全文获取类型
收费全文 | 7885篇 |
免费 | 944篇 |
国内免费 | 724篇 |
专业分类
化学 | 3882篇 |
晶体学 | 18篇 |
力学 | 37篇 |
综合类 | 68篇 |
数学 | 210篇 |
物理学 | 976篇 |
无线电 | 4362篇 |
出版年
2024年 | 23篇 |
2023年 | 99篇 |
2022年 | 189篇 |
2021年 | 319篇 |
2020年 | 358篇 |
2019年 | 206篇 |
2018年 | 172篇 |
2017年 | 247篇 |
2016年 | 350篇 |
2015年 | 393篇 |
2014年 | 593篇 |
2013年 | 558篇 |
2012年 | 515篇 |
2011年 | 550篇 |
2010年 | 418篇 |
2009年 | 481篇 |
2008年 | 489篇 |
2007年 | 516篇 |
2006年 | 503篇 |
2005年 | 438篇 |
2004年 | 400篇 |
2003年 | 308篇 |
2002年 | 222篇 |
2001年 | 183篇 |
2000年 | 155篇 |
1999年 | 145篇 |
1998年 | 134篇 |
1997年 | 116篇 |
1996年 | 102篇 |
1995年 | 85篇 |
1994年 | 76篇 |
1993年 | 55篇 |
1992年 | 32篇 |
1991年 | 22篇 |
1990年 | 19篇 |
1989年 | 20篇 |
1988年 | 13篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有9553条查询结果,搜索用时 218 毫秒
1.
Edward G. Sheetz Zhao Zhang Alyssa Marogil Minwei Che Dr. Maren Pink Dr. Veronica Carta Prof. Dr. Krishnan Raghavachari Prof. Dr. Amar H. Flood 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(60):e202201584
The recognition of boron compounds is well developed as boronic acids but untapped as organotrifluoroborate anions (R−BF3−). We are exploring the development of these and other designer anions as anion-recognition motifs by considering them as substituted versions of the parent inorganic ion. To this end, we demonstrate strong and reliable binding of organic trifluoroborates, R−BF3−, by cyanostar macrocycles that are size-complementary to the inorganic BF4− progenitors. We find that recognition is modulated by the substituent's sterics and that the affinities are retained using the common K+ salts of R−BF3− anions. 相似文献
2.
Xiaopo Wu Yangming Shi Weibo Meng Xiaofei Ma Nian Fang 《International Journal of Satellite Communications and Networking》2019,37(3):283-291
Electromagnetic signal emitted by satellite communication (satcom) transmitters are used to identify specific individual uplink satcom terminals sharing the common transponder in real environment, which is known as specific emitter identification (SEI) that allows for early indications and warning (I&W) of the targets carrying satcom furnishment and furthermore the real time electromagnetic situation awareness in military operations. In this paper, the authors are the first to propose the identification of specific transmitters of satcom by using probabilistic neural networks (PNN) to reach the goal of target recognition. We have been devoted to the examination by exploring the feasibility of utilizing the Hilbert transform to signal preprocessing, applying the discrete wavelet transform to feature extraction, and employing the PNN to perform the classification of stationary signals. There are a total of 1000 sampling time series with binary phase shift keying (BPSK) modulation originated by five types of satcom transmitters in the test. The established PNNs classifier implements the data testing and finally yields satisfactory accuracy at 8 dB(±1 dB) carrier to noise ratio, which indicates the feasibility of our method, and even the keen insight of its application in military. 相似文献
3.
Wenqing Zhang Dr. Jiuxing Li Prof. Dr. Bruno Salena Prof. Dr. Yingfu Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(3):592-596
DNA detection is usually conducted under nondenaturing conditions to favor the formation of Watson–Crick base-paring interactions. However, although such a setting is excellent for distinguishing a single-nucleotide polymorphism (SNP) within short DNA sequences (15–25 nucleotides), it does not offer a good solution to SNP detection within much longer sequences. Here we report on a new detection method capable of detecting SNP in a DNA sequence containing 35–90 nucleotides. This is achieved through incorporating into the recognition DNA sequence a previously discovered DNA molecule that forms a stable G-quadruplex in the presence of 7 molar urea, a known condition for denaturing DNA structures. The systems are configured to produce both colorimetric and fluorescent signals upon target binding. 相似文献
4.
5.
6.
7.
本文提出了全真信息、信息的亲善性等概念,讨论了信息的有关性质及运算的关系,得到了信息的运算与普通集合运算之间存在着差异的结论,说明了引起该差异的原因.同时,以认知模式为基础,定义了信息函数,并得到了有关的命题及运算. 相似文献
8.
Laser welding is one of the most precise welding processes in joining sheet metals. In laser welding, performing real time evaluation of the welding quality is very important to enhance the efficiency of the welding process. In this study, the plasma and spatter, which are generated during laser welding, are measured using UV and IR photodiodes. The factors that influence weld quality are classified into five categories; optimal heat input, slightly low heat input, low heat input, partial joining due to gap mismatch, and nozzle deviation. The data number deviated from reference signals and their standard deviations were also considered to evaluate the qualities. A system was also formulated to perform real time evaluations of the weld quality using a fuzzy multi-feature pattern recognition with the measured signals. 相似文献
9.
10.