全文获取类型
收费全文 | 982篇 |
免费 | 72篇 |
国内免费 | 1篇 |
专业分类
化学 | 822篇 |
晶体学 | 2篇 |
力学 | 12篇 |
数学 | 137篇 |
物理学 | 82篇 |
出版年
2023年 | 9篇 |
2022年 | 17篇 |
2021年 | 23篇 |
2020年 | 35篇 |
2019年 | 23篇 |
2018年 | 14篇 |
2017年 | 15篇 |
2016年 | 52篇 |
2015年 | 49篇 |
2014年 | 68篇 |
2013年 | 68篇 |
2012年 | 88篇 |
2011年 | 80篇 |
2010年 | 56篇 |
2009年 | 50篇 |
2008年 | 51篇 |
2007年 | 44篇 |
2006年 | 37篇 |
2005年 | 37篇 |
2004年 | 34篇 |
2003年 | 14篇 |
2002年 | 25篇 |
2001年 | 16篇 |
2000年 | 7篇 |
1999年 | 12篇 |
1998年 | 6篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 7篇 |
1992年 | 6篇 |
1988年 | 4篇 |
1986年 | 4篇 |
1968年 | 3篇 |
1961年 | 3篇 |
1932年 | 3篇 |
1916年 | 3篇 |
1912年 | 4篇 |
1907年 | 4篇 |
1904年 | 3篇 |
1900年 | 2篇 |
1883年 | 2篇 |
1878年 | 3篇 |
1877年 | 2篇 |
1876年 | 4篇 |
1875年 | 2篇 |
1872年 | 3篇 |
1871年 | 3篇 |
1868年 | 2篇 |
1867年 | 3篇 |
1862年 | 3篇 |
排序方式: 共有1055条查询结果,搜索用时 15 毫秒
21.
Lips F Hołyńska M Clérac R Linne U Schellenberg I Pöttgen R Weigend F Dehnen S 《Journal of the American Chemical Society》2012,134(2):1181-1191
Two K([2.2.2]crypt) salts of lanthanide-doped semimetal clusters were prepared, both of which contain at the same time two types of ternary intermetalloid anions, [Ln@Sn(7)Bi(7)](4-) and [Ln@Sn(4)Bi(9)](4-), in 0.70:0.30 (Ln = La) or 0.39:0.61 (Ln = Ce) ratios. The cluster shells represent nondeltahedral, fullerane-type arrangements of 14 or 13 main group metal atoms that embed the Ln(3+) cations. The assignment of formal +III oxidation states for the Ln sites was confirmed by means of magnetic measurements that reveal a diamagnetic La(III) compound and a paramagnetic Ce(III) analogue. Whereas the cluster anions with a 14-atomic main-group metal cage represent the second examples in addition to a related Eu(II) cluster published just recently, the 13-atomic cages exhibit a yet unprecedented enneahedral topology. In contrast to the larger cages, which accord to the Zintl-Klemm-Busmann electron number-structure correlation, the smaller clusters require a more profound interpretation of the bonding situation. Quantum chemical investigations served to shed light on these unusual complexes and showed significant narrowing of the HOMO-LUMO gap upon incorporation of Ce(3+) within the semimetal cages. 相似文献
22.
Glassford S Chan KL Byrne B Kazarian SG 《Langmuir : the ACS journal of surfaces and colloids》2012,28(6):3174-3179
The use of self-assembled monolayers is an established method to study the effect of surface properties on proteins and other biological materials. The generation of a monolayer with a gradient of chemical properties allows for the study of multiple surface properties simultaneously in a high throughput manner. Typically, in order to detect the presence of proteins or biological material on a surface, the use of additional dyes or tags is required. Here we present a novel method of studying the effect of gradient surface properties on protein adsorption and crystallization in situ through the use of ATR-FTIR spectroscopic imaging, which removes the need for additional labeling. We describe the successful application of this technique to the measurement of the growth of a gradient monolayer of octyltrichlorosilane across the surface of a silicon ATR element. ATR-FTIR imaging was also used to study the adsorption of lysozyme, as a model protein, onto the modified surface. The sensitivity of measurements obtained with a focal plane array (FPA) detector were improved though the use of pixel averaging which allowed small absorption bands to be detected with minimal effect on the spatial resolution along the gradient. Study of the effect of surface hydrophobicity on both adsorption of lysozyme to the element and lysozyme crystallization revealed that more lysozyme adsorbed to the hydrophobic side of the ATR element and more lysozyme crystals formed in the same region. These findings strongly suggest a correlation exists between surface protein adsorption and protein crystallization. This method could be applied to the study of other proteins and whole cells. 相似文献
23.
Paulina Lewandowska Izabela Szczuka Iwona Bednarz-Misa Berenika M. Szczniak-Siga Katarzyna Neubauer Magdalena Mierzchaa-Pasierb Marek Zawadzki Wojciech Witkiewicz Magorzata Krzystek-Korpacka 《Molecules (Basel, Switzerland)》2021,26(23)
The mechanisms underlying the antineoplastic effects of oxicams have not been fully elucidated. We aimed to assess the effect of classic and novel oxicams on the expression/secretion of macrophage-associated chemokines (RTqPCR/Luminex xMAP) in colorectal adenocarcinoma cells, and on the expression of upstream the non-steroidal anti-inflammatory drug (NSAID)-activated genes NAG1, NFKBIA, MYD88, and RELA, as well as at the chemokine profiling in colorectal tumors. Meloxicam downregulated CCL4 9.9-fold, but otherwise the classic oxicams had a negligible/non-significant effect. Novel analogues with a thiazine ring substituted with arylpiperazine and benzoyl moieties significantly modulated chemokine expression to varying degree, upregulated NAG1 and NFKBIA, and downregulated MYD88. They inhibited CCL3 and CCL4, and their effect on CCL2 and CXCL2 depended on the dose and exposure. The propylene linker between thiazine and piperazine nitrogens and one arylpiperazine fluorine substituent characterized the most effective analogue. Only CCL19 and CXCL2 were not upregulated in tumors, nor was CXCL2 in tumor-adjacent tissue compared to normal mucosa. Compared to adjacent tissue, CCL4 and CXCL2 were upregulated, while CCL2, CCL8, and CCL19 were downregulated in tumors. Tumor CCL2 and CCL7 increased along with advancing T and CCL3, and CCL4 along with the N stage. The introduction of arylpiperazine and benzoyl moieties into the oxicam scaffold yields effective modulators of chemokine expression, which act by upregulating NAG1 and interfering with NF-κB signaling. 相似文献
24.
25.
26.
Dr. Yumei Lin Dewang Xie Prof. Dr. Werner Massa Dr. Leonhard Mayrhofer Sina Lippert Benjamin Ewers Dr. Alexey Chernikov Prof. Dr. Martin Koch Prof. Dr. Stefanie Dehnen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(27):8806-8813
In situ transformations of selenidostannate frameworks in ionic liquids (ILs) were initiated by treatment of the starting phase K2[Sn2Se5] and the consecutive reaction products by means of temperature increase and/or amine addition. Along the reaction pathway, the framework dimensionalities of the five involved selenidostannate anions develop from 3D to 1D and back, both in top‐down and bottom‐up style. Addition of ethane‐1,2‐diamine (en) led to the reversion of the 2D→1D step from 2D‐{[Sn24Se56]16?} to 1D‐{[Sn6Se14]4?}. As rationalized by DFT investigations, the 2D anion is thermodynamically favored. Photoconductivity measurements reveal that all samples show Schottky contact behavior with absolute thresholds below 10 V. One of the samples exhibits conductive states within the energy range of visible photons. 相似文献
27.
Dr. Freddi Philippart Marcus Arlt Steve Gotzen Dr. Stefanie‐Joana Tenne Dr. Marco Bocola Dr. Hsui‐Hui Chen Dr. Leilei Zhu Prof. Ulrich Schwaneberg Prof. Jun Okuda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(41):13865-13871
A β‐barrel protein hybrid catalyst was prepared by covalently anchoring a Grubbs–Hoveyda type olefin metathesis catalyst at a single accessible cysteine amino acid in the barrel interior of a variant of β‐barrel transmembrane protein ferric hydroxamate uptake protein component A (FhuA). Activity of this hybrid catalyst type was demonstrated by ring‐opening metathesis polymerization of a 7‐oxanorbornene derivative in aqueous solution. 相似文献
28.
Synthesis of Phosphido Chalcogenido Bridged Dirhenium Complexes of the Type Re2(μ‐PCy2)(μ‐ER)(CO)8 (E = S, Se, Te; R = org. Residue) The reaction of Re2(μ‐Br)(μ‐PCy2)(CO)8 with nucleophiles MER (M = Na, Li; E = S, Se, Te; R = org. residue) gives via substitution of the bromido bridge phosphido chalcogenido bridged dirhenium complexes of the general formula Re2(μ‐PCy2)(μ‐ER)(CO)8. The new compounds were characterized by IR, 1H and 13C NMR spectroscopic data and by elemental analyses. In addition the molecular structures for E = S, Se, Te and R = Ph as well as for E = S and R = H, n‐Bu, 2‐pyridyl have been established by single crystal X‐ray analysis. 13C NMR spectra of Re2(μ‐PCy2)(μ‐EPh)(CO)8 (E = S, Se, Te) prove that the sulfur and selenium compounds are at room temperature dynamic molecules due to inversion of the pyramidal chalcogenido bridge. The tellurium compound, however, is rigid on the time scale of 13C NMR spectroscopy. Eventually the reactivity of the SH function of the novel complex Re2(μ‐PCy2)(μ‐SH)(CO)8 was investigated by reaction with Re2(CO)8(MeCN)2. In toluene at 90 °C the novel spirocyclic complex Re2(μ‐PCy2)(CO)8(μ4‐S)Re2(μ‐H)(CO)8 was formed by SH oxidative addition. 相似文献
29.
Perovskites as Precursors for Ni/La2O3 Catalysts in the Dry Reforming of Methane: Synthesis by Constant pH Co‐Precipitation,Reduction Mechanism and Effect of Ru‐Doping 下载免费PDF全文
Stefanie Kühl Hendrik Düdder Frank Girgsdies Kevin Kähler Martin Muhler Malte Behrens 《无机化学与普通化学杂志》2017,643(16):1088-1095
LaNiO3 perovskite is an interesting precursor for Ni/La2O3 catalysts for the dry reforming of methane at high temperatures. Precursors have been synthesized by co‐precipitation without, with 2.5 at %, and with 5 at % Ru doping. The presence of Ru leads to a stabilization of the perovskite structure and hinders the decomposition into NiO and Ruddlesden‐Popper mixed oxides Lan+1NinO3n+1, which was observed for the Ru‐free sample upon calcination at 1000 °C (n = 3). Upon reduction in hydrogen, a mechanism involving at least two steps was observed and the first major step was identified as the partial reduction of the precursor leading to a LaNiO2.5‐like intermediate. The second major step is the reduction to Ni metal supported on La2O3 independent of the Ru content of the catalyst. In the presence of Ru, indications for Ni‐Ru alloy formation and for a higher dispersion of the metallic phase were found. The catalytic activity in DRM of the catalyst containing 2.5 % Ru was superior to the catalysts with more or without Ru. Furthermore, the propensity of coke formation was reduced by the presence of Ru. 相似文献
30.