全文获取类型
收费全文 | 23450篇 |
免费 | 3481篇 |
国内免费 | 2423篇 |
专业分类
化学 | 12702篇 |
晶体学 | 186篇 |
力学 | 1202篇 |
综合类 | 140篇 |
数学 | 2032篇 |
物理学 | 5999篇 |
无线电 | 7093篇 |
出版年
2024年 | 93篇 |
2023年 | 546篇 |
2022年 | 669篇 |
2021年 | 839篇 |
2020年 | 844篇 |
2019年 | 855篇 |
2018年 | 670篇 |
2017年 | 715篇 |
2016年 | 947篇 |
2015年 | 1002篇 |
2014年 | 1275篇 |
2013年 | 1523篇 |
2012年 | 1920篇 |
2011年 | 1893篇 |
2010年 | 1337篇 |
2009年 | 1314篇 |
2008年 | 1492篇 |
2007年 | 1333篇 |
2006年 | 1329篇 |
2005年 | 1112篇 |
2004年 | 828篇 |
2003年 | 753篇 |
2002年 | 763篇 |
2001年 | 651篇 |
2000年 | 526篇 |
1999年 | 518篇 |
1998年 | 423篇 |
1997年 | 401篇 |
1996年 | 408篇 |
1995年 | 326篇 |
1994年 | 266篇 |
1993年 | 198篇 |
1992年 | 225篇 |
1991年 | 210篇 |
1990年 | 157篇 |
1989年 | 145篇 |
1988年 | 99篇 |
1987年 | 78篇 |
1986年 | 99篇 |
1985年 | 77篇 |
1984年 | 64篇 |
1983年 | 49篇 |
1982年 | 38篇 |
1981年 | 33篇 |
1980年 | 30篇 |
1978年 | 24篇 |
1977年 | 26篇 |
1976年 | 25篇 |
1974年 | 25篇 |
1973年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
介绍了高可靠电镀Ni/Au工艺在PTFE微波印制电路上的应用,并分析了氨基磺酸盐镀软镍和亚硫酸盐镀软金工艺的影响因素及提高Ni/Au镀层之间附着力的措施。通过实验及应用证明了与直接镀金工艺相比,在软基材PTFE敷铜箔板上镀Ni/Au工艺能大大提高微波电路的可焊性,高温稳定性和长期可靠性,并且用其所制作的微波器件的高频性能也优于直接镀金工业。 相似文献
44.
One of the shortcomings of R&D evaluation is a lack of emphasis on analytical assessment of the value of an on-going R&D project. This paper addresses the problem concerning the distributive aspect of access to superior knowledge. Decision tree analysis and probability models appear to be appropriate tools for assessing the values of an intermediate result and patent reward of a firm's R&D decision in an environment of perfect information and oligopolistic competition. The assessed values are used as minimum prices acceptable to the firm when the knowledge is disseminated to the public. This paper will attempt to resolve this problem through the determination of the appropriate values of the reservation price of the first-stage invention in terms of the final reward and of a patent reward for which the inventor is willing to apply. 相似文献
45.
The radiation emitted by a time-harmonic elementary current in magnetized electron plasma half-space, bounded by an ideal electric plane, is investigated using an exact formulation. It is found that: conventional image principle holds for vertical magnetization case; while for parallel magnetization case, coupled image principle seems to be valid. 相似文献
46.
The loss performance of tagged and normal ATM cells at a first-in-first-out (FIFO) buffer is studied. The authors show that if a partial buffer sharing mechanism is adopted the loss probability of normal cells can be firmly guaranteed, regardless of the traffic intensity of tagged cells 相似文献
47.
48.
To incorporate an acceptor type polythiophene segment onto a supramolecular block copolymer for potential light harvesting applications, effective synthetic routes for the end‐functionalized and acceptor‐substituted polythiophenes are critical. The Ullmann coupling reaction can be utilized to obtain electron‐deficient polythiophenes and to attach terminal thiophene units that carry functional groups. In this article, the reactions involving a 2,5‐dibromothiophene monomer containing an electron‐withdrawing fluorinated ester and 5‐bromo‐2‐thiophenecarboxaldehyde (the end‐capper) were studied in detail. It was found that the Ullmann coupling reaction of the dibromide is very fast (completed in a few minutes) and the terminal bromine group does not survive long under the reaction condition. These findings lead to the development of an effective procedure for aldehyde end‐capping of electron‐deficient polythiophenes. Polymers with molecular weights around 4000 Da are routinely obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 41–47, 2007 相似文献
49.
50.
Jing Cheng 《量子光学学报》2006,12(B08):71-72
The effect of finite control beam on the transverse spatial profile of the slow light propagation in an electromagnetically induced transparency medium is studied. From the second-order wave equation and linear response of an EIT medium to the signal field, we find it is possible to produce an effective waveguide for the signal field. The existence and properties of a set of localized, stationary transverse modes are demonstrated. Especially, by carefully manipulating the profile of the control beam, we can realize single-mode propagation for the signal field, which may be important for potential applications. 相似文献