全文获取类型
收费全文 | 14279篇 |
免费 | 658篇 |
国内免费 | 102篇 |
专业分类
化学 | 10446篇 |
晶体学 | 78篇 |
力学 | 218篇 |
数学 | 2057篇 |
物理学 | 2240篇 |
出版年
2023年 | 113篇 |
2022年 | 164篇 |
2021年 | 197篇 |
2020年 | 349篇 |
2019年 | 284篇 |
2018年 | 166篇 |
2017年 | 163篇 |
2016年 | 449篇 |
2015年 | 371篇 |
2014年 | 431篇 |
2013年 | 686篇 |
2012年 | 818篇 |
2011年 | 858篇 |
2010年 | 513篇 |
2009年 | 466篇 |
2008年 | 768篇 |
2007年 | 750篇 |
2006年 | 732篇 |
2005年 | 699篇 |
2004年 | 604篇 |
2003年 | 441篇 |
2002年 | 530篇 |
2001年 | 243篇 |
2000年 | 244篇 |
1999年 | 211篇 |
1998年 | 223篇 |
1997年 | 198篇 |
1996年 | 212篇 |
1995年 | 170篇 |
1994年 | 186篇 |
1993年 | 163篇 |
1992年 | 154篇 |
1991年 | 136篇 |
1990年 | 120篇 |
1989年 | 109篇 |
1988年 | 96篇 |
1987年 | 98篇 |
1986年 | 80篇 |
1985年 | 138篇 |
1984年 | 129篇 |
1983年 | 93篇 |
1982年 | 126篇 |
1981年 | 128篇 |
1980年 | 101篇 |
1979年 | 116篇 |
1978年 | 104篇 |
1977年 | 105篇 |
1976年 | 97篇 |
1975年 | 75篇 |
1973年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Laurens Kooijman Dr. Matthias Schuster Christian Baumann Simon Jurt Dr. Frank Löhr Dr. Boris Fürtig Prof. Dr. Peter Güntert Prof. Dr. Oliver Zerbe 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(47):21151-21158
To achieve efficient proton pumping in the light-driven proton pump bacteriorhodopsin (bR), the protein must be tightly coupled to the retinal to rapidly convert retinal isomerization into protein structural rearrangements. Methyl group dynamics of bR embedded in lipid nanodiscs were determined in the dark-adapted state, and were found to be mostly well ordered at the cytosolic side. Methyl groups in the M145A mutant of bR, which displays only 10 % residual proton pumping activity, are less well ordered, suggesting a link between side-chain dynamics on the cytosolic side of the bR cavity and proton pumping activity. In addition, slow conformational exchange, attributed to low frequency motions of aromatic rings, was indirectly observed for residues on the extracellular side of the bR cavity. This may be related to reorganization of the water network. These observations provide a detailed picture of previously undescribed equilibrium dynamics on different time scales for ground-state bR. 相似文献
2.
3.
Iodine(III)‐Catalyzed Rearrangements of Imides: A Versatile Route to α,α‐Dialkylated α‐Hydroxy Carboxylamides 下载免费PDF全文
Anna Ulmer Dr. Maciej Stodulski Stefanie V. Kohlhepp Christoph Patzelt Dr. Alexander Pöthig Dr. Wolfgang Bettray Dr. Tanja Gulder 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1444-1448
A tertiary hydroxy group α to a carboxyl moiety comprises a key structural motif in many bioactive substances. With the herein presented metal‐free rearrangement of imides triggered by hypervalent λ3‐iodane, an easy and selective way to gain access to such a compound class, namely α,α‐disubstituted‐α‐hydroxy carboxylamides, was established. Their additional methylene bromide side chain constitutes a useful handle for rapid diversification, as demonstrated by a series of further functionalizations. Moreover, the in situ formation of an iodine(III) species under the reaction conditions was proven. Our findings clearly corroborate that hypervalent λ3‐benziodoxolones are involved in these organocatalytic reactions. 相似文献
4.
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
5.
Dr. Sebastian Lars Müller Xinglong Zhou Dr. Peter Leonard Oxana Korzhenko Dr. Constantin Daniliuc Prof. Dr. Frank Seela 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(12):3077-3090
Silver-mediated α-dC–Ag+–β-dC hybrid base pairs decorated with 5-iodo- or 5-octadiynyl residues are well accommodated in duplex DNA. A strong Tm increase and favorable thermodynamic data for duplex DNA were observed after addition of silver ions. The phenomenon is particularly obvious when both nucleobases of the base pairs are functionalized. Neither the position of the base pair, nor the type of 5-substituent had a negative influence. On the contrary, functionalization of conventional silver-mediated β-dC–Ag+–β-dC homo base pairs showed a negative impact induced by the bulky substituents. To this end, cytosine modified 12-mer oligodeoxynucleotides were prepared by solid-phase synthesis employing new α-anomeric 2′-deoxycytidine phosphoramidites. A multigram scale synthesis was developed for 5-iodo-α-d -2′-deoxycytidine ( 1 ) employing the direct glycosylation of cytosine with Hoffer's α-d -halogenose followed by separation of anomeric DMT nucleosides. Regarding base-pair stability and functionalization silver-mediated α/β-dC hybrid base pairs were found to be superior to β/β-dC homo pairs. According to their extraordinary properties, they might find applications in DNA diagnostics, material science, or nanotechnology. 相似文献
6.
Prof. Dr. Frank Glorius 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8047-8051
A general and efficient methodology for the direct transition metal free trifluoromethylthiolation of a broad range of biologically relevant N‐heteroarenes is reported employing abundant sodium chloride as the catalyst. This method is operationally simple, exhibits high functional group tolerance, and does not require protecting groups. 相似文献
7.
8.
9.
Photobleaching was studied during recording of confocal scanning laser microscopy. Studies on fluorescent gels of FITC-labeled
dextran were used to evaluate differential bleaching along thez-axis. Differential bleaching along the z-axis was observed and it was seen that this was related to the numerical aperture
of the objective in use. This points to the conclusion that photon energy flux density is an important parameter in photobleaching.
To check if photon energy flux density heterogeneity is affected by local variation in the refractive index of the sample,
photobleaching rates were calculated for different fluorescent objects (sections of seeds, animal cells stained with nuclear
stains, immunocytochemistry preparations) and a pronounced similarity was found between photobleaching rates and DIC images. 相似文献
10.