全文获取类型
收费全文 | 1718篇 |
免费 | 55篇 |
国内免费 | 11篇 |
专业分类
化学 | 1098篇 |
晶体学 | 23篇 |
力学 | 45篇 |
数学 | 326篇 |
物理学 | 292篇 |
出版年
2023年 | 9篇 |
2022年 | 13篇 |
2021年 | 43篇 |
2020年 | 27篇 |
2019年 | 39篇 |
2018年 | 21篇 |
2017年 | 21篇 |
2016年 | 60篇 |
2015年 | 56篇 |
2014年 | 59篇 |
2013年 | 84篇 |
2012年 | 122篇 |
2011年 | 123篇 |
2010年 | 72篇 |
2009年 | 69篇 |
2008年 | 98篇 |
2007年 | 119篇 |
2006年 | 95篇 |
2005年 | 101篇 |
2004年 | 95篇 |
2003年 | 74篇 |
2002年 | 65篇 |
2001年 | 16篇 |
2000年 | 16篇 |
1999年 | 23篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1996年 | 18篇 |
1995年 | 14篇 |
1994年 | 6篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 13篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 16篇 |
1982年 | 13篇 |
1981年 | 13篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1976年 | 3篇 |
1973年 | 4篇 |
1960年 | 5篇 |
1911年 | 2篇 |
排序方式: 共有1784条查询结果,搜索用时 31 毫秒
121.
122.
Dr. Vincenzo Grande Dr. Filippo Doria Prof. Dr. Mauro Freccero Prof. Dr. Frank Würthner 《Angewandte Chemie (International ed. in English)》2017,56(26):7520-7524
G-quadruplexes (G4s) are peculiar DNA or RNA tertiary structures that are involved in the regulation of many biological events within mammalian cells, bacteria, and viruses. Although their role as versatile therapeutic targets has been emphasized for 35 years, G4 selectivity over ubiquitous double-stranded DNA/RNA, as well as G4 differentiation by small molecules, still remains challenging. Here, a new amphiphilic dicyanovinyl-substituted squaraine, SQgl , is reported to act as an NIR fluorescent light-up probe discriminating an extensive panel of parallel G4s while it is non-fluorescent in the aggregated state. The squaraine can form an unconventional sandwich π-complex binding two quadruplexes, which leads to a strongly fluorescent (ΦF=0.61) supramolecular architecture. SQgl is highly selective against non-quadruplex and non-parallel G4 sequences without altering their topology, as desired for applications in selective in vivo high-resolution imaging and theranostics. 相似文献
123.
Paolo Ferruti Elisabetta Ranucci Amedea Manfredi Nicolò Mauro Elena Ferrari Riccardo Bruni Francesco Colombo Patrizia Mussini Manuela Rossi 《Journal of polymer science. Part A, Polymer chemistry》2012,50(24):5000-5010
Traditional precipitation methods for inorganic micropollutant removal from waters are increasingly being replaced by sorption methods based on both natural and synthetic materials. In this context, two novel effective heavy metal ions absorbers are presented. These resins, LYMA and LMT85, were crosslinked poly(amidoamine)s carrying amine and carboxyl groups in their repeating units. In particular, the LYMA‐repeating unit contains one carboxyl and two amine groups and is a mimic of L ‐lysine, whereas LMT85 contains two amine and five carboxyl groups and is a mimic of EDTA. Both resins were prepared at moderate cost by simple eco‐friendly procedures. The heavy metal ion set adopted as benchmark was Cu2+, Cd2+, Pb2+, Zn2+, Ni2+, and Co2+. LYMA proved selective for Cu2+ and Ni2+, the other ions tested being negligibly absorbed, whereas LMT85 proved capable of rapidly and quantitatively absorbing all the ions tested either singly or in mixed solution. The absorption process was reversible, and the resins were easily regenerated by acidification. The absorption of several metal ions imparted intense coloring to the resins, a feature possibly exploitable for analytical purposes. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
124.
Giovana de Fátima Menegotto Paulo César Borges Eduardo Mauro do Nascimento Carlos Maurício Lepienski Elaine Cristina Azevedo 《Brazilian Journal of Physics》2011,41(4-6):223-228
The influence of hydrogen loading temperature on the mechanical strength of optical fibers is investigated. Fibers subjected to high-pressure hydrogen loading at different temperatures were submitted to bend tests, and the results compared with those for pristine fibers. The Weibull probability distribution function was used to analyze the data of the mechanical bending strength of the fibers. Fiber strength is reduced by the presence of hydrogen, and this decrease is greater for higher hydrogen loading temperatures. The mechanical properties of the polymers used to coat fibers are affected by the hydrogen loading process and also by the increase in temperature. However, there is no evidence of cracks formation that might allow water to penetrate to the surface of the glass. Observation using scanning electron microscopy revealed that the morphology of fractures in nonhydrogen-loaded fibers have distinct fracture characteristics to that of fibers that are hydrogen loaded at 90°C and 120°C. 相似文献
125.
Daciberg L. Gon?alves Mauro Spreafico Oziride Manzoli Neto 《Journal of Fixed Point Theory and Applications》2011,9(2):285-294
In this work, we show for which odd-dimensional homotopy spherical space forms the Borsuk–Ulam theorem holds. These spaces
are the quotient of a homotopy odd-dimensional sphere by a free action of a finite group. Also, the types of these spaces
which admit a free involution are characterized. The case of even-dimensional homotopy spherical space forms is basically
known. 相似文献
126.
Sfarra Stefano Regi Mauro Tortora Mariagrazia Casieri Cinzia Perilli Stefano Paoletti Domenica 《Journal of Thermal Analysis and Calorimetry》2018,132(2):1367-1387
Journal of Thermal Analysis and Calorimetry - The aim of this work is to evaluate the potentiality of a multi-technique nondestructive approach for characterizing the state of conservation of... 相似文献
127.
128.
129.
A recent analysis of the experimental data on some physical phenomena ruled by the four fundamental interactions (electromagnetic, weak, strong and gravitational) seems to show the possibility of describing such interactions in terms of a deformation of the usual Minkowski spacetime, with a metric whose coefficients do depend on the energy of the process considered. In this paper, we show that such results can be accounted for in terms of a Kaluza-Klein-like scheme, based on a five-dimensional Riemannian space in which energy plays the role of the fifth dimension. The corresponding five-dimensional Einstein equations in vacuum are solved in some cases of physical relevance and it is shown that all the phenomenological metrics describing the four fundamental forces are recovered as special cases of the classes of solutions found. Possible developments of the formalism are also briefly outlined. 相似文献
130.
Mauro Cerasoli 《Journal of Mathematical Analysis and Applications》1983,94(1):150-165
In occupancy problems we randomize the number of balls with a Poisson process of intensity α. Thus some classical formulas are very easily demonstrated and generalized with the aid of inclusion-exclusion principle. Then we give a general theorem to calculate the distributions and moments of particular random variables or waiting times when infinite balls are considered. This theorem can be applied to the well-known birthday and coupon collectors problems. 相似文献