全文获取类型
收费全文 | 16643篇 |
免费 | 2209篇 |
国内免费 | 2015篇 |
专业分类
化学 | 12947篇 |
晶体学 | 128篇 |
力学 | 1328篇 |
综合类 | 88篇 |
数学 | 1128篇 |
物理学 | 5248篇 |
出版年
2024年 | 27篇 |
2023年 | 155篇 |
2022年 | 356篇 |
2021年 | 468篇 |
2020年 | 600篇 |
2019年 | 496篇 |
2018年 | 397篇 |
2017年 | 468篇 |
2016年 | 629篇 |
2015年 | 692篇 |
2014年 | 888篇 |
2013年 | 1327篇 |
2012年 | 1013篇 |
2011年 | 1258篇 |
2010年 | 1023篇 |
2009年 | 1121篇 |
2008年 | 1188篇 |
2007年 | 1155篇 |
2006年 | 1105篇 |
2005年 | 915篇 |
2004年 | 836篇 |
2003年 | 666篇 |
2002年 | 683篇 |
2001年 | 434篇 |
2000年 | 398篇 |
1999年 | 351篇 |
1998年 | 291篇 |
1997年 | 276篇 |
1996年 | 250篇 |
1995年 | 230篇 |
1994年 | 186篇 |
1993年 | 163篇 |
1992年 | 148篇 |
1991年 | 119篇 |
1990年 | 98篇 |
1989年 | 71篇 |
1988年 | 73篇 |
1987年 | 43篇 |
1986年 | 40篇 |
1985年 | 41篇 |
1984年 | 41篇 |
1983年 | 15篇 |
1982年 | 35篇 |
1981年 | 16篇 |
1980年 | 20篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 13篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Xiao‐Hui Liu Yan‐Guo Li Ying Lin Yue‐Sheng Li 《Journal of polymer science. Part A, Polymer chemistry》2007,45(7):1272-1281
The reversible addition–fragmentation chain transfer (RAFT) polymerization of acrylonitrile (AN) mediated by 2‐cyanoprop‐2‐yl dithiobenzoate was first applied to synthesize polyacrylonitrile (PAN) with a high molecular weight up to 32,800 and a polydispersity index as low as 1.29. The key to success was ascribed to the optimization of the experimental conditions to increase the fragmentation reaction efficiency of the intermediate radical. In accordance with the atom transfer radical polymerization of AN, ethylene carbonate was also a better solvent candidate for providing higher controlled/living RAFT polymerization behaviors than dimethylformamide and dimethyl sulfoxide. The various experimental parameters, including the temperature, the molar ratio of dithiobenzoate to the initiator, the molar ratio of the monomer to dithiobenzoate, the monomer concentration, and the addition of the comonomer, were varied to improve the control of the molecular weight and polydispersity index. The molecular weights of PANs were validated by gel permeation chromatography along with a universal calibration procedure and intrinsic viscosity measurements. 1H NMR analysis confirmed the high chain‐end functionality of the resultant polymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1272–1281, 2007 相似文献
102.
The reactions of 5-methyl-3-hydroxyisoxazole with 2, 2-dimethyl, 3-substituted cyclopropanecarboxylic chlorides give O-acyl-5-methyl-3-hydroxyisoxazole and N-acyl-5-methylisoxazolin-3-one derivatives. The ratio of O-acyl to N-acyl product depends upon the acylation reagents. O-acyl derivatives can be converted to the N-acyl compounds by isomerization under acidic conditions or heating. 相似文献
103.
《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(27):7007-7007
104.
We consider the problem of solving the integral form of the radiative transfer equation in an atmosphere with optical thickness τ0?1. We propose two methods transforming this problem to a finite set of the independent problems of the same type set in an atmosphere with optical thickness much less then τ0. The error estimates are derived. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
105.
Applied Biochemistry and Biotechnology - 相似文献
106.
107.
氨酪酸(am inobutyric acid),化学名称为γ-氨基丁酸。本品在体内与血氨结合生成尿毒排出体外,有降低血氨及促进大脑新陈代谢的作用,能够增强葡萄糖磷酸酯化酶的活性,利于脑细胞功能的恢复。主要用于脑卒中后遗症、脑动脉硬化症、头部外伤后以及一氧化碳中毒所致昏迷的辅助治疗 相似文献
108.
磁电子学器件应用原理 总被引:13,自引:0,他引:13
本文介绍几种重要的磁电子器件的基本结构和工作原理,包括巨磁电阻与隧穿磁电阻传感器、巨磁电阻隔离器、巨磁电阻与隧穿磁电阻硬盘读出磁头、磁电阻随机存取存储器、自旋转移磁化反转与微波振荡器。自旋晶体管作为未来磁电子学或自旋电子学时代的基本元素,目前大都还处在概念型阶段,本文也将对几种自旋晶体管的大致原理作简要介绍。 相似文献
109.
Arabinda Mallick 《Journal of luminescence》2006,118(2):165-172
Solvatochromic effects on the fluorescence behavior of 7-hydroxy-4-methyl-8-(4′-methyl-piperazine-1′ yl)methylcoumarin (HMMC) was studied in different solvents. The fluorescence of HMMC was found to be highly sensitive to both the polarity and the protic character of the solvent. Exploiting the polarity-sensitive fluorescence property of HMMC, its excited-state dipole moment has been determined. Fluorescence (Förster) resonance energy transfer (FRET) process from HMMC to a potent bioactive molecule 3-acetyl-4-oxo-6,7-dihydro-12 H indolo-[2,3-a] quinolizine (AODIQ) was studied. From the determined KSV and R0 values, it is argued that a long-range dipole-dipole interaction is operating for the energy transfer mechanism. The energy transfer efficiency (E) and the distance between the acceptor and the donor (r0) have been determined. 相似文献
110.
We have studied the characteristic features of carbazole phosphorescence quenching by benzophenone in toluene at 77 K. We
have shown that the decrease in the relative phosphorescence intensity for carbazole (energy donor) by a greater factor than
we see for the relative change in its decay time is due to the fact that a change in the phosphorescence decay time occurs
only for carbazole molecules participating in triplet-triplet energy transfer, while the substantial decrease in the phosphorescence
intensity for carbazole with no change in the phosphorescence decay time is connected with quenching of its singlet states.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 554–556, July–August, 2006. 相似文献