全文获取类型
收费全文 | 413473篇 |
免费 | 5236篇 |
国内免费 | 1996篇 |
专业分类
化学 | 229255篇 |
晶体学 | 5922篇 |
力学 | 16621篇 |
综合类 | 67篇 |
数学 | 48495篇 |
物理学 | 120345篇 |
出版年
2020年 | 3733篇 |
2019年 | 4108篇 |
2018年 | 5282篇 |
2017年 | 5257篇 |
2016年 | 7713篇 |
2015年 | 4915篇 |
2014年 | 7331篇 |
2013年 | 17640篇 |
2012年 | 14248篇 |
2011年 | 17306篇 |
2010年 | 12249篇 |
2009年 | 11909篇 |
2008年 | 16231篇 |
2007年 | 16402篇 |
2006年 | 15369篇 |
2005年 | 13996篇 |
2004年 | 12481篇 |
2003年 | 11118篇 |
2002年 | 10907篇 |
2001年 | 11550篇 |
2000年 | 9074篇 |
1999年 | 6725篇 |
1998年 | 5685篇 |
1997年 | 5711篇 |
1996年 | 5575篇 |
1995年 | 4771篇 |
1994年 | 4895篇 |
1993年 | 4778篇 |
1992年 | 5151篇 |
1991年 | 5202篇 |
1990年 | 4954篇 |
1989年 | 4863篇 |
1988年 | 4712篇 |
1987年 | 4624篇 |
1986年 | 4571篇 |
1985年 | 5964篇 |
1984年 | 6157篇 |
1983年 | 5030篇 |
1982年 | 5498篇 |
1981年 | 5222篇 |
1980年 | 4821篇 |
1979年 | 5192篇 |
1978年 | 5477篇 |
1977年 | 5481篇 |
1976年 | 5488篇 |
1975年 | 5105篇 |
1974年 | 5227篇 |
1973年 | 5354篇 |
1972年 | 3938篇 |
1971年 | 3257篇 |
排序方式: 共有10000条查询结果,搜索用时 917 毫秒
171.
G.E. Farr 《Discrete Mathematics》2019,342(5):1510-1519
This paper continues the study of combinatorial properties of binary functions — that is, functions such that , where is a finite set. Binary functions have previously been shown to admit families of transforms that generalise duality, including a trinity transform, and families of associated minor operations that generalise deletion and contraction, with both these families parameterised by the complex numbers. Binary function representations exist for graphs (via the indicator functions of their cutset spaces) and indeed arbitrary matroids (as shown by the author previously). In this paper, we characterise degenerate elements – analogues of loops and coloops – in binary functions, with respect to any set of minor operations from our complex-parameterised family. We then apply this to study the relationship between binary functions and Tutte’s alternating dimaps, which also support a trinity transform and three associated minor operations. It is shown that only the simplest alternating dimaps have binary representations of the form we consider, which seems to be the most direct type of representation. The question of whether there exist other, more sophisticated types of binary function representations for alternating dimaps is left open. 相似文献
172.
Differential inequalities for polynomials generalizing the well-known Smirnov, Rahman, Schmeisser, and Bernstein inequalities are obtained.
相似文献173.
Tereshchenko E. D. Cherniakov S. M. Yurik R. Yu. Rietveld M. T. Häggström I. 《Radiophysics and Quantum Electronics》2020,62(10):667-676
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar... 相似文献
174.
175.
176.
Journal of Structural Chemistry - An analysis is presented for the results obtained in the studies initiated by A. E. Shvelashivili, Corresponding Member, Academy of Sciences of Georgia, and... 相似文献
177.
178.
Facile non‐lithographic route to highly aligned silica nanopatterns using unidirectionally aligned polystyrene‐block‐polydimethylsiloxane films
下载免费PDF全文
![点击此处可从《Journal of Polymer Science.Polymer Physics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Zhe Qiang Maurice L. Wadley Bryan D. Vogt Kevin A. Cavicchi 《Journal of Polymer Science.Polymer Physics》2015,53(15):1058-1064
Thin films (monolayer and bilayer) of cylinder forming polystyrene‐block‐polydimethylsiloxane (PS‐b‐PDMS) were shear aligned by the swelling and deswelling of a crosslinked PDMS pad that was physically adhered to the film during solvent vapor annealing. The nanostructures formed by self‐assembly were exposed to ultraviolet‐ozone to partially oxidize the PDMS, followed by calcination in air at 500 °C. In this process, the PS segments were fully decomposed, while the PDMS yielded silica nanostructures. The highly aligned PDMS cylinders were thus deposited as silica nanolines on the silicon substrate. Using a bilayer film, the center‐to‐center distance of these features were effectively halved from 38 to 19 nm. Similarly, by sequential shear‐alignment of two distinct layers, a rhombic array of silica nanolines was fabricated. This methodology provides a facile route to fabricating complex topographically patterned nanostructures. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1058–1064 相似文献
179.
Pan Huang Dawen Xu Robert M. Reich Felix Kaiser Boping Liu Fritz E. Kühn 《Tetrahedron letters》2019,60(24):1574-1577
A first example of an Et2Zn mediated silylation of 1-aklynes is reported. A series of functional groups are tolerated in this reaction. Mechanistic studies support Zn alkynilides as intermediates in the reaction. This reaction protocol provides a practical method for the preparation of alkynylsilanes and expands the application of organometallic zinc in organic synthesis. 相似文献
180.
Vanessa R. Machado Louis P. Sandjo Giovanni L. Pinheiro Milene H. Moraes Mario Steindel Moacir G. Pizzolatti 《Natural product research》2018,32(3):275-281
The natural product lupeol 1 was isolated from aerial parts of Vernonia scorpioides with satisfactory yield, which made it viable to be used as starting material in semisynthetic approach. Ten lupeol derivatives 2–11 were prepared by classical procedures. Including, five new esters derivatives 7–11, which were obtained by structural modifications in the isopropylidene fragment. All semisynthetic compounds and lupeol 1–11 were confirmed by 1H NMR, 13C NMR and HRMS. Their antiprotozoal activity was evaluated in vitro against L. amazonensis and T. cruzi. Derivative 6 showed the best antitrypanosomal activity (IC50 = 12.48 μg/mL) and the lowest cytotoxic derivative (CC50 = 161.50 μg/mL). The mechanism of action of the most active derivatives (4, 6 and 11) is not dependent from the enzyme trypanothione reductase. 相似文献