全文获取类型
收费全文 | 30413篇 |
免费 | 4487篇 |
国内免费 | 16300篇 |
专业分类
化学 | 34773篇 |
晶体学 | 1105篇 |
力学 | 1087篇 |
综合类 | 859篇 |
数学 | 3815篇 |
物理学 | 9561篇 |
出版年
2024年 | 272篇 |
2023年 | 1031篇 |
2022年 | 1016篇 |
2021年 | 1217篇 |
2020年 | 1091篇 |
2019年 | 1402篇 |
2018年 | 922篇 |
2017年 | 1320篇 |
2016年 | 1462篇 |
2015年 | 1611篇 |
2014年 | 2261篇 |
2013年 | 2649篇 |
2012年 | 2636篇 |
2011年 | 2510篇 |
2010年 | 2374篇 |
2009年 | 2516篇 |
2008年 | 2954篇 |
2007年 | 2774篇 |
2006年 | 3017篇 |
2005年 | 2660篇 |
2004年 | 2806篇 |
2003年 | 2011篇 |
2002年 | 1210篇 |
2001年 | 1090篇 |
2000年 | 895篇 |
1999年 | 960篇 |
1998年 | 629篇 |
1997年 | 476篇 |
1996年 | 396篇 |
1995年 | 359篇 |
1994年 | 359篇 |
1993年 | 375篇 |
1992年 | 428篇 |
1991年 | 447篇 |
1990年 | 320篇 |
1989年 | 321篇 |
1988年 | 207篇 |
1987年 | 96篇 |
1986年 | 58篇 |
1985年 | 30篇 |
1984年 | 16篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
[Na(18-C-6)]2[Cu(i-mnt)2]的合成与结构分析 总被引:2,自引:2,他引:0
研究了18-冠-6与Na2[Cu(i-mnt)2][i-mnt=异丁二腈烯二硫醇阴离子,S2CC(CN)2-2]的反应,得到的配合物[Na(18-C-6)]2[Cu(i-mnt)2](1)通过元素分析、红外光谱、X射线单晶衍射进行了结构分析.配合物为单斜晶系,空间群P2(1)/c.晶体学结构数据a=1.2819(11),b=1.1793(10),c=1.4928(13)nm,β=99.121(16)°,V=2.228(3)nm3,Z=2,Dcaled.=1.369g/cm3,F(000)=958,R1=0.0521,wR2=0.1003.1中的[Cu(i-mnt)2]基团通过配体i-mnt的氮原子与两个[Na(18-C-6)]基团中的钠原子成键,形成稳定的中性配合物. 相似文献
53.
Hydrodynamic Properties of Fe3O4 Kerosene-Based Ferrofluids with Narrow Particle Size Distribution 下载免费PDF全文
We investigate the hydrodynamic properties of Fe3O4 kerosene-based ferrofluids with narrow particle size distribution. The ferrofluids are synthesized by improving chemical coprecipitation technique. A narrow distribution of 8.6-10.8nm particle sizes is obtained from the magnetization curve with the free-form model based on the Bayesian inference theory. The fitting result is consistent with average particle size obtained from x-ray diffraction. With the increase of applied magnetic field and magnetic particle concentration, apparent viscosity of ferrofluids increases. At concentration 4.04%, the type of flow for the ferrofluid transforms from Newtonian to Bingham plastic fluid as the applied magnetic field increases. 相似文献
54.
55.
56.
By using the quasi-Lyapunov function, some sufficient conditions of global exponential stability for impulsive systems are established, which is the basis for the following discussion. Then, by employing Riccati inequality and Hamilton-Jacobi inequality approach, some sufficient conditions of robust exponential stability for uncertain linear/nonlinear impulsive systems are derived, respectively. Finally, some examples are given to illustrate the applications of the theory. 相似文献
57.
The coordination polymer {[Co(phth)(phen)(H2O)]·(C2H5OH)}n (phth = phthalate, phen = 1,10-phenanthroline) with formula C22H20CoN2O6 (Mr = 467.33) was synthesized by the solvothermal method under low temperature, and its crystal structure was determined by singlecrystal X-ray diffraction. The complex belongs to monoclinic system, space group P21/n with a =12.7352(16), b = 8.8125(11), c = 18.677(2) (A), β = 102.633(2)°, V = 2045.3(4) (A)3, Z = 4, Dc =1.518 g/cm3,μ = 0.882 mm-1, F(000) = 964, S = 1.053, the final R = 0.0401 and wR = 0.0984 for 3135 observed reflections (I > 2σ(I)). Single-crystal X-ray analysis revealed that the Co(Ⅱ) ion is six-coordinated. The cobalt complex forms a one-dimensional chain structure via phthalate bridging ligand. In the cobalt complex, a 3D network structure is formed by π-π stacking interaction of 1,10-phenanthroline as well as intermolecular hydrogen bonding interactions. 相似文献
58.
What Is Its Real Existing Form?——Theoretical and Experimental Studies on 2-Mercaptobenzothiazole 总被引:1,自引:0,他引:1
1 INTRODUCTION The study of heterocyclic molecules with aroma- tic rings and their absorptions on metals is of con- siderable importance from both theoretical and te- chnological points of view. These molecules are in- teresting because of their applications as corrosion inhibitors and flotation collectors, and their abilities to form self-assembly layers[1]. 2-Mercaptobenzo- thiazole (C7H5NS2, in the following MBT) is an important heterocyclic molecule, which can be used as corrosion … 相似文献
59.