全文获取类型
收费全文 | 24338篇 |
免费 | 3937篇 |
国内免费 | 3288篇 |
专业分类
化学 | 18383篇 |
晶体学 | 366篇 |
力学 | 1285篇 |
综合类 | 239篇 |
数学 | 2911篇 |
物理学 | 8379篇 |
出版年
2024年 | 18篇 |
2023年 | 421篇 |
2022年 | 522篇 |
2021年 | 772篇 |
2020年 | 945篇 |
2019年 | 944篇 |
2018年 | 797篇 |
2017年 | 789篇 |
2016年 | 1093篇 |
2015年 | 1195篇 |
2014年 | 1438篇 |
2013年 | 1867篇 |
2012年 | 2172篇 |
2011年 | 2290篇 |
2010年 | 1673篇 |
2009年 | 1571篇 |
2008年 | 1812篇 |
2007年 | 1580篇 |
2006年 | 1469篇 |
2005年 | 1207篇 |
2004年 | 945篇 |
2003年 | 758篇 |
2002年 | 754篇 |
2001年 | 607篇 |
2000年 | 459篇 |
1999年 | 451篇 |
1998年 | 395篇 |
1997年 | 274篇 |
1996年 | 298篇 |
1995年 | 282篇 |
1994年 | 236篇 |
1993年 | 215篇 |
1992年 | 176篇 |
1991年 | 204篇 |
1990年 | 175篇 |
1989年 | 145篇 |
1988年 | 106篇 |
1987年 | 102篇 |
1986年 | 76篇 |
1985年 | 83篇 |
1984年 | 40篇 |
1983年 | 42篇 |
1982年 | 31篇 |
1981年 | 25篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1976年 | 11篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
11.
Liu Jingze Fei Qingguo Wu Shaoqing Tang Zhenhuan Zhang Dahai 《Nonlinear dynamics》2021,106(3):1869-1890
Nonlinear Dynamics - Rolling bearing and squeeze film damper will introduce structural nonlinearity into the dynamic model of aeroengine. Rubbing will occur due to the clearance reduction design of... 相似文献
12.
Jie Pan Yan Bao Hao Wang Fucong Lyu Lu Liu Chong Wang Xinxue Tang Jian Lu Yang Yang Li 《Particle & Particle Systems Characterization》2021,38(10):2100094
The high-entropy materials have raised much attention in recent years due to their extraordinary performances in mechanical, catalysis, energy storage fields. Herein, a new type of high-entropy hydroxides (e.g., NiFeCoMnAl(OH)x) that are amorphous and capable of broad solar absorption is reported. A facile one-pot co-precipitation method is employed to synthesize these amorphous high-entropy hydroxides (a-HEHOs) under ambient conditions. The a-HEHOs thus obtained display widely tunable bandgap (e.g., from 2.6 to 1.1 eV) due to their high-entropy and amorphous characteristics, enabling efficient light absorbance and photothermal conversion in the solar regime. Further solar water evaporation measurements show that the a-HEHOs delivered a considerable energy conversion efficiency of 55%, comparable to black titanium oxides that are synthesized using more complex and expensive methods. 相似文献
13.
Acta Mathematicae Applicatae Sinica, English Series - So far there have been few results presented on the exponential stability for time-changed stochastic differential equations. The main aim of... 相似文献
14.
The Ramanujan Journal - In this paper we investigate several infinite products with vanishing Taylor coefficients in arithmetic progressions. These infinite products are closely related to... 相似文献
15.
为进一步提高对偏硼酸钠电催化还原的效率,采用化学镀的方法,以铜片为基体,PdCl2乙醇胶体溶液为活化剂,乙醇为化学镀溶剂,制备了稀土复合电极La-Ni-B.并采用XRD、SEM、EDS方法对催化剂进行表征分析,结果表明稀土合金以纳米颗粒的形式附着在基体表面,所得合金膜是非晶态的.通过循环伏安法研究了复合电极La-Ni-B用于电解偏硼酸钠制备硼氢化钠的可行性.以硼氢化钠实际生产量为指标,探讨了直流、脉冲两种不同供电方式、脉冲电流频率、电解时间对电解行为的影响.结果表明稀土镧对电解偏硼酸钠有催化作用,以20 mL镀液制备的复合电极,在脉冲频率阳极时间T1=1 s,阴极时间T2=1 s时,最佳电解时间为4h.复合电极在重复使用3次的情况下,硼氢化钠产量降低15;,催化剂的重复使用性能良好. 相似文献
16.
Qi-Jun Li Ya-Jie Ren Qin Xie Min Wu Hua-Xing Feng Li-Mei Zheng Hua-Xin Zhang Jin-Qiao Long Tian-Shun Wang 《应用有机金属化学》2020,34(10):e5813
Two nickel complexes, [Ni(tpen)](ClO4)2.0.5CH3COCH3 ( 1 ) and [Ni(tpbn)](ClO4)2 ( 2 ), of tetrapyridyl ligands N,N,N′,N′-tetrakis(2-pyridyl-methyl)-1,2-ethanediamine (tpen) and N,N,N′,N′-tetrakis(2-pyridyl-methyl)-1,4-butanediamine (tpbn) were prepared and their catalysis for water oxidation reaction (WOR) studied. In 0.1 M phosphate buffer solution (PBS) of pH 8.0, complex 1 is a homogeneous molecular catalyst with an overpotential of ~440 mV and a Faradaic efficiency of 89%. At pH ≥ 9.0, complex 1 degraded gradually during the catalytic process and formed NiOx composite (nickel oxide with general formula NixOyHz) active for WOR. In contrast, complex 2 deteriorated under measured conditions (pH 8.0–12.0) and formed NiOx composite active for WOR. The NiOx composite derived from 1 in 0.1 M PBS at pH 11.0 showed an activity with an overpotential of ~500 mV, a Tafel slope of ~90 mV/decade and a Faradaic efficiency of 97%. Mechanisms were proposed for water oxidation catalyzed by 1 and 2 . This work revealed that the catalytic activity of the nickel complexes was related to the flexibility of the tetrapyridyl ligands and the adaptability of the coordination sphere of the nickel(II) center. 相似文献
17.
Nonlinear Dynamics - This paper aims at computing M-lump solutions for the $$(3+1)$$ -dimensional nonlinear evolution equation. These solutions in all directions decline to an identical state... 相似文献
18.
以六水氯化镁和六次甲基四胺为原料,采用水热法合成四方体MgO,考察其对有机染料甲基橙和亚甲基蓝的吸附行为.通过TGA-DTA、SEM、XRD、N2-sorption和FT-IR等手段表征样品.结果表明,原料浓度、温度和表面活性剂对四方体MgO结构的形成影响较小,而反应时间的延长有助于有序结构的组装.温度170℃、时间24h、MgCl2·6H2O与C6H12N4浓度比为1∶2和表面活性剂PVP是制备四方体MgO的最佳条件.在溶液浓度10mg · L-1的单一吸附实验过程中,四方体MgO对甲基橙和亚甲基蓝的去除率分别为91.3;和22.3;,吸附过程均为单层吸附且符合Langmuir等温吸附模型和伪二级吸附动力学方程.在溶液浓度40 mg·L-1、甲基橙和亚甲基蓝浓度比3∶1的混合溶液吸附过程中,四方体MgO对甲基橙和亚甲基蓝的去除率分别为80.1;和97.9;. 相似文献
19.
Jian-Kun Sun Linlin Zhang Liang Yue Tang Tang Wen-Jie Jiang Yun Zhang Zhenxiao Pan Xinhua Zhong Jin-Song Hu Li-Jun Wan 《中国科学:化学(英文版)》2018,61(10):1338-1344
Developing efficient counter electrodes (CEs) and quantum dots made of earth-abundant and non-toxic elements is essential but still challenging for quantum dot-sensitized solar cells (QDSSCs). Here, we report a facile strategy to prepare self-supported and robust CoS2 and NiS nanocrystals-assembled nanosheets directly grown on carbon paper (MSx NS@CP) as efficient counter electrodes for QDSSCs. Such CEs integrate the merits of fast electron transfer from interconnected conductive scaffold, efficient mass transfer from hierarchically vertical nanosheet on 3D open substrate, as well as abundant highly active catalytic sites from metal sulphide nanocrystal units. As a result, QDDSCs based on such CoS2 NS@CP and NiS NS@CP CEs achieve a PCE of 8.88% and 7.53%, respectively. The detailed analyses suggest that CoS2 NS@CP has the highest catalytic activity and shows the lowest charger transfer resistance, leading to the highest PCE. These findings may inspire the design and exploration of other self-supported efficient CEs by integrating highly active catalysts onto 3D conductive networks for efficient QDSSCs. 相似文献
20.
Dr. Wenyan Hao Yuchen Sha Dr. Yi Deng Yi Luo Li Zeng Shan Tang Dr. Yue Weng Prof. Dr. Chien-Wei Chiang Prof. Dr. Aiwen Lei 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(19):4931-4934
An in situ generated oxidation species of nickel quinolinylpropioamide intermediate was produced. Characterization by X-ray absorption near edge structure (XANES) and EPR provides complementary insights into this oxidized nickel species. With aliphatic amides and isocyanides as substrates, a nickel-catalyzed facile synthesis of structurally diverse five-membered lactams could be achieved. 相似文献