全文获取类型
收费全文 | 6743篇 |
免费 | 988篇 |
国内免费 | 841篇 |
专业分类
化学 | 4253篇 |
晶体学 | 72篇 |
力学 | 274篇 |
综合类 | 74篇 |
数学 | 541篇 |
物理学 | 1796篇 |
无线电 | 1562篇 |
出版年
2024年 | 21篇 |
2023年 | 111篇 |
2022年 | 183篇 |
2021年 | 189篇 |
2020年 | 228篇 |
2019年 | 243篇 |
2018年 | 182篇 |
2017年 | 191篇 |
2016年 | 307篇 |
2015年 | 333篇 |
2014年 | 403篇 |
2013年 | 545篇 |
2012年 | 537篇 |
2011年 | 496篇 |
2010年 | 480篇 |
2009年 | 417篇 |
2008年 | 520篇 |
2007年 | 435篇 |
2006年 | 400篇 |
2005年 | 377篇 |
2004年 | 324篇 |
2003年 | 275篇 |
2002年 | 226篇 |
2001年 | 217篇 |
2000年 | 164篇 |
1999年 | 126篇 |
1998年 | 101篇 |
1997年 | 75篇 |
1996年 | 56篇 |
1995年 | 52篇 |
1994年 | 44篇 |
1993年 | 47篇 |
1992年 | 50篇 |
1991年 | 41篇 |
1990年 | 22篇 |
1989年 | 17篇 |
1988年 | 18篇 |
1987年 | 16篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1974年 | 5篇 |
1964年 | 2篇 |
1963年 | 2篇 |
1935年 | 2篇 |
排序方式: 共有8572条查询结果,搜索用时 0 毫秒
991.
模糊综合评价模型在教师评价中的应用 总被引:12,自引:0,他引:12
冯梅 《数学的实践与认识》2004,34(11):35-38
教师评价是教育评价的一个重要环节 ,我国教师评价的历史不长 ,所以目前尚未建立起科学的评价体系 ,由于教师评价的多因素性及评价因素的模糊性 ,可以用模糊数学建立综合评价模型 . 相似文献
992.
Weidong Huang Xuhong Wang Li Wang Mei Sheng Liqiang Xu Frank Stubhan Le Luo 《Journal of Electronic Materials》2004,33(2):101-105
The moisture diffusion in globtop material for a chip-on-board (COB) package coated with SiNx and silicone, respectively, or coated with SiNx plus silicone were measured by embedding a humidity sensor in the globtop and recording the capacitive change in three different
temperature/humidity environments. The experimental results were simulated by Fick’s diffusion law with finite-element method
modeling. The moisture diffusion coefficients and activation energies were calculated to quantitatively compare the moisture-resistance
effects of different coatings. For example, at 85°C/85% RH, the moisture diffusion coefficients for the uncoated reference,
SiNx-coated, silicone-coated, and silicone/SiNx double-layered coated samples are 1E-5, 0.8E-5, 0.7E-5, and 0.2E-5 mm2/s, respectively. The experimental and simulation results show that double-layered coating with silicone/SiNx has excellent moisture-resistance properties because it not only smoothes the steps on a printed circuit board (PCB) but
also keeps the good moisture resistance of the inorganic films. 相似文献
993.
In this work we prepared a nematic monomer (4'-allyloxybiphenyl 4'-ethoxybenzoate, M1), a chiral crosslinking agent (isosorbide 4-allyloxybenzoyl bisate, M2) and a series of new side chain cholesteric liquid crystalline elastomers derived from M1 and M2. The chemical structures of the monomers and polymers were confirmed by FTIR and 1H NMR spectroscopy. The mesomorphic properties were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy and X-ray diffraction. The effect of the content of the crosslinking unit on phase behaviour of the elastomers is discussed. Polymer P1 showed a nematic phase, P2-P7 showed a cholesteric phase; P6 formed a blue Grandjean texture over a broad temperature range 145-209.6°C, with no changed on the cooling. Polymers P4-P7, with more than 6 mol % of chiral crosslinking agent, gave rise to selective reflection. Elastomers containing less than 15 mol % of the crosslinking units displayed elasticity, reversible phase transition with wide mesophase temperature ranges, and high thermal stability. Experimental results demonstrated that, with increasing content of crosslinking agent, the glass transition temperatures first fell and then increased; the isotropization temperatures and mesophase temperature ranges decreased. 相似文献
994.
介绍了无电解镀镍的应用领域,研究了Ni-P镀层在各种应用环境下的耐蚀性能及在油田管路上的应用,并研究了Ni-P-PTFE镀层的性能开发及应用前景。 相似文献
995.
报道了0.53μm高功率激光辐照金盘靶产生的受激拉曼散射光光谱和散射光谱能量角分布,由散射光角分布计算的散射光能量与实验通过打靶透镜测得的受激拉曼散射能量不符,而且角的分布的实验结果与受激布里渊散射理论也不符。 相似文献
996.
Temporal Mueller matrix solution for polarimetric scattering from inhomogeneous random media of nonspherical scatterers 总被引:1,自引:0,他引:1
Mei Chang Ya-Qiu Jin 《Antennas and Propagation, IEEE Transactions on》2003,51(4):820-832
Polarimetric scattering from inhomogeneous random media of nonspherical scatterers under a pulse incidence is studied. The time-dependent Mueller matrix solution of vector radiative transfer for layering random media is derived. Copolarized and cross-polarized bistatic and back- scattering are numerically calculated. The shape and intensity of polarized echoes well depict the inhomogeneous fraction profile of random scatterers. Its functional dependence upon the fraction profile, layering thickness, and other parameters are discussed. This technique is applicable to reconstruction of inhomogeneous fraction profile and inversion of the media thickness. 相似文献
997.
Jun‐Feng Wu Dong‐Mei Li Li‐Feng Cui Chang‐Fu Zhuang Sai‐Nan Song Tie‐Gang Wang Ji‐Qing Xu Heng‐Qing Jia Ning‐Hai Hu 《应用有机金属化学》2007,21(12):1033-1040
Mo2O2S2(HGly)(Gly)2 1 and K6[Mo2O2S2(nta)2][Mo2O2S2(ntaH)2]·4H2O 2 were synthesized by the reactions of (NH4)2MoS4 and amino acids L (L = glycine, nitrilotriacetic acid) in ethanol–water medium at ambient temperature. The two complexes were characterized by elemental analysis, infrared spectra, UV–visible spectra, TG–DTA and XPS. X‐ray crystallographic structural analyses revealed that compound 1 is a binuclear Mo? S? glycinate complex, a glycinate ligand is coordinated to each molybdenum atom through its amine nitrogen and carboxylato oxygen, respectively, and the third glycinate acts as a bridge through its two carboxylato oxygens linking the two molybdenum atoms. Compound 2 is also a binuclear Mo? S complex with two nitrilotriacetate ligands, each of which is coordinated to a molybdenum atom via its two β‐carboxylato oxygens and a nitrogen atom. Simultaneously, each molybdenum atom in 1 and 2 is chelated to a terminal oxygen and two bridging sulfurs to complete the octahedral configuration. Their catalytic activities in the reduction from C2H2 to C2H4 as well as other binuclear Mo? S? polycarboxylate complexes, a [Fe4S4] single cubane and a chainlike Mo? Fe? S compound were investigated and it was found that 1 exhibited relatively good catalytic activity. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
998.
The Mueller matrix solution of the vector radiative transfer equation with time dependence is derived in this paper. It is applied to simulation of polarimetric bistatic scattering from a layer of non-uniformly oriented, random non-spherical scatterers when a Gaussian plane pulse is incident upon. Co-polarized and cross-polarized bistatic scattering are numerically calculated. The pulse echoes are compared with the incidence, and demonstrate its functional dependence on the physical parameters of random medium, such as spatial orientation and fractional volume of scatterers, incidence angle and polarization, the layer depth and others. 相似文献
999.
1000.
原子发射光谱内标法测量误差的研究 总被引:4,自引:1,他引:3
证明了原子发射光谱内标法的测量误差。当分析线和内标线的相对强度等于1时,测量误差最小。 相似文献