全文获取类型
收费全文 | 662篇 |
免费 | 12篇 |
国内免费 | 2篇 |
专业分类
化学 | 493篇 |
晶体学 | 11篇 |
力学 | 10篇 |
数学 | 90篇 |
物理学 | 72篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 12篇 |
2019年 | 5篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 12篇 |
2015年 | 9篇 |
2014年 | 10篇 |
2013年 | 36篇 |
2012年 | 41篇 |
2011年 | 43篇 |
2010年 | 25篇 |
2009年 | 21篇 |
2008年 | 32篇 |
2007年 | 46篇 |
2006年 | 43篇 |
2005年 | 31篇 |
2004年 | 36篇 |
2003年 | 35篇 |
2002年 | 31篇 |
2001年 | 8篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 15篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1971年 | 3篇 |
1967年 | 2篇 |
排序方式: 共有676条查询结果,搜索用时 421 毫秒
431.
Carol A. Boliek Thomas J. Hixon Peter J. Watson Wayne J. Morgan 《Journal of voice》1997,11(4):373-390
Vocalization and breathing were studied in 40 healthy young children,including 5 boys and 5 girls at each, of ages of 18, 24, 30, and 36 months. A variable inductance plethysmograph was used to obtain estimates of volume changes of the rib cage, abdomen, and lung, as well as estimates of selected temporal features of the breathing cycle. Results indicated that breathing behavior was influenced by height and age, but not by vocalization type or sex. Such behavior was found to be highly variable, demonstrating that these young children had multiple degrees of freedom of performance available to accomplish the aeromechanical drive required. 相似文献
432.
An innovative teacher preparation course which integrates methods of teaching elementary mathematics and science was the context of this study. The course was developed as a prototype for the Teachers As Reflective Problem Solvers model for the preparation of elementary mathematics and science teachers. Data from 35 preservice elementary teachers' performance-portfolios were analyzed to reveal patterns of change in their reflections and problem-solving performance during the semester. Many of the students' reflections changed from task-focused learning to broader teaching applications. No relationship was discerned between changes in students' reflections and changes in their levels of problem-solving performance, although both increased during the semester. A significant correspondence was found, however, between students' perceptions of their problem-solving abilities and their actual performance in solving teaching problems in integrated mathematics and science contexts. 相似文献
433.
Can participation in a 4‐day workshop change science teachers’ beliefs about reformed science teaching? We observe a significant difference between pre‐ and post‐workshop surveys and explore an unexpected relationship involving teaching experience. Results of this exploratory study indicate a significant correlation between high school science teachers’ years of teaching experience and positive changes in beliefs about reformed teaching practices. Novice teachers hold more reformed beliefs pre‐institute, but post‐institute surveys revealed the two groups, experienced and novice, are statistically indistinguishable. We use our observations of the statistically significant changes in biology teachers’ responses on the Beliefs About Reformed Science Teaching and Learning instrument (BARSTL) to support our claim that a 4‐day Advanced Placement Summer Institute (APSI) in Biology can advance teachers’ beliefs toward more reformed teaching. Furthermore, these findings provided evidence for us to suggest that veteran teachers are more malleable in their beliefs about reformed science teaching than one might expect (AP®, Advanced Placement®, and AP Biology® are trademarks registered by the College Board, which is not affiliated with, and does not endorse, this article). 相似文献
434.
Susith R. Galle Kankanamge Jianbo Ma Robert T. Mackin Fedra M. Leonik Carol M. Taylor Igor V. Rubtsov Daniel G. Kuroda 《Angewandte Chemie (International ed. in English)》2020,59(39):17012-17017
Hydrogen bonds (H bonds) play a major role in defining the structure and properties of many substances, as well as phenomena and processes. Traditional H bonds are ubiquitous in nature, yet the demonstration of weak H bonds that occur between a highly polarized C?H group and an electron‐rich oxygen atom, has proven elusive. Detailed here are linear and nonlinear IR spectroscopy experiments that reveal the presence of H bonds between the chloroform C?H group and an amide carbonyl oxygen atom in solution at room temperature. Evidence is provided for an amide solvation shell featuring two clearly distinguishable chloroform arrangements that undergo chemical exchange with a time scale of about 2 ps. Furthermore, the enthalpy of breaking the hydrogen bond is found to be 6–20 kJ mol?1. Ab‐initio computations support the findings of two distinct solvation shells formed by three chloroform molecules, where one thermally undergoes hydrogen‐bond making and breaking. 相似文献
435.
Dr. Jani Reddy Bolla Dr. Robin A. Corey Dr. Cagla Sahin Dr. Joseph Gault Alissa Hummer Dr. Jonathan T. S. Hopper Prof. David P. Lane Prof. David Drew Dr. Timothy M. Allison Dr. Phillip J. Stansfeld Prof. Carol V. Robinson Dr. Michael Landreh 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(9):3551-3556
Membrane proteins engage in a variety of contacts with their surrounding lipids, but distinguishing between specifically bound lipids, and non-specific, annular interactions is a challenging problem. Applying native mass spectrometry to three membrane protein complexes with different lipid-binding properties, we explore the ability of detergents to compete with lipids bound in different environments. We show that lipids in annular positions on the presenilin homologue protease are subject to constant exchange with detergent. By contrast, detergent-resistant lipids bound at the dimer interface in the leucine transporter show decreased koff rates in molecular dynamics simulations. Turning to the lipid flippase MurJ, we find that addition of the natural substrate lipid-II results in the formation of a 1:1 protein–lipid complex, where the lipid cannot be displaced by detergent from the highly protected active site. In summary, we distinguish annular from non-annular lipids based on their exchange rates in solution. 相似文献
436.
Zheng Sun Mingji Li Qingsheng Qi Cuijuan Gao Carol Sze Ki Lin 《Applied biochemistry and biotechnology》2014,174(5):1822-1833
Mixed food waste, which was directly collected from restaurants without pretreatments, was used as a valuable feedstock in succinic acid (SA) fermentation in the present study. Commercial enzymes and crude enzymes produced from Aspergillus awamori and Aspergillus oryzae were separately used in hydrolysis of food waste, and their resultant hydrolysates were evaluated. For hydrolysis using the fungal mixture comprising A. awamori and A. oryzae, a nutrient-complete food waste hydrolysate was generated, which contained 31.9 g L?1 glucose and 280 mg L?1 free amino nitrogen. Approximately 80–90 % of the solid food waste was also diminished. In a 2.5 L fermentor, 29.9 g L?1 SA was produced with an overall yield of 0.224 g g?1 substrate using food waste hydrolysate and recombinant Escherichia coli. This is comparable to many similar studies using various wastes or by-products as substrates. Results of this study demonstrated the enormous potential of food waste as renewable resource in the production of bio-based chemicals and materials via microbial bioconversion. 相似文献
437.
Bis(o-nitrophenyl) carbonate reacts under mild conditions with chirals 1,2-amino alcohols and, after addition of DMAP, affords the corresponding oxazolidin-2-ones in very good yields. 相似文献
438.
The electrical percolation threshold of different polyethylene/carbon nanotube nanocomposites was studied as a function of chain structure, matrix viscosity, and the effect of compatibilizer. The lower the viscosity of the matrix the lower is the percolation threshold, regardless of the chain architecture and degree of crystallization. To improve dispersion a series of acrylic acid copolymer are introduced into the system. The highest concentration of acid co‐monomer that maintain miscibility with the polyethylene matrix is 5 wt.%. The compatibilizer in its pristine form does not have a significant effect on dispersion and on volume resistivity. When the acidic copolymer was modified with aminomethylpyridine, in order to facilitate π–π interaction with the nanotubes, a 4‐decade reduction was recorder for the high viscosity matrices at 10 wt.% compatibilizer loading. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
439.