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151.
The geometry, energy, internal rotation, vibrational spectra, dipole moments and molecular polarizabilities of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) of α- and β-chain models were studied with density functional theory at B3PW91/6-31G(d) level and compared with those of the poly(vinylidene fluoride) (PVDF) homopolymer. The chain length and the trifluoroethylene (TrFE) concentration were examined to discuss the copolymer chain stabilities, chain conformations and electric properties. The asymmetrical internal-rotation potential energy curve shows that the angles for the g and g′ conformations in the α-chain (tg and tg′) models are 53° and −70°, respectively, and the β-chain (ttt) conformation is a slightly distorted all-trans plane with dihedral angle at 177°. The energy differences, Eβ − Eα(g) and Eβ − Eα(g′), between the β- and the α-conformation are 2.1 and 7.8 kJ/mol, respectively. These values are smaller than that in PVDF (8.4 kJ/mol), suggesting that the β-conformation in the copolymer will be more stable than in PVDF. The energy barriers for β → α(g) and β → α(g′) transitions are 16.2 and 5.8 kJ/mol, respectively. The former is almost twice of the energy barrier in PVDF by 8.2 kJ/mol and the latter is slightly smaller (by 2.4 kJ/mol) than that in PVDF. The respective energy barriers for α(g) → β and α(g′) → β transitions are 18.3 and 13.6 kJ/mol compared with the value 16.3 kJ/mol in PVDF. The asymmetrical energy barriers may be one of the reasons for the copolymers with 0.5-0.6 (mole fraction) VDF exhibiting complicated phase transition behavior. The conformation of α-chain P(VDF-TrFE) exhibits from a helical (containing higher TrFE) to a nearly beeline (containing lower TrFE). This behavior is different from that in the PVDF and the nearly beeline conformation might be responsible for the increasing crystallizability. The helical might also be associated with the complicated phase transition behavior and the larger lattice strain in the P(VDF-TrFE)s with higher TrFE concentration. The energy difference per monomer unit between the β- and α-chain decreases with increasing TrFE content. The ideal β-chain is curved with a radius of about 30 Å, which is similar to that in PVDF. The chain curvature and the TrFE content will affect the dipole moment contribution per monomer. The chain length and TrFE content will not significantly affect the mean polarizability. The calculations indicated that there are some additional characteristic vibrational modes that may be used in identification of the α- or β-phase P(VDF-TrFE)s with different TrFE contents. 相似文献
152.
Dieter Heymann 《Carbon》2005,43(11):2235-2242
The mean lifetimes of polyyne C8H2 in hexane were determined at 50, 60, 80, and 100 °C and in methanol at 60 °C. The reactions are second order at all temperatures: ln k2 = 20.5 ± 1.5-10303 ± 520T−1 and the corresponding activation energy is 85.7 ± 6.3 kJ mol−1 (7164 cm−1). Extrapolation suggests that solutions at 1 mM concentration are significantly unstable at room temperature. Quantum chemical calculations show that polyynes CmH2 + CnH2 (m + n = 16) could be products, but these were not detected. Alternatively, C16H2 isomers could form. IR spectra of the solid residues from hexane and methanol solutions were obtained. 相似文献
153.
溴碘化银核壳乳剂中电子的捕获和复合 总被引:2,自引:0,他引:2
本文应用双注仪制备了在核表面进行不同程度还原增感和一系列溴碘化银核壳乳剂,在没条件下测定了核表面形成的不同还原增感中心对乳剂微晶光电子衰减动力学及发光光谱的影响。结果表明:在一定增感温度和时间条件下,当Na2SO3用量低于5.4mg/molAg时光电子衰减动力学为二级反应,而当Na2SO3用量超过27mg/molAg时,增感中心一部分作为穴陷阱,另一部分作为电子陷阱,光电子衰减速率决定了电子的捕获 相似文献
154.
In this paper, the effect of wall conduction of an autothermal tubular methane microreformer is investigated numerically. It is found that the axial wall conduction can strongly influence the performance of the microreactor and should not be neglected without a careful a priori investigation of its impact. By increasing the wall thermal conductivity, the maximum wall surface temperature is decreased. Due to the complex exothermic–endothermic nature of the chemistry of reforming, the axial variation of the wall temperature is not monotonic. Methane conversion and hydrogen yield are strongly dependent on the wall inner surface temperature, hence the heat conduction through the channel wall. The equivalence ratio and the wall thickness also significantly affect the reforming effectiveness and must be carefully considered in reactor optimization. Furthermore, it is found that exothermic oxidation reaction mechanisms, especially partial oxidation, are responsible for syngas (hydrogen and carbon monoxide) production near the inlet. Farther downstream, in the oxygen deficient region, endothermic steam reforming is the main hydrogen producing mechanism. By increasing the thermal conductivity, steam reforming becomes stronger and partial oxidation becomes weaker. For all investigated inlet conditions, the highest hydrogen yield is obtained for no or very low conductive walls. 相似文献
155.
156.
在充分分析利用已获资料的前提下,采用基于迦辽金(Galerkin)有限单元方法的软件包AQUA3D对山西省晋城市三姑泉域的岩溶地下水资源进行了评价,通过识别和检验,确定了泉域的数学模型和水文地质参数,求出了岩溶地下水可开采资源量。 相似文献
157.
158.
159.
离子液体以其独特的性质广受关注,被称为"绿色设计者溶剂",人们对其潜在的应用价值做了大量的研究.实验采用HyperChem软件构建了1-乙基-3-甲基咪唑四氟硼酸盐([EMIM][BF4])离子液体分子结构的3D模型,并用PM3法进行预优化,然后应用Gaussian 03w程序分别在RHF/6.31G(d)和BLYP/6-31G(d)计算水平上进行量子化学计算,并经振动频率和强度分析得到理论红外谱图.结果表明,[EMIM][BF4]离子液体的阴阳离子存在着氢键等弱相互作用. 相似文献
160.
张永江 《安徽水利水电职业技术学院学报》2010,10(4):58-60,63
文章分析了地下水开发利用现状与存在问题,提出地下水开发利用保护方案和缺水对策,为该区地下水可持续开发利用提供技术支撑. 相似文献