, residual stress, and dislocation density of the ceramics sintered under high pressure and low temperature were higher than those of the samples sintered without additional pressure. Plastic deformation occurring at the contact area of the adjacent particles was proved to be the dominant mechanism for sintering under high pressure, and a mathematical model based on the plasticity mechanics and close packing of equal spheres was established. Based on the mathematical model, the predicted relative density of an Al2O3 compact can reach ~80 % via the plastic deformation mechanism, which fits well with experimental observations. The densification kinetics were investigated from the sintering parameters, i.e., the holding temperature, dwell time, and applied pressure. Diffusion, grain boundary sliding, and dislocation motion were assistant mechanisms in the final stage of sintering, as indicated by the stress exponent and the microstructural evolution. During the sintering of the 220 nm alumina at 1125 °C and 100 MPa, the deformation tends to increase defects and vacancies generation, both of which accelerate lattice diffusion and thus enhance grain growth. 相似文献
2.
3.
4.
To benefit from recent advances in modeling and computational algorithms,as well as the availability of new covariance data,sensitivity and uncertainty analyses are needed to quantify the impact of uncertain sources on the design parameters of small prismatic high-temperature gas-cooled reactors(HTGRs).In particular,the contribution of nuclear data to the keff uncertainty is an important part of the uncertainty analysis of small-sized HTGR physical calculations.In this study,a small-sized HTGR designed by China Nuclear Power Engineering Co.,Ltd.was selected for keff uncertainty analysis during full lifetime burnup calculations.Models of the cold zero power(CZP)condition and full lifetime burnup process were constructed using the Reactor Monte Carlo Code RMC for neutron transport calculation,depletion calculation,and sensitivity and uncertainty analysis.For the sensitivity analysis,the Contribution-Linked eigenvalue sensitivity/Uncertainty estimation via Track length importance Characterization(CLUTCH)method was applied to obtain sensitive infor-mation,and the"sandwich"method was used to quantify the keff uncertainty.We also compared the keff uncertainties to other typical reactors.Our results show that 235U is the largest contributor to keff uncertainty for both the CZP and depletion conditions,while the contribution of 239Pu is not very significant because of the design of low discharge burnup.It is worth noting that the radioactive capture reaction of 28Si significantly contributes to the keff uncer-tainty owing to its specific fuel design.However,the keff uncertainty during the full lifetime depletion process was relatively stable,only increasing by 1.12%owing to the low discharge burnup design of small-sized HTGRs.These numerical results are beneficial for neutronics design and core parameters optimization in further uncertainty prop-agation and quantification study for small-sized HTGR. 相似文献
5.
良好的负荷预测模型能够精准且快速地计算预测值,有利于合理地规划分配电能,提升电网运行稳定性.基于MATLAB搭建灰色Elman网络电力负荷预测模型,参考安徽省淮南市"十三五"能源规划[1],以对淮南市进行中长期电力负荷预测为例,同时设置基于MATLAB搭建的Elman网络和灰色理论中的GM(1,1)模型为对照组进行对比仿真实验.提出灰色Elman网络相比对照组具有更高的运算精度,灰色Elman网络对比Elman网络有更好的训练效果. 相似文献
6.
于潞璐 《辽东学院学报(自然科学版)》2021,28(3):207-210
运用八段锦进行女大学生篮球教学后疲劳恢复,并与传统恢复手段拉伸运动进行比较实验,探索快速消除运动性疲劳的方法.研究结果显示:女大学生运用八段锦进行篮球教学后的疲劳恢复,其心率恢复明显的优于传统拉伸运动;学生的主观感觉疲劳恢复程度也明显的优于传统拉伸运动.结果表明,八段锦能够有效促进女大学生生理和心理疲劳的恢复. 相似文献
7.
Suk-Young Song Soonil Pyo Sungchul Choi Hee Sang Oh Jung Hwa Seo Ji Hea Yu Ahreum Baek Yoon-Kyum Shin Hoo Young Lee Ja Young Choi Sung-Rae Cho 《International journal of molecular sciences》2021,22(7)
Hypoxic–ischemic encephalopathy (HIE) is a devastating neonatal brain condition caused by lack of oxygen and limited blood flow. Environmental enrichment (EE) is a classic paradigm with a complex stimulation of physical, cognitive, and social components. EE can exert neuroplasticity and neuroprotective effects in immature brains. However, the exact mechanism of EE on the chronic condition of HIE remains unclear. HIE was induced by a permanent ligation of the right carotid artery, followed by an 8% O2 hypoxic condition for 1 h. At 6 weeks of age, HIE mice were randomly assigned to either standard cages or EE cages. In the behavioral assessments, EE mice showed significantly improved motor performances in rotarod tests, ladder walking tests, and hanging wire tests, compared with HIE control mice. EE mice also significantly enhanced cognitive performances in Y-maze tests. Particularly, EE mice showed a significant increase in Cav 2.1 (P/Q type) and presynaptic proteins by molecular assessments, and a significant increase of Cav 2.1 in histological assessments of the cerebral cortex and hippocampus. These results indicate that EE can upregulate the expression of the Cav 2.1 channel and presynaptic proteins related to the synaptic vesicle cycle and neurotransmitter release, which may be responsible for motor and cognitive improvements in HIE. 相似文献
8.
9.
建立高效液相色谱法检测伐地昔布的有关物质.采用α-酸性糖蛋白键合硅胶的手性色谱柱,以乙腈-醋酸铵缓冲液(0.01 mol/L,pH4.0)作为流动相进行梯度洗脱,检测波长215 nm.伐地昔布与5个已知杂质均可达到基线分离,在各自浓度范围内线性关系良好,平均回收率95.13%~99.77%,RSD1.10%~1.77%,检测限0.017 9~0.060 1 μg/mL,定量限0.059 7~0.200 0 μg/mL.方法专属性强,准确度好,灵敏度高,可为伐地昔布的质量控制及后续分离提纯和帕瑞昔布的质量控制提供指导. 相似文献
10.