全文获取类型
收费全文 | 34055篇 |
免费 | 5266篇 |
国内免费 | 3908篇 |
专业分类
化学 | 18043篇 |
晶体学 | 282篇 |
力学 | 1884篇 |
综合类 | 228篇 |
数学 | 3035篇 |
物理学 | 9815篇 |
无线电 | 9942篇 |
出版年
2024年 | 155篇 |
2023年 | 869篇 |
2022年 | 1064篇 |
2021年 | 1342篇 |
2020年 | 1360篇 |
2019年 | 1241篇 |
2018年 | 1096篇 |
2017年 | 1016篇 |
2016年 | 1465篇 |
2015年 | 1592篇 |
2014年 | 1864篇 |
2013年 | 2396篇 |
2012年 | 2759篇 |
2011年 | 2944篇 |
2010年 | 1975篇 |
2009年 | 2006篇 |
2008年 | 2037篇 |
2007年 | 1918篇 |
2006年 | 1955篇 |
2005年 | 1591篇 |
2004年 | 1283篇 |
2003年 | 1016篇 |
2002年 | 956篇 |
2001年 | 814篇 |
2000年 | 802篇 |
1999年 | 750篇 |
1998年 | 708篇 |
1997年 | 568篇 |
1996年 | 568篇 |
1995年 | 494篇 |
1994年 | 458篇 |
1993年 | 360篇 |
1992年 | 351篇 |
1991年 | 292篇 |
1990年 | 250篇 |
1989年 | 200篇 |
1988年 | 126篇 |
1987年 | 117篇 |
1986年 | 96篇 |
1985年 | 92篇 |
1984年 | 51篇 |
1983年 | 54篇 |
1982年 | 44篇 |
1981年 | 31篇 |
1980年 | 18篇 |
1979年 | 11篇 |
1977年 | 10篇 |
1975年 | 7篇 |
1973年 | 6篇 |
1957年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Zhang Bing Yang Jie-qin Liu Ying Hu Bin Yang Yang Zhao Li Lu Qiang 《Cellulose (London, England)》2022,29(12):6565-6578
Cellulose - Heating is essential in various biomass pre-treatments and thermal conversion processes. It is of practical significance to study the characteristics of cellulose-lignin and... 相似文献
2.
Xiao Zhu Chen Yanxun Jiang Hongbo Hu Zhenzhen Lui John C. S. Min Geyong Dustdar Schahram 《Wireless Networks》2022,28(7):3305-3322
Wireless Networks - Unmanned aerial vehicles (UAV) have been widely used in various fields because of their high mobility and portability. At the same time, due to the rapid development of... 相似文献
3.
该文基于掺钪AlN薄膜制备了高次谐波体声波谐振器(HBAR),研究了钪(Sc)掺杂浓度对AlN压电薄膜材料特性及器件性能的影响。研究表明,当掺入Sc的摩尔分数从0增加到25%时,压电应力系数e33增加、刚度 下降,导致Al1-xScxN压电薄膜的机电耦合系数 从5.6%提升至15.8%,从而使HBAR器件的有效机电耦合系数 提升了3倍。同时,当Sc掺杂摩尔分数达25%时,Al1-xScxN(x为Sc掺杂摩尔分数)压电薄膜的声速下降13%,声学损耗提高,导致HBAR器件的谐振频率和品质因数降低。 相似文献
4.
5.
6.
7.
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
8.
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
9.
10.
S. Q. Hou W. Wang Z. Y. Wang Z. W. Hu K. Liu 《Journal of Applied Mechanics and Technical Physics》2018,59(1):153-162
In order to investigate the characteristics of force chains in a granular flow system, a parallel plate shear cell is constructed to simulate the shear movement of an infinite parallel plate and observe variations in relevant parameters. The shear dilatancy process is divided into three stages, namely, plastic strain, macroscopic failure, and granular recombination. The stickslip phenomenon is highly connected with the evolution of force chains during the shear dilatancy process. The load–distribution rate curves and patterns of the force chains are utilized to describe the load-carrying behaviors and morphologic changes of force chains separately. Force chains, namely, “diagonal gridding,” “tadpole-shaped,” and “pinnate” are defined according to the form of the force chains in the corresponding three stages. 相似文献