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991.
原假设的合理设定是单位根检验的首要问题,至今尚无学者对此进行深入研究。通过剖析以往单位根检验原假设设定存在的缺陷,在同时考虑原假设的可信度和检验可靠性的前提下,本文提出了单位根检验原假设的一种合理的设定策略及改进的检验程序。 相似文献
992.
《Macromolecular theory and simulations》2017,26(5)
The formation of channel membrane of polystyrene‐block‐poly(4‐vinyl pyridine) block copolymer is studied by computer simulations with the nonsolvent induced phase separation (SNIPS) method. Dissipative particle dynamics is employed to study the microphase separation process and the SNIPS mechanism. Simulation results indicate that polymer concentration has a significant effect on the membrane structure. Channel membranes form in the copolymer concentration range of 44–58%. Block ratio plays an important role in shaping the membrane structure. Solvent exchange rate also affects the degree of microphase separation at each evolution stage of simulation. The time evolution of morphologies shows that the microphase separation processes happen with the following sequences: the polymer self‐assembled and many small pores appear, then they form irregular cavities and cross‐link gradually, finally the channel membrane forms. These results throw light on the formation mechanism of polymer membranes and provide insightful guidance for future membrane design and preparation. 相似文献
993.
Computer-assisted optimization of chromatographic separations is still a fruitful activity. In fact, advances in computerized
data handling should make the application of systematic optimization strategies much easier. However, in most contemporary
applications, the optimization criterion is not considered to be a key issue (Vanbel, J Pharm Biomed, 21:603–610, 1999). In this paper, an update of the importance of selecting adequate criteria in chromatographic separation is presented. 相似文献
994.
Transport of biomolecules in asymmetric nanofilter arrays 总被引:1,自引:0,他引:1
Zi Rui Li G. R. Liu Jongyoon Han Yu Zong Chen Jian-Sheng Wang Nicolas G. Hadjiconstantinou 《Analytical and bioanalytical chemistry》2009,394(2):427-435
We propose a theoretical model for describing the electric-field-driven migration of rod-like biomolecules in nanofilters
comprising a periodic array of shallow passages connecting deep wells. The electrophoretic migration of the biomolecules is
modeled as transport of point-sized Brownian particles, with the orientational degree of freedom captured by an entropy term.
Using appropriate projections, the formulation dimensionality is reduced to one physical dimension, requiring minimal computation
and making it ideal for device design and optimization. Our formulation is used to assess the effect of slanted well walls
on the energy landscape and resulting molecule mobility. Using this approach, we show that asymmetry in the well shape, such
as a well with one slanted and one vertical wall, may be used for separation using low-frequency alternating-current fields
because the mobility of a biomolecule is different in the two directions of travel. Our results show that, compared to methods
using direct-current fields, the proposed method remains effective at higher field strengths and can achieve comparable separation
using a significantly shorter device. 相似文献
995.
The 1 /fα noise was measured on a variety of Al-based thin metal films with widely varying microstructure using an ac bridge technique.
The magnitude of the current noise in response to a small, non-destructive ac signal was found to vary several orders of magnitude
between 0.01 and 10 Hz and was correlated to the microstructural differ-ences of the films. These differences have a strong
affect on film lifetimes as measured in an accelerated electromigration test. Variation in microstructure was accomplished
by different deposition temperatures and annealing parameters, and verified using TEM micrographs. Following fabrication,
the current noise magnitude was measured and found to be sensitive to film width and grain size. The use of this technique
to discriminate differences in film microstructure is discussed along with the correlations between ex-cess noise and the
quality of the thin film as a metallic interconnection. 相似文献
996.
The process of infrared multiple photon dissociation (IRMPD) of molecules is of great fundamental importance and has practical
significance, such as isotope separation etc. Unfortunately, a clear insight into the process has been hindered by the bewildering
array of important variables affecting MPD. The dissociation probability γ (φ) i.e. the yield has been found to be a sensitive
function of laser fluence φ along with numerous other parameters like laser frequency, gas pressure etc. We have shown that
in single frequency IRMPD, an accurate quantitative characterization of the dissociation probability can be adequately expressed
by a ‘power law’ model with two fitting parameters namely critical fluence, φc and multiphoton order,m. This model was exploited in analysing our MPD results on various systems. However, the small isotope shift encountered in
heavy elements and the sticking phenomenon observed in small light molecules restrict respectively the separation factor and
the dissociation yield. These problems can effectively be tackled by irradiation with multifrequency laser beams which can
be chosen appropriately on the basis of spectroscopic features. Based on our success in single frequency model, multifrequency
IRMPD is modelled by a functional form containing the product of power law terms for individual fluences on irradiation frequencies.
This model is successfully benchmarked with our experimental results on multifrequency LIS of tritium. Such knowledge can
be utilized for appropriate separation process design, evaluation and optimization. 相似文献
997.
Manoj Kumar Anant Deshpande Chintan Gupta A. K. Biswas A. K. Nath 《Journal of Chemical Sciences》2002,114(6):659-673
Selective multi-photon dissociation (MPD) of Freon-22 (CF2HC1) molecules has been carried out using a TEA CO2 laser at various CO2 laser lines (9P(20)-9P(26)) in order to maximize the yield of C-13 isotope in the product (C2F4) at an enrichment factor of 100. The effects of laser pulse tail due to the presence of N2 in the laser mixture on the enrichment factor and yield of C-13 are investigated. It is found that the addition of a small
amount of N2 is possible in the laser mixture without a significant drop in the yield at desired enrichment factor. Addition of a small
amount of N2 improves the laser efficiency considerably. At a given pulse energy, a slight change in the near field intensity distribution
of a laser severely affects the selectivity of C-13 isotope. The computed far-field intensity distributions of the measured
near-field intensities show marked spatial variation in the focal spots that leads to a drop in selectivity. For macroscopic
production of C-13 isotope a simple and novel multi-pass cavity has been designed and tested to focus the energy repeatedly
keeping the optimum fluence constant at each focal spot. 相似文献
998.
宽开通信侦察中多信号盲分离应用研究 总被引:1,自引:0,他引:1
许士敏 《电子信息对抗技术》2005,20(4):12-14
宽开通信侦察系统可以大大提高搜索速度,提高信号的截获概率,但如何快速有效地分离出同时截获的多信号是一个急待解决的难题,盲分离技术为多信号分离提供了一种新的思路,实验结果表明盲分离技术在宽开通信侦察中的有效性,并显示出它在通信侦察中的广阔前景。 相似文献
999.
1000.