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91.
The discrimination between cyclomonomers and various oligomers formed during a ring-closing metathesis (RCM) process is not an easy task. Their (1)H NMR patterns are often very similar, and the use of mass spectrometry techniques is usually recommended. Here, we show that the DOSY-NMR method is a reliable tool to help in the identification of cyclomonomers versus cyclodimers by comparing the translational diffusion coefficient of the compounds issued from RCM reactions with the diffusion coefficient of their respective precursors. 相似文献
92.
93.
Jacqueline Arguello Hérica A. Magosso Thiago C. Canevari Richard Landers Yoshitaka Gushikem 《Electroanalysis》2011,23(2):334-338
Selective electroanalytical responses for ascorbic acid, dopamine and uric acid at a carbon modified electrode based on 3‐n‐propyl‐1‐azonia‐4‐azabicyclo[2.2.2]octane silsesquioxane chloride (SiDbCl) is reported. The overlapped peaks observed at an unmodified electrode are resolved into three well defined voltammetric peaks allowing the simultaneous determination of the three species. Detection limits of 37, 0.3 and 0.1 μmo L−1 of ascorbic acid, dopamine and uric acid, respectively, were calculated from calibration curves based on differential pulse voltammetric experiments performed in Britton ‐ Robinson buffer solution at pH 7.04. 相似文献
94.
Xu F Du S Liu Y Hassan J Zhang J Bond AM 《Dalton transactions (Cambridge, England : 2003)》2011,40(41):10907-10917
A potential model complex for the hydrogenase active site, [Fe(2){(μ-CH(2)S)(2)R}(CO)(6)] (1) (R = quinoxaline), was synthesized by condensation of [(μ-LiS)(2)Fe(2)(CO)(6)] with 2,3-bis(bromomethyl)quinoxaline. Reactions of 1 with bis(diphenylphosphino)methane (dppm) under a range of conditions yielded substituted complexes [Fe(2){(μ-CH(2)S)(2)R}(CO)(5)(dppm)] (2), [Fe(2){(μ-CH(2)S)(2)R}(CO)(4)(k(2)-dppm)] (3) and [Fe(2){(μ-CH(2)S)(2)R}(CO)(4)(μ-dppm)] (4). X-ray crystallography confirms that in 2, the dppm is terminally bonded to an iron atom via one phosphorus atom, whereas in 3, it acts as a chelating ligand to coordinate to an iron center in a dibasal-substituted manner. In 4, the dppm bridges the two iron atoms in a cis basal/basal fashion with one phosphorus bonded to each iron atom. Treatment of 1 with various tertiary phosphines at room temperature in acetonitrile (MeCN) generates a range of mono-substituted products [Fe(2){(μ-CH(2)S)(2)R}(CO)(5)L] (5, L = PEt(3); 6, PMe(3); 7, PPh(3); 8, Me(2)PPh). With Bu(t)NC, mono- and di-substituted [Fe(2){(μ-CH(2)S)(2)R}(CO)(5)(Bu(t)NC)] (9) and [Fe(2){(μ-CH(2)S)(2)R}(CO)(4)(Bu(t)NC)(2)] (10) complexes are generated. All the complexes were characterized by elemental analysis, IR, MS and NMR spectroscopy. IR and NMR spectroscopic studies suggest that addition of excess HBF(4)·OEt(2) acid to 1-4 led to the protonation of quinoxaline nitrogen atoms. In contrast, 5-10 were not stable in acidic media. Electrochemistry of 1-4 was investigated in the acetonitrile medium (0.1 M Bu(4)NPF(6)). The electrochemical instability of the reduced ligand, quinoxaline, and the reduced forms of these complexes revealed from the electrochemical studies suggests that they do not provide ideal models of the hydrogenase active site. 相似文献
95.
Volkov AG Baker K Foster JC Clemmons J Jovanov E Markin VS 《Bioelectrochemistry (Amsterdam, Netherlands)》2011,81(1):39-45
The circadian clock regulates a wide range of electrophysiological and developmental processes in plants. This paper presents, for the first time, the direct influence of a circadian clock on biologically closed electrochemical circuits in vivo. Here we show circadian variation of the plant responses to electrical stimulation. The biologically closed electrochemical circuits in the leaves of Aloe vera and Mimosa pudica, which regulate their physiology, were analyzed using the charge stimulation method. The electrostimulation was provided with different timing and different voltages. Resistance between Ag/AgCl electrodes in the leaf of Aloe vera was higher during the day than at night. Discharge of the capacitor in Aloe vera at night was faster than during the day. Discharge of the capacitor in a pulvinus of Mimosa pudica was faster during the day. The biologically closed electrical circuits with voltage gated ion channels in Mimosa pudica are also activated the next day, even in the darkness. These results show that the circadian clock can be maintained endogenously and has electrochemical oscillators, which can activate ion channels in biologically closed electrochemical circuits. We present the equivalent electrical circuits in both plants and their circadian variation to explain the experimental data. 相似文献
96.
Nethravathi C Rajamathi JT George P Rajamathi M 《Journal of colloid and interface science》2011,354(2):793-797
A new anionic clay, α-magnesium hydroxide, was synthesized by hydrolysis of magnesium acetate in propylene glycol. The structure of this α-hydroxide is similar to that of hydrotalcites. It consists of positively charged magnesium hydroxide layers arising out of partial protonation of the hydroxyl groups of the [Mg(OH)(2)] layers and loosely held anions in the interlayer region. As expected it ages readily in water to give β-magnesium hydroxide, brucite. While anion-exchange reactions of α-magnesium hydroxide could not be carried out in aqueous medium a number of anion-exchange reactions could be carried out successfully in ethanol medium. 相似文献
97.
Aspinall HC Bacsa J Jones AC Wrench JS Black K Chalker PR King PJ Marshall P Werner M Davies HO Odedra R 《Inorganic chemistry》2011,50(22):11644-11652
Thin films of ceria (CeO(2)) have many applications, and their synthesis by liquid-injection MOCVD (metal-organic chemical vapor deposition) or ALD (atomic layer deposition) requires volatile precursor compounds. Here we report the synthesis of a series of homoleptic and heteroleptic Ce(IV) complexes with donor-functionalized alkoxide ligands mmp (1-methoxy-2-methylpropan-2-olate), dmap (1-(dimethylamino)propan-2-olate), and dmop (2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)propan-2-olate) and their potential as precursors for MOCVD and ALD of CeO(2). New complexes were synthesized by alcohol exchange reactions with [Ce(OBu(t))(4)]. [Ce(mmp)(4)] and [Ce(dmap)(4)] were both found to be excellent precursors for liquid-injection MOCVD of CeO(2), depositing high purity thin films with very low carbon contamination, and both have a large temperature window for diffusion controlled growth (350-600 °C for [Ce(mmp)(4)]; 300-600 °C for [Ce(dmap)(4)]). [Ce(mmp)(4)] is also an excellent precursor for liquid-injection ALD of CeO(2) using H(2)O as oxygen source and demonstrates self-limiting growth from 150 to 350 °C. [Ce(dmap)(4)] has lower thermal stability than [Ce(mmp)(4)] and does not show self-limiting growth in ALD. Heteroleptic complexes show a tendency to undergo ligand redistribution reactions to form mixtures in solution and are unsuitable as precursors for liquid-injection CVD. 相似文献
98.
Driesschaert B Robiette R Lucaccioni F Gallez B Marchand-Brynaert J 《Chemical communications (Cambridge, England)》2011,47(16):4793-4795
We report that tetrathiatriarylmethyl (trityl) EPR probes are chiral molecules at room temperature, the two stereoisomers that differ in their helicity being configurationally stable enough to be separated and stored independently. 相似文献
99.
Flow boiling heat transfer and pressure drop of R-134a in a mini tube: an experimental investigation 总被引:1,自引:0,他引:1
Jacqueline B. Copetti Mario H. MacagnanFlávia Zinani Nicole L.F. Kunsler 《Experimental Thermal and Fluid Science》2011,35(4):636-644
This paper presents the results of an experimental study carried out with R-134a during flow boiling in a horizontal tube of 2.6 mm ID. The experimental tests included (i) heat fluxes in the range from 10 to 100 kW/m2, (ii) the refrigerant mass velocities set to the discrete values in the range of 240-930 kg/(m2 s) and (iii) saturation temperature of 12 and 22 °C. The study analyzed the heat transfer, through the local heat transfer coefficient along of flow, and pressure drop, under the variation of these different parameters. It was possible to observe the significant influence of heat flux in the heat transfer coefficient and mass velocity in the pressure drop, besides the effects of saturation temperature. In the low quality region, it was possible to observe a significant influence of heat flux on the heat transfer coefficient. In the high vapor quality region, for high mass velocities, this influence tended to vanish, and the coefficient decreased. The influence of mass velocity in the heat transfer coefficient was detected in most tests for a threshold value of vapor quality, which was higher as the heat flux increased. For higher heat flux the heat transfer coefficient was nearly independent of mass velocity. The frictional pressure drop increased with the increase in vapor quality and mass velocity. Predictive models for heat transfer coefficient in mini channels were evaluated and the calculated coefficient agreed well with measured data within a range 35% for saturation temperature of 22 °C. These results extend the ranges of heat fluxes and mass velocities beyond values available in literature, and add a substantial contribution to the comprehension of boiling heat transfer phenomena inside mini channels. 相似文献
100.