全文获取类型
收费全文 | 1078篇 |
免费 | 51篇 |
国内免费 | 3篇 |
专业分类
化学 | 767篇 |
晶体学 | 6篇 |
力学 | 8篇 |
数学 | 139篇 |
物理学 | 212篇 |
出版年
2023年 | 9篇 |
2022年 | 16篇 |
2021年 | 14篇 |
2020年 | 21篇 |
2019年 | 22篇 |
2018年 | 7篇 |
2017年 | 14篇 |
2016年 | 35篇 |
2015年 | 43篇 |
2014年 | 37篇 |
2013年 | 55篇 |
2012年 | 81篇 |
2011年 | 71篇 |
2010年 | 44篇 |
2009年 | 33篇 |
2008年 | 63篇 |
2007年 | 80篇 |
2006年 | 43篇 |
2005年 | 44篇 |
2004年 | 43篇 |
2003年 | 40篇 |
2002年 | 47篇 |
2001年 | 28篇 |
2000年 | 12篇 |
1999年 | 10篇 |
1998年 | 11篇 |
1997年 | 16篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1984年 | 7篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 14篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 4篇 |
1973年 | 9篇 |
1971年 | 7篇 |
1969年 | 3篇 |
1966年 | 3篇 |
排序方式: 共有1132条查询结果,搜索用时 0 毫秒
21.
Torsten Barfels Bernd Schmidt Andreas von Czarnowski Hans-Joachim Fitting 《Mikrochimica acta》2002,139(1-4):11-16
For investigation of the luminescent center profile cathodoluminescence measurements are used under variation of the primary
electron energy E
0 = 2…30 keV. Applying a constant incident power regime (E
0·I
0 = const), the depth profiles of luminescent centers are deduced from the range of the electron energy transfer profiles dE/dx.
Thermally grown SiO2 layers of thickness d = 500 nm have been implanted by Ge+-ions of energy 350 keV and doses (0.5–5)1016 ions/cm2. Thus Ge profiles with a concentration maximum of (0.4 – 4) at% at the depth of dm≅240 nm are expected. Afterwards the layers have been partially annealed up to T
a = 1100 °C for one hour in dry nitrogen. After thermal annealing, not only the typical violet luminescence (λ = 400 nm) of
the Ge centers is strongly increased but also the luminescent center profiles are shifted from about 250 nm to 170 nm depth
towards the surface. This process should be described by Ge diffusion processes, precipitation and finally Ge nanocluster
formation. Additionally, a Ge surface layer is piled-up extending to a depth of roughly 25 nm. 相似文献
22.
The microwave spectrum of ethyl fluoroformate displays strong a-type R branch transitions from two rotameric forms. One species (extended form) has rotational constants A0 = 9191.3(9) MHz, B0 = 2112.61(1) MHz, C0 = 1756.73(1) MHz which are consistent with a syn-anti (τ1(OCOC) = 0°, r2(cocc) = 180°) planar heavy atom structure. The second species (compact form) has rotational constants A0 = 7760(3) MHz, B0 = 2388.38(4) MHz, C0 = 2102.47(3) MHz which are consistent with a syn-gauche (τ1(ococ) = 0°, τ2(cocc) ˜ 90°) structure. The two conformational forms have approximately equal energy (0 ± 40 cm−1). Four vibrational satellites of the extended species have been analyzed yielding a torsional frequency around the O-ethyl bond of 70(10) cm−1. Three vibrational satellites attributed to the O-ethyl torsion of the compact species have been analyzed yielding a vibrational frequency of 90(10) cm−1. Approximate Fourier coefficients of a three term potential function for internal rotation about the O-ethyl bond have been determined. Vibrational satellites attributed to the first excited states of the O-ester torsion have been analyzed for both conformers. The torsional vibrational frequency around the O-ester bond is 110(15) cm−1 for the extended conformers and 120(20) cm−1 for the compact. 相似文献
23.
We present the results of acid–base experiments performed at the single ion (H+ or OH−) limit in ∼6 aL volume nanopores incorporating electrochemical zero-mode waveguides (E-ZMWs). At pH 3 each E-ZMW nanopore contains ca. 3600H+ ions, and application of a negative electrochemical potential to the gold working electrode/optical cladding layer reduces H+ to H2, thereby depleting H+ and increasing the local pH within the nanopore. The change in pH was quantified by tracking the intensity of fluorescein, a pH-responsive fluorophore whose intensity increases with pH. This behavior was translated to the single ion limit by changing the initial pH of the electrolyte solution to pH 6, at which the average pore occupancy 〈n〉pore ∼3.6H+/nanopore. Application of an electrochemical potential sufficiently negative to change the local pH to pH 7 reduces the proton nanopore occupancy to 〈n〉pore ∼0.36H+/nanopore, demonstrating that the approach is sensitive to single H+ manipulations, as evidenced by clear potential-dependent changes in fluorescein emission intensity. In addition, at high overpotential, the observed fluorescence intensity exceeded the value predicted from the fluorescence intensity-pH calibration, an observation attributed to the nucleation of H2 nanobubbles as confirmed both by calculations and the behavior of non-pH responsive Alexa 488 fluorophore. Apart from enhancing fundamental understanding, the approach described here opens the door to applications requiring ultrasensitive ion sensing, based on the optical detection of H+ population at the single ion limit.Visualizing dynamic change in the number of protons during electroreduction of protons in attoliter volume zero-mode waveguides. 相似文献
24.
Preparations of compound 4 and of truxene derivatives 5, 6a,b, 7, 8, 10a, b, 11, 12a,b, and 13a,b are described. These substances are potential starting materials for the synthesis of bowl shaped polyaromatic compounds containing structural elements of fullerenes. 相似文献
25.
Dr. Sunewang R. Wang Dr. Merle Arrowsmith Julian Böhnke Prof. Dr. Holger Braunschweig Dr. Theresa Dellermann Dr. Rian D. Dewhurst Hauke Kelch Dr. Ivo Krummenacher James D. Mattock Jonas H. Müssig Torsten Thiess Dr. Alfredo Vargas Dr. Jiji Zhang 《Angewandte Chemie (International ed. in English)》2017,56(27):8009-8013
The diborene 1 was synthesized by reduction of a mixture of 1,2-di-9-anthryl-1,2-dibromodiborane(4) ( 6 ) and trimethylphosphine with potassium graphite. The X-ray structure of 1 shows the two anthryl rings to be parallel and their π(C14) systems perpendicular to the diborene π(B=B) system. This twisted conformation allows for intercalation of the relatively high-lying π(B=B) orbital and the low-lying π* orbital of the anthryl moiety with no significant conjugation, resulting in a small HOMO–LUMO gap (HLG) and ultimately a C−H borylation of the anthryl unit. The HLG of 1 was estimated to be 1.57 eV from the onset of the long wavelength band in its UV/Vis absorption spectrum (THF, λonset=788 nm). The oxidation of 1 with elemental selenium afforded diboraselenirane 8 in quantitative yield. By oxidative abstraction of one phosphine ligand by another equivalent of elemental selenium, the B−B and C1−H bonds of 8 were cleaved to give the cyclic 1,9-diborylanthracene 9 . 相似文献
26.
Toxicological screening of human plasma by on‐line SPE‐HPLC‐DAD: identification and quantification of acidic and neutral drugs 下载免费PDF全文
Ludmila Mut Thomas Grobosch Torsten Binscheck‐Domaß Wolfgang Frenzel 《Biomedical chromatography : BMC》2016,30(3):343-362
A multi‐analyte screening method for the quantification of 50 acidic/neutral drugs in human plasma based on on‐line solid‐phase extraction (SPE)–HPLC with photodiode array detection (DAD) was developed, validated and applied for clinical investigation. Acetone and methanol for protein precipitation, three different SPE materials (two electro‐neutral, one strong anion‐exchange, one weak cation‐exchange) for on‐line extraction, five HPLC‐columns [one C18 (GeminiNX), two phenyl‐hexyl (Gemini C6‐Phenyl, Kinetex Phenyl‐Hexyl) and two pentafluorophenyl (LunaPFP(2), KinetexPFP)] for analytical separation were tested. For sample pre‐treatment, acetone in the ratio 1:2 (plasma:acetone) showed a better baseline and fewer matrix peaks in the chromatogram than methanol. Only the strong anion‐exchanger SPE cartridge (StrataX‐A, pH 6) allowed the extraction of salicylic acid. Analytical separation was carried out on a Gemini C6‐Phenyl column (150 × 4.6 mm, 3 µm) using gradient elution with acetonitrile–water 90:10 (v/v) and phosphate buffer (pH 2.3). Linear calibration curves with correlation coefficients r ≥ 0.9950/0.9910 were obtained for 46/four analytes. Additionally, this method allows the quantification of 23 analytes for therapeutic drug monitoring. Limits of quantitation ranged from 0.1 (amobarbital) to 23 mg/L (salicylic acid). Inter‐/intra‐day precisions of quality control samples (low/high) were better than 13% and accuracy (bias) ranged from ?14 to 10%. A computer‐assisted database was created for automated detection of 223 analytes of toxicological interests. Four cases of multi‐drug intoxications are presented. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
27.
Theo Steininger Jait Dixit Philipp Frank Maksim Greiner Sebastian Hutschenreuter Jakob Knollmüller Reimar Leike Natalia Porqueres Daniel Pumpe Martin Reinecke Matev raml Csongor Varady Torsten Enßlin 《Annalen der Physik》2019,531(3)
NIFTy , “Numerical Information Field Theory,” is a software framework designed to ease the development and implementation of field inference algorithms. Field equations are formulated independently of the underlying spatial geometry allowing the user to focus on the algorithmic design. Under the hood, NIFTy ensures that the discretization of the implemented equations is consistent. This enables the user to prototype an algorithm rapidly in 1D and then apply it to high‐dimensional real‐world problems. This paper introduces NIFTy 3, a major upgrade to the original NIFTy framework. NIFTy 3 allows the user to run inference algorithms on massively parallel high performance computing clusters without changing the implementation of the field equations. It supports n‐dimensional Cartesian spaces, spherical spaces, power spaces, and product spaces as well as transforms to their harmonic counterparts. Furthermore, NIFTy 3 is able to handle non‐scalar fields, such as vector or tensor fields. The functionality and performance of the software package is demonstrated with example code, which implements a mock inference inspired by a real‐world algorithm from the realm of information field theory. NIFTy 3 is open‐source software available under the GNU General Public License v3 (GPL‐3) at https://gitlab.mpcdf.mpg.de/ift/NIFTy/tree/NIFTy_3 . 相似文献
28.
29.
30.
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