全文获取类型
收费全文 | 42790篇 |
免费 | 18113篇 |
国内免费 | 54篇 |
专业分类
化学 | 55157篇 |
晶体学 | 47篇 |
力学 | 2034篇 |
数学 | 2633篇 |
物理学 | 1086篇 |
出版年
2024年 | 157篇 |
2023年 | 4076篇 |
2022年 | 1424篇 |
2021年 | 2475篇 |
2020年 | 4617篇 |
2019年 | 2308篇 |
2018年 | 2273篇 |
2017年 | 595篇 |
2016年 | 5579篇 |
2015年 | 5518篇 |
2014年 | 4936篇 |
2013年 | 5124篇 |
2012年 | 3178篇 |
2011年 | 1027篇 |
2010年 | 3401篇 |
2009年 | 3356篇 |
2008年 | 1032篇 |
2007年 | 750篇 |
2006年 | 105篇 |
2005年 | 85篇 |
1997年 | 80篇 |
1995年 | 139篇 |
1994年 | 83篇 |
1993年 | 213篇 |
1992年 | 97篇 |
1988年 | 114篇 |
1987年 | 100篇 |
1986年 | 85篇 |
1985年 | 98篇 |
1984年 | 108篇 |
1983年 | 102篇 |
1982年 | 127篇 |
1981年 | 154篇 |
1980年 | 194篇 |
1979年 | 184篇 |
1978年 | 189篇 |
1977年 | 309篇 |
1976年 | 361篇 |
1975年 | 456篇 |
1974年 | 471篇 |
1973年 | 284篇 |
1972年 | 369篇 |
1971年 | 355篇 |
1970年 | 541篇 |
1969年 | 413篇 |
1968年 | 456篇 |
1967年 | 114篇 |
1966年 | 89篇 |
1965年 | 83篇 |
1963年 | 112篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
Dr. Alexander A. Larin Alexander V. Shaferov Dr. Alexander S. Kulikov Prof. Dr. Alla N. Pivkina Konstantin A. Monogarov Dr. Artem O. Dmitrienko Dr. Ivan V. Ananyev Dr. Dmitry V. Khakimov Prof. Dr. Leonid L. Fershtat Prof. Dr. Nina N. Makhova 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(59):14628-14637
A series of novel energetic materials comprising of azo-bridged furoxanylazoles enriched with energetic functionalities was designed and synthesized. These high-energy materials were thoroughly characterized by IR and multinuclear NMR (1H, 13C, 14N) spectroscopy, high-resolution mass spectrometry, elemental analysis, and differential scanning calorimetry (DSC). The molecular structures of representative amino and azo oxadiazole assemblies were additionally confirmed by single-crystal X-ray diffraction and X-ray powder diffraction. A comparison of contributions of explosophoric moieties into the density of energetic materials revealed that furoxan and 1,2,4-oxadiazole rings are the densest motifs while the substitution of the azide and amino fragments on the nitro and azo ones leads to an increase of the density. Azo bridged energetic materials have high nitrogen-oxygen contents (68.8–76.9 %) and high thermal stability. The synthesized compounds exhibit good experimental densities (1.62–1.88 g cm−3), very high enthalpies of formation (846–1720 kJ mol−1), and, as a result, excellent detonation performance (detonation velocities 7.66–9.09 km s−1 and detonation pressures 25.0–37.7 GPa). From the application perspective, the detonation parameters of azo oxadiazole assemblies exceed those of the benchmark explosive RDX, while a combination of high detonation performance and acceptable friction sensitivity of azo(1,2,4-triazolylfuroxan) make it a promising potential alternative to PETN. 相似文献
993.
994.
Weichao Dong Dr. Yuchao Wang Yajing Zhang Dr. Xiangju Song Prof. Hui Peng Prof. Heqing Jiang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(69):17428-17436
Interfacial evaporation has emerged as a promising approach to produce freshwater. However, an urgent concern is that, due to the illegal discharge of industrial wastewater, most water bodies are polluted by trace volatile organic compounds (VOCs), which are easily volatilized and enriched in the collected water during the interfacial evaporation process. Herein, a bilayer photothermal evaporator was reasonably designed for contaminated water purification. The bottom hydrophilic rGO-sodium alginate (SA) sheets purposefully disintegrate water transport channels, thus quickly removing VOCs through physical adsorption. The rGO-SA-TiO2 upper layer sufficiently absorbs incident light and therefore persistently generates reactive oxidizing species to degrade upward VOCs. Notably, the oriented microchannels inside the evaporator allow sustained light reflections to improve the utilization of solar energy. The evaporation rate can reach 1.63 kg m−2 h−1 with a considerably high VOC removal efficiency of up to 96 %. Such an integrated bilayer evaporator provides an effective strategy to obtain clean water via solar distillation. 相似文献
995.
Product Control using Substrate Design: Ruthenium‐Catalysed Oxidative C−H Olefinations of Cyclic Weinreb Amides 下载免费PDF全文
Riki Das Dr. Manmohan Kapur 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):16986-16990
A new class of Weinreb amides has been developed as directing groups for the ruthenium‐catalysed regioselective oxidative C?H olefination. The new Weinreb amides successfully inhibit the N?O bond reductive cleavage usually associated with the cationic ruthenium system, thereby keeping intact the synthetic utility of Weinreb amides. Mechanistic studies reveal interesting aspects of the directing group capabilities of Weinreb amides when compared to simple amides of similar structures. 相似文献
996.
997.
998.
Jose R. Cabrero‐Antonino Dr. Antonio Leyva‐Pérez Prof. Dr. Avelino Corma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(35):11107-11114
The triflimide iron(III) salt [Fe(NTf2)3] promotes the direct hydration of terminal and internal alkynes with very good Markovnikov regioselectivities and high yields. The enhanced carbophilic Lewis acidity of the FeIII cation mediated by the weakly‐coordinating triflimide anion is crucial for the catalytic activity. The iron(III) metal salt can be recycled in the form of the OPPh3/[Fe(NTf2)3] system with similar activity and selectivity. However, spectroscopic and kinetic studies show that [Fe(NTf2)3] hydrolyzes under the reaction conditions and that catalytically less active Brønsted species are formed, which points to a Lewis/Brønsted co‐catalysis. This triflimide‐based catalytic system is regioselective for the hydration of internal aryl‐alkynes and opens the door to a new synthetic route to alkyl ketophenones. As a proof of concept, the synthesis of two antipsychotics Haloperidol and Melperone, with general butyrophenone‐like structure, is shown. 相似文献
999.
1000.