全文获取类型
收费全文 | 2594篇 |
免费 | 333篇 |
国内免费 | 594篇 |
专业分类
化学 | 2729篇 |
晶体学 | 82篇 |
力学 | 182篇 |
综合类 | 31篇 |
数学 | 7篇 |
物理学 | 490篇 |
出版年
2024年 | 4篇 |
2023年 | 30篇 |
2022年 | 71篇 |
2021年 | 96篇 |
2020年 | 119篇 |
2019年 | 96篇 |
2018年 | 87篇 |
2017年 | 102篇 |
2016年 | 118篇 |
2015年 | 121篇 |
2014年 | 118篇 |
2013年 | 211篇 |
2012年 | 166篇 |
2011年 | 176篇 |
2010年 | 164篇 |
2009年 | 180篇 |
2008年 | 161篇 |
2007年 | 173篇 |
2006年 | 162篇 |
2005年 | 149篇 |
2004年 | 158篇 |
2003年 | 142篇 |
2002年 | 142篇 |
2001年 | 79篇 |
2000年 | 85篇 |
1999年 | 52篇 |
1998年 | 70篇 |
1997年 | 53篇 |
1996年 | 57篇 |
1995年 | 32篇 |
1994年 | 32篇 |
1993年 | 20篇 |
1992年 | 22篇 |
1991年 | 15篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1972年 | 1篇 |
排序方式: 共有3521条查询结果,搜索用时 78 毫秒
21.
22.
Vapor pressure,speciation, and chemical activities in highly concentrated sodium borate solutions at 277 and 317°C 总被引:2,自引:0,他引:2
Oleh Weres 《Journal of solution chemistry》1995,24(5):409-438
The system H2O-B2O3-Na2O has been studied experimentally at 277 and 317°C. The activities of water and boric acid have been determined at mole ratios Na/B from 0 to 1.5, and total dissolved solids 3 to 80 weight percent. The activity of boric acid has been fitted to within experimental error using a speciation model with eight complex species. This model is consistent with the model previously published by Mesmer et al. The electrolyte properties of the liquid are modeled using the Pitzer-Simonson model of very concentrated electrolyte solutions. The calculated values of water activity agree with experiment, and the activity of NaOH and pOH have also been calculated. The potassium borate system also was briefly studied at 317°C, and is adequately described by a model with five complex species. The potassium borate liquid is more alkaline at K/B= 1 than a sodium borate liquid at the same mole ratio, but pOH in the two systems is the same at lower mole ratios. 相似文献
23.
The interaction of AlR2(BHT)(OEt2) and AlMe(BHT)2 with methylmethacrylate (MMA) leads to the formation of the Lewis acid-base complexes AlR2(BHT)(MMA) [R = Me (1), Et (2)] and AlMe-(BHT)2(MMA) (3), respectively. The molecular structure of 1 has been determined by X-ray crystallography. The decrease in the C=O and C=C stretching frequencies in the IR spectrum, and downfield shift in the 13C NMR spectrum of the - and γ-carbons of the MMA, when compared to free MMA, is presented with respect to the activator ability of sterically crowded aryloxide compounds of aluminum to aluminum-porphyrin catalyzed (Inoue) polymerization of MMA. 相似文献
24.
A. I. Sizov T. M. Zvukova A. A. Gorkovskii Z. A. Starikova B. M. Bulychev 《Russian Chemical Bulletin》2004,53(10):2175-2178
The [Cp2HfH2Al(H)Br(OBu)]2 complex (1) was prepared by the reaction of Cp2HfBr2 with AlH3 in THF and characterized by X-ray crystallography. The formation of dinuclear complex 1 proceeds through the intermediate formation (as a result of cleavage of THF molecules) of the >Al(μ-OBu)2Al< fragment. The latter is linked to two hafnocene dihydride molecules by the Hf-H-Al hydrogen bridges. The Hf atom in complex 1 has a 16-electron environment.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2082–2085, October, 2004. 相似文献
25.
26.
This is the first report on the determination of proteins with tetra-substituted sulphonated aluminum phthalocyanine (AlS4Pc) by resonance light-scattering (RLS). At pH 3.0, the weak RLS of AlS4Pc can be enhanced by the addition of proteins. Based on this, a novel quantitative method has been developed for the determination of proteins in aqueous solutions. Under optimal conditions, the linear ranges of the calibration curves were 0.050–2.0 μg ml−1 for both human serum albumin (HSA) and human r-IgG. The detection limits were 12.7 ng ml−1 for HSA and 16.1 ng ml−1 for human r-IgG. The method has been applied to the analysis of total protein in human serum samples collected from the hospital and the results were in good agreement with those reported by the hospital, which indicates that the method presented here is not only sensitive, simple, but also reliable and suitable for practical applications. 相似文献
27.
The reaction of diethyl 3-ethoxycarbonyl-2-methyl-2-propenylphosphonate (1a) with 3-methylbutanal (2) in heterogeneous MOH (solid)-benzene systems in the presence of 5–10 mol.% of benzyltriethylammonium chloride (BTEAC) gives the reaction product (3) with a higher, for M=K, or lower, for M=Li, ratio of 2E,4E and 2Z,4E-stereoisomers than that observed in the absence of BTEAC. Tetrabutylammonium bromide (TBAB) as a catalyst of the reaction1a + 2 3 in the system KOH (solid)-wet benzene leads to a higher [2E,4E-3][2Z,4E-3] ratio than BTEAC; this ratio grows from 4456 without TBAB to 8020 at 100 mol.% of TBAB. In the latter case the stereochemical outcome of the reaction is similar to that obtained when tetrabutylammonium hydroxide in dry benzene is used as the deprotonating agent. The corresponding diisopropyl phosphonate (1b) and 3,7-dimethyloctanal (4a) interact in the system KOH (solid)-wet benzene-TBAB to give hydroprene (5) containing 88 % of the 2E,4E-isomer (5a) while in the case of 1 equiv. of [(n-Bu4)N]OH in dry benzene the content of5a is 92 %. Diisopropyl 3-isopropoxycarbonyl-2-methyl-2-propenylphosphonate (1c) and 7-methoxy-3,7-dimethyloctanal (4b) under either of these conditions afford methoprene (6) containing 93 % of the 2E,4E-isomer.Part 6, see ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1094–1098, June, 1993. 相似文献
28.
Thermogravimetric analysis is used to determine the amounts of Mg(OH)2 and Mg(CH3COO)2in a mixture thereof. The application and suitability of different analysis methods are discussed. In the first method the
mass losses in the temperature ranges as indicated by the decomposition of the pure compounds were used. Results obtained
using these temperature ranges were unusable. The percentage mass losses due to the decomposition of Mg(OH)2 and Mg(CH3COO)2 were then determined in a second method using the minimum in the derivative mass vs. temperature curves. The results obtained
by this method compared well with the actual values for mixtures containing more than 15% magnesium acetate. The third method
employed the total experimental mass loss of both decomposition reactions. The results obtained using this method compared
well to the actual values, giving a R
2 value of more than 0.99. This method of using the total mass losses can however only be used for binary mixtures that consist
only of magnesium hydroxide and magnesium acetate.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
29.
30.