全文获取类型
收费全文 | 1615066篇 |
免费 | 35623篇 |
国内免费 | 11106篇 |
专业分类
化学 | 713998篇 |
晶体学 | 20892篇 |
力学 | 77064篇 |
综合类 | 217篇 |
数学 | 248724篇 |
物理学 | 395116篇 |
无线电 | 205784篇 |
出版年
2021年 | 15783篇 |
2020年 | 18309篇 |
2019年 | 18456篇 |
2018年 | 17002篇 |
2017年 | 15320篇 |
2016年 | 32017篇 |
2015年 | 23245篇 |
2014年 | 34261篇 |
2013年 | 80771篇 |
2012年 | 45294篇 |
2011年 | 45050篇 |
2010年 | 43693篇 |
2009年 | 48107篇 |
2008年 | 46712篇 |
2007年 | 44671篇 |
2006年 | 48095篇 |
2005年 | 41755篇 |
2004年 | 41398篇 |
2003年 | 38378篇 |
2002年 | 38840篇 |
2001年 | 38721篇 |
2000年 | 33672篇 |
1999年 | 30271篇 |
1998年 | 28261篇 |
1997年 | 28112篇 |
1996年 | 27507篇 |
1995年 | 25187篇 |
1994年 | 24626篇 |
1993年 | 23959篇 |
1992年 | 23961篇 |
1991年 | 24126篇 |
1990年 | 22894篇 |
1989年 | 22413篇 |
1988年 | 21572篇 |
1987年 | 20291篇 |
1986年 | 19150篇 |
1985年 | 25634篇 |
1984年 | 26700篇 |
1983年 | 22533篇 |
1982年 | 23881篇 |
1981年 | 23046篇 |
1980年 | 22338篇 |
1979年 | 22340篇 |
1978年 | 23512篇 |
1977年 | 23096篇 |
1976年 | 22735篇 |
1975年 | 21361篇 |
1974年 | 21023篇 |
1973年 | 21490篇 |
1972年 | 15643篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
241.
Metabolic profiles of dioscin in rats revealed by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry 下载免费PDF全文
He Zhu Jin‐Di Xu Qian Mao Hong Shen Ming Kong Jian‐Ping Chen Song‐Lin Li 《Biomedical chromatography : BMC》2015,29(9):1415-1421
Dioscin (DIS), one of the most abundant bioactive steroidal saponins in Dioscorea sp., is used as a complementary medicine to treat coronary disease and angina pectoris in China. Although the pharmacological activities and pharmacokinetics of DIS have been well demonstrated, information regarding the final metabolic fates is very limited. This study investigated the in vivo metabolic profiles of DIS after oral administration by ultra‐performance liquid chromatography quadrupole time‐of‐flight mass spectrometry method. The structures of the metabolites were identified and tentatively characterized by means of comparing the molecular mass, retention time and fragmentation pattern of the analytes with those of the parent compound. A total of eight metabolites, including seven phase I and one phase II metabolites, were detected and tentatively identified for the first time. Oxidation, deglycosylation and glucuronidation were found to be the major metabolic processes of the compound in rats. In addition, a possible metabolic pathway on the biotransformation of DIS in vivo was proposed. This study provides valuable and new information on the metabolism of DIS, which will be helpful for further understanding its mechanism of action. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
242.
243.
244.
E. A. Andrianova V. D. Davidenko V. F. Tsibulskiy S. V. Tsibulskiy 《Physics of Atomic Nuclei》2015,78(11):1252-1258
Influence of the nuclear energy structure, the conditions of fuel burnup, and accumulation of new fissile isotopes from the raw isotopes on the main parameters of a closed fuel cycle is considered. The effects of the breeding ratio, the cooling time of the spent fuel in the external fuel cycle, and the separation of the breeding area and the fissile isotope burning area on the parameters of the fuel cycle are analyzed. 相似文献
245.
246.
247.
248.
New Phenomena in Organometallic‐Mediated Radical Polymerization (OMRP) and Perspectives for Control of Less Active Monomers 下载免费PDF全文
Prof. Dr. Rinaldo Poli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(19):6988-7001
The impact of reversible bond formation between a growing radical chain and a metal complex (organometallic‐mediated radical polymerization (OMRP) equilibrium) to generate an organometallic intermediate/dormant species is analyzed with emphasis on the interplay between this and other one‐electron processes involving the metal complex, which include halogen transfer in atom transfer radical polymerization (ATRP), hydrogen‐atom transfer in catalytic chain transfer (CCT), and catalytic radical termination (CRT). The challenges facing the controlled polymerization of “less active monomers” (LAMs) are outlined and, after reviewing the recent achievements of OMRP in this area, the perspectives of this technique are analyzed. 相似文献
249.
250.
Photoisomerisation in Aminoazobenzene‐Substituted Ruthenium(II) Tris(bipyridine) Complexes: Influence of the Conjugation Pathway 下载免费PDF全文
Dr. Anissa Amar Dr. Paul Savel Dr. Huriye Akdas‐Kilig Dr. Claudine Katan Prof. Hacène Meghezzi Prof. Abdou Boucekkine Dr. Jean‐Pierre Malval Dr. Jean‐Luc Fillaut 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8262-8270
Transition‐metal complexes containing stimuli‐responsive systems are attractive for applications in optical devices, photonic memory, photosensing, as well as luminescence imaging. Amongst them, photochromic metal complexes offer the possibility of combining the specific properties of the metal centre and the optical response of the photochromic group. The synthesis, the electrochemical properties and the photophysical characterisation of a series of donor–acceptor azobenzene derivatives that possess bipyridine groups connected to a 4‐dialkylaminoazobenzene moiety through various linkers are presented. DFT and TD‐DFT calculations were performed to complement the experimental findings and contribute to their interpretation. The position and nature of the linker (ethynyl, triazolyl, none) were engineered and shown to induce different electronic coupling between donor and acceptor in ligands and complexes. This in turn led to strong modulations in terms of photoisomerisation of the ligands and complexes. 相似文献