全文获取类型
收费全文 | 27480篇 |
免费 | 2816篇 |
国内免费 | 1141篇 |
专业分类
化学 | 5478篇 |
晶体学 | 65篇 |
力学 | 1021篇 |
综合类 | 349篇 |
数学 | 2475篇 |
物理学 | 3957篇 |
无线电 | 18092篇 |
出版年
2024年 | 65篇 |
2023年 | 266篇 |
2022年 | 664篇 |
2021年 | 1018篇 |
2020年 | 1094篇 |
2019年 | 552篇 |
2018年 | 529篇 |
2017年 | 1069篇 |
2016年 | 1263篇 |
2015年 | 1191篇 |
2014年 | 1956篇 |
2013年 | 1630篇 |
2012年 | 1879篇 |
2011年 | 1803篇 |
2010年 | 1353篇 |
2009年 | 1402篇 |
2008年 | 1578篇 |
2007年 | 1799篇 |
2006年 | 1672篇 |
2005年 | 1450篇 |
2004年 | 1274篇 |
2003年 | 1186篇 |
2002年 | 882篇 |
2001年 | 719篇 |
2000年 | 568篇 |
1999年 | 419篇 |
1998年 | 378篇 |
1997年 | 280篇 |
1996年 | 259篇 |
1995年 | 282篇 |
1994年 | 210篇 |
1993年 | 166篇 |
1992年 | 138篇 |
1991年 | 101篇 |
1990年 | 57篇 |
1989年 | 47篇 |
1988年 | 36篇 |
1987年 | 22篇 |
1986年 | 33篇 |
1985年 | 40篇 |
1984年 | 31篇 |
1983年 | 12篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 15篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1971年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
文章首先对智能化电子信息技术进行了深入的研究,而后分析了该技术在应用过程中出现的问题,最后结合该技术的相关特点给出了相应的问题解决措施,希望能够对智能化电子信息技术的发展提供帮助。 相似文献
2.
《Arabian Journal of Chemistry》2022,15(1):103492
Matrix metalloproteinases (MMPs) are a large family of zinc-dependent endoproteases known to exert multiple regulatory roles in tumor progression. A variety of chemical classes have been explored for targeting individual MMP isoforms. In the present study, we further developed our isatin based scaffold BB0223107 capable of binding to and inactivating MMP-2 in a zinc-independent manner (Agamennone et al., 2016). Forty four new compounds were synthesized based on the modified BB0223107. All compounds were tested in enzyme inhibition assays against MMP-2, ?8 and ?13. SAR studies demonstrated that 5-het(aryl)-3-aminoindolin-2-ones (37–39) were active toward MMP-2 and MMP-13. The most potent compounds 33 and 37 displayed an IC50 of 3 µM against MMP-13 and showed a negligible activity toward MMP-8; almost all new compounds were inactive toward MMP-8. Replacement of the isatin ring with a biaryl system (compound 33) did not decrease the potency against MMP-13 but reduced the selectivity. Structure-based computational studies were carried out to rationalize the inhibitory activity data. The analysis of binding geometries confirmed that all fragments occupied the S1′ site in the three enzymes while no ligand was able to bind the catalytic zinc ion. To the best of our knowledge, this is the first example of 3-aminoindolin-2-one-based MMP inhibitors that, based on the computer modeling study, do not coordinate the zinc ion. Thus, the het(aryl)-3-aminoindolin-2-one derivatives emerge as a drug-like and promising chemotype that, along with the hetaryl variations, represents an alternative and thrifty tool for chemical space exploration aimed at MMP inhibitor design. 相似文献
3.
4.
5.
Quadrature spatial modulation (QSM) utilizes the in‐phase and quadrature spatial dimensions to transmit the real and imaginary parts of a single signal symbol, respectively. The improved QSM (IQSM) transmits two signal symbols per channel use through a combination of two antennas for each of the real and imaginary parts. The main contributions of this study can be summarized as follows. First, we derive an upper bound for the error performance of the IQSM. We then design constellation sets that minimize the error performance of the IQSM for several system configurations. Second, we propose a double QSM (DQSM) that transmits the real and imaginary parts of two signal symbols through any available transmit antennas. Finally, we propose a parallel IQSM (PIQSM) that splits the antenna set into equal subsets and performs IQSM within each subset using the same two signal symbols. Simulation results demonstrate that the proposed constellations significantly outperform conventional constellations. Additionally, DQSM and PIQSM provide a performance similar to that of IQSM while requiring a smaller number of transmit antennas and outperform IQSM with the same number of transmit antennas. 相似文献
6.
Vyacheslav V. Sentyurin Oleg A. Levitskiy Tatiana V. Magdesieva 《Current Opinion in Electrochemistry》2020
This mini-review highlights key structural features that should be taken into account when creating ambipolar redox-active closed-shell metal-free molecules. This type of compound is strongly required for the fabrication of all-organic ‘poleless’ batteries and semiconductors. The suggested strategies aimed at stabilization of both oxidized (cationic) and reduced (anionic) redox-states are based on the comprehensive analysis of the most successful structures taken from the recent publications. 相似文献
7.
为了提升高校实验数据处理水平,高校实验室的相关建设工作已经步入正轨,但层出不穷的信息安全问题也向高校实验室计算机网络维护工作提出了新的挑战。文章从现阶段高校实验室计算机网络的相关建设工作出发,简要论述引发网络故障的具体原因,并对其诊断技术进行探讨。 相似文献
8.
9.
本文结合HTH电路的复杂性等特征分析与实际应用现状,研究了HTH电路的具体检测技术方法并对当前热点技术进行对比分析,探讨了HTH电路检测方法的技术发展趋势。 相似文献
10.
本文对国内外的电视技术发展现状进行了充分的研究和分析,并对超高清电视系统的相关图像技术参数进行了分析和介绍。 相似文献