全文获取类型
收费全文 | 14649篇 |
免费 | 592篇 |
国内免费 | 25篇 |
专业分类
化学 | 10177篇 |
晶体学 | 107篇 |
力学 | 374篇 |
综合类 | 1篇 |
数学 | 1925篇 |
物理学 | 2682篇 |
出版年
2023年 | 118篇 |
2022年 | 95篇 |
2021年 | 337篇 |
2020年 | 304篇 |
2019年 | 284篇 |
2018年 | 294篇 |
2017年 | 261篇 |
2016年 | 595篇 |
2015年 | 469篇 |
2014年 | 500篇 |
2013年 | 995篇 |
2012年 | 1020篇 |
2011年 | 1107篇 |
2010年 | 668篇 |
2009年 | 620篇 |
2008年 | 978篇 |
2007年 | 953篇 |
2006年 | 767篇 |
2005年 | 695篇 |
2004年 | 544篇 |
2003年 | 516篇 |
2002年 | 436篇 |
2001年 | 311篇 |
2000年 | 276篇 |
1999年 | 196篇 |
1998年 | 155篇 |
1997年 | 129篇 |
1996年 | 149篇 |
1995年 | 116篇 |
1994年 | 110篇 |
1993年 | 133篇 |
1992年 | 115篇 |
1991年 | 82篇 |
1990年 | 64篇 |
1989年 | 55篇 |
1988年 | 51篇 |
1987年 | 44篇 |
1986年 | 46篇 |
1985年 | 90篇 |
1984年 | 86篇 |
1983年 | 55篇 |
1982年 | 56篇 |
1981年 | 49篇 |
1980年 | 51篇 |
1979年 | 28篇 |
1978年 | 44篇 |
1977年 | 29篇 |
1976年 | 29篇 |
1975年 | 33篇 |
1974年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
21.
Activated carbon production from almond shells using phosphoric acid activation agent was achieved by applying both conventional heating and microwave heating in succession. The morphology and surface properties of activated carbon were studied using thermogravimetric and differential gravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, and Brunauer–Emmett–Teller analysis. A surface area of 1128 m2/g was achieved by optimizing the microwave power (500?W), microwave application time (15?minutes), conventional heating time (45?minutes), conventional heating temperature (500?°C), and the phosphoric acid:sample ratio (0.7:1). An adsorption capacity of methylene blue of 148?mg/g and an iodine value of 791?mg/g was obtained for the prepared activated carbon. 相似文献
22.
Brandão Pedro Francisco Ramos Rui Miguel Rodrigues José António 《Analytical and bioanalytical chemistry》2018,410(26):6873-6880
Analytical and Bioanalytical Chemistry - Formaldehyde is often applied in the industrial production of different products, such as textiles, insulation materials, or cosmetics, due to its... 相似文献
23.
24.
25.
Alcindo A. Dos Santos Renan S. Ferrarini Jefferson L. Princival João V. Comasseto 《Tetrahedron letters》2006,47(50):8933-8935
A masked lithium homoenolate, generated by tellurium/lithium exchange, was reacted with epoxides. The lithium compound was also converted into other organometallics such as Grignard, and cuprates and the reactivity of those organometallics with epoxides was evaluated. The same building block was employed in the synthesis of (+/−)-frontalin. 相似文献
26.
We study a site analogue of directed percolation. Random trajectories are generated and their critical behavior is studied. The critical behavior corresponds to that of simple percolation in some of the parameter space, but elsewhere the exponents reveal new universality classes. As a byproduct, we use the model to make an improved estimate of the percolation hull exponents and to calculate the site percolation probability for the square lattice. 相似文献
27.
Ana Luísa Daniel‐da‐Silva João Carlos Moura Bordado José Miguel Martín‐Martínez 《Journal of Polymer Science.Polymer Physics》2007,45(22):3034-3045
The degree of phase separation in several moisture‐cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X‐ray diffraction (WAXD), and temperature‐modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol‐based PUUs, whereas for triol‐based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3034–3045, 2007 相似文献
28.
In order to reduce infant mortality in the municipality of Rio de Janeiro it is desired to encourage all mothers-to-be to attend the appropriate health care facilities. A 3-level hierarchical prenatal–neonatal health care system is described together with a basic model for optimising accessibility to facilities. A genetic algorithm to solve the basic model is developed and some numerical experience reported. Extensions to the basic model and planned future research are briefly indicated. 相似文献
29.
Flávio A. Pavan Yoshitaka Gushikem Celso C. Moro Tania M. Costa Edilson V. Benvenutti 《Colloid and polymer science》2003,281(2):173-177
Anilinepropylsilica xerogel was obtained by using an appropriate organosilane and tetraethyl orthosilicate as precursor reagents. The gelation was carried out using HF and NaF as catalysts. The presence of Na+ (when NaF was used) resulted in a decrease in the final organic content of the materials. This effect was interpreted as an inhibition of the organosilane polycondensation possibly due to the Na+ interaction with the SiO- groups of the hydrolyzed organosilane. The presence of Na+ also results in morphological changes in the xerogels. 相似文献
30.