全文获取类型
收费全文 | 838785篇 |
免费 | 80400篇 |
国内免费 | 47959篇 |
专业分类
电工技术 | 39559篇 |
综合类 | 20854篇 |
化学工业 | 123042篇 |
金属工艺 | 48876篇 |
机械仪表 | 25848篇 |
建筑科学 | 28115篇 |
矿业工程 | 14358篇 |
能源动力 | 27134篇 |
轻工业 | 83951篇 |
水利工程 | 12250篇 |
石油天然气 | 17641篇 |
武器工业 | 3514篇 |
无线电 | 115749篇 |
一般工业技术 | 151831篇 |
冶金工业 | 134951篇 |
原子能技术 | 11640篇 |
自动化技术 | 107831篇 |
出版年
2023年 | 5831篇 |
2022年 | 8004篇 |
2021年 | 10884篇 |
2020年 | 12573篇 |
2019年 | 22978篇 |
2018年 | 27441篇 |
2017年 | 28696篇 |
2016年 | 29290篇 |
2015年 | 25450篇 |
2014年 | 28328篇 |
2013年 | 48927篇 |
2012年 | 33596篇 |
2011年 | 36582篇 |
2010年 | 30204篇 |
2009年 | 29683篇 |
2008年 | 28788篇 |
2007年 | 27566篇 |
2006年 | 24556篇 |
2005年 | 22289篇 |
2004年 | 24698篇 |
2003年 | 23376篇 |
2002年 | 22152篇 |
2001年 | 21627篇 |
2000年 | 19562篇 |
1999年 | 20929篇 |
1998年 | 46430篇 |
1997年 | 33009篇 |
1996年 | 25972篇 |
1995年 | 20338篇 |
1994年 | 17692篇 |
1993年 | 17250篇 |
1992年 | 12836篇 |
1991年 | 11792篇 |
1990年 | 10796篇 |
1989年 | 10368篇 |
1988年 | 9808篇 |
1987年 | 7792篇 |
1986年 | 7684篇 |
1985年 | 8805篇 |
1984年 | 7882篇 |
1983年 | 7315篇 |
1982年 | 6824篇 |
1981年 | 6813篇 |
1980年 | 6429篇 |
1979年 | 5932篇 |
1978年 | 5630篇 |
1977年 | 6846篇 |
1976年 | 9617篇 |
1975年 | 4833篇 |
1973年 | 4517篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
101.
102.
Within the framework of the effective-mass approximation and the dipole approximation, considering the three-dimensional confinement of the electron and hole and the strong built-in electric field(BEF) in strained wurtzite Zn O/Mg0:25Zn0:75O quantum dots(QDs), the optical properties of ionized donor-bound excitons(D+, X)are investigated theoretically using a variational method. The computations are performed in the case of finite band offset. Numerical results indicate that the optical properties of(D+, X) complexes sensitively depend on the donor position, the QD size and the BEF. The binding energy of(D+, X) complexes is larger when the donor is located in the vicinity of the left interface of the QDs, and it decreases with increasing QD size. The oscillator strength reduces with an increase in the dot height and increases with an increase in the dot radius. Furthermore, when the QD size decreases, the absorption peak intensity shows a marked increment, and the absorption coefficient peak has a blueshift. The strong BEF causes a redshift of the absorption coefficient peak and causes the absorption peak intensity to decrease remarkably. The physical reasons for these relationships have been analyzed in depth. 相似文献
103.
C. Doga Demirhan William W. Tso Joseph B. Powell Efstratios N. Pistikopoulos 《American Institute of Chemical Engineers》2019,65(7):e16498
Current ammonia production technologies have a significant carbon footprint. In this study, we present a process synthesis and global optimization framework to discover the efficient utilization of renewable resources in ammonia production. Competing technologies are incorporated in a process superstructure where biomass, wind, and solar routes are compared with the natural gas-based reference case. A deterministic global optimization-based branch-and-bound algorithm is used to solve the resulting large-scale nonconvex mixed-integer nonlinear programming problem (MINLP). Case studies for Texas, California, and Iowa are conducted to examine the effects of different feedstock prices and availabilities. Results indicate that profitability of ammonia production is highly sensitive to feedstock and electricity prices, as well as greenhouse gas (GHG) restrictions. Under strict 75% GHG reductions, biomass to ammonia route is found to be competitive with natural gas route, whereas wind and solar to ammonia routes require further improvement to compete with those two routes. © 2018 American Institute of Chemical Engineers AIChE J, 65: e16498 2019 相似文献
104.
Magnetic Resonance Materials in Physics, Biology and Medicine - To investigate the value of using diffusion-weighted imaging (DWI) and intravoxel incoherent motion DWI (IVIM-DWI) to assess the... 相似文献
105.
Babilas R. Łoński W. Młynarek K. Bajorek A. Radoń A. 《Metallurgical and Materials Transactions A》2020,51(8):4215-4227
Metallurgical and Materials Transactions A - The influence of the chemical composition on the crystallization process, amorphous phase formation, and the anticorrosion properties of Al-Zr-Ni-Fe-Y... 相似文献
106.
Sustainable and efficient food supply chain has become an essential component of one’s life. The model proposed in this paper is deeply linked to people's quality of life as a result of which there is a large incentive to fulfil customer demands through it. This proposed model can enhance food quality by making the best possible food quality accessible to customers, construct a sustainable logistics system considering its environmental impact and ensure the customer demand to be fulfilled as fast as possible. In this paper, an extended model is examined that builds a unified planning problem for efficient food logistics operations where four important objectives are viewed: minimising the total expense of the system, maximising the average food quality along with the minimisation of the amount of CO2 emissions in transportation along with production and total weighted delivery lead time minimisation. A four objective mixed integer linear programming model for intelligent food logistics system is developed in the paper. The optimisation of the formulated mathematical model is proposed using a modified multi-objective particle swarm optimisation algorithm with multiple social structures: MO-GLNPSO (Multi-Objective Global Local Near-Neighbour Particle Swarm Optimisation). Computational results of a case study on a given dataset as well as on multiple small, medium and large-scale datasets followed by sensitivity analysis show the potency and effectiveness of the introduced method. Lastly, there has been a scope for future study displayed which would lead to the further progress of these types of models. 相似文献
107.
108.
The Journal of Supercomputing - Infrastructure-as-a-service container-based virtualization is gaining interest as a platform for running distributed applications. With increasing scale of cloud... 相似文献
109.
110.
Diffusional limitations (the gel, glass, and cage effects) are manifested in several bulk free radical homopolymerizations as well as in random copolymerizations. These are associated with decreases of several orders of magnitude of the rate constants of termination, propagation, and initiation (the initiator efficiency), respectively. These phenomena have been modeled earlier using the free volume theory for the diffusivities of primary radicals, macro‐radicals, and monomer molecules, and have been applied to homopolymerizations. In this study, a similar model is developed for random bulk copolymerizations. The parameters of the model are fitted using isothermal data on styrene acrylonitrile random copolymerization carried out in small ampoules. Thereafter, best‐fit global correlations have been developed for this system. This enables the model to be used for studying non‐isothermal copolymerizations, as well as for carrying out optimization of industrial reactors, where non‐isothermal conditions are a norm. POLYM. ENG. SCI., 55:2098–2110, 2015. © 2014 Society of Plastics Engineers 相似文献