全文获取类型
收费全文 | 4632篇 |
免费 | 559篇 |
国内免费 | 176篇 |
专业分类
化学 | 4433篇 |
晶体学 | 3篇 |
力学 | 25篇 |
综合类 | 18篇 |
数学 | 650篇 |
物理学 | 238篇 |
出版年
2024年 | 5篇 |
2023年 | 60篇 |
2022年 | 233篇 |
2021年 | 196篇 |
2020年 | 208篇 |
2019年 | 151篇 |
2018年 | 169篇 |
2017年 | 130篇 |
2016年 | 213篇 |
2015年 | 241篇 |
2014年 | 277篇 |
2013年 | 398篇 |
2012年 | 245篇 |
2011年 | 307篇 |
2010年 | 235篇 |
2009年 | 279篇 |
2008年 | 257篇 |
2007年 | 268篇 |
2006年 | 228篇 |
2005年 | 206篇 |
2004年 | 165篇 |
2003年 | 153篇 |
2002年 | 203篇 |
2001年 | 59篇 |
2000年 | 65篇 |
1999年 | 65篇 |
1998年 | 56篇 |
1997年 | 44篇 |
1996年 | 43篇 |
1995年 | 28篇 |
1994年 | 31篇 |
1993年 | 23篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有5367条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
95.
96.
97.
《Analytical letters》2012,45(3):455-463
ABSTRACT A spectrophotometric method for determination of silica in herbs and herbal pharmaceutical products has been developed and validated. The method showed excellent accuracy and precision with S.D. 1.67 and RSD 1.72%, 2.75%, respectively. The established linearity range was 0.05–0.5 μg/mL(r2 > 0.99974). The recovery of silica from spiked placebo was > 95% over the linear range. The method has been successfully used in the analysis of silica in raw material and herbal pharmaceutical formulations. This validated method proved to be rapid and less costly. 相似文献
98.
Catalytic Enantioselective CH Functionalization of Alcohols by Redox‐Triggered Carbonyl Addition: Borrowing Hydrogen,Returning Carbon 下载免费PDF全文
John M. Ketcham Inji Shin T. Patrick Montgomery Prof. Michael J. Krische 《Angewandte Chemie (International ed. in English)》2014,53(35):9142-9150
The use of alcohols and unsaturated reactants for the redox‐triggered generation of nucleophile–electrophile pairs represents a broad, new approach to carbonyl addition chemistry. Discrete redox manipulations that are often required for the generation of carbonyl electrophiles and premetalated carbon‐centered nucleophiles are thus avoided. Based on this concept, a broad, new family of enantioselective C? C coupling reactions that are catalyzed by iridium or ruthenium complexes have been developed, which are summarized in this Minireview. 相似文献
99.
Emmanuel Richaud Octavie Okamba Diogo Bruno Fayolle Jacques Verdu Jean Guilment François Fernagut 《Polymer Degradation and Stability》2013
The literature on oxidation kinetics of polyamides and model compounds has been reviewed in order to try to extract suitable information for non-empirical kinetic modeling. Polyamide characteristics are systematically compared to polyolefin ones, these latter being more extensively studied. From kinetic analysis point of view, it is shown that oxidation attacks predominantly α amino methylenes of which C–H bond is considerably weaker than the other methylenes. As a result, propagation by H abstraction is considerably faster in polyamides than in polyethylene for instance. Termination by radical combination is also very fast. Another cause of PA oxidizability is the instability of α amino hydroperoxides linked to the inductive effect of nitrogen. This instability is responsible for many key features of oxidation kinetics especially the absence of induction period. 相似文献
100.
Dr. Azusa Kondoh Dipl.‐Chem. Alexander Arlt Barbara Gabor Prof. Alois Fürstner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(24):7731-7738
The lichen‐derived glycoconjugate gobienine A is structurally more complex than most glycolipids isolated from higher plants by virtue of the all‐cis substituted γ‐lactone substructure embedded into its macrocyclic frame. A concise entry into this very epimerization‐prone and hence challenging structural motif is presented, which relies on an enantioselective cyanohydrin formation, an intramolecular Blaise reaction, a palladium‐catalyzed alkoxycarbonylation, and a diastereoselective hydrogenation of the tetrasubstituted alkene in the resulting butenolide. This strategy, in combination with ring‐closing olefin metathesis for the formation of the macrocyclic perimeter, allowed the proposed structure of gobienine A ( 1 ) to be formed in high overall yield. The recorded spectral data show that the structure originally attributed to gobienine A is incorrect and that it is not the epimerization‐prone ester site on the butanolide ring that is the locus of misassignment; rather, the discrepancy must be more profound. 相似文献