全文获取类型
收费全文 | 5436篇 |
免费 | 533篇 |
国内免费 | 936篇 |
专业分类
化学 | 3993篇 |
晶体学 | 80篇 |
力学 | 146篇 |
综合类 | 60篇 |
数学 | 381篇 |
物理学 | 603篇 |
无线电 | 1642篇 |
出版年
2024年 | 7篇 |
2023年 | 83篇 |
2022年 | 104篇 |
2021年 | 127篇 |
2020年 | 191篇 |
2019年 | 207篇 |
2018年 | 205篇 |
2017年 | 207篇 |
2016年 | 231篇 |
2015年 | 216篇 |
2014年 | 327篇 |
2013年 | 471篇 |
2012年 | 560篇 |
2011年 | 357篇 |
2010年 | 280篇 |
2009年 | 305篇 |
2008年 | 337篇 |
2007年 | 364篇 |
2006年 | 337篇 |
2005年 | 269篇 |
2004年 | 258篇 |
2003年 | 219篇 |
2002年 | 192篇 |
2001年 | 143篇 |
2000年 | 152篇 |
1999年 | 125篇 |
1998年 | 115篇 |
1997年 | 87篇 |
1996年 | 87篇 |
1995年 | 60篇 |
1994年 | 52篇 |
1993年 | 39篇 |
1992年 | 52篇 |
1991年 | 32篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 17篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1973年 | 2篇 |
1971年 | 1篇 |
排序方式: 共有6905条查询结果,搜索用时 610 毫秒
101.
Anil K. Singh Nirmalya Majumdar 《Journal of photochemistry and photobiology. B, Biology》1995,30(2-3):105-113
All-trns-N-retinylidenetryptamine Schiff base was incorporated into aerosol-OT (AOT, sodium bis(2-ethylhexyl)sulphosuccinate)/heptane reverse micelles. This micellar system was used as a model to study the retinal-tryptophan interactions in retinal proteins. The retinylidene Schiff base remains stable in the presence of reverse micelle-solubilized water pools. Partition coefficient and microviscosity measurements show that the Schiff base is located in the micellar interphase. The results are discussed in terms of the interaction between the retinylidene chromophore and the active site environment of rhodopsin and bacteriorhodopsin. In the present model, the quencher and emitting units are covalently attached, and are separated by two carbon spacer units. The fluorescence emission data obtained for the micelle-intercalated Schiff base chromophore are compared with the fluorescence of the native protein and intermediates in the photochemical cycle of bacteriofhodopsin. A comparison of the data obtained for tryptamine and the Schiff base with the results available for bacteriorhodopsin and bacterioopsin reveals that there is a large degree of quenching on intercalation of the retinylidene chromophore in the vicinity of the fluorophore. Evidence provided by this model suggests that energy transfer to retinal can occur from tryptophan residues located in the retinal pocket in the native protein. Thus the retinylidene unit can act as a quencher of the energy of tryptophan, the nature and extent of which may depend on the conformation and relative orientation of the protein-bound fluorophore. 相似文献
102.
Vinod K. Tiwari Archana Singh Hakkim A. Hussain Bhuwan B. Mishra Vyasji Tripathi 《Monatshefte für Chemie / Chemical Monthly》2007,138(7):653-658
Summary. A convenient and high yielding method for the synthesis of diverse dithiocarbamates having various substituents including
alkyl, aryl, heteroaryl, and alkylaryl at the thiol chain or at the amine chain or at both thiol and amine chains were developed
by the one-pot reaction of mercaptans, amines, and bis(benzotriazolyl)methanethione in presence of amidine base under mild
reaction conditions. 相似文献
103.
104.
Michiharu Sugiura Natsuyo YamaguchiKoosuke Asai Isamu Maeba 《Tetrahedron letters》2003,44(33):6241-6243
Diphenyl 1-phenoxycarbonyl-1,4-dihydroquinoline-4-phosphonates 5c-g, obtained from the reaction of corresponding quinoline derivatives 1 with phenyl chloroformate and triphenyl phosphite in one step, were ozonized in CHCl3 and CH3COOH. Treatment of the resulting mixture with NaHCO3 produced the 3-formyl-1-phenoxycarbonylindole derivatives 8a-e in high yields. The ring transformation of quinolines 1 to indoles 8 proceeds under mild conditions. 相似文献
105.
Six palladium(Ⅱ) complexes with isonitrosoethylacetoacetate imine Schiff base ligands, Pd(R-IEAI)2, were prepared and characterized by IR, Raman and electronic spectra. Complex tran Pd(p-CH3C6H4-IEAI)2 (2) cry- stallizes in the monoclinic system, space group P21/c,with a=1.2002(2),b=0.9972(2),c=1.1121(2)nm,β=90.43(3)°,Z=2,F(000)=616,μ=7.44cm-1. The final R and wR are 0.0244 and 0.0625 for 2620 ob-served reflections with I≥2σ(I), respectively. The geometry around the Pd(Ⅱ) ions in those complexes has a distorted PdN4 square plane, the Schiff base ligands R-IEAI- being coordinated through their oximino-nitrogen atoms and imino-nitrogen atoms. 相似文献
106.
Macrocyclic Schiff‐base ligand, bisacetylaceton‐ethylenediimine (BAE) and its transition metal complexes M(BAE) (M = Cu2+, Ni2+) were synthesized. The complexes having characteristics of aromatic systems and well‐defined one‐dimensional structures, reacted with p‐phthaloyl chloride, to obtain polymer complexes. The complexes were characterized by elemental analysis, inductively coupled plasma (ICP), FT‐IR, and thermal analysis and show good thermal stability. ESR spectra analysis discovered that there are free radicals in the chain of polymers, indicating that a weak magnetic spin‐exchange interaction operates between the metal ions and free radicals. It is found that, as the bridging p‐phthaloyl group is able to propagate the magnetic exchange interaction, the polymer complexes show paramagnetic properties by measurement of temperature dependence of the magnetic property, and obey Curie–Weiss law. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
107.
邻苯二亚胺纤维素水溶液的荧光行为 总被引:3,自引:0,他引:3
目前,用于制造光致发光材料的基材均为合成高分子材料,如聚氯乙烯(PVC)等热塑性材料以及不饱和聚酯等热固性材料[1].天然高分子材料发光性能的研究并不多见.而与合成高分子相比,纤维素的结构特征决定了它易参与化学反应,可用以制备各种用途的功能材料,如高... 相似文献
108.
109.
利用Mn^2+,Ba^2+及Sr^2+作为模板离子,合成了一类新型的含呋喃环系 Schiff碱型大环化合物,如L^1和配合物L^2Ba(ClO4)2,L^3Ba(ClO4)2和L^4Ba (ClO4)2.L^2-L^4的Ba^2+配合物经与NaSO4水溶液反应解络,得到自由配体L^2, L^3和L^4,配体L^2和L^3分别与Sr^2+作用,得到配合物L^2Sr(ClO4)2和L^3Sr (ClO4)2。上述大环配体和各种配合物均经元素分析,IR,^1H NMR,MS等证实了它 们的结构和组成。 相似文献
110.
Victor Barba Julián Vázquez Rosa Santillan 《Journal of organometallic chemistry》2005,690(9):2351-2357
The syntheses of eight [4.3.0] heterobicyclic boronates containing a N → B coordinative bond are described. The monomeric compounds were prepared by reaction of arylboronic acids with a tridentate ligand having the ONO donor set of atoms. It was shown that substituents at the para-position of the B-phenyl moiety transmit electronic effects to the CN bond which in turn is polarized by formation of the N → B coordination bond. At the same time, related tridentate ligands were also reacted with 1,4-benzenediboronic acid in order to prepare benzene diboron complexes. The structure of this type of compounds was confirmed by X-ray analysis for one of the derivatives. 相似文献