全文获取类型
收费全文 | 6855篇 |
免费 | 888篇 |
国内免费 | 2013篇 |
专业分类
化学 | 4680篇 |
晶体学 | 267篇 |
力学 | 2076篇 |
综合类 | 52篇 |
数学 | 340篇 |
物理学 | 2341篇 |
出版年
2024年 | 33篇 |
2023年 | 124篇 |
2022年 | 326篇 |
2021年 | 341篇 |
2020年 | 303篇 |
2019年 | 231篇 |
2018年 | 172篇 |
2017年 | 314篇 |
2016年 | 373篇 |
2015年 | 320篇 |
2014年 | 419篇 |
2013年 | 528篇 |
2012年 | 471篇 |
2011年 | 505篇 |
2010年 | 461篇 |
2009年 | 496篇 |
2008年 | 487篇 |
2007年 | 567篇 |
2006年 | 430篇 |
2005年 | 405篇 |
2004年 | 405篇 |
2003年 | 359篇 |
2002年 | 277篇 |
2001年 | 219篇 |
2000年 | 196篇 |
1999年 | 149篇 |
1998年 | 136篇 |
1997年 | 121篇 |
1996年 | 108篇 |
1995年 | 79篇 |
1994年 | 76篇 |
1993年 | 45篇 |
1992年 | 63篇 |
1991年 | 44篇 |
1990年 | 31篇 |
1989年 | 21篇 |
1988年 | 28篇 |
1987年 | 21篇 |
1986年 | 24篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1979年 | 8篇 |
1978年 | 1篇 |
1974年 | 1篇 |
1971年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有9756条查询结果,搜索用时 9 毫秒
71.
Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers with polygonal porosity and highly ordered structures. The most prominent feature of the COFs is their excellent crystallinity and highly ordered modifiable one-dimensional pores. Since the first report of them in 2005, COFs with various structures were successfully synthesized and their applications in a wide range of fields including gas storage, pollution removal, catalysis, and optoelectronics explored. In the meantime, COFs also exhibited good performance in chemical and biological sensing, because their highly ordered modifiable pores allowed the selective adsorption of the analytes, and the interaction between the analytes and the COFs’ skeletons may lead to a detectable change in the optical or electrical properties of the COFs. In this review, we firstly demonstrate the basic principles of COFs-based chemical and biological sensing, then briefly summarize the applications of COFs in sensing some substances of practical value, including some gases, ions, organic compounds, and biomolecules. Finally, we discuss the trends and the challenges of COFs-based chemical and biological sensing. 相似文献
72.
V. Efimova A. Derzsi A. Zlotorowicz V. Hoffmann Z. Donkó J. Eckert 《Spectrochimica Acta Part B: Atomic Spectroscopy》2010
The energy transfer to the discharge gas due to various collision processes in the plasma and the heating of the sample are widely known effects in glow discharge (GD) spectroscopy. Despite of the considerable thermal effects and their serious influence on the performance of GD devices, measurements of the discharge gas and sample temperatures are not common at all. The gas temperature depends on the power absorption of the discharge as well as on the temperature of boundaries (sample and anode). In this work the influence of different anode materials in a Grimm-type source on the voltage–current characteristics, crater shapes and GD spectra is investigated. Anodes made of titanium and copper alloys, graphite, and steel with thermal conductivities covering a wide range of values are used. For a fixed voltage and pressure a decrease of the measured current is observed for bad thermal conductive anodes. Cooling of the sample results in an increase of the measured current. Both observations can be explained by changes of the discharge gas temperature. The temperature of the sample is measured from the back side and compared for different anodes. Further, it is found that the choice of the anode material (i) has no significant influence on the crater shape, (ii) results in slightly different sputtering rates and (iii) strong differences of the GD spectra. 相似文献
73.
J. Agrisuelas J. J. García-Jareño D. Gimenez-Romero F. Negrete F. Vicente 《Journal of Solid State Electrochemistry》2009,13(10):1599-1603
Electrochemical techniques are applied to estimate the fractal dimension value of electroactive surface structures. However,
the fractal dimension value is an abstract concept, which sometimes is hard to understand. Herein, this abstract concept is
used to calculate the fractional content of the nickel/graphite–polypropylene hybrid composite material, putting into practice
this concept in the study of composite materials. 相似文献
74.
Graded PZT ceramics for piezoelectric transformers 总被引:1,自引:0,他引:1
In the present study two types of the synthesized Pb(Zr1−xTix)O3 (PZT) powders differing in Zr/Ti ratio were used to prepare the spatially inhomogeneous (i.e., graded) structure. A position-dependent chemical composition was expected to cause the property gradient. Disk-shaped compacts were prepared in a way such that two different orientations of the radial gradients were formed. The solid state sintering under pressure was utilized to prepare ceramics. Simultaneous thermal analysis was used to study thermal behavior of the ceramic powders. Graded PZT ceramics were characterized using X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. It was also characterized in terms of its dielectric properties by both bridge technique and the impedance spectroscopy. On the basis of graded PZT ceramics the disk-shaped radial mode piezoelectric transformer was developed and fabricated. 相似文献
75.
Due to the high capacity,moderate voltage platform,and stable structure,Li3VO4(LVO) has attracted close attention as feasible anode material for lithium-ion capacitor.However,the intrinsic low electronic conductivity and sluggish kinetics of the Li+ insertion process severely impede its practical application in lithium-ion capacitors(LICs).Herein,a carbon-coated Li3VO4(LVO/C) hierarchical structure was prepared by a facial one-step solid-sta... 相似文献
76.
在水热体系中, 以2,2'-(乙烯二氧)双(乙胺)为模板剂, 合成了3种含二价金属杂原子的开放骨架磷酸铝化合物M(Ⅱ)-CJ50(|C6H17N2O2| [MAl3P4O16], 其中M=Mg, Mn和Fe). 单晶及粉末X射线衍射分析表明, 这3种化合物与以咪唑为模板剂合成的含三价金属杂原子的M(Ⅲ)-CJ50具有相似的骨架拓扑结构. 二者的区别在于: 由于使用了还原性较强的醚胺作模板剂, M(Ⅱ)-CJ50结构中的金属杂原子具有比M(Ⅲ)-CJ50更低的氧化态; M(Ⅱ)-CJ50中的金属杂原子与1个醚胺模板剂分子中的2个醚氧原子形成双齿配位, 而M(Ⅲ)-CJ50中的金属杂原子则与2个咪唑模板剂分别形成单齿配位. 此外, 磁性测试结果表明, 由于金属杂原子的氧化态以及配体模板剂分子的差异, 导致M(Ⅱ)-CJ50中的过渡金属杂原子处于电子高自旋态, 而M(Ⅲ)-CJ50中的杂原子则处于低自旋态. 相似文献
77.
HAN Yun-Yu ZHOU Rui-Ling YANG Yu-Guo ZHOU WuDepartment of Chemistry Shandong Teachers'''' University Jinan Shandong ChinaRUAN Xiao-Lan Technological School Jinan Steel Plant Jinan Shandong China 《中国化学》1995,13(2):118-123
The photovoltaic effects of chlorophyll-a(chla) and the effects of stearic acid, egg phosphatide and cholesterol on those were investigated by means of measuring the photoinduced potentials of SnO2/chla electrodes. Because of the formation of liquid crystal states, appropriate concentrations of stearic acid and egg phosphatide added in a certain system could increase the photovoltaic effects of chla. Cholesterol always decreased the photovoltaic effects of chla because there was no liquid crystal state formed with it. 相似文献
78.
应用修正的BET热力学模型对Mg(NO3)2-NH4NO3-H2O三元体系和LiNO3-Mg(NO3)2-NH4NO3-H2O四元体系在273~320 K的相图进行预测,并找到一个相变温度较低的四元共晶点Mg(NO3)2.6H2O-LiNO3.3H2O-NH4NO3,其质量百分数组成为:25.5%的硝酸铵,28.4%的硝酸锂,13.8%的硝酸镁和32.3%的水,通过实验对共晶点组成材料的吸放热行为进行测定,发现其熔化温度为286.3 K,且DSC测试其相变热焓为192.7 J.g-1,表明该材料可用作潜在的低温相变储能材料。 相似文献
79.
80.
Nano-crystalline FeOOH particles(5~10 nm) have been uniformly mixed with electric matrix of single-walled carbon nanotubes(SWNTs)for forming FeOOH/SWNT composite via a facile ultrasonication method. Directly using the FeOOH/SWNT composite(containing 15 wt%SWNTs) as anode material for lithium battery enhances kinetics of the Li+insertion/extraction processes, thereby effectively improving reversible capacity and cycle performance, which delivers a high reversible capacity of 758 mAh g-1under a current density of 400 mA g-1even after 180 cycles, being comparable with previous reports in terms of electrochemical performance for FeOOH anode. The good electrochemical performance should be ascribed to the small particle size and nano-crystalline of FeOOH, as well as the good electronic conductivity of SWNT matrix. 相似文献