全文获取类型
收费全文 | 153682篇 |
免费 | 10626篇 |
国内免费 | 5894篇 |
专业分类
电工技术 | 9256篇 |
技术理论 | 27篇 |
综合类 | 15541篇 |
化学工业 | 17830篇 |
金属工艺 | 2388篇 |
机械仪表 | 4899篇 |
建筑科学 | 25957篇 |
矿业工程 | 7923篇 |
能源动力 | 6894篇 |
轻工业 | 6861篇 |
水利工程 | 21395篇 |
石油天然气 | 9400篇 |
武器工业 | 498篇 |
无线电 | 6962篇 |
一般工业技术 | 7306篇 |
冶金工业 | 8022篇 |
原子能技术 | 1547篇 |
自动化技术 | 17496篇 |
出版年
2024年 | 200篇 |
2023年 | 1313篇 |
2022年 | 2681篇 |
2021年 | 3507篇 |
2020年 | 3811篇 |
2019年 | 2971篇 |
2018年 | 2868篇 |
2017年 | 3627篇 |
2016年 | 4284篇 |
2015年 | 4515篇 |
2014年 | 10829篇 |
2013年 | 9560篇 |
2012年 | 11427篇 |
2011年 | 11820篇 |
2010年 | 8891篇 |
2009年 | 9432篇 |
2008年 | 8856篇 |
2007年 | 11225篇 |
2006年 | 10134篇 |
2005年 | 8979篇 |
2004年 | 7375篇 |
2003年 | 6642篇 |
2002年 | 5551篇 |
2001年 | 4275篇 |
2000年 | 3480篇 |
1999年 | 2642篇 |
1998年 | 1868篇 |
1997年 | 1483篇 |
1996年 | 1133篇 |
1995年 | 1024篇 |
1994年 | 750篇 |
1993年 | 566篇 |
1992年 | 431篇 |
1991年 | 333篇 |
1990年 | 234篇 |
1989年 | 268篇 |
1988年 | 181篇 |
1987年 | 159篇 |
1986年 | 161篇 |
1985年 | 167篇 |
1984年 | 162篇 |
1983年 | 135篇 |
1982年 | 51篇 |
1981年 | 28篇 |
1980年 | 27篇 |
1979年 | 30篇 |
1977年 | 22篇 |
1976年 | 11篇 |
1961年 | 9篇 |
1959年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Yuanming Xie Tianda Yu Chaojun Deng Xuefei Hu 《Journal of Nuclear Science and Technology》2020,57(9):1074-1090
ABSTRACT In the lower chamber of pressurized water reactor (PWR), the flow distribution device is the core module to distribute coolant into the core. It has complex structure and numerous design parameters. Therefore, it has important theoretical and practical significance to optimize the device. The mesh independence verification, turbulence model selection, and data processing all can influence the numerical simulation results of the lower chamber, in order to research the influence, a numerical simulation method based on the original model of CNP1000 reactor lower chamber is proposed in this paper. In the method, an optimization design method of flow distribution device is established based on surrogate model. The main design variables and optimization objectives are determined based on the device’s structure and function characteristics. And then it respectively adopts Kriging algorithm and multi-objective genetic algorithm to establish a surrogate model of flow distribution device and optimize it globally. Finally, the optimal design variables are obtained. Compared with the device’s performance before optimization, the after optimization has smaller total pressure loss and more uniform flow. The effectiveness and practicability of proposed optimization design method can be verified. 相似文献
32.
添加剂是铜电解精炼生产管理的最关键要素,合适的添加剂使用方案可以有效保障电解生产系统长期稳定。结合添加剂生产实践和其它电解厂添加剂管理优点,提出探索添加剂精细化管理,进一步保障和提升铜电解添加剂管理实效。 相似文献
33.
34.
陈彦名 《电信工程技术与标准化》2015,(5)
介绍了目前最炙手可热的REST架构风格,该风格顺应Web2.0的兴起,完美的匹配了云计算时代来临的可扩展要求,在各种应用场景中都得到了充分的表现。根据其技术特点,分析了该风格的API在移动通信网络管理中的应用,从网管系统内部、网管系统之间以及网管系统与上层APP应用之间等多方面对是否适用于REST风格以及如何在合适的位置使用REST API进行了分析。 相似文献
35.
SPEEK/cSMM membrane for simultaneous electricity generation and wastewater treatment in microbial fuel cell 下载免费PDF全文
36.
We present a framework for the formulation of MIP scheduling models based on multiple and nonuniform discrete time grids. In a previous work we showed that it is possible to use different (possibly non-uniform) time grids for each task, unit, and material. Here, we generalize these ideas to account for general resources, and a range of processing characteristics such as limited intermediate storage and changeovers. Each resource has its own grid based on resource consumption and availability allowing resource constraints to be modeled more accurately without increasing the number of binary variables. We develop algorithms to define the unit-, task-, material-, and resource-specific grids directly from problem data. Importantly, we prove that the multi-grid formulation is able to find a schedule with the same optimal objective as the discrete-time single-grid model with an arbitrarily fine grid. The proposed framework leads to the formulation of models with reduced number of binary variables and constraints, which are able to find good solutions faster than existing models. 相似文献
37.
Qingna Gong Songtao Cao Yu Zhou Ruixin Wang Weizhou Jiao 《International Journal of Hydrogen Energy》2021,46(41):21442-21453
Ni2P nanoparticles and CdS nanorods were grew together on a mesoporous g-C3N4 through a facile in-situ solvothermal approach. Under visible light (λ > 400 nm), the as-prepared ternary PCN–CdS-5% Ni2P composite displays a high H2 evolution rate with 2905.86 μmol g?1 h?1, which is about 14, 18 and 279 times that of PCN–CdS, PCN–Ni2P and PCN, respectively. The enhanced photocatalytic activity is mainly attributed to the improved separation efficiency of the photocarriers by the type II PCN–CdS heterojunction and the effective extraction of photogenerated electrons by Ni2P. Meanwhile, Ni2P acts as co-catalyst to provide the photocatalytic active site for hydrogen reduction. In addition, PCN–CdS-5% Ni2P composite exerts good stability in 12-h cycles. 相似文献
38.
With the emergence of distributed ledger technology (DLT), numerous practitioners and researchers have proclaimed its beneficial impact on supply chain transactions in the future. However, the vast majority of DLT initiatives are discontinued after a short period. With the full potential of DLT laying far down the road, especially managers in supply chain management (SCM) seek for short-term cost-saving effects of DLT in order to achieve long-term benefits of DLT in the future. However, the extant research has bypassed grounding long-term as well as short-term effects of DLT on supply chain transaction with empirical data. We address this shortcoming, following an abductive research approach and combining empirical data from a multiple case study design with the corresponding literature. Our study reveals that the effects of DLT on supply chain transactions are two-sided. We found six effects of DLT solutions that have a cost-reducing or cost avoidance impact on supply chain transactions. In addition, we found two effects that change the power distribution between buyers and suppliers in transactions and a single effect that reduces the dependency of supply chain transactions on third parties. While cost-reducing and avoidance as well as dependency-reducing effects are positive effects, the change in power distribution might come with disadvantages. With these findings, the paper provides the first empirical evidence of the impact of DLT on supply chain transactions, which will enable managers to improve their assessment of DLT usage in supply chains. 相似文献
39.
Chengxiao Zhao Zupeng Chen Run Shi Xiaofei Yang Tierui Zhang 《Advanced materials (Deerfield Beach, Fla.)》2020,32(28):1907296
With the ambition of solving the challenges of the shortage of fossil fuels and their associated environmental pollution, visible-light-driven splitting of water into hydrogen and oxygen using semiconductor photocatalysts has emerged as a promising technology to provide environmentally friendly energy vectors. Among the current library of developed photocatalysts, organic conjugated polymers present unique advantages of sufficient light-absorption efficiency, excellent stability, tunable electronic properties, and economic applicability. As a class of rising photocatalysts, organic conjugated polymers offer high flexibility in tuning the framework of the backbone and porosity to fulfill the requirements for photocatalytic applications. In the past decade, significant progress has been made in visible-light-driven water splitting employing organic conjugated polymers. The recent development of the structural design principles of organic conjugated polymers (including linear, crosslinked, and supramolecular self-assembled polymers) toward efficient photocatalytic hydrogen evolution, oxygen evolution, and overall water splitting is described, thus providing a comprehensive reference for the field. Finally, current challenges and perspectives are also discussed. 相似文献
40.
《Geotextiles and Geomembranes》2020,48(6):897-911
Dynamic responses of the geosynthetic-encased stone column (GESC) supported embankment under traffic loads have become a hot topic. This study investigates the responses of GESC improved ground under vertical cyclic loading. A series of laboratory tests in a designed model test tank have been carried out with different loading parameters (varied loading amplitudes and frequencies), different column dimensions (varied encasement lengths and column diameters). In the tests, the soil-column stress distribution, accumulated settlement of loading plate, excess pore water pressure in the surrounding soil and lateral bulging of the stone column are monitored. Experimental results indicate that the vertical stress on the stone column increases with the increment of encasement length, and decreases with the increment of column diameter, loading amplitude and loading frequency. The increasing stress on the surrounding soil leads to a greater accumulated settlement of the loading plate and excess pore water pressure, while the increasing stress on the column leads to larger lateral bulging of the column. Excess pore water pressure dissipates effectively through vertical and horizontal drainage channels provided by the stone column and the sand bed. The geosynthetic encasement prevents the clay from obstructing the drainage channel by filtration and guarantees the drainage effect. 相似文献