全文获取类型
收费全文 | 15567篇 |
免费 | 2788篇 |
国内免费 | 1833篇 |
专业分类
化学 | 11147篇 |
晶体学 | 163篇 |
力学 | 1137篇 |
综合类 | 65篇 |
数学 | 1657篇 |
物理学 | 6019篇 |
出版年
2024年 | 36篇 |
2023年 | 339篇 |
2022年 | 386篇 |
2021年 | 533篇 |
2020年 | 630篇 |
2019年 | 585篇 |
2018年 | 530篇 |
2017年 | 483篇 |
2016年 | 837篇 |
2015年 | 728篇 |
2014年 | 919篇 |
2013年 | 1132篇 |
2012年 | 1459篇 |
2011年 | 1444篇 |
2010年 | 982篇 |
2009年 | 921篇 |
2008年 | 1070篇 |
2007年 | 944篇 |
2006年 | 855篇 |
2005年 | 762篇 |
2004年 | 530篇 |
2003年 | 435篇 |
2002年 | 423篇 |
2001年 | 348篇 |
2000年 | 305篇 |
1999年 | 324篇 |
1998年 | 269篇 |
1997年 | 239篇 |
1996年 | 270篇 |
1995年 | 266篇 |
1994年 | 188篇 |
1993年 | 147篇 |
1992年 | 152篇 |
1991年 | 145篇 |
1990年 | 125篇 |
1989年 | 101篇 |
1988年 | 85篇 |
1987年 | 67篇 |
1986年 | 50篇 |
1985年 | 41篇 |
1984年 | 30篇 |
1983年 | 25篇 |
1982年 | 14篇 |
1981年 | 16篇 |
1980年 | 9篇 |
1978年 | 2篇 |
1972年 | 1篇 |
1957年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
本文利用主成分分析方法,针对66例肝硬化建立主成分分析模型,利用spss16.0求解模型。所得的结果简化了问题研究的复杂度,有助于医生的诊断。 相似文献
992.
Ao Yu Guoming Ma Jintian Jiang Yajing Hu Mingming Su Wangtao Long Shixin Gao Dr. Hsien-Yi Hsu Dr. Ping Peng Prof. Fang-Fang Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(40):10405-10412
Inspired by the spongy bone structures, three-dimensional (3D) sponge-like carbons with meso-microporous structures are synthesized through one-step electro-reduction of CO2 in molten carbonate Li2CO3−Na2CO3−K2CO3 at 580 °C. SPC4-0.5 (spongy porous carbon obtained by electrolysis of CO2 at 4 A for 0.5 h) is synthesized with the current efficiency of 96.9 %. SPC4-0.5 possesses large electrolyte ion accessible surface area, excellent wettability and electronical conductivity, ensuring the fast and effective mass and charge transfer, which make it an advcanced supercapacitor electrode material. SPC4-0.5 exhibits a specific capacitance as high as 373.7 F g−1 at 0.5 A g−1, excellent cycling stability (retaining 95.9 % of the initial capacitance after 10000 cycles at 10 A g−1), as well as high energy density. The applications of SPC4-0.5 in quasi-solid-state symmetric supercapacitor and all-solid-state flexible devices for energy storage and wearable piezoelectric sensor are investigated. Both devices show considerable capacitive performances. This work not only presents a controllable and facile synthetic route for the porous carbons but also provides a promising way for effective carbon reduction and green energy production. 相似文献
993.
994.
δ-Glyconolactams were first synthesized by the intramolecular Schmidt–Boyer reaction using corresponding δ-azidosugars as starting material. The reaction could be efficiently performed in good yields of 61–69% under microwave radiation in acid condition, providing an alternative protocol to iminosugar δ-lactam. 相似文献
995.
采用实时红外光谱仪(RT-FTIR)研究了单体结构、单体配比以及活性稀释剂结构对樟脑醌(CQ)/胡椒环(BDO)引发的光聚合动力学的影响,结果发现,UDMA虽然黏度较低,但是易发生链转移反应且在聚合体系中含量较高(70 wt%),可作为氢给体猝灭激发态CQ,从而影响CQ和BDO之间的相互作用.Bis-GMA虽然黏度大,但是反应活性高,当其与少量具有给氢能力的活性稀释剂TEGDMA配合使用时,不仅对聚合体系的反应活性影响较小,而且可显著降低体系的黏度,大大提高自由基的活动能力,有利于改善CQ/BDO的引发活性. 相似文献
996.
Xiaoye Ma Chuanqing Kang Wenhui Chen Rizhe Jin Haiquan Guo Xuepeng Qiu Lianxun Gao 《Journal of polymer science. Part A, Polymer chemistry》2016,54(4):570-581
To investigate the influence of hydrogen bonding on the properties of polyimides (PIs) containing rigid rod‐like groups, five symmetrical diamines containing benzimidazole, benzoxazole, and hydroxy group were synthesized, and then a series of PIs were prepared. Results showed that hydroxyl‐containing poly(benzoxazole imide)s possess higher glass transition temperature (Tg) and dimensional stabilities than their corresponding poly(benzoxazole imide)s. Moreover, the corresponding poly(benzimidazole imide)s presented the best performances, such as the highest Tg, the highest char yield and the highest dimensional stabilities. The influence of hydrogen bonding of benzimidazole on the properties of PIs was stronger than that of hydroxyl groups. Hydroxyl‐containing poly(benzoxazole imide)s were formed in crosslinking structures after heat treatment at 400 °C. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 570–581 相似文献
997.
Mild Synthesis of Pt/SnO2/Graphene Nanocomposites with Remarkably Enhanced Ethanol Electro‐oxidation Activity and Durability 下载免费PDF全文
Dr. Yunteng Qu Dr. Yunzhi Gao Dr. Long Wang Dr. Jiancun Rao Dr. Geping Yin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(1):193-198
We have designed a new Pt/SnO2/graphene nanomaterial by using L ‐arginine as a linker; this material shows the unique Pt‐around‐SnO2 structure. The Sn2+ cations reduce graphene oxide (GO), leading to the in situ formation of SnO2/graphene hybrids. L ‐Arginine is used as a linker and protector to induce the in situ growth of Pt nanoparticles (NPs) connected with SnO2 NPs and impede the agglomeration of Pt NPs. The obtained Pt/SnO2/graphene composites exhibit superior electrocatalytic activity and stability for the ethanol oxidation reaction as compared with the commercial Pt/C catalyst owing to the close‐connected structure between the Pt NPs and SnO2 NPs. This work should have a great impact on the rational design of future metal–metal oxide nanostructures with high catalytic activity and stability for fuel cell systems. 相似文献
998.
Michael Addition Catalyzed by Chiral Secondary Amine Phosphoramide Using Fluorinated Silyl Enol Ethers: Formation of Quaternary Carbon Stereocenters 下载免费PDF全文
Jin‐Sheng Yu Fu‐Min Liao Wei‐Ming Gao Kui Liao Run‐Lin Zuo Prof. Dr. Jian Zhou 《Angewandte Chemie (International ed. in English)》2015,54(25):7381-7385
A chiral secondary amine phosphoramide was developed and identified as a powerful catalyst for the Mukaiyama–Michael addition of fluorinated enol silyl ethers to tetrasubstituted olefins. The resulting products are obtained with high enantioselectivities and contain a quaternary carbon stereocenter bearing either a difluoroalkyl or monofluoroalkyl group. 相似文献
999.
Reduced Graphene‐Wrapped MnO2 Nanowires Self‐Inserted with Co3O4 Nanocages: Remarkable Enhanced Performances for Lithium‐Ion Anode Applications 下载免费PDF全文
Qi Zhu Yunhui Li Prof. Ying Gao Prof. Xiao Wang Prof. Shuyan Song 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(20):6876-6880
A simple synthetic approach for graphene‐templated nanostructured MnO2 nanowires self‐inserted with Co3O4 nanocages is proposed in this work. The Co3O4 nanocages were penetrated in situ by MnO2 nanowires. As an anode, the as‐obtained MnO2–Co3O4–RGO composite exhibits remarkable enhanced performance compared with the MnO2–RGO and Co3O4–RGO samples. The MnO2–Co3O4–RGO electrode delivers a reversible capacity of up to 577.4 mA h g?1 after 400 cycles at 500 mA g?1 and the Coulombic efficiency of MnO2–Co3O4–RGO is about 96 %. 相似文献
1000.
Qingqing Gao Aijun Yang Xiaohua Wang Anthony B. Murphy Yunjia Li Chaojun Zhang Yanhui Lu Li Huan Zhaofang Zhu Mingzhe Rong 《Plasma Chemistry and Plasma Processing》2016,36(5):1301-1323
It has become increasingly clear that deviations from local thermodynamic equilibrium occur in thermal plasmas. This paper is devoted to investigating the non-equilibrium characteristics of CO2 thermal plasmas, which have wide application in industry. A two-temperature chemical kinetic model with a comprehensive chemical system is developed to calculate the non-equilibrium characteristics of CO2 thermal plasmas for a wide temperature range, from 12,000 to 500 K, at atmospheric pressure. The non-equilibrium results are compared to the equilibrium composition obtained by Gibbs free energy minimization, and significant deviations are found at lower temperatures. Based on the dependence of molar fractions on temperature, the dominant species are determined in three temperature ranges. The dominant reactions are then obtained by considering their contribution to the generation and loss of the dominant species. Using the dominant species and reactions, the full model is simplified into three simpler models and the accuracy of the simplified models is evaluated. It is shown that this approach greatly reduces the number of species and reactions considered, while showing good agreement with the full model, with a root-mean-square error of no more than 4 %. Thus, the complicated physicochemical processes in non-equilibrium CO2 thermal plasmas can be characterized by relatively few species and reactions. It is suggested that the two-temperature chemical kinetic model developed in this paper can be applied to the full range of pressures that occur in arc welding, arc quenching and other industrial applications. In addition, the simplified methods can be applied in multi-dimensional models to reduce the chemical complexity and computing time while capturing the main physicochemical processes in non-equilibrium CO2 thermal plasmas. 相似文献