全文获取类型
收费全文 | 30942篇 |
免费 | 5785篇 |
国内免费 | 3310篇 |
专业分类
化学 | 22043篇 |
晶体学 | 353篇 |
力学 | 1809篇 |
综合类 | 137篇 |
数学 | 3003篇 |
物理学 | 12692篇 |
出版年
2024年 | 135篇 |
2023年 | 693篇 |
2022年 | 1205篇 |
2021年 | 1296篇 |
2020年 | 1400篇 |
2019年 | 1382篇 |
2018年 | 1172篇 |
2017年 | 1051篇 |
2016年 | 1596篇 |
2015年 | 1538篇 |
2014年 | 1953篇 |
2013年 | 2409篇 |
2012年 | 2862篇 |
2011年 | 2876篇 |
2010年 | 1878篇 |
2009年 | 1790篇 |
2008年 | 1998篇 |
2007年 | 1741篇 |
2006年 | 1627篇 |
2005年 | 1281篇 |
2004年 | 978篇 |
2003年 | 767篇 |
2002年 | 760篇 |
2001年 | 593篇 |
2000年 | 475篇 |
1999年 | 602篇 |
1998年 | 518篇 |
1997年 | 499篇 |
1996年 | 499篇 |
1995年 | 439篇 |
1994年 | 347篇 |
1993年 | 285篇 |
1992年 | 282篇 |
1991年 | 229篇 |
1990年 | 204篇 |
1989年 | 158篇 |
1988年 | 97篇 |
1987年 | 85篇 |
1986年 | 107篇 |
1985年 | 76篇 |
1984年 | 39篇 |
1983年 | 47篇 |
1982年 | 28篇 |
1981年 | 22篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1957年 | 4篇 |
1923年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Yu Chen Youyi Zhao Ming Wang Hao Sun Yunfa Dong Xu Feng 《Chemistry of Natural Compounds》2012,47(6):940-943
An original triterpenoid saponin, named lonimacranthoide I, was isolated from the flower buds of Lonicera macranthoides (Caprifoliaceae). It has hederagenin as aglycone. Lonimacranthoide I is a rare chlorogenic acid ester acylated at C-23 of
hederagenin. The structure of the saponin was established based on chemical and spectral methods. 相似文献
993.
A general, efficient, and more practical protocol for the base-mediated intermolecular or intramolecular S-arylation leading to the 2-aminobenzothiazole derivatives is reported. Remarkably, all reactions were carried out under transition-metal-free conditions with good to excellent yields, rendering the methodology presented herein highly valuable from both environmental and economic points of view. 相似文献
994.
995.
Linghan Xiao Xin Zheng Tianyi Zhao Liying Sun Fengqi Liu Ge Gao Alideertu Dong 《Colloid and polymer science》2013,291(10):2359-2364
A novel route was introduced to synthesize dense polyacrylamide (PAM) onto the glass slide surface. To investigate the surface chemistry of the PAM on the glass slides, X-ray photoelectron spectroscopy (XPS) was utilized to obtain detailed chemical state information on the PAM layer constituents. The XPS peak data were consistent with the presented model of the PAM on the glass slide surface. Scanning electron microscopy and atomic force microscope data indicated the presence of PAM on the glass slides, which consist of nodules. The results showed that PAM was successfully immobilized onto glass slides with a two-tier structure under aqueous condition and a monolayer structure under anhydrous condition. Compared with those under aqueous condition, the controllability of the molecular layer on glass slides and the reproducibility under anhydrous condition were much better, which makes anhydrous condition an advisable condition for the study of the reaction mechanisms of glass slides modified by PAM. 相似文献
996.
Development and validation of a UPLC‐MS/MS method for the determination of cucurbitacin B in rat plasma and application to a pharmacokinetic study
下载免费PDF全文
![点击此处可从《Biomedical chromatography : BMC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Waiou Zhao Dahai Xu Weiwei Yan Yushi Wang Nan Zhang 《Biomedical chromatography : BMC》2016,30(4):503-507
Cucurbitacin B (CuB), one of the most abundant forms of cucurbitacins, is a promising natural anticancer drug candidate. Although the anticancer activity of CuB has been well demonstrated, information regarding the pharmacokinetics is limited. A rapid, selective and sensitive UPLC‐MS/MS for CuB was developed and validated using hemslecin A (HeA) as internal standard (IS). Plasma samples were pre‐treated by liquid–liquid extraction with dichloromethane. Separation was achieved on a reversed‐phase C18 column (50 × 4.6 mm, 5 µm) at 35°C using isocratic elution with water–methanol (25:75, v/v) at a flow rate of 0.3 mL/min. The analytes were monitored by a triple quadrupole tandem mass spectrometer with positive electrospray ionization mode. The calibration curve was linear (r > 0.995) in a concentration range of 0.3–100 ng/mL with a limit of quantification of 0.3 ng/mL. Intra‐ and inter‐day accuracy and precision were validated by percentage relative error and relative standard deviation, respectively, which were both lower than the limit of 15%. This assay was successfully applied to a pharmacokinetic study of CuB in Wistar rats. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
997.
Kinetics and Mechanism of the Reaction of a Ruthenium(VI) Nitrido Complex with HSO3− and SO32− in Aqueous Solution
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Qian Wang Hong Yan Zhao Dr. Wai‐Lun Man Dr. William W. Y. Lam Dr. Kai‐Chung Lau Prof. Tai‐Chu Lau 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(31):10754-10758
The kinetics and mechanism of the reaction of SIV (SO32?+HSO3?) with a ruthenium(VI) nitrido complex, [(L)RuVI(N)(OH2)]+ (RuVIN, L=N,N′‐bis(salicylidene)‐o‐cyclohexyldiamine dianion), in aqueous acidic solutions are reported. The kinetic results are consistent with parallel pathways involving oxidation of HSO3? and SO32? by RuVIN. A deuterium isotope effect of 4.7 is observed in the HSO3? pathway. Based on experimental results and DFT calculations the proposed mechanism involves concerted N?S bond formation (partial N‐atom transfer) between RuVIN and HSO3? and H+ transfer from HSO3? to a H2O molecule. 相似文献
998.
999.
1000.
Controlled release formulation of pesticides is highly desirable for attaining the most effective utilization of the pesticide as well as reducing environmental pollution. Nano-sized controlled release formulations can provide better penetration through cuticle and deliver the active ingredients efficiently to the targeted tissue. In this study, a novel strategy for the preparation of a nanoconjugate derived from kasugamycin with amino-modified silica was developed. The kasugamycin was connected with amino-modified silica matrix by an amide bond, which could avoid the initial burst release effectively and prolong the duration remarkably. The results showed the kasuga-silica can protect kasugamycin against photo-degradation effectively and the release rate of the active ingredient of nanoconjugate was related to the temperature, pH value, and the particle size (52.5–315.4 nm). With reduced particle size as well as increased temperature and acidity, the release of the active ingredient was faster. This amide linkage of kasuga-silica could be degraded by amidase effectively. This nanoconjugate displayed a better and a sustained bactericidal efficacy against E. coli than kasugamycin technical, which makes it a potential candidate as a controlled release conjugate for kasugamycin in the future. 相似文献