全文获取类型
收费全文 | 7507篇 |
免费 | 550篇 |
国内免费 | 38篇 |
专业分类
化学 | 5672篇 |
晶体学 | 41篇 |
力学 | 191篇 |
综合类 | 1篇 |
数学 | 1166篇 |
物理学 | 1024篇 |
出版年
2022年 | 43篇 |
2021年 | 62篇 |
2020年 | 75篇 |
2019年 | 145篇 |
2018年 | 87篇 |
2017年 | 79篇 |
2016年 | 237篇 |
2015年 | 265篇 |
2014年 | 259篇 |
2013年 | 456篇 |
2012年 | 368篇 |
2011年 | 402篇 |
2010年 | 322篇 |
2009年 | 320篇 |
2008年 | 393篇 |
2007年 | 332篇 |
2006年 | 329篇 |
2005年 | 278篇 |
2004年 | 317篇 |
2003年 | 261篇 |
2002年 | 328篇 |
2001年 | 184篇 |
2000年 | 176篇 |
1999年 | 92篇 |
1998年 | 89篇 |
1997年 | 96篇 |
1996年 | 108篇 |
1995年 | 79篇 |
1994年 | 86篇 |
1993年 | 85篇 |
1992年 | 90篇 |
1991年 | 71篇 |
1990年 | 69篇 |
1989年 | 61篇 |
1988年 | 56篇 |
1987年 | 52篇 |
1986年 | 53篇 |
1985年 | 67篇 |
1984年 | 82篇 |
1983年 | 75篇 |
1982年 | 83篇 |
1981年 | 81篇 |
1980年 | 83篇 |
1979年 | 93篇 |
1978年 | 82篇 |
1977年 | 88篇 |
1976年 | 81篇 |
1975年 | 81篇 |
1974年 | 77篇 |
1973年 | 54篇 |
排序方式: 共有8095条查询结果,搜索用时 62 毫秒
941.
Jean‐Philippe Boisvert Jacques Persello Aurlien Guyard 《Journal of Polymer Science.Polymer Physics》2003,41(23):3127-3138
Poly(vinyl alcohol) (PVA) composite films filled with nanometric, monodisperse, and spherical silica particles were prepared by the mixing of an aqueous PVA solution and SiO2 colloidal suspension and the evaporation of the solvent. Adjusting the solution pH to 5 and 9 controlled the PVA‐SiO2 interaction. Adsorption isotherms showed a higher PVA/surface affinity at a lower pH. This interaction influenced the composite structure and the particle distribution within the polymer matrix, which was investigated by small‐angle neutron scattering, electron microscopy, and swelling measurements. Most of the mechanical properties could be related to the composite structure, that is, the distribution of clusters within the polymer matrix. The progressive creation of a cluster network within the polymeric matrix as the silica volume fraction increased reduced the extensibility or swelling capacity of the composite. The effect was more acute at a higher pH, at which the surface interaction with PVA was weaker and promoted the interconnection between clusters. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3127–3138, 2003 相似文献
942.
D. Wayne Cooke Melvin Leon Michael A. Paciotti Peter F. Meier Stephen F. J. Cox Edward A. Davis Thomas L. Estle Bassam Hitti Roger L. Lichti Carolus Boekema John Lam Anny Morrobel-Sosa Jean Oostens 《Hyperfine Interactions》1994,86(1):699-704
A distinctive longitudinal magnetic field dependence of the muon polarization for anomalous muonium in polycrystalline semiconductor targets has been predicted. The polarization exhibits a cusp,i.e., a discontinuous jump in the slope from negative to positive. Measurements of the longitudinal polarization for polycrystalline silicon in fields up to 0.5 T, and temperatures 53 and 200 K have been made at LAMPF. A cusp in the field dependence indeed occurs at 0.345 T, in excellent agreement with the prediction. No cusp is observed at 200 K because Mu* has been thermally ionized. 相似文献
943.
Electrical model of a liquid crystal pixel with dynamic, voltage history-dependent capacitance value
The voltage history-dependent nature of a liquid crystal pixel capacitance becomes an important issue in active matrix addressing as large storage capacitors are replaced with more intelligent circuitry such as in-pixel frame buffers. In this paper, a simple but flexible Spice macro model is introduced that allows accurate simulations of the electrical behaviour of a nematic liquid crystal pixel capacitance. The model correctly predicts voltage drops caused by the increasing dielectric constant when liquid crystal molecules align themselves to the electric field. An internal node of the macro model represents the average director orientation and can also be used to predict the optical response. In its basic embodiment, the model uses a first-order, low pass RMS filter to implement the dynamic behaviour of the pixel, which suffices to predict response delays and asymmetric rise and fall times. However, the model also supports more elaborated filters that offer more control over the simulated dynamic behaviour. A number of simulations are performed that illustrate the usefulness of the new model during the design of novel 'smart' pixel architectures. 相似文献
944.
945.
Yvon Pointud Claude Bernard Sébastien Touzain Lionel Astier Béatrice Sabatier Jean Juillard 《Journal of solution chemistry》1997,26(5):479-495
The standard Gibbs functions, enthalpies, and entropies for the formation of the complexes of monensin acid with monovalent
metal cations in acetonitrile were obtained using various methods (conductometry, potentiometry, and calorimetry). Complexation
is appreciable (from 2.0 to 4.5 in terms of association constant logarithm) and controlled mainly by the enthalpic effect.
Comparison with formation of the corresponding neutral complexes permits a comparison to the process of monensin mediated
transport of cation in membranes. A two-step process involving first the formation of the acidic complex is suggested. 相似文献
946.
We have directly measured the free-volume hole distributions in semicrystalline polypropylene by positron lifetime annihilation spectroscopy. A Laplace inversion technique was engaged to analyze the positron lifetime spectra measured under quasi-isotropic external pressures of 0, 4.2, and 14.7 kbar into continuous lifetime distributions. The hole radii distributions as determined from the ortho-positronium lifetime distributions are found to be between 4.0 and 0.5 Å and to have maxima at 3.0, 1.9, and 1.1 Å under the external pressures of 0, 4.2, and 14.7 kbar, respectively. © 1992 John Wiley & Sons, Inc. 相似文献
947.
Tsao George T. Zheng Yizhou Lu Jean Gong Cheng S. 《Applied biochemistry and biotechnology》1997,63(1):731-741
Applied Biochemistry and Biotechnology - Phytic acid (myoinositol hexaphosphate) or its calcium salt, phytate, is an important plant constituent. It accounts for up to 85% of total phosphorus in... 相似文献
948.
949.
A flow-injection spectrofluorimetric determination of paracetamol is reported, based on the oxidation of the analyte with potassium hexacyanoferrate(III) immobilized on an anion-exchange resin, the fluorescence being enhanced with N,N′-dimethylformamide. Concentrations of paracetamol in the range 0.04–17.60 mg l?1 are determined with a relative standard deviation of 1.5%. The injection rate is 25 samples h?1. The influence of foreign species and the determination of paracetamol in several pharamaceutical formulations are also reported. 相似文献
950.