全文获取类型
收费全文 | 10083篇 |
免费 | 218篇 |
国内免费 | 20篇 |
专业分类
化学 | 6009篇 |
晶体学 | 162篇 |
力学 | 269篇 |
数学 | 748篇 |
物理学 | 3133篇 |
出版年
2023年 | 95篇 |
2022年 | 216篇 |
2021年 | 164篇 |
2020年 | 180篇 |
2019年 | 247篇 |
2018年 | 211篇 |
2017年 | 237篇 |
2016年 | 322篇 |
2015年 | 214篇 |
2014年 | 410篇 |
2013年 | 792篇 |
2012年 | 557篇 |
2011年 | 664篇 |
2010年 | 427篇 |
2009年 | 415篇 |
2008年 | 473篇 |
2007年 | 461篇 |
2006年 | 350篇 |
2005年 | 292篇 |
2004年 | 233篇 |
2003年 | 176篇 |
2002年 | 189篇 |
2001年 | 118篇 |
2000年 | 126篇 |
1999年 | 86篇 |
1998年 | 59篇 |
1997年 | 57篇 |
1996年 | 93篇 |
1995年 | 105篇 |
1994年 | 98篇 |
1993年 | 93篇 |
1992年 | 124篇 |
1991年 | 90篇 |
1990年 | 80篇 |
1989年 | 93篇 |
1988年 | 87篇 |
1987年 | 91篇 |
1986年 | 74篇 |
1985年 | 106篇 |
1984年 | 119篇 |
1983年 | 85篇 |
1982年 | 101篇 |
1981年 | 98篇 |
1980年 | 104篇 |
1979年 | 97篇 |
1978年 | 104篇 |
1977年 | 85篇 |
1976年 | 56篇 |
1975年 | 61篇 |
1974年 | 76篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The role of voids and cracks in solid-state reaction between 8-hydroxyquinoline and phthalic anhydride has been investigated. 8-hydroxyquinoline reacts with phthalic anhydride both in solution and in solid state, forming a 1:1 yellow-colored complex. X-ray diffraction studies prove that the complex obtained from the solid-state reaction is the same as that obtained from solution. Several techniques have been used to study the kinetics of the reaction in the solid state. Kinetic studies by capillary technique showed that surface migration is the mode of diffusion of reactant concerned. Dilatometric technique confirms the formation of cracks and voids in the systems and shows that the reaction is propagated through the channels. 相似文献
92.
Reactions of 4,4'-bipyridine (1) with excess of polyfluoroalkyl iodides (2a-d) at 100-110 degrees C, under neat conditions, led to the formation of monoquaternary salts (3a-d) in > 90% yields. Salts 3a-d were metathesized with LiN(SO2CF3)2 either in water or water/acetone mixtures to form ionic liquids (4a-d), respectively, in > 88% yields. When 1 was reacted with 2.5 equivalent of 2a-c in DMF at 110 degrees C, the diquaternary salts 5a-c were formed in > 85% yields. Alternatively, 5a-c were also synthesized by heating a mixture of 3a-c and 2a-c (1.25 equivalent) in DMF. The metathesis reaction of 5a-c with LiN(SO2CF3)2 produced dicationic ionic liquids (6a-c) in > 86% yield. 相似文献
93.
Anuradha Rout Swoyam P. Rout Nigamananda Mallick Baishnab C. Singh M. Santappa 《Journal of polymer science. Part A, Polymer chemistry》1978,16(2):391-397
The polymerization of acrylonitrile (M) initiated by the Ce(IV)–acetophenone (AP) redox pair has been studied in acetic–sulfuric acid mixtures in a nitrogen atmosphere. The rate of polymerization is proportional to [M]3/2, [AP]1/2 and [Ce(IV)]1/2. The rate of disappearance of ceric ion,–RCe, is proportional to [AP], [M], and [Ce(IV)]. The effect of certain salts, solvent, acid and temperature on both the rates have been investigated. A suitable kinetic scheme has been proposed, and the composite rate constants kp 2(k/k/t) and k0/ki are reported. 相似文献
94.
A. I. Meyers A. H. Reine J. C. Sircar K. B. Rao S. Singh H. Weidmann M. Fitzpatrick 《Journal of heterocyclic chemistry》1968,5(2):151-159
The cyclization of enamines derived from β-aminoesters and β-aminonitriles into bi- and tricyclic enaminoketones ( 6,9,13 and 24 ) has been investigated. The enamines derived from aminonitriles cyclize smoothly with magnesium perchlorate in benzene or toluene, whereas the enamines derived from aminoesters cyclize spontaneously during their formation. The scope and limitation of this process is discussed. 相似文献
95.
Chloramine-T has been used as an oxidizing agent in hydrochloric acid medium' for the volumetric estimations of potassium iodide, hydrazine sulphate, arscnious oxide, stannous chloride, mercurous chloride, tartar-emetic, potassium thiocyanate and ferrous ammonium sulphate, using iodine monochloride as a catalyst and pre-oxidizer. Chloroform is used as an indicator. It is coloured pink owing to the liberation of iodine during the titration and becomes very pale yellow at the end-point because of the formation of iodine monochloride. 相似文献
96.
Miss S. Baluja R. N. Singh R. Tripathi B. M. Shukla 《Journal of Radioanalytical and Nuclear Chemistry》1985,94(4):233-239
Tracer diffusion of131I– ions is studied at different temperatures /20°C–50°C/ in 2.5% agar gel containing sodium and potassium sulphate solutions over a wide range of concentrations. The results are in qualitative agreement with the theoretical values in the concentration range 10–6–10–1M. Agar gel shows an obstruction effect to diffusional flow. The activation energy for tracer diffusion was found to be of the order of 16.3 kJ mol–1. 相似文献
97.
The analysis of dehydration of the complexes, [La(C8H8NO3)3.2H2O] and [Yb(C8H8NO3)3.3H2O] for the evaluation of kinetic parameters (Z, E &S
*) and mechanism of dehydration by non-isothermal methods are reported. The complexes decompose in three well defined steps involving random nucleation mechanism. First two steps involving the dehydration and the third step the loss of the ligand moiety. The intermediates formed during decomposition were found to be unstable for carrying out any significant studies.
Zusammenfassung Zwecks Ermittlung der kinetischen Parameter (Z, E undS *) und des Mechanismus der Dehydratierung durch nichtisotherme Verfahren wird die Analyse der Dehydratierung der Komplexe [La(C8H8NO3)3·2H2O] und [Yb(C8H8NO3)3·3H2O] beschrieben. Die Komplexe zersetzen sich in drei gut definierten Schritten mit Random-Keimbildungsmechanismus. Die ersten zwei Schritte beinhalten die Dehydratierung, der dritte Schritt den Verlust der Liganden. Die wÄhrend der Zersetzung entstandenen Zwischenprodukte erwiesen sich für jegliche signifikante Untersuchung als zu unstabil.相似文献
98.
99.
100.