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141.
142.
用丁二酮肟流动注射光散射法测定微量镍,将经典的丁二酮肟-镍沉淀法改为光散射法并采用流动注射技术克服这类沉淀光散射法的稳定性问题。建立测定微量镍(Ⅱ)的丁二酮肟(DMG)-流动注射光散射法。将DMG-NaOH溶液与含镍(Ⅱ)水样流混合,在430nm处对反应形成的Ni(DMG)2沉淀微粒进行光散射检测,线性范围为5—20μg/mL,检出限为0.171μg/mL,测定频率为34次/h。本法的测定灵敏度较高、选择性较好、分析速度快,应用本法测定废水中镍含量,结果满意。 相似文献
143.
144.
The problem of determining the optimal contour of a two-dimensional jet engine outlet system was solved in [1] using the direct method of the calculus of variations. In this study the method is developed for designing the optimal contour of a three-dimensional outlet system providing maximum thrust in a given direction. 相似文献
145.
Properties and applications of cold supersonic gas jet 总被引:1,自引:1,他引:0
By analyzing the formation mechanism of a supersonic gas jet, a set of equations which describe the atomic beam properties
were established. The influence of initial temperature, initial pressure, background gas pressure and pumping speed was discussed
in detail. A simulation program was developed based on the equations, and the results under different initial conditions were
obtained. The results are in good agreement with the experimental data, and suggest that, in order to get much smaller transverse
momentum in collision experiments, it is necessary to lower the initial temperature and the initial pressure of the supersonic
gas jet, together with increasing the pumping speed. These results are very instructive for construction of a new generation
of cold supersonic gas jets. 相似文献
146.
X. Wu K. L. Averett S. Maimon M. W. Koch G. W. Wicks 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):511
InAs bipolar junction transistors (BJTs), grown by molecular beam epitaxy, are reported with common emitter current gains (β's) as large as 400. The factors affecting the common emitter current gain have been studied by estimating the magnitudes of the base transport factor (αT) and emitter injection efficiency (γ). This has been accomplished by studying a sequence of InAs BJTs with varying emitter doping densities, NE. Minority carrier diffusion length in the base (LB), αT, and γ have been extracted from measured electrical characteristics. The results of the study of these InAs BJTs are as follows: LB≈0.4 μm, αT≈98% and γ ranges from 92% to nearly 100% depending on NE. This knowledge of the magnitudes of the injection efficiencies suggests when it would be useful to move from the simple BJT structure to the more advanced heterojunction bipolar transistor (HBT) structure. Lower γ BJTs would be improved, however high-γ BJTs would benefit little, by the use of the widegap emitters of HBTs. The method developed here to estimate γ, αT and LB is not specific to InAs BJTs, but should be useful for study of BJTs and HBTs in any material system. 相似文献
147.
Ascorbic acid is determined by a simple Bead Injection Spectroscopy–Flow Injection Analysis (BIS–FIA) system with spectrophotometric detection. The sensor is based on the decrease of absorbance obtained (720 nm) when Prussian blue (PB) is reduced by ascorbic acid. Commercial available flow-cell (Hellma 138-OS) is used and an appropriate volume of homogeneous bead suspension of Sephadex QAE A-25 was injected to fill this flow-cell for each measurement. The chromogenic reagent (PB) is injected into the carrier and immobilized on beads. When sample is injected, reaching the bead surface where PB is sorbed, ascorbic acid converts it to Prussian white form, which is transparent, producing the discoloration of the detection zone. At the end of the analysis, beads are discarded by reversing the flow and instantaneously transported out of the system.The calibration graph was linear over the range 5.1×10−6–6.8×10−5 M. The detection limit and RSD (%) were 4.5×10−7 M and 5.0%, respectively, using 800 μl of sample volume. This method is highly selective in the presence of other species that are normally encountered with the analyte. The sensor was applied satisfactorily to the determination ascorbic acid in fruit juices, pharmaceuticals, sweets and conservative liquids. 相似文献
148.
149.
Z. Ebru Seçkin 《Analytica chimica acta》2005,547(1):104-108
An automated flow injection analysis system was developed for the fluorometric determination of dopamine in pharmaceutical injections. The method is based on the quenching effect of dopamine on m-dansylaminophenyl boronic acid (DAPB) fluorescence due to the reverse photo induced electron transfer (PET) mechanism. Effects of pH and interfering species on the determination of dopamine were examined. Calibration for dopamine, based on quenching data, was linear in the concentration range of 1.0 × 10−5 to 1.0 × 10−4 M. Detection limit (3 s) of the method was found to be 3.7 × 10−6 M. Relative standard deviation of 1.2% (n = 10) was obtained with 1.0 × 10−5 M dopamine standard solution. The proposed method was applied successfully for the determination of dopamine in pharmaceutical injection sample. The sampling rate was determined as 24 samples per hour. 相似文献
150.
A new design for a gas chromatographic surface ionization detector based upon hyperthermal positive surface ionization has been developed: There were two requirements: supersonic free jet nozzle and the high work function surface of Re-oxide. This detector, which is highly sensitive in response to all organic compounds, can be operated as an universal detector with an additional selectivity towards some species that have low ionization energy, but with selectivity to a much lesser degree than a conventional surface ionization detector. The minimum detectable amount of toluene is ca. 10−12 g/s with a linearity greater than 104. Some applications are demonstrated using three examples for the analysis of different formulations: (1), terpene mixture, (2), polycyclic aromatic hydrocarbon mixture and (3), alkyl alcohol mixture. 相似文献