全文获取类型
收费全文 | 5335篇 |
免费 | 1236篇 |
国内免费 | 364篇 |
专业分类
化学 | 1292篇 |
晶体学 | 22篇 |
力学 | 1437篇 |
综合类 | 75篇 |
数学 | 652篇 |
物理学 | 3457篇 |
出版年
2024年 | 12篇 |
2023年 | 50篇 |
2022年 | 142篇 |
2021年 | 181篇 |
2020年 | 168篇 |
2019年 | 161篇 |
2018年 | 157篇 |
2017年 | 244篇 |
2016年 | 287篇 |
2015年 | 224篇 |
2014年 | 386篇 |
2013年 | 376篇 |
2012年 | 361篇 |
2011年 | 376篇 |
2010年 | 278篇 |
2009年 | 301篇 |
2008年 | 336篇 |
2007年 | 317篇 |
2006年 | 293篇 |
2005年 | 276篇 |
2004年 | 208篇 |
2003年 | 218篇 |
2002年 | 195篇 |
2001年 | 189篇 |
2000年 | 167篇 |
1999年 | 153篇 |
1998年 | 127篇 |
1997年 | 105篇 |
1996年 | 110篇 |
1995年 | 84篇 |
1994年 | 66篇 |
1993年 | 56篇 |
1992年 | 57篇 |
1991年 | 39篇 |
1990年 | 28篇 |
1989年 | 30篇 |
1988年 | 19篇 |
1987年 | 25篇 |
1986年 | 18篇 |
1985年 | 22篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 18篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1971年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有6935条查询结果,搜索用时 78 毫秒
61.
IntroductionThemethoxyradical (CH3O)isanimportantinter mediateinthephotochemicaloxidationofhydrocarbonsintheatmosphere ,1 3andplaysasignificantroleintrans formingnitricoxidetonitrogendioxide .4 Similarly ,thereactionmechanismsofhydroxylandcarbonmonoxide5,6ando… 相似文献
62.
分离变量法与等腰直角三角形波导的边值问题 总被引:4,自引:0,他引:4
根据叠加原理,讨论等腰直角三角形波导边值问题的IE波解和TM波解,纠正有关文献中的错误解法,指出分离变量法的适用条件。 相似文献
63.
64.
Xinyu Huang Roham Solasi Yue Zou Matthew Feshler Kenneth Reifsnider David Condit Sergei Burlatsky Thomas Madden 《Journal of Polymer Science.Polymer Physics》2006,44(16):2346-2357
The life of proton exchange membrane fuel cells (PEMFC) is currently limited by the mechanical endurance of polymer electrolyte membranes and membrane electrode assemblies (MEAs). In this paper, the authors report recent experimental and modeling work toward understanding the mechanisms of delayed mechanical failures of polymer electrolyte membranes and MEAs under relevant PEMFC operating conditions. Mechanical breach of membranes/MEAs in the form of pinholes and tears has been frequently observed after long‐term or accelerated testing of PEMFC cells/stacks. Catastrophic failure of cell/stack due to rapid gas crossover shortly follows the mechanical breach. Ex situ mechanical characterizations were performed on MEAs after being subjected to the accelerated chemical aging and relative humidity (RH) cycling tests. The results showed significant reduction of MEA ductility manifested as drastically reduced strain‐to‐failure of the chemically aged and RH‐cycled MEAs. Postmortem analysis revealed the formation and growth of mechanical defects such as cracks and crazing in the membranes and MEAs. A finite element model was used to estimate stress/strain states of an edge‐constrained MEA under rapid RH variations. Damage metrics for accelerated testing and life prediction of PEMFCs are discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2346–2357, 2006 相似文献
65.
负关联噪声驱动下单模激光的定态分析 总被引:2,自引:1,他引:1
研究了负关联的加法和乘法高斯白噪声驱动下单模激光损失模型的定态情况。文中推导了负关联情况下,定态时的激光场幅的几率分布,光强的平均值,光强的协方差以及光强的偏斜率。并和文献〔1,2〕中正关联时的定态分析作了比较,发现了有意义的新现象。 相似文献
66.
有机薄膜电致发光器件失效过程的动态观测及分析 总被引:4,自引:0,他引:4
对有机薄膜电致发光器件失效的全过程进行了显微动态观察,发现器件工作时,有机层/金属界面形成的气泡逐渐变大变多,最终导致器件完全失效,气泡不仅含有水汽,还存在大量有机气体。 相似文献
67.
A method is described for the rapid and automatic analysis of flexible molecular alignments using multidimensional scaling and a normalized scoring scheme. A projection scheme was devised to separate orientational and conformational effects. It is shown that the approach can be utilized for the identification of common binding orientations or to the study of differences in partioning behavior. It is suggested that the method can be employed as a novel approach exploring molecular similarity as a dynamic property, so that it includes aspects of motion (by way of mutual orientations), conformations and molecular properties. 相似文献
68.
A series of acrylic ester copolymers with viologen group as pendant were synthesizedthrough the reaction of MMA-EBA (Ethenyl bromoacetate) copolymer with 4-(4'-pyridyl)-N-alkyl (or arylalkyl) pyridiniums. These viologen copolymers can exchange their anionwith NH_4PF_6 in methanol to improve their solubility in organic solvents such as DMFand acetone. Compared with the corresponding low molecular viologens, these viologencopolymers have relatively lower color development rate under UV light and fade fasterin air due to less affinity to photo-reductant and deficiency of association between theircation radicals. Their photofatigue resistant ability is also slightly better than that of lowmolecular vinlogens. 相似文献
69.
Delayed feedbacks are quite common in many physical and biological systems and in particular many physiological systems. Delay
can cause a stable system to become unstable and vice versa. One of the well-studied non-biological chemical oscillators is
the Belousov-Zhabotinskii (BZ) reaction. This gives relaxation oscillations for a considerable period of time under batch
conditions. This paper deals with the effect of perturbing the limit cycle oscillation of BZ reaction by employing a delayed
electrical feedback to the system under batch conditions. The parameters chosen to study are external resistance and delay.
For various resistances and delays the system was electrically perturbed and found to exhibit various complex mixed mode oscillations.
The dynamic features are accounted for by the Oregonator model, with time delay incorporated in one of the variables.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
70.
煤中砷,铅,铍,铬等元素的存在状态 总被引:20,自引:3,他引:20
煤是由有机物和无机物组成的混合物。无机物按其在煤中的浓度大小可分为三类:(1)常量元素,在煤中浓度大于0.5%,如Si,Al,Fe,Ca等。(2)次要元素,约占煤的0.02%—.5%,包括K,Mg,Na,Ti,有时还有P,Ba等。(3)微量元素,在煤中浓度<0.02%,这类元素目前已测出60种左右。60年代以来,基于能源需求的增加,国内外煤炭消耗量都很大,考虑到有害的微量元素对环境的污染,国外进行了大量的煤 相似文献