全文获取类型
收费全文 | 3476篇 |
免费 | 124篇 |
国内免费 | 18篇 |
专业分类
化学 | 2406篇 |
晶体学 | 20篇 |
力学 | 78篇 |
数学 | 485篇 |
物理学 | 629篇 |
出版年
2023年 | 30篇 |
2022年 | 41篇 |
2021年 | 83篇 |
2020年 | 56篇 |
2019年 | 51篇 |
2018年 | 43篇 |
2017年 | 48篇 |
2016年 | 100篇 |
2015年 | 100篇 |
2014年 | 100篇 |
2013年 | 166篇 |
2012年 | 201篇 |
2011年 | 278篇 |
2010年 | 157篇 |
2009年 | 143篇 |
2008年 | 206篇 |
2007年 | 242篇 |
2006年 | 222篇 |
2005年 | 172篇 |
2004年 | 143篇 |
2003年 | 118篇 |
2002年 | 110篇 |
2001年 | 70篇 |
2000年 | 68篇 |
1999年 | 49篇 |
1998年 | 32篇 |
1997年 | 45篇 |
1996年 | 43篇 |
1995年 | 38篇 |
1994年 | 23篇 |
1993年 | 35篇 |
1992年 | 33篇 |
1991年 | 18篇 |
1990年 | 28篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1986年 | 23篇 |
1985年 | 18篇 |
1984年 | 27篇 |
1983年 | 14篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 14篇 |
1979年 | 20篇 |
1978年 | 11篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 11篇 |
1930年 | 6篇 |
排序方式: 共有3618条查询结果,搜索用时 15 毫秒
81.
Determination of rotenone residues in raw honey by solid-phase extraction and high-performance liquid chromatography 总被引:8,自引:0,他引:8
Jiménez JJ Bernal JL del Nozal MJ Novo M Higes M Llorente J 《Journal of chromatography. A》2000,871(1-2):67-73
A method for determining residues of the insecticide rotenone in raw-honey by high-performance liquid chromatography (HPLC) is described. To extract the residues, organic solvents such as ethyl acetate, n-hexane/dichloromethane and solid-phase extraction with octadecylsilane cartridges or Florisil packed columns were tested. Determination was carried out by reversed-phase HPLC using acetonitrile-buffer phosphate (pH 7) (60:40, v/v) as mobile phase and detection at 210 nm. Although the data showed that the two extraction methods were able to isolate the pesticide residues, the extraction on octadecylsilane cartridges was preferred due to its simplicity and higher recovery. Recoveries depended strongly on the fortification level for the two extraction procedures. Practical determination limits of 0.015 mg/kg were obtained. In the analysis of honeys, from beehives treated with rotenone at therapeutical doses for 1 month, residual amounts below 0.2 mg/kg were found. 相似文献
82.
Istratescu's characterization of complex strict convex (csc) Banach spaces is used to show that a modulared sum of a sequence ofcsc Banach spaces is again acsc Banach space. The equivalence of the Strong Maximum Modulus Property and complex strict convexity is used to show thatL
1(,X) iscsc whenX is (real) strictly convex and thatl
1(X
n) iscsc if and only if eachX
n iscsc. 相似文献
83.
84.
85.
R. Roque-Malherbe A. Berazain J. A. del Rosario 《Journal of Thermal Analysis and Calorimetry》1987,32(3):949-951
The ionexchange heats of homoionic heulandite and mordenite were measured with a microcalorimeter. In the case of K, NH4, Na, Mg and Ca, the selectivity of the zeolite is determined by the heat of hydration.We are very grateful to Dr. Ingemar Wadso from the Division of Thermochemistry of the University of Lund, Sweden, and to Dr. R. Ohlen from LKB, Sweden, for their advice, and to Ing. Valentina Zelenenko and Lic. Jose Sosa for providing homoionic samples. 相似文献
86.
Toribio L del Nozal MJ Bernal JL Jiménez JJ Alonso C 《Journal of chromatography. A》2004,1046(1-2):249-253
The enantiomeric separation of six triazole pesticides: cyproconazole, propiconazole, diniconazole, hexaconazole, tebuconazole and tetraconazole, using supercritical fluid chromatography and the Chiralpak AD column, is presented in this work. The effect of different organic modifiers such as methanol, ethanol and 2-propanol on the retention and resolution was studied as well as the presence of additives in the mobile phase. The results obtained were highly successful, all the compounds were enantiomerically separated and in most of the cases the analysis time was close to 10 min. The type of organic modifier that provided the best results depended on the compound. 相似文献
87.
Y. Pesheva N. Abadzhjieva E. Vrachnou Y. Kovanis V. Rives C. del Hoyo D. Klissurski 《Reaction Kinetics and Catalysis Letters》1994,53(2):283-288
Methanol oxidation on V2O5 and V2O5–MoO3 catalysts supported on montmorillonite has been studied in the temperature range of 250–500°C. The V2O5–MoO3 containing sample shows higher selectivity towards formaldehyde formation than the V2O5 catalyst. 相似文献
88.
Summary A model of the mechanism for recognition of the D1 receptor has been developed. Conformational analysis for 10 agonists from diverse chemical families was carried out as a first step toward the characterization of the bioactive form. First, maximum structural overlap of the features common to all ligands allowed a simple identification of the candidate bioactive form for each ligand. At a second level of characterization, steric and electronic properties were computed for all accessible structures to analyze those properties that may modulate receptor recognition. 相似文献
89.
Li I Bandara J Shultz MJ 《Langmuir : the ACS journal of surfaces and colloids》2004,20(24):10474-10480
Many interfacial studies on solid surfaces, for example, quartz/water, assume that a standard cleaning procedure regenerates the surface reproducibly. In the reported work, the results of two surface specific techniques, sum frequency generation (SFG) spectroscopy and atomic force microscopy, show that the effects of prolonged exposure to Nanopure water and to pH 10 NaOH are distinctly different. In conjunction with the experimental data, molecular mechanics is used to correlate the SFG spectral frequencies to the hydrogen stretching vibrations of the surface-bound water molecules. It is found that after 17 days of soaking in water, water molecules penetrate into the SiO2 matrix to produce a swollen and amorphous layer; it is likely that broken Si-O bonds from the polishing process serve as nucleation sites for hydration and swelling. Disorder introduced in the interfacial water layer is detected by the rising intensity of the weakly hydrogen-bonded SFG peak at 3450 cm(-1). Dominance of the 3450 cm(-1) is absent in a pH 10, NaOH-soaked quartz disk, indicating that the strong hydrogen-bonded network in water remains intact. 相似文献
90.
Aimée Arias-Carbajal Reádigos Roberto Cao Vázquez José R. del Bosque Arin 《Transition Metal Chemistry》1989,14(1):42-44
Summary The electronic properties of a series of cobalt(III)trans-furyldioximato-complexes of the type [CoB(FH)2X] (B=NH3, X=Cl, Br, I or NO2; B=pyridine (py) or thiocarbamide (thio), X=Cl or Br; B=imidazole (imid), X=Br), [Co(FH2)(FH)Cl2] and [Co(thio)2(FH)2]NO3 were studied by i.r., u.v. and1H and13C n.m.r. spectra The results were compared with those from the corresponding dimethylglyoximato-complexes. It was concluded that -conjugation over the equatorial plane in the furyldioximates is greater than in the dimethylglyoximates. There is some evidence of thetrans-influence of the anionic ligands in the ammines which are in the order NO
2
–
>Br–>Cl–. 相似文献