全文获取类型
收费全文 | 8701篇 |
免费 | 1404篇 |
国内免费 | 678篇 |
专业分类
化学 | 5833篇 |
晶体学 | 90篇 |
力学 | 511篇 |
综合类 | 45篇 |
数学 | 1015篇 |
物理学 | 3289篇 |
出版年
2024年 | 22篇 |
2023年 | 165篇 |
2022年 | 289篇 |
2021年 | 289篇 |
2020年 | 376篇 |
2019年 | 314篇 |
2018年 | 283篇 |
2017年 | 271篇 |
2016年 | 436篇 |
2015年 | 436篇 |
2014年 | 482篇 |
2013年 | 614篇 |
2012年 | 810篇 |
2011年 | 778篇 |
2010年 | 551篇 |
2009年 | 499篇 |
2008年 | 561篇 |
2007年 | 428篇 |
2006年 | 464篇 |
2005年 | 337篇 |
2004年 | 268篇 |
2003年 | 225篇 |
2002年 | 177篇 |
2001年 | 139篇 |
2000年 | 148篇 |
1999年 | 179篇 |
1998年 | 157篇 |
1997年 | 128篇 |
1996年 | 133篇 |
1995年 | 118篇 |
1994年 | 100篇 |
1993年 | 81篇 |
1992年 | 78篇 |
1991年 | 79篇 |
1990年 | 44篇 |
1989年 | 38篇 |
1988年 | 39篇 |
1987年 | 35篇 |
1986年 | 29篇 |
1985年 | 21篇 |
1984年 | 20篇 |
1983年 | 20篇 |
1982年 | 9篇 |
1981年 | 14篇 |
1980年 | 9篇 |
1977年 | 6篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1973年 | 8篇 |
1972年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
291.
Crystal structure of meso‐substituted pyrazolyl porphyrin complexes and their highly active catalyst for oxidation of alkylbenzenes 下载免费PDF全文
During the past few years, a great deal of effort has been devoted to the anchoring of catalytic oxidation. In this work, three new catalysts CuPp, MnPp and ZnPp by solvothermal methods with 5, 10, 15, 20‐tetrakis(4‐N‐pyrazolyl)‐phenyl porphyrin (H2Pp) and the corresponding metal salts have been synthesized and structurally characterized. The single crystal structures determined by X‐ray diffraction show the bond distances of M‐N in porphyrin cores determined the conformation of porphyrin rings. We explored the catalytic activity of CoPp, CuPp, MnPp and ZnPp for oxidation of alkylbenzenes. The experimental results display these products exhibit high catalytic activities and selectivities for oxidation of ethylbenzene to acetophenone, and can be reused by filtration without appreciable decrease in catalytic activity and selectivity. 相似文献
292.
293.
Liwei Zhang Guiqiang Du Yewen Zhang 《Applied Physics A: Materials Science & Processing》2012,109(4):851-856
We present a theoretical investigation into the energy transport and transient wave propagation in metamaterial tunneling structures consisting of ??-negative (ENG) and ??-negative (MNG) materials. It is proved that a conjugated matched ENG/MNG bilayer and a (zero-index-material doped) photonic crystal heterostructure can work as a sub-wavelength resonator at tunneling frequency. The tunneling modes need a certain time to achieve the steady state and the charge up characteristic time increases (nearly) exponentially with the thickness of the structures. Under the steady state, the wave in the single-negative-material structures is not evanescent, but a hybrid of a traveling wave and a reactive standing wave. The phase difference between the electric field and the magnetic field varies with the position and time. The investigation of transient wave propagation in the metamaterial tunneling structures will help us to understand the interaction process between wave and metamaterial and to design special functional apparatus. 相似文献
294.
Weishi Du Yaokang Lv Hongliang Lu Zaihua Chen Dominic S. Wright Cheng Zhang 《中国化学快报》2017,28(12):2285-2289
An efficient and cost-effective strategy to modificate the surface of active carbon (AC), form a 3D-conductive network, and therefore improve the electrochemical performance of AC based supercapacitor was developed. 相似文献
295.
296.
Nonlinear Dynamics - The chemical synapses in a neural network are known to be modulated by the neuronal firing activities through the spike-timing-dependent plasticity (STDP) rule. In this paper,... 相似文献
297.
298.
Meng Liu Dr. Hao Fan Dr. Ou Zhuo Xiao Du Longqi Yang Prof. Peng Wang Lijun Yang Prof. Qiang Wu Prof. Xizhang Wang Prof. Zheng Hu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3843-3848
Molybdenum disulfide (MoS2) is an intensively studied anode material for lithium-ion batteries (LIBs) owing to its high theoretical capacity, but it is still confronted by severe challenges of unsatisfactory rate capability and cycle life. Herein, few-layer MoS2 nanosheets, vertically grown on hierarchical carbon nanocages (hCNC) by a facile hydrothermal method, introduce pseudocapacitive lithium storage owing to the highly exposed MoS2 basal planes, enhanced conductivity, and facilitated electrolyte access arising from good hybridization with hCNC. Thus, the optimized MoS2/hCNC exhibits reversible capacities of 1670 mAh g−1 at 0.1 A g−1 after 50 cycles, 621 mAh g−1 at 5.0 A g−1 after 500 cycles, and 196 mAh g−1 at 50 A g−1 after 2500 cycles, which are among the best for MoS2-based anode materials. The specific power and specific energy, which can reach 16.1 kW and 252.8 Wh after 3000 cycles, respectively, indicate great potential in high-power and long-life LIBs. These findings suggest a promising strategy for exploring advanced anode materials with high reversible capacity, high-rate capability, and long-term recyclability. 相似文献
299.
Li Ma Wei Zhang Mingxia Hou Dong Li Fengjuan Liu Xi Du Peng Jiang Zongkui Wang Rong Zhang Haijun Cao Shengliang Ye Changqing Li 《Biomedical chromatography : BMC》2019,33(4)
Intravenous immunoglobulin (IVIg) is increasingly used for the treatment of autoimmune and systemic inflammatory diseases with both licensed and off‐label indications. Recent studies indicated that IVIg‐mediated immunomodulation and anti‐inflammation are closely associated with the IgG sialylation, especially with IgG crystallizable fragment (Fc) sialylation. The sialic acid levels of the IgG molecules and Fc fragments in 12 IVIg preparations from six Chinese manufacturers were evaluated. The Fc fragments were derived from the papain digestion of IVIg, followed by affinity and size exclusion chromatography. The sialic acid levels in Fc fragments and IVIg preparations were determined by high‐performance liquid chromatography with fluorescence detection, after the sialic acid residues were released from the proteins. The results showed that the sialic acid levels in Chinese IVIg preparations ranged from 0.875 (mol/mol IgG) to 1.085 (mol/mol IgG), and the sialic acid levels in Fc fragments were from 0.321 (mol/mol Fc) to 0.361 (mol/mol Fc). Furthermore, the sialic acid levels of IVIg preparations and Fc fragments from different Chinese manufactures were significantly different. These findings will contribute to an increased understanding of Chinese IVIg preparations and the relationship between the sialic acid levels in IVIg preparations and their clinical efficacy in future clinical studies. 相似文献
300.
Comparison of the effects of K4Fe(CN)6 and K3Fe(CN)6 on TICT dual fluorescence of sodium p-dimethylaminobenzoate (SDMAB) in cetyltrimethyl ammonium chloride (CTAC) micelle yields a conclusion that the presence of a magnetic effect un favors the TICT process, which is verified by inserting the sample in a stationary magnetic field of 100G in which a decrease in the relative quantum yield of TICT state is observed. 相似文献