全文获取类型
收费全文 | 90570篇 |
免费 | 14050篇 |
国内免费 | 5049篇 |
专业分类
化学 | 79542篇 |
晶体学 | 1718篇 |
力学 | 3659篇 |
综合类 | 268篇 |
数学 | 6518篇 |
物理学 | 17964篇 |
出版年
2024年 | 78篇 |
2023年 | 314篇 |
2022年 | 872篇 |
2021年 | 1105篇 |
2020年 | 1786篇 |
2019年 | 3294篇 |
2018年 | 3106篇 |
2017年 | 3646篇 |
2016年 | 4359篇 |
2015年 | 6432篇 |
2014年 | 6282篇 |
2013年 | 9611篇 |
2012年 | 7021篇 |
2011年 | 6909篇 |
2010年 | 5747篇 |
2009年 | 5551篇 |
2008年 | 6032篇 |
2007年 | 5417篇 |
2006年 | 5034篇 |
2005年 | 4606篇 |
2004年 | 4064篇 |
2003年 | 3683篇 |
2002年 | 4120篇 |
2001年 | 2432篇 |
2000年 | 2255篇 |
1999年 | 1321篇 |
1998年 | 676篇 |
1997年 | 532篇 |
1996年 | 477篇 |
1995年 | 462篇 |
1994年 | 375篇 |
1993年 | 308篇 |
1992年 | 295篇 |
1991年 | 221篇 |
1990年 | 191篇 |
1989年 | 146篇 |
1988年 | 149篇 |
1987年 | 126篇 |
1986年 | 124篇 |
1985年 | 98篇 |
1984年 | 96篇 |
1983年 | 55篇 |
1982年 | 68篇 |
1981年 | 36篇 |
1980年 | 36篇 |
1979年 | 43篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1976年 | 8篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
This paper investigated phase change Si1Sb2Te3 material for application of chalcogenide random access memory. Current-voltage performance was conducted to determine threshold current of phase change from amorphous phase to polycrystalline phase. The film holds a threshold current about 0.155 mA, which is smaller than the value 0.31 mA of Ge2Sb2Te5 film. Amorphous Si1Sb2Te3 changes to face-centred-cubic structure at ~ 180℃ and changes to hexagonal structure at ~ 270℃. Annealing temperature dependent electric resistivity of Si1Sb2Te3 film was studied by four-point probe method. Data retention of the films was characterized as well. 相似文献
952.
The geometric phase of the quantum systems with slow but finite
rate of the external time-dependent field 下载免费PDF全文
With the help of the time-dependent gauge transformation technique, we have
studied the geometric phase of a spin-half particle in a rotating magnetic
field. We have found that the slow but finite frequency of the rotating
magnetic field will make the difference between the adiabatic geometric phase and
the exact geometric phase. When the frequency is much smaller than the
energy space and the adiabatic condition is perfectly guaranteed, the
adiabatic approximation geometric phase is exactly consistent with the
adiabatic geometric phase. A simple relation for the accuracy of the
adiabatic approximation is given in terms of the changing rate of the frequency of
the rotating magnetic field and the energy level space. 相似文献
953.
A. D?browski M. Barczak N.V. Stolyarchuk O.K. Matkovskii 《Applied Surface Science》2007,253(13):5747-5751
Ethylene and phenylene bridged polysilsesquioxane xerogels having amine and thiol groups attached to the surface have been obtained by the sol-gel method from 1,2-bis(triethoxysilyl)ethane or 1,4-bis(triethoxysilyl)benzene and functionalized silanes in the presence of an ammonium fluoride catalyst in an ethanol solution. The synthesized samples have a porous structure (700-850 m2/g) and a high content of functional groups (1.4-1.9 mmol/g). The obtained porous bridged polysilsesquioxanes exhibit a considerable affinity for adsorbing several organic compounds (n-hexane, n-heptane, benzene, cyclohexane, acetonitrile and triethylamine) from the gas phase. The sample with an ethylene bridge and amino groups in the surface layer has the highest uptake of all compounds. Data from adsorption measurements show that functionalized organosilicon materials can be used as effective adsorbents of organic contaminants from the gas phase. 相似文献
954.
A status report on rapidly advancing femtosecond laser technology, three-dimensional (3D) microstructuring by multiphoton illumination technique, is given. Taking its origin from multiphoton microscopy, this technique is now becoming an important microfabrication tool. In our work we apply near-infrared Ti:sapphire femtosecond laser pulses (at 800/780 nm) for 3D material processing. When tightly focused into the volume of a photosensitive material (or photoresist), they initiate 2PP process by, for example, transferring liquid into the solid state. This allows the fabrication of any computer generated 3D structure by direct laser “recording” into the volume of photosensitive material. 2PP of photosensitive materials irradiated by femtosecond laser pulses is now considered as enabling technology for the fabrication of 3D photonic crystals and photonic crystal templates. In particular, 2PP allows one to introduce defects at any desired locations, which is crucial for the practical applications. Recently, we studied possible applications of 2PP technique in biomedicine. 2PP is a very interesting technique for the fabrication of drug delivery systems, scaffolds for tissue engineering, and medical implants. These and other biomedical applications of 2PP will be reviewed. 相似文献
955.
956.
Stanislaw Dzwigaj Lorenzo Stievano Michel Che 《Journal of Physics and Chemistry of Solids》2007,68(10):1885-1891
Fe-containing SiBEA zeolites were prepared by a two-step postsynthesis method: creation of vacant T-sites by dealumination of tetraethylammonium BEA zeolite with nitric acid and then impregnation of the resulting SiBEA zeolite with an aqueous solution of Fe(NO3)3. X-ray diffraction shows that iron is incorporated in SiBEA at lattice sites. The presence of Fe in its oxidation state +3 and at isolated tetrahedral sites for low metal content, was demonstrated by diffuse reflectance UV-vis, EPR and Mössbauer spectroscopy. For high iron content, diffuse reflectance UV-vis and Mössbauer spectra revealed the additional presence of extra-lattice FeOx oligomers and superparamagnetic Fe-oxyhydroxide. Mössbauer spectroscopy identified superparamagnetic Fe-oxyhydroxide as the main phase when basic conditions are used for the preparation. 相似文献
957.
Surface morphology in 3.5 × 3.5 μm2 area of spinel LiMn2O4, which is a typical cathode material for Li ion secondary batteries, is studied using an atomic force microscopy (AFM) with a conductive probe. Negative bias voltage is applied to the probe to attract Li+ ions toward LiMn2O4 surface during the AFM observation. Before applying the voltage (0 V), the whole LiMn2O4 surface is covered with scale-shaped grains. Under the negative voltage of 5.5 V, electric current abruptly increases, indicating Li+ ionic conduction. Simultaneously, part of the scale-shaped grains expand and flatten. Jahn-Teller phase transition, which is induced by the repulsive interaction between the Mn-eg and O-2p electrons in Li accumulated layer, is proposed as a possible origin of these results. 相似文献
958.
Laredo E Prutsky N Bello A Grimau M Castillo RV Müller AJ Dubois P 《The European physical journal. E, Soft matter》2007,23(3):295-303
Thermally stimulated depolarization currents, TSDC, wide-angle X-ray scattering, WAXS, differential scanning calorimetry,
DSC, and polarized light optical microscopy, PLOM, have been used to examine poly(L-lactide)-b -poly(
-caprolactone) diblock copolymers in a wide composition range. Both components are crystallizable and the miscibility in
the amorphous phase has been determined from the behavior of the primary relaxations which are the dielectric manifestation
of the glass transition, and also from the superstructural morphology revealed by PLOM and the compositional dependence of
the melting points as determined by DSC. Distinct segmental mobilities in the amorphous phase which can be well resolved by
TSDC are present; the
mode of the slower component shifts to lower temperatures as the PCL content increases while the glass transition of neat
PCL is present for all compositions. A relaxation times bimodal distribution is apparent for PCL-rich copolymers. The composition
dependence of the multiple glass transitions detected in these weakly segregated copolymers are predicted by the self-concentration
model for a miscible blend made of components with a large Tg contrast. 相似文献
959.
A mathematical model based on a straightforward geometrical background is developed which enables predictions of a transition of one dispersed phase to a cocontinuous one (i.e., the percolation threshold) on addition of another dispersed phase during melt mixing in ternary polymer blends. The present work concerns only ternary blends with two separate dispersions of the inner phases in which no encapsulation takes place. In addition, in order to simplify the model, one of the inner phases was represented by hard, nondeformable microspheres The expression developed describes well an experimental relationship between the percolation threshold, the concentration above which the former dispersed phase transforms to a continuous one, and concentrations of both inner phases. The results agree well with the experimental data obtained in a previous work. 相似文献
960.