全文获取类型
收费全文 | 19724篇 |
免费 | 799篇 |
国内免费 | 56篇 |
专业分类
化学 | 13048篇 |
晶体学 | 278篇 |
力学 | 628篇 |
综合类 | 2篇 |
数学 | 1616篇 |
物理学 | 5007篇 |
出版年
2023年 | 209篇 |
2022年 | 330篇 |
2021年 | 525篇 |
2020年 | 589篇 |
2019年 | 629篇 |
2018年 | 609篇 |
2017年 | 570篇 |
2016年 | 821篇 |
2015年 | 601篇 |
2014年 | 934篇 |
2013年 | 1554篇 |
2012年 | 1471篇 |
2011年 | 1535篇 |
2010年 | 993篇 |
2009年 | 796篇 |
2008年 | 982篇 |
2007年 | 979篇 |
2006年 | 784篇 |
2005年 | 683篇 |
2004年 | 543篇 |
2003年 | 458篇 |
2002年 | 371篇 |
2001年 | 239篇 |
2000年 | 203篇 |
1999年 | 156篇 |
1998年 | 111篇 |
1997年 | 150篇 |
1996年 | 144篇 |
1995年 | 121篇 |
1994年 | 150篇 |
1993年 | 173篇 |
1992年 | 173篇 |
1991年 | 122篇 |
1990年 | 116篇 |
1989年 | 120篇 |
1988年 | 89篇 |
1987年 | 94篇 |
1986年 | 78篇 |
1985年 | 96篇 |
1984年 | 90篇 |
1983年 | 94篇 |
1982年 | 94篇 |
1981年 | 95篇 |
1980年 | 90篇 |
1979年 | 95篇 |
1978年 | 84篇 |
1977年 | 91篇 |
1976年 | 74篇 |
1975年 | 62篇 |
1973年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
61.
Gel polymer electrolyte (GPE) films comprising of poly(vinylidenefluoride), propylene carbonate, ethylene carbonate and zinc trifluoromethane sulfonate are prepared and characterized. The composition of GPE is optimized to contain minimum liquid components with a maximum specific conductivity of 3.94×10−3 S cm−1 at (25±1) °C. A detailed investigation on the properties such as ionic conductivity, transport number, electrochemical stability window, reversibility of Zn/Zn2+ couple and Zn/gel electrolyte interfacial stability have been carried out. The ionic conductivity follows a VTF behaviour with an activation energy of about 0.0014 eV. Cationic transport number varies from 0.51 at 25 °C to 0.18 at 70 °C. Several cells have been assembled with GPE as the electrolyte, zinc as the anode, γ-MnO2 as the cathode and their charge–discharge behaviour followed. Capacity values of 105, 82, 64 and 37 mAh/g of MnO2 have been achieved at 10, 50, 100 and 200 μA/cm2 discharge current densities, respectively. The discharge capacity values are almost constant for about 55 cycles for all values of current densities. Cyclic voltammetric study of MnO2 electrode in Zn/GPE/MnO2 cell clearly shows intercalation/deintercalation of Zn2+. 相似文献
62.
Using lower-cost lasers, 30% savings are possible for 10-Gb/s uncompensated metro transmission over NZDF, compared to G.652 fiber. We present WDM transmission results for a mixed plant of NZDF rings interconnected to G.652.C-fiber access laterals. 相似文献
63.
Anirudh Pradhan Sudhir Kumar Srivastav Kanti R. Jotania 《Czechoslovak Journal of Physics》2004,54(2):255-272
Some cylindrically symmetric inhomogeneous viscous-fluid cosmological models with electromagnetic field are obtained. To get
a solution a supplementary condition between metric potentials is used. The viscosity coefficient of bulk viscous fluid is
assumed to be a power function of mass density. Without assuming anyad hoc law, we obtain a cosmological constant as a decreasing function of time. The behaviour of the electromagnetic field tensor
together with some physical aspects of the model are also discussed. 相似文献
64.
65.
66.
We discuss the concept of coarse wavelength-division multiplexing (CWDM) for metro networks. After reviewing the requirements on components such as lasers and fiber, we propose different architectures for a flexible upgrade of existing CWDM systems. 相似文献
67.
M.K. Gupta Vijay Gupta Manoj Kumar 《Journal of Mathematical Analysis and Applications》2007,330(2):799-816
In the present paper we introduce a new family of linear positive operators and study some direct and inverse results in simultaneous approximation. 相似文献
68.
MDF materials are chemically bonded ceramic materials free of the macrodefects typical of hydraulic cement-based materials. MDF materials arising through reactions of sulfo-aluminate-ferrite belitic (SAFB) clinkers and/or Portland cements (PC) with two types of water-soluble polymer (hydroxy-propylmethyl cellulose {HPMC}, polyphosphate glass {poly-P}) are discussed. Mixes of low energy SAFB clinkers with Portland cement, HPMC and, especially poly-P comprise promising cross-linked compositions additional to the better known MDF materials formed from high alumina cement with polyvinylalcohol/acetate. The principles of co-ordination of P and C atoms (of the polymer) with Al and Fe atoms (originating from the cement) are highlighted from spectroscopic information on next-nearest-neighbour interactions, along with the effects of second co-ordination spheres. Polymers modify the interface through functional bonding/grafting of polymer chains onto the surfaces of cement grains. Both the cross-linked atomic structure and the interface coincide well with the model of functional polymers and represent a new type of atomic-level structure in polymer-modified cements. Interpretation is based on previous magnetic resonance and thermal analysis studies. The compactness of Al(Fe)-O-P cross-links reduces transport through the interfaces, increasing the interfacial interactions and resisting the unfavourable uptake of moisture and carbonation. 相似文献
69.
Vattoly J. MajoJaya Prabhakaran J.John MannJ.S. Dileep Kumar 《Tetrahedron letters》2003,44(47):8535-8537
A novel and convergent palladium catalyzed synthesis of 2-arylbenzothiazoles has been investigated. The key step in the synthesis is a Suzuki biaryl coupling of 2-bromobenzothiazole with aryl boronic acids to provide a variety of 2-arylbenzothiazole derivatives in good yield. The synthetic utility of this methodology is demonstrated by the synthesis of 2-(4-aminophenyl)-6-methoxybenzothiazole, a PET probe precursor for the in vivo imaging of Alzheimer's disease. 相似文献
70.
We demonstrate the phenomenon of Talbot self-image plane shift by tuning the wavelength of the broadband light source. A superluminescent diode (SLD) is used as a broad-band light source and an acousto-optic tunable filter (AOTF) as wavelength-scanning device. A periodic grating is illuminated by the wavelength tuned light of SLD using AOTF and Talbot self-image plane is shifted continuously in the longitudinal direction without mechanically moving the grating. The wavelength-scanning Talbot effect is then implemented for the measurement of arbitrary step-height of discontinuous objects with extended range. The main advantages of the proposed system are non-mechanical scanning, high stability because of it’s common-path geometry and compactness. Since the measurement of the phase is not required the system is free from phase ambiguity problem and therefore, the range of measurement is large as compare to interferometric techniques. 相似文献