全文获取类型
收费全文 | 3127篇 |
免费 | 787篇 |
国内免费 | 210篇 |
专业分类
化学 | 462篇 |
晶体学 | 32篇 |
力学 | 863篇 |
综合类 | 22篇 |
数学 | 678篇 |
物理学 | 2067篇 |
出版年
2024年 | 13篇 |
2023年 | 61篇 |
2022年 | 116篇 |
2021年 | 100篇 |
2020年 | 114篇 |
2019年 | 105篇 |
2018年 | 90篇 |
2017年 | 115篇 |
2016年 | 189篇 |
2015年 | 127篇 |
2014年 | 219篇 |
2013年 | 250篇 |
2012年 | 178篇 |
2011年 | 242篇 |
2010年 | 188篇 |
2009年 | 216篇 |
2008年 | 215篇 |
2007年 | 211篇 |
2006年 | 212篇 |
2005年 | 145篇 |
2004年 | 140篇 |
2003年 | 136篇 |
2002年 | 125篇 |
2001年 | 89篇 |
2000年 | 71篇 |
1999年 | 72篇 |
1998年 | 68篇 |
1997年 | 34篇 |
1996年 | 44篇 |
1995年 | 45篇 |
1994年 | 31篇 |
1993年 | 28篇 |
1992年 | 18篇 |
1991年 | 25篇 |
1990年 | 14篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 5篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 6篇 |
1957年 | 1篇 |
排序方式: 共有4124条查询结果,搜索用时 328 毫秒
981.
982.
983.
Stella K. Papadopoulou Ioannis Karapanagiotis Costas Panayiotou 《European Polymer Journal》2010,46(2):202-78
A fluorinated methacrylic homopolymer, poly(2,2,3,3,3-pentafluoropropyl methacrylate) (PPFPMA) was synthesized by a free radical polymerization reaction. The dispersive component of the surface energy () of PPFPMA was determined by contact angle measurements and inverse gas chromatography (IGC). An extensive surface characterization was conducted by means of IGC. Surface characterization demonstrated that PPFPMA has low value, even at 35 °C and is a Lewis amphoteric polymer with predominantly basic character, as confirmed by the Lewis acidity and basicity constants KA and KB, respectively. The values of obtained by IGC are slightly higher than those obtained by the contact angle method. This trend can be attributed to the fact that IGC evaluates, primarily, high energy sites of a surface. 相似文献
984.
Review: Aptamers in microfluidic chips 总被引:1,自引:0,他引:1
This review, covering reports published from 2002 to August 2010, shows how aptamers have made significant contributions in the improvements of microfluidic chips for affinity extraction, separations and detections. Furthermore, microfluidic chip methods for studying aptamer-target interactions and performing aptamer selections have also been summarized. Accordingly, research vacancies and future development trends in these areas are discussed. 相似文献
985.
High-frequency surface acoustic wave (SAW) filters using undoped and V-doped ZnO films were fabricated on diamond. Compared with their counterparts, the SAW filters using V-doped ZnO films have higher electromechanical coupling coefficient of ∼2.9% and lower insertion loss. The filtering performance improvement is considered to be due to the ferroelectricity in V-doped ZnO films and the resultant high piezoresponse (∼110 pm/V), which is one order of magnitude larger than that of undoped ZnO films. In addition, more perfect (0 0 2) preferred orientation, better uniform grains and smoother surface of V-doped ZnO films also contribute to the filtering performance improvement. 相似文献
986.
The inter-carrier interference (ICI) of Orthogonal Frequency Division Multiplexing (OFDM) symbols, which is caused by the transducer’s dynamics, has been analysed and simulated in this paper. The small Cyclic Prefix (CP) method is proposed to overcome the ICI caused by the transducer in order to maintain the orthogonality between sub-carriers without much loss of the energy and the bandwidth efficiency. The simulation results show that the small CP whose length is longer than the transient response of the transducer can eliminate the ICI problem. 相似文献
987.
In this work we demonstrate the properties of spatial solitary waves in chiral nematic liquid crystals with an external electric field. Such self-trapped beams, called nematicons, were created due to the optical reorientation nonlinearity for a light power of a few tens of milliwatts. We show that the direction of propagation of such nematicons can be changed by applying an external electric field. Additionally, this effect can be modified by changing the input polarization of the light beam. The experimental results were obtained in four independent guiding layers created by a chiral nematic structure. 相似文献
988.
Contact angle and the wetting behaviour of solid particles are influenced by many physical and chemical factors such as surface roughness and heterogeneity as well as particle shape and size. A significant amount of effort has been invested in order to probe the correlation between these factors and surface wettability. Some of the key investigations reported in the literature are reviewed here.It is clear from the papers reviewed that, depending on many experimental conditions such as the size of the surface heterogeneities and asperities, surface cleanliness, and the resolution of measuring equipment and data interpretation, obtaining meaningful contact angle values is extremely difficult and such values are reliant on careful experimental control. Surface wetting behaviour depends on not only surface texture (roughness and particle shape), and surface chemistry (heterogeneity) but also on hydrodynamic conditions in the preparation route. The inability to distinguish the effects of each factor may be due to the interplay and/or overlap of two or more factors in each system. From this review, it was concluded that:
- •
- Surface geometry (and surface roughness of different scales) can be used to tune the contact angle; with increasing surface roughness the apparent contact angle decreases for hydrophilic materials and increases for hydrophobic materials.
- •
- For non-ideal surfaces, such as mineral surfaces in the flotation process, kinetics plays a more important role than thermodynamics in dictating wettability.
- •
- Particle size encountered in flotation (10-200 μm) showed no significant effect on contact angle but has a strong effect on flotation rate constant.
989.
Laurent Poinsot 《Discrete Applied Mathematics》2009,157(8):1848-1857
The left-regular multiplication is explicitly embedded in the notion of perfect nonlinearity. But there exist many other group actions. By replacing translations by another group action the new concept of group action-based perfect nonlinearity has been introduced. In this paper we show that this generalized concept of nonlinearity is actually equivalent to a new bentness notion that deals with functions defined on a finite Abelian group G that acts on a finite set X and with values in the finite-dimensional vector space of complex-valued functions defined on X. 相似文献
990.
The paper presents an iterative method for obtaining footprint, pressure distribution, local deformation and sub-surface stress field for the contact between a rigid cylindrical indenter and an elastic flat substrate. The methodology is applicable for semi-infinite, as well as for thin or thick bonded elastic layered solids with high or low elastic moduli. All findings are in accord with the observed behaviour of hard wear resistant and soft solid lubricating coatings. It is shown that the decomposed contact pressure distribution into a series of harmonic waves induces sub-surface stress fields that decay into the depth of the solid according to their wavelengths. Consequently, conditions vis-à-vis fatigue spalling and adhesion performance may be predicted for given thickness of layered bonded elastic solids. 相似文献