全文获取类型
收费全文 | 108569篇 |
免费 | 11541篇 |
国内免费 | 7305篇 |
专业分类
化学 | 27398篇 |
晶体学 | 604篇 |
力学 | 8354篇 |
综合类 | 1018篇 |
数学 | 30692篇 |
物理学 | 35108篇 |
无线电 | 24241篇 |
出版年
2024年 | 318篇 |
2023年 | 1259篇 |
2022年 | 2122篇 |
2021年 | 2585篇 |
2020年 | 3132篇 |
2019年 | 2756篇 |
2018年 | 2581篇 |
2017年 | 3043篇 |
2016年 | 3616篇 |
2015年 | 3227篇 |
2014年 | 5215篇 |
2013年 | 7678篇 |
2012年 | 5589篇 |
2011年 | 6029篇 |
2010年 | 5070篇 |
2009年 | 6371篇 |
2008年 | 6838篇 |
2007年 | 7273篇 |
2006年 | 6205篇 |
2005年 | 5369篇 |
2004年 | 4526篇 |
2003年 | 4679篇 |
2002年 | 4664篇 |
2001年 | 3648篇 |
2000年 | 3392篇 |
1999年 | 2914篇 |
1998年 | 2733篇 |
1997年 | 1929篇 |
1996年 | 1732篇 |
1995年 | 1515篇 |
1994年 | 1403篇 |
1993年 | 1039篇 |
1992年 | 1068篇 |
1991年 | 794篇 |
1990年 | 768篇 |
1989年 | 545篇 |
1988年 | 453篇 |
1987年 | 409篇 |
1986年 | 373篇 |
1985年 | 357篇 |
1984年 | 349篇 |
1983年 | 198篇 |
1982年 | 298篇 |
1981年 | 273篇 |
1980年 | 177篇 |
1979年 | 215篇 |
1978年 | 164篇 |
1977年 | 150篇 |
1976年 | 98篇 |
1973年 | 76篇 |
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
991.
992.
D.P. Woodruff 《Surface science》2002,500(1-3):147-171
The range of surface structural problems of interest in understanding the physics and chemistry of solid surfaces is reviewed with reference to the available methods and their strengths and limitations. Key challenges being addressed currently concern the achievable precision of measurements and their physical and chemical significance, and the complexity of the problems which may be solved. Past progress and future problems are illustrated with a series of examples ranging from the relaxation of simple clean metal surfaces through complex semiconductor reconstructions to large molecular adsorption and coadsorption systems and complex adsorbate-induced reconstructions. The strengths and limitations of scanning tunnelling microscopy as a complement to true quantitative structural methods are discussed, as is the role of chemical state specificity and elemental specificity in solving complex molecular adsorbate systems. 相似文献
993.
Backlund transformation and variable separation solutions for the generalized Nozhnik—Novikov—Veselov equation
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Using the extended homogeneous balance method, the B?cklund transformation for a (2+1)-dimensional integrable model, the generalized Nizhnik-Novikov-Veselov (GNNV) equation, is first obtained. Also, making use of the B?cklund transformation, the GNNV equation is changed into three equations: linear, bilinear and trilinear form equations. Starting from these three equations, a rather general variable separation solution of the model is constructed. The abundant localized coherent structures of the model can be induced by the entrance of two variable-separated arbitrary functions. 相似文献
994.
ODLC是当今用户接入网的新型设备,它一方面可取代端局,解决通信线路紧张和远距离大容量放号问题,另一方面也可满足日益增多的增值业务的需求。本文ODLC技术的基本原理,结合目前国内外常见ODLC系统,总结和对比了其基本特点,优势,并指明ODLC的技术发展方向和中国应用的前景。 相似文献
995.
本文基于Volterra级数法和非线性转移函数理论,提出了一种分析毫米波谐波振荡器的新方法,给出了描述其非线性特性的决定方程,通过求解一组非线性代数方程,便可计算出谐波振荡器的振荡频率和幅度。文中给出了具体分析实例,并与谐波平衡法等进行了比较,结果表明:这种方法具有理论严密、准确性高、适用范围广等特点,特别是利用一次决定方程的结果作为其它非线性数值分析方法的初始估值,则可大大地节约计算时间,并容易 相似文献
996.
采用信息融合技术的IR/MMW复合导引头的目标跟踪 总被引:2,自引:0,他引:2
从误差测量环节入手,基于IR/MMW双模结构,采用信息融合处理技术提高其估计跟踪精度,最终达到降低制导误差,提高武器性能的目的,仿真结果验证了该方法的有效性。 相似文献
997.
R. Souzy B. Ameduri B. Boutevin 《Journal of polymer science. Part A, Polymer chemistry》2004,42(20):5077-5097
The radical co‐ and terpolymerization of 4‐[(α,β,β‐trifluorovinyl)oxy]bromo benzene (TFVOBB) with 1,1‐difluoroethylene (or vinylidene fluoride, VDF, or VF2), hexafluoropropene (HFP), perfluoromethyl vinyl ether (PMVE), and chlorotrifluroroethylene (CTFE) is presented. Although TFVOBB could be thermocyclodimerized, it could not homopolymerize under radical initiation. TFVOBB could be copolymerized in solution under a radical initiator with VDF or CTFE comonomers, while its copolymerization with HFP or PMVE were unsuccessful. The terpolymerization of TFVOBB with VDF and HFP, or VDF and PMVE, or VDF and CTFE also led to original fluorinated terpolymers bearing bromoaromatic side‐groups. The conditions of co‐ and terpolymerization were optimized in terms of the nature of the radical initiators, and of the nature of solvents (fluorinated or nonhalogenated). Various monomer concentrations in the co‐ and terpolymers were assessed by 19F and 1H‐NMR spectroscopy. The thermal and physico chemical properties were also studied. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5077–5097, 2004 相似文献
998.
吕海深 《Annals of Differential Equations》2004,20(2):133-139
Under suitable conditions on f(·,u), it is shown that the two-point boundaryvalue problem((u'))' + λq(t)f(u) = 0in (0, 1),u(0) = u(1) = 0,has two positive solution or at least one positive solution for λ in a compatibleinterval. 相似文献
999.
1000.
THE ASYMPTOTIC SOLUTION FOR A CLASS OF SINGULARLY PERTURBED PROBLEM FOR SEMILINEAR SINGULAR EQUATION
The singularly perturbed boundary value problem for a class of semilinearsingular equation is considered. Using a simple and special method the asym-ptotic behavior of solution is studied. 相似文献