全文获取类型
收费全文 | 75284篇 |
免费 | 8074篇 |
国内免费 | 5238篇 |
专业分类
电工技术 | 6687篇 |
技术理论 | 2篇 |
综合类 | 6864篇 |
化学工业 | 10008篇 |
金属工艺 | 4561篇 |
机械仪表 | 5395篇 |
建筑科学 | 6757篇 |
矿业工程 | 2302篇 |
能源动力 | 2301篇 |
轻工业 | 6384篇 |
水利工程 | 1999篇 |
石油天然气 | 3268篇 |
武器工业 | 935篇 |
无线电 | 8873篇 |
一般工业技术 | 6942篇 |
冶金工业 | 2804篇 |
原子能技术 | 961篇 |
自动化技术 | 11553篇 |
出版年
2024年 | 363篇 |
2023年 | 1123篇 |
2022年 | 2302篇 |
2021年 | 3001篇 |
2020年 | 2335篇 |
2019年 | 1798篇 |
2018年 | 2103篇 |
2017年 | 2336篇 |
2016年 | 2137篇 |
2015年 | 3107篇 |
2014年 | 4092篇 |
2013年 | 4505篇 |
2012年 | 5452篇 |
2011年 | 5654篇 |
2010年 | 5341篇 |
2009年 | 5236篇 |
2008年 | 5354篇 |
2007年 | 4876篇 |
2006年 | 4743篇 |
2005年 | 3805篇 |
2004年 | 3078篇 |
2003年 | 2926篇 |
2002年 | 3641篇 |
2001年 | 3055篇 |
2000年 | 1827篇 |
1999年 | 1204篇 |
1998年 | 647篇 |
1997年 | 527篇 |
1996年 | 445篇 |
1995年 | 371篇 |
1994年 | 315篇 |
1993年 | 198篇 |
1992年 | 162篇 |
1991年 | 133篇 |
1990年 | 89篇 |
1989年 | 80篇 |
1988年 | 45篇 |
1987年 | 41篇 |
1986年 | 33篇 |
1985年 | 8篇 |
1984年 | 12篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 2篇 |
1966年 | 1篇 |
1959年 | 17篇 |
1951年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
为落实健康中国发展战略,推进中国健康服务业的发展,中国工程院于2015年启动"中国健康服务业发展战略研究"重大咨询项目。课题自启动以来,组织了28位院士和150余位专家,对京上广深等一至三线共12个城市进行了广泛的社会调查。本文在大量社会调查的基础上,从健康服务业的概念、内涵、发展特点入手,深入分析了国内健康服务业的发展现状;以全方位、全覆盖、全过程建立健康服务保障体系为目标,对健康服务业的定位、发展思路,城乡理想模式等进行了深入探讨;并针对健康管理体系建设、养生养老、医养结合、健康保险、社会办医、金融保障等重点问题,提出了为顺应中国健康服务业发展战略顺畅实施的保障措施和相关建议。 相似文献
972.
973.
974.
975.
Jinsheng?Xu Long?Han Jian?Zheng Xiong?ChenEmail author Changsheng?Zhou 《Mechanics of Time-Dependent Materials》2017,21(4):577-595
A thermo-damage-viscoelastic model for hydroxyl-terminated polybutadiene (HTPB) composite propellant with consideration for the effect of temperature was implemented in ABAQUS. The damage evolution law of the model has the same form as the crack growth equation for viscoelastic materials, and only a single damage variable \(S\) is considered. The HTPB propellant was considered as an isotropic material, and the deviatoric and volumetric strain-stress relations are decoupled and described by the bulk and shear relaxation moduli, respectively. The stress update equations were expressed by the principal stresses \(\sigma_{ii}^{R}\) and the rotation tensor \(M\), the Jacobian matrix in the global coordinate system \(J_{ijkl}\) was obtained according to the fourth-order tensor transformation rules. Two models having complex stress states were used to verify the accuracy of the constitutive model. The test results showed good agreement with the strain responses of characteristic points measured by a contactless optical deformation test system, which illustrates that the thermo-damage-viscoelastic model perform well at describing the mechanical properties of an HTPB propellant. 相似文献
976.
977.
978.
Haotian Wang Jian Sun Hong Ding Ganlin Shan Zhuang Chang 《Journal of Failure Analysis and Prevention》2017,17(6):1182-1190
Performance degradation modeling plays an important role in prognostics and health management of mechanical system. Influenced by the complex structure of the hydraulic pump and the limited experiment standards, it is hard to establish an appropriate performance degradation model. To fulfill current requirements, a method for establishing the performance degradation model based on accelerated experiment is proposed. In order to describe the general trend of the degradation, the double-stress exponential model is firstly established as the theoretical degradation model. On this basement, combined with the characteristics of the experiment, the accelerating coefficient is settled; meanwhile, the procedures for assuring the model parameters are presented. Furthermore, based on the accelerated experiment of the hydraulic pump under various stresses, the performance degradation model is finally established. Result of the experimental analysis indicates that the proposed method is applicable and the presented model is effective to measure the performance degradation of pump. 相似文献
979.
Ren Zhang Yunhua Zhou Yiyi Zhu Yangyang Li Liang Chu Yonggang Min Jian Zhang Jianping Yang Xing’ao Li 《Journal of Superconductivity and Novel Magnetism》2017,30(9):2471-2479
Tetragonal BiFeO3 (BFO), which has a giant spontaneous polarization, has attracted a great deal of attention recently. In this paper, we systematically study the structural, magnetic, electronic and optic properties of BFO, BiFe0.75Mn0.25 O 3 (BFMM), and BiFe0.75Ti0.125Mn0.125 O 3 (BFMT). Results show that doping Ti and Mn into the Fe sites increases the c/a ratio and enhances the magnetization of BiFeO3 from 0 to 5 μB. The crystal symmetry changes from orthogonality to tetragonality with half of the Mn atoms being replaced by Ti in BiFe0.75Mn0.25 O 3, which suppresses the energy splitting of the Mn 3d orbitals and thus enlarge the band gap to 1.21 eV for BiFe0.75Ti0.125Mn0.125 O 3. Our calculated Bader charge and charge density difference show that the smallest volume of BiFe0.75Mn0.25 O 3 arises from the strong Mn–O bonds in BiFe0.75Mn0.25 O 3. Further investigations indicate similar optical behaviors for BiFeO3 and BiFe0.75Ti0.125Mn0.125 O 3. However, BiFe0.75Mn0.25 O 3 exhibits strong absorption in the infrared region for the transition from O 2p to Mn \({e_{g}^{2}}\) and \(t_{2g}^{3}\). 相似文献
980.
Chao‐Yu Li Zhen‐Wei Yang Jin‐Chao Dong Tapan Ganguly Jian‐Feng Li 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(8)
Shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS), due to its versatility, has been able to break the long‐term limitations of the material‐ and substrate‐specific generalities in the traditional field of surface‐enhanced Raman spectroscopy. With a shell‐isolated work principle, this method provides an opportunity to investigate successfully in surface, biological systems, energetic materials, and environmental sciences. Both the shell material and core morphology are being improved continuously to meet the requirements in diverse systems, such as the electrochemical studies at single crystal electrode surfaces, in situ monitoring of photoinduced reaction processes, practical applications in energy conversion and storage, inspections in food safety, and the surface‐enhanced fluorescence. Predictably, the concept of shell‐isolated nanoparticle‐enhancement could be expanded to the wider range for the performance of plasmon‐enhanced spectral modifications. 相似文献