全文获取类型
收费全文 | 6181篇 |
免费 | 1376篇 |
国内免费 | 817篇 |
专业分类
化学 | 4123篇 |
晶体学 | 290篇 |
力学 | 1025篇 |
综合类 | 53篇 |
数学 | 322篇 |
物理学 | 2561篇 |
出版年
2024年 | 36篇 |
2023年 | 71篇 |
2022年 | 190篇 |
2021年 | 211篇 |
2020年 | 284篇 |
2019年 | 237篇 |
2018年 | 217篇 |
2017年 | 239篇 |
2016年 | 368篇 |
2015年 | 336篇 |
2014年 | 372篇 |
2013年 | 596篇 |
2012年 | 422篇 |
2011年 | 412篇 |
2010年 | 350篇 |
2009年 | 333篇 |
2008年 | 323篇 |
2007年 | 362篇 |
2006年 | 376篇 |
2005年 | 341篇 |
2004年 | 291篇 |
2003年 | 312篇 |
2002年 | 279篇 |
2001年 | 149篇 |
2000年 | 165篇 |
1999年 | 134篇 |
1998年 | 152篇 |
1997年 | 156篇 |
1996年 | 121篇 |
1995年 | 109篇 |
1994年 | 81篇 |
1993年 | 57篇 |
1992年 | 45篇 |
1991年 | 40篇 |
1990年 | 40篇 |
1989年 | 24篇 |
1988年 | 31篇 |
1987年 | 20篇 |
1986年 | 19篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 20篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有8374条查询结果,搜索用时 0 毫秒
991.
Anke Schwarzer Sabine Fels Uwe Bhme 《Acta Crystallographica. Section C, Structural Chemistry》2015,71(6):511-516
Dimethyl[N‐(4‐oxidopent‐3‐en‐2‐ylidene)valinato‐κ3O,N,O′]silicon(IV), C12H21NO3Si, (II), crystallizes in the orthorhombic space group P212121. The chiral compound undergoes two sharp enantiotropic phase transitions upon cooling. The first transformation occurs at 163 K to yield a unit cell with one axis having double length. This intermediate‐temperature form has the monoclinic space group P21. The second transition takes place at 142 K and converts the single crystal into the low‐temperature form in the orthorhombic space group P212121. This transition proceeds under tripling of the a axis of the high‐temperature form. Both phase transitions are fully reversible and correspond to order–disorder transitions of the isopropyl group of the valine unit in the ligand backbone. The phase transitions presented here raise questions, since they do not fit into the rules of group–subgroup relationships. 相似文献
992.
Maurizio Casalino Giuseppe Coppola Richard M. De La Rue Dylan F. Logan 《Laser \u0026amp; Photonics Reviews》2016,10(6):895-921
Silicon‐based technologies provide an ideal platform for the monolithic integration of photonics and microelectronics. In this context, a variety of passive and active silicon photonic devices have been developed to operate at telecom and datacom wavelengths, at which silicon has minimal optical absorption ‐ due to its bandgap of 1.12 eV. Although in principle this transparency window limits the use of silicon for optical detection at wavelengths above 1.1 μm, in recent years tremendous advances have been made in the field of all‐silicon sub‐bandgap photodetectors at telecom and datacom wavelengths. By taking advantage of emerging materials and novel structures, these devices are becoming competitive with the more well‐established technologies, and are opening new and intriguing perspectives. In this paper, a review of the state‐of‐the‐art is presented. Devices based on defect‐mediated absorption, two‐photon absorption and the internal photoemission effect are reported, their working principles are elucidated and their performance discussed and compared.
993.
Strongly Coupled Pt–Ni2GeO4 Hybrid Nanostructures as Potential Nanocatalysts for CO Oxidation 下载免费PDF全文
Zhuo Wang Shuang Yao Jing Feng Dapeng Liu Shuyan Song Prof. Hongjie Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(42):14768-14771
A facile and low‐cost method has been developed to successfully fabricate 3D flower‐like and sphere‐like Ni2GeO4 nanostructures with tunable sizes and shapes. It is found that the hard template, polymethyl methacrylate (PMMA) nanopsheres, is essential to the formation of the final products. The as‐prepared nanostructures can serve as an outstanding support for Pt nanoparticles after surface modification with L ‐lysine. In the catalytic test of CO oxidation, Pt–Ni2GeO4 nanoflowers exhibited much higher catalytic performance compared with Pt–Ni2GeO4 nanospheres, representing a typical size‐dependent catalytic property. 相似文献
994.
Direct On‐Surface Patterning of a Crystalline Laminar Covalent Organic Framework Synthesized at Room Temperature 下载免费PDF全文
Alejandro de la Peña Ruigómez David Rodríguez‐San‐Miguel Dr. Kyriakos C. Stylianou Dr. Massimiliano Cavallini Dr. Denis Gentili Dr. Fabiola Liscio Prof. Silvia Milita Dr. Otello Maria Roscioni Dr. Maria Luisa Ruiz‐González Carlos Carbonell Prof. Daniel Maspoch Dr. Rubén Mas‐Ballesté Dr. José Luis Segura Dr. Félix Zamora 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(30):10666-10670
We report herein an efficient, fast, and simple synthesis of an imine‐based covalent organic framework (COF) at room temperature (hereafter, RT‐COF‐1 ). RT‐COF‐1 shows a layered hexagonal structure exhibiting channels, is robust, and is porous to N2 and CO2. The room‐temperature synthesis has enabled us to fabricate and position low‐cost micro‐ and submicropatterns of RT‐COF‐1 on several surfaces, including solid SiO2 substrates and flexible acetate paper, by using lithographically controlled wetting and conventional ink‐jet printing. 相似文献
995.
Asymmetric Catalysis with Silicon‐Based Cuprates: Enantio‐ and Regioselective Allylic Substitution of Linear Precursors 下载免费PDF全文
Alexander Hensel Prof. Dr. Martin Oestreich 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(25):9062-9065
An enantio‐ and regioselective allylic silylation of linear allylic phosphates that makes use of catalytically generated cuprate‐type silicon nucleophiles is reported. The method relies on soft bis(triorganosilyl) zincs as silicon pronucleophiles that are prepared in situ from the corresponding hard lithium reagents by transmetalation with ZnCl2. With a preformed chiral N‐heterocyclic carbene–copper(I) complex as catalyst, exceedingly high enantiomeric excesses are achieved. The new method is superior to existing ones using a silicon–boron reagent as the source of the silicon nucleophile. 相似文献
996.
Heng Zhou Mingle Liao Shu‐Wei Huang Linjie Zhou Kun Qiu Chee Wei Wong 《Laser \u0026amp; Photonics Reviews》2016,10(6):1054-1061
Nonlinear wave mixing in mesoscopic silicon structures is a fundamental nonlinear process with broad impact and applications. Silicon nanowire waveguides, in particular, have large third‐order Kerr nonlinearity, enabling salient and abundant four‐wave‐mixing dynamics and functionalities. Besides the Kerr effect, in silicon waveguides two‐photon absorption generates high free‐carrier densities, with corresponding fifth‐order nonlinearity in the forms of free‐carrier dispersion and free‐carrier absorption. However, whether these fifth‐order free‐carrier nonlinear effects can lead to six‐wave‐mixing dynamics still remains an open question until now. Here we report the demonstration of free‐carrier‐induced six‐wave mixing in silicon nanowires. Unique features, including inverse detuning dependence of six‐wave‐mixing efficiency and its higher sensitivity to pump power, are originally observed and verified by analytical prediction and numerical modeling. Additionally, asymmetric sideband generation is observed for different laser detunings, resulting from the phase‐sensitive interactions between free‐carrier six‐wave‐mixing and Kerr four‐wave‐mixing dynamics. These discoveries provide a new path for nonlinear multi‐wave interactions in nanoscale platforms.
997.
采用悬浮液直接进样电感耦合等离子体发射光谱法(ICP–OES)测定高纯氢氧化铝中铁、钛、硅、铬的含量。悬浮液用电磁搅拌器搅拌,均匀地分散在溶液中,通过仪器蠕动泵进入雾化室,均匀无阻地导入ICP光源。Fe,Ti,Si,Cr的分析谱线分别为259.940,336.112,251.611,205.552 nm;RF功率为1 300W,等离子体气流量为13.0 L/min,雾化器气体流量为0.60 L/min,辅助气流量为1.00 L/min。Fe,Ti,Si,Cr的质量浓度分别在0.0~30.0,0.0~15.0,0.0~90.0,0.0~15.0μg/m L范围内与信号强度呈良好的线性,线性相关系数均大于0.999,方法的检出限为0.027 6~0.993 9μg/m L,测量结果的相对标准偏差为0.65%~6.84%(n=11),回收率为95.0%~104.8%。该法抗干扰能力强、线性范围宽,适用于高纯氢氧化铝中铁、钛、硅、铬含量的分析。 相似文献
998.
《Macromolecular rapid communications》2017,38(15)
Controlling self‐assembly behaviors of liquid crystals is a fundamental issue for designing them as intelligent actuators. Here, anisotropic porous polyvinylidene fluoride film is utilized as a template to induce homogeneous alignment of liquid crystals. The mechanism of liquid crystal alignment induced by anisotropic porous polyvinylidene fluoride film is illustrated based on the relationship between the alignment behavior of liquid crystals and surface microstructure of anisotropic polyvinylidene fluoride film. Liquid crystal elastomer actuators with fast responsiveness, large strain change, and reversible actuation behaviors are achieved by the photopolymerization of liquid crystal monomer in liquid crystal cells coated with anisotropic porous films.
999.
《Macromolecular rapid communications》2017,38(16)
Porous polymeric monoliths with densities as low as ≈0.060 g cm−3 are prepared in a gel‐emulsion template way, of which the stabilizer employed is a newly discovered acidified aramid fiber that is so efficient that 0.05% (w/v, accounts for continuous phase) is enough to gel the system. The porous monoliths as obtained can be dried at ambient conditions, avoiding energy‐consuming processes. Importantly, the monoliths show selective adsorption to HCHO, and the corresponding adsorption capacity ( M6 ) is ≈2700 mg g−1, the best result that is reported until now. More importantly, the monoliths can be reused after drying. 相似文献
1000.
《Angewandte Chemie (International ed. in English)》2017,56(33):9990-9993
The thermal reduction of N2O by CO mediated by the metal‐free cluster cations [Si2Ox].+ (x =2–5) has been examined in the gas phase using Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometry in conjunction with quantum chemical calculations. Three successive oxidation/reduction steps occur starting from [Si2O2].+ and N2O to form eventually [Si2O5].+; the latter as well as the intermediate oxide cluster ions react sequentially with CO molecules to regenerate [Si2O2].+. Thus, full catalytic cycles occur at ambient conditions in the gas phase. Mechanistic aspects of these sequential redox processes have been addressed to reveal the electronic origins of these unparalleled reactions. 相似文献