全文获取类型
收费全文 | 9218篇 |
免费 | 925篇 |
国内免费 | 1036篇 |
专业分类
化学 | 4614篇 |
晶体学 | 54篇 |
力学 | 306篇 |
综合类 | 79篇 |
数学 | 2162篇 |
物理学 | 1360篇 |
综合类 | 2604篇 |
出版年
2024年 | 15篇 |
2023年 | 66篇 |
2022年 | 107篇 |
2021年 | 150篇 |
2020年 | 247篇 |
2019年 | 217篇 |
2018年 | 226篇 |
2017年 | 287篇 |
2016年 | 279篇 |
2015年 | 310篇 |
2014年 | 443篇 |
2013年 | 1146篇 |
2012年 | 438篇 |
2011年 | 466篇 |
2010年 | 431篇 |
2009年 | 493篇 |
2008年 | 511篇 |
2007年 | 528篇 |
2006年 | 532篇 |
2005年 | 445篇 |
2004年 | 411篇 |
2003年 | 365篇 |
2002年 | 945篇 |
2001年 | 276篇 |
2000年 | 291篇 |
1999年 | 208篇 |
1998年 | 216篇 |
1997年 | 164篇 |
1996年 | 158篇 |
1995年 | 142篇 |
1994年 | 131篇 |
1993年 | 106篇 |
1992年 | 79篇 |
1991年 | 78篇 |
1990年 | 76篇 |
1989年 | 62篇 |
1988年 | 41篇 |
1987年 | 24篇 |
1986年 | 19篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1968年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Jamie M. Messman Robson F. Storey 《Journal of polymer science. Part A, Polymer chemistry》2006,44(23):6817-6835
Ethylene glycol (EG) initiated, hydroxyl‐telechelic poly(L ‐lactide) (PLLA) was employed as a macroinitiator in the presence of a stannous octoate catalyst in the ring‐opening polymerization of 5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one (MBC) with the goal of creating A–B–A‐type block copolymers having polycarbonate outer blocks and a polyester center block. Because of transesterification reactions involving the PLLA block, multiblock copolymers of the A–(B–A)n–B–A type were actually obtained, where A is poly(5‐methyl‐5‐benzyloxycarbonyl‐1,3‐dioxan‐2‐one), B is PLLA, and n is greater than 0. 1H and 13C NMR spectroscopy of the product copolymers yielded evidence of the multiblock structure and provided the lactide sequence length. For a PLLA macroinitiator with a number‐average molecular weight of 2500 g/mol, the product block copolymer had an n value of 0.8 and an average lactide sequence length (consecutive C6H8O4 units uninterrupted by either an EG or MBC unit) of 6.1. For a PLLA macroinitiator with a number‐average molecular weight of 14,400 g/mol, n was 18, and the average lactide sequence length was 5.0. Additional evidence of the block copolymer architecture was revealed through the retention of PLLA crystallinity as measured by differential scanning calorimetry and wide‐angle X‐ray diffraction. Multiblock copolymers with PLLA crystallinity could be achieved only with isolated PLLA macroinitiators; sequential addition of MBC to high‐conversion L ‐lactide polymerizations resulted in excessive randomization, presumably because of residual L ‐lactide monomer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6817–6835, 2006 相似文献
92.
Makoto Kume Yuya Maki Bungo Ochiai Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》2006,44(24):7040-7053
Spiro orthocarbonate (SOC) monomers having either an exomethylene group {3,3‐dimethyl‐9‐methylene‐1,5,7,11‐tetraoxaspiro[5.5]undecane (ExoSOC)} or an allyl group {9‐allyl‐3,3‐dimethyl‐1,5,7,11‐tetraoxaspiro[5.5]undecane (AllylSOC)} were radically copolymerized with vinyl monomers at several feed ratios to obtain the corresponding copolymers having SOC moieties in the side chain. The obtained copolymers were crosslinked via the double ring‐opening polymerization of the SOC moieties by a treatment with boron trifluoride etherate. The volume changes during the crosslinking of the copolymers were evaluated by density measurements with a gas pycnometer. As the SOC moiety composition increased, the volume shrinkage during the crosslinking was suppressed, and that finally changed into volume expansion. The volume changes during the crosslinking of the copolymers from AllylSOC were slightly larger than those of the copolymers from ExoSOC. The higher volume expansions in the crosslinking of AllylSOC‐based copolymers were ascribable to the lower steric hindrance around the SOC moieties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 7040–7053, 2006 相似文献
93.
Lourdes Callau Marta Giamberini Jos Antonio Reina Ana Mantecn 《Journal of polymer science. Part A, Polymer chemistry》2006,44(6):1877-1889
The synthesis of two vinyl‐terminated side‐chain liquid‐crystalline polyethers containing benzylideneaniline moieties as mesogenic cores was approached in two different ways: by chemically modifying poly(epichlorohydrin) with suitable mesogenic acids or by polymerizing analogous glycidyl ester or glycidyl ether derivatives. In all the conditions tested, the first approach led to materials in which the imine group was hydrolyzed. The second approach led to the desired polymers PG2a and PG2b , but only from the glycidyl ether derivatives and when the initiator was the system that combined polyiminophosphazene base t‐Bu‐P4 and 3,5‐di‐t‐butylphenol. These polymers were chemically characterized by IR and 1H and 13C NMR spectroscopies. The estimated degrees of polymerization ranged from 30 to 36. The liquid crystalline behavior of the synthesized polymers was studied by differential scanning calorimetry, polarized optical microscopy (POM) and X‐ray diffraction. Both polymers behave like liquid crystals and exhibited a single mesophase, which was recognized as a smectic C mesophase, probably with a bilayer arrangement, i.e., a smectic C2 mesophase. The crosslinking of both polymers was performed with dicumyl peroxide as initiator, which led to liquid crystalline thermosets. POM and X‐ray diffraction confirmed that the mesophase organization mantained on the crosslinked materials. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1877–1889, 2006 相似文献
94.
一、引言 磁镜运行中,为了要知道它在电子回旋共振加热(ECRH)下形成热电子的参数,我们测量了硬X射线能谱、硬X射线发射的时间特性、不同磁场强度下形成热电子环的位置、以及热电子的脉冲幅度分布等。 HER是中国科学院等离子体物理研究所简单型磁镜装置,它的几何尺寸是,真空室长 相似文献
96.
陈平 《浙江海洋学院学报(自然科学版)》2005,24(2):168-170
以红岩6-250ZCD柴油机故障为例,发现并分析了柴油机排气呈白色的特殊原因,有利于今后故障的快速确诊. 相似文献
97.
L-fuzzyRingandL-fuzzyModuleL-fuzzyRingandL-fuzzyModule¥SunRongguangJiangBaoqing(HumanUniversity,Kaifeng,475001)RenXuejun(Minq... 相似文献
98.
通过“新甜二号”块根三生构造的形成及发育过程观察看出:甜菜块根三生构造的形成始于一对真叶期,从二对真叶到块根糖分增长期前期是块根三生维管束环的主要形成时期。块根内对三生维管束环上的三生维管束束数随块根三生维管束环数的增加而增加,二者之间里显著的直线相关。而且块根内的三生维管束环数及环上的束数都具有极限性。块根最外2—3环上的三生维管束束数虽多,但成熟的较少。块根内各环间距随三生维管束环数的增加而呈动态变化,环间距增长最快在叶丛繁茂中期到块根糖分增长期中后期。生育后期,根内以第三环间距最大,而且根内各环间距的大小与环数之间呈Y=ae~(bx)·x的函数关系。 相似文献
99.
The results of variational solutions of the repeated ring and self-consistent repeated ring equations for the two-and three-dimensional overlapping Lorentz gas (LG), as formulated in a previous report, are presented. Calculations of the full velocity correlation function (VCF) for the 2D LG, including long-time tails, are compared with those from molecular dynamics. The trial functions chosen lead to predictions for the long-time tails that improve as the density of the scatterers is increased. At a value of 0.24 for* (=
2, where is the density and the radius of scatterers), the self-consistent amplitudes of the long-time tail are within 40% of the molecular dynamics. A limited number of 3D results for the short-time behavior of the repeated ring VCF are presented. The 3D solutions agree with the molecular dynamics to within 10%. 相似文献
100.
本文综述了中环萜类化合物的各种合成方法,它们根据成环方式可以分为四类:1.双环或三环化合物的桥键断裂,2.无环化合物的环合,3.常规环化合物的环扩大,4.大环化合物的环缩小。 相似文献