全文获取类型
收费全文 | 16734篇 |
免费 | 2896篇 |
国内免费 | 2248篇 |
专业分类
化学 | 12692篇 |
晶体学 | 256篇 |
力学 | 911篇 |
综合类 | 153篇 |
数学 | 1728篇 |
物理学 | 6138篇 |
出版年
2024年 | 51篇 |
2023年 | 357篇 |
2022年 | 558篇 |
2021年 | 618篇 |
2020年 | 710篇 |
2019年 | 765篇 |
2018年 | 617篇 |
2017年 | 607篇 |
2016年 | 814篇 |
2015年 | 838篇 |
2014年 | 1009篇 |
2013年 | 1369篇 |
2012年 | 1552篇 |
2011年 | 1705篇 |
2010年 | 1154篇 |
2009年 | 1122篇 |
2008年 | 1126篇 |
2007年 | 1069篇 |
2006年 | 873篇 |
2005年 | 720篇 |
2004年 | 617篇 |
2003年 | 481篇 |
2002年 | 450篇 |
2001年 | 385篇 |
2000年 | 353篇 |
1999年 | 264篇 |
1998年 | 227篇 |
1997年 | 172篇 |
1996年 | 194篇 |
1995年 | 148篇 |
1994年 | 156篇 |
1993年 | 118篇 |
1992年 | 117篇 |
1991年 | 97篇 |
1990年 | 89篇 |
1989年 | 77篇 |
1988年 | 44篇 |
1987年 | 41篇 |
1986年 | 43篇 |
1985年 | 40篇 |
1984年 | 29篇 |
1983年 | 17篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 11篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
LIANG Liang 《原子与分子物理学报》2003,20(4):575-578
By using the multichannel quantum defect theory(MQDT),we have evaluated the energy levels and lifetimes of 2sns ^3 S1,2snd ^3D(n=3-25)of BeI and 1 sns ^3s1,1snd ^3D(n=3-25)of BeⅢ,These energies and lifetimes that we have calculated not only agree with the recent measurements and theoretical calculation of Ref.4 and Ref.3, but also predict the lifetimes of 66 other highly excited states. 相似文献
82.
A polarization-insensitive 40-Gb/s time-division demultiplexer was demonstrated in a polarization-diversity loop configuration. The power penalty was measured to be 2.3 dB at a bit error rates of 10-9 for 10 Gb/s output signals. 相似文献
83.
84.
Huang H. X. Liang Z. A. Pardalos P. M. 《Journal of Optimization Theory and Applications》2004,120(1):53-71
A flow search approach is presented in this paper. In the approach, each iterative process involves a subproblem, whose variables are the stepsize parameters. Every feasible solution of the subproblem corresponds to some serial search stages, the stepsize parameters in different search stages may interact mutually, and their optimal values are determined by evaluating the total effect of the interaction. The main idea of the flow search approach is illustrated via the minimization of a convex quadratic function. Based on the flow search approach, some properties of the m-step linear conjugate gradient algorithm are analyzed and new bounds on its convergence rate are also presented. Theoretical and numerical results indicate that the new bounds are better than the well-known ones. 相似文献
85.
Cellular neural network to detect spurious vectors in PIV data 总被引:2,自引:0,他引:2
86.
The optical-limiting property of an optically active phthalocyanine derivative with different configuration in chloroform solution was measured at 532 nm with 10 ns pulses. The excited state absorption cross-section σex of the derivative was determined with the Z-scan technique. The results showed that the phthalocyanine derivative possesses larger σex than the ground state absorption cross-section σ0, indicating that it is a material for reverse saturable absorption. And it is specially noticed that the change in the optically active configuration affects its optical-limiting property significantly. 相似文献
87.
KF-Al2O3催化合成2-甲基-1-苄基苯并咪唑 总被引:1,自引:0,他引:1
苯并咪唑类杂环化合物具有杀菌、消炎、抗癌、抗氧化的活性,广泛用于食品的防虫和防腐,用于动、植物病毒的防治,人体疾病和肿瘤的防治[1-3],本文用KF Al2O3作催化剂,用DMF为溶剂,利用2 甲基苯并咪唑与苄基溴反应合成2 甲基 1 苄基苯并咪唑的新型方法,考察了诸因素对产率的影响,找出了最佳的反应条件。合成路线如下:1 实验部分1 1 仪器与试剂Brurer AM 500超导核磁共振波谱仪(溶剂CDCl3);CarloErbal1106型元素分析仪,NicoletIm pact410型红外光谱仪,KBr压片,HP1100型和Finnigan FTMS 2000型质谱仪(以上均由华东理工大学分析… 相似文献
88.
89.
This study investigates the robust output tracking problem for a class of uncertain linear systems. The uncertainties are assumed to be time invariant and to satisfy the matching conditions. According to the selected nominal parameters, an optimal solution with a prescribed degree of stability is determined. Then, an auxiliary input via the use of an adapting factor, connected to the nominal optimal control, is introduced to guarantee the robustness and prescribed degree of stability for the output tracking control of the uncertain linear systems. This method is very simple and effective and can reject bounded uncertainties imposed on the states. A maglev vehicle model example is given to show its effectiveness. 相似文献
90.
A new scheme of optical film sensor is presented. The sensor is based on p-polarized reflectance, consisting of a sensing coated substrate, is easily optimized for maximum sensitivity in different applications. The resolutions of refractive index nf, extinction coefficient kf and thickness hf of the sensitive films are predicted to be 10−7, 10−5 and 10−3 nm, respectively. Experimentally, we selected the sol–gel derived SnO2 films as gas-sensitive films and conducted preliminary gas-sensing test. The results indicate that novel optical film sensor scheme has higher sensitivity, and the detection sensitivity is available to 10−1 ppm on the condition of optimum optical parameters and incident angle. 相似文献