全文获取类型
收费全文 | 2770篇 |
免费 | 320篇 |
国内免费 | 309篇 |
专业分类
化学 | 445篇 |
晶体学 | 4篇 |
力学 | 1778篇 |
综合类 | 59篇 |
数学 | 308篇 |
物理学 | 805篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 56篇 |
2021年 | 88篇 |
2020年 | 74篇 |
2019年 | 61篇 |
2018年 | 57篇 |
2017年 | 104篇 |
2016年 | 152篇 |
2015年 | 95篇 |
2014年 | 150篇 |
2013年 | 180篇 |
2012年 | 163篇 |
2011年 | 166篇 |
2010年 | 118篇 |
2009年 | 166篇 |
2008年 | 161篇 |
2007年 | 176篇 |
2006年 | 165篇 |
2005年 | 141篇 |
2004年 | 126篇 |
2003年 | 123篇 |
2002年 | 101篇 |
2001年 | 88篇 |
2000年 | 96篇 |
1999年 | 73篇 |
1998年 | 58篇 |
1997年 | 54篇 |
1996年 | 58篇 |
1995年 | 54篇 |
1994年 | 45篇 |
1993年 | 44篇 |
1992年 | 37篇 |
1991年 | 27篇 |
1990年 | 24篇 |
1989年 | 22篇 |
1988年 | 19篇 |
1987年 | 4篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1971年 | 4篇 |
1967年 | 1篇 |
1957年 | 7篇 |
排序方式: 共有3399条查询结果,搜索用时 343 毫秒
51.
52.
V. Bruder-Hubscher F. LagardeM.J.F. Leroy C. CoughanowrF. Enguehard 《Analytica chimica acta》2002,451(2):285-295
The release of five elements (Cr, Cu, Mn, Pb and Zn) from a municipal solid waste incineration bottom ash (BA) under different extraction conditions has been investigated by performing the three-step sequential extraction procedure proposed by the Standards, Measurements and Testing Program of the European Union. A fourth step (strong acid attack) has been added in order to calculate the mass balance. The results of this study provide information on the potential mobility of the studied elements. Almost all of the Cr and part of the Mn are extracted with strong acid which indicates low potential mobility in the environment. Most of the Cu is extracted under oxidizing conditions. Pb and Zn are released under acidic condition, indicating the possibility of their mobilization by changes in pH. The reproducibility of the sequential extraction procedure is also discussed. 相似文献
53.
Functional organic molecular materials and conjugated oligomers or polymers now allow the low-cost fabrication of thin films for insertion into new generations of electronic and optoelectronic devices. The performance of these devices relies on the understanding and optimization of several complementary processes. Our goal is to discuss the relationship between the molecular stacking structures and their optoelectronic properties that are of importance in all these areas. The concept of intermolecular interaction should be taken here in the special sense that is inter-dipole coupling. Specifically, we will address the impact of inter-dipole interaction between adjacent molecules in aggregate state on the solid-state emission properties. 相似文献
54.
The use of capillary column gas chromatography and gas chromatography/mass spectrometry for the analysis of a series of standard solutions (0.1 to 10 μg/ml) of 2,4,6-trinitrotoluene (TNT) and eight other nitroaromatic components was evaluated. The techniques included gas chromatography with electron capture detection (GC/ECD), full scan and selected ion monitoring gas chromatography/mass spectrometry with electron impact ionization (EI/FS and EI/SIM), full scan and selected ion monitoring gas chromatography/mass spectrometry with positive ion chemical ionization using methane reagent gas (PICI/FS and PICI/SIM), and full scan and selected ion monitoring gas chromatography/mass spectrometry with negative ion chemical ionization using methane reagent gas (NICI/FS and NICI/SIM). The performance of the techniques was comapared by determining the linear response range, precision, and detection limits of the analyses. 相似文献
55.
Norio Manabe Kenichi Kawamura Masanao Ishikawa Shoutarou Suzuki Boping Liu Minoru Terano Hisayuki Nakatani 《Polymer Testing》2005,24(8):994-997
In this study, a novel potentiometric titration of hydroperoxide in degraded polypropylene (PP) is proposed. This titration is quite sensitive compared with the conventional ones such as UV and manual titrations, and its detection limit was about 2 meq/kg. The sensitivity was equal to that of molecular weight measurement by GPC for the degraded PP and, in addition, the volatilization behavior of the hydroperoxide could be detected. This titration was found to be very effective for the determination of PP degradation. 相似文献
56.
Dushmantha Kannangara Hailong Zhang Wei Shen 《Colloids and surfaces. A, Physicochemical and engineering aspects》2006,280(1-3):203-215
The spreading and recoiling of water drops on several flat and macroscopically smooth model surfaces and on sized paper surfaces were studied over a range of drop impaction velocities using a high-speed CCD camera. The water drop spreading and recoiling results on several model hydrophobic and hydrophilic surfaces were found to be in agreement with observations reported in the literature. The maximum drop spreading diameter for those model surfaces at impact was found to be dependent upon the initial drop kinetic energy and the degree of hydrophobicity/hydrophilicity of the surface. The extent of the maximum drop recoiling was found to be much weaker for hydrophilic substrates than for hydrophobic substrates. Sized papers, however, showed an interesting switch of behaviour in the process of water drop impaction. They behave like a hydrophobic substrate when a water drop impacts on it, but like a hydrophilic substrate when water drop recoils. Although the contact angle between water and hydrophilic or hydrophobic non-porous surfaces changes from advancing to receding as reported in literature, the change of contact angle during water impact on paper surface is unique in that the level of sizing was found to have a smaller than expected influence on the degree of recoil. Atomic force microscopy (AFM) was used to probe fibres on a sized filter paper surface under water. The AFM data showed that water interacted strongly with the fibre even though the paper was heavily sized. Implications of this phenomenon were discussed in the context of inkjet print quality and of the surface conditions of sized papers. Results of this study are very useful in the understanding of inkjet ink droplet impaction on paper surfaces which sets the initial condition for ink penetration into paper after impaction. 相似文献
57.
The deformation processes in impact-modified PMMA, which deforms homogeneously, were determined by means of the stress/strain experiment (, ) with simultaneous lateral strain measurement (lat) in a wide range of strain rates () up to 105%/min (impact stress). The elastic, plastic cavitation and plastic shear processes were determined as a function of strain. Therefore we calculated the elastic strain (
el), the elastic volume expansion (
vol el), the cavitation strain (
cav), which is identical with the plastic volume expansion (
vol pl), the shear strain (
sh) and the energy densities (Wel, Wcav, Wsh) related to these three processes.For strains of 3 % onward it was found that plastic shear processes and plastic cavitation processes are responsible for a partial loss of elastically stored energy. Both plastic processes turn out to be mostly anelastic deformations, their amount depending strongly on the strain rate. The contributions of the processes to the total deformation of the unmodified PMMA in its strain range are similar to those of the impact-modified PMMA, and the high impact strength is caused by a shift of the catastrophic rupture to very high strains. 相似文献
58.
D. S. Robertson 《Speculations in Science and Technology》1998,21(3):187-197
It has been established from geological studies that change in the atmospheric content of carbon dioxide gas commenced about one hundred million years ago. The likely origin of this change is advanced as being the onset of the Brewer circulation caused by the rise in terrain induced by tectonic plate movement. It is demonstrated that tectonic plate movement can be affected by impacts from external bodies which penetrate the crust of the Earth. The consequences of the change in atmospheric concentration of carbon dioxide are proposed as first, extinctions and reductions in animal numbers, including primates, as a result of changes in body chemistry of these animals and second, a change in the rate of weathering of rocks giving rise to changes in the availability of chemicals such as calcium and potassium which are essential for plant and animal life. This latter change contributing to the extinctions and reductions in animal numbers. It is shown that the change in weathering can account for the rise to dominance of angiosperm plants. It is concluded that there were several simultaneous evolutionary environments on Earth which were a function of altitude which gave rise to a vertical variation in atmospheric content of carbon dioxide. This variation disappeared with rise of terrain and the onset of the Brewer circulation. Such changes are advanced and being much more important than any changes in temperature caused by greenhouse effects since the disappearance of atmospheric variations in carbon dioxide allowed animal migration. It is demonstrated that the conditions of extinction could be reintroduced by human activities. 相似文献
59.
60.
In this review, thin films of SiO2 on Mo(1 1 2) and MgO(1 0 0) on Mo(1 0 0) have been characterized using metastable impact electron and ultraviolet photoelectron spectroscopies (metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy). The electronic and chemical properties of the thin films are identical to those of the corresponding bulk oxides. For different prepared defective SiO2 surfaces, additional features are observed in the band-gap region. These features arise from vacancies or excess oxygen and are consistent with theoretical predictions of additional occupied states in the band-gap due to point defects. Extended defect sites on SiO2 and MgO are identified using MIES by a narrowing of the O(2p) features with a reduction in the density of extended defect sites. MIES of adsorbed Xe (MAX) is also used to estimate the density of extended defect sites. Furthermore, it is shown that CO is an appropriate probe molecule for estimating the defect density of MgO surfaces. Upon Ag exposure, the change in the work function of a low defect MgO(1 0 0) versus a high defect surface is markedly different. For a sputter-damaged MgO(1 0 0) surface, an initial decrease of the work function was found, implying that small Ag clusters on this surface are electron deficient. In contrast, for SiO2 no significant change of the work function upon Ag exposure with increasing defect density was observed. On MgO(1 0 0), the presence of defect sites markedly alter the electronic and chemical properties of supported Ag clusters. Such a strong influence of defect sites was not found for Ag clusters on SiO2. 相似文献