全文获取类型
收费全文 | 167768篇 |
免费 | 17008篇 |
国内免费 | 9152篇 |
专业分类
电工技术 | 12675篇 |
技术理论 | 17篇 |
综合类 | 14260篇 |
化学工业 | 25501篇 |
金属工艺 | 9947篇 |
机械仪表 | 10795篇 |
建筑科学 | 13361篇 |
矿业工程 | 5039篇 |
能源动力 | 4856篇 |
轻工业 | 14391篇 |
水利工程 | 3674篇 |
石油天然气 | 8351篇 |
武器工业 | 1804篇 |
无线电 | 18640篇 |
一般工业技术 | 17884篇 |
冶金工业 | 6431篇 |
原子能技术 | 2014篇 |
自动化技术 | 24288篇 |
出版年
2024年 | 703篇 |
2023年 | 2823篇 |
2022年 | 5837篇 |
2021年 | 7902篇 |
2020年 | 5897篇 |
2019年 | 4570篇 |
2018年 | 5116篇 |
2017年 | 5707篇 |
2016年 | 5100篇 |
2015年 | 7503篇 |
2014年 | 9412篇 |
2013年 | 10947篇 |
2012年 | 12701篇 |
2011年 | 13716篇 |
2010年 | 12065篇 |
2009年 | 11385篇 |
2008年 | 11174篇 |
2007年 | 10342篇 |
2006年 | 9782篇 |
2005年 | 7890篇 |
2004年 | 5514篇 |
2003年 | 4421篇 |
2002年 | 4325篇 |
2001年 | 3594篇 |
2000年 | 3125篇 |
1999年 | 2729篇 |
1998年 | 1995篇 |
1997年 | 1562篇 |
1996年 | 1475篇 |
1995年 | 1074篇 |
1994年 | 883篇 |
1993年 | 626篇 |
1992年 | 528篇 |
1991年 | 361篇 |
1990年 | 265篇 |
1989年 | 221篇 |
1988年 | 162篇 |
1987年 | 113篇 |
1986年 | 85篇 |
1985年 | 53篇 |
1984年 | 28篇 |
1983年 | 33篇 |
1982年 | 36篇 |
1981年 | 32篇 |
1980年 | 42篇 |
1979年 | 16篇 |
1977年 | 4篇 |
1976年 | 11篇 |
1959年 | 17篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
271.
根据某雷达系统对测量信号的快速传输要求,提出采用滑动帧的处理方法并在FPGA中实现,克服了传统帧处理难以满足快速传输要求的不足。阐述了滑动帧结构的构造思想,详述了滑动帧结构的特点及具体功能模块的实现。根据实际应用需求构造了滑动帧结构处理器,试验和应用结果表明设计可行有效,能充分满足实时数据传输的要求。 相似文献
272.
273.
274.
Manipulation of molecular orientation alignment in MCTLCPs (main-chain thermotropic liquid crystalline polymers) by pure shear at nano scale has been investigated for the first time using molecular dynamics (MD) simulation. Results indicate that high planar shear induces long-range uniform orientation ordering (liquid crystalline phase) of initially randomly orientated molecules of MCTLCP fluid confined in a nanochannel, which is confirmed by analyzing the orientation order parameter and the snapshots of MCTLCP liquid in a nanochannel under different shear rates. Insights into the origin of the phase transition phenomena are given at molecular level through investigating the thermodynamic density distribution of MCTLCP molecules in the nanochannel, suggesting that the energy shift due to a radical jump of system density affects both the magnitude and the orientation of the molecular ordering. Simulation results also show that there is a critical shear rate for transforming isotropic phase into liquid crystalline phase. The critical shear rate is dependent on the temperature of the MCTLCP system. Findings in this paper may present useful information for processing TLCP molecules at nano scale and the understanding of nanoflow. 相似文献
275.
通过测试连铸二冷喷嘴性能,对比同型号喷嘴使用前后两种状态下特性参数,分析了喷嘴参数变化的原因。提出了对使用中的喷嘴特性进行检测与校核的建议,以确保喷嘴特性满足铸坯二冷工艺条件,保证铸坯质量。 相似文献
276.
风管摩擦阻力的直接计算方法 总被引:2,自引:1,他引:1
提出用高精度的反映密度、黏度和温度关系的经验公式和Colebrook公式计算风管摩擦阻力系数的方法。分析和算例表明,用该方法计算,计算结果比采用常用工程设计方法更为准确,为应用计算机进行风道设计提供了直接、简便的方法。 相似文献
277.
Wei Feng Jianping Wen Xiaoqiang Jia Qing Yuan Yan Sun Cuiyun Liu 《American Institute of Chemical Engineers》2006,52(8):2864-2875
A coupled three-dimensional (3-D) model, combining hydrodynamics with biochemical reactions, was developed to simulate the local transient flow patterns and the dynamic behaviors of cell growth and phenol biodegradation by yeast Candida tropicalis in the bubble-column bioreactor, using the computational fluid dynamic (CFD) method. In order to validate this proposed model effectively, the validation of the local hydrodynamic characteristics of the gas-mineral salt solution (gas-liquid) two-phase system, with the phenol concentration of 1200 mg/L, and with the absence of cells, was performed in a square-sectioned bubble column bioreactor using the LDA system and conductivity probe. Furthermore, the validation of phenol biodegradation behaviors by yeast Candida tropicalis at different initial concentrations of phenol and cell was also carried out in the above bubble-column bioreactor. The results indicated that the model simulations had a satisfying agreement with the experimental data. Finally, the local instantaneous flow and phenol biodegradation features including gas holdup, gas velocity, liquid velocity, cell concentration and phenol concentration inside the bioreactor were successfully predicted in different-scale bubble columns by the proposed model. © 2006 American Institute of Chemical Engineers AIChE J, 2006 相似文献
278.
Calculations and detailed first principle and thermodynamic analyses have been performed to understand the formation mechanism of K2Ti6O13 nanowires (NWs) by a hydrothermal reaction between bulk Na2Ti3O7 crystals and a KOH solution. It is found that direct ion exchange between K+ and Na+ plus H+ interactions with [TiO6] octahedra in Na2Ti3O7 promote the formation of an intermediate H2K2Ti6O14 phase. The large lattice mismatch between this intermediate phase and the bulk Na2Ti3O7 structure, and the large energy reduction associated with the formation of this intermediate phase, drive the splitting of the bulk crystal into H2K2Ti6O14 NWs. However, these NWs are not stable because of large [TiO6] octahedra distortion and are subject to a dehydration process, which results in uniform K2Ti6O13 NWs with narrowly distributed diameters of around 10 nm. 相似文献
279.
This paper presents an investigation on a single-mode-multimode-single-mode fiber structure. A one-way guided-mode propagation analysis for the circular symmetry waveguide is employed to model the light propagation and the approximated formulations are derived and evaluated concerning the accuracy. Phase conjunction of the multimode interference within the fiber structure is revealed. A simple way to predict and analyze the spectral response of the structure is presented through the space to wavelength mapping with the derived approximated formulations. The prediction of spectral response is verified numerically and experimentally. 相似文献
280.
边坡支护中多种技术措施的综合应用 总被引:1,自引:0,他引:1
通过工程实例,介绍了锚杆喷射混凝土支护技术与高压喷射混凝土搅拌桩支护技术在工程中的综合利用,同时也验证了该技术的可行性及经济性。 相似文献