全文获取类型
收费全文 | 48861篇 |
免费 | 11630篇 |
国内免费 | 3752篇 |
专业分类
化学 | 51014篇 |
晶体学 | 503篇 |
力学 | 1362篇 |
综合类 | 190篇 |
数学 | 3690篇 |
物理学 | 7484篇 |
出版年
2024年 | 28篇 |
2023年 | 250篇 |
2022年 | 360篇 |
2021年 | 648篇 |
2020年 | 1727篇 |
2019年 | 2996篇 |
2018年 | 1422篇 |
2017年 | 1082篇 |
2016年 | 3925篇 |
2015年 | 4033篇 |
2014年 | 4206篇 |
2013年 | 4966篇 |
2012年 | 4092篇 |
2011年 | 3463篇 |
2010年 | 3740篇 |
2009年 | 3647篇 |
2008年 | 3355篇 |
2007年 | 2583篇 |
2006年 | 2215篇 |
2005年 | 2382篇 |
2004年 | 2019篇 |
2003年 | 1854篇 |
2002年 | 2618篇 |
2001年 | 1895篇 |
2000年 | 1673篇 |
1999年 | 730篇 |
1998年 | 351篇 |
1997年 | 285篇 |
1996年 | 241篇 |
1995年 | 184篇 |
1994年 | 192篇 |
1993年 | 145篇 |
1992年 | 164篇 |
1991年 | 145篇 |
1990年 | 116篇 |
1989年 | 101篇 |
1988年 | 74篇 |
1987年 | 48篇 |
1986年 | 62篇 |
1985年 | 50篇 |
1984年 | 23篇 |
1983年 | 27篇 |
1982年 | 23篇 |
1981年 | 13篇 |
1980年 | 13篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1975年 | 9篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
931.
标题配合物 [Cu(C8H4 F3O2 S) 2 (C12 H8N2 ) ]·C3H6 O属于三斜晶系 ,空间群为P1,并测得如下晶胞参数a =10 .5 77(3) ,b =15 .72 2 (4) ,c =10 .133(2 ) ,α =94 .5 3(2 ) ,β =10 0 .81(2 ) ,γ =96 .18(2 )° ,V =16 37.0 3 3,Z =2 ,Mr =74 4.18,Dx =1.5 1× 10 6 g·m- 3,F(0 0 0 ) =5 2 6 ,μ =8 2 4cm- 1,最终偏差因子为R =0 .0 83,Rw=0 .0 74。Cu(II)与 2个 4 ,4 ,4 三氟 1 (2 噻吩基 )丁二酮 1,3中的四个氧原子和菲咯啉中的两个氮原子 ,组成了一个畸变的八面体构型。 相似文献
932.
This work presents a method to separate polar naphthalenesulfonate (NS) isomers by capillary zone electrophoresis (CZE) with ultraviolet detection in industrial effluents and river water samples. The method involves extraction of samples by a polystyrene‐divinylbenzene copolymer (PS‐DVB) solid‐phase extraction (SPE) cartridge. The most effective CZE separation conditions were obtained in 20 mM borate buffer with 30% acetonitrile at pH 9.0 and 30 °C. The method proposed herein provides a high precision and sensitivity for NS isomers, to quantitation at ≤ 1.0 μg/L in 200 mL of the water samples. Recovery of the NS isomers in spiked water samples ranged from 73% to 87% while RSD ranging from 5.6 to 9.7%. The analysis of industrial effluents and river water samples was performed and naphthalene‐2‐sulfonate was found as a major pollutant. The difficulties in quantitating and identifying analytes in complex environmental samples can be resolved by using an internal standard response factor to calculate concentrations and relative migration times for peak confirmation. 相似文献
933.
Ji‐Jiang Wang Meng‐Lin Yang Huai‐Ming Hu Prof. Dr. Gang‐Lin Xue Dong‐Sheng Li Qi‐Zhen Shi 《无机化学与普通化学杂志》2007,633(2):341-345
To determine the influence of the size of the aromatic chelate ligands on the frameworks of metal tretracarboxylate polymers, two new coordination polymers [Cd(btc)0.5 (2,2′‐bpy)] ( 1 ) and [Cd(btc)0.5(phen)]·H2O ( 2 ) (H4btc = biphenyl‐3,3′,4,4′‐tetracarboxylic acid, 2,2′‐bpy = 2,2′‐bipyridine, phen = 1,10‐phenanthroline) have been synthesized under similar hydrothermal conditions. In complex 1 , the dimeric Cd2 units are linked by bridging btc4? ligand to form a 2D layered network, whereas complex 2 possesses a 3D metal‐organic framework consisting of the dimeric Cd2 units. The differences of two metal‐organic frameworks demonstrate that the size of the rigid aromatic chelate ligands have an important effect on the structures of their complexes. Additionally, the two complexes show strong fluorescence in the solid state at room temperature. 相似文献
934.
Groups 5 and 6 metal chlorides such as MoCl5, WCI6, NbCl5 and TaCl5 were found to be simple and very efficientcatalysts for the aromatic H/D exchange reactions. Compared with other metal chlorides such as ZnCl2, SnCl4 and TiCl4, groups 5 and 6 metal chlorides showed better catalytic activity in the H/D exchange reaction of naphthalene with C6D6. Deuteration of anthracene using MoC15 as a catalyst proceeded within 24 h at room temperature. Other aromatic compounds such as toluene, diphenylmethane and 1,1,2-triphenylethane were also deuterated smoothly in C6D6 within 24 h at room temperature. 相似文献
935.
936.
苯基荧光酮荧光分光光度法测定痕量锗的研究 总被引:10,自引:0,他引:10
锗具有增血、抗炎症、抗衰老等多种医疗功能 ,因此 ,越来越受到人们的关注。荧光光度法测定微量锗已有报道[1~ 4] 。用苯基荧光酮荧光度法测定锗未见报道。本文利用苯基荧光酮与锗在醋酸 醋酸钠缓冲溶液中络合物形成速度快的优势 ,使其先在缓冲溶液中显色 ,然后在 0 .3mol LHCl介质中测定其荧光强度 ,用于粉煤灰中痕量锗的测定 ,得到满意结果。1 实验部分1 1 仪器与试剂RF - 5 4 0荧光分光光度计 (日本岛津 )。锗标准溶液 ( 1g L) :称取 0 .1 0 0 0g纯锗粉于 5 0ml小烧杯中 ,加入 5mlNaOH ,再加入几滴 30 %H2 O2… 相似文献
937.
In the system of SDS/n-C5H11OH/n-C7H16/H2O with the weight ratio of SDS/n-C5H11OH/H2O system at5.0/47.5/47.5, the upper phase of the system was W/O microemulsion, and the lower phase was the bicontinuous microemulsion. When the n-heptane content was less than 1%, with the increase of the n-heptane content, the capacitance (Co, Cod) in the upper phase (W/O) dropped, the capacitance (CB1, CBld) in the lower phase (BI) raised. At the same time, the W/O-BI inteffacial potential (ΔE), capacitance (Ci), and charge-transfer current (ict) decreased.After the n-heptane content reached 1%, with the increase of the n-heptane content, ΔE, Ci and ict demonstrated no significant change. 相似文献
938.
The Benzonitrile Adducts [Ho2Cl6(PhCN)6] and equation/tex2gif-stack-4.gif [HoCl3(PhCN)]: Syntheses, Crystal Structures, FarIR and MIR Spectroscopy Investigations Transparent light pink crystals of the compound [Ho2Cl6(PhCN)6] were obtained by the reaction of a mixture of HoCl3 and AlCl3 with benzonitrile at 150μ °C. Transparent pink crystals of the compound equation/tex2gif-stack-5.gif[HoCl3(PhCN)] were obtained by the same reaction under solvothermal conditions at 200μ °C. [Ho2Cl6(PhCN)6] exhibits a dimeric structure of linked pentagonal bipyramids whereas equation/tex2gif-stack-6.gif[HoCl3(PhCN)] forms a layer structure of trigonal Cl prisms around Ho, linked via corners and separated by coordinating PhCN molecules. 相似文献
939.
调制式DSC在高聚物研究中的应用 总被引:4,自引:0,他引:4
综述了一种新的热分析技术--调制式差示扫描量热示(Modulated Differentail Scanning Calorimetry)。对其工作原理,优点及在高聚物研究中的应用作了简介。 相似文献
940.
The many fold aromatic ketones 2a‐d are versatile compounds for the synthesis of the many fold 1,2,3‐selenadiazole aromatic derivatives 5a‐d . The preparation starts with the reaction between the many fold bromomethylene benzene derivatives 1a‐d and 4‐hydroxyacetophenone, which are transformed through the reaction with semicarbazide hydrochloride or ethylhydrazine carboxylate into the corresponding semicarbazones derivatives 3a‐d or hydrazones 4a‐d . The reaction with selenium dioxide leads to regiospecific ring closure of semicarbazones or hydrazones to give the many fold 1,2,3‐selenadiazole aromatic derivatives in high yield. 相似文献