全文获取类型
收费全文 | 105483篇 |
免费 | 10193篇 |
国内免费 | 6159篇 |
专业分类
电工技术 | 7548篇 |
技术理论 | 9篇 |
综合类 | 8978篇 |
化学工业 | 15983篇 |
金属工艺 | 6121篇 |
机械仪表 | 6678篇 |
建筑科学 | 8421篇 |
矿业工程 | 2870篇 |
能源动力 | 2818篇 |
轻工业 | 11668篇 |
水利工程 | 2486篇 |
石油天然气 | 4762篇 |
武器工业 | 1173篇 |
无线电 | 11670篇 |
一般工业技术 | 10493篇 |
冶金工业 | 3950篇 |
原子能技术 | 1247篇 |
自动化技术 | 14960篇 |
出版年
2024年 | 328篇 |
2023年 | 1607篇 |
2022年 | 3103篇 |
2021年 | 4318篇 |
2020年 | 3351篇 |
2019年 | 2608篇 |
2018年 | 3050篇 |
2017年 | 3303篇 |
2016年 | 3060篇 |
2015年 | 4605篇 |
2014年 | 5665篇 |
2013年 | 6809篇 |
2012年 | 8090篇 |
2011年 | 8749篇 |
2010年 | 7876篇 |
2009年 | 7551篇 |
2008年 | 7675篇 |
2007年 | 6996篇 |
2006年 | 6370篇 |
2005年 | 5243篇 |
2004年 | 3726篇 |
2003年 | 2988篇 |
2002年 | 2879篇 |
2001年 | 2430篇 |
2000年 | 1921篇 |
1999年 | 1638篇 |
1998年 | 1178篇 |
1997年 | 984篇 |
1996年 | 804篇 |
1995年 | 714篇 |
1994年 | 506篇 |
1993年 | 385篇 |
1992年 | 301篇 |
1991年 | 255篇 |
1990年 | 180篇 |
1989年 | 137篇 |
1988年 | 107篇 |
1987年 | 55篇 |
1986年 | 72篇 |
1985年 | 32篇 |
1984年 | 28篇 |
1983年 | 16篇 |
1982年 | 16篇 |
1981年 | 25篇 |
1980年 | 38篇 |
1979年 | 13篇 |
1976年 | 11篇 |
1975年 | 6篇 |
1959年 | 10篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
ABSTRACT This study investigates the effects of strain, strain rates, and forming directions (RD-rolling direction, TD-transverse direction, and ND-normal direction) on adiabatic shear, via dynamic impact compression tests using the Split Hopkinson Pressure Bar (SHPB) apparatus. A modified Johnson-Cook (J-C) constitutive model is proposed, which used to analyse the influence of the constitutive parameters on the sensitivity of adiabatic shear, employing a finite element software. The different sensitivities of adiabatic shear under different directions are explained by combining microscopic analysis and results from mechanical responses. The results show that the sensitivity of adiabatic shear can be related to the time of stress collapse in the following trend: ND?>?TD?>?RD; the sensitivities of these constitutive parameters on adiabatic shear are calculated and compared. 相似文献
42.
Rapid synthesis of silver nanowires(Ag NWs) with high quality and a broad processing window is challenging because of the low selectivity of the formation of multiply twinned particles at the nucleation stage for subsequent Ag NWs growth.Herein we report a systematic study of the water-involved heterogeneous nucleation of Ag NWs with high rate(less than 20 min) in a simple and scalable preparation method.Using glycerol as a reducing agent and a solvent with a high boiling point,the reaction is rapidly heated to 210 ℃ in air to synthesize Ag NWs with a very high yield in gram level.It is noted that the addition of a small dose of water plays a key role for obtaining highly pure Ag NWs in high yield,and the optimal water/glycerol ratio is0.25%.After investigating a series of forming factors including reaction temperature and dose of catalysts,the formation kinetics and mechanism of the Ag NWs are proposed.Compared to other preparation methods,our strategy is simple and reproducible.These Ag NWs show a strong Raman enhancement effect for organic molecules on their surface. 相似文献
43.
To realize joint optimization of spatial diversity and equalization combining in the intersymbol interference (ISI) channel, an iterative equalization combining algorithm is proposed. The proposed algorithm uses the coefficients of Turbo equalization to calculate the combination weights without estimating the signal to noise ratio in each diversity branch. The equalized symbols from different diversity branches are combined, and the extrinsic information output from the decoder is fed back to the equalizers, so as to exchange soft information between the equalizers and the decoder. The performance of the proposed algorithm is analyzed using the extrinsic information transfer (EXIT) chart and verified by simulations. Results show that our approach fully exploits time domain information from the multipath channel and spatial domain information from multi receiving antennas, which efficiently improve the performance of the receiver in the severe ISI channel. 相似文献
44.
Ting Liu Huimin Zhang Panfei Ma Aimin Chang Hui Jiang 《Journal of the American Ceramic Society》2019,102(8):4393-4398
Core–shell structures have been proposed to improve the electrical properties of negative-temperature coefficient (NTC) thermistor ceramics. In this work, Al2O3-modified Co1.5Mn1.2Ni0.3O4 NTC thermistor ceramics with adjustable electrical properties were prepared through citrate-chelation followed by conventional sintering. Co1.5Mn1.2Ni0.3O4 powder was coated with a thin Al2O3 shell layer to form a core–shell structure. Resistivity (ρ) increased rapidly with increasing thickness of the Al2O3 layer, and the thermal constant (B) varied moderately between 3706 and 3846 K. In particular, Co1.5Mn1.2Ni0.3O4@Al2O3 ceramic with 0.08 wt% Al2O3 showed the increase of ρ double, and the change in its B was less than 140 K. The Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics showed high stability, and their grain size was relatively uniform due to the protection offered by the shell. The aging coefficient of the ceramic was less than 0.2% after aging for 500 hours at 125°C. Taken together, the results indicate that as-prepared Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics with a core–shell structure may be promising candidates for application as wide-temperature NTC thermistor ceramics. 相似文献
45.
Volcano 是集汽车电子网络设计、实现和测试于一体的完整工具链。它包括整车网络规划及优化设计工具VNA,网络节点(TCU等)实现工具VTP以及网络测试工具Tellus。本文着重介绍了基于TCU的VTP。 相似文献
46.
为确保原CO压缩机在净化系统升级改造项目实施后能安全稳定运行,采取了流程优化、工艺条件论证、设备缺陷排查、联锁指标重新确定等一系列措施。改造措施实施后,CO压缩机出口压力稳定在3.23 MPa左右,有效缓解了前后工序压力波动对压缩机稳定运行的影响,各级水冷却器的换热效果也得到了较大的改善。 相似文献
47.
以废菌渣为原料制备活性炭,采用能量-色散光谱(EDS)和傅里叶变换红外光谱仪(FTIR)进行表征,结果表明:活性炭表面具有多种官能团,有利于提高对硝基苯的吸附。并研究了活性炭吸附硝基苯的影响因素(pH、初始浓度、吸附时间、投加量)、吸附等温线及热力学。结果表明:在常温中性pH条件下,初始浓度为50mg/L,活性炭用量为0.15g时硝基苯去除率可达98%,出水水质满足《污水综合排放标准》(GB 8978-1996)中对硝基苯浓度低于2.0mg/L的要求。活性炭对硝基苯的吸附具有较快的吸附速率,即1min接近平衡。该吸附行为是自发放热反应,可以用Freundlich模型很好地拟合。废菌渣活性炭对硝基苯的吸附主要是疏水作用和氧化钼活化共同作用的结果。因此,以农业废弃物-废菌渣制备得到的废菌渣活性炭具有良好的经济实用性,可用于废水处理中,实现以废治废的目的。 相似文献
48.
49.
Initialization speed is one of the most important factors in network real time kinematic (NRTK) performance. Owing to the low correlation among the error s 相似文献
50.