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991.
Masaki Okamoto 《Research on Chemical Intermediates》2006,32(3):317-330
In the direct synthesis of silicon compounds by reactions of elemental silicon with methyl chloride, methanol and hydrogen
chloride, silylene formed on surface of silicon grains during the reaction is an intermediate. The reaction of surface silylene
with a variety of unsaturated hydrocarbons provides new direct synthesis of organosilanes. In the direct synthesis of methylchlorogermanes
from elemental germanium, surface germylene is not an intermediate, while tetrachlorogermane is synthesized by the direct
reaction of germanium with hydrogen chloride via dichlorogermylene intermediate. Various unsaturated hydrocarbons or organic chlorides added to the system of tetrachlorogermane
synthesis give new methods for the synthesis of organogermanes. 相似文献
992.
Binary carbon-supported platinum (Pt) nanoparticles were prepared by a chemical reduction method of Pt precursor on two types
of carbon materials such as carbon blacks (CBs) and graphite nanofibers (GNFs). Average sizes and loading levels of Pt metal
particles were dependent on a mixing ratio of two carbon materials. The highest electroactivity for methanol oxidation was
obtained by preparing the binary carbon supports consisting of GNFs and CBs with a weight ratio of 30:70. Furthermore, with
an increase of GNFs content from 0% to 30%, a charge-transfer resistance changed from 19 Ohm cm2 to 11 Ohm cm2. The change of electroactivity or the resistance of catalyst electrodes was attributed to the changes of specific surface
area and morphological changes of carbon-supported catalyst electrodes by controlling the mixing ratio of GNFs and CBs. 相似文献
993.
A rapid and sensitive method to determine volatile organohalides in different types of waters has been developed. The chromatographic system is based on the resolving power of the glass capillary column and the high sensitivity of the electron capture detector. The capillary columns were connected to the detector so that the eluate from the column is mixed with thermostatted purge gas to minimize band broadening due to dead volumes. The low column bleeding and decreased band spreading from capillary columns enhance the sensitivity to very low levels: 1 fg (10?15g) for carbon tetrachloride, despite dilution of the column eluate by the purge gas. The water samples of 100 ml were extracted with 1 to 10 ml n-pentane which is the most practical alkane with respect to purity. When using high water to pentane ratios corrections had to be made, due to low extraction yield, to get accurate quantifications. A column with Carbowax 400 stationary phase permits direct tap water injection. The water peak concealed the substances eluated after CHCl3 and CHBrCl2. The gas chromatographic separation of haloforms in tap water could be shortened to 30 seconds using a 10 m SE–52 column with an increased film thickness. Besides tap water and seawater, industrial waste water from a pulp mill was analyzed. Ten different halogenated organic compounds, ranging from 1 ng/I to 760 μg/I, were quantified in the different waters. Bromoform, which had not previously been found in seawater, was detected. Chromatogram of a standard mixture containing 11 organohalides. Stationary phase, SE-52; 33 m × 0.3 mm i.d. inj. temp. 200°, column temp. 50°, interface 250°, detector temp. 250°. Helium carrier gas flow rate, 36 cm/s, scavenger'gas flow 30 ml/min. Split ratio 1:20, 1 = CH2CI2, 2 = CHC13, 3 = CH3CC13, 4 = CC14, 5 = CHCICCI2, 6 = CHBrCI2, 7 = CBrC13, 8 = CHBr2Cl, 9 = CCl2CC12, 10 = CHCl2l, 11 = CHBr3. 相似文献
994.
PLLA-PEG共聚物的非等温结晶行为 总被引:1,自引:1,他引:1
采用熔融共聚法制备PLLA-PEG嵌段共聚物, 用WAXD和DSC方法研究其结晶行为, 并用Avrami方程的Jeziorny修正分析了非等温结晶动力学行为. 结果表明, PLLA结晶明显, 而PEG结晶难以观察到, PEG的柔性能促进PLLA结晶. PEG分子量的增加和投料量的增加都能使得结晶温度升高, 结晶度增大, 结晶速度加快. 相似文献
995.
K. M. Bichinho Gilvan P. Pires F. C. Stedile J. H. Z. dos Santos 《Spectrochimica Acta Part B: Atomic Spectroscopy》2002,57(12):1877-1884
Metal contents in polymerization catalysts were comparatively determined by Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence (XRF) spectroscopy. Catalysts were prepared by grafting metallocene onto bare silica or onto silica chemically modified with methylaluminoxane (MAO). Catalysts were compressed as self-supporting pellets (RBS and XRF), or mounted on adhesive copper tape (XPS). The proximity of the mass of the atomic nuclei did not allow resolution by RBS of the signals corresponding to Zr and Nb, nor Si and Al in catalyst systems such as (nBuCp)2ZrCl2/Cp2NbCl2/MAO/SiO2. On the other hand, Zr, Nb, Si and Al lines were completely resolved in an XRF spectrum. For supported metallocenes on bare silica, XPS measurement was ca. 40% higher than that obtained by RBS. Silica-supported zirconocene showed good agreement in Zr content determination by XRF and RBS. 相似文献
996.
Robert G. Syvret William J. Casteel Jr. Jaidev S. Goudar 《Journal of fluorine chemistry》2004,125(1):33-35
Fluoroaryl 1,2,4-triazolin-5-ones are an important class of herbicidal compounds useful in a variety of crop protection applications, primarily for the control of grassy and broad-leaf plant species. While a number of different synthetic strategies can be used for the step-wise preparation of these complex molecules, it is generally preferred to introduce fluorine later in the synthetic pathway, since the presence of fluorine and other halogens has a dominant effect on all subsequent synthetic steps. We have investigated the reactions that occur between aryl triazolinones and a variety of fluorination agents, including F2/N2, XeF2, (CF3SO2)2NF, Selectfluor®, CF2(OF)2, CF3OF, CH3COOF, and CF3COOF, and have used this knowledge to develop several alternative high-yielding routes to fluoroaryl 1,2,4-triazolin-5-ones. The fluorine introduction strategy and experimental results for a representative example of this important class of compounds are discussed herein. 相似文献
997.
Matschat R Hassler J Traub H Dette A 《Analytical and bioanalytical chemistry》2005,383(7-8):1060-1074
The members of the committee NMP 264 “Chemical analysis of non-oxidic raw and basic materials” of the German Standards Institute
(DIN) have organized two interlaboratory comparisons for multielement determination of trace elements in silicon carbide (SiC)
powders via direct solid sampling methods. One of the interlaboratory comparisons was based on the application of inductively
coupled plasma optical emission spectrometry with electrothermal vaporization (ETV ICP OES), and the other on the application
of optical emission spectrometry with direct current arc (DC arc OES). The interlaboratory comparisons were organized and
performed in the framework of the development of two standards related to “the determination of mass fractions of metallic
impurities in powders and grain sizes of ceramic raw and basic materials” by both methods. SiC powders were used as typical
examples of this category of material. The aim of the interlaboratory comparisons was to determine the repeatability and reproducibility
of both analytical methods to be standardized. This was an important contribution to the practical applicability of both draft
standards. Eight laboratories participated in the interlaboratory comparison with ETV ICP OES and nine in the interlaboratory
comparison with DC arc OES. Ten analytes were investigated by ETV ICP OES and eleven by DC arc OES. Six different SiC powders
were used for the calibration. The mass fractions of their relevant trace elements were determined after wet chemical digestion.
All participants followed the analytical requirements described in the draft standards. In the calculation process, three
of the calibration materials were used successively as analytical samples. This was managed in the following manner: the material
that had just been used as the analytical sample was excluded from the calibration, so the five other materials were used
to establish the calibration plot. The results from the interlaboratory comparisons were summarized and used to determine
the repeatability and the reproducibility (expressed as standard deviations) of both methods. The calculation was carried
out according to the related standard. The results are specified and discussed in this paper, as are the optimized analytical
conditions determined and used by the authors of this paper. For both methods, the repeatability relative standard deviations
were <25%, usually ~10%, and the reproducibility relative standard deviations were <35%, usually ~15%. These results were
regarded as satifactory for both methods intended for rapid analysis of materials for which decomposition is difficult and
time-consuming. Also described are some results from an interlaboratory comparison used to certify one of the materials that
had been previously used for validation in both interlaboratory comparisons. Thirty laboratories (from eight countries) participated
in this interlaboratory comparison for certification. As examples, accepted results are shown from laboratories that used
ETV ICP OES or DC arc OES and had performed calibrations by using solutions or oxides, respectively. The certified mass fractions
of the certified reference materials were also compared with the mass fractions determined in the interlaboratory comparisons
performed within the framework of method standardization. Good agreement was found for most of the analytes. 相似文献
998.
Ricardo Q. Aucélio Roseli Martins de SouzaReinaldo Calixto de Campos Norbert MiekeleyCarmem L. Porto da Silveira 《Spectrochimica Acta Part B: Atomic Spectroscopy》2007
The determination of trace metals in lubricating oils using atomic spectrometric methods is reviewed. The importance of such analyses for technical diagnostics as well as the specific sample characteristics related to the analyte form (metallo-organic and metal particles) is discussed. Problems related to sample pre-treatment for appropriate sample introduction and calibration are addressed as well as the strategies to overcome them. Recent trends aimed at simplifying sample manipulation are presented. The applications and scope of AAS, ICP OES and ICP MS techniques for the determination of trace metals in lubricating oil is individually discussed, as well as some present instrumental trends. 相似文献
999.
DongMeiSUN ChenXinCAI WeiXING TianHongLU 《中国化学快报》2004,15(4):453-454
It is reported for the first time that horseradish peroxidase (HRP) immobilized on the active carbon can undergo a direct quasi-reversible electrochemical reaction.In addition,the immobilized HRP showed the stable bioelectrocatalytic activity for the reduction of H2O2. 相似文献
1000.
High pressure, induced by water freezing, has been successfully applied to the direct catalytic asymmetric aldol reaction, in which higher yield and better enantioselectivity can be realized than in the reaction at room temperature under 0.1 MPa. 相似文献