全文获取类型
收费全文 | 663篇 |
免费 | 18篇 |
国内免费 | 18篇 |
专业分类
化学 | 306篇 |
晶体学 | 5篇 |
力学 | 4篇 |
数学 | 311篇 |
物理学 | 73篇 |
出版年
2023年 | 3篇 |
2022年 | 16篇 |
2021年 | 23篇 |
2020年 | 12篇 |
2019年 | 17篇 |
2018年 | 10篇 |
2017年 | 10篇 |
2016年 | 21篇 |
2015年 | 24篇 |
2014年 | 25篇 |
2013年 | 48篇 |
2012年 | 53篇 |
2011年 | 49篇 |
2010年 | 38篇 |
2009年 | 37篇 |
2008年 | 47篇 |
2007年 | 41篇 |
2006年 | 37篇 |
2005年 | 25篇 |
2004年 | 26篇 |
2003年 | 24篇 |
2002年 | 13篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1971年 | 1篇 |
排序方式: 共有699条查询结果,搜索用时 15 毫秒
101.
We consider the family of fibres of a polynomial function f on a smooth noncompact algebraic real surface and we characterise the regular fibres of f which are atypical due to their asymptotic behaviour at infinity. We compare to the similar problem in the complex case.
Received: 5 May 1998 / Revised version: 20 March 1999 相似文献
102.
C. Berbecaru H.V. Alexandru A. Popescu G. Socol F. Sima Ion Mihailescu 《Applied Surface Science》2009,255(10):5476-5479
Pulsed laser deposition (PLD) method was used to obtain bioglass (BG) thin film coatings on titanium substrates. An UV excimer laser KrF* (λ = 248 nm, τ = 25 ns) was used for the multi-pulse irradiation of the BG targets with 57 or 61 wt.% SiO2 content (and Na2O-K2O-CaO-MgO-P2O5 oxides). The depositions were performed in oxygen atmosphere at 13 Pa and for substrates temperature of 400 °C. The PLD films displayed typical BG of 2-5 μm particulates nucleated on the film surface or embedded in. The PLD films stoichiometry was found to be the same as the targets. XRD spectra have shown, the glass coatings obtained, had an amorphous structure. One set of samples, deposited in the same conditions, were dipped in simulated body fluids (SBFs) and subsequently extracted one by one after several time intervals 1, 3, 7, 14 and 21 days. After washing in deionized water and drying, the surface morphology of the samples and theirs composition were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), IR spectroscopy (FTIR) and energy dispersive X-ray analysis (EDX). After 3-7 days the Si content substantially decreases in the coatings and PO43− maxima start to increase in FTIR spectra. The XRD spectra also confirm this evolution. After 14-21 days the XRD peaks show a crystallized fraction of the carbonated hydroxyapatite (HAP). The SEM micrographs show also significant changes of the films surface morphology. The coalescence of the BG droplets can be seen. The dissolution and growth processes could be assigned to the ionic exchange between BG and SBFs. 相似文献
103.
Alexandru Nedelcu Vincent Guériaux Alexandre Bazin Lydie Dua Arnaud Berurier Eric Costard Philippe Bois Xavier Marcadet 《Infrared Physics & Technology》2009,52(6):412-418
A 30 months European Space Agency project started in March 2008, whose overall purpose is to expand and assess the performance of broadband (11–15 μm) quantum detectors for spectro-imaging applications: Dispersive Spectrometers and Fourier Transform Spectrometers. We present here the technical requirements, the development approach chosen as well as preliminary experimental results. Our approach is fully compatible with the final array format (1024 × 256, pitch 50–60 μm). We expect the requested uniformity, operability and SNR levels to be achieved at temperatures close to the goal values. The performance level will be demonstrated on 256 × 256, 50 μm pitch arrays. Also, operability and uniformity issues will be addressed on large mechanical 1024 × 256 hybrid arrays. 相似文献
104.
Elisabeth Schmoeger Eva Berger Alexandru Trefilov Alois Jungbauer Rainer Hahn 《Journal of chromatography. A》2009,1216(48):8460-8469
Refolding of proteins must be performed under very dilute conditions to overcome the competing aggregation reaction, which has a high reaction order. Refolding on a chromatography column partially prevents formation of the intermediate form prone to aggregation. A chromatographic refolding procedure was developed using an autoprotease fusion protein with the mutant EDDIE from the Npro autoprotease of pestivirus. Upon refolding, self-cleavage generates a target peptide with an authentic N-terminus. The refolding process was developed using the basic 1.8-kDa peptide sSNEVi-C fused to the autoprotease EDDIE or the acidic peptide pep6His, applying cation and anion exchange chromatography, respectively. Dissolved inclusion bodies were loaded on cation exchange chromatographic resins (Capto S, POROS HS, Fractogel EMD SO3−, UNOsphere S, SP Sepharose FF, CM Sepharose FF, S Ceramic HyperD F, Toyopearl SP-650, and Toyopearl MegaCap II SP-550EC). A conditioning step was introduced in order to reduce the urea concentration prior to the refolding step. Refolding was initiated by applying an elution buffer containing a high concentration of Tris–HCl plus common refolding additives. The actual refolding process occurred concurrently with the elution step and was completed in the collected fraction. With Capto S, POROS HS, and Fractogel SO3−, refolding could be performed at column loadings of 50 mg fusion protein/ml gel, resulting in a final eluate concentration of around 10–15 mg/ml, with refolding and cleavage step yields of around 75%. The overall yield of recovered peptide reached 50%. Similar yields were obtained using the anion exchange system and the pep6His fusion peptide. This chromatographic refolding process allows processing of fusion peptides at a concentration range 10- to 100-fold higher than that observed for common refolding systems. 相似文献
105.
We prove global well-posedness and scattering in H 1 for the defocusing nonlinear Schrödinger equationson the hyperbolic spaces \({\mathbb{H}^d}\), d ≥ 2, for exponents \({\sigma \in (0, 2/(d-2))}\). The main unexpected conclusion is scattering to linear solutions in the case of small exponents σ; for comparison, on Euclidean spaces scattering in H 1 is not known for any exponent \({\sigma \in (1/d, 2/d]}\) and is known to fail for \({\sigma \in (0, 1/d]}\). Our main ingredients are certain noneuclidean global in time Strichartz estimates and noneuclidean Morawetz inequalities.
相似文献
$\left\{\begin{array}{ll}(i\partial_t+\Delta_g)u=u|u|^{2\sigma};\\u(0)=\phi,\end{array}\right.$
106.
The task of this study is to investigate the influence of various geometric parameters and pressure ratios on the Coanda ejector performance. For numerically investigations we use an implicit formulation of the compressible Reynolds-average Navier-Stokes equations (RANS) for axisymmetric flow with a shear stress transport k − ω (SST model) turbulence model. The numerically results was obtained for a total pressure range 1-5 Bars, imposed at the reservoir inlet. The effect of various factors, such as, the pressure ratio, primary nozzle and ejector configurations on the system performance has been evaluated based on defined performance parameters. The numerical results have been compared with theoretical and experimental results for a given Coanda ejector configuration. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
107.
Elena-Laura Ursu Florica Doroftei Dragos Peptanariu Mariana Pinteala Alexandru Rotaru 《Journal of nanoparticle research》2017,19(5):181
Single-walled carbon nanotubes (SWNTs) are 1D nanostructures with distinct physical and chemical properties that have shown great promise for applications in many fields, including biomedicine. Since for biomedical application the water solubility is crucial and SWNTs have low solubility, various methods (including polymer and biopolymer wrapping, chemical modifications) have been developed to solubilize and disperse them in water. Due to their unique optical properties such as photoluminescence in the NIR and strong resonant Raman signatures, they can be used as nanoprobes in biomedical imaging and phototherapies. Furthermore, decoration of SWNTs with noble metal nanoparticles will induce an excellent surface-enhanced Raman scattering (SERS) effect of the nanoparticles-SWNTs composites, with applications in cell imaging. Herein, we present a new and facile strategy for the DNA-assisted decoration of SWNTs with gold nanoparticles (AuNPs) and their application in SERS imaging. By ultrasonication at room temperature of SWNTs with AuNPs functionalized with synthetic DNA, SWNT-AuNPs nanocomposites with enhanced Raman signal were obtained. Among the important advantages of the proposed method are the presence of the free DNA overhangs around the SWNT-AuNPs suitable for post-synthetic modification of nanocomposite through hybridization of complementary DNA strands containing molecules of interest attached by well-developed bio-conjugation chemistry. 相似文献
108.
Oyer AJ Carrillo JM Hire CC Schniepp HC Asandei AD Dobrynin AV Adamson DH 《Journal of the American Chemical Society》2012,134(11):5018-5021
Applications requiring pristine graphene derived from graphite demand a solution stabilization method that utilizes an easily removable media. Using a combination of molecular dynamics simulations and experimental techniques, we investigate the solublization/suspension of pristine graphene sheets by an equimolar mixture of benzene and hexafluorobenzene (C(6)H(6)/C(6)F(6)) that is known to form an ordered structure solidifying at 23.7 °C. Our simulations show that the graphene surface templates the self-assembly of the mixture into periodic layers extending up to 30 ? from both sides of the graphene sheet. The solvent structuring is driven by quadrupolar interactions and consists of stacks of alternating C(6)H(6)/C(6)F(6) molecules rising from the surface of the graphene. These stacks result in density oscillations with a period of about 3.4 ?. The high affinity of the 1:1 C(6)H(6)/C(6)F(6) mixture with graphene is consistent with observed hysteresis in Wilhelmy plate measurements using highly ordered pyrolytic graphite (HOPG). AFM, SEM, and TEM techniques verify the state of the suspended material after sonication. As an example of the utility of this mixture, graphene suspensions are freeze-dried at room temperature to produce a sponge-like morphology that reflects the structure of the graphene sheets in solution. 相似文献
109.
Alexandru Kristály 《Journal of Mathematical Analysis and Applications》2012,385(1):179-184
We prove a bifurcation result for a perturbed sublinear elliptic problem defined on a compact Riemannian manifold without boundary. This result is then applied to a singular elliptic problem on even-dimensional Euclidean spaces. 相似文献
110.
Perpendicular structured nanowire arrays interaction field distributions (IFDs), as revealed from first-order reversal curves (FORC) diagrams, are related to the presence of the demagnetizing field in the system. Despite the similarity between the geometric properties of bit patterned media and mentioned nanowire arrays, FORC diagrams of these two types of systems are not similar essentially due to the different number of magnetic entities influencing the switch of an individual element. We show that one Preisach–Krasnosel'skii–Pokrovskii (PKP) symmetrical hysteron can be representative of an ideal infinite nanowire array when the field is applied along the wires. Starting from this observation, we present a very simple model based on PKP symmetrical hysterons that can be applied to real finite ferromagnetic nanowire arrays, and is able to describe a wide class of experimentally observed FORC distributions, revealing features due to size effects. We also present IFDs modeled for different geometric characteristics such as array size, interwire distance, and nanowire dimensions, and an identification procedure for the proposed model. 相似文献