全文获取类型
收费全文 | 111138篇 |
免费 | 19410篇 |
国内免费 | 12025篇 |
专业分类
化学 | 76404篇 |
晶体学 | 1363篇 |
力学 | 7306篇 |
综合类 | 731篇 |
数学 | 13065篇 |
物理学 | 43704篇 |
出版年
2024年 | 114篇 |
2023年 | 2229篇 |
2022年 | 2441篇 |
2021年 | 3654篇 |
2020年 | 4583篇 |
2019年 | 4438篇 |
2018年 | 3783篇 |
2017年 | 3578篇 |
2016年 | 5495篇 |
2015年 | 5235篇 |
2014年 | 6426篇 |
2013年 | 8383篇 |
2012年 | 10174篇 |
2011年 | 10706篇 |
2010年 | 7220篇 |
2009年 | 6933篇 |
2008年 | 7361篇 |
2007年 | 6705篇 |
2006年 | 6161篇 |
2005年 | 5135篇 |
2004年 | 3834篇 |
2003年 | 3008篇 |
2002年 | 2729篇 |
2001年 | 2176篇 |
2000年 | 1853篇 |
1999年 | 2124篇 |
1998年 | 1927篇 |
1997年 | 1751篇 |
1996年 | 1885篇 |
1995年 | 1552篇 |
1994年 | 1504篇 |
1993年 | 1202篇 |
1992年 | 1101篇 |
1991年 | 1016篇 |
1990年 | 820篇 |
1989年 | 589篇 |
1988年 | 474篇 |
1987年 | 389篇 |
1986年 | 384篇 |
1985年 | 330篇 |
1984年 | 243篇 |
1983年 | 157篇 |
1982年 | 141篇 |
1981年 | 108篇 |
1980年 | 77篇 |
1979年 | 46篇 |
1978年 | 34篇 |
1976年 | 37篇 |
1975年 | 35篇 |
1974年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
73.
The first-principles DFT calculations together with microkinetic analysis reveal the complex catalytic mechanism of low-content NO oxidation on CrO2(110) at room temperature. It quantitatively makes clear that CrO2(110) can exhibit considerable activity with the Mars-van-Krevelen mechanism preferred, and the nitrate species serves as the key poisoning species. 相似文献
74.
Ding Wenwen He Yongjia Lu Linnu Rao Meijuan Wang Fazhou 《Journal of Thermal Analysis and Calorimetry》2019,135(4):2009-2018
Journal of Thermal Analysis and Calorimetry - The present task is to investigate the influence of iron on the mineral composition and microstructure of the phase Q (C20A13M3S3, in the text below... 相似文献
75.
Journal of Thermal Analysis and Calorimetry - The fire behavior of one flame-retardant PVC cable used as building wire is investigated in this work. Bench scale tests were performed using a cone... 相似文献
76.
77.
Monoester‐diterpenoid alkaloids are the main bioactive components of Sini decoction, which is a well‐known traditional Chinese medicine formula for the treatment of myocardial infarction (MI) and heart failure in China. In this work, an ultra‐high‐performance liquid chromatography–mass spectrometry combined with microdialysis method was successfully established and applied for investigating for the first time comparative plasma pharmacokinetics of three monoester‐diterpenoid alkaloids (benzoylmesaconitine, benzoylaconitine and benzoylhypacoitine) in normal and MI rats after oral administration of Sini decoction. The statistical results of pharmacokinetic parameters demonstrated that benzoylmesaconitine, benzoylaconitine and benzoylhypacoitine showed lower peak concentration, longer half‐life, smaller area under the concentration–time curve, slower clearance, time to peak concentration and mean residence time in MI rats than in normal rats (p < 0.05), which indicated that monoester‐diterpenoid alkaloids exhibited lower systemic exposure and slower elimination in the MI rats. The results provided the experimental basis for understanding the metabolic fate and therapeutic effects of Sini decoction. 相似文献
78.
Fanfan Du Ying Zheng Wenhua Yuan Guorong Shan Yongzhong Bao Suyun Jie Pengju Pan 《Journal of polymer science. Part A, Polymer chemistry》2019,57(2):90-100
Development of effective organocatalysts for the living ring‐opening polymerization (ROP) of lactones is highly desired for the preparation of biocompatible and biodegradable polyesters with controlled microstructures and physical properties. Herein, a new class of hydrogen‐bond donating bisurea catalysts is reported for the ROP of lactones under solvent‐free conditions. ROP of lactones mediated by the bisurea/7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (MTBD) catalyst exhibits a living/controlled manner, affording the polymers and copolymers with the well‐defined structure, predictable molecular weight, narrow molecular weight distribution, and high selectivity for monomer at low catalyst loadings at ambient temperature. The possible mechanism of bisurea/MTBD‐catalyzed ROP of lactones is proposed, in which the bisurea activates the carbonyl group of lactones while MTBD facilitates the nucleophilic attack of the initiating/propagating alcohol by hydrogen bonding. Moreover, the poly(ε‐caprolactone‐co‐δ‐valerolactone) [P(CL‐co‐VL)] random copolymers with various compositions were synthesized using the bisurea/MTBD catalyst. The measurements of thermal properties and crystalline structure demonstrate that the CL and VL units are cocrystallized in the crystalline phase of P(CL‐co‐VL) copolymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 90–100 相似文献
79.
Acta Mathematicae Applicatae Sinica, English Series - This paper summarizes the parameter estimation of systems with set-valued signals, which can be classified to three catalogs: one-time... 相似文献
80.
Acta Mathematicae Applicatae Sinica, English Series - For the variational inequality with symmetric cone constraints problem, we consider using the inexact modified Newton method to efficiently... 相似文献