全文获取类型
收费全文 | 20540篇 |
免费 | 3792篇 |
国内免费 | 5077篇 |
专业分类
化学 | 16626篇 |
晶体学 | 508篇 |
力学 | 874篇 |
综合类 | 454篇 |
数学 | 2345篇 |
物理学 | 8602篇 |
出版年
2024年 | 46篇 |
2023年 | 327篇 |
2022年 | 678篇 |
2021年 | 772篇 |
2020年 | 810篇 |
2019年 | 836篇 |
2018年 | 729篇 |
2017年 | 907篇 |
2016年 | 981篇 |
2015年 | 1162篇 |
2014年 | 1430篇 |
2013年 | 1776篇 |
2012年 | 2092篇 |
2011年 | 2155篇 |
2010年 | 1728篇 |
2009年 | 1645篇 |
2008年 | 1807篇 |
2007年 | 1598篇 |
2006年 | 1493篇 |
2005年 | 1136篇 |
2004年 | 843篇 |
2003年 | 635篇 |
2002年 | 676篇 |
2001年 | 630篇 |
2000年 | 496篇 |
1999年 | 430篇 |
1998年 | 253篇 |
1997年 | 201篇 |
1996年 | 150篇 |
1995年 | 149篇 |
1994年 | 121篇 |
1993年 | 134篇 |
1992年 | 92篇 |
1991年 | 74篇 |
1990年 | 58篇 |
1989年 | 69篇 |
1988年 | 56篇 |
1987年 | 55篇 |
1986年 | 48篇 |
1985年 | 41篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1976年 | 5篇 |
1971年 | 3篇 |
1966年 | 2篇 |
1959年 | 4篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
横向放大率法确定复合光学系统的基点 总被引:2,自引:0,他引:2
介绍了应用测量横向放大率确定两薄透镜组成的复合光学系统基点的方法。由于采用线阵光电耦合器件(CCD)测量物经光学系统成像的横向放大率,提高了测量精度。 相似文献
62.
In the present study, proteins and glycoproteins of mouse embryos at 2-cell,morula and blastocyst stages were analyzed.The techniques of ~(35)S-Met incorporation,ConA antiserum-precipitating ConA-binding proteins, mini-2D-electrophoresis, fluorography,video densitometer scanning and the computer-lmage system were used for analyses.Results of the investigations indicated that proteins and glycoproteins were synthesized by the embryos in a gradual increase manner from 2-cell to blastocyst. A relatively large amount of glycoproteins was synthesized during the morula and blastocyst stages.Two specific small glycoproteins respectively with molecular weights about 6500 and 9000 and PIs at 5.0 and 6.5 were apparently synthesized in the blastocyst but not in the 2-cell or the morula. 相似文献
63.
以噻吩为单体,在等离子体环境中聚合成致密的有机膜。利用Rutherford背散射(RB2S)和质子弹性反冲(ERD)、傅里叶红外谱(FTIR)测定了膜的成分和结构;从近红外-可见-紫外光的反射和透射谱,运用传递矩阵方法研究了膜的光学性质;此外,还探讨了24keV的I+离子束的注入对等离子体噻吩聚合膜的掺杂效应。结果表明,注入层内电荷载流子的输运机理可用Mott的可变自由程跳跃(VRH)理论给以解释。
关键词: 相似文献
64.
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
65.
Thermal Rate Constants of the N(^4S)+O2(X^3∑g^-) → NO(X^2Ⅱ) +O(^3P) Reaction on the ^2A′ Potential Energy Surface 下载免费PDF全文
A quasiclassical trajectory study with the sixth-order explicit symplectic algorithm for the N(^4S)+O2(X^3∑g^-) → NO(X^2Ⅱ) +O(^3P) reaction has been reported by employing a new ground potential energy surface. We have discussed the influence of the relative translational energy, the vibrational and rotational levels of O2 molecules on the total reaction cross section. Thermal rate constants at temperatures 300, 600, and 1000 K determined in this work for the reaction are 4.4 × 10^7, 1.8 × 10^10, and 3.1 × 10^11 cm^3mol^-1s^-1, respectively. It is found that they are in better agreement with the experimental data than previous theoretical values. 相似文献
66.
67.
当s∈ R,0,〈q, p〈∈∞,0,〈β≤∞且 max{-n/q,-nδ2/qδ1}〈a时,定义了加权Herz—type Triebel-Lizorkin空间kq^q,pF^s β(R^n,ω1,ω2)和Kq^a,pF^sβ(R^n,ω1,ω2),并给出这些空间的一些特征及在这些空间上的Hard—Littlewood极大算子不等式. 相似文献
68.
本文给出了Banach空间广义分解定理的一个初等证明,并利用它来证明两个对称不等式.这是首次在Banach空间获得这样的不等式. 相似文献
69.
In this paper, we discuss non-elementary subgroups and discontinuous subgroups of PU(1,n; C), and give their geometric characterizations. 相似文献
70.