全文获取类型
收费全文 | 2750篇 |
免费 | 277篇 |
国内免费 | 195篇 |
专业分类
化学 | 1966篇 |
晶体学 | 35篇 |
力学 | 121篇 |
综合类 | 12篇 |
数学 | 365篇 |
物理学 | 723篇 |
出版年
2023年 | 44篇 |
2022年 | 67篇 |
2021年 | 80篇 |
2020年 | 103篇 |
2019年 | 113篇 |
2018年 | 101篇 |
2017年 | 65篇 |
2016年 | 120篇 |
2015年 | 109篇 |
2014年 | 132篇 |
2013年 | 189篇 |
2012年 | 229篇 |
2011年 | 228篇 |
2010年 | 152篇 |
2009年 | 125篇 |
2008年 | 161篇 |
2007年 | 146篇 |
2006年 | 139篇 |
2005年 | 133篇 |
2004年 | 81篇 |
2003年 | 63篇 |
2002年 | 83篇 |
2001年 | 51篇 |
2000年 | 42篇 |
1999年 | 35篇 |
1998年 | 34篇 |
1997年 | 32篇 |
1996年 | 34篇 |
1995年 | 32篇 |
1994年 | 25篇 |
1993年 | 23篇 |
1992年 | 34篇 |
1991年 | 17篇 |
1990年 | 26篇 |
1989年 | 17篇 |
1988年 | 19篇 |
1987年 | 17篇 |
1986年 | 9篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 12篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1972年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有3222条查询结果,搜索用时 46 毫秒
961.
962.
Abstract A new series of diphosphonates (I) was synthesized and investigated for their pharmacological activity. 2-Substituted-1,3-propylidene diphosphonates (I) were prepared by reaction of sodium dialkyl phosphite or trialkyl phosphite with ditosylates of 2-substituted-1,3-propanediol or 2-substituted-1,3-dibromopropane. Pharmacological screenings of these 1,3-propylidenediphosphonates have shown that these compounds have potent cardiovascular activity and are potentially useful in the treatment of hypertension. 相似文献
963.
A robust solid‐phase microextraction fiber was fabricated by electropolymerization of thiophene on a stainless steel wire. This fiber was applied for the determination of endocrine‐disruptor pesticides, namely, chlorpyrifos, penconazole, procymidone, bromopropylate, and λ‐cyhalothrin in well waters by a headspace solid‐phase microextraction procedure. Operational parameters, namely, pH, sample volume, adsorption temperature and time, desorption temperature, stirring rate, and salt amount were optimized as 7.0, 8 mL, 70°C and 20 min, 250°C, 600 rpm, and 0.3 g/mL, respectively. The separation power of GC was coupled with the excellent sensitivity of the developed fiber enabling us to determine pesticide mixtures simultaneously in a ng/mL range. The LOD was in the range of 0.02–0.64 ng/mL. The method was successfully applied for the selective and sensitive determination of target pesticides in well water samples with acceptable recovery values (92–110%). The polythiophene fiber gives satisfactory results compared with commercial fibers. Commonly used pesticides with different polarities were chosen as representative compounds to search the applicability of the fiber for well water analysis collected from vineyards. 相似文献
964.
Hongying Zhu Yonggang Feng Jun Yang Wenjie Pan Zhanghai Li Yonggao Tu Xiaolan Zhu Guangming Huang 《Journal of separation science》2013,36(15):2486-2495
Sucrose esters (SEs) were successfully extracted from Oriental tobacco leaves using a new methodology based on accelerated solvent extraction followed by hydrophilic–lipophilic balanced cartridge cleanup step. The SEs were detected by HPLC with ion‐trap MS detection using an electrospray interface operated in the positive ion mode. This methodology combines the high efficiency of extraction provided by a pressurized fluid and the highly sensitive characterization offered by ion‐trap MS. Under the optimized conditions, 14 SEs were first identified among a total of 23 SEs found in Oriental tobacco leaves. Under the same conditions, only four new SEs were extracted by using traditional ultrasound‐assisted extraction and liquid–solid extraction methods. The present method might be potentially useful in high‐efficiency extraction and sensitive characterization of SEs from complex matrices such as tobacco leaves. 相似文献
965.
Zhendong Yan Wei Du Linlin Tu Ping Gu Zhong Huang Peng Zhan Fanxin Liu Zhenlin Wang 《Journal of Raman spectroscopy : JRS》2015,46(9):795-801
Plasmonic systems based on metal nanoparticles on a metal film with high optical absorption have generated great interests for surface‐enhanced Raman scattering (SERS). In this study, we prepare a broadband‐visible light absorber consisting Au nanotriangles on the surface of a continuous optically opaque gold film separated with a dielectric SiO2 layer, which is a typical metal‐insulator‐metal (MIM) system, and demonstrate it as an efficient SERS substrate. The MIM nanostructure, prepared using nanosphere lithography with a very large area, shows a broadband with absorption exceeding 90% in the wavelength regime of 630–920 nm. We observe an average SERS enhancement factor (EF) as large as 4.9 × 106 with a 22‐fold increase compared to a single layer of Au nanotriangles directly on a quartz substrate. A maximum SERS EF can be achieved by optimizing the thicknesses of the dielectric layer to control the optical absorption. Owing to the simple, productive, and inexpensive fabrication technique, our MIM nanostructure could be a potential candidate for SERS applications. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
966.
In this report we described a highly selective and sensitive iodate sensor. Due to its interaction with fluorescent gold nanoclusters, iodate was capable of oxidizing and etching gold core of the nanoclusters, resulting in fluorescence quenching. Furthermore, it was found that extra iodide ion could enhance this etching process, and even a small amount of iodate could lead to significant quenching. Under an optimized condition, linear relationship between the iodate concentration and the fluorescence quenching was obtained in the range 10 nM–1 μM. The developed iodate sensor was found selective and capable of detecting iodate as low as 2.8 nM. The sensor was then applied for the analysis of iodate in real sample and satisfactory recoveries were obtained. 相似文献
967.
New chiral ferrocenylphosphines LB1–LB9 were designed and prepared through simple synthetic approaches. These air-stable ferrocenylphosphines were applied to promote asymmetric [3+2]-cycloaddition of Morita–Baylis–Hillman carbonates with maleimides, among which LB7 was shown to have good catalytic activity to afford the corresponding multifunctional cyclopentenes in up to 59% yield and up to 53% ee under mild reaction conditions. A plausible reaction mechanism was proposed. 相似文献
968.
A new series of calix[4]arene supported N-heterocyclic carbene palladium complexes were developed and fully characterized. A mono-substituted calix[4]arene was prepared through conventional procedures, following with the attachment of imidazolyl derivative groups to compose the precursors of novel NHCs ligands. Undergoing the alkylation with n-butylbromide and corresponding metallation with palladium and pyridine, original complexes were obtained. After a full characterization in solution and solid state, the evaluation of catalytic activity was taken out in Suzuki–Miyaura cross-coupling reactions, which revealed good performances. 相似文献
969.
970.
Vuong Phan Tu He Xiaozheng Thong Duong Viet 《Journal of Optimization Theory and Applications》2021,190(3):915-930
Journal of Optimization Theory and Applications - We investigate the convergence properties of a projected neural network for solving inverse variational inequalities. Under standard assumptions,... 相似文献