全文获取类型
收费全文 | 6743篇 |
免费 | 812篇 |
国内免费 | 1220篇 |
专业分类
化学 | 4326篇 |
晶体学 | 25篇 |
力学 | 228篇 |
综合类 | 10篇 |
数学 | 2007篇 |
物理学 | 2179篇 |
出版年
2025年 | 12篇 |
2024年 | 68篇 |
2023年 | 160篇 |
2022年 | 169篇 |
2021年 | 176篇 |
2020年 | 217篇 |
2019年 | 144篇 |
2018年 | 108篇 |
2017年 | 137篇 |
2016年 | 149篇 |
2015年 | 219篇 |
2014年 | 342篇 |
2013年 | 424篇 |
2012年 | 495篇 |
2011年 | 574篇 |
2010年 | 459篇 |
2009年 | 568篇 |
2008年 | 530篇 |
2007年 | 594篇 |
2006年 | 553篇 |
2005年 | 360篇 |
2004年 | 247篇 |
2003年 | 192篇 |
2002年 | 224篇 |
2001年 | 194篇 |
2000年 | 189篇 |
1999年 | 170篇 |
1998年 | 134篇 |
1997年 | 108篇 |
1996年 | 85篇 |
1995年 | 76篇 |
1994年 | 74篇 |
1993年 | 55篇 |
1992年 | 75篇 |
1991年 | 54篇 |
1990年 | 26篇 |
1988年 | 53篇 |
1987年 | 65篇 |
1986年 | 72篇 |
1972年 | 8篇 |
1971年 | 16篇 |
1970年 | 18篇 |
1969年 | 10篇 |
1968年 | 16篇 |
1967年 | 24篇 |
1966年 | 21篇 |
1965年 | 13篇 |
1964年 | 16篇 |
1963年 | 7篇 |
1962年 | 8篇 |
排序方式: 共有8775条查询结果,搜索用时 15 毫秒
1.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures. 相似文献
2.
《Physics letters. A》2006,355(1):55-58
The absolute single electron detachment (SED) cross sections of carbon group elements C−, Si−, Ge− in the energy range of 0.05–0.29 a.u. (5 keV–30 keV) and oxygen group elements O− and S− 0.08–0.27 a.u. (5 keV–30 keV), incident on helium are measured with growth rate method. In our energy region, the SED cross sections of C−, Si−, S− and Ge− increase with the projectiles velocity, at the same time, O− cross sections reach a conspicuous maximum at 0.18 a.u. Some abnormal behavior occurs in measurement of SED cross sections for the oxygen group collision with helium. Our results have been compared with a previous work. 相似文献
3.
In this paper,we provide a finitely terminated yet efficient approach to compute the Euclidean projection onto the ordered weighted?1(OWL1)norm ball.In particular,an efficient semismooth Newton method is proposed for solving the dual of a reformulation of the original projection problem.Global and local quadratic convergence results,as well as the finite termination property,of the algorithm are proved.Numerical comparisons with the two best-known methods demonstrate the efficiency of our method.In addition,we derive the generalized Jacobian of the studied projector which,we believe,is crucial for the future designing of fast second-order nonsmooth methods for solving general OWL1 norm constrained problems. 相似文献
4.
L. J. Ning Y. P. Wu L. Z. Wang S. B. Fang R. Holze 《Journal of Solid State Electrochemistry》2005,9(7):520-523
Three kinds of silicon-containing disordered carbons have been prepared by pyrolysis of polysiloxanes with different amounts of phenyl side groups. X-ray powder diffraction, X-ray photoelectron spectroscopy and electrochemical capacity measurements were performed to study their behaviors. Graphite crystallites, micropores, and silicon species affect their electrochemical performances. All of them present high reversible capacities, >372 mAh/g. Since the graphite crystallites are very small, they contribute very little to reversible capacity. The number of micropores produced by gas emission during the heat-treatment process decides whether they exhibit reversible capacity. Si mainly exists in the form C–Si–O and influences the irreversible capacity. There is no evident capacity fading in the first ten cycles, indicating promising properties for these disordered carbons. 相似文献
5.
LI Tatsien 《偏微分方程(英文版)》2006,19(1):10-15
In this paper we present a necessary and sufficient condition to guarantee the complete reducibility for quasilinear hyperbolic systems and give some examples. 相似文献
6.
WU Bo LI WenBin YU HaoMiao YOU YinTao CHEN XiaoQing HE Yun HOU XiaoYuan 《中国科学:物理学 力学 天文学(英文版)》2013,56(10):2012-2015
Transient photovoltage of ITO/organic/Al cells is studied under different bias polarities and voltages.It is found that for an ITO/NPB/Al cell,light incidence on the Al side induces more bias-dependent transient photovoltage variation when the photovoltage is positive than when it is negative.However,for an ITO/C60 /Al cell,the variation characteristics of transient photovoltage is reversed.These results support the previously proposed mechanism that Al could inject charges into the organic layer upon photon excitation,indicating that the absorption of electrode can also contribute to photovoltaic effect. 相似文献
7.
Jinchun Jiang Bin Li Lin Zhang Zhengquan Zhang Fengshan Zhang Huansheng Cheng Fujia Yang 《International Journal of Infrared and Millimeter Waves》2002,23(4):535-544
Optical coatings are designed and produced for the multichannel scanning radiometer meteorological space instrument operating in the spectral range 6.37.6m. First the choice of substrates and layers materials is discussed. Then the substrate temperatures dependent effects of three different Te-enriched PbTe single layers on the dispersion and absorption characteristics and carrier concentration are studied. The experimental results demonstrate that the performance of the coating made using PbTe + 0.3 at. % Te material is better than that of the others. Finally, details of the spectral design and manufacture of such a filter which meets the demanding bandwidth and transparency requirements of the application are presented. This design model is based on the optical and semiconductor properties of a multilayer filter containing PbTe layer materials in combination with the dielectric dispersion of ZnSe deposited on the a Ge substrate. Comparisons between the computed spectral performance of the model and spectral measurements from manufactured coatings over a wavelength range of 6.37.6m are presented. 相似文献
8.
The Mueller matrix solution of the vector radiative transfer equation with time dependence is derived in this paper. It is applied to simulation of polarimetric bistatic scattering from a layer of non-uniformly oriented, random non-spherical scatterers when a Gaussian plane pulse is incident upon. Co-polarized and cross-polarized bistatic scattering are numerically calculated. The pulse echoes are compared with the incidence, and demonstrate its functional dependence on the physical parameters of random medium, such as spatial orientation and fractional volume of scatterers, incidence angle and polarization, the layer depth and others. 相似文献
9.
Ge Zhang Yangping Wen Yuzhen Li Jingkun Xu Chaoqun Guo Baoyang Lu Danhua Zhu 《Journal of fluorescence》2013,23(5):1053-1063
A variety of carboxylates were recognized using poly(9-aminofluorene) (P9AF) in the HEPES buffer (pH 7.4), and a proposed possible mechanism was proposed as following. The intermolecular hydrogen bonding interactions resulted in electron transfer between P9AF and carboxylates. P9AF was facilely electrosynthesized in boron trifluoride diethyl etherate and could be used as an efficient fluorescent sensing material for the detection of AcO?. On binding to AcO?, fluorescence quenching of P9AF was demonstrated by a maximum 80 % reduction in the fluorescence intensity, while no obvious fluorescence change could be observed in the presence of some other common anions. Some different carboxylates could be recognized at different levels by P9AF. Substituent groups in carboxylates could affect the intermolecular interaction between carboxylates and P9AF. These could be explained by a possible mechanism that hydrogen bonding was the main way of intermolecular interactions between P9AF and carboxylates, which was further confirmed by absorption spectra monitoring and density functional calculations. The significant advantage of this strategy is that it does not require a prequenching procedure and the polymer can be used directly for analyte detection. 相似文献
10.
The ferroelectric polarization of triangular-lattice antiferromagnets induced by helical spin-spiral order is not explained by any existing model of magnetic-order-driven ferroelectricity. We resolve this problem by developing a general theory for the ferroelectric polarization induced by spin-spiral order and then by evaluating the coefficients needed to specify the general theory on the basis of density functional calculations. Our theory correctly describes the ferroelectricity of triangular-lattice antiferromagnets driven by helical spin-spiral order and incorporates known models of magnetic-order-driven ferroelectricity as special cases. 相似文献