全文获取类型
收费全文 | 410篇 |
免费 | 2篇 |
国内免费 | 246篇 |
专业分类
化学 | 605篇 |
力学 | 5篇 |
数学 | 3篇 |
物理学 | 45篇 |
出版年
2019年 | 1篇 |
2018年 | 7篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 1篇 |
2012年 | 9篇 |
2011年 | 12篇 |
2010年 | 12篇 |
2009年 | 119篇 |
2008年 | 162篇 |
2007年 | 42篇 |
2006年 | 95篇 |
2005年 | 88篇 |
2004年 | 29篇 |
2003年 | 14篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 11篇 |
1999年 | 16篇 |
1998年 | 1篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有658条查询结果,搜索用时 46 毫秒
41.
42.
W18Cr4V 总被引:2,自引:1,他引:1
The frictionand
wear characteristics of the surfa ce compound layer of W18Cr4V steel by combined treatment
of ion nitrocarburizing-ion sulphurizing were investigated. The friction coefficient of
the compound l ayer against GCr15 steel was determined witha block-ring friction tester.
The wear test was carried out with a reciprocating wear tester. The worn surface was
analyzedby scanning electron microscopy(SEM). The experimental results reveale d that the
friction coefficient was lower for treatedW18Cr4V steel against GCr1 5 steel. The wear
resistance of the compound layer was higher because the nitroc arbonide andthe sulphide in
the compound layer were capable of friction-reduct ion and adhesion-inhibition. 相似文献
43.
Xuexi Tie a Junji Cao b a National Center for Atmospheric Research Boulder CO USA b SKLLQG Institute of Earth Environment Chinese Academy of Sciences No. Fenghui South Road High-Tech Zone Xi’an China 《中国颗粒学报》2010,8(1)
PARTICUOLOGY regrets that the above paper was mistakenly classified as a ‘Review’ rather than an ‘Invited paper’ when originally published in volume 7, issue 6, 426–431. 相似文献
44.
LI Hao-Honga CHEN Zhi-Ronga② REN Yong-Gang LI Jun-Qiana b HUANG Chang-Canga ZHAO Bina a 《结构化学》2005,(12)
1 INTRODUCTION terested in the unique effects associated with substituents at 4- and 7-positions of the phenan- The coordination chemistry of 1,l0-phenanthroline throline ring. Thus, when phenyl groups are present, and its derivatives has captured the attention of che- the absorptivities of the CT transitions are increased mists for years. The reports on biological importance[1~4], markedly due to the extension of the dipole moment supramolecular chemistry[5], electronic spectra[6], conne… 相似文献
45.
Yong Nian Ni a b Xue Zhi Zhong a a Department of Chemistry Nanchang University Nanchang China b The Key Laboratory of Food Science of MOE Nanchang University Nanchang China 《中国化学快报》2007,(5)
The binding characteristics of neutral red (NR) with DNA were investigated by fluorescence spectrometry. Chemometrics approach as singular value decomposition (SVD) was used to evaluate the number of spectral species in the drug-DNA binding process, and then the intrinsic binding constant of 1.6 104 in base pairs and the binding site number of 0.97 were obtained from the Scatchard plot. 相似文献
46.
Dráb T Kračmerová J Tichá I Hanzlíková E Tichá M Liberda J 《Journal of separation science》2011,34(14):1692-1695
Native polyacrylamide electrophoresis in the presence of two reversible protein anionic stains (Ponceau S and Ponceau 2R) was used to study the oligomeric states of soluble proteins. A mild binding of the used protein stains to nondissociated protein oligomers imposed a charge shift on the proteins resulting into separation of protein species according to their size under physiological conditions. Adsorbed stains could be easily removed after electrophoresis by washing of polyacrylamide gel with buffer and protein complexes could be visualized either by the detection of their enzyme activity or by using a nonspecific protein stain. The specific detection of enzyme activity of glycosidases, lactate dehydrogenase, or phosphatases was shown as an example. 相似文献
47.
Chenglong Yu a b Xin Hao a Hongtao Jiang a Lili Wang a a School of Materials Science Engineering Shaanxi University of Science & Technology Xi’an China b Research Laboratory of Hydrothermal Chemistry Faculty of Science Kochi University Kochi Japan 《中国颗粒学报》2011,9(1)
Fe 3 O 4 nano-whiskers were synthesized via ultrasonic-aided reduction of FeCl 2 ·4H 2 O with N 2 H 4 ·H 2 O in concentrated NaOH solution. Phase identification and morphology observation were conducted by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM). Face scanning energy dispersive spectrum (face scanning EDS) and two-dimensional fast Fourier transform (2DFFT) for element distribution were carried out for confirming compos... 相似文献
48.
在pH 7.0HEPES(4-羟乙基哌嗪乙磺酸)缓冲溶液中和0.19mol.L-1 NaCl存在下,单链底物DNA(SS)和酶链DNA(ES)在80℃杂交形成双链DNA(dsDNA)。Cu2+可切割dsDNA中的底物链释放出单链DNA(ssDNA),此ssDNA与金纳米粒子(NG)作用形成NGssDNA结合物不被NaCl聚集,而未保护的NG聚集形成较大粒径的聚集体(NGA),在627nm处有一个较强的共振瑞利散射峰。随着Cu2+浓度的增大,该共振瑞利散射峰降低,其降低值ΔI与Cu2+浓度在15~1 250nmol.L-1范围呈线性关系,其回归方程为ΔI=0.17c-2.3,线性相关系数为0.989 5,检出限为8nmol.L-1。据此建立了一个高灵敏、高选择性、简便测定Cu2+的共振瑞利散射光谱分析法。该法用于水样中Cu2+的检测,结果满意。 相似文献
49.
Hai-xia Yang Jin-gang Liu Xiao-juan Zhao Yan-feng Li Lin Fan Shi-yong Yang a School of Chemistry Chemical Engineering Lanzhou University Lanzhou China b Laboratory of Advanced Polymer Materials Institute of Chemistry Chinese Academy of Sciences Beijing China 《高分子科学》2005,(5)
A new type of aromatic tetraamine containing biphenyl moiety in the side chain was synthesized via a modified Chichibabin's reaction.3-Nitro-4-acetamidoacetophenone was reacted with 4-phenyl benzaldehyde in the presence of ammonium acetate to obtain 2,6-bis(3',4'-diaminophenyl)-4-biphenyl pyridine(DPPA).A series of polypyrrolones(PPys) were prepared using tetraamine and various aromatic dianhydrides via a two-step cyclization procedure.All the PPys show excellent high temperature stabilities with the initial decomposition temperatures of 530-549℃ and residual weight ratio of 49%-80% at 750℃ in nitrogen.The polymers exhibit no apparent glass transition temperatures(T_gs)except PPy-1 (T_g=327℃),which is derived from tetraamine DPPA and 2,2-bis[4-(3',4'-dicarboxyphenoxy)-phenyl]propane dianhydride (BPADA).In addition,the polymers have acceptable mechanical properties with the tensile strength of 65-94 MPa.The PPy films show excellent hydrolysis-resistance in alkaline aqueous medium and could maintain most of the properties even after boiling in 10% aqueous sodium hydroxide solution for a week. 相似文献
50.
The title compound belongs to monoclinic,space group C2/c with a=5.2694(1),b=12.6659(4),c=19.4108(2) ,β=91.504(2)°,V=1295.06(5) 3,Z=4 and Dc=5.599 g/cm3. The structure of BaGd2(MoO4)4 contains a MoO4 tetrahedron,a distorted GdO8 polyhedron,and Ba2+ ions in a tenfold coordination. The GdO8 polyhedra are linked together through edge-sharing to give a two-dimensional Gd layer. The MoO4 tetrahedra connected to the Gd atoms are capped up and down the Gd layer through common oxygen apices,thus forming a new Gd-Mo layer. Finally,the Gd-Mo layers are held together through bridging BaO10 polyhedra to form a three-dimensional framework. Since the Ba-μ3-O bond has a large average distance of 2.888 ,this structural characteristic will result in a cleavage along the (001) plane. 相似文献