全文获取类型
收费全文 | 6506篇 |
免费 | 1070篇 |
国内免费 | 675篇 |
专业分类
化学 | 4274篇 |
晶体学 | 59篇 |
力学 | 328篇 |
综合类 | 43篇 |
数学 | 815篇 |
物理学 | 2732篇 |
出版年
2024年 | 29篇 |
2023年 | 144篇 |
2022年 | 233篇 |
2021年 | 272篇 |
2020年 | 274篇 |
2019年 | 237篇 |
2018年 | 204篇 |
2017年 | 200篇 |
2016年 | 322篇 |
2015年 | 294篇 |
2014年 | 364篇 |
2013年 | 440篇 |
2012年 | 550篇 |
2011年 | 598篇 |
2010年 | 362篇 |
2009年 | 364篇 |
2008年 | 395篇 |
2007年 | 349篇 |
2006年 | 348篇 |
2005年 | 293篇 |
2004年 | 214篇 |
2003年 | 185篇 |
2002年 | 212篇 |
2001年 | 166篇 |
2000年 | 139篇 |
1999年 | 183篇 |
1998年 | 145篇 |
1997年 | 117篇 |
1996年 | 114篇 |
1995年 | 83篇 |
1994年 | 58篇 |
1993年 | 59篇 |
1992年 | 56篇 |
1991年 | 61篇 |
1990年 | 33篇 |
1989年 | 31篇 |
1988年 | 25篇 |
1987年 | 17篇 |
1986年 | 27篇 |
1985年 | 18篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有8251条查询结果,搜索用时 15 毫秒
991.
The electron transport characters in a nanostructure with the periodic magnetic-electric barriers 下载免费PDF全文
This paper detailedly studies the transmission probability, the spin
polarization and the conductance of the ballistic electron in a
nanostructure with the periodic magnetic-electric barriers. These
observable quantities are found to be strongly dependent not only on
the magnetic configuration, the incident electron energy and the
incident wave vector, but also on the number of the periodic
magnetic-electric barriers. The transmission coefficient and the spin
polarization show a periodic pattern with the increase of the
separation between two adjacent magnetic fields, and the resonance
splitting increases as the number of periods increases. Surprisingly,
it is found that a polarization can be achieved by spin-dependent
resonant tunnelling in this structure, although the average magnetic
field of the structure is zero. 相似文献
992.
Weixia Gao Li WangDenglu Hou Yuchan HuQian Zhang Li MaCongmian Zhen 《Applied Surface Science》2011,257(21):8871-8875
Ge1−xMnx (x = 0, 0.013, 0.0226, 0.0339, 0.0565, 0.0678, 0.0904, 0.113) films prepared by magnetron sputtering at 773 K had a Ge cubic structure except for x = 0.1130. Co ion implantation into these films can effectively prevent the formation of a second phase. Both single-doped and co-doped samples were ferromagnetic at room temperature. The d-d exchange interaction between the interstitial Mn (MnT) and the substituted Mn (MnGe) resulted in ferromagnetism in the sputtered films. Since Co ion implantation destroyed the MnT-MnGe-MnT complex, the saturated magnetization decreased. Hall measurements revealed that the Co ion implanted films were n-type semiconductors, and the anomalous Hall Effect (AHE) suggested the ferromagnetism was carrier-mediated in the implanted films. 相似文献
993.
994.
995.
讨论了无源超高频射频识别(UHF RFID)系统的信号传输过程及性能测试方法,以软件定义无线电方式实现了符合ISO/IEC18000-6C标准的无源标签的部分性能测试,研究了部分通信参数动态变化时标签应答功率的变化,并对不同标签的灵敏度进行了测试.所有实验在常规条件下完成,测试研究表明在基带编码采用较小的Tari值、PW为50%以及较高的调制系数时,阅读器能够接收到标签反射回来的最大功率,系统的识别距离最远.
关键词:
射频识别
无源电子标签
标签灵敏度
性能测试 相似文献
996.
In the last decade, much attention has been focused on examining the nonlocality of various quantum networks, which are fundamental for long-distance quantum communications. In this paper, we consider the nonlocality of any forked tree-shaped network, where each node, respectively, shares arbitrary number of bipartite sources with other nodes in the next “layer”. The Bell-type inequalities for such quantum networks are obtained, which are, respectively, satisfied by all -local correlations and all local correlations, where denotes the total number of nodes in the network. The maximal quantum violations of these inequalities and the robustness to noise in these networks are also discussed. Our network can be seen as a generalization of some known quantum networks. 相似文献
997.
针对超表面在透镜方面的应用, 本文设计了一种交叉极化透射聚焦超表面, 实现了将圆极化波转化为交叉极化波的同时聚焦电磁波的功能. 设计了一款旋转型单元, 单元为一层且厚度仅为1.5 mm, 分析了旋转型单元提供不同相移的原理并设计了相邻单元相移差为60°的相位梯度超表面, 在中心频率f=15 GHz附近发生奇异折射, 折射角与理论计算结果一致, 验证了设计单元的有效性, 基于该单元设计了尺寸为90 m mm×90 mm、单元数为15×15 的透射型聚焦超表面, 在中心频率f=15 GHz附近, 左旋圆极化平面波照射时, 透射波聚焦于L=40 mm 的实焦点且透射波为照射波的交叉极化波. 该超表面透镜效率高、厚度薄且为单层, 易于加工, 相对于传统透镜, 优势明显, 在操控电磁波、改善透镜性能方面有潜在应用价值. 相似文献
998.
A theoretical analysis of the pump-induced temperature change and associated thermal phase shift occurring in a fiber laser is presented. The temperature rise and thermal phase shift from the moment when pump is turned on to steady-state in fiber lasers, such as Yb-doped fiber laser, are numerical calculated.With the same parameters, the numerical solution is in good agreement with the finite-element (ANSYS software) simulation. 相似文献
999.
Go A Bay A Abe K Aihara H Anipko D Aulchenko V Aushev T Bakich AM Barberio E Belous K Bitenc U Bizjak I Blyth S Bozek A Bracko M Browder TE Chang P Chao Y Chen A Chen KF Chen WT Cheon BG Chistov R Choi Y Choi YK Cole S Dalseno J Danilov M Dash M Drutskoy A Eidelman S Epifanov D Fratina S Gabyshev N Gershon T Gokhroo G Golob B Gorisek A Ha H Hastings NC Hayasaka K Hayashii H Hazumi M Heffernan D Hokuue T Hoshi Y Hou S Hou WS Iijima T Ikado K Imoto A Inami K Ishikawa A Ishino H Itoh R Iwasaki M 《Physical review letters》2007,99(13):131802
The neutral B meson pair produced at the Upsilon(4S) should exhibit a nonlocal correlation of the type discussed by Einstein, Podolsky, and Rosen. We measure this correlation using the time-dependent flavor asymmetry of semileptonic B(0) decays, which we compare with predictions from quantum mechanics and two local realistic models. The data are consistent with quantum mechanics, and inconsistent with the other models. Assuming that some B pairs disentangle to produce B(0) and B(0) with definite flavor, we find a decoherent fraction of 0.029 +/ -0.057, consistent with no decoherence. 相似文献
1000.
Lv Z Fu Y Hou S Wang D Wu H Zhang C Chu Z Zou D 《Physical chemistry chemical physics : PCCP》2011,13(21):10076-10083
A high-efficiency dye-sensitized solar cell prototype has been designed and fabricated, in which the working electrode and counter electrode are in direct contact and singly twisted. The cell is sealed in a capillary. In this solar cell configuration, the area ratio between the counter and working electrode is extremely low which allows the independent adjustment of electrolyte volume and the distance between counter electrode and photo-anode. Also it is more easily sealed compared to planar solar cell. The effects of TiO(2) film thickness, twisted pitch of counter electrode and length of device have been investigated. Our results indicate that this novel configuration has demonstrated excellent modularization function, three dimensional light harvesting capacities and the relative independence of incident light angles due to the symmetry structure. The power conversion efficiency of one cell of 9.5 cm in length can reach up to 5.41% at standard test condition (100 mW cm(-2)) and the power output may double under intense diffuse illumination. As far as we know, this is the longest and most efficient fiber-shaped dye-sensitized solar cell consisting of liquid electrolyte. The longer the fiber-shaped solar cell is, the more suitable it is for woven solar power textile if it is encapsulated in transparent flexible plastic capillary. 相似文献