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排序方式: 共有957条查询结果,搜索用时 156 毫秒
951.
Shui G Cheong WF Jappar IA Hoi A Xue Y Fernandis AZ Tan BK Wenk MR 《Journal of chromatography. A》2011,1218(28):4357-4365
Direct measurement of various sterols in crude lipid extracts in a single experiment from limited biological samples is challenging. Current mass spectrometry (MS) based approaches usually require chemical derivatization before subjecting to MS analysis. Here, we present a derivatization-independent method for analyzing various sterols, including cholesterol and its congeners, using liquid chromatography and atmospheric pressure chemical ionization mass spectrometry. Based on the specific tandem mass spectrometry pattern of cholesterol, multiple reaction monitoring (MRM) transitions were used to quantify free cholesterol and its fatty acyl esters. Several cholesterol oxidation products could also be measured using the upfront liquid chromatography separation and specific MRM transitions. The method was validated alongside established enzymatic assays in measuring total cholesterol. As a proof of concept, we analyzed plasma sterols in rabbits administrated with a high cholesterol diet (HCD) which is a classical atherosclerotic model. Free cholesterol, cholesterol esters, 7-hydroxycholesterol, and 7-ketocholesterol were elevated in plasma of rabbits on HCD. This method could also serve as an excellent tool for quantitative analysis of other sterols such as ergosterol and sitosterol in other organisms beside mammalian. In Saccharomyces cerevisiae, our results indicated dramatic increases of the ratio of ergosterol esters to free ergosterol in both yeh2Δ and tgl1Δ cells, which are consistent with the function of the respective enzymes. 相似文献
952.
Mohammad Rafiqul Haque Mohamed Fayed Amy-Lee Gunter Othman Smadi Lyes Kadem Hoi Dick Ng 《显形杂志》2011,14(4):311-314
Abstract
With the aid of computational fluid dynamics (CFD) and simple flow visualization technique using flowing soap-film, we present here the wake structures behind an array of cylinders for Reynolds numbers corresponding to both laminar and turbulent flow regimes. The image results illustrate interesting vortex interactions past these equally spaced cylinders; for low Reynolds number flow, well-organized wake pattern persists and manifests unsteadily to different symmetry states. An increase of free stream flow velocity causes the wake transition, resulting in the formation of asymmetric flow wake with chaotic mixing at the far wake. Observations from both the numerical simulations and soap-film are in good agreement at least qualitatively. 相似文献953.
ZK60A nanocomposite containing Al2O3 nanoparticle reinforcement (50 nm average size) was fabricated using solidification processing followed by hot extrusion.
The nanocomposite exhibited similar grain size to the monolithic alloy, reasonable Al2O3 nanoparticle distribution, non-dominant (0 0 0 2) texture in the longitudinal direction, and 15% higher hardness than the
monolithic alloy. Compared to the monolithic alloy (in tension), the nanocomposite exhibited lower yield strength (0.2%TYS)
(−4%) and higher ultimate strength (UTS), failure strain, and work of fracture (WOF) (+13%, +170%, and +200%, respectively).
Compared to the monolithic alloy (in compression), the nanocomposite exhibited lower yield strength (0.2%CYS) (−5%) and higher
ultimate strength (UCS), failure strain, and WOF (+6%, +41%, and +43%, respectively). The effects of Al2O3 nanoparticle addition on the enhancement of tensile and compressive properties of ZK60A are investigated in this article. 相似文献
954.
In recent years, a variety of effective chaos-based image cryptosystems have been proposed. One of the architectures of this kind of cryptosystems is composed of multiple rounds of substitution and diffusion. As the confusion and diffusion effects are solely contributed by the substitution and the diffusion stages, respectively, the required overall rounds of operations in achieving a certain level of security is found more than necessary. In this Letter, we suggest to introduce a certain diffusion effect in the substitution stage by simple sequential add-and-shift operations. Although this leads to a longer processing time in a single round, the overall encryption time is reduced as fewer rounds are required. Simulation results show that at a similar performance level, the proposed cryptosystem needs less than one-third the encryption time of an existing fast cryptosystem. The effective acceleration of chaos-based image cryptosystems is thus achieved. 相似文献
955.
In Tae Kim Sang Woo Lee Tae Hyoung Kwak Jung Youl Lee Hyang Suk Park So Young Kim Chang Min Lee Hoi Eun Jung Jun‐Gill Kang Tack‐Jin Kim Hee‐Jung Kang ChangMoon Park Ronald L. Elsenbaumer 《Macromolecular rapid communications》2002,23(9):551-554
Oxidative coupling reaction of 1‐hexyl–3,4‐dimethylpyrrole affords a conjugated conducting poly(1‐hexyl‐3,4‐dimethyl‐2,5‐pyrrolylene) (PHDP), which is completely soluble in common organic solvents. The luminescence of PHDP is comparable to that of poly(N‐vinylcarbazole) (PVK), which has been widely used in electroluminescence devices. The quantum efficiency of PHDP is 2.5 times higher than that of PVK. A rationalization is presented relating the conductivity of PHDP to its polymer structure. 相似文献
956.
Varun Kumar Sing Souvik Sur Mohd. Musharraf Ratan Kumar Dey Sanjay Kumar Swain Suman Shekhar 《Macromolecular Symposia》2024,413(1):2300045
In the present study, the degradation process of piperazine (PP) immobilized silica gel (SiPP) is investigated under dynamic conditions. The degradation of SiPP is studied with thermogravimetric analyzer (TGA). The kinetics of degradation process is analyzed by Kissinger method, Flynn–Wall–Ozawa's (FWO) method, and Deconvolution method. It is found that degradation of SiPP can be described by parallel independent two-portion process model, which includes two processing state of the system (marked by processes 1 and 2), where process 1 and 2 can be attributed to decomposition processes of organic moiety attached on silica surface. The apparent activation energy (Ea) is calculated by Flynn–Wall–Ozawa's (FWO) method and deconvolution method. 相似文献
957.