全文获取类型
收费全文 | 2453篇 |
免费 | 97篇 |
国内免费 | 7篇 |
专业分类
化学 | 1930篇 |
晶体学 | 7篇 |
力学 | 22篇 |
数学 | 305篇 |
物理学 | 293篇 |
出版年
2023年 | 14篇 |
2022年 | 14篇 |
2021年 | 31篇 |
2020年 | 58篇 |
2019年 | 39篇 |
2018年 | 14篇 |
2017年 | 13篇 |
2016年 | 72篇 |
2015年 | 62篇 |
2014年 | 77篇 |
2013年 | 124篇 |
2012年 | 158篇 |
2011年 | 163篇 |
2010年 | 89篇 |
2009年 | 78篇 |
2008年 | 143篇 |
2007年 | 116篇 |
2006年 | 120篇 |
2005年 | 123篇 |
2004年 | 132篇 |
2003年 | 90篇 |
2002年 | 98篇 |
2001年 | 47篇 |
2000年 | 43篇 |
1999年 | 35篇 |
1998年 | 27篇 |
1997年 | 38篇 |
1996年 | 38篇 |
1995年 | 38篇 |
1994年 | 46篇 |
1993年 | 41篇 |
1992年 | 36篇 |
1991年 | 22篇 |
1990年 | 25篇 |
1989年 | 26篇 |
1988年 | 29篇 |
1987年 | 15篇 |
1985年 | 28篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 19篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 18篇 |
1978年 | 11篇 |
1977年 | 17篇 |
1976年 | 13篇 |
1975年 | 11篇 |
1973年 | 9篇 |
1970年 | 10篇 |
排序方式: 共有2557条查询结果,搜索用时 15 毫秒
111.
112.
Oliver Brücher Uwe Bergsträßer Harald Kelm Jens Hartung Marco Greb Ingrid Svoboda Hartmut Fuess 《Tetrahedron》2012,68(34):6968-6980
A cascade, composed of (i) oxovanadium(V)-catalyzed oxidation of bromide by tert-butyl hydroperoxide and (ii) stereoselective 6-endo-bromocyclization, affords 3-bromo-2-aryl-2,6,6-trimethyltetrahydropyrans from styrene-type tertiary alkenols in synthetically useful yields. (E)-Alkenols add the bromo- and the alkoxy substituent anti-selectively across the double bond, indicating a bromonium ion-mechanism for the ring closure. 6-endo-control of the alkenol cyclization thereby arises from the polar effect of the aryl substituent. Two methyl substituents bound to the alkene terminus are not similarly able to favor 6-endo-cyclization, because strain arising from methyl group repulsion, as the bromonium-activated π-bond and the hydroxyl oxygen approach, directs bromocyclization of tertiary prenyl-type substrates toward tetrahydrofuran formation. A hexasubstituted bromotetrahydropyran prepared from the oxidation/bromocyclization cascade served as starting material for synthesis of racemic aplysiapyranoid A, in a sequence of free radical and polar functional group interconversion. 相似文献
113.
Bali Barume Uwe Naeher Désirée Ruppen Philip Schütte 《Current Opinion in Green and Sustainable Chemistry》2016
The growing public awareness of conflict minerals used in consumer electronics and various other devices (e.g. GPS in vehicles, medical equipment, airplane equipment and instruments, etc.) is accompanied by increasing regulatory obligations for companies affected by different laws and certification standards e.g. Dodd Frank Act section 1502, the ICGLR Regional Certification, the OECD Due Diligence Guidance or the planned EU Certification regulation.The so called conflicts minerals are natural mineral resources such as tin, tantalum, tungsten and Gold (3TG) that are critical resources for the electronic and automotive industries but also for other industries (aviation, medical equipment, etc.).Extraction of the 3TGs is widespread and includes primary industrial mining and artisanal mining as well as recycling. 相似文献
114.
Kamel Abbas Izabela Cydzik Riccardo Del Torchio Massimo Farina Efrat Forti Neil Gibson Uwe Holzwarth Federica Simonelli Wolfgang Kreyling 《Journal of nanoparticle research》2010,12(7):2435-2443
Industrially manufactured titanium dioxide nanoparticles have been successfully radiolabelled with 48V by irradiation with a cyclotron-generated proton beam. Centrifugation tests showed that the 48V radiolabels were stably bound within the nanoparticle structure in an aqueous medium, while X-ray diffraction indicated
that no major structural modifications to the nanoparticles resulted from the proton irradiation. In vitro tests of the uptake
of cold and radiolabelled nanoparticles using the human cell line Calu-3 showed no significant difference in the uptake between
both batches of nanoparticles. The uptake was quantified by Inductively Coupled Plasma Mass Spectrometry and high resolution
γ-ray spectrometry for cold and radiolabelled nanoparticles, respectively. These preliminary results indicate that alterations
to the nanoparticles’ properties introduced by proton bombardment can be controlled to a sufficient extent that their further
use as radiotracers for biological investigations can be envisaged and elaborated. 相似文献
115.
116.
Uwe J. Meierhenrich Prof. Dr. Jean‐Jacques Filippi Dr. Cornelia Meinert Pierre Vierling Dr. Jason P. Dworkin Dr. 《Angewandte Chemie (International ed. in English)》2010,49(22):3738-3750
Recent major discoveries in membrane biophysics hold the key to a modern understanding of the origin of life on Earth. Membrane bilayer vesicles have been shown to provide a multifaceted microenvironment in which protometabolic reactions could have developed. Cell‐membrane‐like aggregates of amphiphilic molecules capable of retaining encapsulated oligonucleotides have been successfully created in the laboratory. Sophisticated laboratory studies on the origin of life now show that elongation of the DNA primer takes place inside fatty acid vesicles when activated nucleotide nutrients are added to the external medium. These studies demonstrate that cell‐like vesicles can be sufficiently permeable to allow for the intake of charged molecules such as activated nucleotides, which can then take part in copying templates in the protocell interior. In this Review we summarize recent experiments in this area and describe a possible scenario for the origin of primitive cells, with an emphasis on the elongation of encapsulated nucleotides. 相似文献
117.
118.
Uwe Herzog Uwe Böhme Gerd Rheinwald 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):281-286
The reactions of Me2MCl2 (M = Si, Ge, Sn), Si2Me4Cl2, Si2Me2Cl3, Si2Me2Cl4 and CH2(SiCl2Me)2, and suitable mixtures thereof, with H2S / NEt3 and Li2E (E = Se, Te) have been investigated and lead to a variety of new group 14 chalcogenide systems. 相似文献
119.
Uwe Lindner Jana Lingott Silke Richter Norbert Jakubowski Ulrich Panne 《Analytical and bioanalytical chemistry》2013,405(6):1865-1873
Hydrophilic interaction chromatography (HILIC) coupled with inductively coupled plasma mass spectrometry (ICP-MS) was optimized for speciation analysis of gadolinium-based contrast agents in environmental samples, in particular surface river waters and plants. Surface water samples from the Teltow channel, near Berlin, were investigated over a distance of 5 km downstream from the influx of a wastewater treatment plant. The total concentration of gadolinium increased significantly from 50 to 990 ng?L?1 due to the influx of the contrast agents. After complete mixing with the river water, the concentration remained constant over a distance of at least 4 km. Two main substances [Dotarem® (Gd-DOTA) and Gadovist® (Gd-BT-DO3A)] have been identified in the river water using standards. A gadolinium-based contrast agent, possibly Gd-DOTA (Dotarem®), was also detected in water plant samples taken from the Teltow channel. Therefore, uptake of contrast agents [Gadovist® (Gd-BTDO3A), Magnevist® (Gd-DTPA), Omniscan® (Gd-DTPA-BMA), Dotarem® (Gd-DOTA), and Multihance® (Gd-BOPTA)] by plants was investigated in a model experiment using Lepidium sativum (cress plants). HILIC–ICP-MS was used for identification of different contrast agents, and a first approach for quantification using aqueous standard solutions was tested. For speciation analysis, all investigated contrast agents could be extracted from the plant tissues with a recovery of about 54 % for Multihance® (Gd-BOPTA) up to 106 % for Gadovist® (Gd-BT-DO3A). These experiments demonstrate that all contrast agents investigated are transported from the roots to the leaves where the highest content was measured. 相似文献
120.
Elisabeth Siebert Marius Horch Yvonne Rippers Johannes Fritsch Stefan Frielingsdorf Oliver Lenz Francisco VelazquezEscobar Friedrich Siebert Lars Paasche Uwe Kuhlmann Friedhelm Lendzian Maria‐Andrea Mroginski Ingo Zebger Peter Hildebrandt 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2013,125(19):5267-5270