全文获取类型
收费全文 | 650篇 |
免费 | 33篇 |
国内免费 | 15篇 |
专业分类
化学 | 465篇 |
晶体学 | 2篇 |
力学 | 43篇 |
数学 | 76篇 |
物理学 | 112篇 |
出版年
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 12篇 |
2020年 | 26篇 |
2019年 | 25篇 |
2018年 | 35篇 |
2017年 | 33篇 |
2016年 | 60篇 |
2015年 | 38篇 |
2014年 | 41篇 |
2013年 | 99篇 |
2012年 | 52篇 |
2011年 | 73篇 |
2010年 | 28篇 |
2009年 | 34篇 |
2008年 | 26篇 |
2007年 | 24篇 |
2006年 | 11篇 |
2005年 | 14篇 |
2004年 | 9篇 |
2003年 | 18篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1984年 | 1篇 |
1976年 | 2篇 |
排序方式: 共有698条查询结果,搜索用时 15 毫秒
1.
2.
Mohammad Reza Ganjali Morteza Rezapour Mohammad Reza Pourjavid Masoud Salavati-Niasari 《Analytical sciences》2003,19(8):1127-1131
A cobalt(II) derivative was used as a suitable ionophore for the preparation of a polymeric membrane nitrite-selective electrode. The electrode reveals a Nemstian behavior over a very wide NO2- ion concentration range (1.0 x 10(-6)-1.0 x 10(-1) M) and a very low detection limit (5.0 x 10(-7) M). The potentiometric response is independent of the pH of solution in the pH range 4.0-9.5. The electrode shows advantages such as low resistance, fast response and, most importantly, good selectivity relative to a wide variety of inorganic and organic anions. In fact, the selectivity behavior of the proposed NO2- ion-selective electrode shows great improvements compared to the previously reported electrodes for nitrite ion. The proposed electrodes could be used for at least 2 months without any significant changes in potentials. The electrode was successfully applied to the determination of nitrate ion concentrations in sausage and milk samples. 相似文献
3.
Polyfunctional quinolines were synthesized using Friedlander method catalyzed by molecular iodine in high yields at 60 °C under solvent‐free conditions. 相似文献
4.
Bahram Hemmateenejad Hashem Sharghi Morteza Akhond Mojtaba Shamsipur 《Journal of solution chemistry》2003,32(3):215-226
The influence of solvent properties on acidity constants of some newly synthesized 9,10-anthraquinone and 9-anthrone derivatives was studied in methanol-water mixtures in a composition range of 0.57 to 1.0 methanol mole fraction. The model was established by using both multiple linear regression and target factor analysis. Both methods revealed that the solvent polarity/polarizability parameter * is a major factor in controlling the acidity behavior of the anthraquinones and anthrones studied in binary methanol-water mixed solvents. A QSPR study was conducted to drive the relationships between the * coefficient s and the polarity/polarizability of molecules. Both dipole moment and polarizability were found to have a linear relationship with s. The results confirm that, in the dipolar protic solvents used, the dipole-dipole interaction (for neutral molecules) and the ion-dipole interaction (for ionized molecules) are the major factors controlling the acidity behavior of these compounds. 相似文献
5.
Sodium-dicyclohexyl- 18-crown-6 complex cation was used as carrier for the uphill transport of zinc as Zn(SCN)42? complex anion. By using L-cysteine as a metal ion acceptor in the receiving phase at the optimized pH of 7.6, the amount of zinc transport through the liquid membrane after 90 min was 97.2 ± 1.0%. The selectivity and efficiency of zinc transport from aqueous solutions containing equimolar mixtures of Ag+, Cd2+ Co2+, Cu2+, Fe2+, Ni2+, Pb2+, Pd2+, Sr2+, Bi3+, Cr3+ and Fe3+ ions was investigated. In the presence of NH2OH.HCl as a suitable masking agent in the source phase, the interfering effect of Cu2+ and Pb2+ ions was diminished drastically. 相似文献
6.
A method for improving separations of peptides and other positively charged species in capillary zone electrophoresis with untreated capillaries using acidic buffers containing tetraalkylammonium cations is described. Tetramethylammonium and tetrabutylammonium cations dynamically modify the capillary surface, leading to a reversal in the direction of the electroosmotic flow. As a result, the adsorption of positively charged peptides and proteins is minimized, and resolution and peak capacity are improved as the migration of cationic analytes is counterbalanced by the electroosmotic flow. The combining effect of reversing electroosmotic flow and cyclodextrin inclusion complexation on separations of closely related peptides and a protein mixture, as well as tryptic digest of hemoglobin is demonstrated. 相似文献
7.
Summary In the present study the effects of addition of iron on the catalytic activity and Si tolerability of Pt/g-Al2O3in the total oxidation of volatile organic compounds were investigated. Preliminary results showed that there is a noticeable
improvement effect on Si-tolerance of catalyst, particularly for short term poison exposure. Bulk analysis of deposited silicon
on the catalyst surface indicated that both Pt/g-Al2O3and iron-doped pellets had roughly the same silicone uptakes. Deactivation of catalyst was reversible and much faster for
iron doped sample. The promoting effects of iron were related to its electronegativity and, to blocking of fewer Pt sites
when iron is present at the surface of the catalyst. 相似文献
8.
A new micelle-mediated phase preconcentration method for preconcentration of ultra-trace quantities of beryllium as a prior step to its determination by spectrophotometry has been developed. Chrome Azurol S (CAS) and cetyltrimethylammonium bromide (CTAB) were used as chelating agent and cationic surfactant, respectively. The method evaluates and eliminates the blank bias error present in such procedures using mean centering of ratio spectra. This procedure gives more accurate results than the traditional approach using absorbance values against reagent blank. The optimal extraction and reaction conditions were studied and the analytical characteristics of the method (e.g., limit of detection, linear range, preconcentration and improvement factors) were obtained. Linearity was obeyed in the range of 0.9-18.0 ng mL−1 (1.00 × 10−7-2.00 × 10−6 mol L−1) of beryllium. The detection limit of the method is 0.51 ng mL−1 (5.66 × 10−8 mol L−1) of beryllium. The interference effect of some anions and cations was also tested. The method was applied to the determination of beryllium in spring water samples. 相似文献
9.
Mohammad Reza Ganjali Morteza HosseiniFatemeh Basiripour Mehran JavanbakhtOmid Reza Hashemi Majid Faal RastegarMojtaba Shamsipur Gerald.W Buchanen 《Analytica chimica acta》2002,464(2):181-186
A novel selective membrane electrode for determination of ultra-trace amount of lead was prepared. The PVC membrane containing N,N′-dimethylcyanodiaza-18-cown-6 (DMCDA18C6) directly coated on a graphite electrode, exhibits a Nernstian response for Pb2+ ions over a very wide concentration range (from 1.0×10−2 to 1.0×10−7 M) with a limit of detection of 7.0×10−8 M (∼14.5 ppb). It has a fast response time of ∼10 s and can be used for at least 2 months without any major deviation in potential. The electrode revealed very good selectivity with respect to all common alkali, alkaline earth, transition and heavy metal ions. The proposed sensor was used as an indicator electrode in potentiometric titration of lead ions and in determination of lead in edible oil, human hair and water samples. The proposed sensor was found to be superior to the best Pb2+-selective electrodes reported in terms of detection limit and selectivity coefficient. 相似文献
10.
Prof. Dr. Fritz Sauter Peter Stanetty Hans Potužak Morteza Baradar 《Monatshefte für Chemie / Chemical Monthly》1976,107(3):669-673
The title substances1 and2 were prepared by acylation of the corresponding ethyl 2-amino-thiophene- (or:-4,5,6,7-tetrahydro-benzo[b]thiophene)-3-carboxylates, in some cases followed by reactions introducing a basic substituent.Additionally a group of 2-aroylamino-thiophene-(or:-4,5,6,7-tetrahydro-benzo[b]thiophene)-3-carboxamides was subjected to ring closure reactions, yielding the corresponding 2-aryl-thieno[2,3-d]pyrimidin-4(3H)-ones and 2-aryl-[1]benzothieno[2,3-d]pyrimidin-4(3H)-ones (both:3).
Zum Teil unter Mitarbeit vonFerdinand Fuhrmann 相似文献
Zum Teil unter Mitarbeit vonFerdinand Fuhrmann 相似文献