全文获取类型
收费全文 | 11974篇 |
免费 | 1267篇 |
国内免费 | 1275篇 |
专业分类
化学 | 10074篇 |
晶体学 | 94篇 |
力学 | 1052篇 |
综合类 | 184篇 |
数学 | 553篇 |
物理学 | 2559篇 |
出版年
2024年 | 28篇 |
2023年 | 164篇 |
2022年 | 434篇 |
2021年 | 504篇 |
2020年 | 587篇 |
2019年 | 423篇 |
2018年 | 429篇 |
2017年 | 453篇 |
2016年 | 592篇 |
2015年 | 520篇 |
2014年 | 570篇 |
2013年 | 1230篇 |
2012年 | 690篇 |
2011年 | 691篇 |
2010年 | 526篇 |
2009年 | 595篇 |
2008年 | 578篇 |
2007年 | 684篇 |
2006年 | 604篇 |
2005年 | 540篇 |
2004年 | 477篇 |
2003年 | 406篇 |
2002年 | 409篇 |
2001年 | 272篇 |
2000年 | 295篇 |
1999年 | 248篇 |
1998年 | 237篇 |
1997年 | 195篇 |
1996年 | 166篇 |
1995年 | 148篇 |
1994年 | 110篇 |
1993年 | 121篇 |
1992年 | 109篇 |
1991年 | 78篇 |
1990年 | 63篇 |
1989年 | 36篇 |
1988年 | 43篇 |
1987年 | 36篇 |
1986年 | 29篇 |
1985年 | 32篇 |
1984年 | 31篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 21篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
81.
In this paper we describe the experimental analysis of a novel ion-exchange polymer metal composite (IPMC) actuator under
large external voltage. The experimental analysis is supplemented with a coupled thermodynamic model, which includes mass
transport across the thickness of the polymer actuator, chemical reactions at boundaries, and deformation as a function of
the solvent (water) distribution. In this paper, the case of large electrode potentials (over 1.2 V) has been analyzed experimentally
and theoretically. At these voltage levels, electrochemical reactions take place at both electrodes. These are used in the
framework of overpotential theory to develop boundary conditions for the water transport in the bulk of polymer. The model
is then simplified to a three-component system comprised of a fixed negatively charged polymeric matrix, protons, and free
water molecules within the polymer matrix. Among these species, water molecules are considered to be the dominant species
responsible for the deformation of the IPMC actuators. Experiments conducted at different initial water contents are described
and discussed in the context of the proposed deformation mechanism. Comparison of numerical simulations with experimental
data shows good agreement. 相似文献
82.
软x射线近贴显微技术 总被引:1,自引:0,他引:1
软x射线近贴显微技术不但可使活的生物样品成象,分辨率高于光学显微镜,而且人为的样品准备程序在该技术中都可避免。本文描述了用高功率激光打靶产生的等离子体作为软x射线源而进行的近贴显微研究,并得到了分辨率好于1μm的结果。 相似文献
83.
84.
A new ternary complex [Ni(phen)(pmal)]·8H2O (phen = 1,10-phenanthroline,pmal2- = phenethyl malonic acid) has been synthesized by the reaction of nickel acetate, phen and phenethyl malonic acid. Elemental analysis, IR spectra and X-ray single-crystal diffraction were carried out to determine the composition and crystal structure. Crystal data for this complex: triclinic system, space group P1, a = 10.387(5), b = 13.112(6), c = 14.229(6) (A), α = 76.176(7), β =83.778(8), y = 71.770(6)°, C35H42N4O12Ni, Mr= 769.44, Z = 2, F(000) = 808, V = 1786.1 (A)3, Dc =1.431 g/cm3, μ = 0.612 mm-1, the final R = 0.0653 and wR = 0.1033 for 9379 (Rint = 0.0244)independent reflections and 4730 observed reflections (I > 2σ(I)). Structural analysis shows that the coordination geometry of Ni(Ⅱ) is a distorted octahedron. A novel two-dimensional structure is constructed from (H2O)4 and (H2O)12 water clusters, and the complex forms a 3-D network supramolecular structure by hydrogen bonds and π-π stacking of neighboring phens. 相似文献
85.
Susanne K. Wiedmer Toni Andersson Marika Sündermann Marja‐Liisa Riekkola Heikki Tenhu 《Journal of Polymer Science.Polymer Physics》2007,45(19):2655-2663
Cationic polyelectrolytes were synthesized and used as semipermanent coating materials for capillaries in electrophoresis. The polyelectrolytes used were a homopolymer of poly(methacryl oxyethyl trimethylammonium chloride) (PMOTAC) and its poly(ethylene glycol) (PEG)‐grafted analogue. Two PMOTAC polyelectrolytes, with molar masses of 85,000 and 300,000 g/mol, and PEG‐grafted PMOTAC with a molar mass of 280,000 g/mol were synthesized and then characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. Attachment of the polyelectrolytes to the wall of the fused silica capillary for electrophoresis caused the electroosmotic flow (EOF) to reverse. The polyelectrolyte coatings were tested over the pH range 2–11 at different buffer ionic strengths, and the most stable and strongest anodic EOFs were obtained at acidic pH values with low ionic strength buffers. Between runs the capillary is merely rinsed for 2 or 3 min with the background electrolyte solution. With the PMOTAC coatings at pH values ≤5, the RSDs of the EOFs were less than 2.9% after 60 injections. The effects of the molar mass of the polycation and of PEGylation of PMOTAC on the interactions between the polycations and basic proteins were studied at acidic pH values. The differences in the effective electrophoretic mobilities, resolution values, and plate numbers of the proteins with the different coatings were due to the EOF, as demonstrated through calculations of reduced mobilities, relative resolution values, and relative plate numbers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2655–2663, 2007 相似文献
86.
A multiparameter boundary-value problem of fresh infiltration water seepage in a drained fringe above quiescent saline water is solved in the direct statement and studied in detail. 相似文献
87.
This paper is aimed at investigating the effect of the initial water content in a vertisol sample on the whole wetting-drying
process leading the system to a change in volume. In order to do this, an experimental setup was realized and employed with
very thin soil layers wetted from below (“per ascensum”). The results show that the effect of the initial water content on
the swelling-shrinkage process is to shift the corresponding curve e-ϑ towards bigger-smaller values of the humidity but does not seem to affect the dynamics of the process.
The text was submitted by the authors in English. 相似文献
88.
Wen-Yin Chen Bo-Jung Chen Hung-Hsin Shih Chien-Hong Cheng 《Applied Surface Science》2006,252(19):6594-6596
A model organic light-emitting diodes (OLEDs) with structure of tris(8-hydroxyquinoline) aluminum (Alq3)/N,N′-diphenyl-N,N′-bis[1-naphthy-(1,1′-diphenyl)]-4,4′-diamine (NPB)/indium tin oxide (ITO)-coated glass was fabricated for diffusion study by ToF-SIMS. The results demonstrate that ToF-SIMS is capable of delineating the structure of multi-organic layers in OLEDs and providing specific molecular information to aid deciphering the diffusion phenomena. Upon heat treatment, the solidity or hardness of the device was reduced. Complicated chemical reaction might occur at the NPB/ITO interface and results in the formation of a buffer layer, which terminates the upper diffusion of ions from underlying ITO. 相似文献
89.
Chien-Cheng Tsai 《Applied Surface Science》2006,253(4):1898-1902
Nanotube aggregates with high porosity were prepared from hydrothermal treatment of TiO2 particles in NaOH at 130 °C, followed by HCl rinsing to different pH values. Pore structure of the aggregates, which were mainly mesoporous, was characterized by analyzing the N2 sorption isotherm with different methods including the t-plot and density function theory. The surface area, pore volume and mean pore size of the aggregates increased with the rinsing acidity to reach a maximum (e.g. 400 m2/g in surface area) at pH 1.6 and then decreased with further increase of the acidity. The crystalline phase and composition of the aggregates were, as well, significantly affected by the acidity of the post-treatment rinsing. Large-surface area aggregates were of loosely-attached nanotubes, composed of both anatase TiO2 and H2Ti2O5·H2O, obtained under a mildly acidic rinsing condition, while basic or highly acidic conditions resulted in the formation of closely coagulated dense structures consisting of different crystalline phases. 相似文献
90.
Bekir Dizman Mohamed O. Elasri Lon J. Mathias 《Journal of polymer science. Part A, Polymer chemistry》2006,44(20):5965-5973
New water‐soluble methacrylate polymers with pendant quaternary ammonium (QA) groups were synthesized and used as antibacterial materials. The polymers with pendant QA groups were obtained by the reaction of the alkyl halide groups of a previously synthesized functional methacrylate homopolymer with various tertiary alkyl amines containing 12‐, 14‐, or 16‐carbon alkyl chains. The structures of the functional polymer and the polymers with QA groups were confirmed with Fourier transform infrared and 1H and 13C NMR. The degree of conversion of alkyl halides to QA sites in each polymer was determined by 1H NMR to be over 90% in all cases. The number‐average molecular weight and polydispersity of the functional polymer were determined by size exclusion chromatography to be 32,500 g/mol and 2.25, respectively. All polymers were thermally stable up to 180 °C according to thermogravimetric analysis. The antibacterial activities of the polymers with pendant QA groups against Staphylococcus aureus and Escherichia coli were determined with broth‐dilution and spread‐plate methods. All the polymers showed excellent antibacterial activities in the range of 32–256 μg/mL. The antibacterial activity against S. aureus increased with an increase in the alkyl chain length for the ammonium groups, whereas the antibacterial activity against E. coli decreased with increasing alkyl chain length. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5965–5973, 2006 相似文献