全文获取类型
收费全文 | 3912篇 |
免费 | 710篇 |
国内免费 | 485篇 |
专业分类
化学 | 802篇 |
晶体学 | 53篇 |
力学 | 204篇 |
综合类 | 19篇 |
数学 | 20篇 |
物理学 | 1290篇 |
无线电 | 2719篇 |
出版年
2024年 | 11篇 |
2023年 | 39篇 |
2022年 | 71篇 |
2021年 | 111篇 |
2020年 | 127篇 |
2019年 | 102篇 |
2018年 | 102篇 |
2017年 | 167篇 |
2016年 | 199篇 |
2015年 | 205篇 |
2014年 | 254篇 |
2013年 | 258篇 |
2012年 | 300篇 |
2011年 | 353篇 |
2010年 | 244篇 |
2009年 | 277篇 |
2008年 | 307篇 |
2007年 | 338篇 |
2006年 | 270篇 |
2005年 | 221篇 |
2004年 | 209篇 |
2003年 | 198篇 |
2002年 | 139篇 |
2001年 | 147篇 |
2000年 | 99篇 |
1999年 | 65篇 |
1998年 | 69篇 |
1997年 | 47篇 |
1996年 | 41篇 |
1995年 | 23篇 |
1994年 | 26篇 |
1993年 | 12篇 |
1992年 | 14篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 9篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有5107条查询结果,搜索用时 78 毫秒
91.
Yingjie Zhang Ping Ning Xueqian Wang Langlang Wang Yixing Ma Qiang Ma Yibing Xie 《应用有机金属化学》2019,33(6)
Manganese‐ and cerium oxide‐modified titania catalysts were prepared by the deposition precipitation for the removal of elemental mercury (Hg0) from simulated yellow phosphorus off‐gas at low temperature. In addition, these catalysts were characterized by X‐ray diffraction, Brunauer–Emmett–Teller measurements, X‐ray photoelectron spectroscopy and field‐emission scanning electron microscope to determine the surface morphology of the obtained compounds and explore their formation mechanism. The results revealed that a Mn–Ce loading and reaction temperature of 10% and 150 °C, respectively, as well as a Mn/Ce molar ratio of 2:1, led to an optimal efficiency for the oxidation of elemental mercury. Furthermore, the effects of flue gas components were investigated. The presence of O2 clearly promoted the oxidation of Hg0. A CO atmosphere did not affect the Hg0 oxidation, when compared with N2, whereas the presence of H2S and water vapor inhibited the oxidation process. Furthermore, the X‐ray photoelectron spectroscopy spectra of Hg 4f revealed that the elemental mercury adsorbed by the catalyst is present as HgO. Finally, the Hg0 catalytic oxidation mechanism was discussed on the basis of the experimental results and characterization analysis. 相似文献
92.
Jian-Hua Huang Hua-Lin Xie Jun Yan Hong-Mei Lu Qing-Song Xu Yi-Zeng Liang 《Analytica chimica acta》2013
T-lymphocyte (T-cell) is a very important component in human immune system. T-cell epitopes can be used for the accurately monitoring the immune responses which activation by major histocompatibility complex (MHC), and rationally designing vaccines. Therefore, accurate prediction of T-cell epitopes is crucial for vaccine development and clinical immunology. In current study, two types peptide features, i.e., amino acid properties and chemical molecular features were used for the T-cell epitopes peptide representation. Based on these features, random forest (RF) algorithm, a powerful machine learning algorithm, was used to classify T-cell epitopes and non-T-cell epitopes. The classification accuracy, sensitivity, specificity, Matthews correlation coefficient (MCC), and area under the curve (AUC) values for proposed method are 97.54%, 97.22%, 97.60%, 0.9193, and 0.9868, respectively. These results indicate that current method based on the combined features and RF is effective for T-cell epitopes prediction. 相似文献
93.
This work aims at elucidating the mechanism of solvation of a radical ion pair (RIP) in a micro‐heterogeneous binary solvent mixture using magnetically affected reaction yield (MARY) spectroscopy. For the exciplex‐forming 9,10‐dimethylanthracene/N,N‐dimethylaniline system a comparative, composition‐dependent MARY line‐broadening study is undertaken in a heterogeneous (toluene/dimethylsulfoxide) and a quasi‐homogenous (propyl acetate/butyronitrile) solvent mixture. The half‐saturation field extrapolated to zero‐quencher concentration, B1/2, and the self‐exchange rate constants are analyzed in the light of solvent dynamical properties of the mixtures and a dielectric continuum solvation model. The dependence of B1/2 on the solvent composition is explained by cluster formation giving rise to shortened RIP lifetimes. The results are in qualitative agreement with the continuum solvation model suggesting that it could serve as a theoretical basis for quantitative modeling. 相似文献
94.
The influences of N2 introduction to a sputtering gas on structural and optical properties of vanadium-doped ZnO (VZO) films, grown by using reactive RF magnetron sputtering on a quartz substrate at room temperature, were investigated. In the VZO films, V doping caused to form a large number of O vacancies (VO) and degraded both the c-axis orientation and optical transmittance. While, on the contrary, the ZnO(002) diffraction intensity of 3.5-at.% VZO films increased adding N2 with a partial pressure ratio (αN2) >2% reaching a maximum at αN2 =5%. The average optical transmittance (wavelengths: 450−800 nm) of the 3.5-at.% VZO films was also improved by the N2 introduction and reached 74% at αN2 =5%. As a result of the analyses of the chemical binding states of the incorporated N atoms via the Raman spectroscopy and XPS, it was confirmed that the O sites were substituted by the N atoms and the amount of incorporated N increased by the high V doping. From the above, the N2 introduction was effective to suppress the VO formation even in room-temperature-grown VZO films, so it enables to improve both the c-axis orientation and optical transmittance. 相似文献
95.
96.
射频连接器与射频电缆被广泛应用于军民品的通信设备中,其关键工序射频电缆芯线与射频连接器插针的连接常采用手钳式阻焊工具。由于射频电缆较细,手钳式阻焊工具在阻焊操作时,要求电装工双手不能抖动,否则易产生废品。通过对手钳式阻焊工具进行技术改进,重新设计了一种预压紧方式的阻焊装置,并通过试验确定了电阻焊接头的结构形式和尺寸,提高了手工阻焊成品率和生产效率,降低了对电装工的技能要求。 相似文献
97.
98.
提出了基于双同步斩波模式的微功耗LED声控灯驱动电源设计方法。该驱动电源用一个单片机控制两个开关管分别为主电源和待机电源提供工作电流。主电源采用全波斩波工作模式为LED灯组提供工作电流;待机电源采用半波斩波工作模式,从而大幅降低了待机功耗。该驱动电源结构简单,可在50~60 Hz频率的180~250 V的宽电压范围内工作,具有恒流驱动功能和微功耗特性,且稳定可靠和较高的性价比。 相似文献
99.
针对近年来LTE 毫微微蜂窝基站商用加快和规模扩大,减小LTE 毫微微蜂窝基站的尺寸和降低其成
本就变得越来越重要。在保证基站性能的基础上,如何设计无线电收发器以减少尺寸和成本成为很大的挑战。设
计了一种应用于LTE 毫微微蜂窝基站中的低成本MIMO 射频收发器。分析了发射机和接收机的各项需求指标,提
出了块级的射频参数。据此,射频收发器被系统地分为几个子模块,分别设计了这些不同的子模块,同时区分各个
子模块的特点。所得到的测定结果表明,充分集成的射频收发器的设计不仅具有小尺寸,也符合LTE 毫微微基站的
各项指标。 相似文献
100.
Dr. Tran Quang Hung Dr. Ferial Terki Dr. Souleymane Kamara Mourad Dehbaoui Prof. Salam Charar Brajalal Sinha Prof. CheolGi Kim Dr. Philippe Gandit Il'ya A. Gural'skiy Dr. Gabor Molnar Dr. Lionel Salmon Dr. Helena J. Shepherd Dr. Azzedine Bousseksou 《Angewandte Chemie (International ed. in English)》2013,52(4):1058-1058