全文获取类型
收费全文 | 842篇 |
免费 | 86篇 |
国内免费 | 364篇 |
专业分类
化学 | 495篇 |
晶体学 | 2篇 |
力学 | 16篇 |
综合类 | 2篇 |
数学 | 467篇 |
物理学 | 310篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 10篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 9篇 |
2015年 | 19篇 |
2014年 | 27篇 |
2013年 | 49篇 |
2012年 | 61篇 |
2011年 | 76篇 |
2010年 | 98篇 |
2009年 | 128篇 |
2008年 | 122篇 |
2007年 | 122篇 |
2006年 | 111篇 |
2005年 | 79篇 |
2004年 | 78篇 |
2003年 | 63篇 |
2002年 | 44篇 |
2001年 | 34篇 |
2000年 | 36篇 |
1999年 | 26篇 |
1998年 | 21篇 |
1997年 | 11篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有1292条查询结果,搜索用时 229 毫秒
1.
In this paper,we investigate the non-autonomous Hamilton-Jacobi equation ■ where H is 1-periodic with respect to t and M is a compact Riemannian manifold without boundary.We obtain the viscosity solution denoted by T_(t_0)~tφ(x) and show T_(t_0)~tφ(x) converges uniformly to a time-periodic viscosity solution u~*(x,t) of ?_tu+H(t,x,?_xu,u)=0. 相似文献
2.
An adaptive smooth unsaturated bistable stochastic resonance (ASUBSR) system for bearing fault signal detection is established. Based on the problem of output saturation and poor low-frequency suppression performance of classical bistable stochastic resonance (CBSR) system, an SUBSR with unsaturated characteristics is proposed. An ASUBSR system is designed by extracting the envelope spectrum of the input signal and resampling it to satisfy the adiabatic approximation condition, combining high-pass filter to filter out low-frequency interference, and using genetic algorithm to select the optimal system parameters. Through simulations and experiments, we found that the system can effectively suppress the interference of low-frequency and high-frequency, indicates that the system performs like a band-pass filter, and the output signal-to-noise ratio is better than that of the CBSR system. The proposed ASUBSR system has great application in the field of fault detection of rolling bearings. 相似文献
3.
In this research, the graphene with excellent dispersity is prepared successfully by introducing gold nanoparticle to separate the individual sheets. Various techniques are adopted to characterize the prepared graphene and graphene-gold nanoparticle composite materials. This fabricated new composite material is used as the support material to construct a novel tyrosinase based biosensor for detection of bisphenol A (BPA). The electrochemical performances of the proposed new enzyme biosensor were investigated by differential pulse voltammetry (DPV) method. The proposed biosensor exhibited excellent performance for BPA determination with a wide linear range (2.5 × 10−3–3.0 μM), a highly reproducible response (RSD of 2.7%), low interferences and long-term stability. And more importantly, the calculated detection limit of the proposed biosensor was as low as 1 nM. Compared with other detection methods, this graphene-gold nanoparticle composite based tyrosinase biosensor is proved to be a promising and reliable tool for rapid detection of BPA for on-site analysis of emergency BPA related pollution affairs. 相似文献
4.
As the very first step of food consumption, food oral processing is not only of great importance to food intake and the following digestion and adsorption, but also provides the necessary sensory attributes that please the consumer. Starting from the first bite, to oral manipulation including mastication and transportation, until bolus formation and swallowing, food products undergo a variety of physical and biochemical changes over a wide range of time and length scales. A number of efforts had been made to uncover the mechanisms in each oral processing step; some of which are still poorly understood. This review covers some of the most recent progress made in the area of food oral processing, with an emphasis on eating and swallowing difficulties in the elderly and the corresponding model food development. It also includes the oral surface coating and lubrication and the dynamic textural perception during food oral processing. The authors hope that this will facilitate food scientists, psychologists, dentists and other clinical researchers to further understand and reveal the detailed controlling mechanisms and governing principles of food oral processing. 相似文献
5.
6.
An extended traffic flow model on a gradient highway with the consideration of the relative velocity
In this paper, an extended traffic flow model on a single-lane gradient highway is proposed with the consideration of the relative velocity. The stability condition is obtained by the use of linear stability analysis. It is shown that the stability of traffic flow on the gradient varies with the slope and the coefficient of the relative velocity: when the slope is constant, the stable regions increase with the increase of the coefficient of the relative velocity; when the coefficient of the relative velocity is constant, the stable regions increase with the decrease of the slope in downhill and increase with the increase of the slope in uphill. The Burgers, Korteweg-de Vries, and modified Korteweg-de Vries equations are derived to describe the triangular shock waves, soliton waves, and kink-antikink waves in the stable, metastable, and unstable region, respectively. The numerical simulation shows a good agreement with the analytical result, which shows that the traffic congestion can be suppressed by introducing the relative velocity. 相似文献
7.
《Chinese Journal of Physics (Taipei)》2018,56(6):3033-3038
Structural and electronic properties of vacancy, water and ethylenediamine substitutions in nitromethane were calculated using the first-principles density-functional theory. The results indicate both vacancy and substitution decrease the band gaps, which suggests the sensitivity of nitromethane has been enhanced. Compared with vacancy and water substitution, ethylenediamine substitution even more distinctly decreases the band gap. It suggests that ethylenediamine substitution has a more remarkable effect on the sensitivity of nitromethane. The calculated formation energies show that the formations of these defects from pure crystals need extra energies. And the elastic constants of defective crystals imply a weak performance in elastic deformation. 相似文献
8.
9.
针对大多数中学缺乏光电比色计和分光光度计的现状,基于朗伯比尔定律和3D打印技术自制光电比色计,测定透明有色溶液的吸光度和浓度。利用自制光电比色计测定了琥珀酸亚铁片中铁的含量和硫酸铜晶体中结晶水的含量,实验结果表明自制光电比色计的精度高、准确性好。将3D打印技术引入化学实验创新改进,体现了跨学科融合和创新设计的思想。 相似文献
10.
Electric field-induced stress birefringence in layered composites PbZr1-xTixO3/Polycarbonate 下载免费PDF全文
Electro-optical composites based on the product of electro-strictive and elasto-optical effects are developed.Layered composites of PbZr 1 x Ti x O 3 and polycarbonate are synthesised.Their electro-optical properties are studied.The nominal transverse electro-optical coefficient of the composite is observed to be about 3.6 times larger than that of LiNbO 3.Experiments and theoretical analyses show that the electro-optical effect of the composite has a strong ’size effect’.With the ratio of thickness/length decreasing or the width of elasto-optical phase increasing,the half-wave electric field intensity increases but the transverse electro-optical coefficient decreases for the layered composite. 相似文献