全文获取类型
收费全文 | 332篇 |
免费 | 9篇 |
专业分类
化学 | 211篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 37篇 |
物理学 | 46篇 |
无线电 | 42篇 |
出版年
2021年 | 2篇 |
2019年 | 1篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 10篇 |
2014年 | 9篇 |
2013年 | 11篇 |
2012年 | 18篇 |
2011年 | 24篇 |
2010年 | 17篇 |
2009年 | 8篇 |
2008年 | 26篇 |
2007年 | 31篇 |
2006年 | 29篇 |
2005年 | 21篇 |
2004年 | 25篇 |
2003年 | 20篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 2篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有341条查询结果,搜索用时 702 毫秒
91.
Costa-Balogh FO Aberg C Sousa JJ Sparr E 《Langmuir : the ACS journal of surfaces and colloids》2005,21(23):10307-10310
In this paper, we demonstrate, for the first time, how an external osmotic gradient can be used to regulate diffusion of solutes across a lipid membrane. We present experimental and theoretical studies of the transport of different solutes across a monoolein membrane in the presence of an external osmotic gradient. The osmotic gradient introduces phase transformations in the membrane, and it causes nonlinear transport behavior. The external gradient can thus act as a kind of switch for diffusive transport in the skin and in controlled release drug formulations. 相似文献
92.
Jarkko Ihanus Eric Lambers Paul H. Holloway Mikko Ritala Markku Leskel 《Journal of Crystal Growth》2004,260(3-4):440-446
SrS1−xSex and ZnS1−xSex thin films were deposited by the atomic layer deposition (ALD) technique using elemental selenium as the Se source, thus avoiding use of H2Se or organometallic selenium compounds. X-ray diffraction (XRD) analysis showed that the films were solid solutions and X-ray photoelectron spectroscopy (XPS) data showed that the surface of both ZnS1−xSex and SrS1−xSex were covered with an oxide and carbon-containing contaminants from exposure to air. The oxidation of SrS1−xSex extended into the film and peak shifts from sulfate were found on the surface. Luminance measurements showed that emission intensity of the ZnS1−xSex:Mn alternating current thin film electroluminescent (ACTFEL) devices at fixed voltage was almost the same as that of the ZnS:Mn device, while emission intensity of the SrS1−xSex:Ce devices decreased markedly as compared to the SrS:Ce device. Emission colors of the devices were altered only slightly due to selenium addition. 相似文献
93.
Erkki Aitola Arto Puranen Harri Setl Sami Lipponen Markku Leskel Timo Repo 《Journal of polymer science. Part A, Polymer chemistry》2006,44(22):6569-6574
Vinylcyclohexane (VCH) was copolymerized with ethene and propene using methylaluminoxane‐activated metallocene catalysts. The catalyst precursor for the ethene copolymerization was rac‐ethylenebis(indenyl)ZrCl2 ( 1 ). Propene copolymerizations were further studied with Cs‐symmetric isopropylidene(cyclopentadienyl)(fluorenyl)ZrCl2 ( 2 ), C1‐symmetric ethylene(1‐indenyl‐2‐phenyl‐2‐fluorenyl)ZrCl2 ( 3 ), and “meso”‐dimethylsilyl[3‐benzylindenyl)(2‐methylbenz[e]indenyl)]ZrCl2 ( 4 ). Catalyst 1 produced a random ethene–VCH copolymer with very high activity and moderate VCH incorporation. The highest comonomer content in the copolymer was 3.5 mol %. Catalysts 1 and 4 produced poly(propene‐co‐vinylcyclohexane) with moderate to good activities [up to 4900 and 15,400 kg of polymer/(mol of catalyst × h) for 1 and 4 , respectively] under similar reaction conditions but with fairly low comonomer contents (up to 1.0 and 2.0% for 1 and 4 , respectively). Catalysts 2 and 3 , both bearing a fluorenyl moiety, gave propene–VCH copolymers with only negligible amounts of the comonomer. The homopolymerization of VCH was performed with 1 as a reference, and low‐molar‐mass isotactic polyvinylcyclohexane with a low activity was obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6569–6574, 2006 相似文献
94.
Markku Niemenmaa 《Monatshefte für Mathematik》1986,101(3):183-191
We say that a near-ring (N,+,·) has an almost trivial multiplication (ATM) if the product of two elements belongs to the intersection of the additive cyclic groups generated by these two elements. We show that every finite near-ring with ATM can be decomposed to a direct sum where the summands are either near-rings defined on cyclic groups or near-rings whose minimal ideals are zero near-rings. Finally, we show how to construct these summands on cyclic groups. 相似文献
95.
A micro-optics replication process with UV-curable liquid pre-polymers is considered. Filling of the master structure is improved by controlling the viscosity of the pre-polymer by heat during the process. A novel process step, solvent-assisted filling, is introduced to avoid the harmful effect of the residual trapped air; a pyramidal retro-reflector structure with the face width of 400 μm is used as an example. Complete filling can be achieved without vacuum assisted replication or without application of compression force in the mould. Material studies showed no signs of chemical changes, solvent inclusion in the replicated structure, or a change of the optical properties of the material during the process. The replication fidelity is compared with conventional UV-moulding and commercial UV-NIL replication. The new heat and solvent assisted replication technique allows the use of high-viscosity pre-polymers with suitable material properties if the process temperature window is optimized. 相似文献
96.
Arto Rantala David Gomes Martins Markku Åberg 《Analog Integrated Circuits and Signal Processing》2007,50(1):69-79
This paper presents a clock generator circuit for a high-speed analog-to-digital converter (ADC). A time-interleaved ADC requires accurate clocking for the converter fingers. The target ADC has 12 interleaved fingers each running at a speed of 166 MS/s, which corresponds to an equivalent sampling frequency of 2 GS/s. A delay-locked loop (DLL) based clock generator has been proposed to provide multiple clock signals for the converter. The DLL clock generator has been implemented with a 0.35 μm SiGe BiCMOS process (only MOS-transistor were used in DLL) by Austria Micro Systems and it occupies a 0.6 mm2 silicon area. The measured jitter of the DLL is around 1 ps and the delay between phases can be adjusted using 1 ps precision. 相似文献
97.
Maçôas EM Khriachtchev L Pettersson M Fausto R Räsänen M 《The journal of physical chemistry. A》2005,109(16):3617-3625
The conformational system of propionic acid (CH3CH2COOH) is studied in solid argon. It is predicted by the ab initio calculations that this molecule has four stable conformers. These four structures are denoted Tt, Tg+/-, Ct, and Cg+/-, and they differ by the arrangement around the C-O and Calpha-C bonds. The ground-state Tt conformer is the only form present at 8 K after deposition of an argon matrix containing propionic acid. For the CH3CH2COOH and CH3CH2COOD isotopologues, narrow-band excitation of the first hydroxyl stretching overtone of the conformational ground state promotes the Calpha-C and C-O internal rotations producing the Tg+/- and Ct conformers, respectively. A subsequent vibrational excitation of the produced Tg+/- form induces its conversion to the Cg+/- conformer by rotation around the C-O bond. In the dark, all of the produced conformers decay to the conformational ground state at different rates. The decay kinetics and its temperature dependence allow the identification of the conformers by IR absorption spectroscopy, which is supported by ab initio calculations of their vibrational spectra. For the CH3CH2COOD isotopologue, the excitation of molecules isolated in different matrix sites results in site-dependent photoisomerization rates for the Calpha-C and C-O internal rotations, which also confirm the identification of the photoproducts. 相似文献
98.
Andreoiu C Døssing T Fahlander C Ragnarsson I Rudolph D Aberg S Austin RA Carpenter MP Clark RM Janssens RV Khoo TL Kondev FG Lauritsen T Rodinger T Sarantites DG Seweryniak D Steinhardt T Svensson CE Thelen O Waddington JC 《Physical review letters》2003,91(23):232502
The decay-out process of the yrast superdeformed band in 59Cu has been investigated. The firm determination of spin, parity, excitation energy, and configuration of the states involved in this process constitutes a unique situation for a detailed understanding of the decay-out mechanism. A theoretical model is introduced that includes a residual interaction and tunneling matrix element between bands, calculated in the configuration-dependent cranked Nilsson-Strutinsky model. This interaction causes the decay to occur via a small number of observed doorway states. 相似文献
99.
Chakraborty Shyam S. Liinaharja Markku Lindroos Petri 《Wireless Personal Communications》2003,26(4):347-363
In this article, an adaptive SR ARQ scheme is analyzed and optimized in a time-varying channel environment with unreliable feedback. To have an operational scheme, we choose the smaller packet size to be half of the bigger one. Thus, there is only one independent design parameter related to packet size. The other two parameters are associated with channel sensing. The performance of the adaptive scheme is measured by its average throughput, which is upper-bounded by the throughput of the so-called ideal adaptive scheme. This upper bound is very useful in the optimization of the packet size and other design parameters. 相似文献
100.
Svensson CE Macchiavelli AO Juodagalvis A Poves A Ragnarsson I Aberg S Appelbe DE Austin RA Baktash C Ball GC Carpenter MP Caurier E Clark RM Cromaz M Deleplanque MA Diamond RM Fallon P Furlotti M Galindo-Uribarri A Janssens RV Lane GJ Lee IY Lipoglavsek M Nowacki F Paul SD Radford DC 《Physical review letters》2000,85(13):2693-2696
A superdeformed rotational band has been identified in 36Ar, linked to known low-spin states, and observed to its high-spin termination at Ipi = 16(+). Cranked Nilsson-Strutinsky and spherical shell model calculations assign the band to a configuration in which four pf-shell orbitals are occupied, leading to a low-spin deformation beta(2) approximately 0.45. Two major shells are active for both protons and neutrons, yet the valence space remains small enough to be confronted with the shell model. This band thus provides an ideal case to study the microscopic structure of collective rotational motion. 相似文献