全文获取类型
收费全文 | 213篇 |
免费 | 56篇 |
国内免费 | 18篇 |
专业分类
化学 | 186篇 |
晶体学 | 4篇 |
力学 | 16篇 |
综合类 | 2篇 |
数学 | 24篇 |
物理学 | 55篇 |
出版年
2022年 | 5篇 |
2021年 | 8篇 |
2020年 | 4篇 |
2019年 | 9篇 |
2018年 | 15篇 |
2017年 | 18篇 |
2016年 | 21篇 |
2015年 | 13篇 |
2014年 | 23篇 |
2013年 | 20篇 |
2012年 | 21篇 |
2011年 | 13篇 |
2010年 | 5篇 |
2009年 | 16篇 |
2008年 | 10篇 |
2007年 | 6篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 16篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1988年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有287条查询结果,搜索用时 15 毫秒
71.
Target projection (TP) also called target rotation (TR) was introduced to facilitate interpretation of latent‐variable regression models. Orthogonal partial least squares (OPLS) regression and PLS post‐processing by similarity transform (PLS + ST) represent two alternative algorithms for the same purpose. In addition, OPLS and PLS + ST provide components to explain systematic variation in X orthogonal to the response. We show, that for the same number of components, OPLS and PLS + ST provide score and loading vectors for the predictive latent variable that are the same as for TP except for a scaling factor. Furthermore, we show how the TP approach can be extended to become a hybrid of latent‐variable (LV) regression and exploratory LV analysis and thus embrace systematic variation in X unrelated to the response. Principal component analysis (PCA) of the residual variation after removal of the target component is here used to extract the orthogonal components, but X‐tended TP (XTP) permits other criteria for decomposition of the residual variation. If PCA is used for decomposing the orthogonal variation in XTP, the variance of the major orthogonal components obtained for OPLS and XTP is observed to be almost the same, showing the close relationship between the methods. The XTP approach is tested and compared with OPLS for a three‐component mixture analyzed by infrared spectroscopy and a multicomponent mixture measured by near infrared spectroscopy in a reactor. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
72.
通过主成分分析方法,选取2006、2011和2016年广东省各市邮电业务数据,对广东省21个地级市的邮政和通信事业发展状况进行分析和发展水平层次划分,从时间和地域空间两个维度对广东省各地区邮电业发展情况进行排名分组.结果表明,当前广东省各地区邮电业发展状况存在显著的地区差异. 相似文献
73.
Preparation and functionalization of linear and reductively degradable highly branched cyanoacrylate‐based polymers
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Houliang Tang Nicolay V. Tsarevsky 《Journal of polymer science. Part A, Polymer chemistry》2016,54(23):3683-3693
Ethyl cyanoacrylate (ECA) was polymerized radically in the presence of small amounts of trifluoroacetic acid as effective inhibitor of incidental anionic polymerization. Methyl methacrylate and other functional vinyl monomers (e.g., 2‐chloroethyl and 2‐bromoethyl methacrylate) were copolymerized with ECA, yielding linear ECA‐rich copolymers, which could readily undergo further modifications, for instance nucleophilic substitution with azide. In the presence of a disulfide‐containing dimethacrylate crosslinker and a chain transfer agent (CBr4) during the free radical copolymerizations of ECA with methacrylates, highly branched ECA‐based polymers containing disulfide groups at the branching points were obtained prior to gelation. The polymers degraded upon addition of reducing agents. The prepared polymers, which contained peripheral (chain end) alkyl bromide groups as well as pendant alkyl chloride or bromide groups were then reacted with sodium azide, affording azide‐containing polymers that were reacted with functional alkynes under copper‐catalyzed “click” chemistry conditions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3683–3693 相似文献
74.
Apparent molar heat capacities and volumes of pentanol, 0.05m in decyl-, tetradecyl- and hexadecyltrimethylammonium bromides micellar solutions, were measured at 25°C. They were assumed to approach the standard infinite dilution values and rationalized by means of previously reported equations following which the distribution constant between the aqueous and the micellar phase, heat capacity, and volume of pentanol in both phases are simultaneously derived. The present results show that the volume of the micellar core does not seem to have a significant effect on the apparent molar volume and heat capacity of pentanol in the micellar phase and on the free energy of transfer of pentanol from the aqueous to the micellar phase. We report an equation correlating the free energy of transfer of alcohols in alkyltrimethylammonium bromides as a function of the number of carbon atoms in the alcohol and surfactant alkyl chain. Also, the apparent molar heat capacities of pentanol in micellar solutions as a function of surfactant concentration show evidence of two maxima, which, by increasing the alkyl chain length of surfactant display an opposite dependence on concentration. The second maximum can be attributed to a sphere to rod transition. The second transition was also found in the case of butoxyethanol in hexadecyltrimethylammonium bromide. It is more difficult to explain the nature of the first maximum although an attempt is made. 相似文献
75.
Van Driessche G Vandenberghe I Jacquemotte F Devreese B Van Beeumen JJ 《Journal of mass spectrometry : JMS》2002,37(8):858-866
The complete amino acid sequence of a novel high-potential iron-sulfur protein (HiPIP) isozyme 1 from the moderately halophilic phototrophic bacterium Ectothiorhodospira mobilis was determined by a combined approach of chemical and mass spectrometric sequencing techniques. By mass analysis of the apo- and holo-protein in the positive electrospray ionization mode using different electrospray solvents, the protein was found to be post-translationally modified by a moiety of 43 Da. Further analysis showed the nature and location of this modification to be a carbamyl group at the N-terminus of the HiPIP. This rare type of modification has previously been reported to occur in the water-soluble human lens alphaB-crystallin, class D beta-lactamases and some prokaryotic ureases, albeit at an internal lysine residue. In this paper, we discuss the mass spectrometric features of a carbamylated residue at the N-terminus of a peptide or a lysine side-chain during sequence analysis by collision-induced dissociation tandem mass spectrometry. Our data provide evidence for the first case of a prokaryotic carbamylated electron transport protein occurring in vivo. 相似文献
76.
采用后合成修饰法成功制备出一系列双金属Agx-Ni-MOF-74催化剂, 并应用于CO选择性催化还原NO (CO-SCR)反应. 研究结果发现, 相较于单金属Ni-MOF-74催化剂, 双金属Ag-Ni-MOF-74具有更加优良的低温CO催化还原NO能力, 其中Ag1-Ni-MOF-74催化剂在200~300 ℃的温度范围达到接近100% NO转化率. 利用X射线衍射分析(XRD)、傅氏转换红外线光谱分析(FT-IR)、场发射扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、氢气程序升温还原性能测试(H2-TPR)等技术对样品的结构和性能进行了探究, 发现Ag的加入有利于丰富催化剂活性位点和提高催化剂的比表面积, 并促进反应物的有效活化和传输. 此外, 基于原位红外光谱分析, 发现了CO-SCR反应过程遵循具有较高低温催化效率的Langmuir-Hinshelwood (L-H)机理. 相似文献
77.
78.
由于数字投影和采集系统的非线性失真,传统的方法通常需对采集到的条纹进行低通或带通滤波从而抑制高次谐波并获取基频分量。基于广义分析模型针对数字条纹轮廓术提出一种对测量后的物体形貌进行后滤波的算法,消除了非线性失真对测量结果所造成的影响并提高了数字条纹轮廓术的测量精度。论述了条纹轮廓术的原理和广义分析模型,分析推导出后滤波算法。仿真和实验结果表明,后滤波方法能够快速准确地实现基于数字投影的三维形貌重建。 相似文献
79.
80.