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931.
932.
933.
934.
Rainer Niewa Andreas Czulucki Gudrun Auffermann Martin Meven Frank Steglich 《Journal of solid state chemistry》2010,183(6):1309-1313
Large single crystals of ZrAsxSey (x>y, x+y≤2, PbFCl type of structure, space group P4/nmm) were grown by Chemical Transport. Structural details were studied by single crystal neutron diffraction techniques at various temperatures. One single crystal specimen with chemical composition ZrAs1.595(3)Se0.393(1) was studied at ambient temperature (R1=5.10 %, wR2=13.18 %), and a second crystal with composition ZrAs1.420(3)Se0.560(1) was investigated at 25 K (R1=2.70%, wR2=5.70 %) and 2.3 K (R1=2.30 %, wR2=4.70 %), respectively. The chemical compositions of the crystals under investigation were determined by wavelength dispersive X-ray spectroscopy. The quantification of trace elements was carried out by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry. According to the crystal structure refinements the crystallographic 2a site is occupied by As, together with a significant amount of vacancies. One of the 2c sites is fully occupied by As and Se (random distribution). With respect to the fractional coordinates of the atoms, the crystal structure determinations based on the data obtained at 25.0 K and 2.3 K did not show significant deviations from ambient temperature results. The temperature dependence of the displacement parameters indicates a static displacement of As on the 2a sites (located on the (0 0 1) planes) for all temperatures. No indications for any occupation of interstitial sites or the presence of vacancies on the Zr (2a) site were found. 相似文献
935.
Continuous electrochemical sensing is often carried out in order to track the growth of cells as an alternative to optical monitoring. Planar sensors and multi-sensor chips are applied in case of adhered growing cells, and usually introduced into lab-on-chip systems. Repeated recalibration is necessary with most chemosensors so far and this limits the operational lifetime of such lab-on-chip systems to a few days. An assembly is presented here that eliminates this disadvantage and enables the monitoring of a long-term cultivation of tissue. Cell cultures and sensor are arranged such that they can be separated or contacted at variable times without having an impact on the growth of the cells. The use of a biocompatible nano-porous membrane is especially important. A multi-well system is described where each well is supplied with a planar multi-sensor chip below the adhered cells to determine (a) pH, (b) glucose, (c) oxygen, and—optionally—impedance, for example during the cultivation of cartilage tissue. 相似文献
936.
Pietro Lura Frank Winnefeld Stefanie Klemm 《Journal of Thermal Analysis and Calorimetry》2010,101(3):925-932
Isothermal calorimetry and chemical shrinkage measurements are two independent techniques used to study the development of
hydration in cementitious systems. In this study, calorimetry and chemical shrinkage measurements were combined and simultaneously
performed on hydrating cement paste samples. Portland cement pastes with different water to cement ratios and a cement paste
containing calcium sulfoaluminate clinker and anhydrite were studied. The combined calorimetry/chemical shrinkage test showed
good reproducibility and revealed the different hydration behavior of sealed samples and open samples, i.e., samples exposed
to external water during hydration. Large differences between sealed and open samples were observed in a Portland cement paste
with low water to cement ratio and in the calcium sulfoaluminate paste; these effects are attributed to self-desiccation of
the sealed pastes. Once the setup is fully automatized, it is expected that combined calorimetry/chemical shrinkage measurements
can be routinely used for investigating cement hydration. 相似文献
937.
Katarzyna Szot John D. Watkins Steven D. Bull Frank Marken Marcin Opallo 《Electrochemistry communications》2010,12(6):737-739
Three dimensional carbon film electrodes were prepared from oppositely charged carbon nanoparticles (ca. 9 to 18 nm diameter) by a layer-by-layer approach. This was done by alternative immersion of indium tin oxide plates into suspension of positively and negatively charged particles. A stable film is formed already after single immersion and withdrawal step as confirmed by scanning electron microscopy. Up to ten immersion and withdrawal steps can be used to systematically increase the amount of nanoparticulate carbon material. The capacitive current density and current density of hydrogen peroxide reduction are proportional to the number of immersion and withdrawal steps. The same can be seen for adsorbed redox active 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate). After adsorption of bilirubin oxidase into the film efficient bioelectrocatalytic dioxygen reduction is observed. 相似文献
938.
Frank Jensen 《Theoretical chemistry accounts》2010,126(5-6):371-382
The previously proposed pcJ-n basis sets, optimized for calculating indirect nuclear spin–spin coupling constants using density functional methods, are re-evaluated for finding the optimum contraction scheme as a compromise between computational efficiency and minimizing contraction errors. An exhaustive search is performed for the H2, F2 and P2 molecules, and candidates for optimum contraction schemes are evaluated for a larger test set of 21 molecules. Using the criterion that the contraction error should not exceed the basis set error relative to the basis set limit, the optimum contraction is defined for each basis set. The results show that it is difficult to contract basis sets for calculating spin–spin coupling constants to any significant degree without losing the inherent accuracy. The work provides guidelines for searching for optimum contraction schemes for other properties and/or at theoretical levels where a systematic search is impractical. 相似文献
939.
940.
Wolfgang Baether Stefan Zimmermann Frank Gunzer 《International Journal for Ion Mobility Spectrometry》2010,13(3-4):95-101
Ion mobility spectrometry (IMS) is a well-known method for detecting hazardous compounds in air. Most ion mobility spectrometers use a radioactive source to provide electrons with high energy (5–50 keV) to ionize analytes in a series of chemical reactions. Instead of a radioactive source, we use a non-radioactive electron gun which can be operated in pulsed mode. Thus a delay time between ionization and ion extraction can be introduced which offers the possibility to use the signal decay characteristic of substances as a further discrimination parameter. The influence of voltages supplied to the reaction region and to the electron gun on signal intensities and decay times will be investigated in order to obtain further insight into the dependence of this signal decay on different experimental parameters and correspondingly into the underlying mechanisms. 相似文献