全文获取类型
收费全文 | 8748篇 |
免费 | 1732篇 |
国内免费 | 1031篇 |
专业分类
化学 | 6555篇 |
晶体学 | 94篇 |
力学 | 422篇 |
综合类 | 91篇 |
数学 | 848篇 |
物理学 | 3501篇 |
出版年
2024年 | 40篇 |
2023年 | 198篇 |
2022年 | 344篇 |
2021年 | 368篇 |
2020年 | 423篇 |
2019年 | 470篇 |
2018年 | 377篇 |
2017年 | 344篇 |
2016年 | 507篇 |
2015年 | 495篇 |
2014年 | 572篇 |
2013年 | 696篇 |
2012年 | 869篇 |
2011年 | 820篇 |
2010年 | 603篇 |
2009年 | 502篇 |
2008年 | 577篇 |
2007年 | 539篇 |
2006年 | 433篇 |
2005年 | 335篇 |
2004年 | 241篇 |
2003年 | 225篇 |
2002年 | 266篇 |
2001年 | 250篇 |
2000年 | 139篇 |
1999年 | 180篇 |
1998年 | 121篇 |
1997年 | 80篇 |
1996年 | 75篇 |
1995年 | 54篇 |
1994年 | 58篇 |
1993年 | 57篇 |
1992年 | 49篇 |
1991年 | 47篇 |
1990年 | 40篇 |
1989年 | 33篇 |
1988年 | 22篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1959年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
Yuhua Xue Jun Liu Hao Chen Ruigang Wang Dingqiang Li Jia Qu Liming Dai 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2012,124(48):12300-12300
212.
From a complex network perspective, this study sets out two aims around the US airport network (USAN) which is built from en-route location information of domestic flights in the US. First, we analyze the structural properties of the USAN with respect to its binary and weighted graphs, and second we explore the airport patterns, which have wide-ranging implications. Results from the two graphs indicate the following. (1) The USAN exhibits scale-free, small-world and disassortative mixing properties, which are consistent with the mainstream perspectives. Besides, we find (2) a remarkable power relationship between the structural measurements in the binary graph and the traffic measurements in the weighted counterpart, namely degree versus capacity and attraction versus volume. On the other hand, investigation of the airport patterns suggests (3) that all the airports can be classified into four categories based on multiple network metrics, which shows a complete typology of the airports. And it further indicates (4) that there is a subtle relationship between the airport traffic and the geographical constraints as well as the regional socioeconomic indicators. 相似文献
213.
A simple wet chemical method was used to synthesize Fe-doped MnO2 composites with iron amount ranging from 0 to 90 M percent. X-ray diffraction, electron probe micro-analyzer, scanning electron microscopy and vector network analyzer were employed to investigate the effect of iron doping on the microstructure and electromagnetic performance of the as-synthesized samples. Results indicate that relative small content of Fe-doping cannot change the α-MnO2 structure but can promote the formation of hollow-structural morphology. The as-obtained products are transformed into a novel compound (Fe0.67Mn0.33)OOH with the increase of Fe-doping to 30 mol%. The possible formation mechanism was proposed in detail. Compared with the pure MnO2, the Fe-doped samples exhibit decreased dielectric loss but increased magnetic loss with increasing the iron content below 20 mol% while relatively poor electromagnetic properties with the iron content above 30 mol%. 相似文献
214.
The effects of beam wander corrected and pointing errors on the average capacity of a non-Kolmogorov turbulent atmosphere communication channel are studied. The gamma–gamma irradiance probability density function model has been considered to include the effects of non-Kolmogorov turbulence. An expression for the average capacity under beam wander corrected, pointing errors and the spectral index of refractive-index fluctuation. Simulation results for effects of circular detection aperture of radius, atmosphere turbulence strength and wavelength on average capacity are presented. Our results show that the average capacity has an oscillation in the case of short propagation distance, but in the case of long propagation distance, it has gradually reduced curves. And the turbulence strength has a strong influence on average capacity. In general, turbulence reduces the average capacity; it can reduce average capacity by increasing of the power law α. We can ignore the little effects of wavelength increases on the average capacity. 相似文献
215.
Dr. Yuyang Zhou Assistant Prof. Junli Jia Prof. Xiaomei Wang Dr. Weiqiang Guo Prof. Zhengying Wu Prof. Nan Xu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):16796-16800
Seven luminescent iridium(III) complexes were prepared to investigate the relationships between chemical structures and properties of protein staining. For the first time, the effect of the main ligand, the π conjugation effect of the ancillary ligand, and the charge effect of organometallic complexes on protein staining has been revealed. Most importantly, this study gives the first experimental evidence of the potential applications of charge‐neutral organometallic complexes in protein staining, which could open an avenue of exploiting novel protein staining agents in the future. 相似文献
216.
A rapid UPLC‐MS/MS method for the determination of oleanolic acid in rat plasma and liver tissue: application to plasma and liver pharmacokinetics 下载免费PDF全文
Tian‐xue Li Chao‐sen Chu Jia‐yu Zhu Tian‐yi Yang Jie Zhang Yu‐tao Hu Xing‐hao Yang 《Biomedical chromatography : BMC》2016,30(4):520-527
A reliable high‐throughput ultra‐high performance liquid chromatography–tandem mass spectrometry (UPLC‐MS/MS) method was developed and validated for oleanolic acid (OA) determination in rat plasma and liver tissue using glycyrrhetic acid as the internal standard (IS). Plasma and liver homogenate samples were prepared using solid‐phase extraction. Chromatographic separation was achieved on a C18 column using an isocratic mobile phase system. The detection was performed by multiple reaction monitoring mode via positive electrospray ionization interface. The calibration curves showed good linearity (R2 > 0.9997) within the tested concentration ranges. The lower limit of quantification for plasma and liver tissue was ≤0.75 ng/mL. The intra‐ and inter‐day precision and accuracy deviations were within ±15% in plasma and liver tissue. The mean extraction recoveries ranged from 80.8 to 87.0%. In addition, the carryover, matrix effect, stability and robustness involved in the method were also validated. The method was successfully applied to the plasma and hepatic pharmacokinetics of OA after oral administration to rats. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
217.
Jiajian Gao Chunmiao Jia Jing Li Meiju Zhang Fangna Gu Guangwen Xu Ziyi Zhong Fabing Su 《天然气化学杂志》2013,(6):919-927
The correlation between phase structures and surface acidity of Al2O3 supports calcined at different temperatures and the catalytic performance of Ni/Al2O3 catalysts in the production of synthetic natural gas(SNG) via CO methanation was systematically investigated. A series of 10 wt% NiO/Al2O3 catalysts were prepared by the conventional impregnation method, and the phase structures and surface acidity of Al2O3 supports were adjusted by calcining the commercial γ-Al2O3 at different temperatures(600–1200 C). CO methanation reaction was carried out in the temperature range of 300–600 C at different weight hourly space velocities(WHSV = 30000 and 120000 mL·g-1h-1) and pressures(0.1 and 3.0 MPa). It was found that high calcination temperature not only led to the growth in Ni particle size, but also weakened the interaction between Ni nanoparticles and Al2O3 supports due to the rapid decrease of the specific surface area and acidity of Al2O3 supports. Interestingly, Ni catalysts supported on Al2O3 calcined at 1200 C(Ni/Al2O3-1200) exhibited the best catalytic activity for CO methanation under different reaction conditions. Lifetime reaction tests also indicated that Ni/Al2O3-1200 was the most active and stable catalyst compared with the other three catalysts, whose supports were calcined at lower temperatures(600, 800 and 1000 C). These findings would therefore be helpful to develop Ni/Al2O3 methanation catalyst for SNG production. 相似文献
218.
Effects of additives and post‐treatment on the thermoelectric performance of vapor‐phase polymerized PEDOT films 下载免费PDF全文
Yanhua Jia Xuejing Li Fengxing Jiang Changcun Li Tongzhou Wang Qinglin Jiang Jian Hou Jingkun Xu 《Journal of Polymer Science.Polymer Physics》2017,55(23):1738-1744
Vapor‐phase polymerization (VPP) is an important method for the fabrication of high‐quality conducting polymers, especially poly(3,4‐ethylenedioxythiophene) (PEDOT). In this work, the effects of additives and post‐treatment solvents on the thermoelectric (TE) performance of VPP‐PEDOT films were systematically investigated. The use of 1‐butyl‐3‐menthylinidazolium tetrafluoroborate ([BMIm][BF4], an ionic liquid) was shown to significantly enhance the electrical conductivity of VPP‐PEDOT films compared with other additives. The VPP‐PEDOT film post‐treated with mixed ethylene glycol (EG)/[BMIm][BF4] solvent displayed the high power factor of 45.3 μW m?1 K?2 which is 122% higher than that prepared without any additive or post‐treatment solvent, along with enhanced electrical conductivity and Seebeck coefficient. This work highlighted the superior effect of the [BMIm][BF4] additive and the EG/[BMIm][BF4] solvent post‐treatment on the TE performance of the VPP‐PEDOT film. These results should help with developing the VPP method to fabricate high‐performance PEDOT films. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 1738–1744 相似文献
219.
The preparation of bisaryl carbodiazone compounds from the aryl substituted carbazides with Ceric Ammonium Nitrate (CAN) has been reported for the first time in excellent yields (80-91%). This method only needs simple instruments and short reaction time. A possible mechanism has been suggested. 相似文献
220.
Using the classical Mie scattering theory,we compute the energy density of an arbitrary partial wave(e.g.,the nth order) and then determine that the interaction between an incident planar wave and a sphere of radius a is the one between the sphere and those partial waves the order of which satisfies n≤ka.We also provide a simple expression to describe the diffracted wave in which the angle-dependent functions are employed.The difference between the accurate and the approximate expressions is demonstrated by numerical calculation. 相似文献