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991.
通过对离子轰击下固体表面电离过程重新考虑认为,在固体表面覆氧或氧离子轰击下除表面原子的直接电离外,激发态双原子间电子交换和断键亦起重要作用。在此基础上修正了局部热力学平衡模型,得到了一个包含各类离子内配分函数、电离能、金属-氧原子键断键能以及表面金属原子与氧原子结合份数等参数决定的新电离几率分析表达式。应用该分析表达式解释了金属表面覆氧、氧离子轰击金属、化合物半导体表面二次离子发射中氧增强效应、充氧量对二次离子发射的影响及其基体效应等实验现象。并由此得到了元素相对灵敏度因子的分析表达式,对化合物半导体及一些陶瓷材料表面二次离子质谱分析中元素灵敏度因子随元素电离能变化曲线给予了相应的物理解释。 相似文献
992.
用具有流通池的分光光度计作测定装置,建立了由平衡移动法测定络合反应中质子释放数的新方法。方法简单、快速,仅用一个标准溶液,适于在变更pH值范围内金属离子不发生水解和没有其他副反应的体系。 相似文献
993.
Woo-Jin Lee Su-Il Pyun Tae-Hyun Yang Joong-Do Kim Young-Ho Baek Han-Gyu Kim 《Journal of Solid State Electrochemistry》1997,1(2):120-125
Hydrogen transport through a Pd-Ni alloy electrodeposited on a Pd substrate (Pd-Ni/Pd bilayer symmetric electrode) has been
investigated using cyclic voltammetry and a.c. impedance spectroscopy combined with the electrochemical hydrogen permeation
method. The permeation build-up current transients and the measured impedance spectra were analyzed using the time-lag method
for the bilayer electrode and a complex non-linear least squares data-fitting method based upon the derived Faradaic admittance
for the hydrogen absorption into and diffusion through the bilayer electrode under the permeable boundary condition, respectively.
The value of the hydrogen diffusivity in the Pd-Ni layer was lower than that in the Pd layer. Furthermore, the values of the
charge transfer resistance and equilibrium absorption constant for the Pd-Ni/Pd bilayer electrode were higher than those for
the Pd single layer electrode. From the experimental results, the role of the thin Ni(OH)2 film formed on the Pd-Ni layer surface in the hydrogen transport through the Pd-Ni/Pd bilayer electrode is discussed in terms
of its passivating effect and extremely large hydrogen solubility.
Received: 22 January 1997 / Accepted: 15 April 1997 相似文献
994.
S. S. Yang 《Chromatographia》1992,33(7-8):309-312
Summary A rapid sample preparation procedure combined with a short reversed-phase HPLC separation for the quantitation of methoprene residue in tobacco samples is described. A ground tobacco sample of 0.5 g is mixed with 3 mL of 2-propanol. The mixture is extracted for twelve minutes with the aid of sonication at an elevated temperature (45–55°C) and then filtered through a 0.45 m disposable filter prior to injection on HPLC. No sample cleanup or solvent evaporation step is required. Chromatographic analysis is performed on a C-18 column and the analysis time is 12.5 minutes. The detection limit for methoprene in tobacco samples is one part per million (g/g). 相似文献
995.
Yunsong Yang 《European Polymer Journal》2004,40(3):531-541
A series of α,ω-dihydroxy polyarylene sulfones (PAES) were synthesized comprising bisphenol A (PAES1, Mn=1800, 4900, and 9500 daltons), 4,4′-biphenol (PAES2, Mn=4100 daltons), and hexafluorobisphenol A (PAES3, Mn=3300 daltons). These were reacted with α,ω-dibromo poly(vinylidene fluoride) (PVDF, Mn=1200 daltons) prepared by telomerization, to yield block copolymers possessing rigid and flexible segments. Block copolymers were characterized by FTIR, NMR, GPC, DSC, TGA and TEM. In several cases the block copolymers exhibited distinct thermal transitions, i.e. Tm and Tg for PVDF and PAES segments, respectively. Where observable, Tg of PAES domains in the block copolymers occurred at a temperature lower than the corresponding PAES homopolymer due to the flexible nature of the surrounding PVDF domains. Block copolymers exhibited a similar thermal stability to the corresponding PAES homopolymers but higher stability than the PVDF homopolymer, and much higher still than α,ω-dibromo PVDF. TEM analyses indicate that phase separation of PAES and PVDF domains occurs on the nanometer scale. 相似文献
996.
Haran TE Cohen I Spasic A Yang K Mohanty U 《Journal of the American Chemical Society》2003,125(37):11160-11161
We have developed a quantitative predictive model capable of describing the dynamics of migration of intrinsically curved DNA fragments on polyacrylamide gels. The model takes into account structural features of DNA, end-to-end distance, screening of hydrodynamic interactions, ionic strength of buffer, electrostatic persistence length, structural fluctuations of the macromolecule, counter condensation, and variation of dielectric constant and viscosity of water with MPD. In doing so, we have also addressed a decade old issue on the effect of the organic solvent 2-methyl-2,4-pentanediol on gel migration of phased A-tracts. We show here that A-tract-solvent interactions are less favored compared with A-tract-A-tract and solvent-solvent interactions. 相似文献
997.
拉制了4种无亲水基团的四苯基卟吩LB膜,用透射电镜、荧光寿命、荧光光谱和紫外-可见光谱测量表征了膜的形貌和结构,发现膜中卟吩主要以聚集体形式存在。 相似文献
998.
S. C. Sheu M. L. Lee H. L. Hwang H. Y. Lin M. H. Yang 《Fresenius' Journal of Analytical Chemistry》1989,334(2):143-147
Summary CuInS2 is one of the important I–III–VI2 ternary compounds which has in recent years received increasing interest in semiconductor science. In this study an electrochemical method has been developed based on a limited amount of available sample (0.5–10mg) for the precise and accurate determination of CuInS2 composition. After decomposition of the sample in concentrated HNO3 under pressure, copper and indium were sequentially determined by constant potential coulometry, and sulfur (as sulfate) by amperometric titration. Various experimental parameters which ensure high precision and accuracy of the results were carefully evaluated and calibrated. The overall errors for the determination of copper, indium and sulfur in a 10 mg sample were found to be +0.10%, –0.12% and +0.16%, respectively, which fullfills the requirement for accurate stoichiometric assessment.
Presented at the 10th International Symposium on Microchemical Techniques, August 25–29, 1986, Antwerp, Belgium 相似文献
Reproduzierbare und genaue Bestimmung der Stöchiometrie von CuInS2-Halbleitermaterial mit Hilfe elektrochemischer Verfahren
Presented at the 10th International Symposium on Microchemical Techniques, August 25–29, 1986, Antwerp, Belgium 相似文献
999.
Equilibrium adsorption isotherms for low-volatile compounds are extremely difficult to measure. A simple technique using temperature programmed desorption (TPD) is proposed. It is demonstrated that the two parameters needed for constructing the Langmuir isotherm can be derived with data from the TPD technique alone. Thus, the Langmuir isotherms of iodine on AX-21 super-activated carbon were obtained with this technique. A series of TPD experiments for samples with different initial loadings of iodine were carried out by varying the heating rates which resulted in different peak desorption temperatures. The peak desorption temperature decreased as the initial loading was increased because of the re-adsorption effect. The Langmuir constant was derived from kinetic theory with the activation energy for desorption obtained from the experiment. The activation energy for desorption was 12.3 kcal/mol. The Langmuir constants determined by this technique were in comparable order of magnitude to the reported values for iodine on activated carbon. The saturation capacity of AX-21 for iodine could also be determined from the TPD data obtained from samples with different initial loadings. The estimated saturation capacity from the TPD experiment was 2.96 g I(2)/g AX-21, which was close to the experimentally measured saturation capacity of 3.25 g I(2)/g AX-21 for the same system. 相似文献
1000.
Rotaxane is a kind of classic supramolecule, which is usually constructed from a number of macrocycles and one axis molecule. Herein, we have expanded the supramolecular structure of [n]rotaxane to offer a precise definition of (pseudo)[n,m]rotaxane for accurately describing the two kinds of (pseudo)rotaxanes structures, which are self‐assembled from cucurbit[7/8]uril (CB[7/8]) and viologen‐naphthalene derivative, respectively. Furthermore, these CB‐based pseudorotaxanes exhibit varied photophysical properties, stimuli‐responsive behavior triggered by competitive guest, and self‐sorting behavior. 相似文献