全文获取类型
收费全文 | 82412篇 |
免费 | 14188篇 |
国内免费 | 9175篇 |
专业分类
化学 | 58660篇 |
晶体学 | 819篇 |
力学 | 5190篇 |
综合类 | 460篇 |
数学 | 9545篇 |
物理学 | 31101篇 |
出版年
2024年 | 195篇 |
2023年 | 1679篇 |
2022年 | 2549篇 |
2021年 | 2923篇 |
2020年 | 3412篇 |
2019年 | 3275篇 |
2018年 | 2796篇 |
2017年 | 2602篇 |
2016年 | 3924篇 |
2015年 | 3797篇 |
2014年 | 4514篇 |
2013年 | 5950篇 |
2012年 | 7431篇 |
2011年 | 7597篇 |
2010年 | 5219篇 |
2009年 | 4886篇 |
2008年 | 5340篇 |
2007年 | 4736篇 |
2006年 | 4396篇 |
2005年 | 3682篇 |
2004年 | 2950篇 |
2003年 | 2410篇 |
2002年 | 2426篇 |
2001年 | 2049篇 |
2000年 | 1726篇 |
1999年 | 1801篇 |
1998年 | 1458篇 |
1997年 | 1400篇 |
1996年 | 1376篇 |
1995年 | 1112篇 |
1994年 | 992篇 |
1993年 | 803篇 |
1992年 | 719篇 |
1991年 | 645篇 |
1990年 | 543篇 |
1989年 | 415篇 |
1988年 | 379篇 |
1987年 | 293篇 |
1986年 | 270篇 |
1985年 | 230篇 |
1984年 | 159篇 |
1983年 | 119篇 |
1982年 | 91篇 |
1981年 | 74篇 |
1980年 | 70篇 |
1979年 | 38篇 |
1978年 | 38篇 |
1977年 | 46篇 |
1976年 | 37篇 |
1973年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Nonlinear Dynamics - Under investigation is a generalized (3 + 1)-dimensional variable- coefficient Kadomtsev– Petviashvili equation in fluid mechanics. Various exact analytical solutions are... 相似文献
42.
The research progress of a novel traffic solution,a submerged floating tunnel(SFT),is reviewed in terms of a study approach and loading scenario.Among existing publications,the buoyancy-weight ratio(BWR) is usually predefined.However,BWR is a critical structural parameter that tremendously affects the dynamic behaviour of not only the tunnel tube itself but also the cable system.In the context of a SFT prototype(SFTP) project in Qiandao Lake(Zhejiang Province,China),the importance of BWR is illustrated by finite element analysis and subsequently,an optimized BWR is proposed within a reasonable range in the present study.In the numerical model,structural damping is identified to be of importance.Rayleigh damping and the corresponding Rayleigh coefficients are attained through a sensitivity study,which shows that the adopted damping ratios are fairly suitable for SFTP.Lastly,the human sense of security is considered by quantifying the comfort index,which helps further optimize BWR in the SFTP structural parameter design. 相似文献
43.
44.
45.
46.
47.
The Effect of the Spacer of Bis(biurea) Ligands on the Structure of A2L3‐type (A=anion) Phosphate Complexes
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Prof. Biao Wu Dr. Shaoguang Li Prof. Yibo Lei Prof. Huaiming Hu Dr. Nader de Sousa Amadeu Prof. Dr. Christoph Janiak Dr. Jennifer S. Mathieson Dr. De‐Liang Long Prof. Leroy Cronin Prof. Xiao‐Juan Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2588-2593
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO43?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes. 相似文献
48.
Single Crystal to Single Crystal (SC‐to‐SC) Transformation from a Nonporous to Porous Metal–Organic Framework and Its Application Potential in Gas Adsorption and Suzuki Coupling Reaction through Postmodification
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Rupam Sen Debraj Saha Dr. Subratanath Koner Dr. Paula Brandão Dr. Zhi Lin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5962-5971
A new amino‐functionalized strontium–carboxylate‐based metal–organic framework (MOF) has been synthesized that undergoes single crystal to single crystal (SC‐to‐SC) transformation upon desolvation. Both structures have been characterized by single‐crystal X‐ray analysis. The desolvated structure shows an interesting 3D porous structure with pendent ?NH2 groups inside the pore wall, whereas the solvated compound possesses a nonporous structure with DMF molecules on the metal centers. The amino group was postmodified through Schiff base condensation by pyridine‐2‐carboxaldehyde and palladium was anchored on that site. The modified framework has been utilized for the Suzuki cross‐coupling reaction. The compound shows high activity towards the C?C cross‐coupling reaction with good yields and turnover frequencies. Gas adsorption studies showed that the desolvated compound had permanent porosity and was microporous in nature with a BET surface area of 2052 m2 g?1. The material also possesses good CO2 (8 wt %) and H2 (1.87 wt %) adsorption capabilities. 相似文献
49.
Rajkumar P. Diwakar K. Subadevi R. Gnanamuthu R. M. Wang Fu-Ming Liu Wei-Ren Sivakumar M. 《Journal of Solid State Electrochemistry》2021,25(3):939-948
Journal of Solid State Electrochemistry - The “shuttle effect” of polysulfides is a serious issue, resulting in a decrease in the life-cycle of lithium-sulfur (Li-S) batteries. To... 相似文献
50.
Synthesis and Photophysical Properties of a Sc3N@C80‐Corrole Electron Donor–Acceptor Conjugate
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Bin Liu Hongyun Fang Prof. Xiaofang Li Wenting Cai Lipiao Bao Marc Rudolf Fabian Plass Prof. Louzhen Fan Prof. Xing Lu Prof. Dirk M. Guldi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):746-752
Embedding endohdedral metallofullerenes (EMFs) into electron donor–acceptor systems is still a challenging task owing to their limited quantities and their still largely unexplored chemical properties. In this study, we have performed a 1,3‐dipolar cycloaddition reaction of a corrole‐based precursor with Sc3N@C80 to regioselectively form a [5,6]‐adduct ( 1 ). The successful attachment of the corrole moiety was confirmed by mass spectrometry. In the electronic ground state, absorption spectra suggest sizeable electronic communications between the electron acceptor and the electron donor. Moreover, the addition pattern occurring at a [5,6]‐bond junction is firmly proven by NMR spectroscopy and electrochemical investigations performed with 1 . In the electronically excited state, which is probed in photophysical assays with 1 , a fast electron‐transfer yields the radical ion pair state consisting of the one‐electron‐reduced Sc3N@C80 and of the one‐electron‐oxidized corrole upon its exclusive photoexcitation. As such, our results shed new light on the practical work utilizing EMFs as building blocks in photovoltaics. 相似文献