全文获取类型
收费全文 | 16464篇 |
免费 | 3178篇 |
国内免费 | 2641篇 |
专业分类
化学 | 9798篇 |
晶体学 | 200篇 |
力学 | 1531篇 |
综合类 | 169篇 |
数学 | 1003篇 |
物理学 | 9582篇 |
出版年
2024年 | 42篇 |
2023年 | 168篇 |
2022年 | 583篇 |
2021年 | 569篇 |
2020年 | 674篇 |
2019年 | 551篇 |
2018年 | 529篇 |
2017年 | 667篇 |
2016年 | 782篇 |
2015年 | 631篇 |
2014年 | 919篇 |
2013年 | 1438篇 |
2012年 | 1045篇 |
2011年 | 1130篇 |
2010年 | 958篇 |
2009年 | 1073篇 |
2008年 | 1120篇 |
2007年 | 1030篇 |
2006年 | 1044篇 |
2005年 | 839篇 |
2004年 | 828篇 |
2003年 | 703篇 |
2002年 | 601篇 |
2001年 | 565篇 |
2000年 | 510篇 |
1999年 | 380篇 |
1998年 | 430篇 |
1997年 | 344篇 |
1996年 | 328篇 |
1995年 | 271篇 |
1994年 | 246篇 |
1993年 | 213篇 |
1992年 | 196篇 |
1991年 | 150篇 |
1990年 | 123篇 |
1989年 | 105篇 |
1988年 | 108篇 |
1987年 | 76篇 |
1986年 | 55篇 |
1985年 | 41篇 |
1984年 | 47篇 |
1983年 | 19篇 |
1982年 | 32篇 |
1981年 | 22篇 |
1980年 | 13篇 |
1979年 | 12篇 |
1978年 | 22篇 |
1977年 | 10篇 |
1974年 | 6篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
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
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
2.
Naoto Takase Junpei Kuwabara Seong Jib Choi Takeshi Yasuda Liyuan Han Takaki Kanbara 《Journal of polymer science. Part A, Polymer chemistry》2015,53(4):536-542
The Pd‐catalyzed polycondensation of 4‐octylaniline with various dibromoarylenes was carried out under microwave heating. Microwave heating led to a decrease in the reaction time and an increase in the molecular weight of the polymers as compared to conventional heating. Microwave heating also allowed the catalyst loading to be reduced to 1 mol %, yielding polymerization results that were comparable to those under conventional heating and 5 mol % catalyst. Investigations regarding field‐effect transistors and organic photovoltaic cells using the obtained poly(arylamine) with azobenzene units revealed that increasing the molecular weight of the polymer led to improved device performance, including hole mobility and power conversion efficiency. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 536–542 相似文献
3.
Alexander Zeller 《Journal of organometallic chemistry》2006,691(21):4379-4385
The ethylene polymerization reaction of a neutral nickel catalyst was studied by DFT calculations at the Becke3LYP/6-31G(d) level of theory. As in related cases a β-agostic bond stabilizes the nickel alkyl ground states. Transition states for the insertion of the olefin show a distinct α-agostic interaction, which has not been observed for late metal polymerization catalysts before. An ethylene-alkyl complex was identified as the resting state of the reaction. The overall barrier height of the reaction amounts to 17.54 kcal/mol, which slightly increases to 17.60 kcal/mol for the polymerization of deuterated ethylene. Therefore, a small positive kinetic isotope effect (kH/kD = 1.09) can be calculated, which is caused by the α-agostic interaction in the transition state. A comparison to other late metal based polymerization systems reveals that the ethylene coordination step of highly active catalysts is significantly lower in energy compared to catalysts which are only moderately active. 相似文献
4.
M. Georgelin A. Pocheau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):169-174
The polycrystalline perovskitelike manganese oxides La1-xAxMnO (A = Na, and K, ) have been fabricated by sol-gel technique. For all the compositions explored in this work, the average manganese oxidation
state is practically constant, at for A = Na, and for A = K, respectively. A close relationship is confirmed to hold between the Curie temperature (Tc) and the bond distance of Mn-O. Results of magnetic measurements show that these materials can be utilized as suitable candidates
for magnetic refrigerants with wide applied temperature span, for their significant entropy change and the easily tuned Curie
temperature.
Received: 12 September 1997 / Revised: 18 December 1997 / Accepted: 21 January 1998 相似文献
5.
6.
7.
8.
Homohelicity induction of a series of propylene-linked zinc bilinone (ZnBL; linear tetrapyrrople-zinc(II) complex) dimers upon complexation with chiral amine and α-amino esters was investigated. Introduction of substituents such as dimethyl and diisobutyl to the central carbon of the propylene spacer gave rise to stabilization of the homohelical (PP and MM) conformers rather than the heterohelical (PM) conformer. As bulkiness of the substituent increased, stability of the homohelical conformers was raised. The preorganization of the homohelical structures led to significantly amplified homohelicity induction upon complexation with chiral amine and α-amino esters. 相似文献
9.
多普勒效应测试仪的改进 总被引:3,自引:0,他引:3
为了解决电磁波多普勒效应在实验室演示的困难,采用单片机和一系列大规模集成电路设计了一种演示电磁波多普勒效应的测试仪器,分析了电磁波的多普勒效应原理,给出了该仪器的组成结构,介绍了该仪器铁特点。 相似文献
10.