全文获取类型
收费全文 | 4250篇 |
免费 | 734篇 |
国内免费 | 531篇 |
专业分类
化学 | 2992篇 |
晶体学 | 58篇 |
力学 | 308篇 |
综合类 | 18篇 |
数学 | 406篇 |
物理学 | 1733篇 |
出版年
2024年 | 11篇 |
2023年 | 106篇 |
2022年 | 127篇 |
2021年 | 172篇 |
2020年 | 189篇 |
2019年 | 202篇 |
2018年 | 174篇 |
2017年 | 158篇 |
2016年 | 265篇 |
2015年 | 199篇 |
2014年 | 230篇 |
2013年 | 289篇 |
2012年 | 423篇 |
2011年 | 429篇 |
2010年 | 274篇 |
2009年 | 241篇 |
2008年 | 258篇 |
2007年 | 253篇 |
2006年 | 215篇 |
2005年 | 177篇 |
2004年 | 131篇 |
2003年 | 127篇 |
2002年 | 98篇 |
2001年 | 64篇 |
2000年 | 79篇 |
1999年 | 82篇 |
1998年 | 81篇 |
1997年 | 74篇 |
1996年 | 64篇 |
1995年 | 43篇 |
1994年 | 49篇 |
1993年 | 47篇 |
1992年 | 47篇 |
1991年 | 30篇 |
1990年 | 22篇 |
1989年 | 12篇 |
1988年 | 16篇 |
1987年 | 9篇 |
1986年 | 20篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1973年 | 1篇 |
1970年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有5515条查询结果,搜索用时 140 毫秒
991.
Yuqing Li Ying Huang Shuhua QiLei Niu Yinling ZhangYanfei Wu 《Applied Surface Science》2012,258(8):3659-3666
Strontium ferrite particles were firstly prepared by sol-gel method and self-propagating synthesis, and then the polyaniline/strontium ferrite/multiwalled carbon nanotubes composites were synthesized through in situ polymerization approach. Structure, morphology and properties of the composite were characterized by various instruments. XRD analysis shows that the output of PANI increases with the increase of the content of MWCNTs, due to the large surface area of MWCNTs. Because of the coating of PANI, the outer diameter of MWCNTs increases from 10 nm to 20-40 nm. The electrical conductivity of the composites increases with the amount increase of MWCNTs and reaches 7.2196 S/cm in the presence of 2 g MWCNTs. The coercive force of the composites prepared with 2 g MWCNTs is 7457.17 Oe, which is much bigger than that of SrFe12O19 particles 6145.6 Oe, however, both the saturation magnetization and the remanent magnetization of the composite become much smaller than those of SrFe12O19 particles. The electromagnetic properties of the composite are excellent in the frequency range of 2-18 GHz, which mainly depend on the dielectric loss in the range of 2-9 GHz, and mainly on the magnetic loss in the range of 9-18 GHz. 相似文献
992.
993.
Qingguo Wang Liangbi Su Hongjun Li Lihe Zheng Xiaodong Xu Feng Wu Huili Tang Dapeng Jiang Weichao Chen Jun Xu 《Crystal Research and Technology》2012,47(5):585-590
Nd‐doped PbClF crystals were grown with modified Bridgman method. Broad and flat emission band at 1.0 μm was observed. The FWHM value of 0.0091 wt.% Nd3+‐doped PbClF crystal at 1064 nm reached up to 30 nm with the peak emission cross‐section of 1.05×10‐19 cm2. All the results indicated that Nd‐doped PbClF crystal should be a promising tunable and ultrafast laser material. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
994.
995.
Jun LuoHai-jun Niu Wen-jun WuCheng Wang Xu-duo Bai Wen Wang 《Solid State Sciences》2012,14(1):145-149
For the purpose of increasing the energy conversion efficiency of dye-sensitized solar cells (DSSCs), multi-wall carbon nanotube (MWCNT)/polythiophene (PTh) composite film counter electrode has been fabricated by electrophoresis and cyclic voltammetry (CV) in sequence. The morphology and chemical structure have been characterized by transmission electron microscopy (TEM), scanning electron microscope (SEM), and Raman spectroscopy respectively. The overall energy conversion efficiency of the DSSC employing the MWCNT/PTh composite film has reached 4.72%, which is close to that of the DSSC with a platinum (Pt) counter electrode (5.68%). Compared with a standard DSSC with MWCNT counter electrode whose efficiency is 2.68%, the energy conversion efficiency has been increased by 76.12% for the DSSC with MWCNT/PTh counter electrode. These results indicate that the composite film with high conductivity, high active surface area, and good catalytic properties for I3− reduction can potentially be used as the counter electrode in a high-performance DSSC. 相似文献
996.
Xuebin Wang Jipeng Si Houzhang Tan Yanqing Niu Chao Xu Tongmo Xu 《Journal of Thermal Analysis and Calorimetry》2012,109(1):403-412
The combustion kinetics of waste capsicum stalk (WCS) in Western China is investigated through thermogravimetric analysis compared with sawdust and coal, and co-combustion of WCS with coal is also investigated. Results show that the ignition characteristics of WCS is better than that of sawdust and coal, and the activation energy E of WCS-volatile combustion and WCS-char combustion are 78.55?kJ?mol?1 and 44.59?kJ?mol?1. However, integrating the characteristics of ignition and burnout, the combustion characteristic factor (S N) of WCS is lower than that of sawdust. With the increasing in the heating rate, the ignition of WCS is delayed. Oxygen concentration $ C_{{{\text{O}}_{2} }} $ affects E and k 0 of volatile combustion largely under rich-oxygen condition, when $ C_{{{\text{O}}_{2} }} $ increases from 0.2 to 0.8, E has increased threefold and k 0 also intensively increases from 106 to 1013?C1022. Oppositely, effect of $ C_{{{\text{O}}_{2} }} $ on the E and k 0 of char combustion is little, and there is an exponential relationship $ S_{\text{N}} = 7. 1 2 8 \times 10^{ - 9} \times { \exp }(C_{{{\text{O}}_{2} }} /0. 3 6 8) - 6. 1 2 6 \times 10^{ - 9} $ between S N and $ C_{{{\text{O}}_{2} }} $ . For the tests of co-combustion, all the experimental and weighted-average curves coincide well, and there is no remarkable synergistic effect. With the increase of mixing ratio that WCS added, E and k 0 of volatile combustion increase, but correspondingly E and k 0 of char combustion decrease. 相似文献
997.
998.
We have prepared the hydrophobic amino-functionalized ionic liquid (IL) 1-(2-aminoethyl)-3-butylimidazolium hexafluorophosphate and investigated its extraction behavior for copper(II) ion as a model cation. The IL, due to the presence of an amino group, is capable of complexing Cu(II) in a ratio of 6:1. The parameters affecting the extraction efficiency were optimized. The IL-based liquid–liquid microextraction was successfully applied to the analysis of Cu(II) in an environmental water standard reference material. The results are promising in terms of liquid–liquid microextraction, separation, and preconcentration of Cu(II). Figure
A hydrophobic amino-functionalized ionic liquid (IL) [NH2C2C4im][PF6] was synthesized. The IL exhibits good extractability for copper (II) ion due to the presence of an amino group. 相似文献
999.
In this work, traditional cloud point extraction (CPE) pattern was changed and improved by the proposed rapidly synergistic CPE. Using octanol as cloud point revulsant and synergic reagent, non-ionic surfactant Triton X-114 (TX-114) accomplished room temperature extraction rapidly without heating in water bath. The improved extraction was named as rapidly synergistic cloud point extraction (RS-CPE). Compared with traditional CPE, RS-CPE was accomplished in 1 min with considerably high extraction efficiency. The improved CPE pattern was coupled with flame atomic absorption spectrometry (FAAS) for the extraction and detection of trace lead in real and certified water samples with satisfactory analytical results. The proposed method greatly improved the sensitivity of FAAS for the determination of lead. Under the optimal conditions, the limit of detection (LOD) for lead was 4.3 μg/L, with enhancement factor (EF) of 39. Factors influencing RS-CPE efficiency, such as concentrations of surfactant TX-114 and octanol, concentration of chelating agent, pH, conditions of phase separation, environmental temperature, salt effect and instrumental conditions, were studied systematically. 相似文献
1000.
Jiaoran Meng Xiaodong Zhang Hao Wu Jing Bu Chenyi Shi Chunhui Deng Yu Mao 《Analytica chimica acta》2012
Conditioned place preference (CPP) is a widely used model to explore the mechanism of context-dependent learning. In this work, we developed a GC–MS method to investigate the metabolites in mice brain which was used to study the mechanism of context-dependent learning associated with rewarding effect of morphine. Metabolites were extracted from brain tissues and derivatized followed by analysis by gas chromatography/mass spectrometry (GC–MS). In total, 69 peaks were identified as known compounds. By a Wilcoxon ran sum test with p value ≤0.05, 21 metabolites were selected and considered as the potential biomarkers of morphine in mice brain. Using principal component analysis (PCA) and receiver-operator characteristic (ROC) curves, a model was constructed with a combination of these 21 metabolic markers. Multivariate statistics of the model yielded separation between the two groups with an area under the curve value of 0.947. Some metabolites were further discussed in detail about their pathway. Results showed that our technique can be successfully applied to profile for biomarkers and in understanding molecular mechanisms of drug abuse. 相似文献