全文获取类型
收费全文 | 46119篇 |
免费 | 1174篇 |
国内免费 | 1211篇 |
专业分类
化学 | 8297篇 |
晶体学 | 80篇 |
力学 | 796篇 |
综合类 | 168篇 |
数学 | 3507篇 |
物理学 | 5285篇 |
综合类 | 30371篇 |
出版年
2024年 | 54篇 |
2023年 | 252篇 |
2022年 | 650篇 |
2021年 | 636篇 |
2020年 | 703篇 |
2019年 | 665篇 |
2018年 | 593篇 |
2017年 | 577篇 |
2016年 | 681篇 |
2015年 | 932篇 |
2014年 | 2273篇 |
2013年 | 2306篇 |
2012年 | 2643篇 |
2011年 | 3063篇 |
2010年 | 2429篇 |
2009年 | 2980篇 |
2008年 | 3149篇 |
2007年 | 3429篇 |
2006年 | 2953篇 |
2005年 | 2363篇 |
2004年 | 2105篇 |
2003年 | 1975篇 |
2002年 | 1864篇 |
2001年 | 1580篇 |
2000年 | 1271篇 |
1999年 | 922篇 |
1998年 | 654篇 |
1997年 | 523篇 |
1996年 | 412篇 |
1995年 | 400篇 |
1994年 | 335篇 |
1993年 | 293篇 |
1992年 | 361篇 |
1991年 | 235篇 |
1990年 | 199篇 |
1989年 | 164篇 |
1988年 | 169篇 |
1987年 | 154篇 |
1986年 | 135篇 |
1985年 | 88篇 |
1984年 | 82篇 |
1983年 | 45篇 |
1982年 | 98篇 |
1981年 | 174篇 |
1980年 | 182篇 |
1979年 | 187篇 |
1978年 | 166篇 |
1977年 | 102篇 |
1976年 | 108篇 |
1973年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
221.
掷铁饼的旋转动作是角运动(运动员绕纵轴或接近纵向的轴旋转)与水平运动(重心在投掷圈内向前移动)的结合。本文主要阐述:怎样利用人体旋转时转轴的变化,形成合理的旋转投掷半径,取得最大限度的旋转角度,从而使整个投掷过程获得理想的角动量。 相似文献
222.
讨论了微分方程组 dx/dt=-y(1 -ax2 n) +bx-cx2 n+ 1,dy/dt=x(1 -ax2 n) ,并且给出了其极限环存在唯一的条件 . 相似文献
223.
The principle of concentrating a substance from a mixture flow in a stationary sorbent layer of infinite length that was previously
developed for gas chromatography is extended to liquid chromatography.
Translated fromIzevestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1063–1065, May, 1997. 相似文献
224.
Hiroshi Ito Masaki Okazaki Dolores C. Miller 《Journal of polymer science. Part A, Polymer chemistry》2004,42(6):1478-1505
Radical copolymerizations of electron‐deficient 2‐trifluoromethylacrylic (TFMA) monomers, such as 2‐trifluoromethylacrylic acid and t‐butyl 2‐trifluoromethylacrylate (TBTFMA), with electron‐rich norbornene derivatives and vinyl ethers with 2,2′‐azobisisobutyronitrile as the initiator were investigated in detail through the analysis of the kinetics in situ with 1H NMR and through the determination of the monomer reactivity ratios. The norbornene derivatives used in this study included bicyclo[2.2.1]hept‐2‐ene (norbornene) and 5‐(2‐trifluoromethyl‐1,1,1‐trifluoro‐2‐hydroxylpropyl)‐2‐norbornene. The vinyl ether monomers were ethyl vinyl ether, t‐butyl vinyl ether, and 3,4‐dihydro‐2‐H‐pyran. Vinylene carbonate was found to copolymerize with TBTFMA. Although none of the monomers underwent radical homopolymerization under normal conditions, they copolymerized readily, producing a copolymer containing 60–70 mol % TFMA. The copolymerization of the TFMA monomer with norbornenes and vinyl ethers deviated from the terminal model and could be described by the penultimate model. The copolymers of TFMA reported in this article were evaluated as chemical amplification resist polymers for the emerging field of 157‐nm lithography. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1478–1505, 2004 相似文献
225.
The blends composed of polyamide 6 (PA6) and polyamide 66 (PA66) were obtained using two different preparation methods, one of which was the melt‐mixing through a twin‐screw extruder and the subsequent injection molding; and the other, the in situ blending through anionic polymerization of ε‐caprolactam in the presence of PA66. For the former, there existed a remarkable improvement in toughness but a drastic drop in strength and modulus; however, for the latter, a reverse but less significant trend of mechanical properties change appeared. Various characterizations were conducted, including the analyses of crystalline morphology, crystallographic form, and crystallization and melting behaviors using polarized optical microscopy (POM), wide‐angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC), respectively; observation of morphology of fractured surface with scanning electron microscope (SEM); measurement of glass transition through dynamic mechanical analysis (DMA); and the intermolecular interaction as well as the interchange reaction between the two components by Fourier transform infrared spectrometry (FT‐IR) and 13C solution NMR. The presence and absence of interchange reaction was verified for the in situ and melt‐mixed blends, respectively. It is believed that the transreaction resulted in a drop in glass transition temperature (Tg) for the in situ blends, contrary to an increase of Tg with increasing PA66 content for the melt‐mixed ones. And the two kinds of fabrication methods led to significant differences in the crystallographic form, spherulite size and crystalline content and perfection as well. Accordingly, it is attempted to explain the reasons for the opposite trends of changes in the mechanical properties for these two blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1176–1186, 2007 相似文献
226.
We provide some inequalities and integral inequalities connected to the Jensen-Hadamard inequalities for convex functions.
In particular, we give some refinements to these inequalities. Some natural applications and further extensions are given.
Sunto Forniamo alcune diseguaglianze e diseguaglianze integrali connesse alle dise-gueglianze di Jensen-Hadamard per funzioni convesse. In particolare, diamo qualche miglioramento di queste diseguaglianze. Alcune applicazioni naturali ed ulteriori estensioni sono date.相似文献
227.
白飞 《贵州师范大学学报(社会科学版)》2002,(1):45-48
以“两金会晤”为转折点,朝鲜外交渐易常态,日益呈现出明显的全方位特征。朝鲜外交模式由保守单一到多边开放的转变是以后冷战时期朝鲜的一系列错综而深刻的国际国内因素为背景的。这决定了朝鲜推行全方位外交路线的战略性而非策略性。 相似文献
228.
薛生辉 《江苏技术师范学院学报》2002,8(3):49-51
CI设计的最大特点就在于广泛的参与、实践和应用,对它的教学目的是让学生在全面深入理解设计理念的基础上开展设计实践活动.然而现实中的CI教学往往只偏重于一方面而忽略另一方面,本文就两者的有机结合作了一些尝试. 相似文献
229.
230.
浅论大学英语教学中的德育教育 总被引:2,自引:0,他引:2
宗云 《东莞理工学院学报》2003,10(1):64-67
通过探讨大学英语教学中的德育教育,提出了四法:中西文化对比法、课堂讨论法、名人名言翻译法和课内外结合法。 相似文献