全文获取类型
收费全文 | 8578篇 |
免费 | 1004篇 |
国内免费 | 1165篇 |
专业分类
化学 | 5205篇 |
晶体学 | 91篇 |
力学 | 1085篇 |
综合类 | 84篇 |
数学 | 681篇 |
物理学 | 3601篇 |
出版年
2024年 | 16篇 |
2023年 | 92篇 |
2022年 | 213篇 |
2021年 | 214篇 |
2020年 | 208篇 |
2019年 | 216篇 |
2018年 | 229篇 |
2017年 | 242篇 |
2016年 | 299篇 |
2015年 | 295篇 |
2014年 | 404篇 |
2013年 | 707篇 |
2012年 | 440篇 |
2011年 | 477篇 |
2010年 | 415篇 |
2009年 | 522篇 |
2008年 | 517篇 |
2007年 | 548篇 |
2006年 | 510篇 |
2005年 | 459篇 |
2004年 | 438篇 |
2003年 | 345篇 |
2002年 | 657篇 |
2001年 | 303篇 |
2000年 | 273篇 |
1999年 | 238篇 |
1998年 | 235篇 |
1997年 | 183篇 |
1996年 | 155篇 |
1995年 | 153篇 |
1994年 | 134篇 |
1993年 | 104篇 |
1992年 | 84篇 |
1991年 | 76篇 |
1990年 | 44篇 |
1989年 | 53篇 |
1988年 | 38篇 |
1987年 | 27篇 |
1986年 | 28篇 |
1985年 | 33篇 |
1984年 | 22篇 |
1983年 | 7篇 |
1982年 | 25篇 |
1981年 | 17篇 |
1980年 | 7篇 |
1979年 | 15篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
The Stokes motions of three-dimensional screw-sensed slender particles in a homogeneous shear field are investigated, including the effects of buoyancy. Conclusions are drawn about the possibility of achieving a separation of mixtures of right- and left-handed particles. The linearity of the Stokes equations allows complex flows to be solved by adding the effects of the several terms which describe the flow in which the particle is immersed. The homogeneous shear flow considered here consists of three such terms; solutions for a series of 12 unit motions are sufficient to determine the hydrodynamic resistance tensors. The forces and torques experienced by screw-sensed particles are calculated from these 51 resistance tensors, using slender-filament theory. The results allow an estimate of the range of buoyancy parameters for which gravitational sedimentation can be neglected. The fundamental component of the particle motion is a rotation, at approximately the same angular velocity as that of the fluid. Superimposed on this are variations, of large period, in the particle orientation. A phase plane analysis is used to find the terminal orientations. Very long calculation times are required for the phase portrait. An approximate method based on azimuthally-averaged equations is developed to avoid the requirements for long time integration. 相似文献
22.
测定了室温下烃类(乙炔、乙烷)烟粒的红外复折射率,并讨论了所获数据在测量烟浓度与烟粒大小分类、计算光谱吸收系数及在特定浓度与温度下评估烟雾辐射率方面的应用。 相似文献
23.
T. Ramanathan S. Stankovich D. A. Dikin H. Liu H. Shen S. T. Nguyen L. C. Brinson 《Journal of Polymer Science.Polymer Physics》2007,45(15):2097-2112
Mechanical, thermal, and electrical properties of graphite/PMMA composites have been evaluated as functions of particle size and dispersion of the graphitic nanofiller components via the use of three different graphitic nanofillers: “as received graphite” (ARG), “expanded graphite,” (EG) and “graphite nanoplatelets” (GNPs) EG, a graphitic materials with much lower density than ARG, was prepared from ARG flakes via an acid intercalation and thermal expansion. Subsequent sonication of EG in a liquid yielded GNPs as thin stacks of graphitic platelets with thicknesses of ~10 nm. Solution‐based processing was used to prepare PMMA composites with these three fillers. Dynamic mechanical analysis, thermal analysis, and electrical impedance measurements were carried out on the resulting composites, demonstrating that reduced particle size, high surface area, and increased surface roughness can significantly alter the graphite/polymer interface and enhance the mechanical, thermal, and electrical properties of the polymer matrix. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2097–2112, 2007 相似文献
24.
基于多站测向定位提供的目标辐射源方位角信息,提出了一种基于粒子滤波的测向定位跟踪算法.该算法采用序贯蒙特卡罗的粒子滤波技术,对目标辐射源方位信息进行粒子滤波融合处理,实现了对机动目标辐射源的无源定位跟踪.仿真实验表明,该算法适用于非线性模型和非高斯噪声的目标跟踪,与传统的基于卡尔曼滤波的多传感器融合跟踪算法相比,定位跟踪更为精确,从而对提高战场电子目标定位跟踪和精确打击具有广泛的应用价值. 相似文献
25.
Chemical techniques were employed to synthesize CdS nanoparticles embedded in polymer (PEG 300) and sol-gel silica matrices. Systematic growth of particles (radius 3–9 nm) was obtained by adjusting post-deposition annealing temperature and time to examine the dependence of surface-state–related luminescence on particle size. Photoluminescence (PL) peak energy showed a linear dependence with a gentle slope in the weak confinement region and a steep slope in the strong confinement region, the divergence being observed near the excitonic Bohr radius for CdS. The empirical relation proposed for the weak confinement region could be used for estimating chemically prepared CdS nanoparticle size with a high degree of reliability from PL peak energy. 相似文献
26.
Backman Ulrika Jokiniemi Jorma K. Auvinen Ari Lehtinen Kari E.J. 《Journal of nanoparticle research》2002,4(4):325-335
We have prepared spherical non-agglomerated silver nanoparticles by an evaporation–condensation–dilution/cooling technique. Silver was evaporated from a crucible in a tubular flow reactor. A porous tube diluter was used to quench the carrier gas at the outlet of the reactor to enhance the formation of small particles and to suppress agglomeration and other particle growth mechanisms. The number size distribution of the prepared particles was measured with a differential mobility analyser–condensation nucleus counter combination and the size and the shape of the particles were analysed with transmission electron microscope. The system was modelled using a sectional aerosol dynamics computer code to estimate the importance of different aerosol processes. In all conditions the particles obtained were non-agglomerated and spherical. The mean particle diameter varied from 4 to 10-nm depending on boundary conditions. From the modelling studies it can be concluded that the nucleation rate is the most important parameter controlling the final particle size. 相似文献
27.
Hiroki Shigehisa 《Tetrahedron letters》2006,47(41):7301-7306
The first total synthesis of a spiro-isoquinoline alkaloid, (±)-annosqualine, was established by employing an enamide-phenol coupling of a 1-methylene-1,2,3,4-tetrahydroisoquinoline derivative with a hypervalent iodine reagent, where the formation of the phenoxide was recognized to be an essential step for the reaction of the phenolic hydroxyl group with the hypervalent iodine reagent leading to the formation of the desired product. 相似文献
28.
29.
Dieter Petrak 《Particle & Particle Systems Characterization》2002,19(6):391-400
The objective of this study was to compare the measuring results of a fiber‐optical probe based on a modified spatial filtering technique with given size distributions of different test powders and also with particle velocity values of laser Doppler measurements. Fiber‐optical spatial filtering velocimetry was modified by fiber‐optical spot scanning in order to determine simultaneously the size and the velocity of particles. The fiber‐optical probe system can be used as an in‐line measuring device for sizing of particles in different technical applications. Spherical test particles were narrow‐sized glass beads in the range 30–100 μm and irregularly shaped test particles were limestone particles in the range 10–600 μm. Particles were dispersed by a brush disperser and the measurements were carried out at a fixed position in a free particle‐laden air stream. Owing to the measurement of chord lengths and to the influence of diffraction and divergent angle, the probe results show differences from the given test particle sizes. Owing to the particle‐probe collisions, the mean velocity determined by the probe is smaller than the laser Doppler mean velocity. 相似文献
30.
T. Hayashita T. Kurosawa T. Miyata K. Tanaka M. Igawa 《Colloid and polymer science》1994,272(12):1611-1619
The cationic azo-surfactants possessing different spacers and tail alkyl chain lengths have been synthesized by azocoupling ofp-alkylaniline orop-ethoxyaniline with phenol, followed by alkylation and quaternalization with dibromoalkane and trimethylamine, respectively. These surfactants showed a good solubility in water. A reversibletrans-cis isomerization of the azosurfactants by photoirradiation was assessed by UV-Vis absorption spectra. Due to a difference in HLB between thetrans- andcis-surfactants, the observed critical micelle concentration (CMC) values and the electric conductivity of the surfactant solution at above the CMC were significantly affected by the photoinducedtrans-cis isomerization. The azo-surfactants bearing moderate alkyl chain lengths such as surfactants 6 (R2=C2H4, R3=C4H9) and 9 (R2=C4H8, R3=C2H5) were found to be effective to achieve large CMC changes (3.6 mmol/L for 6 and 5.9 mmol/L for 9) by UV-light irradiation. The replacement of the tail chain species also affected the photoresponsive function. The surfactant 12, possessingp-ethoxy group as the tail chain, was found to form a stable micelle aggregation as compared with the structurally related surfactant 10 having ethyl unit as its tail group, but it exhibited a large CMC change (5.3 mmol/L) by UV-light irradiation. 相似文献