全文获取类型
收费全文 | 419067篇 |
免费 | 48038篇 |
国内免费 | 32732篇 |
专业分类
电工技术 | 36190篇 |
技术理论 | 10篇 |
综合类 | 43910篇 |
化学工业 | 53521篇 |
金属工艺 | 29000篇 |
机械仪表 | 28965篇 |
建筑科学 | 31609篇 |
矿业工程 | 17801篇 |
能源动力 | 10933篇 |
轻工业 | 46226篇 |
水利工程 | 13485篇 |
石油天然气 | 15834篇 |
武器工业 | 6003篇 |
无线电 | 44095篇 |
一般工业技术 | 36138篇 |
冶金工业 | 18310篇 |
原子能技术 | 6918篇 |
自动化技术 | 60889篇 |
出版年
2024年 | 2332篇 |
2023年 | 6864篇 |
2022年 | 16265篇 |
2021年 | 20924篇 |
2020年 | 14728篇 |
2019年 | 10591篇 |
2018年 | 11440篇 |
2017年 | 13384篇 |
2016年 | 11958篇 |
2015年 | 18637篇 |
2014年 | 23416篇 |
2013年 | 27501篇 |
2012年 | 34079篇 |
2011年 | 35916篇 |
2010年 | 33363篇 |
2009年 | 31710篇 |
2008年 | 33022篇 |
2007年 | 31872篇 |
2006年 | 27660篇 |
2005年 | 22872篇 |
2004年 | 16352篇 |
2003年 | 11067篇 |
2002年 | 10122篇 |
2001年 | 9071篇 |
2000年 | 7708篇 |
1999年 | 4121篇 |
1998年 | 2202篇 |
1997年 | 1766篇 |
1996年 | 1713篇 |
1995年 | 1372篇 |
1994年 | 1168篇 |
1993年 | 889篇 |
1992年 | 717篇 |
1991年 | 520篇 |
1990年 | 479篇 |
1989年 | 435篇 |
1988年 | 296篇 |
1987年 | 211篇 |
1986年 | 157篇 |
1985年 | 112篇 |
1984年 | 87篇 |
1983年 | 79篇 |
1982年 | 90篇 |
1981年 | 95篇 |
1980年 | 131篇 |
1979年 | 81篇 |
1976年 | 14篇 |
1965年 | 12篇 |
1959年 | 70篇 |
1951年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
ZHAO Pengfei TIAN Yuming LIU Aiping KONG Xiangchen CHAI Yuesheng LI Zhangang BAI Pinbo 《中国耐火材料》2015,(2):36-41
Based on the needs of the market,a new 52 MPa medium-density and high-strength ceramic proppant was prepared by adopting third grade bauxite and clay as raw materials and using the solid phase sintering method,and the effect of the firing temperature on the microstructure,phase composition and mechanical properties of the ceramic proppant was studied. The broken resistance mechanism of this ceramic proppant was also discussed. The results show that the main phases of the prepared ceramic proppant are mullite and corundum; the broken rates are 3. 92% and 7. 21% under 52 MPa and69 MPa,respectively. 相似文献
112.
113.
114.
115.
116.
117.
In this work,the ionospheric variability is analyzed by applying the wavelet decomposition technique to the noontime fo F2,F10.7,interplanetary magnetic field(IMF)Bz,Ap,and lower thermospheric temperature at pressure of 10?4 h Pa in 2002.Results show that the variance of periodic oscillations in the ionosphere is largest in the 2–4-day period and declines with the increase of the period.The maximum variance of the periodic oscillations in solar irradiation is in the 16–32-day period.For geomagnetic activities,most of the variance is about equally distributed on intervals of periods shorter than 32 days.Variance distributions of IMF Bz and lower thermospheric temperature are similar to those of the ionosphere.They show the maximum in the 2–4-day period and decline with the increase of the period.By analyzing the distributions of the variances,the potential connections between the ionosphere and the external sources are discussed. 相似文献
118.
Haitang Yang Zilong Lu Bixiong Bie Zeyu Fu Jianling Yue Xiaozhong Huang 《Ceramics International》2019,45(9):11395-11402
SiCf/PyC/SiC and SiCf/BN/SiC mini-composites comprising single tow SiC fibre-reinforced SiC with chemical vapor deposited PyC or BN interface layers are fabricated. The microstructure evolutions of the mini-composite samples as the oxidation temperature increases (oxidation at 1000, 1200, 1400, and 1600?°C in air for 2?h) are observed by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction characterization methods. The damage evolution for each component of the as-fabricated SiCf/SiC composites (SiC fibre, PyC/BN interface, SiC matrix, and mesophase) is mapped as a three-dimensional (3D) image and quantified with X-ray computed tomography. The mechanical performance of the composites is investigated via tensile tests.The results reveal that tensile failure occurs after the delamination and fibre pull-out in the SiCf/PyC/SiC composites due to the volatilization of the PyC interface at high temperatures in the air environment. Meanwhile, the gaps between the fibres and matrix lead to rapid oxidation and crack propagation from the SiC matrix to SiC fibre, resulting in the failure of the SiCf/PyC/SiC composites as the oxidation temperature increases to 1600?°C. On the other hand, the oxidation products of B2O3 molten compounds (reacted from the BN interface) fill up the fracture, cracks, and voids in the SiC matrix, providing excellent strength retention at elevated oxidation temperatures. Moreover, under the protection of B2O3, the SiCf/BN/SiC mini-composites show a nearly intact microstructure of the SiC fibre, a low void growth rate from the matrix to fibre, and inhibition of new void formation and the SiO2 grain growth from room to high temperatures. This work provides guidance for predicting the service life of SiCf/PyC/SiC and SiCf/BN/SiC composite materials, and is fundamental for establishing multiscale damage models on a local scale. 相似文献
119.
In the early design stage, automotive modeling should both meet the requirements of aesthetics and engineering. Therefore, a vehicle CAD (computer aided design) model that can be easily adjusted by feedbacks is necessary. Based on CE-Bézier surface, this paper presents a set of algorithms for parametric segmentation and fairing surface generation in a car model. This model is defined by a simplified automotive template and relevant control points, shape parameters and segmentation parameters, which can be modified to alter the car form efficiently. With this model and the corresponding adjustment method, more than fifty various vehicle models are established in this research according to different parameters. And two methods for calculating similarity index between car models are constructed, which are suitable for brand design trend analysis and modelling design decisionmaking. 相似文献
120.
目的: 探讨自身免疫性溶血性贫血(AIHA)患者外周血中调节性B细胞(Bregs)的表达及其在该病发病中的意义。方法:选择16例自身免疫性溶血性贫血患者和14例健康志愿者为研究对象,用流式细胞术分析外周血CD19+IL-10+调节性B细胞及CD19+CD24hiCD27+调节性B细胞的表达;ELISA方法检测培养上清液中IL-10的水平。结果:自身免疫性溶血性贫血患者外周血中CD19+IL-10+调节性B细胞、CD19+CD24hiCD27+调节性B细胞的表达分别为(1.27±0.39)%、(9.85±2.18)%,健康志愿者组分别为(2.92±0.71)%、(26.47±4.31)%,两组比较差异有统计学意义(P<0.05);自身免疫性溶血性贫血患者细胞培养上清中IL-10的水平低于健康志愿者组(P<0.05)。结论:自身免疫性溶血性贫血患者外周血中CD19+IL-10+调节性B细胞及CD19+CD24hiCD27+调节性B细胞比例降低,提示调节性B细胞可能参与自身免疫性溶血性贫血的发病过程。 相似文献