全文获取类型
收费全文 | 1261篇 |
免费 | 45篇 |
国内免费 | 3篇 |
专业分类
化学 | 1000篇 |
晶体学 | 7篇 |
力学 | 5篇 |
数学 | 139篇 |
物理学 | 158篇 |
出版年
2023年 | 9篇 |
2022年 | 15篇 |
2021年 | 15篇 |
2020年 | 22篇 |
2019年 | 21篇 |
2017年 | 14篇 |
2016年 | 37篇 |
2015年 | 44篇 |
2014年 | 37篇 |
2013年 | 56篇 |
2012年 | 85篇 |
2011年 | 73篇 |
2010年 | 45篇 |
2009年 | 38篇 |
2008年 | 60篇 |
2007年 | 76篇 |
2006年 | 39篇 |
2005年 | 39篇 |
2004年 | 37篇 |
2003年 | 36篇 |
2002年 | 46篇 |
2001年 | 24篇 |
2000年 | 12篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 13篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1990年 | 9篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1975年 | 8篇 |
1973年 | 10篇 |
1971年 | 10篇 |
1970年 | 11篇 |
1969年 | 18篇 |
1968年 | 17篇 |
1967年 | 13篇 |
1966年 | 14篇 |
1965年 | 8篇 |
1964年 | 9篇 |
1963年 | 10篇 |
1962年 | 14篇 |
1961年 | 18篇 |
1960年 | 8篇 |
1959年 | 12篇 |
1958年 | 10篇 |
1957年 | 8篇 |
排序方式: 共有1309条查询结果,搜索用时 0 毫秒
61.
Sarah R. Geenen Lysander Presser Dr. Torsten Hölzel Prof. Dr. Christian Ganter Prof. Dr. Thomas J. J. Müller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(36):8064-8075
Differently 5-substituted 8-methoxypsoralens can be synthesized by an efficient synthetic route with various cross-coupling methodologies, such as Suzuki, Sonogashira and Heck reaction. Compared to previously synthesized psoralens, thereby promising daylight absorbing compounds as potentially active agents against certain skin diseases can be readily accessed. Extensive investigations of all synthesized psoralen derivatives reveal fluorescence in the solid state as well as several distinctly emissive derivatives in solution. Donor-substituted psoralens exhibit remarkable photophysical properties, such as high fluorescence quantum yields and pronounced emission solvatochromicity and acidochromicity, which were scrutinized by Lippert–Mataga and Stern–Volmer plots. The results indicate that the compounds exceed the limit of visible light, a significant factor for potential applications as an active agent. In addition, (TD)DFT calculations were performed to elucidate the underlying electronic structure and to assign experimentally obtained data. 相似文献
62.
The secondary ion mass spectrum of silicon sputtered by high energy C60+ ions in sputter equilibrium is found to be dominated by Si clusters and we report the relative yields of Sim+ (1 ≤ m ≤ 15) and various SimCn+ clusters (1 ≤ m ≤ 11 for n = 1; 1 ≤ m ≤ 6 for n = 2; 1 ≤ m ≤ 4 for n = 3). The yields of Sim+ clusters up to Si7+ are significant (between 0.1 and 0.6 of the Si+ yield) with even numbered clusters Si4+ and Si6+ having the highest probability of formation. The abundances of cluster ions between Si8+ and Si11+ are still significant (>1% relative to Si+) but drop by a factor of ∼100 between Si11+ and Si13+. The probability of formation of clusters Si13+-Si15+ is approximately constant at ∼5 × 10−4 relative to Si+ and rising a little for Si15+, but clusters beyond Si15 are not detected (Sim≥16+/Si+ < 1 × 10−4). The probability of formation of Sim+ and SimCn+ clusters depends only very weakly on the C60+ primary ion energy between 13.5 keV and 37.5 keV. The behaviour of Sim+ and SimCn+ cluster ions was also investigated for impacts onto a fresh Si surface to study the effects that saturation of the surface with C60+ in reaching sputter equilibrium may have had on the measured abundances. By comparison, there are very minor amounts of pure Sim+ clusters produced during C60+ sputtering of silica (SiO2) and various silicate minerals. The abundances for clusters heavier than Si2+ are very small compared to the case where Si is the target.The data reported here suggest that Sim+ and SimCn+ cluster abundances may be consistent in a qualitative way with theoretical modelling by others which predicts each carbon atom to bind with 3-4 Si atoms in the sample. This experimental data may now be used to improve theoretical modelling. 相似文献
63.
Dau T 《The Journal of the Acoustical Society of America》2003,113(2):936-950
A model for the generation of auditory brainstem responses (ABR) and frequency following responses (FFRs) is presented. The model is based on the concept introduced by Goldstein and Kiang [J. Acoust. Soc. Am. 30, 107-114 (1958)] that evoked potentials recorded at remote electrodes can theoretically be given by convolution of an elementary unit waveform (unitary response) with the instantaneous discharge rate function for the corresponding unit. In the present study, the nonlinear computational auditory-nerve model recently developed by Heinz et al. [ARLO 2(3), 91-96 (2001)] was used to calculate the instantaneous discharge rate ri(t) for fibers i in the frequency range from 0.1 and 10 kHz. The summed activity across frequency was convolved with a unitary response which is assumed to reflect contributions from different cell populations within the auditory brainstem, recorded at a given pair of electrodes on the scalp. Predicted potential patterns are compared with experimental data for a number of stimulus and level conditions. Clicks, chirps as defined in Dau et al. [J. Acoust. Soc. Am. 107, 1530-1540 (2000)], long-duration stimuli comprising the chirp, as well as tones and slowly varying tonal sweeps were considered. The results demonstrate the importance of considering the effects of the basilar-membrane traveling wave and auditory-nerve processing for the formation of ABR and FFR. Specifically, the results support the hypothesis that the FFR to low-frequency tones represents synchronized activity mainly stemming from mid- and high-frequency units at more basal sites, and not from units tuned to frequencies around the signal frequency. 相似文献
64.
Torsten C. Schmidt Melanie Less Rainer Haas Eberhard von Lw Klaus Steinbach Gottfried Stork 《Journal of chromatography. A》1998,810(1-2):161-172
A new method for the selective determination of aromatic amines is presented, which is based on the solid-phase extraction at pH 9 and subsequent derivatization of the analytes to the corresponding iodobenzenes. These can selectively and sensitively be determined with gas chromatography and electron-capture detection. Separation of at least 30 compounds in a single chromatographic run in 30 min is possible. With this method, 56 aromatic amines were investigated, and only in six cases no derivatives were obtained. Limits of quantitation were between 0.5 and 8 μg l−1, but may still be lowered with higher sample volumes or different injection techniques. The application to water samples revealed the suitability for the investigation of ground, leachate and wastewater. 相似文献
65.
Seyedhosein Payandeh Damian Goonetilleke Matteo Bianchini Jürgen Janek Torsten Brezesinski 《Current Opinion in Electrochemistry》2022
The recent developments in the application of single-crystalline (SC) cathode materials in solid-state batteries are discussed in this mini-review. The characteristics of SC and poly-crystalline (PC) cathode materials are explored, with emphasis on the kinetic and mechanical properties. The critical factors influencing their performance in liquid electrolyte and solid-state battery cells are investigated. Finally, the advantages and disadvantages of both morphologies are discussed and considerations to ensure a fair comparison between SC and PC cathodes in different systems are raised. 相似文献
66.
We examine how postsynthesis nanoparticle ligand shell modifications as a general approach can help in the understanding of currently proposed mechanisms for gold nanoparticle chirality. We compare the CD response of chirally decorated mixed-monolayer-protected gold nanoparticles synthesized in situ with quasi-identical gold nanoparticles either prepared by place exchange reactions or subjected to an aqueous base, resulting in partial hydrolysis and simultaneous partial racemization. We find that the CD response at wavelengths where the free chiral ligand does not absorb strongly depends on the preparation conditions, i.e., in situ synthesis vs place exchange, and that postsynthesis racemization of the chiral ligand produces racemic nanoparticles with no CD response, i.e., no induction of a chiral bias during reductive nanoparticle formation. Considering all experimental results for the described gold nanoparticle system with a C12H24 spacer between the nanoparticle surface and chiral center, the so-called "vicinal effect" with the formation of a supramolecular assembly of the chiral moieties seems to be active. Finally, we argue that postsynthesis nanoparticle ligand shell modifications such as racemization and/or place exchange reactions are very powerful tools to unravel contributions of the different gold nanoparticle chirality mechanisms. 相似文献
67.
Kinran Lau Felix Niemann Dr. Kaltum Abdiaziz Dr. Markus Heidelmann Yuke Yang Dr. Yujin Tong Dr. Michael Fechtelkord Prof. Torsten C. Schmidt Dr. Alexander Schnegg Prof. R. Kramer Campen Dr. Baoxiang Peng Prof. Martin Muhler Dr. Sven Reichenberger Prof. Stephan Barcikowski 《Angewandte Chemie (International ed. in English)》2023,62(12):e202213968
Both oxygen vacancies and surface hydroxyls play a crucial role in catalysis. Yet, their relationship is not often explored. Herein, we prepare two series of TiO2 (rutile and P25) with increasing oxygen deficiency and Ti3+ concentration by pulsed laser defect engineering in liquid (PUDEL), and selectively quantify the acidic and basic surface OH by fluoride substitution. As indicated by EPR spectroscopy, the laser-generated Ti3+ exist near the surface of rutile, but appear to be deeper in the bulk for P25. Fluoride substitution shows that extra acidic bridging OH are selectively created on rutile, while the surface OH density remains constant for P25. These observations suggest near-surface Ti3+ are highly related to surface bridging OH, presumably the former increasing the electron density of the bridging oxygen to form more of the latter. We anticipate that fluoride substitution will enable better characterization of surface OH and its correlation with defects in metal oxides. 相似文献
68.
The aliphatic anthracene compound 1 and the oligomeric anthracene 2 were synthesized. Thin films of 1 and 2 mixed with the sensitizers tetraphenylporphyrin (TPP) and methylene blue (MB) were irradiated with visible light in air. Upon formation of singlet oxygen, the anthracene units were converted quantitatively to the corresponding endoperoxides. Heating of the irradiated samples afforded the parent anthracenes with high yields. Here, we demonstrate that the kinetics and reversibility of this reaction strongly depend on the microenvironment of the anthracene groups in the two compounds. The photooxidation of thin films of 1 is accompanied by interesting changes in the morphology of the film and allows the first application of 1 as a nondestructive negative-tone photoresist for lithography and as an oxidizing ink. The morphology of 2 remained unchanged after photooxidation as a result of the stabilizing oligomer backbone. This stabilizing effect significantly improves the photochromic performance of 2. The reversibility of the photooxidation is very high (>90 %) for oligomeric films of 2 after several cycles of irradiation and heating. Decomposition of the anthracene and a loss of the activity of the sensitizer diminish slightly the performance of the monomeric species. 相似文献
69.
Two different reaction pathways in the photooxygenation of 9,10-diarylanthracenes are identified, with strong evidence for polar (forward, singlet oxygen addition) and radical (backward, thermolysis) intermediates. 相似文献
70.
B. Mahltig E. Gutmann M. Reibold D. C. Meyer H. Böttcher 《Journal of Sol-Gel Science and Technology》2009,51(2):204-214
Ag and Ag/SiO2 sols containing nanocrystalline silver particles can be advantageously prepared by solvothermal methods using an autoclave
with conventional thermal or microwave heating. In this process, the reduction of silver salts can be realized with alcohols
like ethanol in the presence of polyvinylpyrrolidone at temperatures of more than 120 °C. Furthermore a combination of silver
salt reduction with hydrolysis of alkoxysilanes during the solvothermal process can yield Ag/SiO2 composite sols. Particle size and crystallinity of as-prepared particles are analyzed by means of X-ray diffraction and high-resolution
transmission electron microscopy. Nanosized silver particles gained by this process exhibit antimicrobial properties that
are investigated in detail after application on textile fabrics. 相似文献