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101.
In this article, we report a new method that involves headspace single-drop microextraction and ion chromatography for the preconcentration and determination of fluoride. The method lies in the in situ hydrogen fluoride generation and subsequent sequestration into an alkaline microdrop (15 μL) exposed to the headspace above the stirred aqueous sample. The NaF formed in the drop was then determined by ion chromatography. The influences of some crucial single-drop microextraction parameters such as the extraction temperature, extraction time, sample stirring speed, sulphuric acid concentration and ionic strength of the sample, on extraction efficiency were investigated. In the optimal condition, an enrichment factor of 97 was achieved in 15 min. The calibration working range was from 10 μg L−1 to 2000 μg L−1 (R2 = 0.998), and the limit of detection (signal to noise ratio of 3) was 3.8 μg L−1 of fluoride. Finally, the proposed method was successfully applied to the determination of fluoride in different milk samples. The recoveries of fluoride (at spiked concentrations of 200 μg L−1 and 600 μg L−1 into milk) in real samples ranged from 96.9% to 107.7%. Intra-day precision (N = 3) in terms of peak area, expressed as relative standard deviation, was found to be within the range of 0.24-1.02%. 相似文献
102.
Dan Ben-Yaakov David Andelman Rudi Podgornik Daniel Harries 《Current Opinion in Colloid & Interface Science》2011,16(6):542-550
In aqueous solutions, dissolved ions interact strongly with the surrounding water and surfaces, thereby modifying solution properties in an ion-specific manner. These ion-hydration interactions can be accounted for theoretically on a mean-field level by including phenomenological terms in the free energy that correspond to the most dominant ion-specific interactions. Minimizing this free energy leads to modified Poisson-Boltzmann equations with appropriate boundary conditions. Here, we review how this strategy has been used to predict some of the ways ion-specific effects can modify the forces acting within and between charged interfaces immersed in salt solutions. 相似文献
103.
Gerra L. Bosco 《Trends in analytical chemistry : TRAC》2011,30(8):1189-1211
This report of the 2011 James L. Waters Symposium at Pittcon 2011 highlights the powerful imaging technologies of electron microscopy (EM) and ion microscopy (IM). The four speakers each provided a window into a specific subset of the field:
- •
- David Bell described the history, development, application, and commercialization of transmission EM (TEM) and scanning TEM (STEM);
- •
- David Martin presented the challenges and methodologies of imaging ordered polymers and biomaterials with TEM;
- •
- Joseph Michael explained the history of the commercialization of scanning EM (SEM) and its modern applications; and,
- •
- David Joy, who submitted his talk in absentia, provided a history of EM and a summary of the advantages of IM versus EM.
104.
The 25% niobium substituted crystalline titanosilicate with the composition Na1.5Nb0.5Ti1.5O3SiO4·2H2O (Nb-TS) was synthesized under hydrothermal conditions. Its selectivity for radioactive 137Cs and 89Sr was compared with the TS, Na2Ti2O3SiO4·2H2O, having sitinakite topology. The Nb-TS shows significantly higher uptake value for 137Cs but lower for 89Sr than the TS. To investigate the origin of selectivity, the ion exchanged Cs+ and Sr2+ forms with the composition, CsxNaHyNb0.5Ti1.5O3SiO4·zH2O (x=0.1, 0.2 and 0.3, x+y=0.5 and z=1-2) and Sr0.2Na0.6H0.5Nb0.5Ti1.5O3SiO4·H2O, respectively, were structurally characterized from the X-ray powder diffraction data using the Rietveld refinement technique. Simultaneously the kinetics of 137Cs and 89Sr uptake was investigated for the NbV free and doped samples. While the Cs+ and Sr2+ exchanged form of Nb-TS and the Cs+ exchanged form of TS retain the symmetry of the parent compound, the Sr2+ exchanged form of TS undergoes a symmetry change. The differences in the uptake of Cs+ and Sr2+ result from the different coordination environments of cesium and strontium in the eight-ring channel, that result from various hydration sites in the tunnel. The origin of selectivity appears to arise from the higher coordination number of cesium or strontium. Other effects due to NbV substitution are reflected in the increase of both, the a- and c-dimensions and thus the unit cell volume, and the population of water vs. Na+ in the channel to charge-balance the Nb5+↔Ti4+ substitution. 相似文献
105.
John R. Stutzman Carl A. Luongo Scott A. McLuckey 《Journal of mass spectrometry : JMS》2012,47(6):669-675
Protonated angiotensin II and protonated leucine enkephalin‐based peptides, which included YGGFL, YGGFLF, YGGFLH, YGGFLK and YGGFLR, were subjected to ion/ion reactions with the doubly deprotonated reagents 4‐formyl‐1,3‐benzenedisulfonic acid (FBDSA) and 1,3‐benzenedisulfonic acid (BDSA). The major product of the ion/ion reaction is a negatively charged complex of the peptide and reagent. Following dehydration of [M + FBDSA‐H]? via collisional‐induced dissociation (CID), angiotensin II (DRVYIHPF) showed evidence for two product populations, one in which a covalent modification has taken place and one in which an electrostatic modification has occurred (i.e. no covalent bond formation). A series of studies with model systems confirmed that strong non‐covalent binding of the FBDSA reagent can occur with subsequent ion trap CID resulting in dehydration unrelated to the adduct. Ion trap CID of the dehydration product can result in cleavage of amide bonds in competition with loss of the FBDSA adduct. This scenario is most likely for electrostatically bound complexes in which the peptide contains both an arginine residue and one or more carboxyl groups. Otherwise, loss of the reagent species from the complex, either as an anion or as a neutral species, is the dominant process for electrostatically bound complexes. The results reported here shed new light on the nature of non‐covalent interactions in gas phase complexes of peptide ions that can be used in the rationale design of reagent ions for specific ion/ion reaction applications. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
106.
A novel method for the determination of palladium as a metal ion model was developed by ion pair based surfactant-assisted microextraction (IP-SAME) and inductively coupled plasma-optical detection (ICP-OES). In this methodology, a cationic surfactant was used in extraction process. It has two fundamental functions: (1) the formation of an emulsified phase and (2) the ion pair formation with Pd(II) in the presence of iodide ions and making PdI42− extractable into organic phase (active microextraction). The effective parameters on the extraction recovery such as the types of extraction solvent and the surfactant, surfactant concentration, KI amount and HCl concentration of the sample were investigated and optimized. In the proposed approach, tetradecyl trimethyl ammonium bromide (TTAB) was used as emulsifier and ion pairing agent, and 1-octanol was selected as extraction solvent. Under the optimum conditions, the enhancement factor as large as 146 was obtained. The detection limit for palladium was 0.2 μg L−1, and the relative standard deviation (RSD) was 4.1% (n = 5, C = 10.0 μg L−1). The proposed method was applied for extraction and determination of palladium in different water samples. 相似文献
107.
《Analytical letters》2012,45(4):613-620
Abstract A comparative study of the chromatographic behaviour of anions, iodide, sulphide, phosphate, arsenate, arsenite, vanadate, chroraate, dichromate, thiosulphate, thiocyanate, ferricyanide and ferrocyanide on papers impregnated with hydrated bismuth oxide and untreated Whatman no, 1 papers has been made by employing identical aqueous, non-aqueous and mixed solvent systems. Sharp and compact spots were obtained with impregnated papers whereas the opposite applied to plain papers. Various analytically important binary and ternary separations are reported. 相似文献
108.
Sally M. McIntyre Jill Wisnewski Ferguson R.S. Houk 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(8):581-587
The method of comparing experimental and calculated ion ratios to determine a gas kinetic temperature (Tgas) characteristic of the origin of a polyatomic ion in inductively coupled plasma-mass spectrometry (ICP-MS) is applied to ArO+. Repeated measurements of ion ratios involving this species yield erratic Tgas values. Complications arise from the predicted presence of a low-lying excited electronic state (2Π) above the 4Σ ground state. Omission of this excited state yields unreasonably high temperatures (> 10,000 K) for nine out of nineteen trials. Inclusion of the excited electronic state in the partition function of ArO+ causes temperatures to increase further. The problem appears to be related to the prediction that ArO+ in the 2Π excited state dissociates into Ar+ and O, different products than ArO+ 4Σ which dissociates into Ar and O+. Adjustments to the calculations to account for these different products yield reasonable temperatures (2100 to 3500 K) that are consistent from day-to-day and similar to those seen for other weakly-bound polyatomic ions. 相似文献
109.
介绍了EAST装置新型离子回旋加热(ICRH)天线电流带的设计结构。通过对电流带实际工况的计算得出电流带的工作温度分布,以此来模拟实际工作条件下电流带的热载荷承受能力以及对电流带结构的影响。论证了在实际工况热载荷条件(0.2MW)下,电流带辐射面温度及电流带整体结构强度满足设计要求。 相似文献
110.