全文获取类型
收费全文 | 41847篇 |
免费 | 7065篇 |
国内免费 | 4649篇 |
专业分类
化学 | 23029篇 |
晶体学 | 406篇 |
力学 | 1894篇 |
综合类 | 165篇 |
数学 | 3175篇 |
物理学 | 13267篇 |
无线电 | 11625篇 |
出版年
2024年 | 206篇 |
2023年 | 1162篇 |
2022年 | 1488篇 |
2021年 | 1868篇 |
2020年 | 1877篇 |
2019年 | 1775篇 |
2018年 | 1486篇 |
2017年 | 1382篇 |
2016年 | 2020篇 |
2015年 | 2074篇 |
2014年 | 2580篇 |
2013年 | 3077篇 |
2012年 | 3642篇 |
2011年 | 3636篇 |
2010年 | 2481篇 |
2009年 | 2474篇 |
2008年 | 2795篇 |
2007年 | 2310篇 |
2006年 | 2246篇 |
2005年 | 1832篇 |
2004年 | 1292篇 |
2003年 | 1090篇 |
2002年 | 1066篇 |
2001年 | 879篇 |
2000年 | 695篇 |
1999年 | 843篇 |
1998年 | 747篇 |
1997年 | 701篇 |
1996年 | 714篇 |
1995年 | 583篇 |
1994年 | 484篇 |
1993年 | 372篇 |
1992年 | 369篇 |
1991年 | 285篇 |
1990年 | 244篇 |
1989年 | 180篇 |
1988年 | 112篇 |
1987年 | 85篇 |
1986年 | 114篇 |
1985年 | 80篇 |
1984年 | 47篇 |
1983年 | 53篇 |
1982年 | 39篇 |
1981年 | 30篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Zhihong Zhao Bin Wang Rui Tan Wenjing Liu Minghui Zhang 《Magnetic resonance in chemistry : MRC》2022,60(4):427-433
In this study, the transverse relaxation time (T2) of activated carbon (AC) in different relative environment humidity was detected firstly by low-field nuclear magnetic resonance (LFNMR). The pore size (diameter) of AC distributions was calculated by the relationship between T2 and surface relaxation rate (ρ), where ρ was obtained by the detection of nine porous materials with known pore size. The results showed that the pore size distributions of AC calculated by ρ < 0.19 nm/ms were in good agreement with that obtained by nitrogen adsorption method and proved that LFNMR as a new detection method was feasible for characterizing AC pore size distribution. 相似文献
2.
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
3.
Wireless Networks - Geolocation is important for many emerging applications such as disaster management and recommendation system. In this paper, we propose a multilayer recognition model (MRM) to... 相似文献
4.
Dan Chen Kaixin Du Xiaochen Niu Hongwei Zhang Xue Zhang Yu Tang Jianchun Zhao 《Biomedical chromatography : BMC》2022,36(3):e5288
Amlexanox, an anti-inflammatory and anti-allergic agent, has been widely used clinically for the treatment of canker sores, asthma, and allergic rhinitis. Recently, amlexanox has received considerable attention in curing nonalcoholic fatty liver diseases and hepatitis virus infection. Herein, we first established a sensitive high-performance liquid chromatography-tandem mass spectrum (LC–MS/MS) method for the determination of amlexanox in rat plasma. Propranolol was used as the internal standard (IS). Using a simple protein precipitation method, the amlexanox and IS were separated with Capcell Pak C18 column (2.0 × 50 mm, 5 μm) and eluted with water and acetonitrile each containing 0.1% formic acid using gradient elution condition at a flow rate of 0.4 mL·min−1. Amlexanox and IS were detected by a triple quadrupole mass in multiple reactive monitoring (MRM) under the transitions of m/z 299.2 → 281.2 and m/z 259.9 → 116.1 with positive electrospray ionization, respectively. The calibration curves of amlexanox were established with the range of 50 to 2000 ng·mL−1 (r2 > 0.99). The validation method consisted of selectivity, accuracy, precision, carryover effect, matrix effect, recovery, dilution effect, and stability. The fully validated method was successfully applied to the pharmacokinetic study of amlexanox in Wistar rats. 相似文献
5.
Cellulose - In this research, the production of levoglucosan (LG) and levoglucosenone (LGO) was improved from acid-impregnated cellulose via fast pyrolysis. Thermogravimetric and kinetic analysis... 相似文献
6.
Hao Lu Xiaodong Wang Hang Wang Andong Zhang Xinming Zheng Na Yu Zheng Tang Xinjun Xu Yahui Liu Ya-Nan Chen Zhishan Bo 《中国科学:化学(英文版)》2022,65(3):594-601
Three nonfused ring electron acceptors (NFREAs) TTC6,TT-C8T and TT-TC8 were purposefully designed and synthesized.The molecular geometry can be adjusted by the steric hindrance of lateral substituents.According to the DFT calculations,from TTC6 to TT-C8T and TT-TC8,planarity of the molecular backbone is gradually improved,accompanying with the enhancing of intramolecular charge transfer effect.As for TT-TC8,the two phenyl substituents are almost perpendicular to the molecular backbone,which endues the acceptor with good solubility and suppresses it to form over-aggregation.Multidirectional regular molecular orientation and closer molecular stacking are formed in TT-TC8 film.As a result,TT-TC8 based devices afford the highest PCE of 13.13%,which is much higher than that of TTC6 (4.41%) and TT-C8T (10.42%) and among the highest PCE values based on NFREAs. 相似文献
7.
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
8.
Applied Mathematics and Mechanics - Spiral springs have a wide range of applications in various fields. As a result of the complexity of friction, few theoretical analyses of spring belts under... 相似文献
9.
Geometriae Dedicata - Inspired by a recent work of Grove and Petersen (Alexandrov spaces with maximal radius, 2018), where the authors studied positively curved Alexandrov spaces with largest... 相似文献
10.
5G-oriented Virtual Augmented Reality Scene Construction and Business Information Flow Demonstration
Mobile Networks and Applications - Aiming at the problems of large data volume, long calculation time, and information feedback speed in traditional virtual augmented reality-based scenes, this... 相似文献