全文获取类型
收费全文 | 20658篇 |
免费 | 3628篇 |
国内免费 | 2990篇 |
学科分类
数理化 | 27276篇 |
出版年
2024年 | 47篇 |
2023年 | 405篇 |
2022年 | 578篇 |
2021年 | 742篇 |
2020年 | 889篇 |
2019年 | 969篇 |
2018年 | 747篇 |
2017年 | 698篇 |
2016年 | 1031篇 |
2015年 | 1084篇 |
2014年 | 1274篇 |
2013年 | 1596篇 |
2012年 | 1864篇 |
2011年 | 1951篇 |
2010年 | 1382篇 |
2009年 | 1366篇 |
2008年 | 1399篇 |
2007年 | 1174篇 |
2006年 | 1120篇 |
2005年 | 900篇 |
2004年 | 796篇 |
2003年 | 618篇 |
2002年 | 734篇 |
2001年 | 552篇 |
2000年 | 433篇 |
1999年 | 436篇 |
1998年 | 325篇 |
1997年 | 292篇 |
1996年 | 255篇 |
1995年 | 214篇 |
1994年 | 199篇 |
1993年 | 187篇 |
1992年 | 128篇 |
1991年 | 135篇 |
1990年 | 112篇 |
1989年 | 106篇 |
1988年 | 101篇 |
1987年 | 55篇 |
1986年 | 53篇 |
1985年 | 66篇 |
1984年 | 38篇 |
1983年 | 29篇 |
1982年 | 33篇 |
1981年 | 17篇 |
1979年 | 13篇 |
1978年 | 14篇 |
1977年 | 11篇 |
1976年 | 11篇 |
1975年 | 10篇 |
1974年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
Ching‐Yuan Cheng Kuan‐Jiuh Lin 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):m363-m365
In the title compound, catena‐poly[lithium‐μ3‐ethylenediphosphonato], [Li(C2H7O6P2)]n, the supramolecular monoclinic (C2/c) structure consists of one‐dimensional lithium chains [Li⋯Li = 2.7036 (8) Å] that are embedded within ethylenediphosphonate anions linked by strong symmetric hydrogen bonds [O⋯O = 2.473 (3) Å]. The Li atoms and the H atom in the symmetric hydrogen bond reside on twofold rotation axes and there is an inversion center at the mid‐point of the C—C bond of the ethylenediphosphonate ligand. 相似文献
65.
物理模型教学与创新能力的培养 总被引:1,自引:0,他引:1
现代教学以能力培养为重点.学生获得研究问题、探索问题的能力是十分重要的,物理模型的教学过程对培养学生研究问题、探索问题、发展创造思维、培养辩证唯物主义思想方法都极为有利,因此,必须重视物理模型教学. 相似文献
66.
Briand et al. (Electron. Comm. Probab. 5 (2000) 101–117) gave a counterexample and proposition to show that given g,g-expectations usually do not satisfy Jensen's inequality for most of convex functions. This yields a natural question, under which conditions on g, do g-expectations satisfy Jensen's inequality for convex functions? In this paper, we shall deal with this question in the case that g is convex and give a necessary and sufficient condition on g under which Jensen's inequality holds for convex functions. To cite this article: Z. Chen et al., C. R. Acad. Sci. Paris, Ser. I 337 (2003). 相似文献
67.
A 2D HgII coordination polymer containing ligands 1,2,4‐triazole (Htrz) and thiocyanate, [Hg(μ3‐trz)(SCN)]n ( 1 ) has been synthesized and characterized by elemental analysis and IR spectroscopy. The single‐crystal X‐ray data show the coordination number of Hg atoms is four and the ligand trz? acts as a three‐fold donor. The thermal stability of compound 1 was studied by thermal gravimetric and differential thermal analyses. The composition and formation of the complex in methanol solution were found to be in support of its solid state structure. 相似文献
68.
Mao‐Chuan Yuan Ping‐I Shih Chen‐Han Chien Ching‐Fong Shu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(14):2925-2937
We have synthesized a blue‐light‐emitting polyfluorene (PF) derivative ( PF‐CBZ‐OXD ) that presents bulky hole‐transporting carbazole and electron‐transporting oxadiazole pendent groups functionalized at the C‐9 positions of alternating fluorene units. The results from photoluminescence and electrochemical measurements indicate that both the side chains and the PF main chain retain their own electronic characteristics in the copolymer. An electroluminescent device incorporating this polymer as the emitting layer was turned on at 4.5 V; it exhibited a stable blue emission with a maximum external quantum efficiency of 1.1%. Moreover, we doped PF‐CBZ‐OXD and its analogue PF‐TPA‐OXD with a red‐light‐emitting iridium phosphor for use as components of phosphorescent red‐light emitters to investigate the effect of the host's HOMO energy level on the degree of charge trapping and on the electrophosphorescent efficiency. We found that spectral overlap and individual energy level matching between the host and guest were both crucial features affecting the performance of the electroluminescence devices. Atomic force microscopy measurements indicated that the dipolar nature of PF‐CBZ‐OXD , in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment that allowed homogeneous dispersion of the polar iridium triplet dopant. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2925–2937, 2007 相似文献
69.
黄龙 《新疆大学学报(理工版)》2003,20(2):130-132
用正电子湮没寿命谱技术研究了2.4×1O15/cm2、2.2×1016/cm2注量的85MeV19F离子辐照N型GaP和1.6×1016/cm 2注量的85MeV19F离子辐照P型InP所产生的辐照缺陷.结果表明:两种注量辐照在GaP中均产生较高浓度的单空位.其浓度随着辐照注量的增大而增加;辐照也在InP中产生较高浓度的单空位. 相似文献
70.