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141.
折算频率对翼型动态升力特性影响的初步研究 总被引:2,自引:0,他引:2
本文根据在西北工业大学翼型研究中心(CADR)进行的NACA0012翼型动态特性研究,着重介绍测力法研究中,滤波器截止频率和动态特性研究中最重要的相似准则折算频率影响的研究结果.结果表明,对动态特性研究而言,恰当的滤波器截止频率是获得正确结果的必要条件,在此基础上,通过改变折算频率,得出它对升力特性影响的可信结果. 相似文献
142.
On total chromatic number of planar graphs without 4-cycles 总被引:5,自引:0,他引:5
Min-le SHANGGUAN 《中国科学A辑(英文版)》2007,50(1):81-86
Let G be a simple graph with maximum degree A(G) and total chromatic number Xve(G). Vizing conjectured thatΔ(G) 1≤Xve(G)≤Δ(G) 2 (Total Chromatic Conjecture). Even for planar graphs, this conjecture has not been settled yet. The unsettled difficult case for planar graphs isΔ(G) = 6. This paper shows that if G is a simple planar graph with maximum degree 6 and without 4-cycles, then Xve(G)≤8. Together with the previous results on this topic, this shows that every simple planar graph without 4-cycles satisfies the Total Chromatic Conjecture. 相似文献
143.
144.
Isoroquefortine E and phenylahistin were synthesized using the Horner–Wadsworth–Emmons reaction as the key step to build the dehydroamino acid moiety. The syntheses provided the materials for the biological studies of the roquefortine–phenylahistin molecules. 相似文献
145.
The novel comb-type biodegradable graft copolymers based on ε-caprolactone and l-lactide were synthesized. Firstly, 2-oxepane-1,5-dione (OPD) was synthesized by the Baeyer-Villiger oxidation of 1,4-cyclohexanedione, and was subsequently copolymerized with ε-caprolactone (CL) to produce poly(2-oxepane-1,5-dione-co-ε-caprolactone) (POCL) catalyzed by stannous(II) 2-ethylhexanoate in toluene. Then, POCL was converted into poly(4-hydroxyl-ε-caprolactone-co-ε-caprolactone) (PHCL) using sodium borohydride as reductant. Finally, poly(4-hydroxyl-ε-caprolactone-co-ε-caprolactone)-g-poly(l-lactide) (PHCL-g-PLLA) were prepared successfully by bulk ring-opening polymerization of l-lactide using PHCL as a macro-initiator. All the copolymers have been characterized by 1H and 13C NMR, DSC, and GPC. Compared with the random copolymer of poly(CL-co-LA), the elongation is highly increased. And the thermal analysis showed that the crystallization rate of the PCL backbone in the graft copolymers was greatly reduced compared to the PCL homopolymer. The hydrolytic degradation of the copolymer was much faster in a phosphate buffer (pH = 7.4) at 37 °C, which is confirmed by the weight loss and change of intrinsic viscosity. 相似文献
146.
147.
鉴于不同生理病理状态下组织复折射率实部的变化不大,传统光学相干层析(OCT)成像技术在分子特异性识别上存在先天不足.为此,本文提出了基于受激辐射信号的OCT成像方法,可在实现传统散射成像的同时,实现基于受激辐射信号的分子成像.在超高分辨率谱域OCT系统的基础上,通过增设光谱分光与调制抽运光支路,建立了基于单宽谱光源的抽运探测谱域OCT系统,详细推导了调制抽运下受激辐射信号的获取与成像公式.利用搭建的抽运探测谱域OCT系统,实现了瞬态受激辐射信号的相干探测.基于同时获取的受激辐射OCT信号和传统OCT信号,成功重构了氮化物粉末构建样品的基于受激辐射信号的分子对比OCT图像. 相似文献
148.
Guofeng Jia Suqin Liu Guowei Yang Faqiang Li Kang Wu Zhen He Xuehui Shangguan 《Ionics》2018,24(12):3705-3715
The application of LiNi0.5Mn0.5O2 as a high-voltage cathode material for lithium-ion batteries is limited by its poor cycle performance. Therefore, we attempt to improve the cyclability of this material at high voltage by using a doping method and propose a detailed mechanism for the effect of the doping amount on the structure and electrochemical performance. In this work, LiNi0.5-zAlzMn0.5O2 (z?=?0.00, 0.03, 0.05, 0.08) electrodes were prepared via a simple co-precipitation followed by a solid-state method. X-ray diffraction and Rietveld refinement revealed that a suitable amount of Al doping into LiNi0.5Mn0.5O2 can stabilize the structure and lower the Li/Ni cation mixing, but an excessive doping would lead to Al-ion doping in the lithium layer, which can block lithium diffusion and affect the rate property. Specifically, LiNi0.47Al0.03Mn0.5O2 shows a much higher capacity retention compared to LiNi0.5Mn0.5O2 both at 25 °C (78.5 vs. 68.8% at 0.2 C) and 60 °C (70.8 vs. 69.0% at 0.2 C). Moreover, Al-doping can retard the voltage drop during the discharge-charge state, with the discharge voltage for LiNi0.5-zAlzMn0.5O2 (z?=?0.00, 0.03, 0.05, 0.08) decreasing slowly with increasing Al content. 相似文献
149.
In the last two decades, parent-identifying codes and traceability codes are introduced to prevent copyrighted digital data from unauthorized use. They have important applications in the scenarios like digital fingerprinting and broadcast encryption schemes. A major open problem in this research area is to determine the upper bounds for the cardinalities of these codes. In this paper we will focus on this theme. Consider a code of length N which is defined over an alphabet of size q. Let \(M_{IPPC}(N,q,t)\) and \(M_{TA}(N,q,t)\) denote the maximal cardinalities of t-parent-identifying codes and t-traceability codes, respectively, where t is known as the strength of the codes. We show \(M_{IPPC}(N,q,t)\le rq^{\lceil N/(v-1)\rceil }+(v-1-r)q^{\lfloor N/(v-1)\rfloor }\), where \(v=\lfloor (t/2+1)^2\rfloor \), \(0\le r\le v-2\) and \(N\equiv r \mod (v-1)\). This new bound improves two previously known bounds of Blackburn, and Alon and Stav. On the other hand, \(M_{TA}(N,q,t)\) is still not known for almost all t. In 2010, Blackburn, Etzion and Ng asked whether \(M_{TA}(N,q,t)\le cq^{\lceil N/t^2\rceil }\) or not, where c is a constant depending only on N, and they have shown the only known validity of this bound for \(t=2\). By using some complicated combinatorial counting arguments, we prove this bound for \(t=3\). This is the first non-trivial upper bound in the literature for traceability codes with strength three. 相似文献
150.