全文获取类型
收费全文 | 71405篇 |
免费 | 7940篇 |
国内免费 | 10340篇 |
专业分类
化学 | 23714篇 |
晶体学 | 890篇 |
力学 | 2110篇 |
综合类 | 959篇 |
数学 | 4010篇 |
物理学 | 14524篇 |
综合类 | 43478篇 |
出版年
2024年 | 258篇 |
2023年 | 775篇 |
2022年 | 1807篇 |
2021年 | 1952篇 |
2020年 | 1967篇 |
2019年 | 1715篇 |
2018年 | 1652篇 |
2017年 | 2010篇 |
2016年 | 2165篇 |
2015年 | 2909篇 |
2014年 | 3837篇 |
2013年 | 4711篇 |
2012年 | 5175篇 |
2011年 | 5437篇 |
2010年 | 5087篇 |
2009年 | 5250篇 |
2008年 | 5816篇 |
2007年 | 5561篇 |
2006年 | 5245篇 |
2005年 | 4497篇 |
2004年 | 3507篇 |
2003年 | 2637篇 |
2002年 | 2880篇 |
2001年 | 2729篇 |
2000年 | 2425篇 |
1999年 | 1506篇 |
1998年 | 781篇 |
1997年 | 657篇 |
1996年 | 639篇 |
1995年 | 547篇 |
1994年 | 489篇 |
1993年 | 451篇 |
1992年 | 432篇 |
1991年 | 344篇 |
1990年 | 326篇 |
1989年 | 274篇 |
1988年 | 247篇 |
1987年 | 209篇 |
1986年 | 135篇 |
1985年 | 103篇 |
1984年 | 101篇 |
1983年 | 85篇 |
1982年 | 68篇 |
1981年 | 65篇 |
1980年 | 50篇 |
1979年 | 37篇 |
1978年 | 19篇 |
1977年 | 10篇 |
1965年 | 14篇 |
1964年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
91.
Sang Kyu Lee Min Ju Cho Jung‐Il Jin Dong Hoon Choi 《Journal of polymer science. Part A, Polymer chemistry》2007,45(3):531-542
New photocrosslinkable maleimide copolymers have been synthesized by the attachment of a tricyanopyrrolidene‐based chromophore. The 2‐(3‐cyano‐4‐(2‐{4‐[hexyl‐(6‐hydroxy‐hexyl)‐amino]‐phenyl}‐vinyl)‐5‐oxo‐1‐{4‐[4‐(3‐oxo‐3‐phenyl‐propenyl)‐ phenoxy]‐butyl}‐1,5‐dihydro‐pyrrol‐2‐ylidene)‐malononitrile chromophore exhibits nonlinear optical activity and contains a chalcone moiety that is sensitive to UV light (λ = 330–360 nm) for crosslink formation. The maleimide monomers have also been functionalized with chalcone moieties. The resultant copolymers exhibit great processability, and one of them shows a maximum electrooptic coefficient of 90 pm/V at 1300 nm. We could control the thermal stability of the electrooptic coefficient with the newly synthesized photoreactive copolymers successfully. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 531–542, 2007 相似文献
92.
等腰三角形Mindlin板的自由振动分析 总被引:2,自引:0,他引:2
提出了一种新方法来对基于 Mindlin剪切变形理论的等腰三角形板进行自由振动分析 .此方法采用了一种新的基函数并利用 pb-2 Rayleigh-Ritz边界函数得到了一种新型的 Ritz方法 .这种方法的有效性通过收敛性和对比性分析得到了证实 .数值结果表明此方法相当精确有效 . 相似文献
93.
94.
Effects of Substrate Temperature on Helium Content and Microstructure of Nanocrystalline Titanium Films 下载免费PDF全文
Helium-charged nanocrystalline titanium films have been deposited by HeAr magnetron co-sputtering. The effects of substrate temperature on the helium content and microstructure of the nanocrystalline titanium films have been studied. The results indicate that helium atoms with a high concentration are evenly incorporated in the deposited titanium films. When the substrate temperature increases from 60℃ to 350℃ while the other deposition'parameters are fixed, the helium content decreases gradually from 38.6 at.% to 9.2at.%, which proves that nanocrystalline Ti films have a great helium storage capacity. The 20 angle of the Bragg peak of (002) crystal planes of the He-charged Ti film shifts to a lower angle and that of (100) crystal plane is unchanged as compared with that of the pure Ti film, which indicates that the lattice parameter c increases and a keeps at the primitive value. The grain refining and helium damage result in the diffraction peak broadening. 相似文献
95.
96.
Total Dose Radiation Tolerance of Phase Change Memory Cell with GeSbTe Alloy 总被引:1,自引:0,他引:1 下载免费PDF全文
Phase change memory (PCM) cell array is fabricated by a standard complementary metal-oxide-semiconductor process and the subsequent special fabrication technique. A chalcogenide Ge2Sb2Te5 film in thickness 50hm deposited by rf magnetron sputtering is used as storage medium for the PCM cell. Large snap-back effect is observed in current-voltage characteristics, indicating the phase transition from an amorphous state (higher resistance state) to the crystalline state (lower resistance state). The resistance of amorphous state is two orders of magnitude larger than that of the crystalline state from the resistance measurement, and the threshold current needed for phase transition of our fabricated PCM cell array is very low (only several μA). An x-ray total dose radiation test is carried out on the PCM cell array and the results show that this kind of PCM cell has excellent total dose radiation tolerance with total dose up to 2 ×10^6 rad(Si), which makes it attractive for space-based applications. 相似文献
97.
牛顿弦截法预估校正迭代格式的收敛阶 总被引:2,自引:0,他引:2
研究如下形式的牛顿弦截法的预估校正(P.C.)格式:P(预估):~xk+1=xk-(xk-xk-1)f(xk)f(xk)-f(xk-1)C(校正):xk+1=xk-(~xk+1-xk)f(xk)f~(xk+1)-f(xk)证明了它的收敛阶为2.618. 相似文献
98.
99.
WU Ke ZHAO Weizhong & GUO Hanying Department of Mathematics Capital Normal University Beijing China Institute of Theoretical Physics Chinese Academy of Sciences Beijing China 《中国科学A辑(英文版)》2006,(11)
In a way similar to the continuous case formally, we define in different but equivalent manners the difference discrete connection and curvature on discrete vector bundle over the regular lattice as base space. We deal with the difference operators as the discrete counterparts of the derivatives based upon the differential calculus on the lattice. One of the definitions can be extended to the case over the random lattice. We also discuss the relation between our approach and the lattice gauge theory and apply to the discrete integrable systems. 相似文献
100.
本文介绍了空调冷凝器、蒸发器残留水分量检测系统的组成和工作原理、技术指标、系统的工艺过程,最后说明了系统的考核和应用情况。 相似文献