全文获取类型
收费全文 | 28139篇 |
免费 | 3019篇 |
国内免费 | 2218篇 |
专业分类
化学 | 2454篇 |
晶体学 | 38篇 |
力学 | 1783篇 |
综合类 | 509篇 |
数学 | 14125篇 |
物理学 | 6357篇 |
无线电 | 8110篇 |
出版年
2024年 | 57篇 |
2023年 | 323篇 |
2022年 | 484篇 |
2021年 | 564篇 |
2020年 | 620篇 |
2019年 | 603篇 |
2018年 | 613篇 |
2017年 | 820篇 |
2016年 | 928篇 |
2015年 | 794篇 |
2014年 | 1522篇 |
2013年 | 1872篇 |
2012年 | 1586篇 |
2011年 | 1798篇 |
2010年 | 1556篇 |
2009年 | 1804篇 |
2008年 | 1832篇 |
2007年 | 1885篇 |
2006年 | 1745篇 |
2005年 | 1615篇 |
2004年 | 1359篇 |
2003年 | 1220篇 |
2002年 | 1056篇 |
2001年 | 889篇 |
2000年 | 850篇 |
1999年 | 738篇 |
1998年 | 685篇 |
1997年 | 628篇 |
1996年 | 485篇 |
1995年 | 373篇 |
1994年 | 319篇 |
1993年 | 240篇 |
1992年 | 200篇 |
1991年 | 164篇 |
1990年 | 173篇 |
1989年 | 135篇 |
1988年 | 97篇 |
1987年 | 80篇 |
1986年 | 71篇 |
1985年 | 88篇 |
1984年 | 72篇 |
1983年 | 55篇 |
1982年 | 70篇 |
1981年 | 63篇 |
1980年 | 38篇 |
1979年 | 34篇 |
1978年 | 35篇 |
1977年 | 28篇 |
1976年 | 30篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
2.
3.
《Wave Motion》2018
Large cable net structures have been widely applied in aerospace engineering due to the feature of light-weight, high packaging efficiency, and high thermal stability. Structural vibrations induced by a variety of disturbances are inevitable in the space environment, resulting in the requirement of effective vibration control strategies for large cable net structures. Since the large cable net structures have many closely spaced vibrational modes in the range of low frequencies, traditional modal based control may cause modal truncation and spillover problems. In this paper, a wave-based boundary control strategy is adopted and its effectiveness to control the vibration of cable net structures is investigated, by transfer function analysis and numerical methods. It is found that the structural vibration can be absolutely resisted by applying the wave-based boundary controllers onto all the exterior nodes, when disturbances come from the external boundaries of the cable net. Our results in this paper can provide a theoretical basis for the vibration control of large cable net structures. 相似文献
4.
We report a simple processing method to simultaneously improve the efficiency and stability of organic solar cells (OSCs). Poly(4-styrene sulfonate)-doped poly(3,4-ethylenedioxy-thiophene (PEDOT:PSS), widely used as hole transport layer (HTL) in OSCs, tends to accelerate the degradation of devices because of its hygroscopic and acidic properties. In this regard, we have modified PEDOT:PSS to reduce its hygroscopic and acidic properties through a condensation reaction between PEDOT:PSS and poly(ethylene glycol) methyl ether (PEGME) in order to improve the efficiency and stability of OSCs. As a result, the power conversion efficiency (PCE) increased by 21%, from 2.57% up to 3.11%. A better energy level alignment by the reduced work function of the modified PEDOT:PSS with a highest occupied molecular orbital (HOMO) level of poly(3-hexylthiophene-2,5-diyl) (P3HT) is considered the origin of the improved the efficiency. The half-life of OSCs with PEDOT:PSS modified with PEGME buffer layer also increased up to 3.5 times compared to that of devices with pristine PEDOT:PSS buffer layer. 相似文献
5.
6.
7.
Lithium Insertion Mechanism in Iron-Based Oxyfluorides with Anionic Vacancies Probed by PDF Analysis
Dr. Damien Dambournet Dr. Karena W Chapman Dr. Mathieu Duttine Dr. Olaf Borkiewicz Dr. Peter J Chupas Dr. Henri Groult 《ChemistryOpen》2015,4(4):443-447
The mechanism of lithium insertion that occurs in an iron oxyfluoride sample with a hexagonal–tungsten–bronze (HTB)-type structure was investigated by the pair distribution function. This study reveals that upon lithiation, the HTB framework collapses to yield disordered rutile and rock salt phases followed by a conversion reaction of the fluoride phase toward lithium fluoride and nanometer-sized metallic iron. The occurrence of anionic vacancies in the pristine framework was shown to strongly impact the electrochemical activity, that is, the reversible capacity scales with the content of anionic vacancies. Similar to FeOF-type electrodes, upon de-lithiation, a disordered rutile phase forms, showing that the anionic chemistry dictates the atomic arrangement of the re-oxidized phase. Finally, it was shown that the nanoscaling and structural rearrangement induced by the conversion reaction allow the in situ formation of new electrode materials with enhanced electrochemical properties. 相似文献
8.
无源光网络(Passive Optical Network,PON)作为当今接入网的主要技术解决方案,具有带宽使用效率高、传输距离远、抗干扰能力强等特点.通过研究PON技术的发展动态,本文首先归纳了各种PON技术的产生背景和应用特点,整理出各技术间的连接关系及主要标准;其次介绍了PON技术的帧结构,并对带宽、波长、传输模式等PON技术的主要参数进行了汇总;然后将国内外研究热点进行划分,围绕媒体访问控制协议、帧结构、动态带宽分配算法、节能机制等关键技术,阐述了其研究现状及在PON中的重要作用;最后对PON技术的发展趋势进行了展望. 相似文献
9.
论文提出利用用户提供的个性化信息来随机产生关联大素数,保证了素数选取的随机化、个性化,提高了RSA算法的安全性。 相似文献
10.
主要对各国3G许可证与使用技术标准的抽绑政策.各国对2G/3G网络漫游的管制规定。以及3G网络之间共享的种类及实施方式等方面做了详尽的讲解,并进行比较和分析。 相似文献