全文获取类型
收费全文 | 613篇 |
免费 | 8篇 |
专业分类
化学 | 323篇 |
晶体学 | 3篇 |
力学 | 6篇 |
数学 | 60篇 |
物理学 | 159篇 |
无线电 | 70篇 |
出版年
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 10篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 14篇 |
2012年 | 15篇 |
2011年 | 29篇 |
2010年 | 21篇 |
2009年 | 16篇 |
2008年 | 29篇 |
2007年 | 35篇 |
2006年 | 35篇 |
2005年 | 24篇 |
2004年 | 18篇 |
2003年 | 17篇 |
2002年 | 18篇 |
2001年 | 16篇 |
2000年 | 20篇 |
1999年 | 15篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 8篇 |
1992年 | 17篇 |
1991年 | 10篇 |
1990年 | 3篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 11篇 |
1973年 | 10篇 |
1971年 | 4篇 |
1970年 | 5篇 |
排序方式: 共有621条查询结果,搜索用时 125 毫秒
501.
Stênio Nunes Alves José Eduardo Serr?o Alan Lane Melo 《Micron (Oxford, England : 1993)》2010,41(6):592-597
This study describes morphological alterations in the fat body and midgut of Culex quinquefasciatus larvae following exposure to different insecticides. To this end, both third and fourth instars of C. quinquefasciatus larvae were exposed for 30 and 60 min to organophosphate (50 ppb), pyrethroids (20 and 30 ppb), and avermectin derivates (1.5 and 54 ppb). Following incubation, pH measurements of the larvae gut were recorded. The fat body and midgut were also analyzed by light and transmission electron microscopy. These studies demonstrate a decrease in the pH of the larvae anterior midgut following exposure to all of the tested insecticides. Histochemical tests revealed a strong reaction for neutral lipids in the control group and a marked decrease in the group exposed to cypermethrin. Furthermore, a weak reaction with acidic lipids in larvae exposed to deltamethrin, temephos, ivermectin and abamectin was also observed. Insecticide-exposed larvae also exhibited cytoplasm granule differences, relative to control larvae. Finally, we noted a small reduction in microvilli size in the apex of digestive cells, although vesicles were found to be present. The destructive changes in the larvae were very similar regardless of the type of insecticide analyzed. These data suggest that alterations in the fat body and midgut are a common response to cellular intoxication. 相似文献
502.
A. N. Wilson M. C. East G. D. Dracoulis A. P. Byrne R. M. Clark P. M. Davidson P. Fallon A. G?rgen G. J. Lane A. O. Macchiavelli D. Ward 《The European Physical Journal A - Hadrons and Nuclei》2010,43(2):145-151
Three low-lying 8+ states have been identified in 192Pb . A newly observed cascade of $ \gamma$ -rays built directly on the 8+ 1 state is compared to the previously identified, weakly rotational band above the 11- $ \pi$ i 13/2 , h 9/2 isomer in the same nucleus, and to analogous structures in 194Pb . The similarity of all four structures lends support to the suggestion that the 8+ 1 configurations are of a similar oblate deformation to the 11- isomers. The excitation energies of all three 8+ states in 192Pb and 190Pb are compared to systematics. The possibility that one of the 8+ states in 192Pb is associated with a prolate shape is discounted. 相似文献
503.
504.
William J. Durand Gregory Blachut Michael J. Maher Stephen Sirard Summer Tein Matthew C. Carlson Yusuke Asano Sunshine X. Zhou Austin P. Lane Christopher M. Bates Christopher J. Ellison C. Grant Willson 《Journal of polymer science. Part A, Polymer chemistry》2015,53(2):344-352
This report describes the design and synthesis of a series of lamella-forming, silicon-containing block copolymers (Si-BCPs) and evaluation of these materials as potential candidates for lithographic applications. The interaction parameter χ of each Si-BCP is measured by both the mean-field theory predicted order-disorder transition and by analysis of X-ray scattering profiles. The introduction of more-polar methoxy and less-polar methylsilyl moieties increases χ to about 2–3 times that of the reference material, poly(styrene-block−4-trimethylsilylstyrene). The incremental increases appear to be essentially additive in this family of block copolymers, suggesting that improvements in χ can be predicted from appropriate monomer choice. Perpendicularly oriented thin-films of the ordered Si-BCPs generated by thermally annealing between two “neutral” polymeric surfaces and developed by etching on commercial RIE equipment show excellent image fidelity. These images demonstrate the excellent etch contrast of the Si-BCPs and document improvements in pattern fidelity that are realized with more strongly segregated BCPs. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 344–352 相似文献
505.
Shanquan Chen Haiping Zhou Xing Ye Zuhuang Chen Jinzhu Zhao Sujit Das Christoph Klewe Lei Zhang Eduardo Lupi Padraic Shafer Elke Arenholz Dun Jin Haoliang Huang Yalin Lu Xiaowen Li Meng Wu Shanming Ke Hu Xu Xierong Zeng Chuanwei Huang Lane W. Martin Lang Chen 《Advanced functional materials》2019,29(50)
The ability to tailor a new crystalline structure and associated functionalities with a variety of stimuli is one of the key issues in material design. Developing synthetic routes to functional materials with partially absorbed nonmetallic elements (i.e., hydrogen and nitrogen) can open up more possibilities for preparing novel families of electronically active oxide compounds. Fast and reversible uptake and release of hydrogen in epitaxial ABO3 manganite films through an adapted low‐frequency inductively coupled plasma technology is introduced. Compared with traditional dopants of metallic cations, the plasma‐assisted hydrogen implantations not only produce reversibly structural transformations from pristine perovskite (PV) phase to a newly found protonation‐driven brownmillerite one but also regulate remarkably different electronic properties driving the material from a ferromagnetic metal to a weakly ferromagnetic insulator for a range of manganite (La1?xSrxMnO3) thin films. Moreover, a reversible perovskite‐brownmillerite‐perovskite transition is achieved at a relatively low temperature (T ≤ 350 °C), enabling multifunctional modulations for integrated electronic systems. The fast, low‐temperature control of structural and electronic properties by the facile hydrogenation/dehydrogenation treatment substantially widens the space for exploring new possibilities of novel properties in proton‐based multifunctional materials. 相似文献
506.
The rate constants for the gas‐phase reactions of ground‐state oxygen atoms with CF2?CFCl (1), (E/Z)‐CFCl?CFCl (2), CFCl?CH2 (3), and (E/Z)‐CFH?CHCl (4) have been measured directly using a discharge flow tube coupled to a chemiluminescence detection system. The experiments were carried out under pseudo‐first‐order conditions with [O3P)]0 ? [ethene]0. The temperature dependences of the reactions were studied for the first time in the range 298–359 K. The proposed Arrhenius expressions (in units of cm3 molecule?1 s?1) were k1 = (1.07 ± 0.32) × 10?11 exp{?(8000±1600)/RT}, k2 = (0.56 ± 0.10) × 10?11 exp{?(8700±500)/RT}, k3 = (4.23 ± 1.25) × 10?11 exp{?(12,700 ± 800)/RT}, and k4 = (1.13 ± 0.62) × 10?11 exp{?(10,500 ± 1500)/RT}. All the rate coefficients display a positive temperature dependence, which highlights the importance of the irreversibility of the addition mechanism for these reactions. Halogen substitution in the ethene is discussed in terms of reactivity with O(3P). © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 763–769, 2005 相似文献
507.
The hottest topic in the communications industry is asynchronous transfer mode, or ATM. After hiding out for several years in standards committees around the world, the technology is grabbing headlines in every periodical in the field; the reason is that ATM is the first technology to merge voice and data communications into a common format that is equally and equitably inefficient for both. Here, the author presents an overview of ATM technology and applications 相似文献
508.
509.
Dstl has sponsored the development and use of a family of campaign level models of military operations. The models are required to provide an insight into force structure assessment, procurement decisions and doctrinal developments. The family comprises CLARION (land/air war-fighting), COMAND (maritime/air war-fighting) and DIAMOND (non-war-fighting). The two key features of the family are the core role played by the representation of C3I (command, control, communications and information) and the classification of combat units by their interactions with one another at an aggregated level rather than by treating them as a collection of specific combat platforms. 相似文献
510.