全文获取类型
收费全文 | 21355篇 |
免费 | 3871篇 |
国内免费 | 3754篇 |
专业分类
化学 | 17171篇 |
晶体学 | 318篇 |
力学 | 1163篇 |
综合类 | 304篇 |
数学 | 2629篇 |
物理学 | 7395篇 |
出版年
2024年 | 7篇 |
2023年 | 344篇 |
2022年 | 492篇 |
2021年 | 629篇 |
2020年 | 864篇 |
2019年 | 931篇 |
2018年 | 786篇 |
2017年 | 779篇 |
2016年 | 966篇 |
2015年 | 1158篇 |
2014年 | 1315篇 |
2013年 | 1693篇 |
2012年 | 1951篇 |
2011年 | 2077篇 |
2010年 | 1662篇 |
2009年 | 1560篇 |
2008年 | 1701篇 |
2007年 | 1485篇 |
2006年 | 1275篇 |
2005年 | 1133篇 |
2004年 | 942篇 |
2003年 | 799篇 |
2002年 | 916篇 |
2001年 | 793篇 |
2000年 | 543篇 |
1999年 | 413篇 |
1998年 | 304篇 |
1997年 | 227篇 |
1996年 | 226篇 |
1995年 | 183篇 |
1994年 | 166篇 |
1993年 | 113篇 |
1992年 | 96篇 |
1991年 | 90篇 |
1990年 | 60篇 |
1989年 | 49篇 |
1988年 | 36篇 |
1987年 | 33篇 |
1986年 | 17篇 |
1985年 | 22篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 8篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1976年 | 8篇 |
1974年 | 7篇 |
1971年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 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.
Efficient,robust and cost-effective electrocatalysts that catalyze hydrogen evolution/oxidation reaction(HER/HOR)in alkaline media are highly demanded.Recently,single-atom catalysts(SACs)have emerged as new promising candidates;however,the rational design of supports and the optimization of coordination environment between supports and metal atoms are challenging.In this work,we successfully fabricate atomically dispersed ruthenium(Ru)species,which are strongly coordinated by N and S dual heteroatoms on holey graphene(RuSA/NSG),as an excellent bifunctional catalyst for HER/HOR.In alkaline media,the developed catalyst exhibits high catalytic performance with a low overpotential of 57.3 mV to drive a current density of 10 mA cm-1 for HER,and its mass activity is about 5.8 times higher than that of commercial Pt/C and Ru/C catalysts at an overpotential of 100 mV.Similarly,considerable HOR performance of Ru SA/NSG is verified to be superior to Pt/C and Ru/C.Furthermore,X-ray-based spectroscopy measurements and density-functional theory calculations have confirmed that,compared with Ru–N4,the tailored Ru–N4–S2 with nearby S dopants can act as more active centers to greatly accelerate the sluggish HER/HOR kinetics in alkaline media.The present work provides a new atomic-level engineering strategy to modulate catalytic activities of SACs via the coordination design using dual heteroatoms on the carbon support. 相似文献
3.
4.
We devote to the calculation of Batalin–Vilkovisky algebra structures on the Hochschild cohomology of skew Calabi–Yau generalized Weyl algebras. We first establish a Van den Bergh duality at the level of complex. Then based on the results of Solotar et al., we apply Kowalzig and Krähmer's method to the Hochschild homology of generalized Weyl algebras, and translate the homological information into cohomological one by virtue of the Van den Bergh duality, obtaining the desired Batalin–Vilkovisky algebra structures. Finally, we apply our results to quantum weighted projective lines and Podleś quantum spheres, and the Batalin–Vilkovisky algebra structures for them are described completely. 相似文献
5.
Phosphors with outstanding luminescence thermal stability are desirable for high-power phosphor-converted light-emitting diode (pc-LED) lightings. High structural rigidity and large bandgap of phosphor hosts are helpful to suppress nonradiative relaxation of optical centers and realize excellent thermal stability. Unfortunately, few host materials simultaneously possess aforementioned structural features. Herein, we confirm that Sr3(PO4)2 (SPO) phosphate possesses high structural rigidity (Debye temperature, ΘD = 559 K) and large bandgap (Eg = 8.313 eV) by density functional theory calculations. As expected, Eu2+-doped SPO purple-blue phosphors show extraordinary thermal stability. At 150/300 °C, SPO:5%Eu2+ presents emission loss of only 4%/8% and a predicated ultrahigh thermal quenching temperature of 973 °C. The most strikingly discoveries here are that thermal-induced emission compensation appears within two distinct Eu2+ sites of SPO host. The outstanding thermal stability, on one hand, is attributed to rigid structure and large bandgap of host that inhibits nonradiative relaxation of Eu2+ and on the other hand, the emission self-compensation of Eu2+. Benefiting from synergistic effect of emission compensation and nonradiative transition restriction of Eu2+, as-prepared SPO:5%Eu2+ purple-blue phosphor not only presents superior thermal stability but also high internal quantum efficiency of 95.1% and excellent hydrolysis resistant. Some advanced applications are explored including white LED lighting and wide-color-gamut display. Our work provides in-deep insights into structure-property relationships of thermally stable phosphors. 相似文献
6.
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
7.
甲氧基多溴联苯醚(methoxypolybrominated diphenyl ethers, MeO-PBDEs)广泛存在于生物体和海洋环境。以象山海域的生物体和沉积物为样本,采用固相萃取净化-气相色谱-负化学源质谱法,检测了6种MeO-PBDEs,结果显示,当目标分析物浓度为0.1~20.0 μg?L-1时,线性关系良好(R2>0.999),检出限为0.13~0.22 μg?kg-1,定量限为0.42~0.72 μg?kg-1,实际样品的平均回收率为71.2%~116.2%。MeO-PBDEs的分布状况调查结果显示,藻类样品中仅检出6-MeO-BDE-47,且浓度较低,其他生物体中检出3种MeO-PBDEs,检出率为31.3%,浓度为0.21~2.72 μg?kg-1。沉积物中无MeO-PBDEs被检出。 相似文献
8.
9.
10.
考虑自有平台和第三方平台两种分时租赁方式,将汽车质量划分为性能质量和环境质量,构建销售模式、纯分时租赁模式和混合模式下的产品线策略模型,研究制造商产品线策略与商业模式之间的相互作用。研究发现,同品牌产品间竞争和合并效应是分时租赁模式影响产品线策略的两个关键因素。同品牌产品间竞争的加剧和合并效应的增大都会激励企业选择性能更好的车型而忽略其环境表现。分时租赁模式能同时改进利润与产品环境表现,但存在条件:当消费者价格敏感性较低时,使用成本高且合并效应小是实现同时改进的条件;当消费者价格敏感较高时,使用成本低且合并效应小则是同时改进的条件。 相似文献