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991.
992.
不同温度下钛镍形状记忆合金的超弹性特性 总被引:2,自引:0,他引:2
对国产TiNi形状记忆合金在不同温度下的准静态力学响应、特别是相变超弹性特性进行了试验研究.结果表明,TiNi合金在热弹性马氏体逆相变结束温度AF附近的一定温度范围内显示超弹性特征,且温度对其有显著影响.随着温度的升高,应力诱导热弹性马氏体的临界应力近似地呈线性增加趋势,但在AF附近发生间断性突降.试验结果还表明,随应力之增加,不可逆塑性变形在总变形中所占的比值逐渐增加,且这一比值随温度升高而增大;相应地,超弹性变形别逐渐减弱以至消失. 相似文献
993.
The atomic concentration profiles in 4H and 6H SiC created by Al and B doping turn-on and turn-off during vapor phase epitaxy
(VPE) was investigated by secondary ion mass spectrometry (SIMS). It was found that dopant traces were adsorbed to the reactor
walls and re-evaporated after the dopant precursor flow was switched off. This adsorption/re-evaporation process limits the
doping dynamic range to about three orders of magnitude for Al, and two orders of magnitude for B. An order of magnitude in
doping dynamics could be gained by simultaneously switching the gases and changing the C:Si precursor ratio. By adding a 10
min growth interruption with an H or HC1 etch at the doping turn-off, the background doping tail could be considerably suppressed.
In total, a doping dynamics for Al of almost five orders of magnitude can be controlled within a 30 nm layer. For B, the dynamic
range is more than three orders of magnitude, and the abruptness is most probably diffusion limited. Abackground doping level
of 2 × 1015 cm−3 for Al and 2 × 1016 cm−3 for B was obtained. For Al, the background doping is most probably due to the adsorption/re-evaporation of dopants at the
reactor walls; while for B, the background doping may in addition be limited by diffusion. 相似文献
994.
成组Broyden修正矩阵的紧凑形式与成组记忆修正算法 总被引:1,自引:0,他引:1
1 引言 成组型线性方程组 其中,p是适中的数值,由于其有相当的实际应用背景,人们一直在研究有效的数值方法,特别是近年来,实际问题中归结出来的成组型方程组,其规模越来越大,又具有稀疏结构,因而使用迭代法是一种有效的途径,目前使用比较多的是Krylov子空间方法中的Lanczos方法,CG方法,GMRES方法等等。这种成组型算法的建立,其基本出发点是使算法具有较少的计算量和存储量,具体体现在: 1)成组型算法在应用于问题(1.1)的求解时,也具有有限终止性性质,而其终止步数一般要比单个型算法的步数减少了户倍,由于成组型算法每迭代一步的计算量基本上等同于单个型算法使用户次的计算量,如此,算法的计算量会有明显的改善。 2)当A存储在二级(secondary)内存时,在迭代计算时需要不断地进行存取交换,由于成组型算法的迭代步数减少了户倍,如此,用在这种交换的时间也要减少户倍,相当有效。 3)由于在成组型算法中,出现的多是AX的形式,其中,故成组型算法便于计算并行化。 4)即使用于求解单个方程组,当A的少数几个极端特征值分离甚远时,这种成组型算法也有可能改善其收敛速度,如成组型的CG方法。 目前,这种成组型算法已体现出很大的实用计算价值,然而其进一步的理论分析还有待深入研究。 相似文献
995.
Shape memory polymers are novel materials that can be easily formed into complex shapes, retaining memory of their original
shape even after undergoing large deformations. The temporary shape is stable and return to the original shape is triggered
by a suitable mechanism such as heating. In this paper, we develop constitutive equations to model the mechanical behavior
of crystallizable shape memory polymers. Crystallizable shape memory polymers are called crystallizable because the temporary
shape is fixed by a crystalline phase, while return to the original shape is due to the melting of this crystalline phase.
The modeling is done using a framework that was developed recently for studying crystallization in polymers ([28], [25], [27],
[31]) and is based on the theory of multiple natural configurations. In this paper we formulate constitutive equations for
the original amorphous phase and the semi-crystalline phase that is formed after the onset of crystallization. In addition
we model the melting of the crystalline phase to capture the return of the polymer to its original shape. The model has been
used to simulate a typical uni-axial cycle of deformation, the results of this simulation compare very well with experimental
data. In addition to this we also simulate circular shear of a hollow cylinder and present results for different cases in
this geometry.
Received: January 5, 2005 相似文献
996.
基于基因算法的模糊联想记忆设计方法 总被引:3,自引:2,他引:1
本文提出了一种用基因算法来进行模糊联想记忆系统设计的方法-基因FAM法。同自适应模糊联想记忆和神经网络设计方法相比,该方法不要求有训练样本;而且可以设计出的FAM系统最后,举例说明了该方法的应用。 相似文献
997.
用0.35μm CMOS工艺实现存储接口单元中的数模混合DLL 总被引:1,自引:0,他引:1
论述了一种利用0.35mm、双阱、双层金属、双层多晶硅的CMOS工艺所实现的延迟锁定环(DLL)。该DLL用于RISC处理器中存储接口部件的时钟同步。本文介绍了其应用背景,给出了DLL的系统结构,接着分别介绍了鉴相器、电荷泵以及压控延迟线的电路结构,最后给出相关仿真结果。 相似文献
998.
999.
1000.
Ten synthetic receptors were tested in potentiometric coated wire electrodes. The electrodes were used as sensing devices in classical reversed phase HPLC determinations of dicarboxylic acids present in food materials. All receptors contained amine functionalities. Four of them were podand urea derivatives. The other six were macrocyclic polyamines with lipophilic groups. Three of them had urea functionalities in their side-chains. Glassy carbon (GC) substrate electrodes were coated with PVC-based “liquid membranes” containing plasticizers and receptors. All tested compounds strongly enhanced the detection limits for the dicarboxylic acids (low pg detection limits), in comparison to a non-specific electrode based on methyltridodecylammonium chloride (MTDDACl). Receptors of the podand urea type yielded high sensitivity, but the electrodes had a lower long-time stability (a few weeks) than the electrodes based on macrocyclic polyamines (at least 3 months). 相似文献