首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   99464篇
  免费   5409篇
  国内免费   4629篇
化学   56416篇
晶体学   1335篇
力学   5601篇
综合类   322篇
数学   11922篇
物理学   33906篇
  2023年   749篇
  2022年   1717篇
  2021年   2119篇
  2020年   2317篇
  2019年   2523篇
  2018年   2905篇
  2017年   2843篇
  2016年   3503篇
  2015年   2411篇
  2014年   3492篇
  2013年   4941篇
  2012年   5072篇
  2011年   5363篇
  2010年   4263篇
  2009年   4276篇
  2008年   4471篇
  2007年   4187篇
  2006年   3818篇
  2005年   3383篇
  2004年   3047篇
  2003年   2717篇
  2002年   2843篇
  2001年   2561篇
  2000年   1994篇
  1999年   1604篇
  1998年   1542篇
  1997年   1331篇
  1996年   1296篇
  1995年   1078篇
  1994年   1159篇
  1993年   1096篇
  1992年   1063篇
  1991年   1124篇
  1990年   1122篇
  1989年   1041篇
  1988年   919篇
  1987年   916篇
  1986年   886篇
  1985年   923篇
  1984年   921篇
  1983年   822篇
  1982年   802篇
  1979年   806篇
  1978年   814篇
  1977年   810篇
  1976年   922篇
  1975年   815篇
  1974年   847篇
  1973年   848篇
  1972年   755篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Surface-wave gas discharges sustained under the conditions of a diffusion controlled regime are studied on the basis of the fluid plasma model. The self-consistent behaviour of the plasma density and of the field intensity along the discharge length is obtained. It is shown that the nonlinearity in the particle balance equation due to stepwise ionisation determines the plasma density in terms of the field intensity and ensures self-consistent behaviour of the wave ? discharge characteristics in a diffusion controlled regime.  相似文献   
82.
Two variants of a synthesis for nitropyrazolopyridines from aminopyrazoles and two- or three-carbon nitrosynthons are examined.For Communication 19 see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1560–1564, November, 1992.  相似文献   
83.
84.
We employ the statistical reactions with memory approach to study oscillating excitation functions in the 28 Si(E lab = 120–126.75 MeV)+64 Ni strongly dissipative reaction and the time evolution of the collision process. The nonself-averaging of the oscillations in the excitation functions is interpreted as indication of quantum chaos and damping of the coherent nuclear rotation in dissipative heavy-ion collisions.  相似文献   
85.
Observations indicate that illuminating NaCl crystals by ultraviolet light (λ=350 nm) suppresses the magnetoplastic effect. The processes induced by illumination take place in a subsystem of point defects and are related to a change in the state of magnetically sensitive dislocation pinning sites. Fiz. Tverd. Tela (St. Petersburg) 39, 1389–1391 (1996)  相似文献   
86.
In this contribution, we demonstrate a new effective methodology for constructing highly efficient and durable poly(p‐phenyleneethynylene) (PPE) containing emissive material with nonaggregating and hole‐facilitating properties through the introduction of hole‐transporting blocks into the PPE system as the grafting coils as well as building the energy donor–acceptor architecture between the grafting coils and the PPE backbone. Poly(2‐(carbazol‐9‐yl)ethyl methacrylate) (PCzEMA), herein, is chosen as the hole‐transporting blocks, and incorporated into the PPE system as the grafting coils via atom transfer radical polymerization. The chemical structure of the resultant copolymer, PPE‐g‐PCzEMA, was characterized by NMR and gel permeation chromatography, showing that the desirable copolymer was obtained with the narrow polydispersity. The increased thermal stability of PPE‐g‐PCzEMA was confirmed by thermogravimetric analysis and differential scanning calorimetry along with its macroinitiator. The optoelectronic properties of this copolymer were studied in detail by ultraviolet‐visible absorption, photoluminescence emission and excitation spectra, and cyclic voltammogram (CV). The results indicate that PPE‐g‐PCzEMA exhibits the solid‐state luminescent property dominated by individual lumophores, and also the energy transfer process from the PCzEMA blocks to the PPE backbone with a relatively higher energy transfer efficiency in the solid‐state compared to that of the solution state. Additionally, the hole‐injection property is greatly facilitated due to the presence of PCzEMA, as confirmed by CV profiles. All these data indicate that PPE‐g‐PCzEMA is a good candidate for use in optoelectronic devices. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3776–3787, 2007  相似文献   
87.
88.
A new biodegradable starch graft copolymer, starch‐g‐poly(1,4‐dioxan‐2‐one), was synthesized through the ring‐opening graft polymerization of 1,4‐dioxan‐2‐one onto a starch backbone. The grafting reactions were conducted with various 1,4‐dioxan‐2‐one/starch feed ratios to obtain starch‐g‐poly(1,4‐dioxan‐2‐one) copolymers with various poly(1,4‐dioxan‐2‐one) graft structures. The microstructure of starch‐g‐poly(1,4‐dioxan‐2‐one) was characterized in detail with one‐ and two‐dimensional NMR spectroscopy. The effect of the feed composition on the resulting microstructure of starch‐g‐poly(1,4‐dioxan‐2‐one) was investigated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3417–3422, 2004  相似文献   
89.
90.
We propose a new method for computing multimode wave interactions in towing systems; our method is based on wave splitting of the equations of a model in such a way that each computational step requires computation for only one mode. The efficiency of the method is demonstrated by analysis of a concrete towing system with a turning towboat. Translated fromDinamicheskic Sistermy. Vol. 12, pp. 55–64, 1993.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号