全文获取类型
| 收费全文 | 4793篇 |
| 免费 | 860篇 |
| 国内免费 | 169篇 |
专业分类
| 化学 | 693篇 |
| 晶体学 | 150篇 |
| 力学 | 314篇 |
| 综合类 | 27篇 |
| 数学 | 369篇 |
| 物理学 | 2082篇 |
| 无线电 | 2187篇 |
出版年
| 2025年 | 52篇 |
| 2024年 | 216篇 |
| 2023年 | 167篇 |
| 2022年 | 176篇 |
| 2021年 | 231篇 |
| 2020年 | 197篇 |
| 2019年 | 232篇 |
| 2018年 | 158篇 |
| 2017年 | 196篇 |
| 2016年 | 228篇 |
| 2015年 | 219篇 |
| 2014年 | 291篇 |
| 2013年 | 397篇 |
| 2012年 | 274篇 |
| 2011年 | 279篇 |
| 2010年 | 231篇 |
| 2009年 | 256篇 |
| 2008年 | 286篇 |
| 2007年 | 209篇 |
| 2006年 | 211篇 |
| 2005年 | 186篇 |
| 2004年 | 149篇 |
| 2003年 | 139篇 |
| 2002年 | 107篇 |
| 2001年 | 107篇 |
| 2000年 | 100篇 |
| 1999年 | 77篇 |
| 1998年 | 74篇 |
| 1997年 | 66篇 |
| 1996年 | 58篇 |
| 1995年 | 44篇 |
| 1994年 | 21篇 |
| 1993年 | 31篇 |
| 1992年 | 22篇 |
| 1991年 | 16篇 |
| 1990年 | 18篇 |
| 1989年 | 21篇 |
| 1988年 | 17篇 |
| 1987年 | 17篇 |
| 1986年 | 6篇 |
| 1985年 | 12篇 |
| 1984年 | 6篇 |
| 1983年 | 3篇 |
| 1982年 | 4篇 |
| 1980年 | 3篇 |
| 1979年 | 4篇 |
| 1978年 | 1篇 |
| 1977年 | 4篇 |
| 1976年 | 1篇 |
| 1975年 | 1篇 |
排序方式： 共有5822条查询结果，搜索用时 0 毫秒
121.
V. V. Ivanenko Yu. G. Voloshina M. V. Okhrimenko L. K. Patrilyak K. I. Patrilyak 《Theoretical and Experimental Chemistry》2009,45(3):198-202
Along with oxidation of hydrogen-containing coke structures, we have observed oxidation of compact accumulations of hydrogen-free coke and as a result we can quantitatively differentiate between outer-surface and intraporous burned coke, and the intraporous coke in turn can be quantitatively distributed over the different elements of the zeolite structures. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 3, pp. 185–189, May–June, 2009. 相似文献
122.
123.
利用光学特征矩阵方法,研究了含负折射率缺陷的正负折射率交替一维光子晶体缺陷模的相关特性。研究表明：当缺陷层的光学厚度不变时,随着缺陷层折射率的增加,分布在禁带中心两侧的缺陷模分别向临近的禁带边缘方向移动,并与透射谱形成连续的透射带,随着折射率的增加,透射带的透射率逐渐增加,其半高宽度逐渐减小;而当缺陷层折射率不变时,随着缺陷层的光学厚度增加,缺陷模向长波方向平移,同时缺陷模的个数也随之增加,而由缺陷模和透射谱连成的透射带的带宽逐渐减小。与正折射率缺陷情形相比较,负折射率缺陷层可以获得更多的缺陷膜。 相似文献
124.
《电子学报:英文版》2024,33(6)
The WiFi fingerprint-based localization method is considered one of the most popular techniques for indoor localization.In INFOCOM'14,Li et al.proposed a wireless fidelity(WiFi)fingerprint localization system based on Paillier encryption,which is claimed to protect both client C's location privacy and service provider S's database privacy.However,Yang et al.presented a practical data privacy attack in INFOCOM'18,which allows a polynomial time attacker to obtain S's database.We propose a novel WiFi fingerprint localization system based on Castagnos-Laguillaumie(CL)encryption,which has a trustless setup and is efficient due to the excellent properties of CL en-cryption.To prevent Yang et al.'s attack,the system requires that S selects only the locations from its database that can receive the nonzero signals from all the available access points in C's nonzero fingerprint in order to determine C's location.Security analysis shows that our scheme is secure under Li et al.'s threat model.Furthermore,to enhance the security level of privacy-preserving WiFi fingerprint localization scheme based on CL encryption,we propose a se-cure and efficient zero-knowledge proof protocol for the discrete logarithm relations in C's encrypted localization queries. 相似文献
125.
Functionalized carbon nanomaterials, as significant options for renewable energy systems, are widely utilized in diversified electrochemical reactions in virtue of property advantages. The inevitable defect sites in architectures greatly affect physicochemical properties of carbon nanomaterials, thus defect engineering has recently become a vital research orientation of carbon‐based electrocatalysts. The intentionally introduced intrinsic carbon defect sites in the frameworks can directly serve as the potential active sites owing to the altered surface charge state, modulated adsorption free energy of key intermediates, as well as diminished bandgap. Furthermore, the synergistic sites between intrinsic defects and heteroatom dopants/captured atomic metal species can further optimize the electronic structure and adsorption/desorption behavior, making carbon‐based catalysts comparable to commercial precious metal catalysts in electrocatalysis. With pressing research demands, the common configurations, construction strategies, structure–activity relationships, and characterization methods for intrinsic carbon defect‐involved catalytic centers are systematically summarized. Such theoretical and experimental evidences of intrinsic defect‐induced activity can reveal the active centers and relevant catalytic mechanism, thereby providing necessary guidance for the design and construction of highly efficient carbon‐based electrocatalysts and promoting their commercial applications. 相似文献
126.
Jingjing Tian Jing Wang Qifan Xue Tianqi Niu Lei Yan Zonglong Zhu Ning Li Christoph J. Brabec Hin‐Lap Yip Yong Cao 《Advanced functional materials》2020,30(28)
Cesium‐based inorganic perovskites have recently attracted great research focus due to their excellent optoelectronic properties and thermal stability. However, the operational instability of all‐inorganic perovskites is still a main hindrance for the commercialization. Herein, a facile approach is reported to simultaneously enhance both the efficiency and long‐term stability for all‐inorganic CsPbI2.5Br0.5 perovskite solar cells via inducing excess lead iodide (PbI2) into the precursors. Comprehensive film and device characterizations are conducted to study the influences of excess PbI2 on the crystal quality, passivation effect, charge dynamics, and photovoltaic performance. It is found that excess PbI2 improves the crystallization process, producing high‐quality CsPbI2.5Br0.5 films with enlarged grain sizes, enhanced crystal orientation, and unchanged phase composition. The residual PbI2 at the grain boundaries also provides a passivation effect, which improves the optoelectronic properties and charge collection property in optimized devices, leading to a power conversion efficiency up to 17.1% with a high open‐circuit voltage of 1.25 V. More importantly, a remarkable long‐term operational stability is also achieved for the optimized CsPbI2.5Br0.5 solar cells, with less than 24% degradation drop at the maximum power point under continuous illumination for 420 h. 相似文献
127.
Kai Wang Jiang Liu Jun Yin Erkan Aydin George T. Harrison Wenzhu Liu Shanyong Chen Omar F. Mohammed Stefaan De Wolf 《Advanced functional materials》2020,30(35)
Defects at the surface and grain boundaries of metal–halide perovskite films lead to performance losses of perovskite solar cells (PSCs). Here, organic cyano‐based π‐conjugated molecules composed of indacenodithieno[3,2‐b]thiophene (IDTT) are reported and it is found that their cyano group can effectively passivate such defects. To achieve a homogeneous distribution, these molecules are dissolved in the antisolvent, used to initiate the perovskite crystallization. It is found that these molecules are self‐anchored at the grain boundaries due to their strong binding to undercoordinated Pb2+. On a device level, this passivation scheme enhances the charge separation and transport at the grain boundaries due to the well‐matched energetic levels between the passivant and the perovskite. Consequently, these benefits contribute directly to the achievement of power conversion efficiencies as high as 21.2%, as well as the improved environmental and thermal stability of the PSCs. The surface treatment provides a new strategy to simultaneously passivate defects and enhance charge extraction/transport at the device interface by manipulating the anchoring groups of the molecules. 相似文献
128.
For the influence caused by multipath fading and non-line-of-sight(NLOS)transmission,it is challenging to accurately localize a moving signal source in complex environment by using the wireless sensor network(WSN)on the ground.In this paper,we establish a special WSN in the sky to address this challenge,where each sensor is loaded on an unmanned aerial vehicle(UAV)and the operation center of all the UAVs is fixed on the ground.Based on the analyzing of the optimal distribution and the position error calibration of all the sensors,we formulate the localization scheme to estimate the position of the target source,which combines the time difference of arrival(TDOA)method and the frequency difference of arrival(FDOA)method.Then by employing the semidefinite programming approach,we accurately obtain the position and velocity of the signal source.In the simulation,the validity of the proposed method is verified through the performance comparison. 相似文献
129.
Changan Wang Ching‐Hao Chang Andreas Herklotz Chao Chen Fabian Ganss Ulrich Kentsch Deyang Chen Xingsen Gao Yu‐Jia Zeng Olav Hellwig Manfred Helm Sibylle Gemming Ying‐Hao Chu Shengqiang Zhou 《Advanced Electronic Materials》2020,6(6)
The topological Hall effect (THE) has been discovered in ultrathin SrRuO3 (SRO) films, where the interface between the SRO layer and another oxide layer breaks the inversion symmetry resulting in the appearance of THE. Thus, THE only occurs in ultrathin SRO films of several unit cells. In addition to employing a heterostructure, the inversion symmetry can be broken intrinsically in bulk SRO by introducing defects. In this study, THE is observed in 60‐nm‐thick SRO films, in which defects and lattice distortions are introduced by helium ion irradiation. The irradiated SRO films exhibit a pronounced THE in a wide temperature range from 5 to 80 K. These observations can be attributed to the emergence of Dzyaloshinskii–Moriya interaction as a result of artificial inversion symmetry breaking associated with the lattice defect engineering. The creation and control of the THE in oxide single layers can be realized by ex situ film processing. Therefore, this work provides new insights into the THE and illustrates a promising strategy to design novel spintronic devices. 相似文献
130.
Shamanth Nagaraju Sreejith V Lucy J. Gudino Bhushan V. Kadam Ramesha C. K. Joseph Rodrigues 《International Journal of Communication Systems》2020,33(4)
In common practice, sensor nodes are randomly deployed in wireless sensor network (WSN); hence, location information of sensor node is crucial in WSN applications. Localization of sensor nodes performed using a fast area exploration mechanism facilitates precise location‐based sensing and communication. In the proposed localization scheme, the mobile anchor (MA) nodes integrated with localization and directional antenna modules are employed to assist in localizing the static nodes. The use of directional antennas evades trilateration or multilateration techniques for localizing static nodes thereby resulting in lower communication and computational overhead. To facilitate faster area coverage, in this paper, we propose a hybrid of max‐gain and cost‐utility–based frontier (HMF) area exploration method for MA node's mobility. The simulations for the proposed HMF area exploration–based localization scheme are carried out in the Cooja simulator. The paper also proposes additional enhancements to the Cooja simulator to provide directional and sectored antenna support. This additional support allows the user with the flexibility to feed radiation pattern of any antenna obtained either from simulated data of the antenna design simulator, ie, high frequency structure simulator (HFSS) or measured data of the vector network analyzer (VNA). The simulation results show that the proposed localization scheme exhibits minimal delay, energy consumption, and communication overhead compared with other area exploration–based localization schemes. The proof of concept for the proposed localization scheme is implemented using Berkeley motes and customized MA nodes mounted with indigenously designed radio frequency (RF) switch feed network and sectored antenna. 相似文献