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排序方式: 共有618条查询结果,搜索用时 15 毫秒
491.
Jerome Kretzschmar Anne Wollenberg Satoru Tsushima Katja Schmeide Margret Acker 《Molecules (Basel, Switzerland)》2022,27(13)
Although 2-phosphonobutane-1,2,4,-tricarboxylic acid, PBTC, has manifold industrial applications, relevant and reliable data on the protonation of PBTC are poor. However, these data are critical parameters for ascertaining PBTC speciation, especially with regard to a sound structural and thermodynamic characterization of its metal ion complexes. A rigorous evaluation of pH-dependent 1H, 13C, and 31P chemical shifts along with accessible scalar spin–spin coupling constants (J) was performed in order to determine the pKa values of PBTC in 0.5 molal NaCl aqueous solution by means of nuclear magnetic resonance (NMR) spectroscopy. The phosphonate group revealed pKa values of 0.90 ± 0.02 and 9.79 ± 0.02, and the pKa values associated with the carboxylic groups are 3.92 ± 0.02, 4.76 ± 0.03, and 6.13 ± 0.03. Supported by DFT-calculated structures revealing strong intramolecular hydrogen bonding, the sequence of deprotonation could be unambiguously determined. 相似文献
492.
The effective linear elastic properties of silicon nitride (Si3N4) are estimated based on first–, third–, and fifth–order bounds of the strain energy density. This specific type of material is a mixture of two linear elastic materials with different material symmetries. The β-Si3N4 grains have a hexagonal symmetry with significant amount of anisotropy, whereas the glassy phase is approximately isotropic. The results are as follows: i) The fifth–order upper and lower bounds are almost identical. Therefore, these bounds are sufficient for estimating the effective elastic properties. ii) For fixed elastic constants of the hexagonal β-Si3N4 grains, the effective properties of Si3N4 are determined as a function of properties of the glassy phase and its volume fraction. The corresponding diagrams allow for the inverse identification of the elastic properties of the glassy phase. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
493.
Christiane Ruff Katja Hr Bernhard Weckerle Peter Schreier Thorsten Knig 《Journal of separation science》2000,23(5):357-359
Isotope ratio monitoring gas chromatography‐mass spectrometry of the 2H/1H ratio by pyrolysis isotope ratio mass spectrometry (P‐IRMS) was used to analyze benzaldehyde originating from various sources. Based on the δ2HSMOW value of an authentic reference sample determined with an elemental analyzer (EA), the range of reproducibility and linearity was checked. Correct (EA related) and reproducible data were obtained for sample amounts >0.6 μg benzaldehyde (on column). In another series of experiments, the influence of sample preparation, i. e. simultaneous distillation‐extraction (SDE) was found to be negligible. The following ranges of δ2HSMOW values were determined for benzaldehyde using five types of samples, i. e. (i) synthetic (δ2HSMOW –78 to –85‰, ex benzal chloride; +420 to +668‰, ex toluene) and ‘natural’ (including ‘ex‐cassia’) references (δ2HSMOW –83 to –144‰); (ii) bitter almond oils (δ2HSMOW –113 to –148‰); (iii) fruits (δ2HSMOW –111 to –146‰); (iv) kernels (δ2HSMOW –115 to –188‰); and (v) leaves (δ2HSMOW –165 to –189‰). 相似文献
494.
Peter Kircher Gottfried Huttner Katja Heinze Gerd Renner 《Angewandte Chemie (International ed. in English)》1998,37(12):1664-1666
Octahedral clusters from p-block elements are rare ; however, the only known molecular aggregate of this kind, [{(CO)5Cr}6Sn6]2−, has now been supplemented by the isoelectronic cluster [{(CO)5Cr}6Ge6]2− ( 1 ). 相似文献
495.
Inside Cover: Enzymatic or In Vivo Installation of Propargyl Groups in Combination with Click Chemistry for the Enrichment and Detection of Methyltransferase Target Sites in RNA (Angew. Chem. Int. Ed. 21/2018)
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496.
Borja Mateos Marco Sealey‐Cardona Katja Balazs Judith Konrat Guenther Staffler Robert Konrat 《Angewandte Chemie (International ed. in English)》2020,59(10):3886-3890
Interactions of transmembrane receptors with their extracellular ligands are essential for cellular communication and signaling and are therefore a major focus in drug discovery programs. The transition from in vitro to live cell interaction studies, however, is typically a bottleneck in many drug discovery projects due to the challenge of obtaining atomic‐resolution information under near‐physiological conditions. Although NMR spectroscopy is ideally suited to overcome this limitation, several experimental impairments are still present. Herein, we propose the use of methylcellulose hydrogels to study extracellular proteins and their interactions with plasma membrane receptors. This approach reduces cell sedimentation, prevents the internalization of membrane receptors, and increases cell survival, while retaining the free tumbling of extracellular proteins. 相似文献
497.
498.
499.
Jelka Šuštar-Vozlič Katja Rostohar Andrej Blejec Petra Kozjak Zoran Čergan Vladimir Meglič 《Analytical and bioanalytical chemistry》2010,396(6):2031-2041
In order to comply with the European Union regulatory threshold for the adventitious presence of genetically modified organisms
(GMOs) in food and feed, it is important to trace GMOs from the field. Appropriate sampling methods are needed to accurately
predict the presence of GMOs at the field level. A 2-year field experiment with two maize varieties differing in kernel colour
was conducted in Slovenia. Based on the results of data mining analyses and modelling, it was concluded that spatial relations
between the donor and receptor field were the most important factors influencing the distribution of outcrossing rate (OCR)
in the field. The approach for estimation fitting function parameters in the receptor (non-GM) field at two distances from
the donor (GM) field (10 and 25 m) for estimation of the OCR (GMO content) in the whole receptor field was developed. Different
sampling schemes were tested; a systematic random scheme in rows was proposed to be applied for sampling at the two distances
for the estimation of fitting function parameters for determination of OCR. The sampling approach had already been validated
with some other OCR data and was practically applied in the 2009 harvest in Poland. The developed approach can be used for
determination of the GMO presence at the field level and for making appropriate labelling decisions. The importance of this
approach lies in its possibility to also address other threshold levels beside the currently prescribed labelling threshold
of 0.9% for food and feed. 相似文献
500.
Christoph Frster Daniel Siebler Katja Heinze 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(9):m235-m237
The title compund, [Fe(C5H6N)(C7H7O2)], features one strong intermolecular hydrogen bond of the type N—H...O=C [N...O = 3.028 (2) Å] between the amine group and the carbonyl group of a neighbouring molecule, and vice versa, to form a centrosymmetric dimer. Furthermore, the carbonyl group acts as a double H‐atom acceptor in the formation of a second, weaker, hydrogen bond of the type C—H...O=C [C...O = 3.283 (2) Å] with the methyl group of the ester group of a second neighbouring molecule at (x, −y − , z − ). The methyl group also acts as a weak hydrogen‐bond donor, symmetry‐related to the latter described C—H...O=C interaction, to a third molecule at (x, −y − , z + ) to form a two‐dimensional network. The cyclopentadienyl rings of the ferrocene unit are parallel to each other within 0.33 (3)° and show an almost eclipsed 1,1′‐conformation, with a relative twist angle of 9.32 (12)°. The ester group is twisted slightly [11.33 (8)°] relative to the cylopentadienyl plane due to the above‐mentioned intermolecular hydrogen bonds of the carbonyl group. The N atom shows pyramidal coordination geometry, with the sum of the X—N—Y angles being 340 (3)°. 相似文献