全文获取类型
收费全文 | 956篇 |
免费 | 39篇 |
专业分类
化学 | 806篇 |
晶体学 | 1篇 |
力学 | 6篇 |
数学 | 58篇 |
物理学 | 124篇 |
出版年
2024年 | 3篇 |
2023年 | 7篇 |
2022年 | 11篇 |
2021年 | 13篇 |
2020年 | 15篇 |
2019年 | 16篇 |
2018年 | 9篇 |
2017年 | 5篇 |
2016年 | 29篇 |
2015年 | 25篇 |
2014年 | 32篇 |
2013年 | 39篇 |
2012年 | 58篇 |
2011年 | 65篇 |
2010年 | 61篇 |
2009年 | 42篇 |
2008年 | 75篇 |
2007年 | 56篇 |
2006年 | 48篇 |
2005年 | 63篇 |
2004年 | 48篇 |
2003年 | 41篇 |
2002年 | 28篇 |
2001年 | 15篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 17篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 9篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1938年 | 4篇 |
1936年 | 3篇 |
1914年 | 2篇 |
排序方式: 共有995条查询结果,搜索用时 0 毫秒
21.
22.
A. O. Vyrodov J. Heinze M. Dillmann U. E. Meier W. Stricker 《Applied physics. B, Lasers and optics》1995,61(5):409-414
Laser-Induced Fluorescence (LIF) excitation spectra in the NOA–X (0-0) band were used for temperature measurements in the postflame region of high-pressure CH4/air flames. To improve the quality of the measured spectra and to perform reliable line-shape measurements, the initial mixture was doped with approximately 400 ppm NO. At pressures up to 18 bar, excellent agreement was obtained between NO LIF temperatures and NARS/rotational Raman temperatures. Effective broadening coefficients were also determined in these flames. Problems with quantitative concentration measurements of NO and single-pulse temperature measurements at high pressures are discussed. 相似文献
23.
Juliane Strtz Andrea Liedmann Thomas Heinze Steffen Fischer Thomas Groth 《Macromolecular bioscience》2020,20(2)
Sulfated cellulose (CS) represents an interesting biopolymer due to bioactivity comparable to heparin. However, use of CS for making surface coatings or hydrogels requires the presence of reactive groups for covalent reactions. Here, an approach is presented to oxidize cellulose sulfates for subsequent cross‐linking reactions with amino groups to form imine bonds. Cellulose is sulfated by direct sulfation or acetosulfation, followed by a M alaprade oxidation. The CS obtained is characterized by elemental analysis and 13C‐NMR spectroscopy. The resulting oxidized cellulose sulfates (oxCS) have different degrees of sulfation ranging from 0.79 to 1.13 and oxidation degrees from 0.18 to 0.34, but also different mass average molecular mass (MW). Toxicity studies are carried out with mouse 3T3 fibroblasts exposed to aqueous solutions of oxCS. The results show that all oxCS are non‐toxic at lower concentrations (0.5 mg mL?1), but with both increasing degree of oxidation and concentrations, toxic effects are observed particularly for acetosulfated and lesser for direct sulfated oxCS, which is related to a decrease in the MW of the products. It is concluded that oxCS obtained by direct sulfation with MW above 70 kDa may represent a biocompatible material for the applications suggested above. 相似文献
24.
Michael Zech Matthias Saurer Mario Tuthorn Katja Rinne Roland A. Werner Rolf Siegwolf 《Isotopes in environmental and health studies》2013,49(4):492-502
Although the instrumental coupling of gas chromatography-pyrolysis-isotope ratio mass spectrometry (GC-Py-IRMS) for compound-specific δ18O analysis has been commercially available for more than a decade, this method has been hardly applied so far. Here we present the first GC-Py-IRMS δ18O results for trimethylsilyl-derivatives of plant sap-relevant sugars and a polyalcohol (glucose, fructose, sucrose, raffinose and pinitol). Particularly, we focus on sucrose, which is assimilated in leaves and which is the most important transport sugar in plants and hence of utmost relevance in plant physiology and paleoclimate studies. Replication measurements of sucrose standards and concentration series indicate that the GC-Py-IRMS δ18O measurements are not stable over time and that they are amount (area) dependent. We, therefore, suggest running sample batch replication measurements in alternation with standard concentration series of reference material. This allows for carrying out (i) a drift correction, (ii) a calibration against reference material and (iii) an amount (area) correction. Tests with 18O-enriched water do not provide any evidence for oxygen isotope exchange reactions affecting sucrose and raffinose. We present the first application of GC-Py-IRMS δ18O analysis for sucrose from needle extract (soluble carbohydrate) samples. The obtained δ18Osucrose/ Vienna Standard Mean Ocean Water (VSMOW) values are more positive and vary in a wider range (32.1–40.1 ‰) than the δ18Obulk/ VSMOW values (24.6–27.2 ‰). Furthermore, they are shown to depend on the climate parameters maximum day temperature, relative air humidity and cloud cover. These findings suggest that δ18Osucrose of the investigated needles very sensitively reflects the climatically controlled evaporative 18O enrichment of leaf water and thus highlights the great potential of GC-Py-IRMS δ18Osucrose analysis for plant physiology and paleoclimate studies. 相似文献
25.
Illarion Dorofeyev Harald Fuchs Katja Sobakinskaya 《Central European Journal of Physics》2005,3(3):351-375
Spectral characteristics of stochastic fields and their spatial derivatives in various planar structures composed by lossy
materials described by realistic dielectric functions are numerically calculated based on solutions to the problems of multipolar
electromagnetic fields in a plane layered geometry. A displacement of the maximum of the spectral power densities for spatial
derivatives of fluctuating fields to the high-frequency domain, a resonant increase in the density of states of the fluctuating
fields at the frequencies of interface excitations and interference modes for the radiative part of the spectra, the influence
of geometry on the density of states, and other peculiarities are found by numerical calculations and graphically demonstrated.
Interpretations of the above effects are provided. 相似文献
26.
Flexible and adaptive use of strategies and representations in mathematics education 总被引:1,自引:0,他引:1
The flexible and adaptive use of strategies and representations is part of a cognitive variability, which enables individuals to solve problems quickly and accurately. The development of these abilities is not simply based on growing experience; instead, we can assume that their acquisition is based on complex cognitive processes. How these processes can be described and how these can be fostered through instructional environments are research questions, which are yet to be answered satisfactorily. This special issue on flexible and adaptive use of strategies and representations in mathematics education encompasses contributions of several authors working in this particular field. They present recent research on flexible and adaptive use of strategies or representations based on theoretical and empirical perspectives. Two commentary articles discuss the presented results against the background of existing theories. 相似文献
27.
Yoshida Y Schröder S Ferriani P Serrate D Kubetzka A von Bergmann K Heinze S Wiesendanger R 《Physical review letters》2012,108(8):087205
We report a transverse conical spin spiral as the magnetic ground state of a double-layer Mn on a W(110) surface. Using spin-polarized scanning tunneling microscopy, we find a long-range modulation along the [001] direction with a periodicity of 2.4 nm coexisting with a local row-wise antiferromagnetic contrast. First-principles calculations reveal a transverse conical spin-spiral ground state of this system which explains the observed magnetic contrast. The canting of the spins is induced by higher-order exchange interactions, while the spiraling along the [001] direction is due to frustrated Heisenberg exchange and Dzyaloshinskii-Moriya interaction. 相似文献
28.
Fructosamine-3-kinase (FN3K) mediates the regeneration of lysine from fructosamines formed on proteins as a result of the
‘early’ Maillard reaction. As fructosamines and advanced glycation endproducts derived therefrom are supposed to play an adverse
role in the development of diabetic complications, FN3K is discussed as a protein-repairing enzyme. In this study, a method
for the determination of FN3K activity in erythrocyte lysate is described which overcomes the complexity of currently known
assays. The assay is based on the FN3K-dependent conversion of the synthetic UV-active fructosamine N
α-hippuryl-N
ε-(1-deoxy-D-fructosyl)lysine (BzGFruK) to N
α-hippuryl-N
ε-(phosphofructosyl)lysine (BzGpFruK). The FN3K activity was quantified by measuring the formation of BzGpFruK using RP-HPLC
with UV detection. Identification of the metabolite BzGpFruK was achieved by means of UV and mass spectroscopy. The results
are related to the content of haemoglobin for standardisation. First activity measurements with a chosen number of normoglycaemic
subjects confirmed the convenient applicability of the method and showed distinctly different individual activities, as already
discovered recently. The new established assay needs only the equipment of a routine laboratory with HPLC instrumentation.
This should facilitate further studies about a possible relationship between the FN3K activity and the development of diabetic
complications. 相似文献
29.
Winald R. Kitzmann Prof. Dr. Katja Heinze 《Angewandte Chemie (International ed. in English)》2023,62(15):e202213207
Transition metal complexes with photoactive charge-transfer excited states are pervasive throughout the literature. In particular, [Ru(bpy)3]2+ (bpy=2,2′-bipyridine), with its metal-to-ligand charge-transfer emission, has been established as a key complex. Meanwhile, interest in so-called spin-flip metal-centered states has risen dramatically after the molecular ruby [Cr(ddpd)2]3+ (ddpd=N,N′-dimethyl-N,N′-dipyridin-2-yl-pyridine-2,6-diamine) led to design principles to access strong, long-lived emission from photostable chromium(III) complexes. This Review contrasts the properties of emissive charge-transfer and spin-flip states by using [Ru(bpy)3]2+ and [Cr(ddpd)2]3+ as prototypical examples. We discuss the relevant excited states, the tunability of their energy and lifetimes, and their response to external stimuli. Finally, we identify strengths and weaknesses of charge-transfer and spin-flip states in applications such as photocatalysis and circularly polarized luminescence. 相似文献
30.
The new ternary pnictides, Ti(1-delta)Mo(1+delta)Pn4 (Pn = As, Sb), were uncovered during our search for novel thermoelectric materials. Both compounds crystallize in the OsGe2 type in the monoclinic space group C2/m, with lattice dimensions of a = 10.1222(9) A, b = 3.6080(3) A, c = 8.1884(8) A, beta = 120.230(2) degrees , and V = 258.38(7) A3 (Z = 2) for Ti(0.79(1))Mo(1.21)Sb4 and a = 9.1580(2) A, b = 3.3172(1) A, c = 7.6666(1) A, beta = 119.496(1) degrees , and V = 202.720(4) A3 (Z = 2) for Ti(0.86(2))Mo(1.14)As4. The electronic structure calculations predicted metallic behavior for these compounds, which was in agreement with the measured temperature dependence of the electrical conductivity and Seebeck coefficient. 相似文献