全文获取类型
| 收费全文 | 647篇 |
| 免费 | 17篇 |
专业分类
| 化学 | 569篇 |
| 力学 | 5篇 |
| 数学 | 42篇 |
| 物理学 | 48篇 |
出版年
| 2024年 | 2篇 |
| 2023年 | 9篇 |
| 2022年 | 19篇 |
| 2021年 | 18篇 |
| 2020年 | 36篇 |
| 2019年 | 43篇 |
| 2018年 | 13篇 |
| 2017年 | 7篇 |
| 2016年 | 27篇 |
| 2015年 | 22篇 |
| 2014年 | 40篇 |
| 2013年 | 23篇 |
| 2012年 | 53篇 |
| 2011年 | 43篇 |
| 2010年 | 32篇 |
| 2009年 | 27篇 |
| 2008年 | 33篇 |
| 2007年 | 27篇 |
| 2006年 | 25篇 |
| 2005年 | 31篇 |
| 2004年 | 18篇 |
| 2003年 | 13篇 |
| 2002年 | 18篇 |
| 2001年 | 14篇 |
| 2000年 | 11篇 |
| 1999年 | 8篇 |
| 1998年 | 5篇 |
| 1997年 | 4篇 |
| 1996年 | 2篇 |
| 1995年 | 3篇 |
| 1993年 | 6篇 |
| 1991年 | 6篇 |
| 1990年 | 1篇 |
| 1989年 | 1篇 |
| 1988年 | 1篇 |
| 1987年 | 4篇 |
| 1985年 | 2篇 |
| 1984年 | 1篇 |
| 1982年 | 1篇 |
| 1981年 | 1篇 |
| 1979年 | 2篇 |
| 1976年 | 4篇 |
| 1975年 | 2篇 |
| 1974年 | 3篇 |
| 1972年 | 1篇 |
| 1969年 | 1篇 |
| 1924年 | 1篇 |
排序方式： 共有664条查询结果，搜索用时 15 毫秒
611.
Synthesis and Crystal Structure of Terbium(III) meta‐Oxoborate Tb(BO2)3 (≡ TbB3O6) The terbium meta‐oxoborate Tb(BO2)3 (≡ TbB3O6) is obtained as single crystals by the reaction of terbium, Tb4O7 and TbCl3 with an excess of B2O3 in gastight sealed platinum ampoules at 950 °C after three weeks. The compound appears to be air‐ and water‐resistant and crystallizes as long, thin, colourless needles which tend to growth‐twinning due to their marked fibrous habit. The crystal structure of Tb(BO2)3 (orthorhombic, Pnma; a = 1598.97(9), b = 741.39(4), c = 1229.58(7) pm; Z = 16) contains strongly corrugated oxoborate layers {(BO2)‐} built of vertex‐linked [BO4]5‐ tetrahedra (d(B‐O) = 143 ‐ 154 pm, ?(O‐B‐O) = 102‐115°) which spread out parallel (100). The four crystallographically different Tb3+ cations all exhibit coordination numbers of eight towards the oxygen atoms (d(Tb‐O) = 228‐287 pm). The corresponding metal cation polyhedra [TbO8]13+ too convene to layers (composition: {(Tb2O11)16‐}) which are likewise oriented parallel to the (100) plane. 相似文献
612.
613.
Joris J. Haven;Tanja Junkers; 《European journal of organic chemistry》2017,2017(44):6474-6482
Polymerizations are challenging to monitor online. Next to spectrometric information, which indicates the composition, progress, and identity of polymers, other characterization methods also need to be employed for paramount monitoring. Information on molecular weight distributions and end group patterns are often indispensable for accurate process (and product) control. An overview of existing characterization methods, which can be used for online monitoring, and eventually for automating, multistep polymerizations, is given. 相似文献
614.
2,3-Oxidosqualene cyclases (OSC) are key enzymes in sterol biosynthesis. They catalyze the stereoselective cyclization and skeletal rearrangement of (3S)-2,3-oxidosqualene to lanosterol in mammals and fungi and to cycloartenol in algae and higher plants. Sequence information and proposed mechanism of 2,3-oxidosqualene cyclases are closely related to those of squalene-hopene cyclases (SHC), which represent functional analogs of OSCs in bacteria. SHCs catalyze the cationic cyclization cascade converting the linear triterpene squalene to fused ring compounds called hopanoids. High stereoselectivity and precision of the skeletal rearrangements has aroused the interest of researchers for nearly half a century, and valuable data on studying mechanistic details in the complex enzyme-catalyzed cyclization cascade has been collected. Today, interest in cyclases is still unbroken, because OSCs became targets for the development of antifungal and hypocholesterolemic drugs. However, due to the large size and membrane-bound nature of OSCs, three-dimensional structural information is still not available, thus preventing a complete understanding of the atomic details of the catalytic mechanism. In this work, we discuss results gained from homology modeling of human OSC based on structural information of SHC from Alicyclobacillus acidocaldarius and propose a structural model of human OSC. The model is in accordance with previously performed experimental studies with mechanism-based suicide inhibitors and mutagenesis experiments with altered activity and product specificity. Structural insight should strongly stimulate structure-based design of antifungal or cholesterol-lowering drugs. 相似文献
615.
616.
Chang‐Uk Lee Gernot Hahne Jonas Hanske Tanja Bange David Bier Christoph Rademacher Sven Hennig Tom N. Grossmann 《Angewandte Chemie (International ed. in English)》2015,54(46):13796-13800
PTEN is a dual‐specificity protein tyrosine phosphatase. As one of the central tumor suppressors, a thorough regulation of its activity is essential for proper cellular homeostasis. The precise implications of PTEN inhibition by reactive oxygen species (e.g. H2O2) and the subsequent structural consequences remain elusive. To study the effects of PTEN inhibition, bisperoxidovanadium (bpV) complexes serve as important tools with the potential for the treatment of nerve injury or cardiac ischemia. However, their mode of action is unknown, hampering further optimization and preventing therapeutic applications. Based on protein crystallography, mass spectrometry, and NMR spectroscopy, we elucidate the molecular basis of PTEN inhibition by H2O2 and bpV complexes. We show that both molecules inhibit PTEN via oxidative mechanisms resulting in the formation of the same intramolecular disulfide, therefore enabling the reactivation of PTEN under reductive conditions. 相似文献
617.
Mohammad Tavakkoli Dr. Tanja Kallio Olivier Reynaud Prof. Albert G. Nasibulin Dr. Christoffer Johans Dr. Jani Sainio Dr. Hua Jiang Prof. Esko I. Kauppinen Prof. Kari Laasonen 《Angewandte Chemie (International ed. in English)》2015,54(15):4535-4538
Efficient hydrogen evolution reaction (HER) through effective and inexpensive electrocatalysts is a valuable approach for clean and renewable energy systems. Here, single‐shell carbon‐encapsulated iron nanoparticles (SCEINs) decorated on single‐walled carbon nanotubes (SWNTs) are introduced as a novel highly active and durable non‐noble‐metal catalyst for the HER. This catalyst exhibits catalytic properties superior to previously studied nonprecious materials and comparable to those of platinum. The SCEIN/SWNT is synthesized by a novel fast and low‐cost aerosol chemical vapor deposition method in a one‐step synthesis. In SCEINs the single carbon layer does not prevent desired access of the reactants to the vicinity of the iron nanoparticles but protects the active metallic core from oxidation. This finding opens new avenues for utilizing active transition metals such as iron in a wide range of applications. 相似文献
618.
619.
In this paper the modification of polyolefins, especially polypropylene (PP), with maleimides is discussed. As there are many problems associated with the analysis of the grafting reaction, commercially available squalane and eicosane were used as model compounds for ethylene‐propylene‐copolymer (EPR) and polyethylene (PE). 2,4,6,8‐Tetramethylnonane (TMN) was synthesized as a novel model compound for PP. N‐Phenylmaleimide and maleimido benzoic acid were grafted onto the oligomers in solution using 2,5‐dimethyl‐2,5‐di‐(tert‐butyl‐peroxy)‐3‐hexyne (Luperox 130) as radical initiator. The grafting efficiency was determined by NMR‐, UV‐spectroscopy, gravimetry and gas‐chromatography. The influence of several reaction parameters on homopolymerformation, amount of modified oligomer and grafting efficiency could be elaborated. NMR‐spectroscopy and SEC were used to analyse the nature of the grafts. Grafting yields were almost quantitative using up to more than 10 mol% monomer, but dropped at higher monomer concentrations to about 60%. The amount of modified oligomer could be increased with higher monomer concentrations or reaction temperatures. Grafting of polymers was done by reactive extrusion. Products were analysed by IR‐spectroscopy. Optimal grafting yields could be achieved with 1 wt% monomer and 0.5 wt% peroxide concentration. 相似文献
620.
Kuethe DO Pietrass T Behr VC 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,177(2):212-220
The physics of spin-rotation interaction in roughly spherical perfluorinated gas molecules has been studied extensively. But, it is difficult to calculate a spin-lattice relaxation time constant T1 for any given temperature and pressure using the published literature. We give a unified parameterization that makes use of the Clausius equation of state, Lennard-Jones collision dynamics, and a formulaic temperature dependence for collision cross section for rotational change. The model fits T1s for SF6, CF4, C2F6, and c-C4F8 for temperatures from 180 to 360 K and pressures from 2 to 210 kPa and in mixtures with other common gases to within our limits of measurement. It also fits previous data tabulated according to known number densities. Given a pressure, temperature, and mixture composition, one can now calculate T1s for common laboratory conditions with a known accuracy, typically 0.5%. Given the success of the model's formulaic structure, it is likely to apply to even broader ranges of physical conditions and to other gases that relax by spin-rotation interaction. 相似文献