全文获取类型
收费全文 | 1600篇 |
免费 | 131篇 |
国内免费 | 47篇 |
专业分类
化学 | 801篇 |
晶体学 | 86篇 |
力学 | 409篇 |
综合类 | 22篇 |
数学 | 96篇 |
物理学 | 364篇 |
出版年
2024年 | 4篇 |
2023年 | 14篇 |
2022年 | 26篇 |
2021年 | 17篇 |
2020年 | 35篇 |
2019年 | 24篇 |
2018年 | 24篇 |
2017年 | 37篇 |
2016年 | 55篇 |
2015年 | 41篇 |
2014年 | 65篇 |
2013年 | 89篇 |
2012年 | 68篇 |
2011年 | 77篇 |
2010年 | 68篇 |
2009年 | 91篇 |
2008年 | 93篇 |
2007年 | 83篇 |
2006年 | 93篇 |
2005年 | 106篇 |
2004年 | 85篇 |
2003年 | 76篇 |
2002年 | 62篇 |
2001年 | 57篇 |
2000年 | 47篇 |
1999年 | 38篇 |
1998年 | 47篇 |
1997年 | 38篇 |
1996年 | 36篇 |
1995年 | 40篇 |
1994年 | 28篇 |
1993年 | 17篇 |
1992年 | 16篇 |
1991年 | 17篇 |
1990年 | 14篇 |
1989年 | 8篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有1778条查询结果,搜索用时 31 毫秒
61.
The model proteins cytochrome c, myoglobin, ovalbumin, and beta-lactoglobulin were investigated with regard to their adsorption properties on capillaries for electrophoresis. The model compounds were selected to cover a wide range of properties. Cytochrome c is a basic protein (isoelectric point (pI): 9.6; M(r): 11.7 kDa), beta-lactoglobulin is rather acidic (pI: 5.4, M(r): 18.4 kDa), myoglobin was chosen as a neutral reference protein (pI: 6.8-7.4, M(r): 17.8 kDa), and ovalbumin (pI: 5.1, M(r): 45.0 kDa) was selected as a relatively larger analyte. First, the pH dependence of adsorption was investigated for the bare fused silica. A clear correlation to the respective pIs was noted. For myoglobin and ovalbumin, none or negligible adsorption was found above the pI, whereas strong adsorption was noted just below this parameter. Cytochrome c and beta-lactoglobulin already showed distinct adsorption above their pIs. However, none of the proteins showed any significant adsorption more than one pH unit above the pIs. For linear polyacrylamide-coated capillaries, a decreased but not a complete lack of adsorption was observed. Here, pH-dependent adsorption was noted as well. Regeneration of the capillaries by rinsing with buffers containing 200 mM SDS was also investigated. This method was completely successful for myoglobin, but that too for only freshly-adsorbed protein. After a storage time of 24 h and due to the aging of the adsorbate, a sufficient regeneration was no longer possible. 相似文献
62.
PengZHANG JiCunREN ZuoJunSHEN 《中国化学快报》2004,15(9):1091-1094
In this paper, we first presented a novel method for quantification of circulating DNA in human serum based on capillary zone electrophoresis with laser-induced fluorescence detection (CZE-LIF). The serum was digested by proteinase to release free DNA, and then CZE-LIF system was used for the quantification of total circulating DNA. This method was successfully used to quantify the circulating DNA levels in sera from healthy individuals and certain cancer patients.We found the significantly elevated circulating DNA levels in certain prostate cancer patients. Our results demonstrated that CZE-LIF system has good linearity, excellent sensitivity (0.5 ng/mL DNA),satisfactory reproducibility (RSDs in one day and between days were both less than 5%) and reliability, and is well suitable to the quantification of the circulating DNA in human serum or plasma. 相似文献
63.
Chiral separation method development is usually very time-consuming due to the diversity in chemical structures of pharmaceutical drug substances as well as the suitable separation conditions and the problem to choose the appropriate chiral selector. This paper shows capillary zone electrophoresis (CZE) which was developed for chiral separation of a basic compound - rivastigmine (RIV) using 30 cm × 50 μm i.d. polyacrylamide (PAA)-coated fused-silica capillary (effective length 20 cm), amine-modified phosphate buffer of pH 2.5 and sulfated-β-CD (S-β-CD) as chiral selector. Other selected native or derivatized cyclodextrins (CDs) were also tested: β-CD (5, 30 mM), carboxymethyl-β-CD (5, 30 mM), dimethyl-β-CD (15 mM), hydroxypropyl-β-CD (5, 30 mM), hydroxypropyl-α-CD (5, 30 mM) and hydroxypropyl-γ-CD (5, 30 mM). Complete enantiomeric separation of RIV was achieved at 20 kV, 18 °C and detection at 200 nm within 8 min with R.S.D. for the absolute migration time reproducibility of less than 2.1%. Rectilinear calibration range was 5.0-500.0 μM of each enantiomer (r = 0.9994-0.9995). The CZE method proposed was used for the control of chiral purity of pharmaceutically active S-RIV and for the analysis of Exelon caps preparation. 相似文献
64.
A scheme for separation and detection of eleven priority phenols using capillary zone electrophoresis (CZE) coupled with amperometric detection is described. With a capillary of I.D. 50 μm and length 62.5 cm at 9 kV and an electrophoretic buffer of 20 mM CHES (pH 10.1), complete separation of the eleven compounds was achieved in less than 17 min. Amperometric detection was carried out using a carbon fiber microelectrode of diameter 9 μm inserted into the end of the detection capillary. Linearity over two orders of magnitude was generally obtained for the eleven priority phenols. With an electrode potential+1.10 V (vs. Ag/AgCl reference), the concentration limits of detection were in the sub-ppm (10?6 M) level. This method was successfully applied to analysis of priority phenols in industrial waste water. 相似文献
65.
合并带流动注射分光光度法研究硫羟乳酸掩蔽性能 总被引:1,自引:1,他引:1
本文运用合并带流动注射分析技术,建立了以Yb^3+XO显色体系为参考体系研究硫羟乳酸掩蔽性能的方法,在pH5.6硫羟乳酸能掩蔽Sn^4+,Bi^3+,Tl^3+,Hg^2+,Cu^2+,Cr^3+和Cd^2+测定Yb^3+的线性范围为1.36×10^-6~2.72×10^-5mol/L,采样频率可达120次/h。 相似文献
66.
67.
Takashi Kitae Hiroshi Takashima Koji Kano 《Journal of inclusion phenomena and macrocyclic chemistry》1999,33(3):345-359
Chiral recognition of mandelic acid ( 1), acetylmandelic acid ( 2), 1-methoxyphenylacetic acid ( 3), phenylsuccinic acid ( 4), 2-phenylpropanoic acid ( 5) and ibuprofen ( 6) in their anionic forms by protonated 6A-amino-6A-deoxy--cyclodextrin (mono-NH3+--CD) and 6A,6D-diamino-6A,6D-dideo xy--cyclodextrin (di-NH3+--CD) has been studied by means of capillary zone electrophoresis (CZE) and 1H NMR spectroscopy. Both methods show the preferable guests for mono-NH3+--CD to be the (R)-enantiomers of 1, 3 and 5 and the (S)-enantiomers of 2, 4 and 6. Cooperative work of Coulomb interactions and inclusion is essential for chiral recognition of these anionic guests. 相似文献
68.
Determination of rimantadine in pharmaceutical preparations by capillary zone electrophoresis with indirect detection or after derivatization 总被引:2,自引:0,他引:2
Summary Rimantadine is synthetic analog of amantadine; both are antiviral agents used for prophylaxis and treatment of influenza A.
A capillary zone electrophoretic (CZE) procedure for the determination of rimantadine has been developed. As the direct determination
of rimantadine is poorly sensitive because the compound is almost transparent in the UV/Vis range, several indirect methods
were studied. Two were found to be the particularly useful: (a) indirect detection using 5 mM 4-methylbenzylamine in 1:4 methanol-water
as absorbing background electrolyte, with detection at 210 nm, and (b) derivatization of rimantadine with 1,2-naphthoquinone-4-sulfonic
acid in alkaline medium and subsequent determination of the derivative by CZE (40 mM tetraborate, pH 9.2, detection at 280
nm). Uncoated capillary tubing, 44 cm length ×75 μM i.d., was used for both determinations. The detection limits were 0.1
and 2 ppm for methods a and b, respectively. The methods were used to determine rimantadine in pharmaceutical products and
for dissolution testing of Flumadin? tablets. 相似文献
69.
Heat capacities of concentrated multicomponent aqueous electrolyte solutions at various temperatures
Boris S. Krumgalz Ilan A. Malester Irving J. Ostrich Frank J. Millero 《Journal of solution chemistry》1992,21(7):635-649
The specific heat capacities of the aqueous multicomponent system NaCl +KCl+MgCl2+CaCl2 with ionic strength between 8.3 and 9.6 (resembling Dead Sea waters) were measured between 15°C and 45°C. The obtained data were fitted to an empirical equation as a function of concentration and temperature. The thermodynamic functions of the studied multicomponent system were found to be strongly influenced by changes in MgCl2 concentrations. The application of Young's rule to such concentrated systems was checked at 25°C. The calculated (by Young's rule) specific heat capacitiesC
p and apparent molar heat capacities Cp, of these multicomponent electrolyte solutions were in reasonable agreement with the measured values (–0.008 J-g–1-K–1 and –2.6 J-mol–1-K–1, respectively). 相似文献
70.
A method of quickly determining ascorbic acid and sorbic acid by capillary zone electrophoresis with ultraviolet detection was developed. The choice of background electrolyte, wavelength, injection time and applied voltage were discussed. Ascorbic acid and sorbic acid were well separated in 80 mmol L−1 boric acid-5 mmol L−1borax (pH = 8.0) in 5 min at the detecting wavelength of 270 nm. Under the optimum condition, the method has linear ranges of 2.54-352.00 mg L−1 for ascorbic acid and 1.08-336.39 mg L−1 for sorbic acid with the detection limit of 1.70 mg L−1 for ascorbic acid and 0.54 mg L−1 for sorbic acid, respectively. Other organic acids in fruit juices have no effect on the detection. This method is very feasible and simple and can be used to detect ascorbic acid and sorbic acid in fruit juices. 相似文献