全文获取类型
收费全文 | 713篇 |
免费 | 144篇 |
国内免费 | 298篇 |
专业分类
化学 | 497篇 |
晶体学 | 27篇 |
力学 | 53篇 |
综合类 | 19篇 |
数学 | 153篇 |
物理学 | 406篇 |
出版年
2024年 | 1篇 |
2023年 | 8篇 |
2022年 | 26篇 |
2021年 | 17篇 |
2020年 | 28篇 |
2019年 | 31篇 |
2018年 | 37篇 |
2017年 | 47篇 |
2016年 | 31篇 |
2015年 | 34篇 |
2014年 | 52篇 |
2013年 | 49篇 |
2012年 | 64篇 |
2011年 | 74篇 |
2010年 | 76篇 |
2009年 | 65篇 |
2008年 | 76篇 |
2007年 | 60篇 |
2006年 | 72篇 |
2005年 | 53篇 |
2004年 | 39篇 |
2003年 | 19篇 |
2002年 | 29篇 |
2001年 | 44篇 |
2000年 | 20篇 |
1999年 | 26篇 |
1998年 | 14篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 9篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1990年 | 9篇 |
1989年 | 2篇 |
1988年 | 7篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1155条查询结果,搜索用时 31 毫秒
1.
In this paper, we introduce and study differential graded(DG for short) polynomial algebras. In brief, a DG polynomial algebra A is a connected cochain DG algebra such that its underlying graded algebra A~# is a polynomial algebra K[x_1, x_2,..., x_n] with |xi| = 1 for any i ∈ {1, 2,..., n}. We describe all possible differential structures on DG polynomial algebras, compute their DG automorphism groups, study their isomorphism problems, and show that they are all homologically smooth and Gorenstein DG algebras. Furthermore, it is proved that the DG polynomial algebra A is a Calabi-Yau DG algebra when its differential ?_A≠ 0 and the trivial DG polynomial algebra(A, 0) is Calabi-Yau if and only if n is an odd integer. 相似文献
2.
3.
利用静电纺丝技术制备了聚乙烯醇(PVA)/银纳米粒子高活性SERS柔性基底.将硝酸银、聚乙烯醇按照一定比例混合配置纺丝溶液,纺丝成膜后采用紫外光照射还原法得到纳米纤维基底.采用扫描电子显微镜(SEM),透射电子显微镜(TEM),傅立叶红外光谱(FT-IR),拉曼光谱(Raman),紫外可见光谱(UV-Vis)等技术,对合成的纳米纤维基底进行表征.研究表明,银纳米颗粒呈球形分布在复合纤维中,粒径小于10 nm.以罗丹明为探针分子,硝酸银含量16 wt;,紫外光照射3 h制备的基底具备最优的SERS性能.同时将此基底应用于烟酸药品检测,拉曼检测极限可达10-5 mol·L-1. 相似文献
4.
Yuan‐Yuan Che Yanni Yue Ling‐Zhi Lin Bingbing Pei Xuezu Deng Chao Feng 《Angewandte Chemie (International ed. in English)》2020,59(38):16414-16419
Herein, we report a highly efficient and practical method for pyridine‐derived heterobiaryl synthesis through palladium‐catalyzed electrophilic functionalization of easily available pyridine‐derived quaternary phosphonium salts. The nice generality of this reaction was goes beyond arylation, enabling facile incorporation of diverse carbon‐based fragments, including alkenyl, alkynyl, and also allyl fragments, onto the pyridine core. Notably, the silver salt additive is revealed to be of vital importance for the success of this transformation and its pivotal role as transmetallation mediator, which guarantees a smooth transfer of pyridyl group to palladium intermediate, is also described. 相似文献
5.
Yuan-Yuan Che Yanni Yue Ling-Zhi Lin Bingbing Pei Xuezu Deng Prof. Dr. Chao Feng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(38):16556-16561
Herein, we report a highly efficient and practical method for pyridine-derived heterobiaryl synthesis through palladium-catalyzed electrophilic functionalization of easily available pyridine-derived quaternary phosphonium salts. The nice generality of this reaction was goes beyond arylation, enabling facile incorporation of diverse carbon-based fragments, including alkenyl, alkynyl, and also allyl fragments, onto the pyridine core. Notably, the silver salt additive is revealed to be of vital importance for the success of this transformation and its pivotal role as transmetallation mediator, which guarantees a smooth transfer of pyridyl group to palladium intermediate, is also described. 相似文献
6.
用固相反应合成法合成了光催化剂Fe2BiTaO7,通过XRD、SEM、TEM、紫外-可见漫反射等表征方法对其组织结构及光催化性能进行了研究。结果表明Fe2BiTaO7为立方晶系烧绿石结构,空间群为Fd3m,禁带宽度为1.72 e V。通过比较Fe2BiTaO7、P25TiO2、掺氮Ti O2和Bi2In Ta O7的可见光光催化降解罗丹明B,发现Fe2BiTaO7降解效果及催化活性均高于其它催化剂,并且Fe2BiTaO7降解罗丹明B效率是掺氮二氧化钛的1.5倍。Fe2BiTaO7降解罗丹明B的曲线符合一级动力学,一级动力学常数为0.022 93 min-1。研究了罗丹明B可能的降解路径和Fe2BiTaO7在可见光下降解苯酚的效果。Fe2BiTaO7(可见光)光催化剂系统适用于纺织工业废水处理。 相似文献
7.
Jia Fu Qianqian Jia Peida Liang Saisai Wang Huaxin Zhou Liyang Zhang Hong Wang Chunlei Gao Yanni Lv Shengli Han Langchong He 《Journal of separation science》2022,45(14):2498-2507
Cell membrane chromatography is an effective method for screening bioactive components acting on specific receptors in complex systems, which maintains the biological activity of the membrane receptors and improves screening efficiency. However, traditional cell membrane chromatography suffers from poor stability, resulting in a limited life span and low reproducibility, greatly limiting the application of this method. To address this problem, cyanuric chloride-decorated silica gel was used for the covalent immobilization of the cell membranes. Cyanuric chloride reacts with amino groups on the cell membranes and membrane receptors to form covalent bonds. In this way, the cell membranes are not easy to fall off. The column life of the cyanuric chloride-decorated epidermal growth factor receptor/cell membrane chromatography column was extended to more than 8 days, whereas the column life of the normal cell membrane chromatography column dropped sharply in the first 3 days. A cyanuric chloride-decorated epidermal growth factor receptor/cell membrane chromatography online HPLC-IT-TOF-MSn system was applied for screening drug leads from Trifolium pratense L. One potential drug lead, formononetin, which acts on the epidermal growth factor receptor, was screened. Our strategy of covalently immobilizing cell membrane receptors also improved the stability of cell membrane chromatography. 相似文献
8.
9.
微波水解衍生高效液相色谱法测定饲料中的氨基酸 总被引:1,自引:0,他引:1
建立了一种微波水解衍生高效液相色谱同时测定饲料中17种氨基酸含量的方法。采用2,4-二硝基氯苯作为柱前衍生试剂,利用C_(18)色谱柱分离。二极管阵列检测器进行检测,检测波长为360 nm,并对微波水解时间及温度进行优化。17种氨基酸在2.5~50 mg/L范围内呈良好线性关系,相关系数为0.990 7~0.999 9;相对标准偏差为0.88%~4.2%;加标回收率为90.6%~107.2%;检出限为0.15~2.37 mg/L。研究结果表明,150℃下微波水解16 min的结果与传统加热水解(110℃,24 h)的效果基本相同。该方法分析时间较短,灵敏度较高,可用于饲料中氨基酸含量的检测。 相似文献
10.
通过改进Brezis和Merle的方法,结合Moser-Trudinger不等式,移动平面方法及比较原理,得到了方程-Q_Nu=f(u),u∈W_0~(1,N)(Ω)的正解的先验界,其中Ω是R~N中的一个有界光滑区域,非线性项f至多具有指数型增长. 相似文献