全文获取类型
收费全文 | 1032篇 |
免费 | 90篇 |
国内免费 | 225篇 |
专业分类
化学 | 645篇 |
晶体学 | 4篇 |
力学 | 2篇 |
综合类 | 1篇 |
数学 | 404篇 |
物理学 | 291篇 |
出版年
2023年 | 55篇 |
2022年 | 48篇 |
2021年 | 63篇 |
2020年 | 54篇 |
2019年 | 38篇 |
2018年 | 32篇 |
2017年 | 40篇 |
2016年 | 33篇 |
2015年 | 41篇 |
2014年 | 55篇 |
2013年 | 63篇 |
2012年 | 85篇 |
2011年 | 78篇 |
2010年 | 81篇 |
2009年 | 88篇 |
2008年 | 67篇 |
2007年 | 100篇 |
2006年 | 87篇 |
2005年 | 49篇 |
2004年 | 20篇 |
2003年 | 25篇 |
2002年 | 22篇 |
2001年 | 33篇 |
2000年 | 25篇 |
1999年 | 15篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有1347条查询结果,搜索用时 234 毫秒
31.
《中国化学快报》2021,32(9):2914-2918
The silicon-based materials are promising candidates for lithium-ion batteries owing to their high energy density. However, achieving long lifespan under realistic conditions remains a challenge because of the volume expansion and low conductivity. In this work, the highly elastic cobweb-like composite materials consisted by SiO and nanofibers are designed and fabricated for high-efficient lithium storage by ball-milling & electrostatic spinning method. The reconstructed heterostructure and highly elastic nanofibers can simultaneously increase the conductivity and inhibit the “expansion effect” of silicon-based materials. The constructed electrode of n-SiO/CNF delivers an initial capacity of 1700 mAh/g, and maintains the capacities over 1000 mAh/g after 100 cycles at the current density of 500 mA/g. Meanwhile, this electrode can give an initial coulombic efficiency over 85% and maintains at 98% in the following charge/discharge processes. Furthermore, it exhibits efficient long-term electrochemical performance, maintaining the capacity at about 1000 mAh/g at a high current density of 1000 mA/g after 1000 cycles. This work could provide a promising strategy for enhancing the performance of silicon-based composite materials for practical application in lithium-ion batteries. 相似文献
32.
33.
34.
35.
聂昌雄 《数学年刊A辑(中文版)》2015,36(1):31-36
通过对第二共形基本形式的模长平方作拼挤,给出Clifford超柱面的一个共形特征. 相似文献
36.
We study the probability for a random line to intersect a given plane curve, over a finite field, in a given number of points over the same field. In particular, we focus on the limits of these probabilities under successive finite field extensions. Supposing absolute irreducibility for the curve, we show how a variant of the Chebotarev density theorem for function fields can be used to prove the existence of these limits, and to compute them under a mildly stronger condition, known as simple tangency. Partial results have already appeared in the literature, and we propose this work as an introduction to the use of the Chebotarev theorem in the context of incidence geometry. Finally, Veronese maps allow us to compute similar probabilities of intersection between a given curve and random curves of given degree. 相似文献
37.
A new camphor-based 2-phenylimino-2-oxazolidine chiral auxiliary was prepared and it was shown to be a particularly effective chiral auxiliary for asymmetric alkylations affording high yields and diastereoselectivities. The alkylation products were readily cleaved by simple alkaline hydrolysis to give a-alkylated carboxylic acids in good yield and in almost enatiomerically pure form. 相似文献
38.
The modification of prepared MCM-41 by different groups (amino, chloro and oxo) was studied. Prepared materials were treated by acetylsalicylic acid and hybrid materials were characterized, compared from the point of view of immobilized amount of active substance. The highest amount of acetylsalicylic acid was detected using methyl-tert- butyl ether as a solvent and MCM-41 without modification after 1 h (0.35 g per 1 g of the support) or MCM modified by amino group after 5 h (0.37 g per 1 g of the support) as a support. Using amino modified MCM, the longer treatment by acetylsalicylic acid converged to the equilibrium and after 24 h the immobilized amount was 0.3 g per 1 g. A dissolution in vitro study was carried out, comparing the stability of formed interactions. The slowest dissolution was detected using non-modified MCM-41 and oxo modified material. 相似文献
39.
40.
A magnetic cotton/polyester fabric with photocatalytic, sonocatalytic, antibacterial and antifungal activities was successfully prepared through in-situ sonosynthesis method under ultrasound irradiation. The process involved the oxidation of Fe2+ to Fe3+ via hydroxyl radicals generated through bubbles collapse in ultrasonic bath. The treated samples were analyzed by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and vibrating sample magnetometry. Photocatalytic and sonocatalytic activities of magnetite treated fabrics were also evaluated toward Reactive Blue 2 decoloration under sunlight and ultrasound irradiation. Central composite design based on response surface methodology was applied to study the influence of iron precursor, pH and surfactant concentration to obtain appropriate amount for the best magnetism. Findings suggested the potential of one-pot sonochemical method to synthesize and fabricate Fe3O4 nanoparticles on cotton/polyester fabric possessing appropriate saturation magnetization, 95% antibacterial efficiency against Staphylococcus aureus and 99% antifungal effect against Candida albicans, 87% and 70% dye photocatalytic and sonocatalytic decoloration along with enhanced mechanical properties using only one iron rich precursor at low temperature. 相似文献