全文获取类型
收费全文 | 3453篇 |
免费 | 115篇 |
国内免费 | 16篇 |
专业分类
化学 | 1883篇 |
晶体学 | 53篇 |
力学 | 139篇 |
数学 | 802篇 |
物理学 | 707篇 |
出版年
2023年 | 22篇 |
2022年 | 37篇 |
2021年 | 50篇 |
2020年 | 72篇 |
2019年 | 87篇 |
2018年 | 134篇 |
2017年 | 136篇 |
2016年 | 156篇 |
2015年 | 130篇 |
2014年 | 201篇 |
2013年 | 485篇 |
2012年 | 209篇 |
2011年 | 219篇 |
2010年 | 219篇 |
2009年 | 139篇 |
2008年 | 205篇 |
2007年 | 172篇 |
2006年 | 116篇 |
2005年 | 68篇 |
2004年 | 65篇 |
2003年 | 45篇 |
2002年 | 51篇 |
2001年 | 43篇 |
2000年 | 34篇 |
1999年 | 23篇 |
1998年 | 28篇 |
1997年 | 21篇 |
1996年 | 19篇 |
1995年 | 17篇 |
1994年 | 18篇 |
1993年 | 10篇 |
1991年 | 11篇 |
1990年 | 19篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 27篇 |
1984年 | 23篇 |
1983年 | 23篇 |
1982年 | 14篇 |
1981年 | 31篇 |
1980年 | 11篇 |
1979年 | 15篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 19篇 |
1974年 | 14篇 |
1973年 | 12篇 |
1968年 | 13篇 |
排序方式: 共有3584条查询结果,搜索用时 484 毫秒
1.
Karakuş Erman Erdemir Eda Suna Garen Liv Lokman Gunduz Simay Can Şevval Arzu 《Journal of fluorescence》2021,31(6):1617-1625
Journal of Fluorescence - We have constructed a novel fluorescein-based fluorescent chemosensor, FL-In, functionalised with an indole moiety and capable of sensing by both the optical... 相似文献
2.
3.
4.
Prof. Piotr Bałczewski Dr. Emilia Kowalska Dr. Ewa Różycka-Sokołowska Dr. Joanna Skalik Dr. Krzysztof Owsianik Dr. Marek Koprowski Dr. Bernard Marciniak Dr. Dariusz Guziejewski Prof. Witold Ciesielski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(62):14148-14161
The highly substituted mono-aryl/alkylthio-(hetero)acenes prepared in this study have been found to be thermally more stable (Tdecomp.=331–354 °C) than the known di-aryl/alkylthio-substituted acenes by an average of 25 °C. They are also much more photostable at 254 and 365 nm (in both argon and air) than the parent anthracene and other reported anthracenes. The most photostable aryl/alkylthio-anthracenes at 254 nm were found to be 60–70 (in air) and 130 (in argon) times more stable in solution than the unsubstituted anthracene, and much more stable than known EDG/EWG-substituted anthracenes (EDG=electron-donating group, EWG=electron-withdrawing group) with an extended aromatic core. Furthermore, the acenes showed significantly higher photostability at 365 nm in both air and argon. The anthracenes were obtained by the novel thio-Friedel–Crafts/Bradsher cyclization reaction of hitherto unknown [o-(1,3-dithian-2-yl)aryl](aryl)methyl thioethers. The developed approach provides a general access to mono-aryl/alkylthio-substituted (hetero)acene frameworks containing at least three fused (hetero)aromatic rings. The characteristic feature of this approach, which leads to highly substituted acenes, is that the substituents, unlike in other methods, may be introduced at an early stage of the synthesis. DFT and TD-DFT calculations confirmed the stabilizing role of the aryl/alkylthio substituent in the mono-aryl/alkylthio-substituted anthracenes, which are the most stable anthracenes prepared to date. Their high photostability is mainly due to the quenching of singlet oxygen by the acene and the quenching of the acene S1 state by molecular oxygen. 相似文献
5.
In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and
their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically
using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L−1 using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition
on the protonation constants is discussed. The log10 K2 values of esters generally decreased with increasing ethanol content. However, the log10 K1 values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content
in contrast those of L-lysine and L-histidine esters. 相似文献
6.
Suppose there exists a global solution u to the incompressible Navier–Stokes equations, such that . We prove that its norm goes to 0 at infinity. We next use this fact to control the norm of u, and finally we prove that such a solution is stable. To cite this article: I. Gallagher et al., C. R. Acad. Sci. Paris, Ser. I 334 (2002) 289–292. 相似文献
7.
Stefan Cobzaş 《Acta Appl Math》2004,80(3):363-363
8.
Mustafa Çelebier Ertan Şahin Nilgün Ancın Nurşen Altuntaş Öztaş Selma Gül Öztaş 《应用有机金属化学》2007,21(10):viii-viii
The article referenced above was first published online on 30 August 2007 with incorrect pagination; the pagination has now been corrected online and in print. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
9.
F. Forkusuz S. Işıklı S. Akın M. Ungan A. Şenköylü N. K. Aras 《Journal of Radioanalytical and Nuclear Chemistry》2004,259(3):365-368
The standard method to diagnose and follow-up osteoporosis is the measurement of bone mineral density (BMD) using dual X-ray
absorptiometry (DEXA). Manufacturers' manuals of DEXA devices state the intrascanner coefficient of variance is less than
0.01 g/cm2. The aim of this study was to evaluate the in vivo coefficient of variance of a Lunar DPX scanner in male and female healthy
adult subjects. Average BMD for females and males were 1.170±0.091 g/cm2 and 1.272±0.115 g/cm2, respectively. Monthly phantom measurements provided and controlled by the manufacturer were 1.243±0.008 g/cm2 (range 1.222 to 1.257) and the coefficient of variance was 0.006. It is concluded that the in vivo coefficient of variance
of DEXA devices can slightly be higher than that proposed by the manufacturer.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
The influence of hydrogen bonds on the physical and chemical properties of hydrogen bonding fluid system of A a D d type is investigated from two viewpoints by the principle of statistical mechanics. In detail, we proposed two new ways that can be used to obtain the equilibrium size distribution of the hydrogen bonding clusters, and derived the analytical expression of a relationship between the hydrogen bonding free energy and hydrogen bonding degree. For the nonlinear hydrogen bonding systems, it is shown that the sol-gel phase transition can take place under proper conditions, which is further proven to be a kind of geometrical phase transition rather than a thermodynamic one. Moreover, several problems associated with the geometrical phase transition and liquid-solid phase transition in nonlinear hydrogen bonding systems are discussed. 相似文献