全文获取类型
收费全文 | 932篇 |
免费 | 70篇 |
国内免费 | 111篇 |
专业分类
化学 | 526篇 |
晶体学 | 21篇 |
力学 | 53篇 |
综合类 | 12篇 |
数学 | 78篇 |
物理学 | 423篇 |
出版年
2023年 | 8篇 |
2022年 | 21篇 |
2021年 | 25篇 |
2020年 | 27篇 |
2019年 | 13篇 |
2018年 | 18篇 |
2017年 | 27篇 |
2016年 | 23篇 |
2015年 | 26篇 |
2014年 | 27篇 |
2013年 | 51篇 |
2012年 | 63篇 |
2011年 | 72篇 |
2010年 | 57篇 |
2009年 | 49篇 |
2008年 | 62篇 |
2007年 | 60篇 |
2006年 | 47篇 |
2005年 | 52篇 |
2004年 | 43篇 |
2003年 | 25篇 |
2002年 | 32篇 |
2001年 | 35篇 |
2000年 | 27篇 |
1999年 | 16篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 13篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1989年 | 5篇 |
1986年 | 5篇 |
1985年 | 13篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1974年 | 9篇 |
1973年 | 6篇 |
1972年 | 7篇 |
1971年 | 4篇 |
1968年 | 5篇 |
排序方式: 共有1113条查询结果,搜索用时 31 毫秒
101.
以荧光法研究了土霉素(OTC)与环糊精(β-CD)的包合作用,并利用β-CD对OTC荧光的增敏作用建立了一种高灵敏度测定OTC的新方法,土霉素在9.19×10^-8-1.66×10^-5mol/L范围内与荧光强度成正比,方法的检出限为7.4×10^-9mol/L,方法用于药物制剂中土霉素的测定,结果与标示量吻合。荧光光度法测得OTC与β-CD形成1∶1包合物,包合物形成常数为3.68×10^2L/mol。从土霉素和环糊精的分子结构出发,对包合物的形成机理进行了探讨。 相似文献
102.
The copper sulfide mineral flotation collector, N‐n‐butyl‐N′‐ethoxycarbonyl‐thiourea (H2bectu), and the 1:1 hexameric copper(I) thioureate complex, [Cu(Hbectu)]6, have been characterized by single crystal X‐ray diffraction. H2bectu crystallizes in the triclinic space group with a = 5.2754(4), b = 9.0042(7), c = 12.6030(9) Å, α = 80.528(6), β = 90.173(6), γ = 76.472(7)°. An intramolecular N‐H···O hydrogen bond between the thioamide proton and carbonyl oxygen forms a planar six‐membered ring in the central core of the molecule with C=O, C=S and C‐N bond lengths in accord with those reported for other N‐alkyl/aryl‐N′‐acyl‐thiourea compounds. [Cu(Hbectu)]6 crystallizes in the monoclinic space group C2/c with a = 23.269(5), b = 13.243(4), c = 23.037(7) Å, β = 91.81(2)° as discrete hexameric clusters disposed about a crystallographic centre of symmetry with a Cu6S6 core consisting of two Cu3S3 chair‐shaped rings linked by coordination of the deprotonated amide nitrogen atom to a copper atom in the adjacent ring. The six ligands assemble as a paddlewheel structure with the ethoxy and n‐butyl substituents packing in an alternating head to tail arrangement. Temperature dependent solution 1H NMR spectroscopic studies show that the hexameric structure of the complex is maintained in solution. 相似文献
103.
104.
105.
106.
X. Y. Wu R. H. Pelton K. C. Tam D. R. Woods A. E. Hamielec 《Journal of polymer science. Part A, Polymer chemistry》1993,31(4):957-962
Conductometric titration of poly(N-isopropylacrylamide) (polyNIPAM) with sodium dodecyl sulfate (SDS) gave two apparent transitions labeled C1 and C2. The C1 transition was independent of polyNIPAM concentration in the 0.05–0.3 wt % range, whereas C2 was proportional to the polymer concentration. C1 corresponded to the onset of binding of surfactant with polymer. Arguments based on a simple mass action model for micellization are presented to show that C2, the second transition, is not due to any simple explanation such as being the point above which only free micelles are formed with surfactant addition. The cloud point of polyNIPAM increased with the amount of bound surfactant. This was attributed to electrostatic contribution of bound sulfate groups to the increased solubility of polyNIPAM. © 1993 John Wiley & Sons, Inc. 相似文献
107.
Development and evaluation of gas and liquid chromatographic methods for the analysis of fatty amines 下载免费PDF全文
Zachary S. Breitbach Choyce A. Weatherly Ross M. Woods Chengdong Xu Glenda Vale Alain Berthod Daniel W. Armstrong 《Journal of separation science》2014,37(5):558-565
In contrast to the plethora of publications on the separation of fatty acids, analogous studies involving fatty amines are scarce. A recently introduced ionic‐liquid‐based capillary column for GC was used to separate trifluoroacetylated fatty amines focusing on the analysis of a commercial sample. Using the ionic liquid column (isothermal mode at 200°C) it was possible to separate linear primary fatty amines from C12 to C22 chain length in less 25 min with MS identification. The log of the amine retention factors are linearly related to the alkyl chain length with a methylene selectivity of 0.117 kcal/mol for the saturated amines and 0.128 kcal/mol for the mono‐unsaturated amines. The sp2 selectivity for unsaturated fatty amines also could be calculated as 0.107 kcal/mol for the ionic liquid column. The commercial sample was quantified by GC with flame ionization detection (FID). An LC method also was developed with a reversed phase gradient separation using acetonitrile/formate buffer mobile phases and ESI‐MS detection. Native amines could be detected and identified by their single ion monitoring chromatograms even when partial coelution was observed. The analysis of the commercial sample returned results coherent with those obtained by GC–FID and with the manufacturer's data. 相似文献
108.
109.
研究了MgO在不同温度下对HCN的脱除作用,并用XRD对反应后固相产物进行分析。研究了温度、MgO质量分数、HCN初始体积分数和停留时间等因素对HCN脱除效率的影响,并求出MgO与HCN反应的动力学参数。结果表明,673 K时,MgO已经开始与HCN发生反应,当温度高于873 K时,HCN中气态"N"已转化到固相产物MgCN2中;HCN脱除效率随温度、MgO质量分数和停留时间的增加呈线性增加,但随HCN初始体积分数增加呈负幂函数的规律下降;MgO与HCN的反应级数α为0.72,表观活化能E为32.2 kJ/mol。 相似文献
110.
Strong Direct Magnetic Coupling in a Dinuclear CoII Tetrazine Radical Single‐Molecule Magnet 下载免费PDF全文
Toby J. Woods Dr. Maria Fernanda Ballesteros‐Rivas Sergei M. Ostrovsky Andrew V. Palii Oleg S. Reu Sophia I. Klokishner Dr. Kim R. Dunbar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(29):10302-10305
The ligand‐centered radical complex [(CoTPMA)2‐μ‐bmtz.?](O3SCF3)3 ? CH3CN (bmtz=3,6‐bis(2′‐pyrimidyl)‐1,2,4,5‐tetrazine, TPMA=tris‐(2‐pyridylmethyl)amine) has been synthesized from the neutral bmtz precursor. Single‐crystal X‐ray diffraction studies have confirmed the presence of the ligand‐centered radical. The CoII complex exhibits slow paramagnetic relaxation in an applied DC field with a barrier to spin reversal of 39 K. This behavior is a result of strong antiferromagnetic metal–radical coupling combined with positive axial and strong rhombic anisotropic contributions from the CoII ions. 相似文献