全文获取类型
收费全文 | 178377篇 |
免费 | 42387篇 |
国内免费 | 41275篇 |
专业分类
化学 | 80951篇 |
晶体学 | 3132篇 |
力学 | 8601篇 |
综合类 | 2176篇 |
数学 | 17702篇 |
物理学 | 76564篇 |
无线电 | 72913篇 |
出版年
2024年 | 1195篇 |
2023年 | 2626篇 |
2022年 | 4639篇 |
2021年 | 4525篇 |
2020年 | 4444篇 |
2019年 | 5186篇 |
2018年 | 5047篇 |
2017年 | 6850篇 |
2016年 | 6544篇 |
2015年 | 8694篇 |
2014年 | 9453篇 |
2013年 | 12023篇 |
2012年 | 13269篇 |
2011年 | 14468篇 |
2010年 | 17350篇 |
2009年 | 17740篇 |
2008年 | 12124篇 |
2007年 | 11143篇 |
2006年 | 10604篇 |
2005年 | 9340篇 |
2004年 | 9021篇 |
2003年 | 6660篇 |
2002年 | 6494篇 |
2001年 | 6371篇 |
2000年 | 5780篇 |
1999年 | 4274篇 |
1998年 | 3039篇 |
1997年 | 2663篇 |
1996年 | 2976篇 |
1995年 | 3280篇 |
1994年 | 3274篇 |
1993年 | 3439篇 |
1992年 | 2932篇 |
1991年 | 2586篇 |
1990年 | 2121篇 |
1989年 | 2237篇 |
1988年 | 2108篇 |
1987年 | 1324篇 |
1986年 | 1348篇 |
1985年 | 945篇 |
1984年 | 1091篇 |
1983年 | 464篇 |
1982年 | 961篇 |
1981年 | 798篇 |
1980年 | 832篇 |
1979年 | 593篇 |
1978年 | 555篇 |
1977年 | 650篇 |
1976年 | 1053篇 |
1972年 | 542篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
We investigate the effect of dopant random fluctuation on threshold voltage and drain current variation in a two-gate nanoscale transistor. We used a quantum-corrected technology computer aided design simulation to run the simulation (10000 randomizations). With this simulation, we could study the effects of varying the dimensions (length and width), and thicknesses of oxide and dopant factors of a transistor on the threshold voltage and drain current in subthreshold region (off) and overthreshold (on). It was found that in the subthreshold region the variability of the drain current and threshold voltage is relatively fixed while in the overthreshold region the variability of the threshold voltage and drain current decreases remarkably, despite the slight reduction of gate voltage diffusion (compared with that of the subthreshold). These results have been interpreted by using previously reported models for threshold current variability, load displacement, and simple analytical calculations. Scaling analysis shows that the variability of the characteristics of this semiconductor increases as the effects of the short channel increases. Therefore, with a slight increase of length and a reduction of width, oxide thickness, and dopant factor, we could correct the effect of the short channel. 相似文献
32.
33.
The research progress of a novel traffic solution,a submerged floating tunnel(SFT),is reviewed in terms of a study approach and loading scenario.Among existing publications,the buoyancy-weight ratio(BWR) is usually predefined.However,BWR is a critical structural parameter that tremendously affects the dynamic behaviour of not only the tunnel tube itself but also the cable system.In the context of a SFT prototype(SFTP) project in Qiandao Lake(Zhejiang Province,China),the importance of BWR is illustrated by finite element analysis and subsequently,an optimized BWR is proposed within a reasonable range in the present study.In the numerical model,structural damping is identified to be of importance.Rayleigh damping and the corresponding Rayleigh coefficients are attained through a sensitivity study,which shows that the adopted damping ratios are fairly suitable for SFTP.Lastly,the human sense of security is considered by quantifying the comfort index,which helps further optimize BWR in the SFTP structural parameter design. 相似文献
34.
35.
The Effect of the Spacer of Bis(biurea) Ligands on the Structure of A2L3‐type (A=anion) Phosphate Complexes 下载免费PDF全文
Prof. Biao Wu Dr. Shaoguang Li Prof. Yibo Lei Prof. Huaiming Hu Dr. Nader de Sousa Amadeu Prof. Dr. Christoph Janiak Dr. Jennifer S. Mathieson Dr. De‐Liang Long Prof. Leroy Cronin Prof. Xiao‐Juan Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2588-2593
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO43?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes. 相似文献
36.
37.
38.
提供了一种简便易行的靶面激光光斑尺寸原位测量的方法。从高斯光束的横向光强分布特性出发,建立了激光烧蚀斑半径与辐照激光能量、光斑尺寸、烧蚀阈值间的关系式,模拟分析发现辐照激光光斑尺寸对烧蚀斑半径随辐照能量变化曲线有较大影响。对于脉宽为2 ms,波长为1064 nm的激光,实验测量了不同能量激光辐照下相纸烧蚀斑半径,并用推导出的关系式拟合测量数据,获得了靶面处光斑尺寸和样品烧蚀阈值。同时,也测量了不同位置处的光斑尺寸和样品烧蚀阈值,对高斯光束束腰位置和样品烧蚀阈值的光斑尺寸效应进行了验证。研究结果表明该技术结果可靠,简单高效。该技术可以为高能激光与固体物质相互作用的基础研究和激光加工等应用领域中实现简单方便地测量靶面光斑尺寸提供帮助。 相似文献
39.
刘伟 《信息技术与信息化》2015,(2):80-81
本文据国内矫直机的使用情况,提出完善弯辊功能,解决辊缝标定清零及运行中的问题,提升轧钢厂运行效率与产品质量。 相似文献
40.