全文获取类型
收费全文 | 584篇 |
免费 | 78篇 |
国内免费 | 113篇 |
专业分类
化学 | 573篇 |
晶体学 | 1篇 |
力学 | 18篇 |
综合类 | 10篇 |
数学 | 55篇 |
物理学 | 118篇 |
出版年
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 8篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 8篇 |
2014年 | 39篇 |
2013年 | 54篇 |
2012年 | 52篇 |
2011年 | 12篇 |
2010年 | 14篇 |
2009年 | 10篇 |
2008年 | 27篇 |
2007年 | 24篇 |
2006年 | 34篇 |
2005年 | 32篇 |
2004年 | 31篇 |
2003年 | 40篇 |
2002年 | 87篇 |
2001年 | 195篇 |
2000年 | 31篇 |
1999年 | 21篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1986年 | 2篇 |
排序方式: 共有775条查询结果,搜索用时 15 毫秒
1.
~~Formation of α,α'-Bis(substituted benzylidene)cycloalkanones from Masked Aldehydes Promoted by Samarium(III) Triiodide~~ 相似文献
2.
有界连通区域上Dirichlet空间及其算子 总被引:1,自引:0,他引:1
本文主要讨论了有界连通区域Dirichlet空间上Toeplitz算子的Fredholm性质,计算了符号在C1中的Toeplitz算子的本性谱和Fredholm指标. 相似文献
3.
针对高功率二极管重复率抽运的V型非稳腔Yb3+∶YAG激光头,提出了利用金刚石窗口冷却和直接水冷相结合的复合冷却设计.在YAG片的抽运面进行直接水冷,同时在激光提取面利用金刚石窗口冷却介质.金刚石优异的导热性能不仅能够有效地冷却激光介质,还能消除横向的温度梯度,解决了高功率激光器冷却和高功率抽运的矛盾.模拟结果表明对掺杂10 at %厚度为1.6 mm的Yb3+∶YAG片在抽运功率密度为20 kW/cm2,重复频率为10 Hz的条件下,要将最高温度控制在可接受的范围内(比如320 K),周围冷却水的对流换热系数约为4000 W/m2K. 相似文献
4.
王晓峰 《数学年刊B辑(英文版)》1989,(3)
In this paper, the author classifies the finite inner π′-closed groups, and proves the following results1. If each proper subgroup K of a group G is weak π-homogeneous and weak π′-homogeneous, then G is a Schmidt group, or a direct product of two Hall subgroups.2. If G is a weak π-homogeneous group, then G is π′-closed if one of the following statements is true: (1)Each π-subgroup of G is 2-closed. (2) Each π-subgroup of G is 2′-closed.3. Let G be a group and π be a set of odd primes. If N_G(Z(J(P))) has a normal π-completement for a Sytow p-subgroup of G with prime ρ in π then so does G. 相似文献
5.
Jing Lin CHEN Gang Qiang YIN Zhong Ning CHEN* State Key Laboratory of Structural Chemistry Fujian Institute of Research on the Structure of Matter Fuzhou 《中国化学快报》2003,(5)
Great attention is currently paid to the synthesis of polynuclear transition metal complexes as well as their photochemical, photophysical, and electrochemical properties. The design of multicomponent systems capable of performing useful light- and/or redox-induced function is of special interest1. The oxo-centered carboxylate-bridge trinuclear ruthenium clusters have been investigated extensively during recent decades because they have remarkable electron-transfer properties, intense visibl… 相似文献
6.
Jing Ping WANG Qiang WU Jing Yang NIU* School of Chemistry Chemical Engineering Henan University Kaifeng 《中国化学快报》2002,13(9):915-918
It is becoming a focus to synthesize and assemble organic-inorganic materials, especially, to synthesize charge-transfer complexes formed by polyoxometalate and organic donors. They have attracted much attention because such complexes are active in their electric, magnetic and optic properties1-4, many investigations about them have been done and some crystal structures of them were reported5-6. But, the disadvantage of these crystals is instability at room temperature. According to the view… 相似文献
7.
Structural Features of a Polysaccharide from Centella asiatica 总被引:3,自引:0,他引:3
Xue Song WANG Jin You DUAN Ji Nian FANG* Shanghai Institute of Materia Medica Shanghai Institutes for Biological Sciences Chinese Academy of Sciences Shanghai 《中国化学快报》2004,15(2):187-190
Centella asiatica has been used as remedy for sodation, stabilization and against lepra, anabrosis1 in the oriental countries. The low-molecular-weight constituents in Centella asiatica have been investigated1. However, no polysaccharides have been reported. 1BI was the first polysaccharide isolated from C. asiatica, which had immunostimulating activity in vitro. In present study, we report the structural features of 1BI. Experimental Extraction, isolation and purification Dried C.… 相似文献
8.
Thermal decomposition kinetics of titanium hydride and Al alloy melt foaming process 总被引:3,自引:0,他引:3
YANG Donghui* HE Deping*& YANG Shangrun* . Department of Materials Science Engineering Southeast University Nanjing China . Department of Chemistry Nanjing University Nanjing China 《中国科学B辑(英文版)》2004,47(6):512-520
Metal foams, now one of research foci, are a newclass of materials with low densities and novel physi-cal, mechanical, thermal, electrical and acoustic prop-erties[1—8]. Demands from high-tech make Al alloyfoam, which has much higher specific strength than ofpure Al foam, the new development focus[9—11]. Melt foaming process is one of the approaches tofabricate Al foam and Al alloy foam and their porestructure (pore diameter and porosity) has close rela-tionship with the thermal decompo… 相似文献
9.
XU Long Ya * WANG Qing Xia LIN Li Wu XU Yi De Dalian Institute of Chemical Physics The Chinese Academy of Sciences Dalian Liaoning 《天然气化学杂志》1998,7(1):7-15
Ni/Si2催化剂具有较好的低碳烷烃与二氧化碳重整制合成气的反应性能,添加La2O3助剂和K2O助剂可提高催化剂活性和合成气收率,从而进一步改善催化剂的低碳烷烃与CO2重整制合成气的反应性能,研制的KLaNi/Si2催化剂,用于天然气与CO2重整反应制合成气可达97%的低碳烷烃转化率和95%以上的合成气收率。 相似文献
10.