全文获取类型
收费全文 | 10636篇 |
免费 | 527篇 |
国内免费 | 130篇 |
专业分类
化学 | 7518篇 |
晶体学 | 103篇 |
力学 | 523篇 |
综合类 | 3篇 |
数学 | 1322篇 |
物理学 | 1824篇 |
出版年
2024年 | 21篇 |
2023年 | 85篇 |
2022年 | 295篇 |
2021年 | 448篇 |
2020年 | 370篇 |
2019年 | 457篇 |
2018年 | 466篇 |
2017年 | 388篇 |
2016年 | 620篇 |
2015年 | 438篇 |
2014年 | 590篇 |
2013年 | 1097篇 |
2012年 | 830篇 |
2011年 | 812篇 |
2010年 | 573篇 |
2009年 | 470篇 |
2008年 | 515篇 |
2007年 | 468篇 |
2006年 | 330篇 |
2005年 | 348篇 |
2004年 | 207篇 |
2003年 | 213篇 |
2002年 | 176篇 |
2001年 | 95篇 |
2000年 | 64篇 |
1999年 | 66篇 |
1998年 | 45篇 |
1997年 | 54篇 |
1996年 | 51篇 |
1995年 | 39篇 |
1994年 | 41篇 |
1993年 | 26篇 |
1992年 | 40篇 |
1991年 | 36篇 |
1990年 | 37篇 |
1989年 | 37篇 |
1988年 | 36篇 |
1987年 | 38篇 |
1986年 | 34篇 |
1985年 | 37篇 |
1984年 | 35篇 |
1983年 | 21篇 |
1982年 | 28篇 |
1981年 | 19篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1978年 | 18篇 |
1976年 | 15篇 |
1975年 | 13篇 |
1974年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
191.
Mohammad Ali Karimi Mohammad Mazloum Ardakani Omran Moradlou Reza Behjatmanesh‐Ardakani Fatemeh Banifatemeh 《中国化学会会志》2007,54(1):15-21
Simultaneous kinetic‐spectrophotometric determination of a ternary mixture of hydrazine (HZ) and its derivatives by principal component regression (PCR) and partial least squares (PLS) calibration is described. The methods were based on the difference observed in the reduction rate of iron(III) with HZ, thiosemicarbazide (TSCZ) and phenylhydrazine (PHZ) in the presence of 2,2′‐bipyridine (Bpy). The colored complex of [Fe(Bpy)3]2+ was formed in sodium dodecyl sulfate (SDS) as micellar media, and then monitored at 520 nm. The results showed that simultaneous determination of HZ, TSCZ and PHZ could be performed in their concentration ranges of 1.0–70.0, 0.2–6.0 and 0.1–10.0 μg mL?1, respectively. The root mean squares errors of prediction (RMSEP) of HZ, TSCZ and PHZ were 0.719, 0.164 and 0.105 (for PLS) 0.788, 0.166 and 0.993 (for PCR), respectively. Both methods (PCR and PLS) were validated using a set of synthetic sample mixtures and then applied for simultaneous determination of HZ, TSCZ and PHZ in water samples. 相似文献
192.
I. M. Ali 《Journal of Radioanalytical and Nuclear Chemistry》2004,260(1):149-157
A new form of semicrystalline sodium titanate was synthesized at high temperature (1100-1150 °C) by a reaction of TiO2 with Na2CO3 in an equimolar ratio. The obtained product was characterized using IR, DTA-TG, X-ray diffraction and elemental analyses.
According to X-ray patterns, H2Ti5O11
.
nH2O with monoclinic structure has been formed on dehydration of semicrystalline sodium titanate. Kinetic studies of the order
and activation energy of a new phase transformation have been determined from DTA-thermograms. The ion exchange behavior of
semicrystalline sodium titanate was studied at different g-doses as well as at different drying temperatures. The laboratory-scale
ion exchange capacity, distribution studies and exchange performance for some radionuclides of a thermally prepared material
were investigated. It was found that the exchange capacity was not changed after 100 kGy irradiation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
193.
Al Electrode Modified by Au Atoms as a Novel Electrode for Electrocatalytic Oxidation of Thiosulfate
An aluminum electrode modified with gold atoms was introduced as a novel electrode. Gold atoms were deposited both chemically and electrochemically onto the aluminum electrode to make an aluminum/gold (Al/Au) modified electrode (ME). The experimental results showed that the Al/Au modified electrode prepared by chemical deposition, exhibits much more current than the electrochemical deposition method. The electrochemical behavior of the Al/Au modified electrode was studied by cyclic voltammometry. This modified electrode showed two pairs of peaks, a1c1 and a2c2, with surface‐confined characteristics in a 0.5 M phosphate buffer. The dependence of Epa of the second peak (a2c2) on pH shows a Nernestian behavior with a slope of 55 mV per unit pH. The effect of different supporting electrolytes, solution's pH and different scan rates on electrochemical behavior of Al/Au modified electrode was studied. Au deposited electrochemically on a Pt electrode (Pt/Au) was also used as another modified electrode. A comparative study of electrochemical behavior of bare Al, Pt/Au and Al/Au modified electrodes showed that both Pt/Au and Al/Au electrodes have the ability of electrocatalytic oxidation of S2O32?, but the electrocatalytic oxidation on the latter was better than the former. The kinetics of the catalytic reaction was investigated by using cyclic voltammetry and chronoamperometry techniques. The average value of the rate constant for the catalytic reaction and the diffusion coefficient were evaluated by means of chronoamperometry technique. 相似文献
194.
The oxidation of CoIIW by bromine(V) is a complex process involving an induction period. The reaction was found to be first-order in both [CoIIW] and [Brv], and exhibits a complex dependence on [H+]. These observations were successfully explained by considering HBrO2, one of the intermediates formed in the direct but slow reaction between CoIIW and bromine(V), as the reacting species. The first-order limiting dependence in [H+] was due to the involvement of a protic equilibrium of HBrO2. The induction period appears due to the scavenging effect of Br– inadvertently present in the medium. It appears to be the first report where HBrO2 was found to be the reacting intermediate in the oxidation of metal ions and complexes by BrO–
3. 相似文献
195.
[structure: see text] We have combined carborane chemistry with the newly developed directional bonding strategy to synthesize neutral macrocycles. The m- and p-carborane dicarboxylates were utilized as the donor linkers in conjunction with 1,8-bis[trans-Pt(PEt3)2NO3]anthracene 3, 2,9-bis[trans-Pt(PEt3)2NO3]phenanthrene 5, and cis-Pt(PEt3)2(NO3)2 unit 6. Three new platinum-based macrocycles, 4, 7, and 8, were thus synthesized. 31P{1H} NMR as well as the X-ray characterization of Pt-metallacycles reveal the formation of single highly symmetrical neutral species. 相似文献
196.
197.
Silica gel-loaded (E)-N-(1-thien-2'-ylethylidene)-1,2-phenylenediamine (TEPDA) phase was synthesized based on physical adsorption approaches. The stability of a chemically modified TEPDA especially in concentrated hydrochloric acid that was then used as a recycling and preconcentration reagent allowed the further uses of silica gel-loaded immobilized TEPDA phase. The application of this silica gel-loaded phase to sorption of a series of metal ions was performed by using different controlling factors such as the pH of the metal ion solution and the equilibration shaking time by the static technique. This difference was interpreted on the basis of selectivity incorporated in these sulfur containing silica gel-loaded TEPDA phases. Hg(Ⅱ) was found to exhibit the highest affinity towards extraction by these silica gel-loaded TEPDA phases. The pronounced selectivity was also confirmed by the determined distribution coefficients (Kd) of all the metal ions, showing the highest value reported for mercury(Ⅱ) extraction by the silica gel immobilized TEPDA phase. The potential applications of the silica gel immobilized TEPDA phase to selective extraction of mercury(Ⅱ) from aqueous solution were successfully accomplished and preconcentration of low concentration of Hg(Ⅱ) (30 pg·mL^-1) from natural tap water with a preconcentration factor of 200 for Hg(Ⅱ) off-line analysis was conducted by cold vapor atomic absorption analysis. 相似文献
198.
Rangwalla H Schwab AD Yurdumakan B Yablon DG Yeganeh MS Dhinojwala A 《Langmuir : the ACS journal of surfaces and colloids》2004,20(20):8625-8633
A new and direct approach to verify surface heterogeneity as the microscopic origin of contact-angle hysteresis is demonstrated. IR-visible sum-frequency-generation spectroscopy (SFG) was used to selectively probe the molecules at the interface of an alkyl-side-chain polymer [poly(vinyl n-octadecyl carbamate-co-vinyl acetate)] with water. The spectra indicate that in contact with water, the polymer surface is heterogeneous (having areas of differing surface energies). This evidence of surface heterogeneity supports the hysteresis observed in the advancing and receding contact angles of the polymer surface with water. The same measurements made for the chemically and structurally similar surface of an octadecyltrichlorosilane self-assembled monolayer indicates a homogeneous surface at the water interface. In this case, contact-angle hysteresis measurements implicate surface roughness as the cause of hysteresis. Atomic force microscopy measurements of roughness for these surfaces further support our conclusions. The polymer-water interface was probed using SFG at above-ambient temperatures, and an order-to-disorder transition (ODT) of alkyl side chains at the interface was observed, which closely follows the melting of crystalline side chains in the bulk. This transition explains the increased wettability of the polymer, by water, when the temperature is raised above the bulk melting temperature. Furthermore, the irreversibility of this ODT suggests that the disordered polymer-water interface is the thermodynamic equilibrium state, whereas the before-heating structure of this interface is a kinetically hindered metastable state. 相似文献
199.
Maria E. Sulbaran Gerzon E. Delgado Asilo J. Mora Ali Bahsas Hector Novoa de Armas Norbert Blaton 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(9):o543-o545
In the title compound, C6H8N2O2S, also known as N‐acetyl‐2‐thiohydantoin–alanine, the molecules are joined by N—H...O hydrogen bonds, forming centrosymmetric R22(8) dimers; these dimers are linked by C—H...O interactions to form R22(10) rings, thus forming C22(10) chains that run along the [101] direction. 相似文献
200.
Mohamed M. El-Kerdawy Ali A. El-Emam Hussein I. El-Subbagh Elie Abushanab 《Monatshefte für Chemie / Chemical Monthly》1990,121(1):45-50
Summary A new series of thiophenic isosters of thioxanthones, namely: 2-substituted-4H-thieno[2,3-b][1]benzothiopyran-4-ones and 5-substituted-2-nitro-8-methyl-4H-thieno[2,3-b][1]benzothiopyran-4-ones were synthesized as potential schistosomicidal agents. The synthesized compounds were characterized by their1H-NMR data.
Synthese von substituierten 4H-Thieno[2,3-b][1]benzothiopyran-4-onen als mögliche schistosomicide Wirkstoffe
Zusammenfassung Es wurde eine neue Serie von thiophenischen Isosteren des Thioxanthons, nämlich 2-substituierte 4H-Thieno[2,3-b][1]benzothiopyran-4-one und 5-substituierte 2-Nitro-8-methyl-4H-thieno[2,3-b][1]benzothiopyran-4-one als potentielle schistosomicide Wirkstoffe synthetisiert. Die synthetisierten Verbindungen wurden mittels ihrer1H-NMR Daten charakterisiert.相似文献