全文获取类型
收费全文 | 18185篇 |
免费 | 2941篇 |
国内免费 | 4585篇 |
专业分类
化学 | 14751篇 |
晶体学 | 355篇 |
力学 | 937篇 |
综合类 | 384篇 |
数学 | 2618篇 |
物理学 | 6666篇 |
出版年
2024年 | 30篇 |
2023年 | 142篇 |
2022年 | 476篇 |
2021年 | 466篇 |
2020年 | 501篇 |
2019年 | 595篇 |
2018年 | 519篇 |
2017年 | 628篇 |
2016年 | 687篇 |
2015年 | 878篇 |
2014年 | 1002篇 |
2013年 | 1387篇 |
2012年 | 1528篇 |
2011年 | 1534篇 |
2010年 | 1304篇 |
2009年 | 1369篇 |
2008年 | 1547篇 |
2007年 | 1369篇 |
2006年 | 1233篇 |
2005年 | 1226篇 |
2004年 | 1013篇 |
2003年 | 770篇 |
2002年 | 882篇 |
2001年 | 835篇 |
2000年 | 801篇 |
1999年 | 447篇 |
1998年 | 347篇 |
1997年 | 289篇 |
1996年 | 220篇 |
1995年 | 196篇 |
1994年 | 185篇 |
1993年 | 159篇 |
1992年 | 151篇 |
1991年 | 116篇 |
1990年 | 138篇 |
1989年 | 94篇 |
1988年 | 101篇 |
1987年 | 80篇 |
1986年 | 70篇 |
1985年 | 37篇 |
1984年 | 38篇 |
1983年 | 48篇 |
1982年 | 46篇 |
1981年 | 41篇 |
1980年 | 26篇 |
1979年 | 18篇 |
1978年 | 17篇 |
1977年 | 13篇 |
1976年 | 11篇 |
1964年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
973.
974.
Total synthesis of α-elvucitabine was achieved in 26% overall yield by a concise nine-step procedure starting from L-lyxose, with trimethylsilyl trifluoromethaneoulfonate (TMSOTf)–mediated stereocontrolled α-N-glycosidation and olefination through Barton–McCombie deoxygenation being the key steps, and the stereochemistry of the product was determined by nuclear Overhauser effect spectroscopy. 相似文献
975.
Zhenhua Gu Kongzhai Li Hua Wang Yonggang Wei Dongxia Yan Tianqiang Qiao 《Kinetics and Catalysis》2013,54(3):326-333
A series of mixed oxides Ce1 ? x Fe x O2 was prepared by a hydrothermal method. XRD and Raman spectra were measured to study the structure of the prepared materials. The temperature-programmed reduction was undertaken to estimate reducibility of the oxides. Syngas generation from methane using these materials as oxygen carriers/catalysts via a chemical-looping procedure was investigated in detail. This procedure includes catalytic oxidation and decomposition of methane to produce H2-rich gas at the first step followed by the production of the CO-rich gas by oxidizing the carbon deposited on deactivated catalysts. The results showed that all iron ions were incorporated into the ceria lattice with the formation of oxygen vacancies in the Ce0.9Fe0.1O2 sample, while isolated Fe2O3 particles were distributed on the surface of the Ce0.8Fe0.2O2 sample. TPR measurements and the analysis of the two-step chemical-looping reactions indicated a strong interaction between the Ce and Fe species which accounts for an increased activity of the mixed oxides in the syngas generation compared to that of individual oxides. Among the several samples, the Ce0.8Fe0.2O2 catalyst showed the highest activity for methane partial oxidation due to the synergetic effects caused by the interaction of surface iron entities and Ce-Fe solid solution. In addition, selective oxidation of carbon by oxygen to CO can also be found over this material since gaseous products are formed at the carbon oxidation step with the selectivity to CO reaching 91.2%. Evidence is presented that syngas can be feasibly produced from methane with high selectivity via the chemical-looping procedure over the CeO2-Fe2O3 mixed oxides. 相似文献
976.
Dodecylbenzenesulfonic acid (DBSA) was proved to be an efficient catalyst for Prins cyclization of styrenes and formaldehyde or acetaldehyde in water. A tandem dehydration/Prins cyclization reaction using a tertiary alcohol and formaldehyde as substrates proceeded very well by using DBSA as catalyst. Acetophenone, which is less reactive compared with styrene, can also react with formaldehyde when catalyzed by DBSA in water to afford 1,3-dioxan-5-ylphenylmethanone in good yield. 相似文献
977.
Fu-Qiang Jin Jian-Chun Zhang Min Li Xin-Min Hao Hua Zhang 《Journal of Dispersion Science and Technology》2013,34(8):1148-1151
NaOH/poly(sodium acrylate) composites were prepared by in situ polymerization of acrylic acid with an overneutralization level by adding excess NaOH. The composites were studied by XRD, IR and 23Na MAS NMR spectroscopy. The results showed that the high neutralization degree (>100%) may lead to a complete polymerization. Both XRD and 23Na MAS NMR spectra did not show any peaks of phase-separated NaOH or Na2CO3 until the neutralization degree was up to 217.5%. It can be presumed that the aggregates of Na+ ions can contain approximately two Na+ units for every carboxyl group before the phase separation. 相似文献
978.
Xue‐Jun Wu Xiao Huang Xiaoying Qi Hai Li Bing Li Hua Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(34):9075-9079
Two‐dimensional (2D) copper‐based ternary and quaternary semiconductors are promising building blocks for the construction of efficient solution‐processed photovoltaic devices at low cost. However, the facile synthesis of such 2D nanoplates with well‐defined shape and uniform size remains a challenge. Reported herein is a universal template‐mediated method for preparing copper‐based ternary and quaternary chalcogenide nanoplates, that is, CuInS2, CuInxGa1−xS2, and Cu2ZnSnS4, by using a pre‐synthesized CuS nanoplate as the starting template. The various synthesized nanoplates are monophasic with uniform thickness and lateral size. As a proof of concept, the Cu2ZnSnS4 nanoplates were immobilized on a Mo/glass substrate and used as semiconductor photoelectrode, thus showing stable photoelectrochemical response. The method is general and provides future opportunities for fabrication of cost‐effective photovoltaic devices based on 2D semiconductors. 相似文献
979.
A novel one-pot two-step protocol has been developed to synthesize various spiro[benzofuran-2,2′-naphthalen]-1′-one derivatives from the three-component reaction of tetralones, 2-hydroxyphenyl functionalized α,β-unsaturated ketones, and iodine. One C–C bond and one C–O bond have formed during this process. The notable features of this protocol are simple and mild reaction conditions, applicable to a wide range of readily available starting materials, good yields (up to 91%), and excellent stereoselectivities (up to 97:3). 相似文献
980.
Bin Zhou Yedi Xing Prof. Shu Miao Prof. Mingrun Li Prof. Wen‐Hua Zhang Prof. Can Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(39):12426-12431
A facile colloidal approach to synthesize Ag8(Ge1?x,Snx)(S6?y,Sey) nanocrystals (NCs) in a highly controlled way across the entire compositional ranges (0≤x≤1, 0≤y≤6) has been developed. The NCs exhibit a uniform size distribution, highly crystalline structure, over 1 g scalable synthesis, and tunable band gaps in the range of 0.88–1.45 eV by varying their chemical compositions. The Ag8GeS6 NCs with a band gap of approximately 1.45 eV were employed as a model light harvester to assess their applicability in solar cells by a full solution‐processing device, yielding an efficiency of 0.28 % under AM1.5 illumination, demonstrating their application potential in solar energy utilization. 相似文献