全文获取类型
收费全文 | 179225篇 |
免费 | 15646篇 |
国内免费 | 8430篇 |
专业分类
电工技术 | 11377篇 |
技术理论 | 13篇 |
综合类 | 11645篇 |
化学工业 | 29312篇 |
金属工艺 | 9913篇 |
机械仪表 | 11250篇 |
建筑科学 | 13707篇 |
矿业工程 | 5432篇 |
能源动力 | 5292篇 |
轻工业 | 12431篇 |
水利工程 | 3271篇 |
石油天然气 | 10719篇 |
武器工业 | 1403篇 |
无线电 | 21530篇 |
一般工业技术 | 21503篇 |
冶金工业 | 8736篇 |
原子能技术 | 1922篇 |
自动化技术 | 23845篇 |
出版年
2024年 | 900篇 |
2023年 | 3413篇 |
2022年 | 6340篇 |
2021年 | 8497篇 |
2020年 | 6398篇 |
2019年 | 5059篇 |
2018年 | 5723篇 |
2017年 | 6392篇 |
2016年 | 5703篇 |
2015年 | 7583篇 |
2014年 | 9391篇 |
2013年 | 11250篇 |
2012年 | 12243篇 |
2011年 | 12872篇 |
2010年 | 10990篇 |
2009年 | 10374篇 |
2008年 | 9901篇 |
2007年 | 9121篇 |
2006年 | 9298篇 |
2005年 | 7960篇 |
2004年 | 5310篇 |
2003年 | 4468篇 |
2002年 | 4001篇 |
2001年 | 3603篇 |
2000年 | 3533篇 |
1999年 | 4147篇 |
1998年 | 3453篇 |
1997年 | 2932篇 |
1996年 | 2741篇 |
1995年 | 2213篇 |
1994年 | 1798篇 |
1993年 | 1297篇 |
1992年 | 1044篇 |
1991年 | 785篇 |
1990年 | 567篇 |
1989年 | 465篇 |
1988年 | 367篇 |
1987年 | 252篇 |
1986年 | 209篇 |
1985年 | 129篇 |
1984年 | 116篇 |
1983年 | 86篇 |
1982年 | 86篇 |
1981年 | 68篇 |
1980年 | 62篇 |
1979年 | 29篇 |
1978年 | 25篇 |
1977年 | 24篇 |
1976年 | 26篇 |
1975年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
为保证工作空间测量定位系统的现场测量精度,需要在发射站姿态受到温度、震动等环境因素影响时对其定向参数进行修正。提出了一种以固定接收器为基准的定向参数修正方法,通过在工作空间内稳定参考点处安装的冗余接收器监控发射站工作状态并对定向参数进行实时在线修正,采用光平面参数描述的发射站几何模型推导了接收器坐标测量方程。在此基础上,以参考点坐标为已知条件,建立了基于共面约束的定向参数修正量优化方程,给出了平差解算方法。实验结果表明,当采用6个接收器进行修正时,系统坐标测量偏差在0.15 mm以内,满足现场大尺寸坐标测量的精度要求,有效提高了系统的可靠性、实用性。 相似文献
992.
993.
994.
以AAO/Si为模板,采用化学气相沉积(CVD)的方法在不同温度下,通过煅烧Zn粉和C粉的混合物制备ZnO/AAO/Si组装体系,并对其结构和性质进行了研究。扫描电镜(SEM)结果表明:随着煅烧温度的升高,AAO表面的孔洞逐渐被封堵,当温度达到900℃时,在AAO的表面出现了一层ZnO薄膜。X射线衍射(XRD)结果显示,700℃时在XRD图谱上观看到六角纤锌矿的ZnO的衍射峰,并且随着温度的升高,ZnO的衍射峰逐渐增强,当温度升至800和900℃时出现了ZnAl2O4的衍射峰。因此,化学气相沉积制备组装体系时的最适温为700℃。在700℃时煅烧不同恒温时间制备的ZnO/AAO/Si组装体系SEM图显示,随着恒温时间的延长,孔的封闭效应逐渐明显。 相似文献
995.
996.
Due to the limited carrier concentration, 2D transition metal dichalcogenides have lower intrinsic dark current, and thus, are widely studied for high performance room photodetection. However, the light-matter interaction is still unclear, thus tuning the photoexcitation and further manipulating the photodetection is a challenge. Herein, large-area PtS films are synthesized, and the growth mechanism is investigated. It is demonstrated that PtS has an orthorhombic structure and exhibits the p-type semiconducting behavior. Then, MoS2/PtS p–n heterojunction is fabricated, and its energy diagram is discussed based on the Kelvin probe force microscopy. The contact potential difference is about 160 mV, which is much larger than previous 2D junctions facilitating the charge separation. Furthermore, the phototransistor based on MoS2/PtS p–n heterojunction is prepared, showing broadband photoresponse from visible to near-infrared. The manipulation of an external field on photoresponse, detectivity, and rise/fall time are explored and discussed. The responsivity can reach up to 25.43 A W−1, and the detectivity is 8.54 × 1012 Jones. These results indicate that PtS film is a prospective candidate for high-performance optoelectronic devices and broaden the scope of infrared detection materials. 相似文献
997.
Xia Wang Junping Meng Xuguang Lin Yadi Yang Shuang Zhou Yaping Wang Anqiang Pan 《Advanced functional materials》2021,31(48):2106114
The uneven electrodeposition and inferior corrosion resistance are the fundamental obstacles to achieve stable Zn metal anodes. The features of the electrode surface/interface are closely correlated with the properties. Herein, the Zn surface with more exposed (002)Zn planes is modified through a simple acid-etching approach. The in situ generated zinc compounds form an interface layer with strong adhesion to the Zn electrode, which can enhance the Zn2+ ion kinetics and regulate the deposition/dissolution behaviors. A variety of acids with functional cations are selected, among which the phosphoric acid etches the Zn with a higher extent of texturing and generates a more compact layer. The obtained zinc phosphate@Zn electrode enables stable cycling and fast kinetics in symmetrical and full Zn metal batteries. This study provides a new example of combined surface and interface modification toward high-performance aqueous zinc metal anodes. 相似文献
998.
Dynamic inter-cell interference (ICI) causes channel quality indicator mismatch such that system throughput is reduced. In this paper, an enhanced link adaptation scheme based on cooperative interference prediction is proposed to reduce the mismatch. The scheme predicts the dynamic ICI within a cluster of base stations (BSs) for improving the link adaptation accuracy. With the dynamic ICI prediction, more accurate modulation and coding scheme can be selected without increasing the overhead over the air. System level simulations show that the proposed scheme significantly improves the system spectral efficiency (SE), especially the cell-edge SE. 相似文献
999.
Zhenjun Tang Xianquan Zhang Xuan Dai Jianzhong Yang Tianxiu Wu 《AEUE-International Journal of Electronics and Communications》2013,67(8):717-722
Conventional image hash functions only exploit luminance components of color images to generate robust hashes and then lead to limited discriminative capacities. In this paper, we propose a robust image hash function for color images, which takes all components of color images into account and achieves good discrimination. Firstly, the proposed hash function re-scales the input image to a fixed size. Secondly, it extracts local color features by converting the RGB color image into HSI and YCbCr color spaces and calculating the block mean and variance from each component of the HSI and YCbCr representations. Finally, it takes the Euclidian distances between the block features and a reference feature as hash values. Experiments are conducted to validate the efficiency of our hash function. Receiver operating characteristics (ROC) curve comparisons with two existing algorithms demonstrate that our hash function outperforms the assessed algorithms in classification performances between perceptual robustness and discriminative capability. 相似文献
1000.
Xin Gu Xuegong Yu Jinglin Xu Ruixin Fan Deren Yang 《Progress in Photovoltaics: Research and Applications》2013,21(4):456-461
Using thinner wafers can largely reduce the cost of silicon solar cells. One obstacle of using thinner wafers is that few methods can provide good dopant concentration for the back surface field (BSF) and good ohmic contact while generated only in low bowing. In this paper, we have demonstrated the screening–printing B and Al (B/Al) mixture metallization film technique, making use of the screen‐printing technique and the higher solubility of B in silicon to form a B/Al‐BSF. This technique can raise the carrier concentration in the BSF by more than one order of magnitude and reduce the back surface recombination at a low firing temperature (≤800 °C). We have also shown that through the new technique, the metallization paste thickness at the rear could be reduced largely, which however did not degrade the solar cell efficiency. All these efforts are aiming for pushing forward the application of thinner wafers. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献