全文获取类型
收费全文 | 11837篇 |
免费 | 1698篇 |
国内免费 | 1396篇 |
专业分类
化学 | 8044篇 |
晶体学 | 145篇 |
力学 | 854篇 |
综合类 | 96篇 |
数学 | 1422篇 |
物理学 | 4370篇 |
出版年
2023年 | 169篇 |
2022年 | 186篇 |
2021年 | 288篇 |
2020年 | 389篇 |
2019年 | 345篇 |
2018年 | 308篇 |
2017年 | 295篇 |
2016年 | 452篇 |
2015年 | 430篇 |
2014年 | 562篇 |
2013年 | 806篇 |
2012年 | 886篇 |
2011年 | 967篇 |
2010年 | 652篇 |
2009年 | 712篇 |
2008年 | 752篇 |
2007年 | 722篇 |
2006年 | 682篇 |
2005年 | 627篇 |
2004年 | 493篇 |
2003年 | 392篇 |
2002年 | 347篇 |
2001年 | 327篇 |
2000年 | 287篇 |
1999年 | 317篇 |
1998年 | 327篇 |
1997年 | 259篇 |
1996年 | 255篇 |
1995年 | 224篇 |
1994年 | 239篇 |
1993年 | 158篇 |
1992年 | 149篇 |
1991年 | 130篇 |
1990年 | 138篇 |
1989年 | 84篇 |
1988年 | 78篇 |
1987年 | 86篇 |
1986年 | 82篇 |
1985年 | 71篇 |
1984年 | 48篇 |
1983年 | 33篇 |
1982年 | 36篇 |
1981年 | 26篇 |
1980年 | 20篇 |
1979年 | 15篇 |
1978年 | 14篇 |
1977年 | 8篇 |
1976年 | 8篇 |
1973年 | 10篇 |
1970年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Ren‐Shen Lee Yi‐Ting Huang 《Journal of polymer science. Part A, Polymer chemistry》2008,46(13):4320-4331
A straightforward strategy is proposed for the synthesis of novel, amphiphilic block–graft MPEG‐b‐(PαN3CL‐g‐alkyne) degradable copolymers. First, the ring‐opening polymerization of α‐chloro‐ε‐caprolactone (αClCL) was initiated by hydroxy‐terminated macroinitiator monomethoxy poly(ethylene glycol) (MPEG) with SnOct2 as the catalyst. In a second step, pendent chlorides were converted into azides by the reaction with sodium azide. Finally, various kinds of terminal alkynes were reacted with pendent azides by copper‐catalyzed Huisgen's 1,3‐dipolar cycloaddition, and thus a “click” reaction. These copolymers were characterized by differential scanning calorimetry (DSC), 1H NMR, IR, and gel permeation chromatography. By fixing the length of the MPEG block and increasing the length of PαClCL (or PαN3CL) block, an increase tendency in Tgs was observed. However, the copolymers of MPEG‐b‐PαClCL and MPEG‐b‐PαN3CL were semicrystalline when the Mn of MPEG was above 2000 g mol?1. The block–graft copolymers formed micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range of 1.4–12.0 mg L?1 depending on the composition of polymers. The lengths of hydrophilic segment influence the shape of the micelle. The mean hydrodynamic diameters of the micelles from dynamic light scattering were in the range of 90–160 nm. In vitro hydrolytic degradation of block–graft copolymers is faster than the corresponding block copolymers. The drug entrapment efficiency and the drug loading content of micelles depending on the composition of block–graft polymers were described. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4320–4331, 2008 相似文献
992.
本工作系统地研究了Ho3+在ZnS中的光谱特性。利用不同激发波长的发射光谱、激发光谱和发光衰减鉴别出29000-14000cm-1范围内的激发谱线和发射谱线所对应的跃迁。共观察到5G5′,5G4,5G5,5G6,3K8,5F2,5F3和5S2八个4f能级的发射和5G6,5G5,3K7,3H6和5G3(3L9)五个4f能级的激发。由发射光强随温度的变化规律,研究了Ho3+的5G5′和5G4,5F3和5S2能级间的多声子弛豫过程以及5G6,3K3,5F2和5F3能级间的热平衡过程。通过近带边激发下的发光行为,提出Ho3+在ZnS中的近带边激发下发光是借助于能量传递过程,不同激发态借助不同的传递途径,而且不同的发光中心也具有不同的传递机制。 相似文献
993.
By the comparison of the reaction products of gem-dihalocyclopropanes under various conditions, it is suggested that similar to the reactions with metals, the reactive radical intermediates which make the reaction results complicated are formed in the reactions of gem-dihalocyclopropanes with alkyl lithium. Studies on the competitions between ring opening and intramolecular C—H insertions of cyclopropylidenes generated by the reactions of gem-dihalocyclopropanes with metals and discussions on the reaction mechanism are also given in this paper. 相似文献
994.
995.
996.
997.
The nonlinear D-S equations on R^d, with general power nonlinearity and with both the focusing and defocusing signs, are proved to be ill-posed in the Sobolev space H^s whenever the exponent s is lower than that predicted by scaling or Galilean invariance, or when the regularity is too low to support distributional solutions. Authors analyze a class of solutions for which the zero-dispersion limit provides good approximations. 相似文献
998.
999.
In this paper, we study the Hausdorff dimension of Cantor attractors of smooth interval maps with non-flat critical points.
We prove that the Hausdorff dimension is bounded from above by a constant less than 1 which depends only on the number and
order of the critical points. 相似文献