全文获取类型
收费全文 | 111447篇 |
免费 | 29046篇 |
国内免费 | 23233篇 |
专业分类
化学 | 74169篇 |
晶体学 | 1507篇 |
力学 | 7444篇 |
综合类 | 594篇 |
数学 | 14099篇 |
物理学 | 65913篇 |
出版年
2024年 | 489篇 |
2023年 | 1250篇 |
2022年 | 1739篇 |
2021年 | 1802篇 |
2020年 | 2191篇 |
2019年 | 2743篇 |
2018年 | 2513篇 |
2017年 | 3145篇 |
2016年 | 3680篇 |
2015年 | 4052篇 |
2014年 | 4282篇 |
2013年 | 6516篇 |
2012年 | 7341篇 |
2011年 | 10091篇 |
2010年 | 12106篇 |
2009年 | 12367篇 |
2008年 | 5956篇 |
2007年 | 4978篇 |
2006年 | 4549篇 |
2005年 | 4609篇 |
2004年 | 5425篇 |
2003年 | 4272篇 |
2002年 | 4106篇 |
2001年 | 4153篇 |
2000年 | 3072篇 |
1999年 | 3177篇 |
1998年 | 2638篇 |
1997年 | 2355篇 |
1996年 | 2637篇 |
1995年 | 3022篇 |
1994年 | 3056篇 |
1993年 | 3225篇 |
1992年 | 2826篇 |
1991年 | 2399篇 |
1990年 | 2073篇 |
1989年 | 2113篇 |
1988年 | 2004篇 |
1987年 | 1186篇 |
1986年 | 1318篇 |
1985年 | 907篇 |
1984年 | 1021篇 |
1982年 | 906篇 |
1981年 | 743篇 |
1980年 | 778篇 |
1979年 | 547篇 |
1978年 | 538篇 |
1977年 | 647篇 |
1976年 | 1048篇 |
1973年 | 443篇 |
1972年 | 536篇 |
排序方式: 共有10000条查询结果,搜索用时 34 毫秒
21.
在中国科学技术大学夏季学期的研究型实验课程"化学科研基础训练"中开设"壳聚糖的制备与表征"综合实验,以龙虾壳为原料,通过除蛋白、脱盐、脱色、脱乙酰等一系列反应,制备得到目标产物壳聚糖。运用红外光谱、核磁共振仪、黏度法、滴定等对产品的结构及性能进行表征。 相似文献
22.
23.
24.
25.
26.
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
27.
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
28.
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
29.
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
30.
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