全文获取类型
收费全文 | 27436篇 |
免费 | 4987篇 |
国内免费 | 3294篇 |
专业分类
化学 | 12529篇 |
晶体学 | 306篇 |
力学 | 3288篇 |
综合类 | 67篇 |
数学 | 4952篇 |
物理学 | 14575篇 |
出版年
2024年 | 15篇 |
2023年 | 1201篇 |
2022年 | 1211篇 |
2021年 | 1391篇 |
2020年 | 1601篇 |
2019年 | 1039篇 |
2018年 | 1221篇 |
2017年 | 1534篇 |
2016年 | 1492篇 |
2015年 | 1642篇 |
2014年 | 1992篇 |
2013年 | 2093篇 |
2012年 | 2419篇 |
2011年 | 2217篇 |
2010年 | 2022篇 |
2009年 | 1942篇 |
2008年 | 1387篇 |
2007年 | 1562篇 |
2006年 | 1651篇 |
2005年 | 980篇 |
2004年 | 656篇 |
2003年 | 620篇 |
2002年 | 556篇 |
2001年 | 789篇 |
2000年 | 397篇 |
1999年 | 699篇 |
1998年 | 460篇 |
1997年 | 340篇 |
1996年 | 88篇 |
1995年 | 68篇 |
1994年 | 53篇 |
1993年 | 68篇 |
1992年 | 61篇 |
1991年 | 40篇 |
1990年 | 36篇 |
1989年 | 23篇 |
1988年 | 22篇 |
1987年 | 16篇 |
1986年 | 23篇 |
1985年 | 22篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 9篇 |
1976年 | 3篇 |
1971年 | 10篇 |
1959年 | 1篇 |
1957年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Understanding the complicated failure mechanisms of hierarchical composites such as fiber yarns is essential for advanced materials design. In this study, we developed a new Monte Carlo model for predicting the mechanical properties of fiber yarns that includes statistical variation in fiber strength. Furthermore, a statistical shear load transfer law based on the shear lag analysis was derived and implemented to simulate the interactions between adjacent fibers and provide a more accurate tensile stress distribution along the overlap distance. Simulations on two types of yarns, made from different raw materials and based on distinct processing approaches, predict yarn strength values that compare favorably with experimental measurements. Furthermore, the model identified very distinct dominant failure mechanisms for the two materials, providing important insights into design features that can improve yarn strength. 相似文献
82.
83.
Tomography phase microscopy (TPM) is a new microscopic method that can quantitatively yield the volumetric 3D distribution of a sample׳s refractive index (RI), which is significant for cell biology research. In this paper, a controllable TPM system is introduced. In this system a circulatory phase-shifting method and piezoelectric ceramic are used which enable the TPM system to record the 3D RI distribution at a more controllable speed, from 1 to 40 fps, than in the other TPM systems reported. The resolution of the RI distribution obtained by this controllable TPM is much better than that in images recorded by phase contrast microscopy and interference tomography microscopy. The realization of controllable TPM not only allows for the application of TPM to the measurement of kinds of RI sample, but also contributes to academic and technological support for the practical use of TPM. 相似文献
84.
Novel self activated green phosphors; K2ZnV2O7 (KZV) and K2MgV2O7 (KMV) have been prepared and characterized in details. Both KZV and KMV were prepared by solid state reaction and systematically characterized by a number of techniques like X-ray diffraction (XRD), Fourier transformed Infrared (FTIR), Raman spectroscopy, Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), diffuse reflectance spectroscopy (DRS) and time resolved photoluminescence spectroscopy (TRPLS). XRD studies confirm tetragonal melilite type layered phase for both of them. The presence of pyrovanadate group in both is supported by FTIR and Raman spectroscopic investigations. Raman bands of KMV are blue shifted w.r.t to KZV which may be due to shorter bond lengths of MgO compared to ZnO and lower atomic weight of magnesium compared to zinc. DRS measurements indicated the optical band gap of KMV and KZV are 3.14 and 3.12 eV, respectively. Optical measurements on these samples show the emission of green color on ultra violet light irradiation. The origin of such emission is attributed to electronic transition (charge transfer) from filled 2p orbital of oxygen ion (O2−) to vacant 3d orbital of vanadium ion (V5+). In KZV there are dual emission band (PL1 and PL2) which are respectively attributed to 3T2 → 1A1 and 3T1 → 1A1transition, and the emission zone varies slightly compared to KMV. KZV emits bluish green (cool green) where KMV emits in yellowish green (warm green) region. This is indeed an important step towards realization of cost effective rare earth free luminescence material. It is also oberved that PL intensity of KZV is very high compared to KMV which is supported by the lifetime measurements. 相似文献
85.
In this work, stable silver nanoparticles (AgNPs) are prepared by borohydride reduction. Autocatalytic oxidation reaction of AgNPs in the presence of hydrogen peroxide (H2O2) is investigated. Sharp silver stripping peak in linear sweep voltammogram is used to reflect H2O2 concentration and the detection limit of 0.5 μM is achieved. We have also explored the application of the simply prepared AgNP modified electrode for electrochemical tracking H2O2 secretion in live cells. This facile strategy shows excellent sensitivity, stability and has great potential use in physiological and pathological applications. 相似文献
86.
Electrically conductive polypropylene/graphite (PP/graphite) composites were prepared via blending granulated PP with maleic anhydride grafted PP and natural graphite. Electrical conductivity of prepared samples containing either 65, 70, or 75 wt% of graphite was measured and the most conductive sample containing 75 wt% of graphite was exposed to UV irradiation for 1 and 24 h or thermally treated at 170 °C for 1 h. The influence of thermal and UV exposure on the structural and electrical changes in such treated samples was studied. Local current measurements on the surface were made using scanning spreading resistance microscopy and morphology of the surface was studied by atomic force microscopy. X-ray diffraction analysis, infrared and Raman spectroscopy were also used for the structural characterization. Properties of treated and untreated samples are compared and differences are discussed. 相似文献
87.
88.
In this paper, the implementation of research-oriented teaching mode in coordination chemistry was introduced, including the strategies, main contents and evaluation. 相似文献
89.
90.