全文获取类型
收费全文 | 26712篇 |
免费 | 2690篇 |
国内免费 | 1726篇 |
专业分类
化学 | 19138篇 |
晶体学 | 226篇 |
力学 | 78篇 |
综合类 | 38篇 |
数学 | 20篇 |
物理学 | 11628篇 |
出版年
2024年 | 46篇 |
2023年 | 211篇 |
2022年 | 708篇 |
2021年 | 722篇 |
2020年 | 845篇 |
2019年 | 824篇 |
2018年 | 700篇 |
2017年 | 787篇 |
2016年 | 1263篇 |
2015年 | 1259篇 |
2014年 | 1257篇 |
2013年 | 2263篇 |
2012年 | 1598篇 |
2011年 | 1758篇 |
2010年 | 1457篇 |
2009年 | 1860篇 |
2008年 | 1741篇 |
2007年 | 1848篇 |
2006年 | 1691篇 |
2005年 | 1337篇 |
2004年 | 1141篇 |
2003年 | 967篇 |
2002年 | 744篇 |
2001年 | 595篇 |
2000年 | 536篇 |
1999年 | 497篇 |
1998年 | 405篇 |
1997年 | 375篇 |
1996年 | 302篇 |
1995年 | 257篇 |
1994年 | 186篇 |
1993年 | 175篇 |
1992年 | 145篇 |
1991年 | 110篇 |
1990年 | 68篇 |
1989年 | 59篇 |
1988年 | 111篇 |
1987年 | 48篇 |
1986年 | 30篇 |
1985年 | 28篇 |
1984年 | 31篇 |
1982年 | 26篇 |
1981年 | 28篇 |
1980年 | 22篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1976年 | 7篇 |
1973年 | 10篇 |
1972年 | 7篇 |
1971年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Marcos Juanes Rizalina Tama Saragi Cristbal Prez Luca Evangelisti Lourdes Enríquez Martín Jaraíz Alberto Lesarri 《Molecules (Basel, Switzerland)》2022,27(8)
Weakly-bound intermolecular clusters constitute reductionist physical models for non-covalent interactions. Here we report the observation of the monomer, the dimer and the monohydrate of 2-adamantanol, a secondary alcohol with a bulky ten-carbon aliphatic skeleton. The molecular species were generated in a supersonic jet expansion and characterized using broadband chirped-pulse microwave spectroscopy in the 2–8 GHz frequency region. Two different gauche-gauche O-H···O hydrogen-bonded isomers were observed for the dimer of 2-adamantanol, while a single isomer was observed for the monomer and the monohydrate. The experimental rotational parameters were compared with molecular orbital calculations using density functional theory (B3LYP-D3(BJ), B2PLYP-D3(BJ), CAM-B3LYP-D3(BJ), ωB97XD), additionally providing energetic and electron density characterization. The shallow potential energy surface makes the dimer an interesting case study to benchmark dispersion-corrected computational methods and conformational search procedures. 相似文献
992.
Federico Wallace Carolina Fontana Fernando Ferreira Cristina Olivaro 《Molecules (Basel, Switzerland)》2022,27(8)
An immunoadjuvant preparation (named Fraction B) was obtained from the aqueous extract of Quillaja brasiliensis leaves, and further fractionated by consecutive separations with silica flash MPLC and reverse phase HPLC. Two compounds were isolated, and their structures elucidated using a combination of NMR spectroscopy and mass spectrometry. One of these compounds is a previously undescribed triterpene saponin (Qb1), which is an isomer of QS-21, the unique adjuvant saponin employed in human vaccines. The other compound is a triterpene saponin previously isolated from Quillaja saponaria bark, known as S13. The structure of Qb1 consists of a quillaic acid residue substituted with a β-d-Galp-(1→2)-[β-d-Xylp-(1→3)]-β-d-GlcpA trisaccharide at C3, and a β-d-Xylp-(1→4)-α-l-Rhap-(1→2)-[α-l-Arap-(1→3)]-β-d-Fucp moiety at C28. The oligosaccharide at C28 was further substituted at O4 of the fucosyl residue with an acyl group capped with a β-d-Xylp residue. 相似文献
993.
ATR-FTIR光谱技术在聚合物膜研究中的应用 总被引:7,自引:0,他引:7
红外光谱是聚合物研究中常用的一种表征手段,而衰减全反射红外光谱(ATR-FTIR)更是由于在研究聚合物薄膜方面具有显著的优势而被广泛使用。逐层组装(layer-by-layer Assembly)技术是一种常用的组装聚合物超薄膜的方法,ATR-FTIR光谱技术的引入可以在获取膜组装过程中相应信息的同时有效地避免表征过程中对样品的损害。另一方面,ATR-FTIR方法与二维相关光谱技术(two-dimensional correlation spectroscopy, 2D correlation spectroscopy)相结合也是研究小分子(主要是水分子)在聚合物薄膜中的渗透行为的有效手段。本文对ATR-FTIR的基本原理和显著特点作了介绍,并以实例阐述该方法在逐层组装技术和水分子在薄膜内渗透行为研究两方面的应用。 相似文献
994.
A short retrospection is given on the development of M?ssbauer spectroscopy and on the early period of its application to
heterogeneous catalysis in Hungary. Besides the historical view, we present results of recent studies of a latest application
on a nanosystem. Namely, catalytic centres in Fe-ZSM-5 are studied by in situ spectroscopy, the results are correlated with
parallel activity measurements in the decomposition of N2O. Changes in paramagnetic relaxation features are interpreted as the effects of Fe2+/Fe3+ interconversions. From the analysis, the dominance of the mononuclear species is suggested at lower temperature (620 K).
The dinuclear Fe(3+)
framework-O-Fe(2+)
extra-framework species play probably more expressed role at higher temperatures (∼ 770 K) in the decompositon of nitrous oxide. 相似文献
995.
Four rapid and low-cost vanguard analytical systems (NIR and UV-vis spectroscopy, a headspace-mass based artificial nose and a voltammetric artificial tongue), together with chemometric pattern recognition techniques, were applied and compared in addressing a food authentication problem: the distinction between wine samples from the same Italian oenological region, according to the grape variety.Specifically, 59 certified samples belonging to the Barbera d’Alba and Dolcetto d’Alba appellations and collected from the same vintage (2007) were analysed.The instrumental responses, after proper data pre-processing, were used as fingerprints of the characteristics of the samples: the results from principal component analysis and linear discriminant analysis were discussed, comparing the capability of the four analytical strategies in addressing the problem studied. 相似文献
996.
Desislava Staneva 《International Journal of Polymer Analysis and Characterization》2013,18(5):390-397
Seven newly synthesized poly(propyleneamine) dendrimers, modified with 1,8-naphthalimides, have been investigated by infrared, UV-vis, and fluorescence spectroscopy. The influence of the nature of the substituents at the C-4 position of the naphthalene ring on the spectral properties of the dendrimers is discussed. 相似文献
997.
998.
Re‐Appearance of Cooperativity in Ultra‐Small Spin‐Crossover [Fe(pz){Ni(CN)4}] Nanoparticles 下载免费PDF全文
Haonan Peng Dr. Simon Tricard Gautier Félix Dr. Gábor Molnár Dr. William Nicolazzi Dr. Lionel Salmon Dr. Azzedine Bousseksou 《Angewandte Chemie (International ed. in English)》2014,53(41):10894-10898
A reverse nanoemulsion technique was used for the elaboration of [Fe(pz){Ni(CN)4}] nanoparticles. Low‐temperature micellar exchange made it possible to elaborate ultra‐small nanoparticles with sizes down to 2 nm. When decreasing the size of the particles from 110 to 12 nm the spin transition shifts to lower temperatures, becomes gradual, and the hysteresis shrinks. On the other hand, a re‐opening of the hysteresis was observed for smaller (2 nm) particles. A detailed 57Fe Mössbauer spectroscopy analysis was used to correlate this unusual phenomenon to the modification of the stiffness of the nanoparticles thanks to the determination of their Debye temperature. 相似文献
999.
用冷冻升华法制备了浓度为1×10-4 和2×10-5 g/mL的单链无规聚苯乙烯(a-PS). 利用FTIR测试方法, 测定a-PS在等温处理时红外吸收峰的时间依赖性与温度依赖性, 研究样品中链缠结和链结构单元的堆积等因素对红外吸收峰的影响, 进而探讨链缠结对a-PS分子运动的影响. 同时, 也通过二维相关分析来研究a-PS等温实验过程中, 链缠结的变化情况以及官能团之间的变化顺序, 推断在a-PS等温时, 与链结构单元的堆积相联系的苯环振动首先发生, 其次才是与链缠结相关联的CH2振动发生变化, 并由此确定缠结对冷冻升华a-PS分子运动的影响. 相似文献
1000.