全文获取类型
收费全文 | 93333篇 |
免费 | 17569篇 |
国内免费 | 9680篇 |
专业分类
化学 | 64165篇 |
晶体学 | 937篇 |
力学 | 6017篇 |
综合类 | 555篇 |
数学 | 10983篇 |
物理学 | 37925篇 |
出版年
2024年 | 107篇 |
2023年 | 2085篇 |
2022年 | 2129篇 |
2021年 | 2992篇 |
2020年 | 4101篇 |
2019年 | 3678篇 |
2018年 | 3297篇 |
2017年 | 2944篇 |
2016年 | 4713篇 |
2015年 | 4454篇 |
2014年 | 5459篇 |
2013年 | 7070篇 |
2012年 | 8667篇 |
2011年 | 9036篇 |
2010年 | 5983篇 |
2009年 | 5781篇 |
2008年 | 6252篇 |
2007年 | 5447篇 |
2006年 | 5154篇 |
2005年 | 4151篇 |
2004年 | 3245篇 |
2003年 | 2491篇 |
2002年 | 2183篇 |
2001年 | 1915篇 |
2000年 | 1652篇 |
1999年 | 1899篇 |
1998年 | 1669篇 |
1997年 | 1649篇 |
1996年 | 1650篇 |
1995年 | 1399篇 |
1994年 | 1246篇 |
1993年 | 1058篇 |
1992年 | 899篇 |
1991年 | 820篇 |
1990年 | 688篇 |
1989年 | 535篇 |
1988年 | 397篇 |
1987年 | 324篇 |
1986年 | 354篇 |
1985年 | 286篇 |
1984年 | 170篇 |
1983年 | 135篇 |
1982年 | 111篇 |
1981年 | 69篇 |
1980年 | 58篇 |
1979年 | 20篇 |
1978年 | 23篇 |
1976年 | 14篇 |
1974年 | 13篇 |
1957年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Feng Sheng Ni Ziqiu Feng Shanshan Zhang Zhihui Liu Shuguang Wang Runbai Hu Jiawei 《Journal of Radioanalytical and Nuclear Chemistry》2019,319(3):737-748
Journal of Radioanalytical and Nuclear Chemistry - In this study, the UiO-66/Fe3O4/GO composite was prepared by one step method for removal of cesium ions (Cs+) in water and exhibited excellent... 相似文献
92.
Jiaxin Fu Yingxiong Wang Kaizhi Shen Qiang Fu Jie Zhang 《Journal of Polymer Science.Polymer Physics》2019,57(10):598-606
Many experimental results have revealed that the re‐entanglement kinetics of disentangled polymers is much slower than that predicted by tube theory. This retarded recovery of fully entangled state is of practical significance that shear‐induced modification may offer a way to improve processability for a polymer by reducing viscosity. This work tried to figure out the shear‐rate dependence variation of viscosity in the view of evolution of entanglement state through disentanglement and re‐entanglement, aiming to provide fundamental insights into application prospect of shear‐induced modification in preparing “in‐pellet” disentangled polymers prior to final processing. High‐density polyethylene was sheared on a parallel‐plate rotational rheometer with a linearly increased shear rate. Results showed that higher shear rate could induce further disentanglement, resulting in a lower viscosity with a reduction rate up to 93.7%, larger molecular weight between entanglements Me , and longer re‐entanglement time. Additionally, less entanglement would give a larger lamellar thickness of sheared samples after nonisothermal crystallization. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 598–606 相似文献
93.
Yong-Li Li Qiang Zhang Jian-Jun Wu Li-Jun Xue Li-Ming Chen Jun-Mian Tian Zhuo-Ni Xu Ying Chen Xian-Wen Yang Xiao-Jiang Hao Jie Li 《Tetrahedron letters》2019,60(10):751-753
From Abies nukiangensis, two novel 13,14-seco-abietane diterpenes, nukiangendines A (1) and B (2) were isolated. Their relative structures were determined by extensive NMR and HRMS spectroscopic analysis. The absolute configuration of 1 was established by ECD calculations. Compound 1 showed significant anti-hepatitis C virus (HCV) effects. 相似文献
94.
95.
Jessica K. Su Zexin Jin Rui Zhang Gang Lu Peng Liu Yan Xia 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(49):17935-17940
Ring‐opening metathesis polymerization (ROMP) has become one of the most important living polymerizations. Cyclopropenes (CPEs) remain underexplored for ROMP. Described here is that the simple swap of 1‐methyl to 1‐phenyl on 1‐(benzoyloxymethyl)CPEs elicited strikingly different modes of reactivity, switching from living polymerization to either selective single‐addition or living alternating ROMP. The distinct reactivity stems from differences in steric repulsions at the Ru alkylidene after CPE ring opening. Possible olefin or oxygen chelation from ring‐opened CPE substituents was also observed to significantly affect the rate of propagation. These results demonstrate the versatility of CPEs as a new class of monomers for ROMP, provide mechanistic insights for designing new monomers with rare single‐addition reactivity, and generate a new functionalizable alternating copolymer scaffold with controlled molecular weight and low dispersity. 相似文献
96.
Fan Yang Shuaishuai Zhang Jingpeng Song Qing Du Guixiang Li Nadezda V. Tarakina Markus Antonietti 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(52):18989-18992
Artificial humic acids (A‐HA) made from biomass in a hydrothermal process turn otherwise highly insoluble phosphates (e.g. iron phosphate as a model) into highly available phosphorus, which contributes to the fertility of soils and the coupled plant growth. A detailed electron microscopy study revealed etching of the primary iron phosphate crystals by the ‐COOH and phenolic groups of humic acids, but also illustrated the importance of the redox properties of humic matter on the nanoscale. The combined effects result in the formation of then bioavailable phosphate nanoparticles stabilized by humic matter. Typical agricultural chemical tests indicate that the content of total P and directly plant‐available P improved largely. Comparative pot planting experiments before and after treatment of phosphates with A‐HA demonstrate significantly enhanced plant growth, as quantified in higher aboveground and belowground plant biomass. 相似文献
97.
Fan‐Li Zhang Jun Yi Wei Peng Petar M. Radjenovic Hua Zhang Zhong‐Qun Tian Jian‐Feng Li 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(35):12261-12265
The fundamental understanding of the subtle interactions between molecules and plasmons is of great significance for the development of plasmon‐enhanced spectroscopy (PES) techniques with ultrahigh sensitivity. However, this information has been elusive due to the complex mechanisms and difficulty in reliably constructing and precisely controlling interactions in well‐defined plasmonic systems. Herein, the interactions in plasmonic nanocavities of film‐coupled metallic nanocubes (NCs) are investigated. Through engineering the spacer layer, molecule–plasmon interactions were precisely controlled and resolved within 2 nm. Efficient energy exchange interactions between the NCs and the surface within the 1–2 nm range are demonstrated. Additionally, optical dressed molecular excited states with a huge Lamb shift of ≈7 meV at the single‐molecule (SM) level were observed. This work provides a basis for understanding the underlying molecule–plasmon interaction, paving the way for fully manipulating light–matter interactions at the nanoscale. 相似文献
98.
Yu Ye Libo Sun Chenghui Zhang Jianfeng Du Yuchuan Liu Xiaowei Song Zhiqiang Liang 《应用有机金属化学》2019,33(12)
A novel luminescent metal–organic framework ( Zn‐TCPP/BPY ) with pillared structure based on 2,3,5,6‐tetrakis(4‐carboxyphenyl)pyrazine (H4TCPP) and 4,4′‐bipyridine (BPY) has been designed and synthesized through a solvothermal reaction. The [Zn2(COO)4] paddlewheel units are linked by TCPP4? ligands to form two‐dimensional layers and further connected by BPY ligands as pillars to construct the twofold interpenetrating three‐dimensional framework. Interestingly, Zn‐TCPP/BPY possesses outstanding stability in organic solvents and water as well as maintains its structural rigidity in aqueous solutions of different pH values (3–12). After activation, Zn‐TCPP/BPY possesses permanent porosity with Brunauer–Emmett–Teller surface area of 630 m2 g–1. Remarkably, Zn‐TCPP/BPY displays excellent fluorescent property in virtue of the aggregation‐induced emission effect of the H4TCPP ligand, which can be highly active and quenched by small amounts of 2,4,6‐trinitrophenol (TNP) and Fe3+ ions. Furthermore, the detection effect of Zn‐TCPP/BPY remains basically the same even after five cycles. The excellent stability, high sensitivity, and recyclability of Zn‐TCPP/BPY make it an outstanding chemical sensor for detecting TNP and Fe3+ ions. 相似文献
99.
Li‐Ming Sun Bo Zhang Yu‐Chen Wang Hao‐Ke He Xiao‐Guang Chen Su‐Juan Wang 《Biomedical chromatography : BMC》2019,33(2)
Alum‐processing is a traditional method to attenuate the toxicity of Pinelliae Rhizoma (tubers of Pinellia ternate, PT). The present study aimed at investigating the chemical and cytotoxic changes during alum processing. Metabolomic profiles of raw and alum‐processed PT were studied based on ultra‐performance liquid chromatography coupled with Orbitrap mass spectrometry. More than 80 chemicals in positive MS mode and 40 chemicals in negative MS mode, such as organic acids, amino acids, glucosides and nucleosides, were identified after multivariate statistical analysis, including principal component analysis and orthogonal partial least‐square discriminant analysis. Almost all of the identified chemical markers were significantly decreased ~10‐ to 100‐fold after alum processing. Meanwhile, the correlations between the chemical markers were assimilated to a positive coefficient from disorderly distribution during the processing. Raw PT extracts could inhibit the proliferation of human carcinoma cells (HCT‐116, HepG2, and A549) at the rate of 40.5, 24.8 and 31.6% more strongly than processed PT. It was concluded that the alum processing of PT could decrease the number of actively water‐soluble principles at the same time as decreasing toxicity. Given the water‐insoluble property of toxic calcium oxalate raphides in PT, we suggest that a more scientific processing method should be sought. 相似文献
100.
Hydrogenation of acetophenone over nano‐Cu/SiO2 catalysts was investigated. The catalysts, prepared by a liquid precipitation method using various precipitating agents, were characterized using low‐temperature nitrogen adsorption, X‐ray diffraction, temperature‐programmed desorption of ammonia, hydrogen temperature‐programmed reduction, transmission electron microscopy and X‐ray photoelectron spectroscopy. It was found that the catalysts prepared by a homogeneous precipitation method had better activity and stability than those prepared by a co‐precipitation method. The catalyst prepared using urea as precipitating agent had well‐dispersed copper species, high surface area and abundant pore structure. The catalytic performance and mechanism of the Cu/SiO2 catalysts were further studied. It was found that the activity and stability of the catalysts could be improved by adjusting the proportion of Cu+/(Cu+ + Cu0). The sample prepared using urea as precipitating agent presented higher activity and selectivity. Also, the catalyst prepared using urea maintained a high catalytic performance while being continuously used for 150 h under the optimal reaction conditions. 相似文献