全文获取类型
收费全文 | 37551篇 |
免费 | 5500篇 |
国内免费 | 3690篇 |
专业分类
化学 | 26011篇 |
晶体学 | 364篇 |
力学 | 2233篇 |
综合类 | 244篇 |
数学 | 4297篇 |
物理学 | 13592篇 |
出版年
2024年 | 113篇 |
2023年 | 764篇 |
2022年 | 1233篇 |
2021年 | 1423篇 |
2020年 | 1456篇 |
2019年 | 1341篇 |
2018年 | 1159篇 |
2017年 | 1077篇 |
2016年 | 1621篇 |
2015年 | 1643篇 |
2014年 | 2015篇 |
2013年 | 2601篇 |
2012年 | 3276篇 |
2011年 | 3240篇 |
2010年 | 2190篇 |
2009年 | 2071篇 |
2008年 | 2220篇 |
2007年 | 1971篇 |
2006年 | 1860篇 |
2005年 | 1553篇 |
2004年 | 1308篇 |
2003年 | 987篇 |
2002年 | 895篇 |
2001年 | 741篇 |
2000年 | 697篇 |
1999年 | 835篇 |
1998年 | 697篇 |
1997年 | 636篇 |
1996年 | 708篇 |
1995年 | 602篇 |
1994年 | 551篇 |
1993年 | 472篇 |
1992年 | 449篇 |
1991年 | 364篇 |
1990年 | 325篇 |
1989年 | 238篇 |
1988年 | 216篇 |
1987年 | 198篇 |
1986年 | 141篇 |
1985年 | 156篇 |
1984年 | 135篇 |
1983年 | 117篇 |
1982年 | 80篇 |
1981年 | 59篇 |
1980年 | 49篇 |
1979年 | 33篇 |
1978年 | 26篇 |
1976年 | 27篇 |
1975年 | 31篇 |
1974年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Zn-doped Li4Ti5O12 was prepared by a ball milling-assisted solid-state method, and the characters were determined by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, cyclic voltammetry, and galvanostatic charge–discharge testing. The results show that Li4Ti5?x Zn x O12 (x?=?0, 0.05) exhibits the pure phase structure, and Zn doping does not change the electrochemical reaction process and basic spinel structure of Li4Ti5O12. The particle size of both samples is about 300–500 nm. The prepared Li4Ti4.95Zn0.05O12 presents an excellent rate capability and capacity retention. At the charge–discharge rate of 1C, the initial discharge capacity of Li4Ti4.95Zn0.05O12 is 268 mAh g?1. After 90 cycles at 5C, the discharge capacity of Li4Ti4.95Zn0.05O12 is obviously higher than that of Li4Ti5O12. The excellent electrochemical performance of the Li4Ti4.95Zn0.05O12 electrode could be attributed to the improvement of reversibility by doping zinc and the sub-micro particle size. 相似文献
992.
993.
994.
Two-phase image segmentation is a fundamental task to partition an image into foreground and background. In this paper, two types of nonconvex and nonsmooth regularization models are proposed for basic two-phase segmentation. They extend the convex regularization on the characteristic function on the image domain to the nonconvex case, which are able to better obtain piecewise constant regions with neat boundaries. By analyzing the proposed non-Lipschitz model, we combine the proximal alternating minimization framework with support shrinkage and linearization strategies to design our algorithm. This leads to two alternating strongly convex subproblems which can be easily solved. Similarly, we present an algorithm without support shrinkage operation for the nonconvex Lipschitz case. Using the Kurdyka-Łojasiewicz property of the objective function, we prove that the limit point of the generated sequence is a critical point of the original nonconvex nonsmooth problem. Numerical experiments and comparisons illustrate the effectiveness of our method in two-phase image segmentation. 相似文献
995.
An atomic-level controlled etching(ACE)technology is invstigated for the fabrication of recessed gate AlGaN/GaN high-electron-mobility transistors(HEMTs)with high power added efficiency.We compare the recessed gate HEMTs with conventional etching(CE)based chlorine,Cl2-only ACE and BCl3/Cl2ACE,respectively.The mixed radicals of BCl3/Cl2were used as the active reactants in the step of chemical modification.For ensuring precise and controllable etching depth and low etching damage,the kinetic energy of argon ions was accurately controlled.These argon ions were used precisely to remove the chemical modified surface atomic layer.Compared to the HEMTs with CE,the characteristics of devices fabricated by ACE are significantly improved,which benefits from significant reduction of etching damage.For BCl3/Cl2ACE recessed HEMTs,the load pull test at 17 GHz shows a high power added efficiency(PAE)of 59.8%with an output power density of 1.6 W/mm at Vd=10 V,and a peak PAE of 44.8%with an output power density of 3.2 W/mm at Vd=20 V in a continuous-wave mode. 相似文献
996.
De-Xing Zhu Hong-Ming Liu Yang-Yang Xu You-Tian Zou Xi-Jun Wu Peng-Cheng Chu Xiao-Hua Li 《中国物理C(英文版)》2022,46(4):044106-044106-6
Considering the preformation probability of the two emitted protons in the parent nucleus, we extend the Coulomb and proximity potential model (CPPM) to systematically study two-proton (2p) radioactivity half-lives of the nuclei close to proton drip line. The proximity potential chosen is Prox. 81 proposed by Blocki et al. in 1981. Furthermore, we apply this model to predict the half-lives of possible 2p radioactive candidates whose 2p radioactivity is energetically allowed or observed but not yet quantified in the evaluated nuclear properties table NUBASE2016. The predicted results are in good agreement with those from other theoretical models and empirical formulas, namely the effective liquid drop model (ELDM), generalized liquid drop model (GLDM), Gamow-like model, Sreeja formula and Liu formula. 相似文献
997.
Haiyan Yu Haochun Zhang Jinchuan Zhao Jing Liu Xinlin Xia Xiaohu Wu 《Frontiers of Physics》2022,17(2):23202
Micro/nano-porous polymeric material is considered a unique industrial material due to its extremely low thermal conductivity, low density, and high surface area. Therefore, it is necessary to establish an accurate thermal conductivity prediction model suiting their applicable conditions and provide a theoretical basis for expanding their applications. In this work, the development of the calculation model of equivalent thermal conductivity of micro/nano-porous polymeric materials in recent years is summarized. Firstly, it reviews the process of establishing the overall equivalent thermal conductivity calculation model for micro/nanoporous polymers. Then, the predicted calculation models of thermal conductivity are introduced separately according to the conductive and radiative thermal conductivity models. In addition, the thermal conduction part is divided into the gaseous thermal conductivity model, solid thermal conductivity model and gas–solid coupling model. Finally, it is concluded that, compared with other porous materials, there are few studies on heat transfer of micro/ nanoporous polymers, especially on the particular heat transfer mechanisms such as scale effects at the micro/nanoscale. In particular, the following aspects of porous polymers still need to be further studied: micro scaled thermal radiation, heat transfer characteristics of particular morphologies at the nanoscales, heat transfer mechanism and impact factors of micro/nanoporous polymers. Such studies would provide a more accurate prediction of thermal conductivity and a broader application in energy conversion and storage systems. 相似文献
998.
By using Lanczos exact diagonalization and quantum Monte Carlo combined with stochastic analytic continuation, we study the dynamical properties of the S = 1 antiferromagnetic Heisenberg chain with different strengths of bond disorder. In the weak disorder region, we find weakly coupled bonds which can induce additional low-energy excitation below the one-magnon mode. As the disorder increases, the average Haldane gap closes at δ∆ ~ 0.5 with more and more low-energy excitations coming out. After the critical disorder strength δc ~ 1, the system reaches a random-singlet phase with prominent sharp peak at ω = 0 and broad continuum at ω > 0 of the dynamic spin structure factor. In addition, we analyze the distribution of random spin domains and numerically find three kinds of domains hosting effective spin-1/2 quanta or spin-1 sites in between. These “spins” can form the weakly coupled longrange singlets due to quantum fluctuation which contribute to the sharp peak at ω = 0. 相似文献
999.
Tong Liu Bao-Qing Guo Yan-Hui Zhou Jun-Long Zhao Yu-Liang Fang Qi-Cheng Wu Chui-Ping Yang 《Frontiers of Physics》2022,17(6):61502
Transferring entangled states between matter qubits and microwave-field (or optical-field) qubits is of fundamental interest in quantum mechanics and necessary in hybrid quantum information processing and quantum communication. We here propose a way for transferring entangled states between superconducting qubits (matter qubits) and microwave-field qubits. This proposal is realized by a system consisting of multiple superconducting qutrits and microwave cavities. Here, „qutrit” refers to a three-level quantum system with the two lowest levels encoding a qubit while the third level acting as an auxiliary state. In contrast, the microwave-field qubits are encoded with coherent states of microwave cavities. Because the third energy level of each qutrit is not populated during the operation, decoherence from the higher energy levels is greatly suppressed. The entangled states can be deterministically transferred because measurement on the states is not needed. The operation time is independent of the number of superconducting qubits or microwave-field qubits. In addition, the architecture of the circuit system is quite simple because only a coupler qutrit and an auxiliary cavity are required. As an example, our numerical simulations show that high-fidelity transfer of entangled states from two superconducting qubits to two microwave-field qubits is feasible with present circuit QED technology. This proposal is quite general and can be extended to transfer entangled states between other matter qubits (e.g., atoms, quantum dots, and NV centers) and microwave- or optical-field qubits encoded with coherent states. 相似文献
1000.
设Bm(f,·)为函数f在d维单纯形σ上的n阶Bernstein多项式,本文对f∈Cr(σ)及f∈Cr+2(σ)给出了f的各阶编导数用Bn(f,·)相应偏导数逼近的误差估计.同时也考虑了整系数Bernstein多项式的Lp模估计 相似文献