全文获取类型
收费全文 | 39658篇 |
免费 | 1398篇 |
国内免费 | 151篇 |
专业分类
化学 | 20777篇 |
晶体学 | 205篇 |
力学 | 1091篇 |
综合类 | 7篇 |
数学 | 6662篇 |
物理学 | 12465篇 |
出版年
2023年 | 254篇 |
2021年 | 345篇 |
2020年 | 499篇 |
2019年 | 385篇 |
2018年 | 525篇 |
2017年 | 516篇 |
2016年 | 1069篇 |
2015年 | 816篇 |
2014年 | 928篇 |
2013年 | 1989篇 |
2012年 | 1782篇 |
2011年 | 1933篇 |
2010年 | 1305篇 |
2009年 | 1080篇 |
2008年 | 1802篇 |
2007年 | 1688篇 |
2006年 | 1621篇 |
2005年 | 1451篇 |
2004年 | 1262篇 |
2003年 | 1034篇 |
2002年 | 921篇 |
2001年 | 877篇 |
2000年 | 704篇 |
1999年 | 490篇 |
1998年 | 428篇 |
1997年 | 424篇 |
1996年 | 522篇 |
1995年 | 461篇 |
1994年 | 498篇 |
1993年 | 505篇 |
1992年 | 553篇 |
1991年 | 382篇 |
1990年 | 390篇 |
1989年 | 352篇 |
1988年 | 329篇 |
1987年 | 342篇 |
1986年 | 313篇 |
1985年 | 500篇 |
1984年 | 482篇 |
1983年 | 403篇 |
1982年 | 427篇 |
1981年 | 422篇 |
1980年 | 422篇 |
1979年 | 406篇 |
1978年 | 394篇 |
1977年 | 394篇 |
1976年 | 364篇 |
1975年 | 357篇 |
1974年 | 346篇 |
1973年 | 294篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
291.
Experiments have been carried out to study the behaviour of organoarsenicals treated with zeolites by means of speciation
analysis. IC-ICP-MS was applied to identify and quantify arsenite, arsenate and the following organoarsenicals: monomethylarsonic
acid (MMA), dimethylarsinic acid (DMA), trimethylarsine oxide (TMAO), tetramethylarsonium bromide (TMA+), arsenobetaine (AsB) and arsenocholine (AsC). Zeolites loaded with ferrous ions did not significantly increase the retention
of inorganic arsenic species compared to the native zeolites, while there was a ten-fold removal of arsenate relating to arsenite.
The formation of As(V) and DMA in the leachates containing clinoptilolites and mordenites was confirmed in the presence of
natural and synthetic zeolites. Arsenobetaine and arsenocholine yielded higher levels of arsenate than the methylated species. 相似文献
292.
Hans-Detlev Gilsing Jürgen Angerer Dietrich Prescher 《Monatshefte für Chemie / Chemical Monthly》2005,1(10):795-801
The synthesis of an oxidative major metabolite of bis(2-ethylhexyl) phthalate is described. The target molecule and its ring-deuterated isomer were obtained via acylation of the appropriate -hydroxy benzyl ester or the corresponding carboxylate with phthalic anhydride or phthalic anhydride-d4. All transformation steps proceed with high yields. 相似文献
293.
Kato H Brink M Möllerstedt H Piqueras MC Crespo R Ottosson H 《The Journal of organic chemistry》2005,70(23):9495-9504
[Figure: see text]. A quantum chemical study has been performed to assess changes in aromaticity along the T1 state Z/E-isomerization pathways of annulenyl-substituted olefins. It is argued that the point on the T1 energy surface with highest substituent aromaticity corresponds to the minimum. According to Baird (J. Am. Chem. Soc. 1972, 94, 4941), aromaticity and antiaromaticity are interchanged when going from S0 to T1. Thus, olefins with S0 aromatic substituents (set A olefins) will be partially antiaromatic in T1 and vice versa for olefins with S0 antiaromatic substituents (set B olefins). Twist of the C=C bond to a structure with a perpendicular orientation of the 2p(C) orbitals (3p*) in T1 should lead to regaining substituent aromaticity in set A and loss of aromaticity in set B olefins. This hypothesis is verified through quantum chemical calculations of T1 energies, geometries (bond lengths and harmonic oscillator measure of aromaticity), spin densities, and nucleus independent chemical shifts whose differences along the T1 PES display zigzag dependencies on the number of -electrons in the annulenyl substituent of the olefin. Aromaticity changes are reflected in the profiles of the T1 potential energy surfaces (T1 PESs) for Z/E-isomerizations because olefins in set A have minima at 3p* whereas those in set B have maxima at such structures. The proper combination (fusion) of the substituents of set A and B olefins could allow for design of novel optical switch compounds that isomerize adiabatically with high isomerization quantum yields. 相似文献
294.
Hiller W Brüll A Argyropoulos D Hoffmann E Pasch H 《Magnetic resonance in chemistry : MRC》2005,43(9):729-735
The application of HPLC-NMR for the analysis of a mixture of fatty alcohol ethoxylates (FAEs) is described. The use of the new generation, cryogenically cooled probes is investigated in respect of the sensitivity advantage that they provide. The FAE mixture is separated using liquid chromatography at the critical point of adsorption. The ability of the method to differentiate between the different end groups and the degree of polymerization of the mixture constituents is investigated. Both on-flow and stop-flow HPLC-NMR techniques were used together with two-dimensional NMR spectroscopy. The results are compared with those obtained by using an evaporative light scattering detector for the HPLC. 相似文献
295.
H. W. Dürbeck 《Analytical and bioanalytical chemistry》1970,251(2):108-111
Separation of isomeric aromatic hydrocarbons from each other has been obtained using packed columns and Bentone 34 modified with silicone oil and lanolin. For maximum resolution the proportions of the modifying agents are very important. Retention data and chromatograms of two different column types are given (column 1∶6% Bentone 34; 2,5% lanolin; 1,5% silicone oil. Column 2∶10% silicone oil; 5% bentone 34; 4% lanolin) 相似文献
296.
297.
Torsten Küppers Martin Köckerling Prof. Dr. Helge Willner Prof. Dr. 《无机化学与普通化学杂志》2007,633(2):280-284
The new tetracyanoborate K[B(CN)4]·CH3CN was synthesized by dissolution of the solvent‐free K[B(CN)4] in acetonitrile and subsequent careful crystallization. The crystal structure has been determined by single‐crystal X‐ray diffraction. It crystallizes in the orthorhombic space group P212121 with Z = 4. Some comparisons with related structures are made, and the vibrational spectrum is discussed. 相似文献
298.
299.
An immobiline DryStrip application method enabling high-capacity two-dimensional gel electrophoresis 总被引:5,自引:0,他引:5
Sabounchi-Schütt F Aström J Olsson I Eklund A Grunewald J Bjellqvist B 《Electrophoresis》2000,21(17):3649-3656
In the field of proteomics the need to detect low-abundance cellular components, such as regulatory proteins, is of critical importance. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) is one of the most commonly used separation tools for these biological investigations. In this paper we report an alternative micropreparative 2-D PAGE sample application method, called the "paper bridge loading" method. This method makes it possible to apply a larger sample volume to commercially available immobilized pH gradient (IPG) strips. The Vh products required for focusing are only marginally longer than those used in analytical experiments. The method was compared to traditional cup loading and in-gel rehydration. With 18 cm long narrow-range Immobiline DryStrip pH 4.5-5.5, the "paper bridge" method allowed the application of 10 mg human plasma proteins compared to 3 mg with traditional loading methods. The corresponding figures using Escherichia coli sample was found to be 6 mg and less than 2 mg, respectively. The paper bridge method also showed the best results in terms of spot resolution and separation of high molecular weight proteins. 相似文献
300.
Ohne Zusammenfassung 相似文献