全文获取类型
收费全文 | 3203篇 |
免费 | 517篇 |
国内免费 | 440篇 |
专业分类
化学 | 1652篇 |
晶体学 | 72篇 |
力学 | 615篇 |
综合类 | 57篇 |
数学 | 214篇 |
物理学 | 1550篇 |
出版年
2024年 | 12篇 |
2023年 | 42篇 |
2022年 | 166篇 |
2021年 | 186篇 |
2020年 | 152篇 |
2019年 | 95篇 |
2018年 | 93篇 |
2017年 | 151篇 |
2016年 | 144篇 |
2015年 | 156篇 |
2014年 | 212篇 |
2013年 | 261篇 |
2012年 | 223篇 |
2011年 | 265篇 |
2010年 | 171篇 |
2009年 | 206篇 |
2008年 | 182篇 |
2007年 | 190篇 |
2006年 | 164篇 |
2005年 | 130篇 |
2004年 | 135篇 |
2003年 | 112篇 |
2002年 | 121篇 |
2001年 | 77篇 |
2000年 | 99篇 |
1999年 | 74篇 |
1998年 | 61篇 |
1997年 | 45篇 |
1996年 | 45篇 |
1995年 | 29篇 |
1994年 | 27篇 |
1993年 | 20篇 |
1992年 | 21篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有4160条查询结果,搜索用时 0 毫秒
1.
Vito Gigante Laura Aliotta Maria Beatrice Coltelli Patrizia Cinelli Luigi Botta Francesco Paolo La Mantia Andrea Lazzeri 《Journal of polymer science. Part A, Polymer chemistry》2020,58(23):3264-3282
The development of biodegradable materials for tailored applications, particularly in the field of polymeric films and sheets, is a challenging technological goal as well as a contribution to help protect the environment. Poly(lactic) acid (PLA) is a promising substitute for several oil-based polymers; however, to overcome its thermal and mechanical drawbacks, researchers have developed solutions such as blending PLA with polybutylene adipate terephthalate (PBAT), which is capable of increasing the ductility of the final material. In this study, PLA/PBAT binary blends, with minimum possible content of nonrenewable materials, were examined from processing, thermal, morphological, and rheological perspective. An optimized PLA/PBAT ratio was chosen as the polymeric basis to obtain a biodegradable formulation by adding a biobased plasticizer and appropriate fillers to produce a micrometer film with tailored flexibility and tear resistance. The processing technology involved flat-die extrusion, followed by calendering. The tearing resistance of the produced film was investigated, and the results were compared with literature data. A study on the essential work of fracture was implemented to explore the mode III out-of-plane fracture resistance starting from a trouser tear test. 相似文献
2.
3.
LiuYuqi LiZhigang YahYakun 《Acta Mechanica Solida Sinica》2004,17(1):58-64
By using the Finite Element Inverse Approach based on the Hill quadratic anisotrop-ically yield criterion and the quadrilateral element, a fast analyzing software-FASTAMP for the sheet metal forming is developed. The blank shapes of three typical stampings are simulated and compared with numerical results given by the AUTOFORM software and experimental results, respectively. The comparison shows that the FASTAMP can predict blank shape and strain distribution of the stamping more precisely and quickly than those given by the traditional methods and the AUTOFORM. 相似文献
4.
以金刚石压腔高压装置为工具,用Ⅱ型金刚石作压砧兼红外窗口,对本征态聚苯胺进行了高压(0~8.4 GPa)就位红外光谱测试。结果表明:在4.8~5.2 GPa压力区间,代表醌环振动的吸收峰相对代表苯环振动的吸收峰变小,表明聚苯胺在此压力区间结构上发生了显著变化,且这种变化是不可逆的。聚苯胺的高压(0~14.5 GPa)电阻测量结果表明:当压力小于7.5 GPa时,电阻随压力升高而显著降低,据此认为聚苯胺为电子性导电物质;在7.5 GPa处电阻出现极小值,然后又缓慢升高,至10 GPa后基本不变。推测聚苯胺电阻极小值是由结构变化引起的。至于红外光谱与电阻测量结果反映聚苯胺结构变化的压力值不一致,可能是由于测试条件不同所致。 相似文献
5.
Nanocomposites (NC) were formed using cationic poly(L ‐lysine) (PLL), a semicrystalline polypeptide, that was reinforced by sodium montmorillonite (MMT) clay via solution intercalation technique. By varying solution conditions such as pH, temperature, and polypeptide concentration in the presence of clay platelets, the secondary structure of PLL was controllably altered into α‐helical, β‐sheet, and random coil. The high molecular weight polypeptide shows a strong propensity to fold into the β‐sheet structure when cast as films, irrespective of the initial secondary structure in solution. Nanocomposite local morphology confirms intercalated MMT platelets with PLL over a wide range of compositions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 239–252, 2007. 相似文献
6.
Effect of a Shock Pulse on a Floating Ice Sheet 总被引:1,自引:0,他引:1
The vibrations of a viscoelastic plate lying on an elastic liquid base subjected to pulse loading have been studied theoretically and experimentally. The effect of the variable depth of the reservoir, plate thickness, and strain relaxation time on the value of the plate vibration amplitude and the length and curvature of the flexural gravity wave profile are analyzed. Good agreement of theoretical and experimental results is obtained. 相似文献
7.
The stability behaviour of a thin-film superconductor under a localized release of thermal disturbance is investigated. Two-dimensional conjugate film/substrate conduction equation with anisotropic thermal conductivity of the film, and Joule heat are employed to investigate effects of substrate and thermal properties on the intrinsic stability and quenching recovery. To consider the thermal boundary resistance between film and substrate, an interfacial-layer model (ILM) with very low diffusivity and an acoustic mismatch model (AMM) are employed. Results show that the thermal boundary resistance influences strongly the intrinsic stability. Thermal boundary resistance increases intrinsic stability if the thermal conductivity of the substrate or the disturbance energy is large. Higher Biot numbers and thermal conductivity ratios of film to substrate in longitudinal direction influence stability favorably. We demonstrate also that operation of a film/substrate system, such as YBCO/MgO, is either intrinsically stable or irrecoverably unstable.The authors wish to express their sincere appreciation to Dr. R. C. Chen for his invaluable advice and suggestions during the course of this paper. This research was supported by the National Science Council of the R. O. C. through grant NSC 83-0401-E-009-006. The computations were performed on the IBM ES/9000 at the National Center For High-Performance Computing. 相似文献
8.
国内研制的20/30Ⅱ代倒象微光管经常出现微通道板真空体电阻偏高或偏低的问题,直接影响Ⅱ代倒象微光管荧光屏的亮度和目标分辨力,严重影响微光管的质量。经过对20/30Ⅱ代倒象微光管的研制和理论分析,证明英国马拉德公司对用于××1383Ⅱ代倒象微光管的H36微通道板技术条件中真空体电阻技术指标的规定也存在一定的问题。本文从目前国内外工艺水平和有关文献资料的分析出发,进行专题研究。本文中所推导的计算公式和对文献资料提供的技术数据的推导分析,同样适用于其他型号微通道板的真空体电阻与相应Ⅱ代、Ⅲ代微光管匹配关系的计算与研究。 相似文献
9.
有机薄膜器件负电阻特性的影响因素 总被引:1,自引:1,他引:0
研究了影响有机染料掺杂聚合物薄膜器件负电阻特性的因素,为探索有机负电阻的机理提供实验依据。实验中制备了多种有机染料掺杂聚合物薄膜器件,研究了有机小分子染料、聚合物基体、薄膜组成及厚度、ITO和聚苯胺阳极等对有机染料掺杂聚合物薄膜器件负电阻特性的影响。在室温、大气环境下,所制备的多种有机染料掺杂聚合物器件在所加电压为3~4V时,观察到明显的负电阻特性,电流峰谷比最大约为8。负电阻现象及峰谷比的大小受膜厚和器件的结构、制备工艺等影响。提出用负电阻和二极管并联组成的等效电路模型解释影响负电阻特性的因素,认为负电阻特性与载流子的不平衡注入有关。在此基础上设计、合成了主链含唔二唑电子传输基团的可溶性聚对苯撑乙烯衍生物,该聚合物兼具空穴和电子传输功能,在空气中具有较稳定的N型负电阻特性。进一步控制相关材料和工艺条件,有可能得到易于控制的负阻效应,开发出新型的有机负电阻器件。 相似文献
10.
Guosong Wu Xiaoqin Zeng Wenbin Ding Xingwu Guo Shoushan Yao 《Applied Surface Science》2006,252(20):7422-7429
Ceramic thin films have been widely used to protect the metal substrate as coatings in the past years. In order to improve the poor corrosion resistance of AZ31 magnesium alloy, the study in this paper used the electron beam evaporation method to prepare ceramic PVD films on its surface with TiO2 and Al2O3 as donors, respectively. Atomic force microscopy (AFM), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) were used to investigate the surface morphology, composition and microstructure of the thin films. Both films deposited on AZ31 took on compact top surface morphologies and grew as amorphous structures on substrate. AES test not only showed that films compositions deviated the standard stoichiometric ratios, but also found that element Mg diffused into films and existed as magnesium oxide in the TiOx film as well as the AlOx film. In the electrochemical corrosion test, the AlOx coating on AZ31 exhibited the largest electrochemical impedance in a 3.5% NaCl solution. But it did not show better corrosion resistance than others for the poorer adhesion. Even if its thickness was small, the TiOx coating on AZ31 exhibited the best corrosion resistance in this study. According to the observation and analysis, the damage of these films on AZ31 in aggressive solutions was mainly due to the existence of pores, microcracks, vacancies and poor adhesion between coating and substrate. 相似文献