首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   11420篇
  免费   367篇
  国内免费   15篇
电工技术   160篇
综合类   22篇
化学工业   1540篇
金属工艺   218篇
机械仪表   402篇
建筑科学   170篇
矿业工程   5篇
能源动力   297篇
轻工业   609篇
水利工程   42篇
石油天然气   22篇
无线电   1459篇
一般工业技术   1361篇
冶金工业   4294篇
原子能技术   89篇
自动化技术   1112篇
  2023年   61篇
  2022年   87篇
  2021年   126篇
  2020年   111篇
  2019年   129篇
  2018年   167篇
  2017年   147篇
  2016年   217篇
  2015年   187篇
  2014年   312篇
  2013年   546篇
  2012年   444篇
  2011年   481篇
  2010年   352篇
  2009年   426篇
  2008年   365篇
  2007年   332篇
  2006年   335篇
  2005年   291篇
  2004年   275篇
  2003年   258篇
  2002年   277篇
  2001年   206篇
  2000年   186篇
  1999年   302篇
  1998年   1609篇
  1997年   884篇
  1996年   556篇
  1995年   375篇
  1994年   301篇
  1993年   353篇
  1992年   94篇
  1991年   118篇
  1990年   97篇
  1989年   88篇
  1988年   65篇
  1987年   85篇
  1986年   63篇
  1985年   54篇
  1984年   29篇
  1983年   27篇
  1982年   24篇
  1981年   39篇
  1980年   34篇
  1979年   10篇
  1978年   19篇
  1977年   79篇
  1976年   134篇
  1975年   9篇
  1973年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Protection of Metals and Physical Chemistry of Surfaces - Cucumis anguria L. (C. anguria L.) commonly known as Indian gherkin is originally from Africa, though now seen widely in southeast,...  相似文献   
992.
Journal of Mechanical Science and Technology - In this paper, the performances of various ILU type parallel preconditioners for the finite element discretization of the incompressible Naiver-Stokes...  相似文献   
993.
A series of anionic conjugated polyelectrolytes (CPEs) is synthesized based on poly(fluorene-co-phenylene) by varying the side-chain ionic density from two to six per repeat units (MPS2-TMA, MPS4-TMA, and MPS6-TMA). The effect of MPS2, 4, 6-TMA as interlayers on top of a hole-extraction layer of poly(bis(4-phenyl)-2,4,6-trimethylphenylamine (PTAA) is investigated in inverted perovskite solar cells (PeSCs). Owing to the improved wettability of perovskites on hydrophobic PTAA with the CPEs, the PeSCs with CPE interlayers demonstrate a significantly enhanced device performance, with negligible device-to-device dependence relative to the reference PeSC without CPEs. By increasing the ionic density in the MPS-TMA interlayers, the wetting, interfacial defect passivation, and crystal growth of the perovskites are significantly improved without increasing the series resistance of the PeSCs. In particular, the open-circuit voltage increases from 1.06 V for the PeSC with MPS2-TMA to 1.11 V for the PeSC with MPS6-TMA. The trap densities of the PeSCs with MPS2,4,6-TMA are further analyzed using frequency-dependent capacitance measurements. Finally, a large-area (1 cm2) PeSC is successfully fabricated with MPS6-TMA, showing a power conversion efficiency of 18.38% with negligible hysteresis and a stable power output under light soaking for 60 s.  相似文献   
994.
Agricultural culture is a productive activity about education and management. It aims at high efficiency and high quality, uses technology as its means, and takes nature as its carrier. Agricultural cultural resources are the product of the rapid development of modern economy. It promotes the development of the national economy and profoundly affects people's production and life. DEA model, also known as data envelope analysis method, is an algorithm that uses multiple data decision units for input and output training to obtain the final model. This article explains the concept and basic characteristics of agricultural culture. Through questionnaire surveys and expert interviews, we collected development data, screened human, material, and financial data, and calculated information on economic and social resources. On this basis, this paper establishes the evaluation index of agricultural culture based on DEA model. Then, through empirical analysis from a specific perspective, it can be concluded that increasing human, material and financial input can achieve economic and social benefits. Generally speaking, cultural investment can promote the development of the industry.The research results of this paper laid a theoretical foundation for the development of agricultural culture, and put forward a development model focusing on technology development, improving investment efficiency, and investing in material resources.  相似文献   
995.
The aim of the study was to evaluate the effects of Saccharomyces cerevisiae fermentation products (SCFP) on performance and health of calves during the first 63 d of age. Sixty Holstein calves (30 males and 30 females) at 2 d of age were blocked by sex and date of birth then randomly assigned within blocks to 1 of 3 treatments. A texturized calf starter was fed ad libitum containing 0 (control), 0.5, or 1% SCFP (Original XPC, Diamond V, Cedar Rapids, IA) of DM. In addition, the supplemented calves were fed 1 g/d SCFP (SmartCare, Diamond V) in milk until d 30. All calves were fed 4 L of colostrum within 1 h of birth and were subsequently fed milk twice daily until weaned at 56 d of age. Male calves were harvested on d 56. Performance and health of weaned female calves were monitored until 63 d of age to determine the effect of preweaning treatment of SCFP on weaning stress. Starter intake, fecal scores, and medical treatments were recorded daily. Body weight measures and blood samples were collected on d 2, 28, 56, and 63. Serum was analyzed for blood urea nitrogen, fatty acids, insulin-like growth factor-1, glucose, and total protein. Oxidative biomarkers and total antioxidant capacity were also evaluated in the serum. Body weight, DMI, blood parameters, and oxidative biomarkers did not differ among treatments. Supplementation of SCFP lowered fecal scores in the pre- and postweaning periods. Saccharomyces cerevisiae fermentation products can be used to reduce the diarrhea in calves grown under normal commercial conditions.  相似文献   
996.
997.
The structural and electrical characteristics of Ag/Ni bilayer metallization on polycrystalline thermoelectric SnSe were investigated. Two difficulties with thermoelectric SnSe metallization were identified for Ag and Ni single layers: Sn diffusion into the Ag metallization layer and unexpected cracks in the Ni metallization layer. The proposed Ag/Ni bilayer was prepared by hot-pressing, demonstrating successful metallization on the SnSe surface without interfacial cracks or elemental penetration into the metallization layer. Structural analysis revealed that the Ni layer reacts with SnSe, forming several crystalline phases during metallization that are beneficial for reducing contact resistance. Detailed investigation of the Ni/SnSe interface layer confirms columnar Ni-Sn intermetallic phases [(Ni3Sn and Ni3Sn2) and Ni5.63SnSe2] that suppress Sn diffusion into the Ag layer. Electrical specific-contact resistivity (5.32 × 10?4 Ω cm2) of the Ag/Ni bilayer requires further modification for development of high-efficiency polycrystalline SnSe thermoelectric modules.  相似文献   
998.
This paper presents a generalised optimal linear quadratic analog tracker (LQAT) with universal applications for the continuous-time (CT) systems. This includes: (1) a generalised optimal LQAT design for the system with the pre-specified trajectories of the output and the control input and additionally with both the input-to-output direct-feedthrough term and known/estimated system disturbances or extra input/output signals; (2) a new optimal filter-shaped proportional plus integral state-feedback LQAT design for non-square non-minimum phase CT systems to achieve a minimum phase-like tracking performance; (3) a new approach for computing the control zeros of the given non-square CT system; and (4) a one-learning-epoch input-constrained iterative learning LQAT design for the repetitive CT system.  相似文献   
999.
Research has found workplace ostracism to negatively impact workplace attitudes and behaviours such as job satisfaction, organisational citizenship behaviour, and job performance. However, research investigating beyond the direct effects of workplace ostracism and findings about boundary conditions for mitigating the negative effects of workplace ostracism are limited in organisational studies. In this regard, this study explored the mediating effects of job satisfaction on the relationship between workplace ostracism and innovative behaviour and the moderating effects of social networking services for work-related purposes for the relationship between workplace ostracism and job satisfaction. The two-wave study consisted of 237 full-time employees in large organisations in South Korea. The hierarchical regression analyses resulted in job satisfaction to mediate the relationship between workplace ostracism and innovative behaviour and social network service to significantly moderate the relationship between workplace ostracism and job satisfaction. Moreover, mediated moderation was found for the study model, which further suggests that using social network services for work-related purposes had indirect effects on innovative behaviour.  相似文献   
1000.
The paper presents a reliability model of a k-out-of-N:G redundant system with M mutually exclusive failure modes and common cause failures. Failed system repair times are arbitrarily distributed. The system is in a failed state when (Nk+1) units failed or a common cause failure occurred. Laplace transforms of the state probabilities and the availability of the system are derived. Finally, the system steady-state availability is also reported.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号