全文获取类型
收费全文 | 172篇 |
免费 | 118篇 |
国内免费 | 111篇 |
专业分类
化学 | 201篇 |
晶体学 | 1篇 |
力学 | 9篇 |
数学 | 19篇 |
物理学 | 171篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 12篇 |
2020年 | 10篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 13篇 |
2016年 | 9篇 |
2015年 | 13篇 |
2014年 | 27篇 |
2013年 | 19篇 |
2012年 | 24篇 |
2011年 | 28篇 |
2010年 | 34篇 |
2009年 | 37篇 |
2008年 | 31篇 |
2007年 | 33篇 |
2006年 | 15篇 |
2005年 | 17篇 |
2004年 | 20篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1993年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有401条查询结果,搜索用时 343 毫秒
31.
32.
采用碳酸盐替代高钼酸盐电解还原的方法成功制备出了准二维电荷密度波导体钾紫青铜单晶.通过x射线衍射、透射电子显微术等方法对单晶进行结构分析表明:晶胞参数a=b=0.5540nm,c=1.3508nm,单晶为三角晶系,对称群为P3.电阻温度关系曲线的测量显示:钾紫青铜KxMo6O17单晶在112K附近发生金属到金属的Peierls相变.
关键词:
钾紫青铜
电荷密度波
Peierls相变 相似文献
33.
Tetramic acid derivatives and polyphenols from sponge-derived fungus and their biological evaluation
Jun-Feng Wang Xiaochu Qin Fu-Quan Xu Tianyu Zhang Shengrong Liao Xiuping Lin 《Natural product research》2015,29(18):1761-1765
Fifteen compounds, including two tetramic acid derivatives, penicillenol A1 (1) and penicillenol A2 (2), six polyphenols containing both phenolic bisabolane sesquiterpenoid and diphenyl ether units, expansols A–F (3–8), together with six phenolic bisabolane sesquiterpenoids (9–14) and diorcinol (15), were isolated from the fermentation broth of the marine-derived fungus ZSDS1-F11 isolated from the sponge Phakellia fusca Thiele collected in the Yongxing island of Xisha. Their structures were elucidated mainly by using extensive NMR spectroscopic and mass spectrometric analyses. Compounds 3–5, 7 and 8 showed potent COX-1 inhibitory activity with IC50 values of 5.3, 16.2, 30.2, 41.0 and 56.8 μM, respectively. Meanwhile, compounds 3–8 showed potent COX-2 inhibitory activity with IC50 values of 3.1, 5.6, 3.0, 5.1, 3.2 and 3.7 μM, respectively. In addition, compound 1 exhibited antituberculosis activity with 96.1% inhibition at concentration of 10 μM. 相似文献
34.
35.
A novel method for achieving a copper(II)-catalyzed domino reaction for the construction of 2-aryl quinazolinones,without the addition of any ligand and additive,has been developed.The domino reaction achieved N-(a-substituted)benzylation,benzylic C–H amidation,and C–C(or C–H) bond cleavage. 相似文献
36.
Xue-Mei Li Rui-Rui Zhao Yan Yang Xue Wei Lv Yu-Ling Wei Rui Tan Jun-Feng Zhang Ying Zhou 《中国化学快报》2017,28(6):1258-1261
A rhodamine-based sensor (1) has been developed for the detection of chromium ions. Cr3+-induced opening of the rhodamine spirocycle in sensor (1) led to the distinct colorimetric and fluorescence responses. Among all the tested ions, only Cr3+ generated a significant fluorescence enhancement of up to 13-fold, which indicated the high selectivity of 1. Sensor (1) was successfully applied in the in vivo fluorescence imaging of Cr3+ in C. elegans. The results provided solid evidences for the future estimation of Cr3+ in environmental applications and tobacco samples. 相似文献
37.
分时偏振成像系统需要通过旋转检偏器获取场景的偏振信息(I, Q, U), 检偏器的前后表面间不平行(也称为楔角)将导致成像光束发生偏离且随检偏器旋转而旋转, 这将降低偏振成像系统的空间分辨率和偏振测量精度. 本文提出调整检偏器相对于入射主光轴倾斜角的方法来补偿上述光束偏离. 以格兰棱镜作为检偏器, 根据几何光学理论, 推导了分时偏振成像系统光束偏离的一阶近似补偿模型, 获得倾斜角与格兰棱镜楔角之间的函数关系, 并通过仿真模拟验证了该补偿方法的可行性和有效性. 研究结果表明, 将格兰棱镜置于汇聚光路中, 光束偏离的一阶误差可以通过调节格兰棱镜的倾斜角有效补偿; 倾斜角大小与棱镜折射率、楔角及棱镜距电荷耦合元件靶面的距离成正比, 与棱镜厚度成反比. 该结果为研制高精度分时偏振成像系统提供了切实可行的理论依据. 相似文献
38.
Microcapsules containing phase change materials (microPCMs) with melamine-formaldehyde (MF) shells have been applied in many
thermo-regulation or thermo-saving fields. However, it is still essential to decrease the residual formaldehyde and enhance
the mechanical properties of MF shells. The objective of this work was to fabricate a series of microPCMs containing paraffin
by an in situ polymerization method using methanol-modified melamine-formaldehyde (MMF) prepolymer as shell material and investigate
the physicochemical properties and mechanical characters of these microPCMs. FT-IR analysis indicates that the methanol-modified
method can reduce the free formaldehyde in shell material through increasing the cross-linking structure. Optical microphotographs
and SEM morphologies show that the microPCMs have regular globe shape with smooth surface. With the increasing of emulsion
stirring rates from 1,000 to 5,000 rpm, the average diameters decreased sharply from 27 to 2.5 μm. The phase change temperature
(T
m) of microPCMs samples with the core/shell ratios of 3/1, 2/1, 1/1, and 2/1 are 22.6, 23.0, 23.4, and 23.9 °C, which are nearly
equaled to the T
m of pure paraffin (22.5 °C). Mechanical properties test data show that the MMF shells have larger yield point value than that
of MF shell for microPCMs with the same core/shell ratio, which means that the methanol-modified method shell can greatly
enhanced the resistance of deformation for MF shells. Moreover, MMF shells can resist the interface extrusion force in epoxy
resin owing to their higher yield point of enhanced MMF shell. 相似文献
39.
Jun-Feng Su Xin-Yu Wang Zhen Huang Yun-Hui Zhao Xiao-Yan Yuan 《Colloid and polymer science》2011,289(14):1535-1542
Microencapsulated phase change materials (microPCMs) have been widely applied in solid matrix as thermal-storage or temperature-controlling
functional composites. The thermal conductivity of these microPCMs/matrix composites is an important property need to be considered.
In this study, a series of microPCMs have been fabricated using the in situ polymerization with various core/shell ratio and
average diameter; the thermal conductivity of microPCMs/epoxy composites were investigated in details. The results show that
the microPCMs have smooth surface and regular global shape with compact methanol–melamine–formaldehyde shell. The shell thickness
does not greatly influence the phase change behaviors of PCM. Moreover, smaller microPCMs embedded in epoxy can improve the
thermal transmission ability of composites. The effect of thermal conductivity of composites can be improved with higher volume
fraction (10–30%) of microPCMs; and smaller size microPCMs with the same content of PCM may also enhance the thermal transmission
area in matrix. Modeling analysis of relative thermal conductivity indicates that mixing higher thermal conductivity additive
in PCM or matrix is an appropriate method to improve the thermal conductivity of microPCMs/matrix composites. 相似文献
40.
采用“预制层硒化法”制备CuIn1-xGaxSe2 (CIGS)薄膜. 基于自主设计的“双层管式硒化装置”, 通过控制硒蒸气浓度优化退火工艺, 研究硒蒸气浓度对薄膜光电性能的影响. 利用俄歇电子能谱(AES)和X射线衍射分析(XRD)等手段对不同硒浓度氛围下生成的CIGS薄膜的成分和物相进行表征, 并在AM1.5、1000 W·m-2的标准光照条件下比较相应CIGS电池器件的输出性能. 实验结果表明: 饱和硒蒸气下退火得到的样品, 基底钼膜遭到严重腐蚀破坏, 失去背电极功能; 在低浓度硒气氛下退火不能有效消除CIGS薄膜的偏析和缺陷, 以致光电转换效率低; 而在无硒惰性氛围下退火的样品, 生成了物相均一化的CIGS薄膜, 由此制备的CIGS电池取得了8.5%的转换效率. 相似文献