全文获取类型
收费全文 | 52948篇 |
免费 | 13143篇 |
国内免费 | 4646篇 |
专业分类
化学 | 52465篇 |
晶体学 | 496篇 |
力学 | 1818篇 |
综合类 | 254篇 |
数学 | 4694篇 |
物理学 | 11010篇 |
出版年
2024年 | 13篇 |
2023年 | 463篇 |
2022年 | 516篇 |
2021年 | 891篇 |
2020年 | 2072篇 |
2019年 | 3358篇 |
2018年 | 1733篇 |
2017年 | 1363篇 |
2016年 | 4308篇 |
2015年 | 4497篇 |
2014年 | 4585篇 |
2013年 | 5530篇 |
2012年 | 4839篇 |
2011年 | 4163篇 |
2010年 | 4194篇 |
2009年 | 4115篇 |
2008年 | 3783篇 |
2007年 | 3063篇 |
2006年 | 2619篇 |
2005年 | 2679篇 |
2004年 | 2228篇 |
2003年 | 1791篇 |
2002年 | 1536篇 |
2001年 | 1379篇 |
2000年 | 983篇 |
1999年 | 548篇 |
1998年 | 520篇 |
1997年 | 409篇 |
1996年 | 393篇 |
1995年 | 391篇 |
1994年 | 304篇 |
1993年 | 269篇 |
1992年 | 207篇 |
1991年 | 214篇 |
1990年 | 156篇 |
1989年 | 125篇 |
1988年 | 104篇 |
1987年 | 78篇 |
1986年 | 57篇 |
1985年 | 59篇 |
1984年 | 39篇 |
1983年 | 35篇 |
1982年 | 30篇 |
1981年 | 23篇 |
1980年 | 14篇 |
1979年 | 14篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 10篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
1.
高端芯片制造所需要的极紫外光刻技术位于我国当前面临35项"卡脖子"关键核心技术之首.高转换效率的极紫外光源是极紫外光刻系统的重要组成部分.本文通过采用双激光脉冲打靶技术实现较强的6.7 nm极紫外光输出.首先,理论计算Gd18+—Gd27+离子最外层4d壳层的4p-4d和4d-4f能级之间跃迁、以及Gd14+—Gd17+离子最外层4f壳层的4d-4f能级之间跃迁对波长为6.7 nm附近极紫外光的贡献.其后开展实验研究,结果表明,随着双脉冲之间延时的逐渐增加,波长为6.7 nm附近的极紫外光辐射强度呈现先减弱、后增加、之后再减弱的变化趋势,在双脉冲延时为100 ns处产生的极紫外光辐射最强.并且,在延时为100 ns处产生的光谱效率最高,相比于单脉冲激光产生的光谱效率提升了33%.此外,发现双激光脉冲打靶技术可以有效地减弱等离子体的自吸收效应,获得的6.7 nm附近极紫外光谱宽度均小于单激光脉冲打靶的情形,且在脉冲延时为30 ns时刻所产生的光谱宽度最窄,约为单独主脉冲产生极紫外光谱宽度的1/3.同时... 相似文献
2.
Fuzzy Optimization and Decision Making - Seepage equation in fissured porous media is a partial differential equation describing the variation of pressure of a given area over time. In traditional... 相似文献
3.
A general framework for describing photofission observables of actinides at an average excitation energy below 30 MeV 下载免费PDF全文
Guan-Lin Wang Hao-Yang Lan Xiao-Ming Shi Zhi-Chao Zhu Wen Luo 《中国物理C(英文版)》2022,46(8):084102-084102-14
A reasonable prediction of photofission observables plays a paramount role in understanding the photofission process and guiding various photofission-induced applications, such as short-lived isotope production, nuclear waste disposal, and nuclear safeguards. However, the available experimental data for photofission observables are limited, and the existing models and programs have mainly been developed for neutron-induced fission processes. In this study, a general framework is proposed for characterizing the photofission observables of actinides, including the mass yield distributions (MYD) and isobaric charge distributions (ICD) of fission fragments and the multiplicity and energy distributions of prompt neutrons (np) and prompt γ rays (γp). The framework encompasses various systematic neutron models and empirical models considering the Bohr hypothesis and does not rely on the experimental data as input. These models are then validated individually against experimental data at an average excitation energy below 30 MeV, which shows the reliability and robustness of the general framework. Finally, we employ this framework to predict the characteristics of photofission fragments and the emissions of prompt particles for typical actinides including 232Th, 235, 238U and 240Pu. It is found that the 238U(γ, f) reaction is more suitable for producing neutron-rich nuclei compared to the 232Th(γ, f) reaction. In addition, the average multiplicity number of both np and γp increases with the average excitation energy. 相似文献
4.
Hierarchical motion planning at the acceleration level based on task priority matrix for space robot
Nonlinear Dynamics - A capacitive micromachined ultrasonic transducer (CMUT) due to many benefits is being considered as an imaging and therapeutic technology recently. The critical challenge is to... 相似文献
5.
Yersak Thomas A. Hao Fang Kang Chansoon Salvador James R. Zhang Qinglin Malabet Hernando Jesus Gonzalez Cai Mei 《Journal of Solid State Electrochemistry》2022,26(3):709-718
Journal of Solid State Electrochemistry - In this study, hot pressing was evaluated as a method of cell fabrication to increase the energy density of next-generation all-solid-state batteries with... 相似文献
6.
Huang Zhiming He Zhimin Ye Yiyong Sheng Xiaokui 《International Journal of Theoretical Physics》2021,60(4):1254-1260
International Journal of Theoretical Physics - Quantum state sharing (QSS) plays significant role in transmitting quantum secret information. However, in practical quantum communication situation,... 相似文献
7.
The purpose of this paper is to investigate the connections between the weak Galerkin (WG) methods with and without stabilizers. The choices of stabilizers directly affect the convergence rates of the corresponding WG methods in general. However, we observed that the convergence rates are independent of the choices of stabilizers for these WG elements with stabilizers being optional. In this paper, we will verify such phenomena theoretically as well as numerically.
相似文献8.
Liu Zhu Sun Wen-Yang Fan Xiao-Gang Wang Dong Ye Liu 《International Journal of Theoretical Physics》2021,60(7):2412-2422
International Journal of Theoretical Physics - In this paper, we investigate Einstein-Podolsky-Rosen steering, Bell non-locality, first-order coherence and concurrence in the spin- $\frac {1}{2}$... 相似文献
9.
Taili Liu Di Zhang Md Rashedul Huqe Wen Wang Juan Antonio Zapien Sai-Wing Tsang Jingdong Luo 《中国科学:化学(英文版)》2022,65(3):584-593
The determination of nonlinearities near the band edge of organic and polymeric electro-optic(EO)materials is important from the viewpoint of molecular nonlinear optics(NLO)and photonic device applications.Based on transmission-mode Stark effect electromodulation(EM)spectroscopy,we study the electric-field-induced changes in optical absorption and refraction of newly developed EO polymers from the visible to near-infrared(NIR)wavelengths and report record-high near-band-edge complex EO effects from poled thin films.Values ofΔn andΔk up to 10-3 and 10-2 are found at an applied electric field of 2.0×105-3.0×105V/cm.The study of linear optical properties of poled films by spectroscopic ellipsometry shows large polinginduced birefringence and a nearly two-fold increase in the extinction coefficients at the extraordinary polarization.Through the Kramers-Kronig analysis,we obtained the real and imaginary second-order nonlinear coefficients up to~3,500 and~5,600 pm/V,respectively,which are believed to be the highest NLO coefficients of poled polymers through the resonance enhancement.Our approach goes beyond the previous works,applicable only to several discrete wavelengths,to a full-spectral analysis with independent verification of slab waveguide measurements.By considering both the electroabsorption and electrorefraction effects,our study overcomes the limitation of the classic qualitative two-level model and provides a quantitative understanding of near-resonance optical nonlinearities of organic EO materials.It can inspire the exploration of high-speed,absorptive,or phase-shifting light-modulators using EO polymers for on-chip applications. 相似文献
10.
Numerical Algorithms - The original solutions of highly oscillatory integral equations usually have rapid oscillation, which means that conventional numerical approaches used to solve these... 相似文献