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排序方式: 共有2370条查询结果,搜索用时 15 毫秒
921.
《Biomedical chromatography : BMC》2017,31(6)
A specific and sensitive LC–MS/MS with protein precipitation– ultrasonic breaking method has been developed and validated for simultaneous determination of doxorubicin (DOX) and curcumin (Cur) in DOX and Cur co‐loaded hyaluronic acid–vitamin E succinatemicelles [(DOX + Cur)–polymeric micelles (PMs)] in subcellular compartments of resistant MCF‐7/Adr cells. Sequential extraction of four subcellular protein fractions (cytosolic, membrane/organelle, nucleic and cytoskeleton) was performed directly from MCF‐7/Adr cells after incubation with (DOX + Cur)–PMs. An ultrasonic breaking–methanol precipitation method was used for extraction of the fractions, and the micelle breaking efficiency with methanol was 98.1 and 97.6% for DOX and Cur, respectively. The analytes were analyzed using positive electrospray ionization coupled with multiple reaction monitoring. The calibration curves were linear over a concentration range of 0.5–400 ng/mL for DOX and 2–2000 ng/mL for Cur, and the recovery for the two analytes were >85% with negligible matrix effect. The intra‐day and inter‐day precision was <10.80% and relative error was within ±7.70%. The developed method was successfully applied for subcellular determination of DOX and Cur in MCF‐7/Adr cells. Moreover, Cur and (DOX + Cur)–PMs had a marked promoting effect on the distribution of DOX in the nucleic protein fraction. 相似文献
922.
For a non-contact ultrasonic material removal process, the control of the standoff position can be crucial to process performance; particularly where the requirement is for a standoff of the order of <20 μm. The standoff distance relative to the surface to be machined can be set by first contacting the ultrasonic tool tip with the surface and then withdrawing the tool to the required position. Determination of this contact point in a dynamic system at ultrasonic frequencies (>20 kHz) is achieved by force measurement or by detection of acoustic emissions (AE). However, where detection of distance from a surface must be determined without contact taking place, an alternative method must be sought. 相似文献
923.
In recent years, green chemistry using environmentally benign reagents and conditions has become one of the most fascinating developments in the synthesis of widely used organic compounds. This review describes the theory and importance of ultrasound as an efficient tool in the synthesis of heterocyclic compounds. 相似文献
924.
Studies on photocrosslinking and flame‐retardant properties of chalcone‐based polyacrylamides 下载免费PDF全文
A photocrosslinkable polycyclic chalcone‐based acrylamide has been synthesized by Claisen–Schmidt condensation reaction and then polymerized via free radical polymerization technique using azobisisobutyronitrile (AIBN) as an initiator. The resulting polymers have been characterized by FT‐IR, 1H‐NMR and 13C‐NMR analytic techniques. The molecular weights of the polymers were determined by gel permeation chromatography. The thermal properties of synthesized polymers were characterized by TGA analysis, and the obtained results show good thermal and thermo‐oxidative stability which is required for a negative photo resist. The high flame‐retardant properties are calculated from limiting oxygen index (LOI) values and are found to be 36.9 and 32.0 for naphthyl and anthryl chalcone‐based polymers, respectively. The experimentally determined LOI values of polymers (PMNPA and PAPA) are 34.3 and 30.2, respectively, and the values are closer to theoretically found LOI values. However, the cone calorimetry of flame‐retardant PMNPA only showed a slight decrease in peak of heat release rate (PHRR) and total heat release (THR) compared to PAPA but the ignition time (TTI) of PMNPA is slightly higher than PAPA. The photocrosslinking properties of the polymers were investigated by UV spectroscopy technique and were found that with the increase in number of aromatic rings, the rate of crosslinking decreases. Thus polyacrylamides are useful in photolithography technology as well as flame‐retardant property in electrical appliances. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
925.
Allocation of transmit power is critical for spectrum sharing and coexistence of mutually interfering wireless systems. In this paper we present a novel approach for allocation of transmit power, which is based on a non-greedy procedure that aims at maximizing transmission rate while also controlling interference levels. The proposed approach is fully distributed and requires no central control or coordination. Numerical results obtained from simulations are presented to illustrate the performance of the proposed approach in both sparse and dense environments. In sparse wireless environments, where there are fewer mutually interfering wireless links than available frequency bands, the proposed approach yields power allocations which outperform those obtained by applying alternative power allocation strategies, while in dense environments, where there are more interfering links than available frequency bands, the proposed approach yields power allocations with performance similar to those of existing power strategies. Thus, the distributed power allocation procedure based on the proposed approach is a drop-in replacement algorithm that yields better system throughput than existing algorithms for spectrum sharing. 相似文献
926.
An acousto-optical reconstruction method for acoustic signals using multidirectional light diffraction by finite amplitude ultrasonic pulses is presented. When crossing the ultrasonic field, the far field diffracted laser light intensity of an incident convergent lightbeam becomes modulated in time. It is found that for special conditions, concerning direction of observation, ultrasonic frequency, power level and interaction length, the modulated light intensity is almost an exact copy of the diffracting acoustic pulse. Reconstruction can be completed by applying a fast Fourier transform (FFT) routine. Examples are provided and applications of this optical probing technique are suggested. 相似文献
927.
928.
H.G. Kraus 《Ultrasonics》1983,21(1):11-18
A technique has been developed for processing ultrasonic focused transducer pulse-echo scan data for improved non-destructive inspection of subjects having non-smooth or analytically discontinuous front surfaces. Synthetic aperture focusing, phase shifted average processing is used where the entire inspection field is focused. This development was for two dimensions but is easily extended to three. The method uses finite elements to define the front surface geometry and includes an arbitrarily varying transducer scan path. Transducer tilt angle and synthetic aperture may take on a full range of values. A general computer code has been written to perform this processing and so prepare data for imaging. A test/comparison example is given. 相似文献
929.
Andrey S. Ostrovsky Ernesto Pino Mota Jesús I. Palma Cuatianquiz 《Optics and Lasers in Engineering》2003,40(1-2):43-53
It is shown that the problem of classification of images that have the perfectly random nature may be solved with the help of synthetic discriminant functions being synthesized by least-squares technique to separate linearly the power spectra of the corresponding random image fields. The realization of the proposed method by means of an optical technique is discussed, and its efficiency is illustrated by two examples of real-life texture classification. 相似文献
930.
Bernard Hosten 《Ultrasonics》1992,30(6):365-370
This paper presents a method of testing the ultrasonic measurements of the stiffness matrix, and the identification of the anisotropic behaviour, of composite materials. Some linear combinations of elastic constants are invariants for a rotation around an axis of symmetry. If the stacking sequence is the only parameter which changes in a set of long-fibre composites made of the superimposition of plies, the composites must own these invariants. So, PEEK-carbon fibre composite samples were constructed in this way to measure their elastic properties by immersion and contact ultrasonic methods, and to compare the results with predicted invariants. By changing the stacking sequence of plies three anisotropic models are tested: orthotropic, hexagonal and quadratic. Measurements of ultrasonic velocities in various planes of propagation permit the identification of the elastic constant and invariants. From the invariance of these linear combinations, the precision of the three-dimensional effective moduli can be estimated. 相似文献