全文获取类型
收费全文 | 48544篇 |
免费 | 5012篇 |
国内免费 | 10497篇 |
专业分类
化学 | 44859篇 |
晶体学 | 1875篇 |
力学 | 634篇 |
综合类 | 426篇 |
数学 | 3311篇 |
物理学 | 12948篇 |
出版年
2024年 | 63篇 |
2023年 | 895篇 |
2022年 | 874篇 |
2021年 | 1768篇 |
2020年 | 1798篇 |
2019年 | 1631篇 |
2018年 | 1334篇 |
2017年 | 1714篇 |
2016年 | 1798篇 |
2015年 | 1561篇 |
2014年 | 2087篇 |
2013年 | 4569篇 |
2012年 | 3169篇 |
2011年 | 3405篇 |
2010年 | 2931篇 |
2009年 | 3534篇 |
2008年 | 3358篇 |
2007年 | 3451篇 |
2006年 | 3272篇 |
2005年 | 2849篇 |
2004年 | 2734篇 |
2003年 | 2269篇 |
2002年 | 1884篇 |
2001年 | 1543篇 |
2000年 | 1429篇 |
1999年 | 1163篇 |
1998年 | 986篇 |
1997年 | 845篇 |
1996年 | 702篇 |
1995年 | 747篇 |
1994年 | 665篇 |
1993年 | 529篇 |
1992年 | 496篇 |
1991年 | 380篇 |
1990年 | 257篇 |
1989年 | 224篇 |
1988年 | 191篇 |
1987年 | 127篇 |
1986年 | 98篇 |
1985年 | 113篇 |
1984年 | 90篇 |
1983年 | 36篇 |
1982年 | 65篇 |
1981年 | 91篇 |
1980年 | 64篇 |
1979年 | 67篇 |
1978年 | 44篇 |
1977年 | 50篇 |
1976年 | 30篇 |
1973年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
含Cu复合氧化物对NO和CO吸附和活化的TPSR研究 总被引:2,自引:2,他引:2
利用MS-TPD法并结合XRD、化学分析等对催化剂进行了表征,探讨了K2NiF4结构La2-x(Sr,Th)xCuO4±λ系催化剂中三个典型样品LaSrCuO4、La2CuO4和La1.7Th0.3CuO4对NO、CO及CO+NO等小分子的吸附性能和活化规律。结果表明:NO吸附量的大小与催化剂中氧空位含量有关,吸附强度和脱附峰种类与金属离子氧化态有关。CO在氧缺陷复合氧化物催化剂上的吸附是首先变为碳酸根,并在高温以CO2物种脱出.在NO和CO的共吸附过程中,有关NO的吸、脱性能与单独NO-TPD中NO的吸脱附规律相似,表明NO在NO+CO共吸附的竞争吸附过程中,优先吸附起决定作用,而受CO的影响较小.NO的吸附是NO活化分解的必要条件. 相似文献
993.
固定n(Ce)/n(Zr)比为0.67/0.33,用共沉淀法制得一系列CeO2-ZrO2-Al2O3固溶体.采用这些固溶体作载体,以Fe2O3为活性组分,用浸渍法制备了一系列催化剂.BET结果显示,将适量Ce0.67Zr0.33O2引入到Al2O3载体中有助于催化剂保持较高的比表面积.TPR结果显示,载体中引入适量的Ce0.67Zr0.33O2可以改善催化剂的氧化还原性能.XRD结果表明,Fe2O3在CeO2-ZrO2-Al2O3载体上呈现出良好的分散状况,老化前后催化剂的晶相结构基本无明显变化.特别是当载体中m(Ce0.67Zr0.33O2)∶m(Al2O3)的值为1∶2时,Fe2O3/CeO2-ZrO2-Al2O3催化剂在甲烷催化燃烧中显示出最佳的催化性能和抗高温老化性能. 相似文献
994.
The exact residues within severe acute respiratory syndrome coronavirus (SARS-CoV) S1 protein and its receptor, human ACE2, involved in their interaction still remain largely undetermined. Identification of exact amino acid residues that are crucial for the interaction of S1 with ACE2 could provide working hypotheses for experimental studies and might be helpful for the development of antiviral inhibitor. In this paper, a molecular docking model of SARS-CoV S1 protein in complex with human ACE2 was constructed. The interacting residue pairs within this complex model and their contact types were also identified. Our model, supported by significant biochemical evidence, suggested receptor-binding residues were concentrated in two segments of S1 protein. In contrast, the interfacial residues in ACE2, though close to each other in tertiary structure, were found to be widely scattered in the primary sequence. In particular, the S1 residue ARG453 and ACE2 residue LYS341 might be the key residues in the complex formation. 相似文献
995.
The nano-ZnFe2O4/TiO2 films possess the functions of desulfurization and degradation for organic pollutants. The sols of ZnFe2O4/TiO2 were prepared by sol-gel method and coated on glass and porous ceramic by vertical coating and dipping-lift processes, respectively, and the samples were obtained after drying and sintering. The composition, appearance, absorption spectrum of the films, and the influence of the film on porous ceramic performances were analyzed using SEM, AFM, UV-Vis spectrometer, and mercury porosimeter, respectively, to determine the operation parameters of the multifunction porous ceramic elements for gas-purification. 相似文献
996.
E. V. Zhernosek S. V. Kvach L. A. Eroshevskaya E. N. Kalinichenko A. I. Zinchenko 《Chemistry of Natural Compounds》2006,42(2):208-211
Previously undescribed conjugates of 2′,3′-dideoxyuridine-5′-monophosphate-(L)-methoxytryptophylphosphoramidate (5) and 2′,3′-dideoxycytidine-5′-monophosphate-(L)-methoxytryptophylphosphoramidate (7) were isolated by a chemical enzymatic method in order to study their pharmacological properties and to prepare new medicinal
preparations based on them.
__________
Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 173–175, March–April, 2006. 相似文献
997.
0IntroductionCobaltcomplexeswithnonmacrocyclicchelatingligandscontainingtheamidefunctionalityhavere鄄ceivedmuchattentioninpastyears[1~3].Somestudieshaverevealedthatdeprotonatednitrogensoforganicamides,beinganionicinnature,arecapableofstabi鄄lizingthetriva… 相似文献
998.
Bhattacharya S Schiavone M Nayak A Bhattacharya SK 《Applied biochemistry and biotechnology》2005,120(3):159-167
Our laboratory has recently developed a device employing immobilized F0F1 adenosine triphosphatase (ATPase) that allows synthesis of adenosine triphosphate (ATP) from adenosine 5′-diphosphate and
inorganic phosphate using solar energy. We present estimates of total solar energy received by Earth’s land area and demonstrate
that its efficient capture may allow conversion of solar energy and storage into bonds of biochemicals using devices harboring
either immobilized ATPase or NADH dehydrogenase. Capture and storage of solar energy into biochemicals may also enable fixation
of CO2 emanating from polluting units. The cofactors ATP and NADH synthesized using solar energy could be used for regeneration
of acceptor d-ribulose-1,5-bisphosphate from 3-phosphoglycerate formed during CO2 fixation. 相似文献
999.
(±)-5,2′-Dihydroxy-6,7,6′-trimethoxyflavanone, (-)-5,2′-dihydroxy-6,7,8,6′-tetramethoxyflavanone, chrysin, wogonin, apigenin, isoscutellarein, scutellarein, cosmosiin, and the new flavonoid wogonin-7-O-β-D-glucopyranoside, the structure of which was established using chemical transformations and spectral data, were isolated from Scutellaria immaculata roots.__________Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 26–28, January–February, 2005. 相似文献
1000.
Capillary electrophoresis with end-column amperometric detection of urinary 8-hydroxy-2'-deoxyguanosine 总被引:1,自引:0,他引:1
Urinary 8-hydroxy-2'-deoxyguanosine (8OHdG) is an excellent marker of oxidative DNA damage. Until now, urinary 8OHdG has been measured by high-performance liquid chromatography with electrochemical detection. A simple and sensitive method for the analysis of urinary 8OHdG by capillary electrophoresis with end-column amperometric detection has been developed in our laboratory. A single-step solid-phase extraction procedure was optimized and used for extracting 8OHdG from human urine. To improve the sensitivity of this method, a new focusing technique based on a dynamic pH junction was used. The limit of detection was 20 nM (signal-to-noise ratio S/N = 3), the linear range was 50 nM-10 microM, and the correlation coefficient was better than 0.999. The relative standard deviation (RSD) was found to be 0.57% for migration time, and 4.79% for peak current. To show the usefulness of the method, the urinary concentration of 8OHdG in nine healthy persons and ten cancer patients was determined. The urinary concentration of 8OHdG in cancer patients was significantly higher than that in healthy persons. 相似文献