全文获取类型
收费全文 | 192篇 |
免费 | 12篇 |
国内免费 | 23篇 |
专业分类
化学 | 38篇 |
晶体学 | 1篇 |
力学 | 9篇 |
综合类 | 1篇 |
数学 | 6篇 |
物理学 | 18篇 |
综合类 | 154篇 |
出版年
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 10篇 |
2015年 | 10篇 |
2014年 | 10篇 |
2013年 | 12篇 |
2012年 | 6篇 |
2011年 | 9篇 |
2010年 | 8篇 |
2009年 | 5篇 |
2008年 | 13篇 |
2007年 | 16篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 9篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有227条查询结果,搜索用时 890 毫秒
31.
32.
The crystallography of interfaces in a duplex stainless steel having an equiaxed microstructure produced through the ferrite to austenite diffusive phase transformation has been studied. The five-parameter interface character distribution revealed a high anisotropy in habit planes for the austenite–ferrite and austenite–austenite interfaces for different lattice misorientations. The austenite and ferrite habit planes largely terminated on (1 1 1) and (1 1 0) planes, respectively, for the austenite–ferrite interfaces associated with Kurdjumov–Sachs (K–S) and Nishiyama–Wasserman (N–W) orientation relationships. This was mostly attributed to the crystallographic preference associated with the phase transformation. For the austenite–ferrite interfaces with orientation relationships which are neither K–S nor N–W, both austenite and ferrite habit planes had (1 1 1) orientations. Σ3 twin boundaries comprised the majority of austenite–austenite interfaces, mostly showing a pure twist character and terminating on (1 1 1) planes due to the minimum energy configuration. The second highest populated austenite–austenite boundary was Σ9, which tended to have grain boundary planes in the tilt zone due to the geometrical constraints. Furthermore, the intervariant crystallographic plane distribution associated with the K–S orientation relationship displayed a general tendency for the austenite habit planes to terminate with the (1 1 1) orientation, mainly due to the crystallographic preference associated with the phase transformation. 相似文献
33.
The electrical coupling of myocytes and fibroblasts can play a role in inhibiting electrical impluse propagation in cardiac muscle. To understand the function of fibroblast–myocyte coupling in the aging heart, the spiral-wave dynamics in the duplex networks with inhibitory coupling is numerically investigated by the Br–Eiswirth model. The numerical results show that the inhibitory coupling can change the wave amplitude, excited phase duration and excitability of the system. When the related parameters are properly chosen, the inhibitory coupling can induce local abnormal oscillation in the system and the Eckhaus instability of the spiral wave. For the dense inhibitory network, the maximal decrement(maximal increment) in the excited phase duration can reach 24.3%(13.4%), whereas the maximal decrement in wave amplitude approaches 28.1%. Upon increasing the inhibitory coupling strength, the system excitability is reduced and even completely suppressed when the interval between grid points in the inhibitory network is small enough. Moreover, the inhibitory coupling can lead to richer phase transition scenarios of the system, such as the transition from a stable spiral wave to turbulence and the transition from a meandering spiral wave to a planar wave. In addition, the self-sustaining planar wave, the unique meandering of spiral wave and inward spiral wave are observed. The physical mechanisms behind the phenomena are analyzed. 相似文献
34.
针对当前无线对讲井下恶劣环境下不能达到远距离高效通信的问题,设计一种将无线对讲信号转光纤网络传输的井下无线对讲通信系统.该系统主要由终端收发模块和三向全双工分路组成,通过终端收发模块将无线信号接入光纤网络进行集群式一体化远距离传输.该系统在实际调试和使用时能达到预期效果,并且性能良好. 相似文献
35.
新型节镍Cr22双相不锈钢中铜的作用 总被引:1,自引:0,他引:1
研究Cu对新型节镍Cr22双相不锈钢(duplex stainless steels,DSS)的显微组织、力学性能及腐蚀性能的影响.研究结果表明,Cu元素在该系列成分双相不锈钢中是较强的奥氏体形成元素,质量分数为0.69%的Cu可使Cr22 DSSs在不同温度固溶处理后的奥氏体体积分数增加约8%.节镍型Cr22 DSS... 相似文献
36.
Anke Dierckx Dr. Francois‐Alexandre Miannay Dr. Nouha Ben Gaied Søren Preus Markus Björck Prof. Dr. Tom Brown Prof. Dr. L. Marcus Wilhelmsson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(19):5987-5997
Fluorescent‐base analogues (FBAs) comprise a group of increasingly important molecules for the investigation of nucleic acid structure and dynamics as well as of interactions between nucleic acids and other molecules. Here, we report on the synthesis, detailed spectroscopic characterisation and base‐pairing properties of a new environment‐sensitive fluorescent adenine analogue, quadracyclic adenine (qA). After developing an efficient route of synthesis for the phosphoramidite of qA it was incorporated into DNA in high yield by using standard solid‐phase synthesis procedures. In DNA qA serves as an adenine analogue that preserves the B‐form and, in contrast to most currently available FBAs, maintains or even increases the stability of the duplex. We demonstrate that, unlike fluorescent adenine analogues, such as the most commonly used one, 2‐aminopurine, and the recently developed triazole adenine, qA shows highly specific base‐pairing with thymine. Moreover, qA has an absorption band outside the absorption of the natural nucleobases (>300 nm) and can thus be selectively excited. Upon excitation the qA monomer displays a fluorescence quantum yield of 6.8 % with an emission maximum at 456 nm. More importantly, upon incorporation into DNA the fluorescence of qA is significantly less quenched than most FBAs. This results in quantum yields that in some sequences reach values that are up to fourfold higher than maximum values reported for 2‐aminopurine. To facilitate future utilisation of qA in biochemical and biophysical studies we investigated its fluorescence properties in greater detail and resolved its absorption band outside the DNA absorption region into distinct transition dipole moments. In conclusion, the unique combination of properties of qA make it a promising alternative to current fluorescent adenine analogues for future detailed studies of nucleic acid‐containing systems. 相似文献
37.
抢劫枪支、弹药、爆炸物罪的犯罪主体应包括已满14周岁不满16周岁的人。该罪犯罪对象的范围应进行的界定。该罪既遂、未遂的标准应根据不同情况加以确定。 相似文献
38.
一种新型的资源节约型高氮超级双相不锈钢00Cr25Ni2Mo3Mn10N开发出来,氮质量分数达到0.5%.研究表明,经热锻和1 050 ℃固溶处理后,基体组织由铁素体和奥氏体组成,铁素体质量分数约为47%,氮质量分数的增加能明显提高材料的机械性能和腐蚀性能.通过对比研究表明,00Cr25Ni2Mo3Mn10N的综合性能相当于或优于00Cr25Ni7Mo4N 超级双相不锈钢. 相似文献
39.
Cooperative Non-Orthogonal Multiple Access (NOMA) with Simultaneous Wireless Information and Power Transfer (SWIPT) communication can not only effectively improve the spectrum efficiency and energy efficiency of wireless networks but also extend their coverage. An important design issue is to incentivize a full duplex (FD) relaying center user to participate in the cooperative process and achieve a win–win situation for both the base station (BS) and the center user. Some private information of the center users are hidden from the BS in the network. A contract theory-based incentive mechanism under this asymmetric information scenario is applied to incentivize the center user to join the cooperative communication to maximize the BS’s benefit utility and to guarantee the center user’s expected payoff. In this work, we propose a matching theory-based Gale–Shapley algorithm to obtain the optimal strategy with low computation complexity in the multi-user pairing scenario. Simulation results indicate that the network performance of the proposed FD cooperative NOMA and SWIPT communication is much better than the conventional NOMA communication, and the benefit utility of the BS with the stable match strategy is nearly close to the multi-user pairing scenario with complete channel state information (CSI), while the center users get the satisfied expected payoffs. 相似文献
40.
双级时效对7A52铝合金组织与性能的影响 总被引:3,自引:0,他引:3
采用拉伸力学性能测试、电导率测定、透射电镜分析等手段研究双级时效处理条件下7A52铝合金的力学性能、电导率和显微组织结构。研究结果表明:7A52铝合金适宜的双级时效工艺为105℃/8 h 130℃/14 h。在此条件下,合金的抗拉强度、屈服强度、伸长率和电导率分别为500 MPa,444 MPa,11.1%和18.44 S/m。与单级峰值时效相比,强度并未明显降低而电导率有明显提高,表明合金抗应力腐蚀性能得到改善。双级时效后,合金的晶内组织为细小弥散分布的η′(MgZn2)相,晶界上有断续分布的晶界析出相MgZn2和较明显的无沉淀析出带。 相似文献