全文获取类型
收费全文 | 1211篇 |
免费 | 40篇 |
国内免费 | 6篇 |
专业分类
化学 | 747篇 |
晶体学 | 12篇 |
力学 | 77篇 |
数学 | 115篇 |
物理学 | 306篇 |
出版年
2023年 | 14篇 |
2022年 | 19篇 |
2021年 | 28篇 |
2020年 | 37篇 |
2019年 | 34篇 |
2018年 | 24篇 |
2017年 | 28篇 |
2016年 | 35篇 |
2015年 | 30篇 |
2014年 | 48篇 |
2013年 | 67篇 |
2012年 | 87篇 |
2011年 | 81篇 |
2010年 | 45篇 |
2009年 | 47篇 |
2008年 | 69篇 |
2007年 | 46篇 |
2006年 | 51篇 |
2005年 | 49篇 |
2004年 | 31篇 |
2003年 | 32篇 |
2002年 | 15篇 |
2001年 | 7篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1996年 | 12篇 |
1995年 | 14篇 |
1994年 | 9篇 |
1993年 | 14篇 |
1992年 | 7篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 14篇 |
1988年 | 8篇 |
1986年 | 6篇 |
1984年 | 14篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 6篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 7篇 |
1964年 | 5篇 |
1963年 | 5篇 |
1961年 | 5篇 |
1936年 | 13篇 |
排序方式: 共有1257条查询结果,搜索用时 15 毫秒
81.
Basi V. Subba Reddy Nagendra Nath Yadav Nikhil Srivastava Jhillu S. Yadav Balasubramanian Sridhar 《Helvetica chimica acta》2012,95(1):76-86
Ionic liquids were found to be a suitable reaction medium for 1,4‐dipolar cycloaddition reactions of an isoquinoline, an activated alkyne, and a 4‐oxo‐4H‐1‐benzopyran‐3‐carboxaldehyde at room temperature to afford [1]benzopyrano‐pyrido‐isoquinoline (=9aH,15H‐benzo[a][1]benzopyrano[2,3‐h]quinolizine) derivatives selectively in good yields. The ionic liquid can be recovered and recycled in further runs without loss of activity. 相似文献
82.
Sudip Pan Diego Moreno Dr. José Luis Cabellos Prof. Gabriel Merino Prof. Pratim K. Chattaraj 《Chemphyschem》2014,15(12):2618-2625
The global minima of Be2N2, Be3N2 and BeSiN2 clusters are identified using a modified stochastic kick methodology. The structure, stability and bonding nature of these clusters bound to noble gas (Ng) atoms are studied at the MP2/def2‐QZVPPD level of theory. Positive Be?Ng bond dissociation energy, which gradually increases down Group 18 from He to Rn, indicates the bound nature of Ng atoms. All of the Ng‐binding processes are exothermic in nature. The Xe and Rn binding to Be2N2 and Be3N2 clusters and Ar?Rn binding to BeSiN2 are exergonic processes at room temperature; however, for the lighter Ng atoms, lower temperatures are needed. Natural population analysis, Wiberg bond index computations, electron density analysis, and energy decomposition analysis are performed to better understand the nature of Be?Ng bonds. 相似文献
83.
Submerged culture fermentation studies were carried out in batch mode for optimizing the environmental parameters and carbon
source requirement by Pseudomonas elodea for the production of gellan gum. The maximum production of gellan gum was obtained with 16-h-old culture and 8% inoculum
at 30°C and pH 7.0 after 52 h of incubation (6.0 g/L). Of the various carbon sources tested, 2% sucrose, glucose, and soluble
starch yielded considerably high amounts of gellan. Studies on the concentration of various carbohydrates on gellan gum production
indicated that the optimum concentration of glucose and starch was 3%, whereas for sucrose it was 4%. The addition of glucose
in the medium above 3% had a detrimental effect on gellan yield. The investigation of intermediate two-step addition of glucose
under identical conditions of fermentation showed an enhanced production of gellan (8.12 g/L) as compared with the control
(6.0 g/L). To optimize the recovery of gellan from fermented broth, different solvents were tested for precipitation of gellan
gum. Among the various solvents tested, tetrahydrofuran gave better recovery of gellan (82%) as compared with the conventional
solvent isopropanol (49%). 相似文献
84.
85.
Francis R. Costa Sudip Pradhan Udo Wagenknecht Anil K. Bhowmick Gert Heinrich 《Journal of Polymer Science.Polymer Physics》2010,48(22):2302-2311
In elastomer/organo clay nanocomposites, the morphological characteristics, and hence the mechanical properties, of the vulcanizates are strongly influenced by the organic modifier and the vulcanization process. When the elastomer itself undergoes strain‐induced crystallization, both the organic modifier and the dispersed filler particles could significantly influence the crystallization process. These phenomena are very common in case of natural rubber‐based vulcanizates. In this study, the similar effects have been demonstrated with carboxylated nitrile rubber (XNBR) and organically modified layered double hydroxide (O‐LDH)‐based nanocomposites. The effect of size of the organic modifier was obviously visible on the interlayer distance of O‐LDH and also on the morphological reorganization of the dispersed O‐LDH particles during vulcanization process. The strain‐induced crystallization of the XNBR was found to be strongly dependent on the morphological change that occurs during vulcanization process. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010 相似文献
86.
S. K. Deb?Nath Hironori Tohmyoh M. A. Salam?Akanda 《Applied Physics A: Materials Science & Processing》2011,103(2):493-496
A testing methodology to determine the elastic-plastic properties of thin metallic wires is reported. A small-scaled bending
test of Pt thin wire and the corresponding finite element analysis are performed. By fitting the load-displacement relationship
obtained by finite element analysis to the experimental one, the elastic, elastic-plastic properties of Pt wire are successfully
determined. 相似文献
87.
To exploit the parallelism of optics in data processing,a suitable number system and an efficient encoding/decoding scheme for handling the data are very essential.In the field of optical computing and parallel information processing,several number systems like binary,quaternary,octal,hexadecimal,etc.have been used for different arithmetic and algebraic operations.Here,we have proposed an all-optical conversion scheme from its binary to its other 2n radix based form with the help of terahertz optical asymmetric demultiplexer (TOAD) based tree-net architecture. 相似文献
88.
89.
Kuzmann E. Nath A. Chechersky V. Li S. Wei Y. Chen X. Li J. Homonnay Z. Gál M. Garg V. K. Klencsár Z. Vértes A. 《Hyperfine Interactions》2002,139(1-4):631-639
57Fe transmission Mössbauer spectroscopy and X-ray diffractometry were used to study - and -polymorphs of iron phthalocyanines (FePc) to get information about their oxygenation in connection with controlled pyrolysis of flat layered phthalocyanines initiated by radicals at relatively low temperatures, to form acicular carbide particles encaged in carbon. Mössbauer spectroscopy and XRD revealed that the oxygenation of both - and -polymorphs of FePc was successfully achieved. New Mössbauer spectral components (doublets) appeared upon the oxygenation in both and FePc. This can be attributed to iron microenvironments containing oxygen between the layers of iron phthalocyanines. 相似文献
90.