全文获取类型
收费全文 | 14691篇 |
免费 | 1300篇 |
国内免费 | 876篇 |
专业分类
电工技术 | 925篇 |
综合类 | 1045篇 |
化学工业 | 2321篇 |
金属工艺 | 762篇 |
机械仪表 | 873篇 |
建筑科学 | 1325篇 |
矿业工程 | 421篇 |
能源动力 | 498篇 |
轻工业 | 1083篇 |
水利工程 | 221篇 |
石油天然气 | 729篇 |
武器工业 | 96篇 |
无线电 | 1631篇 |
一般工业技术 | 1580篇 |
冶金工业 | 674篇 |
原子能技术 | 285篇 |
自动化技术 | 2398篇 |
出版年
2024年 | 95篇 |
2023年 | 311篇 |
2022年 | 483篇 |
2021年 | 654篇 |
2020年 | 495篇 |
2019年 | 410篇 |
2018年 | 460篇 |
2017年 | 531篇 |
2016年 | 440篇 |
2015年 | 613篇 |
2014年 | 757篇 |
2013年 | 837篇 |
2012年 | 864篇 |
2011年 | 984篇 |
2010年 | 876篇 |
2009年 | 837篇 |
2008年 | 807篇 |
2007年 | 800篇 |
2006年 | 842篇 |
2005年 | 705篇 |
2004年 | 489篇 |
2003年 | 402篇 |
2002年 | 421篇 |
2001年 | 377篇 |
2000年 | 426篇 |
1999年 | 392篇 |
1998年 | 282篇 |
1997年 | 243篇 |
1996年 | 234篇 |
1995年 | 168篇 |
1994年 | 149篇 |
1993年 | 97篇 |
1992年 | 81篇 |
1991年 | 78篇 |
1990年 | 42篇 |
1989年 | 42篇 |
1988年 | 32篇 |
1987年 | 18篇 |
1986年 | 30篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 10篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1965年 | 1篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
一种ECC加密芯片抗功耗攻击研究 总被引:2,自引:1,他引:2
设计了随机掩码在ECC加密算法中的应用方法,为了降低加密芯片的功耗和面积,提高运算性能,研究设计了关键步固定值掩码算法,实验证明提出的方法在资源增加非常有限的情况下可以有效抵抗一阶差分功耗攻击.同时,其他加密算法也可参考此关键步固定值掩码算法来高效设计抗功耗攻击加密芯片. 相似文献
103.
104.
It is well known that a rigid in-plane motion can be decomposed into a translation and a rotation around an origin. Based on our previous work, we first extend the Helgason-Ludwig consistency condition (HLCC) to cover a general rigid motion in fan-beam geometry. Then, we model the general motion by several parameters, and develop an iterative scheme for estimation of the in-plane motion parameters. This scheme determines the motion parameters by numerically minimizing an objective function constructed based on the HLCC. After the motion parameters are estimated, image reconstruction can be performed to compensate for the motion effects. Finally, we implement the algorithm and evaluate its performance in numerical simulations. 相似文献
105.
Yuanyuan Meng Jiasen Zhang Chang Liu Kanghui Zheng Lisha Xie Shixiao Bu Bin Han Ruikun Cao Xu Yin Cuirong Liu Ziyi Ge 《Advanced functional materials》2023,33(3):2210600
Formamidinium lead triiodide (FAPbI3) has been demonstrated as the most efficient perovskite system to date, due to its excellent thermal stability and an ideal bandgap approaching the Shockley-Queisser limit. Whereas, there are intrinsic quantum confinement effects in FAPbI3, which lead to unwanted non-radiative recombination. Additionally, the black α-phase of FAPbI3 is unstable under room temperature due to the significant residual tensile stress in the film. To simultaneously address the above issues, a thermally-activated delayed fluorescence polymer P1 is designed in the study to modify the FAPbI3 film. Owing to the spectral overlap between the photoluminescence of P1 and absorption of the above-bandgap quantum wells of FAPbI3, the Förster energy transfer occurs at the P1/FAPbI3 interface, which further triggers the Dexter energy transfer within FAPbI3. The exciton “recycling” can thus be realized, which reduces the non-radiative recombination losses in perovskite solar cells (PSCs). Moreover, P1 is found to introduce compressive stress into FAPbI3, which relieves the tensile stress in perovskite. Consequently, the PSCs with P1 treatment achieve an outstanding power conversion efficiency (PCE) of 23.51%. Moreover, with the alleviation of stress in the perovskite film, flexible PSCs (f-PSCs) also deliver a high PCE of 21.40%. 相似文献
106.
将碳化硅(Si C)微粉、酚醛树脂和炭黑等均匀混合,配置成连接浆料,真空除泡后连接Si C陶瓷素坯,高温反应烧结后得到反应烧结Si C(RBSi C)连接镜坯。讨论了浆料配方对焊缝显微结构的影响,测试了RBSi C连接坯体的力学性能和线膨胀系数。研究表明:连接浆料中加入聚乙二醇200(PEG200)和聚乙烯醇吡咯烷酮(PVP),能够有效分散炭黑,保证反应烧结过程中炭黑与硅完全反应,无残余碳存在,实现焊缝与基材之间显微结构的一致性;Si C连接坯体素坯和反应烧结后的抗弯强度值分别24.9 MPa和322.9 MPa,而且断裂位置在基材上;在-100~400℃范围内,RBSi C连接坯体与基体线膨胀系数差异仅为0.011 4 ppm。 相似文献
107.
激光雷达的距离像是雷达成像系统区别于其他的成像系统(如红外成像系统、可见光成像系统)所特有的信息,它是对目标精确识别、打击的基础。如何对距离像去噪直接决定了下一步目标定位、识别的精确性。针对雷达距离像的特点,提出了一种基于对比度调制方法对条纹管激光雷达的距离像去噪方法,通过提取距离像噪声的对比度信息,用其调制未经过去噪的距离像,从而得到距离像中的噪声图像,最后用未经过处理的距离像减去噪声图像,得到图像即为去噪后距离像。研究表明该方法去噪效果明显,在去噪的同时很好地保持了距离像的边缘信息,去噪后图像的信噪比明显提高,距离像的属性也没有改变,这是其他方法对距离像去噪所不具有的优点。 相似文献
108.
In this paper, we propose and evaluate a novel nonlinear companding transform (NCT) scheme for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems. The key idea of the proposed scheme is to transform the original Gaussian-distributed OFDM signals into a specific statistics form, whose target probability density function is defined by a piecewise function with an inflexion point. By properly choosing the transform parameters, this scheme can enable more flexibility and freedom in the companding form so that a favorable tradeoff between PAPR reduction and bit error rate (BER) performance can be achieved. Moreover, compared to existing NCT techniques, this scheme dramatically decreases the impact of companding distortion on the BER performance to reach a given PAPR level. The analytical expressions regarding the achievable transform gain in PAPR, complementary cumulative density function, attenuation coefficient, and selection criteria of transform parameters are derived. Simulation results justify the significance and accuracy of the analytical expressions presented. 相似文献
109.
Cooperative spectrum sensing has been shown to be an effective approach to improve the detection performance by exploiting the spatial diversity among multiple secondary users (or unlicensed users). However, due to correlated shadowing and cooperation overhead in practical cognitive radio networks, it is desired to select an appropriate set of secondary users which have little correlation with each other to participate in cooperation so as to achieve the effective tradeoff between detection performance and cooperation overhead. In this paper, we first study the hypothesis testing model and detection performance of cooperative spectrum sensing under the correlated log-normal shadowing scenario. Afterwards, based on whether the false-alarm and missed-detection probabilities are constrained, three optimization problems are formulated to find the optimal set of secondary users participating in cooperation, which take into account the tradeoff between detection performance and cooperation overhead. Then the solutions using adaptive genetic algorithms are presented for the optimization problems. Finally, simulation experiments demonstrate that our proposed schemes are very effective. 相似文献