全文获取类型
收费全文 | 6990篇 |
免费 | 1237篇 |
国内免费 | 848篇 |
专业分类
化学 | 3382篇 |
晶体学 | 87篇 |
力学 | 884篇 |
综合类 | 18篇 |
数学 | 1648篇 |
物理学 | 3056篇 |
出版年
2024年 | 32篇 |
2023年 | 174篇 |
2022年 | 304篇 |
2021年 | 322篇 |
2020年 | 368篇 |
2019年 | 275篇 |
2018年 | 320篇 |
2017年 | 335篇 |
2016年 | 409篇 |
2015年 | 456篇 |
2014年 | 556篇 |
2013年 | 585篇 |
2012年 | 605篇 |
2011年 | 601篇 |
2010年 | 475篇 |
2009年 | 415篇 |
2008年 | 288篇 |
2007年 | 387篇 |
2006年 | 337篇 |
2005年 | 217篇 |
2004年 | 123篇 |
2003年 | 151篇 |
2002年 | 106篇 |
2001年 | 131篇 |
2000年 | 63篇 |
1999年 | 122篇 |
1998年 | 87篇 |
1997年 | 57篇 |
1996年 | 61篇 |
1995年 | 42篇 |
1994年 | 33篇 |
1993年 | 38篇 |
1992年 | 29篇 |
1991年 | 25篇 |
1990年 | 27篇 |
1989年 | 26篇 |
1988年 | 80篇 |
1987年 | 144篇 |
1986年 | 134篇 |
1985年 | 22篇 |
1984年 | 15篇 |
1983年 | 8篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 16篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 8篇 |
1936年 | 2篇 |
排序方式: 共有9075条查询结果,搜索用时 15 毫秒
1.
Peng-Yan Gui Xiao-Hui Yan Wen-Juan Yuan Yuan-Liang Ma Xiao Ding Shuai Liu 《Natural product research》2019,33(19):2830-2836
A new A, D-seco limonoid, named 12-acetyloxyperforatin (1), along with three known ones, were isolated from the leaves of Harrisonia perforata. Their structures were elucidated on the basis of spectroscopic analysis, including extensive NMR techniques and computational modelling. These compounds showed no inhibitory activity against the 11β-HSD1 enzyme. 相似文献
2.
3.
4.
《中国化学快报》2020,31(12):3183-3189
Engineered nanomaterials have attracted significantly attention as one of the most promising antimicrobial agents for against multidrug resistant infections. The toxicological responses of nanomaterials are closely related to their physicochemical properties, and establishment of a structure-activity relationship for nanomaterials at the nano-bio interface is of great significance for deep understanding antibacterial toxicity mechanisms of nanomaterials and designing safer antibacterial nanomaterials. In this study, the antibacterial behaviors of well-defined crystallographic facets of a series of Au nanocrystals, including {100}-facet cubes, {110}-facet rhombic dodecahedra, {111}-facet octahedra, {221}-facet trisoctahedra and {720}-facet concave cubes, was investigated, using the model bacteria Staphylococcus aureus. We find that Au nanocrystals display substantial facet-dependent antibacterial activities. The low-index facets of cubes, octahedra, and rhombic dodecahedra show considerable antibacterial activity, whereas the high-index facets of trisoctahedra and concave cubes remained inert under biological conditions. This result is in stark contrast to the previous paradigm that the high-index facets were considered to have higher bioactivity as compared with low-index facets. The antibacterial mechanism studies have shown that the facet-dependent antibacterial behaviors of Au nanocrystals are mainly caused by differential bacterial membrane damage as well as inhibition of cellular enzymatic activity and energy metabolism. The faceted Au nanocrystals are unique in that they do not induce generation of reactive oxygen species, as validated for most antibiotics and antimicrobial nanostructures. Our findings may provide a deeper understanding of facet-dependent toxicological responses and suggest the complexities of the nanomaterial-cell interactions, shedding some light on the development of high performance Au nanomaterials-based antibacterial therapeutics. 相似文献
5.
Transformation hydrodynamics and the corresponding metamaterials have been proposed as a means to exclude the drag force acting on an object. Here, we report a strategy to deploy the hydrodynamic cloaks in a more practical manner by assembling different-shaped cloaking parts. Our strategy is to first model a square-shaped cloak and a carpet cloak and then combine them to conceal a more complex-shaped space in the three-dimensional hydrodynamic flow. With the derivation of transformation hydrodynamics, the coordinate transformations for each hydrodynamic cloaking are demonstrated with the calculated viscosity tensors. The pressure and velocity fields of the square, triangular (carpet), and exemplary three-dimensional house-shaped cloaks are numerically simulated, thus showing a cloaking effect and reduced drag. This study suggests an efficient way of cloaking complex architectures from fluid-dynamic forces. 相似文献
6.
All-optical frequency multiplication/recovery based on a semiconductor optical amplifier ring cavity
Fei Wang 《Optics Communications》2006,257(2):334-339
A novel scheme for all-optical frequency multiplication/recovery based on a semiconductor optical amplifier ring cavity is proposed and investigated numerically. The results show, for a 2.5 GHz driving pulse train, it can be generated 5-25 GHz repetition rate pulse trains with low clock amplitude jitter, polarization independence and high peak power. Furthermore, the extraction of the clock signal from a pseudorandom bit sequence signal can be realized based on the proposed scheme. 相似文献
7.
The method described in this paper allows an investigator to determine the intrinsic stress of a polymer layer in a way that
does not result in damage to devices or test structures. The method requires that a small area of the polymer be released
from the substrate to form a diaphragm. The diaphragm is stimulated with acoustic white noise and the diaphragm movement is
monitored with a laser vibrometer. The first few resonance frequencies of the diaphragm are obtained using a laser vibrometer
and then those frequencies are used to calculate the membrane intrinsic bi-axial tension. 相似文献
8.
Mo2Ni3Si/NiSi metal silicide composite coatings with a fine microstructure consisting of Mo2Ni3Si primary dendrites and the interdendritic Mo2Ni3Si/NiSi eutectics were fabricated on austenitic stainless steel AISI 321 by laser cladding process. Small amplitude reciprocating sliding wear resistance of the coatings is evaluated as functions of normal load and slip amplitude and the wear mechanisms were discussed based on worn surface morphology observations. Results showed that the Mo2Ni3Si/NiSi coatings have excellent small amplitude reciprocating sliding wear resistance. 相似文献
9.
A Nafion-modified glassy carbon electrode incorporated with tobramycin for the voltammetric stripping determination of Cu2+ has been explored. The electrode was fabricated by tobramycin containing Nafion on the glassy carbon electrode surface. The modified electrode exhibited a significantly increased sensitivity and selectivity for Cu2+ compared with a bare glassy carbon electrode and the Nafion modified electrode. Cu2+ was accumulated in HAc-NaAc buffer (pH 4.6) at a potential of -0.6 V (vs. SCE) for 300 s and then determined by differential pulse anodic stripping voltammetry. The effects of various parameters, such as the mass of Nafion, the concentration of tobramycin, the pH of the medium, the accumulation potential, the accumulation time and the scan rate, were investigated. Under the optimum conditions, a linear calibration graph was obtained in the concentration range of 1.0 x 10(-9) to 5.0 x 10(-7) mol l(-1) with a correlation coefficient of 0.9971. The relative standard deviations for eight successive determinations were 4.3 and 2.9% for 1.0 x 10(-8) and 2.0 x 10(-7) mol l(-1) Cu2+, respectively. The detection limit (three times signal to noise) was 5.0 x 10(-10) mol l(-1). A study of interfering substances was also performed, and the method was applied to the direct determination of copper in water samples, and also in analytical reagent-grade salts with satisfactory results. 相似文献
10.
《Nonlinear Analysis: Theory, Methods & Applications》2005,62(3):455-465
The multiplicity results are obtained for solutions of the Neumann problem for nonlinear elliptic equations with unbounded nonlinearity by the Implicit Function Theorem and the Morse theory. 相似文献