全文获取类型
收费全文 | 6805篇 |
免费 | 968篇 |
国内免费 | 750篇 |
专业分类
化学 | 4987篇 |
晶体学 | 79篇 |
力学 | 294篇 |
综合类 | 50篇 |
数学 | 864篇 |
物理学 | 2249篇 |
出版年
2024年 | 18篇 |
2023年 | 107篇 |
2022年 | 202篇 |
2021年 | 232篇 |
2020年 | 259篇 |
2019年 | 253篇 |
2018年 | 231篇 |
2017年 | 199篇 |
2016年 | 281篇 |
2015年 | 329篇 |
2014年 | 327篇 |
2013年 | 507篇 |
2012年 | 563篇 |
2011年 | 600篇 |
2010年 | 386篇 |
2009年 | 349篇 |
2008年 | 466篇 |
2007年 | 369篇 |
2006年 | 320篇 |
2005年 | 310篇 |
2004年 | 245篇 |
2003年 | 262篇 |
2002年 | 256篇 |
2001年 | 229篇 |
2000年 | 164篇 |
1999年 | 133篇 |
1998年 | 118篇 |
1997年 | 80篇 |
1996年 | 136篇 |
1995年 | 94篇 |
1994年 | 82篇 |
1993年 | 65篇 |
1992年 | 53篇 |
1991年 | 51篇 |
1990年 | 38篇 |
1989年 | 43篇 |
1988年 | 28篇 |
1987年 | 23篇 |
1986年 | 29篇 |
1985年 | 25篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1936年 | 2篇 |
排序方式: 共有8523条查询结果,搜索用时 0 毫秒
1.
2.
Let f be a smooth map between unit spheres of possibly different dimensions. We prove the global existence and convergence of the mean curvature flow of the graph of f under various conditions. A corollary is that any area‐decreasing map between unit spheres (of possibly different dimensions) is isotopic to a constant map. © 2004 Wiley Periodicals, Inc. 相似文献
3.
4.
Jing Zhang Dan Shan Shaolin Mu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5573-5582
A copolymer, poly(aniline‐co‐o‐aminophenol), was prepared chemically by using ammonium peroxydisulfate as an oxidant. The monomer concentration ratio of o‐aminophenol to aniline strongly influences the copolymerization rate and properties of the copolymer. The optimum composition of a mixture for the chemical copolymerization consisted of 0.3 M aniline, 0.021 M o‐aminophenol, 0.42 M ammonium peroxydisulfate, and 2 M H2SO4. The result of cyclic voltammograms in a potential region of ?0.20 to 0.80 V (vs.SCE) indicates that the electrochemical activity of the copolymer prepared under the optimum condition is similar to that of polyaniline in more acid solutions. However, the copolymer still holds the good electrochemical activity until pH 11.0. Therefore, the pH dependence of the electrochemical property of the copolymer is improved, compared with poly(aniline‐co‐o‐aminophenol) prepared electrochemically, and is much better than that of polyaniline. The spectra of IR and 1H NMR confirm that o‐aminophenol units are included in the copolymer chain, which play a key role in extending the usable pH region of the copolymer. The visible spectra of the copolymers show that a high concentration ratio of o‐aminophenol to aniline in a mixture inhibits the chain growth. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5573–5582, 2007 相似文献
5.
Leong‐Huat Gan Palaniswamy Ravi Bao Wei Mao Kam‐Chiu Tam 《Journal of polymer science. Part A, Polymer chemistry》2003,41(17):2688-2695
Polymerization of 2‐(diethylamino)ethyl methacrylate (DEAEMA) via homogeneous atom transfer radical polymerization under various reaction conditions is described. The effects of the initiators and solvents were examined. With 1,1,4,7,10,10‐hexamethyl triethylenetetramine/copper(I) chloride/p‐toluenesulfonyl chloride as the ligand/catalyst/initiator system in methanol, poly(DEAEMA) with a polydispersity index as low as 1.07 was synthesized. Kinetic studies demonstrated the polymerization was very well controlled and exhibited the living characteristic of the process. Well‐defined block copolymers of DEAEMA and tert‐butyl methacrylate (tBMA) were successfully synthesized. The copolymers could be synthesized with equally good results by starting with either p(DEAEMA) or p(tBMA) as the macroinitiators. However, only the macroinitiators terminated with chlorine should be used. The corresponding macroinitiators with bromine as a transferable group did not yield well‐defined copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2688–2695, 2003 相似文献
6.
7.
8.
9.
The feature selection consists of obtaining a subset of these features to optimally realize the task without the irrelevant
ones. Since it can provide faster and cost-effective learning machines and also improve the prediction performance of the
predictors, it is a crucial step in machine learning. The feature selection methods using support machines have obtained satisfactory
results, but the noises and outliers often reduce the performance. In this paper, we propose a feature selection approach
using fuzzy support vector machines and compare it with the previous work, the results of experiments on the UCI data sets
show that feature selection using fuzzy SVM obtains better results than using SVM. 相似文献
10.
Tian Le LIN Bao Zhen YAN Gao Fei HU Mei WANG 《中国化学快报》2006,17(7):937-940
Complex formation between aluminium and quercetin(Q) in methanol was investigated by means of 27^Al solid-state, 13^C and 1^H NMR and MS(ESI), UV and IR spectra. Formation of the 1:2 complex was favored in methanol relative to all other solvent and the predominant species observed of Al(Ⅲ) has a 1:2 stoichiometry. The fine structure of 1:2 aluminum complex of quercetin was that the aluminum central atom chelated with two quereetin molecules and two methoxyl groups between two five membered rings, its coordination is six, the chelated site was 3-hydroxy-4-carbonyl. 相似文献