全文获取类型
收费全文 | 698篇 |
免费 | 59篇 |
国内免费 | 1篇 |
专业分类
化学 | 637篇 |
晶体学 | 3篇 |
力学 | 4篇 |
数学 | 50篇 |
物理学 | 64篇 |
出版年
2023年 | 12篇 |
2022年 | 12篇 |
2021年 | 14篇 |
2020年 | 24篇 |
2019年 | 22篇 |
2018年 | 8篇 |
2017年 | 12篇 |
2016年 | 26篇 |
2015年 | 34篇 |
2014年 | 36篇 |
2013年 | 38篇 |
2012年 | 51篇 |
2011年 | 72篇 |
2010年 | 46篇 |
2009年 | 34篇 |
2008年 | 62篇 |
2007年 | 56篇 |
2006年 | 36篇 |
2005年 | 23篇 |
2004年 | 34篇 |
2003年 | 22篇 |
2002年 | 31篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1993年 | 2篇 |
1988年 | 1篇 |
1985年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1925年 | 1篇 |
排序方式: 共有758条查询结果,搜索用时 874 毫秒
681.
For this quantitative study, a total of n = 761 students (58.1% female) from selected fifth- and sixth-grade mathematics classrooms in Alabama were surveyed in order to investigate the relationships between self-regulated learning, motivation, anxiety, attributions and achievement in mathematics. Data analyses revealed that significant contributions are made by motivation and anxiety on both test score and mathematics grade for fifth grade students. Specific factors (e.g., self-efficacy, worry, other, and failure) were related to academic performance while failure attribution was significantly related to mathematics grade. As for sixth grade students, data analyses showed relationships exist between motivation, anxiety and academic performance with specific factors (i.e., self-efficacy, intrinsic value, and worry) significantly predicting both test score and mathematics grade for sixth graders. The findings underlie the importance of motivation and anxiety for students and how these constructs interact to facilitate self-regulation over the course of developing expertise in a domain, such as mathematics. 相似文献
682.
683.
684.
Order and Defects in Ceramic Semiconductor Nanoparticle Superstructures as a Function of Polydispersity and Aspect Ratio
下载免费PDF全文
![点击此处可从《Particle & Particle Systems Characterization》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Melanie Gerigk Jochen Bahner Tom Kollek Stefan Helfrich Rose Rosenberg Helmut Cölfen Sebastian Polarz 《Particle & Particle Systems Characterization》2017,34(2)
The supreme aim of nanoparticle‐based materials is to achieve new properties extending over the features of individual constituents. The emergence of cooperativity necessitates precise positioning and orientation of nanoparticle ensembles. Thus, it is important to understand and learn how to control self‐assembly processes of nanoparticles. Besides shape, the structural uniformity plays a key role for ordering in superstructures. Therefore, it is challenging to synthesize nanorods with narrow polydispersity. An analysis of the systematic variation of aspect ratio and polydispersity is missing. A series of zinc oxide nanorods is presented and it is shown that their formation resembles step‐polymerization with an amorphous precursor state as a monomer and polar ZnO particles as entities capable of growing. The width of nanorods is kept constant (15 nm) and the length is varied between 20 and 100 nm, as well as improving the polydispersity of the nanorod length from 36% to 10%. Best samples have been achieved by post‐preparative treatment using gradient centrifugation. A method has been developed for semiquantitative evaluation of orientational order. Ordering in structures formed by quasispherical particles is always low despite low polydispersity. For rod‐like nanoparticles with increasing aspect ratio, superstructure order depends on the occurrence of different defects, which correlate differently to nanoparticle polydispersity. 相似文献
685.
van Hoesel R Böhm M Pesch J Vandali A Battmer RD Lenarz T 《The Journal of the Acoustical Society of America》2008,123(4):2249-2263
Four adult bilateral cochlear implant users, with good open-set sentence recognition, were tested with three different sound coding strategies for binaural speech unmasking and their ability to localize 100 and 500 Hz click trains in noise. Two of the strategies tested were envelope-based strategies that are clinically widely used. The third was a research strategy that additionally preserved fine-timing cues at low frequencies. Speech reception thresholds were determined in diotic noise for diotic and interaurally time-delayed speech using direct audio input to a bilateral research processor. Localization in noise was assessed in the free field. Overall results, for both speech and localization tests, were similar with all three strategies. None provided a binaural speech unmasking advantage due to the application of 700 micros interaural time delay to the speech signal, and localization results showed similar response patterns across strategies that were well accounted for by the use of broadband interaural level cues. The data from both experiments combined indicate that, in contrast to normal hearing, timing cues available from natural head-width delays do not offer binaural advantages with present methods of electrical stimulation, even when fine-timing cues are explicitly coded. 相似文献
686.
Javier Ceballos Melanie Schwalfenberg George Karageorgis Elena S. Reckzeh Sonja Sievers Claude Ostermann Axel Pahl Magnus Sellstedt Jessica Nowacki Marjorie A. Carnero Corrales Julian Wilke Luca Laraia Kirsten Tschapalda Malte Metz Dominik A. Sehr Silke Brand Konstanze Winklhofer Petra Janning Slava Ziegler Herbert Waldmann 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(47):17172-17181
Bioactive compound design based on natural product (NP) structure may be limited because of partial coverage of NP‐like chemical space and biological target space. These limitations can be overcome by combining NP‐centered strategies with fragment‐based compound design through combination of NP‐derived fragments to afford structurally unprecedented “pseudo‐natural products” (pseudo‐NPs). The design, synthesis, and biological evaluation of a collection of indomorphan pseudo‐NPs that combine biosynthetically unrelated indole‐ and morphan‐alkaloid fragments are described. Indomorphane derivative Glupin was identified as a potent inhibitor of glucose uptake by selectively targeting and upregulating glucose transporters GLUT‐1 and GLUT‐3. Glupin suppresses glycolysis, reduces the levels of glucose‐derived metabolites, and attenuates the growth of various cancer cell lines. Our findings underscore the importance of dual GLUT‐1 and GLUT‐3 inhibition to efficiently suppress tumor cell growth and the cellular rescue mechanism, which counteracts glucose scarcity. 相似文献
687.
688.
Rusanova J Pilkington M Decurtins S 《Chemical communications (Cambridge, England)》2002,(19):2236-2237
The synthetic route to a new fully conjugated phenanthroline appended phthalocyanine is described. This compound has been fully characterised by elemental analysis, UV-VIS, IR, MS and 1H NMR spectroscopy. 相似文献
689.
690.
A new technique for improving the signal-to-noise ratio and the contrast in images recorded with a confocal scanning laser system is presented. The method is based on the incorporation of a polarimeter into the setup. After the spatially resolved Mueller matrix of a sample was calculated, images for incident light with different states of polarization were reconstructed, and both the best and the worst images were computed. In both the microscope and the opthalmoscope modes, the best images are better than the originals. In contrast, the worst images are poorer. This technique may be useful in different fields such as confocal microscopy and retinal imaging. 相似文献