全文获取类型
收费全文 | 387273篇 |
免费 | 3719篇 |
国内免费 | 956篇 |
专业分类
化学 | 207437篇 |
晶体学 | 5694篇 |
力学 | 17547篇 |
综合类 | 15篇 |
数学 | 43147篇 |
物理学 | 118108篇 |
出版年
2019年 | 3246篇 |
2018年 | 4276篇 |
2017年 | 4251篇 |
2016年 | 6483篇 |
2015年 | 3914篇 |
2014年 | 6244篇 |
2013年 | 15976篇 |
2012年 | 11989篇 |
2011年 | 14851篇 |
2010年 | 10488篇 |
2009年 | 10289篇 |
2008年 | 13795篇 |
2007年 | 14056篇 |
2006年 | 13174篇 |
2005年 | 11954篇 |
2004年 | 10792篇 |
2003年 | 9739篇 |
2002年 | 9695篇 |
2001年 | 10625篇 |
2000年 | 8259篇 |
1999年 | 6392篇 |
1998年 | 5578篇 |
1997年 | 5535篇 |
1996年 | 5161篇 |
1995年 | 4800篇 |
1994年 | 4929篇 |
1993年 | 4527篇 |
1992年 | 5206篇 |
1991年 | 5285篇 |
1990年 | 5064篇 |
1989年 | 4960篇 |
1988年 | 4986篇 |
1987年 | 4818篇 |
1986年 | 4578篇 |
1985年 | 6038篇 |
1984年 | 6394篇 |
1983年 | 5337篇 |
1982年 | 5634篇 |
1981年 | 5466篇 |
1980年 | 5380篇 |
1979年 | 5459篇 |
1978年 | 5890篇 |
1977年 | 5708篇 |
1976年 | 5806篇 |
1975年 | 5419篇 |
1974年 | 5521篇 |
1973年 | 5644篇 |
1972年 | 3927篇 |
1971年 | 3373篇 |
1970年 | 3068篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
A high-performance liquid chromatographic procedure was developed for the quantitation of homoharringtonine in plasma. Harringtonine was used as an internal standard, and 1 ml of sample was required. The single-step extraction with dichloromethane resulted in almost 100% recovery for homoharringtonine and harringtonine. Analysis was performed on a reversed-phase CN column with amperometric detection. Chromatography was completed in 12 min. At an oxidation potential of +1.0 V, the detection limit was 1 ng/ml at a signal-to-noise ratio of 2. The mean analytical recovery for homoharringtonine was 99.5%. The within-run precision and between-run precision were both less than 11%. The method is equally applicable for plasma or serum, and it has been demonstrated to be applicable for study of the pharmacokinetics of homoharringtonine in patients suffering from acute non-lymphocytic leukaemia. 相似文献
952.
T. Hansel J. Müller C. Falldorf C. von Kopylow W. Jüptner R. Grunwald G. Steinmeyer U. Griebner 《Applied physics. B, Lasers and optics》2007,89(4):513-516
Digital holographic shape measurements using femtosecond laser pulses are reported. For contouring of very fast moving objects,
the simultaneous generation of at least two spectrally separated ultrashort pulses is required. To deliver this particular
spectral signature at high pulse energies, a chirped-pulse Ti:sapphire laser amplifier was modified to emit two spectrally
separated pulses with energies above 1 μJ each. The wavelength separation of these pulses was adjustable within the 50 nm
gain bandwidth, cutting out two distinct wavelength peaks by a variable double-slit assembly in a prism sequence. A Michelson-type
interferometer was employed to perform the two-wavelength contouring. The phases of the holograms and the phase differences
are calculated numerically, which allow us to deduce the contour lines of the topology of the object. The suitability of the
light source for digital holography is demonstrated with contouring of stationary objects and the potential for high-speed
applications is indicated.
PACS 42.40.-i; 42.60.By 相似文献
953.
954.
T. Peprnicek A. Kalendova J. Simonik J.F. Gerard 《Polymer Degradation and Stability》2006,91(12):3322-3329
The paper concentrates on poly(vinyl chloride) - PVC - from the point of nanocomposite characterisation through thermal degradation of samples, evolution of the changes caused by elevating temperature using TGA, FTIR and Congo Red methods combined with morphological characterisation by XRD and TEM analyses. A novel method of PVC-paste/nanocomposite preparation while processing was used. During preparation, PVC plasticizer was mixed with clay, both natural and organophilic, and the suspension was then compounded with the other components. Two factors were followed: effect of shearing alone, and in combination with temperature. As is presented, the type of nano-filler and its chemical modifier have obvious influence on final properties either thermal or morphological. Presented contribution follows previous part of investigation and brings further information from PVC-paste/nanocomposite field. 相似文献
955.
F.A. Fernández-Lima C.R. Ponciano E. Pedrero E.F. da Silveira 《Applied Surface Science》2006,252(23):8171-8177
Experimental results of laser sputtering of cesium and rubidium iodide secondary ions are presented. A TOF mass spectrometer, operating in linear mode, continuous extraction for positive or negative ions, was used for the analysis of (CsI)nCs+, (CsI)nI−, (RbI)nRb+ and (RbI)nI− ion emission as a function of the laser irradiance. Experimental data show that the cluster ion emission yields decrease exponentially with n, for all the laser irradiances applied. Theoretical analysis of the clusters structure was performed using density functional theory at the B3LYP/LACV3P level, for the positive and negative cluster series. A quasi-equilibrium evolution of the clusters is proposed to extract a parameter characteristic of the cluster recombination process: the effective temperature. The hypothesis of the atomic species’ recombination (during the expansion of a high density highly ionized cloud) leading to cluster formation is confirmed to some extent in a second set of experiments: the UV laser ablation of a mixed and non-mixed cesium iodide and potassium bromide targets. These experiments show that the emission yields contain contributions from both the recombination process and from the sample stoichiometry, even for high laser irradiances. 相似文献
956.
A. I. Fedoseev S. G. Lushnikov S. N. Gvasaliya S. Kojima 《Physics of the Solid State》2006,48(6):1102-1105
The behavior of acoustic phonons in crystals of a relaxor ferroelectric, namely, the lead scandium tantalate PbSc1/2Ta1/2O3 (PST), is studied in the vicinity of the diffuse phase transition. The behavior of longitudinal and transverse acoustic phonons in a PST single crystal is examined using Brillouin scattering. The phonon subsystem is found to behave anomalously in the vicinity of T = 297 K, which can probably be assigned to the existence of a phase transition. Analysis of the results obtained yields the values of the elastic moduli C11, C12, and C44 for the cubic phase of the crystal over a wide temperature range. 相似文献
957.
The atomic structure and magnetic and electric properties of the Cr0.5TiSe2-Cr0.5TiTe2 system of intercalated phases were studied in detail by gradually replacing selenium by tellurium. It was revealed that this replacement changes the crystalline structure from monoclinic in the initial compounds to hexagonal in the compounds containing various types of chalcogen atoms; this is accompanied by disordering of chromium atoms in the van der Waals gaps. The electrical resistance and magnetic characteristics vary nonmonotonically on replacement of selenium by tellurium, which is associated with a change in the degree of atomic disordering during the transition from Cr0.5TiSe2 to Cr0.5TiTe2. 相似文献
958.
Phase synchronization in a system of three virtual-cathode microwave oscillators (vircators) simulated by coupled van der Pol oscillators is studied. The phasing dynamics of the vircators is visualized with the phase portraits of the system in the triangular coordinates. Different phasing conditions are found. 相似文献
959.
Masanobu Haraguchi David F. P. Pile Toshihiro Okamoto Masuo Fukui Dmitri K. Gramotnev 《Optical Review》2006,13(4):228-230
We have numerically shown the existence of coupled wedge plasmons (CWPs) which propagates along a nano gap of a twin metal
wedge. The CWPs are formed by wedge plasmons which can interact with each other. The dispersion relations of the wavenumber,
propagation distance, and beam area of CWPs, are described and show that the characteristics of CWPs are similar to those
of wedge plasmons and of gap plasmons. We also propose a new plasmon waveguide composed of twin metal wedges with a nano gap. 相似文献
960.