全文获取类型
收费全文 | 64429篇 |
免费 | 12621篇 |
国内免费 | 16575篇 |
专业分类
化学 | 48763篇 |
晶体学 | 1784篇 |
力学 | 4335篇 |
综合类 | 1844篇 |
数学 | 8787篇 |
物理学 | 28112篇 |
出版年
2024年 | 76篇 |
2023年 | 884篇 |
2022年 | 1881篇 |
2021年 | 2181篇 |
2020年 | 2400篇 |
2019年 | 2406篇 |
2018年 | 2148篇 |
2017年 | 2657篇 |
2016年 | 2731篇 |
2015年 | 3270篇 |
2014年 | 4051篇 |
2013年 | 5119篇 |
2012年 | 5748篇 |
2011年 | 5989篇 |
2010年 | 5002篇 |
2009年 | 5295篇 |
2008年 | 5910篇 |
2007年 | 5131篇 |
2006年 | 4749篇 |
2005年 | 4108篇 |
2004年 | 3251篇 |
2003年 | 2444篇 |
2002年 | 2584篇 |
2001年 | 2264篇 |
2000年 | 2314篇 |
1999年 | 1589篇 |
1998年 | 929篇 |
1997年 | 776篇 |
1996年 | 712篇 |
1995年 | 624篇 |
1994年 | 623篇 |
1993年 | 533篇 |
1992年 | 489篇 |
1991年 | 367篇 |
1990年 | 371篇 |
1989年 | 332篇 |
1988年 | 295篇 |
1987年 | 239篇 |
1986年 | 193篇 |
1985年 | 132篇 |
1984年 | 133篇 |
1983年 | 122篇 |
1982年 | 68篇 |
1981年 | 84篇 |
1980年 | 72篇 |
1979年 | 64篇 |
1978年 | 22篇 |
1977年 | 21篇 |
1974年 | 23篇 |
1965年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
41.
miRNA (miR)-155 is a potential biomarker for breast cancers. We aimed at developing a nanosensor for miR-155 detection by integrating hybridization chain reaction (HCR) and silver nanoclusters (AgNCs). HCR serves as an enzyme-free and isothermal amplification method, whereas AgNCs provide a built-in fluorogenic detection probe that could simplify the downstream analysis. The two components were integrated by adding a nucleation sequence of AgNCs to the hairpin of HCR. The working principle was based on the influence of microenvironment towards the hosted AgNCs, whereby unfolding of hairpin upon HCR has manipulated the distance between the hosted AgNCs and cytosine-rich toehold region of hairpin. As such, the dominant emission of AgNCs changed from red to yellow in the absence and presence of miR-155, enabling a ratiometric measurement of miR with high sensitivity. The limit of detection (LOD) of our HCR-AgNCs nanosensor is 1.13 fM in buffered solution. We have also tested the assay in diluted serum samples, with comparable LOD of 1.58 fM obtained. This shows the great promise of our HCR-AgNCs nanosensor for clinical application. 相似文献
42.
43.
碲锰镉(CdMnTe)作为性能优异的室温核辐射探测器材料,可用于环境监测和工业无损检测领域。本文中采用Te溶剂Bridgman法生长In掺杂Cd0.9Mn0.1Te晶体,制备成10 mm×10 mm×2 mm大小的室温单平面探测器,研究了该探测器对241Am@59.5 keV γ射线源的能谱响应。通过表征红外透过率、电阻率以及探测器能谱响应等参数,综合评定了探测器用CdMnTe晶体的质量、电学和探测器性能。结果表明,晶片的红外透过率均在55%以上,最好可达到60%。采用湿法钝化,100 V偏压下的漏电流由钝化前的9.48 nA降为钝化后的7.90 nA,钝化后的电阻率为2.832×1010 Ω·cm。在-400 V反向偏压下,CdMnTe探测器对241Am@59.5 keV γ射线源的能量分辨率在钝化前后分别为13.53%和12.51%,钝化后的电子迁移率寿命积为1.049×10-3 cm2/V。研究了探测器的能量分辨率随电压的变化特性,当偏压≤400 V时,探测器的能量分辨率主要由载流子的收集效率决定,而当偏压>400 V时,能量分辨率由漏电流决定。本文研究结果表明,Te溶剂Bridgman法生长的CdMnTe晶体质量较好,电阻率和电子迁移率寿命积满足探测器制备需求。 相似文献
44.
Dr. Yogesh Kumar Maurya Dr. Pingchun Wei Takahide Shimada Dr. Kazuhisa Yamasumi Dr. Shigeki Mori Prof. Dr. Ko Furukawa Dr. Hajime Kusaba Prof. Dr. Tatsumi Ishihara Prof. Dr. Yongshu Xie Dr. Masatoshi Ishida Prof. Dr. Hiroyuki Furuta 《化学:亚洲杂志》2021,16(7):743-747
A facile synthetic strategy towards conformationally stable chiral chromophores based on dimeric porphyrinoids has been established. A peculiar class of face-to-face intramolecularly interlocked corrole dimers were formed by the oxidative C−C coupling linked at the inner carbon sites upon simple treatment of copper(II) ions. Their intrinsic electronic structures were modulated by the peripheral corrole ring annulations, which lead to distinct optical properties and redox profiles. The stereogenic carbon centers implemented in the confused corrole skeleton provided a rationale for designing novel chiral materials. 相似文献
45.
In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated biomaterial is Hyriopsis cumingii, a typical limnetic shell, which consists of two different structural layers, a prismatic "pillar"structure and a nacreous "brick and mortar" structure. The prismatic layer looks like a "pillar forest" with variationsection pillars sized on the order of several tens of microns.The nacreous material looks like a "brick wall" with bricks sized on the order of several microns. Both pillars and bricks are composed of nanoparticles. The mechanical properties of the hierarchical biomaterial are measured by using the nanoindentation test. Hardness and modulus are measured for both the nacre layer and the prismatic layer, respectively.The nanoindentation size effects for the hierarchical structural materials are investigated experimentally. The results show that the prismatic nanostructured material has a higher stiffness and hardness than the nacre nanostructured material.In addition, the nanoindentation size effects for the hierarchical structural materials are described theoretically, by using the trans-scale mechanics theory considering both strain gradient effect and the surface/interface effect. The modeling results are consistent with experimental ones. 相似文献
46.
47.
Guo Yan Li Zhuang Wei Yuxi Zhang Xinxu Shi Kexin 《Journal of Solid State Electrochemistry》2022,26(4):1051-1065
Journal of Solid State Electrochemistry - Polyvinylpyrrolidone (PVP) and graphene (G)-modified iron oxides (Fe2O3-PVP-G) are prepared by a simple hydrothermal reaction. Their morphology and... 相似文献
48.
Journal of Thermal Analysis and Calorimetry - A complete analysis of the thermal process about melamine was presented, in which different methods were applied to determine the characteristic of the... 相似文献
49.
随着光伏行业的快速发展, 对硅单晶的品质和长晶装备的稳定性的要求也不断提高。直拉法是生产硅单晶的主要方法,通过提高单晶炉副室的高度以扩大单晶硅的生产规模。由于副室高度的大幅增加,且单晶炉提拉头质心相对于旋转轴心有一定距离,对单晶炉整体稳定性有较大影响,从而降低了单晶硅的生产质量。针对此问题,对单晶炉建立可靠的力学分析模型,采用数值仿真方法,对单晶炉整体进行动力学响应分析,计算得到副室高度增加后的单晶炉工作时中钨丝绳下端晶棒的运动规律以及最大摆动幅度,为改进设计提供依据。数值仿真分析表明提高单晶炉副室高度后,提拉头较大的质心偏心是单晶炉提拉系统发生摆动的主要原因。在此基础上提出在提拉头上添加质心调节装置,通过控制系统调节可保证提拉头质心位置在旋转轴线上以降低提拉系统的摆动。 相似文献
50.