全文获取类型
收费全文 | 9192篇 |
免费 | 695篇 |
国内免费 | 1162篇 |
专业分类
化学 | 9789篇 |
晶体学 | 49篇 |
力学 | 13篇 |
综合类 | 41篇 |
数学 | 399篇 |
物理学 | 758篇 |
出版年
2024年 | 12篇 |
2023年 | 82篇 |
2022年 | 193篇 |
2021年 | 199篇 |
2020年 | 355篇 |
2019年 | 302篇 |
2018年 | 242篇 |
2017年 | 253篇 |
2016年 | 372篇 |
2015年 | 327篇 |
2014年 | 363篇 |
2013年 | 787篇 |
2012年 | 478篇 |
2011年 | 535篇 |
2010年 | 489篇 |
2009年 | 516篇 |
2008年 | 632篇 |
2007年 | 617篇 |
2006年 | 600篇 |
2005年 | 554篇 |
2004年 | 567篇 |
2003年 | 473篇 |
2002年 | 415篇 |
2001年 | 249篇 |
2000年 | 225篇 |
1999年 | 174篇 |
1998年 | 158篇 |
1997年 | 142篇 |
1996年 | 134篇 |
1995年 | 103篇 |
1994年 | 103篇 |
1993年 | 103篇 |
1992年 | 81篇 |
1991年 | 45篇 |
1990年 | 42篇 |
1989年 | 31篇 |
1988年 | 24篇 |
1987年 | 12篇 |
1986年 | 17篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Prof. Dr. Mieczysław Mąkosza 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(19):5536-5545
In this overview, it is shown that there are many initial reactions between nitroarenes and nucleophiles: addition to the electron‐deficient ring at positions occupied by halogen and hydrogen atoms, addition to the nitro group, single‐electron transfer (SET), and other types of initial reactions. The resulting intermediates react further in a variety of ways to form products of nucleophilic substitution of a halogen atom (SNAr), a hydrogen atom (SNArH), and others. Many variants of these processes are briefly discussed, particularly in relation of rates of the initial reactions and further transformations. 相似文献
992.
Zeng Guangxing 《中国科学A辑(英文版)》1999,42(3):272-280
For an ordered field (K,T) and an idealI of the polynomial ring
, the construction of the generalized real radical
ofI is investigated. When (K,T) satisfies some computational requirements, a method of computing
is presented.
Project supported by the National Natural Science Foundation of China (Grant No. 19661002) and the Climbing Project. 相似文献
993.
Yu. B. Sinkevich A. E. Shchekotikhin Yu. N. Luzikov V. N. Buyanov L. V. Kovalenko 《Chemistry of Heterocyclic Compounds》2007,43(10):1252-1259
4,11-Dihydroxyanthra[2,3-b]thiophene-5,10-dione (thiophenoquinizarine) and its 3-methyl derivative were obtained by the cyclization
of quinizarin-2-yl derivatives of mercaptoacetaldehyde or mercaptoacetone in acid medium. 4,11-Dimethoxy-and 4,11-dibutoxyanthra[2,3-b]thiophene-5,10-dione
were synthesized by the alkylation of the hydroxyl group in the synthesized anthrathiophenes with dimethylformamide dimethylacetal
or butyl iodide respectively. Radical bromination of 4,11-dimethoxy-3-methylanthra[2,3-b]thiophene-5,10-dione, depending on
the amount of N-bromo-succinimide taken, leads to the formation of 3-bromomethyl-or 3-dibromomethyl-4,11-dimethoxy-anthra[2,3-b]thiophene-5,10-diones.
The action of sodium acetate on the obtained bromo derivatives with subsequent hydrolysis of the intermediate acetates led
to the synthesis of 3-hydroxymethyl-or 3-formyl-4,11-dimethoxy-anthra[2,3-b]thiophene-5,10-diones.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1478–1485, October, 2007. 相似文献
994.
The radical telomerisation of vinylidene fluoride (VDF) with 2-mercaptoethanol as chain transfer agent (CTA) was studied to synthesise fluorinated telomers which bear a hydroxy end-group, such as H(VDF)nS(CH2)2OH, under thermal (di-tert-butyl peroxide as the initiator) or photochemical initiations. A careful structural study of a typical H-VDF-S(CH2)2OH telomer was performed by 1H and 19F NMR spectroscopy. These analytical methods allowed us to explore the selective addition of the thiyl radical onto the hydrogenated side of VDF, and the telomer containing one VDF unit was obtained selectively. Surprisingly, for higher [VDF]o initial concentrations, a monoadduct telomer was produced as well as PVDF homopolymer. This feature was related to the fast consumption of the CTA. The kinetics of radical telomerisation led to a quite high transfer constant of the CTA (40 at 140 °C) that evidences the formation of a monoadduct as the only telomer formed. 相似文献
995.
Zdenko asar Ivan Leban Alenka Majcen-le Marechal Lidia Piekara-Sady Dominique Lorcy 《Comptes Rendus Chimie》2009,12(9):1057-1065
The synthesis and the redox behaviour of electroactive donor molecules incorporating an azino spacer group between a benzoselenazole core and another heterocyclic moiety, either a benzoselenazole one or a thiazole one, are reported. Neutral complexes were obtained with TCNQ and, for the first time with dithiadiazafulvalene or diselenadiazafulvalene derivatives, cation radical salts by electrocrystallization. Crystal structures data of these complexes are presented and their geometries compared with those deduced from theoretical calculations. 相似文献
996.
将镜像法和保角变换法相结合,计算由线电荷与接地半无限大导体板所形成的电场,给出其电势分布和场强分布,进一步得出等势线方程和电场线方程,并利用数学软件MATLAB绘制出等势线图和电场线图. 相似文献
997.
The mechanisms of reactions between CC13OO• radical and quercetin, rutin and epigallocatechin gallate (EGCG) have been studied using pulse radiolytic technique. It is
suggested that the electron transfer reaction is the main reaction between CC13OO• radical and rutin, EGCG, but there are two main pathways for the reaction of CC13OO• radical with quercetin, one is the electron transfer reaction, the other is addition reaction. The reaction rate constants
were determined. It is proved that quercetin and rutin are better CC13OO• radical scavengers than EGCG. 相似文献
998.
Atom transfer radical polymerization (ATRP) of ethyl acrylate was carried out in bulk using ethyl 2-bromoisobutyrate as initiator, CuBr as well as CuCl as catalyst in combination with different ligands e.g., 2,2′ bipyridine (bpy)andN,N, N′,N″,N″-pentamethyldiethylenetriamine (PMDETA). In most of the cases very high conversion (72–98%) was achieved. The polymerization was well controlled with a linear increase of molecular weight (MnSEC) with conversion and relatively narrow molecular weight distributions (polydispersity index 1.2–1.3). Use of PMDETA as the ligand resulted in faster polymerization rate (98% conversion in 1 h) than those using bipyridine (72% conversion in 5 h). The MALDI-TOF-MS analysis of poly (ethyl acrylate) (PEA) prepared by using bpy as ligand showed the presence of halogen as the end group. On the contrary, when PMDETA was used as the ligand, the mass analysis showed no trace of this end group. 相似文献
999.
《Angewandte Chemie (International ed. in English)》2017,56(11):3103-3107
In this contribution a convenient synthetic method to obtain tetraacylgermanes Ge[C(O)R]4 (R=mesityl ( 1 a ), phenyl ( 1 b )), a previously unknown class of highly efficient Ge‐based photoinitiators, is described. Tetraacylgermanes are easily accessible via a one‐pot synthetic protocol in >85 % yield, as confirmed by NMR spectroscopy, mass spectrometry, and X‐ray crystallography. The efficiency of 1 a , b as photoinitiators is demonstrated in photobleaching (UV/Vis), time‐resolved EPR (CIDEP), and NMR/CIDNP investigations as well as by photo‐DSC studies. Remarkably, the tetraacylgermanes exceed the performance of currently known long‐wavelength visible‐light photoinitiators for free‐radical polymerization 相似文献
1000.
针对自由基聚合歧化终止和偶合终止两类机理生成的线型高聚物,应用统计物理的基本原理,对其分子量分布重新进行了理论推导,其方法简洁清晰,无须任何附加假定,导出FlorySchulz分布.结果有助于从另一方面理解FlorySchulz分布的物理学基础. 相似文献