全文获取类型
收费全文 | 574篇 |
免费 | 27篇 |
国内免费 | 7篇 |
专业分类
化学 | 435篇 |
力学 | 5篇 |
数学 | 89篇 |
物理学 | 79篇 |
出版年
2023年 | 6篇 |
2022年 | 8篇 |
2021年 | 17篇 |
2020年 | 8篇 |
2019年 | 19篇 |
2018年 | 11篇 |
2017年 | 5篇 |
2016年 | 25篇 |
2015年 | 12篇 |
2014年 | 18篇 |
2013年 | 25篇 |
2012年 | 27篇 |
2011年 | 39篇 |
2010年 | 20篇 |
2009年 | 20篇 |
2008年 | 39篇 |
2007年 | 37篇 |
2006年 | 43篇 |
2005年 | 27篇 |
2004年 | 33篇 |
2003年 | 19篇 |
2002年 | 28篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
排序方式: 共有608条查询结果,搜索用时 15 毫秒
31.
Dr. Heiner Friedrich Dr. Peter M. Frederik Prof. Dr. Gijsbertus de With Dr. Nico A. J. M. Sommerdijk 《Angewandte Chemie (International ed. in English)》2010,49(43):7850-7858
The investigation of solution‐borne nanostructures by transmission electron microscopy (TEM) is a frequently used analytical method in materials chemistry. In many cases, the preparation of the TEM sample involves drying and staining steps, and the collection of images leads to the interaction of the specimen with the electron beam. Both aspects call for cautious interpretation of the resulting electron micrographs. Alternatively, a near‐native solvated state can be preserved by cryogenic vitrification and subsequent imaging by low‐dose cryogenic TEM. In this Minireview, we provide a critical analysis of sample preparation, and more importantly, of the acquisition and interpretation of electron micrographs. This overview should provide a framework for the application of (cryo)‐TEM as a powerful and reliable tool for the analysis of colloidal and self‐assembled structures with nanoscopic dimensions. 相似文献
32.
Nico Smit Ruben Musson Fred Romijn Huub Van Rossum Johannes Van Pelt 《Photochemistry and photobiology》2010,86(2):360-366
Calcineurin (Cn) is the target of immunosuppressive drugs used for maintenance therapy of transplant patients. UV radiation is also known to be immunosuppressive and, like the Cn inhibitors, UV has been shown to positively influence various inflammatory skin diseases. Recently, Cn activity has been demonstrated in skin and skin cell cultures. In the present study we have investigated the effects of UV(A-1) irradiation on Cn activity in skin. In total skin we found a significant reduction in Cn activity after exposure to 450 kJ m−2 of UVA-1 (340–400 nm). In repeated experiments cultures of fibroblasts and keratinocytes also showed dose-dependent and selective reduction in Cn activity after UVA-1 irradiation. UVB irradiation caused a decrease in the Cn activity of one of two fibroblast cultures and was ineffective in keratinocytes. In Jurkat cells and PBMC UVA-1 reduced Cn activity and also the production of cytokines such as interleukin (IL)-2, γ-interferon, IL-4 and IL-10 that are controlled by the Ca2+–Cn pathway. These results indicate that UV(A-1) irradiation may lead to inactivation of Cn in the skin and thus suppress the skin immune system in a similar fashion to the Cn inhibitors. 相似文献
33.
Chin PT Donega Cde M van Bavel SS Meskers SC Sommerdijk NA Janssen RA 《Journal of the American Chemical Society》2007,129(48):14880-14886
In this work we present the preparation of highly luminescent anisotropic CdTe/CdSe colloidal heteronanocrystals. The reaction conditions used (low temperature, slow precursor addition, and surfactant composition) resulted in a tunable shape from prolate to branched CdTe/CdSe nanocrystals. Upon CdSe shell growth the heteronanocrystals show a gradual evolution from type-I to type-II optical behavior. These heteronanocrystals show a remarkably high photoluminescence quantum yield (up to 82%) and negligible thermally induced quenching up to temperatures as high as 373 K. 相似文献
34.
M. Sc. Markus Warnke Tobias Jung Dr. Juri Dermer Karin Hipp Dr. Nico Jehmlich Prof. Dr. Martin von Bergen Sascha Ferlaino Dr. Alexander Fries Prof. Dr. Michael Müller Prof. Dr. Matthias Boll 《Angewandte Chemie (International ed. in English)》2016,55(5):1881-1884
The hydroxylation of vitamin D3 (VD3, cholecalciferol) side chains to give 25‐hydroxyvitamin D3 (25OHVD3) is a crucial reaction in the formation of the circulating and biologically active forms of VD3. It is usually catalyzed by cytochrome P450 monooxygenases that depend on complex electron donor systems. Cell‐free extracts and a purified Mo enzyme from a bacterium anaerobically grown with cholesterol were employed for the regioselective, ferricyanide‐dependent hydroxylation of VD3 and proVD3 (7‐dehydrocholesterol) into the corresponding tertiary alcohols with greater than 99 % yield. Hydroxylation of VD3 strictly depends on a cyclodextrin‐assisted isomerization of VD3 into preVD3, the actual enzymatic substrate. This facile and robust method developed for 25OHVD3 synthesis is a novel example for the concept of substrate‐engineered catalysis and offers an attractive alternative to chemical or O2 /electron‐donor‐dependent enzymatic procedures. 相似文献
35.
General,Highly Selective Synthesis of 1,3‐ and 1,4‐Difunctionalized Building Blocks by Regiodivergent Epoxide Opening 下载免费PDF全文
Nico Funken Felix Mühlhaus Prof. Dr. Andreas Gansäuer 《Angewandte Chemie (International ed. in English)》2016,55(39):12030-12034
We describe a regiodivergent epoxide opening (REO) featuring a catalyst‐controlled synthesis of enantiomerically and diastereomerically highly enriched or pure syn‐ and anti‐ 1,3‐ and 1,4‐difunctionalized building blocks from a common epoxide precursor. The REO is attractive for natural product synthesis and as a branching reaction for diversity‐oriented synthesis with epoxides. 相似文献
36.
Increasing the Chemical‐Shift Dispersion of Unstructured Proteins with a Covalent Lanthanide Shift Reagent 下载免费PDF全文
Dr. Christoph Göbl Moritz Resch Dr. Madeleine Strickland Christoph Hartlmüller Martin Viertler Dr. Nico Tjandra Prof. Dr. Tobias Madl 《Angewandte Chemie (International ed. in English)》2016,55(47):14847-14851
The study of intrinsically disordered proteins (IDPs) by NMR often suffers from highly overlapped resonances that prevent unambiguous chemical‐shift assignments, and data analysis that relies on well‐separated resonances. We present a covalent paramagnetic lanthanide‐binding tag (LBT) for increasing the chemical‐shift dispersion and facilitating the chemical‐shift assignment of challenging, repeat‐containing IDPs. Linkage of the DOTA‐based LBT to a cysteine residue induces pseudo‐contact shifts (PCS) for resonances more than 20 residues from the spin‐labeling site. This leads to increased chemical‐shift dispersion and decreased signal overlap, thereby greatly facilitating chemical‐shift assignment. This approach is applicable to IDPs of varying sizes and complexity, and is particularly helpful for repeat‐containing IDPs and low‐complexity regions. This results in improved efficiency for IDP analysis and binding studies. 相似文献
37.
Nico Schwarze Dr. Simon Steinhauer Beate Neumann Dr. Hans‐Georg Stammler Prof. Dr. Berthold Hoge 《Angewandte Chemie (International ed. in English)》2016,55(52):16161-16164
The tris(pentafluoroethyl)silanide anion is accessible by the deprotonation of Si(C2F5)3H at low temperatures. Subsequent quenching of the resulting salt‐like compounds with suitable electrophiles, such as transition‐metal complexes or Group 14 element halides, leads to a plethora of novel tris(pentafluoroethyl)silane derivatives. This underlines the versatility of Li[Si(C2F5)3] as a powerful nucleophilic transfer reagent. 相似文献
38.
39.
Dr. Nico Röder Dr. Tomasz Marszalek Daniel Limbach Prof. Wojciech Pisula Prof. Heiner Detert 《Chemphyschem》2019,20(3):463-469
π-Conjugated molecules with the shape of St. Andrew′s cross have been synthesized via fourfold Huisgen reaction. Four 2,5-diaryl-1,3,4-oxadiazol arms are attached to a central pyrazine nucleus. These fluorescent stars, when decorated with a rim of eight alkoxy side chains are discotic liquid crystals. Depending on the substitution pattern, the width of the liquid phase varies within a broad range of 25 °C to 250 °C. In their liquid crystalline phase, the molecules assemble in a typical hexagonal columnar supramolecular arrangement. 相似文献
40.
The ligand‐exchange mechanism of solvated Be2+ cations has been studied by means of DFT calculations (RB3LYP/6‐311+G**). Ligand exchange around [BeL4]2+, where L=H2O, NH3, CO2, formaldehyde (H2CO), HCN, N2, and CO, was found to follow an associative interchange (Ia) process in all cases. The size of the activation barrier is almost independent of the type of donor atom, and depends mainly on the hybridization undergone by the donor atom. This, in turn, suggests that steric effects play a major role in solvent‐ and ligand‐exchange reactions in Be2+ systems. 相似文献