全文获取类型
收费全文 | 91928篇 |
免费 | 9273篇 |
国内免费 | 12902篇 |
专业分类
化学 | 77046篇 |
晶体学 | 2174篇 |
力学 | 2978篇 |
综合类 | 1043篇 |
数学 | 8855篇 |
物理学 | 22007篇 |
出版年
2024年 | 176篇 |
2023年 | 921篇 |
2022年 | 1909篇 |
2021年 | 3153篇 |
2020年 | 2921篇 |
2019年 | 2691篇 |
2018年 | 2153篇 |
2017年 | 2420篇 |
2016年 | 3237篇 |
2015年 | 3241篇 |
2014年 | 3917篇 |
2013年 | 6675篇 |
2012年 | 5931篇 |
2011年 | 4952篇 |
2010年 | 4370篇 |
2009年 | 5320篇 |
2008年 | 5697篇 |
2007年 | 5976篇 |
2006年 | 5160篇 |
2005年 | 4309篇 |
2004年 | 4201篇 |
2003年 | 3842篇 |
2002年 | 5851篇 |
2001年 | 3004篇 |
2000年 | 2633篇 |
1999年 | 2161篇 |
1998年 | 1955篇 |
1997年 | 1532篇 |
1996年 | 1544篇 |
1995年 | 1360篇 |
1994年 | 1267篇 |
1993年 | 1075篇 |
1992年 | 1097篇 |
1991年 | 716篇 |
1990年 | 606篇 |
1989年 | 493篇 |
1988年 | 483篇 |
1987年 | 362篇 |
1986年 | 359篇 |
1985年 | 492篇 |
1984年 | 364篇 |
1983年 | 235篇 |
1982年 | 382篇 |
1981年 | 562篇 |
1980年 | 497篇 |
1979年 | 497篇 |
1978年 | 390篇 |
1977年 | 295篇 |
1976年 | 252篇 |
1973年 | 169篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
用分子动力学方法对5%负失配条件下面心立方晶体铝薄膜的原子沉积外延生长进行了三维模拟.铝原子间的相互作用采用嵌入原子法(EAM)多体势计算.模拟结果再现了失配位错的形成现象.分析表明,失配位错在形成之初即呈现为Shockley扩展位错,即由两个伯格斯矢量为〈211〉/6的部分位错和其间的堆垛层错组成,两个部分位错的间距、即层错宽度为1.8 nm,与理论计算结果一致;外延晶体薄膜沉积生长中,位错对会发生滑移,但其间距保持稳定.进一步观察发现,该扩展位错产生于一种类似于“局部熔融-重结晶”的表层局部无序紊乱-
关键词:
失配位错
外延生长
薄膜
分子动力学
铝 相似文献
122.
This paper reports that the m-plane GaN layer is grown on (200)-plane LiAlO2 substrate by metal-organic chemical wpour deposition (MOCVD) method. Tetragonal-shaped crystallites appear at the smooth surface. Raman measurement illuminates the compressive stress in the layer which is released with increasing the layer's thickness. The high transmittance (80%), sharp band edge and excitonic absorption peak show that the GaN layer has good optical quality. The donor acceptor pair emission peak located at -3.41 eV with full-width at half maximum of 120 meV and no yellow peaks in the photoluminescence spectra partially show that no Li incorporated into GaN layer from the LiAlO2 substrate. 相似文献
123.
Homo-apioneplanocin A was efficiently synthesized via stereoselective hydroxymethylation, regio- and chemoselective hydroboration, and chemoselective oxidation as key steps from d-ribose. 相似文献
124.
High temperature oxidation of metals leads to residual stresses both in the metal and in the growing oxide. In this work, the evolution of this residual stresses is theoretically predicted in the growing oxide layers. The origin of these stresses is based on a microstructural model. Using experimental results providing from the oxidation kinetics, and an analysis proposed to describe the growth strain occurring in the thin layers, a set of equations is established allowing determining the stresses evolution with oxidation time. Then, the model is compared with experimental results obtained on both α-Fe and phosphated α-Fe, oxidised at different temperatures. Numerical data are extracted from experiments either with an asymptotic formulation or with an inverse method. These two methods give good agreement with experiments and allow extracting the model parameters. 相似文献
125.
Quenching of the eutectoidal composition of the shape memory alloys (SMA’s) allowed us to display the gradual transition of
the martensitic structure as a function of the composition. Indeed, we have verified that for low Al and Ni percentages, the
martensite structure obtained is β′, while, for high Al and Ni (Al<13.3 mass%) contents, the martensite structure is essentially
of β1′ type. Elsewhere, we have observed that a nickel addition (<4.3 mass%) operates simultaneously on the composition of the
eutectoidal pointand the domain of the different martensitic structures types. During reheating of the quenched structure,
the transformation sequences of the martensite to the parent phase (β1), then the decomposition of the later phase into the
equilibrium phases, and finally, the redissolution of all phases to form the β phase at high temperature, are rather similar.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
126.
127.
The dielectric responses (i.e. the refractive indices and the second order nonlinear susceptibilities) of all orthorhombic rare earth molybdates have been studied on the basis of the relationship between dielectric responses and the average atomic number of constituent atoms of crystals. Both the linear and second order nonlinear optical responses at 1.064 μm decrease with increasing atomic number from La to Lu. 相似文献
128.
Bond covalency and valence of elements in HgBa2Can−1CunO2n+2+δ (n=1, 2, 3, 4) were calculated and their relationship with Tc was discussed. For both oxygen and argon annealed samples, the results indicated that with the increase of n, the trend of bond covalency of Hg-O and Cu-O was the same or opposite compared with that of superconducting temperature. This may suggest that the magnitudes of Cu-O and Hg-O bond covalency are important in governing the superconducting temperature. For the highest Tc sample, Hg had the lowest valence, implying that lower valence of Hg was preferred in order to produce higher Tc. For fixed n, the valence of Cu in oxygen annealed samples was larger than that in argon annealed samples, indicating that oxygen annealed samples produced more carriers than argon annealed samples. 相似文献
129.
The high-temperature cubic phase of non-stoichiometric strontium ferrite SrFeOx (2.5≤x≤3.0) has been studied by in situ neutron powder diffraction in air over the temperature range 300-1273 K. The composition of SrFeOx changes within the range 2.56≤x≤2.81 from 1273 to 673 K, respectively.Rietveld refinements of the diffraction patterns show that the high-temperature cubic phase of SrFeOx is consistent with a face-centred Fm3c structure. This structure leads to agreement with previous density measurements. This cell allows the high-temperature structure of SrFeOx to be described in terms of a solid solution of the composition end members. Cubic SrFeOx at high temperature is found to closely obey Vegard's law. The density of cubic SrFeOx is also found to exhibit a linear relationship with composition. 相似文献
130.
Copper bromide was used as a catalyst for the addition of pyrroles to enones. When both the reactants were used in equimolar amounts, mono and dialkylated products were obtained. However, the use of excess enone furnished only dialkylated products. Thus, copper bromide was shown to be an efficient catalyst for the dialkylation of pyrroles. 相似文献