全文获取类型
收费全文 | 13062篇 |
免费 | 1280篇 |
国内免费 | 1056篇 |
专业分类
化学 | 9706篇 |
晶体学 | 151篇 |
力学 | 392篇 |
综合类 | 74篇 |
数学 | 2088篇 |
物理学 | 2987篇 |
出版年
2024年 | 20篇 |
2023年 | 151篇 |
2022年 | 316篇 |
2021年 | 400篇 |
2020年 | 441篇 |
2019年 | 403篇 |
2018年 | 349篇 |
2017年 | 336篇 |
2016年 | 598篇 |
2015年 | 591篇 |
2014年 | 634篇 |
2013年 | 962篇 |
2012年 | 1160篇 |
2011年 | 1240篇 |
2010年 | 851篇 |
2009年 | 740篇 |
2008年 | 938篇 |
2007年 | 909篇 |
2006年 | 786篇 |
2005年 | 670篇 |
2004年 | 562篇 |
2003年 | 410篇 |
2002年 | 321篇 |
2001年 | 202篇 |
2000年 | 167篇 |
1999年 | 164篇 |
1998年 | 113篇 |
1997年 | 101篇 |
1996年 | 111篇 |
1995年 | 80篇 |
1994年 | 76篇 |
1993年 | 76篇 |
1992年 | 61篇 |
1991年 | 53篇 |
1990年 | 44篇 |
1989年 | 49篇 |
1988年 | 32篇 |
1987年 | 32篇 |
1986年 | 35篇 |
1985年 | 36篇 |
1984年 | 32篇 |
1983年 | 15篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1975年 | 9篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
聚电解质复合物 (Polyelectrolytecomplex)是指带有相反电荷的两种聚电解质之间通过库仑力而结合形成的一类特殊的高分子材料[1 ] .由于生物体内的很多反应以及生物化学合成过程都是通过高分子复合物进行的 ,因此对高分子间相互作用及其聚集体形成的研究受到了人们的极大重视 .目前研究得较多的体系是聚苯乙烯衍生物 ,如Ioplex 1 0 1即由聚苯乙烯磺酸钠和聚氯化乙烯基苄基三甲基铵反应而得[2 ,3] .本文报道了不同电荷密度及相对分子质量的聚苯乙烯 co 4 乙烯基吡啶的硫酸甲酯盐 ,与不同分子质量的聚丙烯酸钠… 相似文献
953.
Laura Seoane Pablo Martínez-Landeira Lina Besada Juan M. Ruso Félix Sarmiento Gerardo Prieto 《Colloid and polymer science》2002,280(7):624-629
The aggregation characteristics of oxacillin in aqueous solutions have been examined by means of conductivity measurements over the temperature range 288.15-313.15 K and by static light scattering measurements at 298.15 K. Two critical concentrations were detected in conductivity and light scattering over the concentration range 0-0.35 mol kg-1. Light scattering measurements indicate the formation of dimers at the first critical concentration (0.024 mol kg-1) and the subsequent formation of aggregates with an aggregation number of 8 at the second critical concentration (0.104 molkg-1). The thermodynamic parameters of aggregation were derived from the critical concentration data using a mass-action model that has been modified for application to systems of low aggregation number. Values for the enthalpy of aggregate formation calculated by this method showed that the aggregation became increasingly exothermic with increasing temperature. The values of the two critical concentrations show that this penicillin, oxacillin, is more hydrophobic than other molecules of similar structure. 相似文献
954.
955.
A stereoselective synthesis of heavily functionalized six-membered ring subunits, which possess functionality at sites appropriate for further elaboration, is described. The cyclopentanone moiety of hydrindenediol is required to achieve total facial selectivity during the pre-domino installation of the second quaternary center, while oxidative cleavage is responsible for the ring-expanding rearrangement. A microwave-assisted version of the key domino transformation and a test of concept approach toward the iridal core structure are also presented. 相似文献
956.
采用化学还原法在离子液体1-丁基-3-甲基咪唑四氟硼酸盐([BMim]BF4)中制备了单分散纳米金属Ru粒子。采用X射线衍射(XRD)、透射电镜(TEM)、傅里叶红外光谱(FTTR)及热重(TG)对所制备样品的形貌和结构进行了表征。XRD表征结果显示:在[BMim]BF4中制备的Ru具有六方紧密堆积结构,无氧化物峰出现;TEM结果显示:采用正滴法制备的Ru纳米粒子为球形颗粒,呈现良好的单分散状态,粒径分布窄,为2~5 nm,而采用反滴法制备的Ru纳米粒子则发生了严重的团聚,团聚体粒径大于10 nm;FTIR表征表明:Ru纳米粒子表面存在[BMim]BF4液体层,分析二者之间存在较强的物理吸附作用,[BMim]BF4在Ru纳米粒子的制备中起到了修饰剂和保护剂的双重作用,这一推论通过TG分析得到了进一步验证。将分散于[BMim]BF4的Ru纳米粒子作为催化剂应用于苯选择加氢反应,结果分析表明:Ru-离子液体-苯反应体系中,苯转化率仅有0.3%;Ru-离子液体-苯-水反应体系中加氢活性较高,但环己烯选择性较低,在一定条件下,加氢30 min,苯转化率为27.3%,环己烯选择性仅为14.5%。 相似文献
957.
Vidal-Iglesias FJ Arán-Ais RM Solla-Gullón J Garnier E Herrero E Aldaz A Feliu JM 《Physical chemistry chemical physics : PCCP》2012,14(29):10258-10265
The electrocatalytic properties of palladium nanocubes towards the electrochemical oxidation of formic acid were studied in H(2)SO(4) and HClO(4) solutions and compared with those of spherical Pd nanoparticles. The spherical and cubic Pd nanoparticles were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The intrinsic electrocatalytic properties of both nanoparticles were shown to be strongly dependent on the amount of metal deposited on the gold substrate. Thus, to properly compare the activity of both systems (spheres and nanocubes), the amount of sample has to be optimized to avoid problems due to a lower diffusion flux of reactants in the internal parts of the catalyst layer resulting in a lower apparent activity. Under the optimized conditions, the activity of the spheres and nanocubes was very similar between 0.1 and 0.35 V. From this potential value, the activity of the Pd nanocubes was remarkably higher. This enhanced electrocatalytic activity was attributed to the prevalence of Pd(100) facets in agreement with previous studies with Pd single crystal electrodes. The effect of HSO(4)(-)/SO(4)(2-) desorption-adsorption was also evaluated. The activity found in HClO(4) was significantly higher than that obtained in H(2)SO(4) in the whole potential range. 相似文献
958.
Dr. Jorge Carballido‐Landeira Sonia Goy‐López Prof. Dr. Alberto P. Muñuzuri Prof. Dr. Pablo Taboada Prof. Dr. Víctor Mosquera 《Chemphyschem》2012,13(5):1347-1353
The spontaneous in situ formation of one‐dimensional (1D) assemblies of gold nanoparticles (NP) in oleylamine/bis(2‐ethylhexyl) sulfosuccinate sodium salt/water/octane (OAm/AOT/w/o) microemulsions by exploiting both the aurophilic bonding between OAm and gold salt, and the interactions between OAm and AOT surfactant is presented. Control on the structure of the resulting assemblies is achieved by changing in the solvent quality, the [Au]/[AOT] molar ratio and the presence of different cosolutes. A possible mechanism of the formation of the 1D parallel Au NP arrays is proposed. 相似文献
959.
The Divergent Synthesis of Nitrogen Heterocycles by Rhodium(II)‐Catalyzed Cycloadditions of 1‐Sulfonyl 1,2,3‐Triazoles with 1,3‐Dienes 下载免费PDF全文
Dr. Hai Shang Yuanhao Wang Dr. Yu Tian Juan Feng Prof. Dr. Yefeng Tang 《Angewandte Chemie (International ed. in English)》2014,53(22):5662-5666
The first rhodium(II)‐catalyzed aza‐[4+3] cycloadditions of 1‐sulfonyl 1,2,3‐triazoles with 1,3‐dienes have been developed, and enable the efficient synthesis of highly functionalized 2,5‐dihydroazepines from readily available precursors. In some cases, the reaction pathway could divert to formal aza‐[3+2] cycloadditions, thus leading to 2,3‐dihydropyrroles. In this context, the titled reaction represents a capable tool for the divergent synthesis of two types of synthetically valuable aza‐heterocycles from common rhodium(II) iminocarbene intermediates. 相似文献
960.
Fraga R Zacconi F Sussman F Ordóñez-Morán P Muñoz A Huet T Molnár F Moras D Rochel N Maestro M Mouriño A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(2):603-612
Based on the crystal structures of human vitamin D receptor (hVDR) bound to 1α,25-dihydroxy-vitamin D(3) (1,25 D) and superagonist ligands, we previously designed new superagonist ligands with a tetrahydrofuran ring at the side chain that optimize the aliphatic side-chain conformation through an entropy benefit. Following a similar strategy, four novel vitamin D analogues with aromatic furan side chains (3a, 3b, 4a, 4b) have now been developed. The triene system has been constructed by an efficient stereoselective intramolecular cyclization of an enol triflate (A-ring precursor) followed by a Suzuki-Miyaura coupling of the resulting intermediate with an alkenyl boronic ester (CD-side chain, upper fragment). The furan side chains have been constructed by gold chemistry. These analogues exhibit significant pro-differentiation effects and transactivation potency. The crystal structure of 3a in a complex with the ligand-binding domain of hVDR revealed that the side-chain furanic ring adopts two conformations. 相似文献