全文获取类型
收费全文 | 16004篇 |
免费 | 2605篇 |
国内免费 | 1988篇 |
专业分类
化学 | 8027篇 |
晶体学 | 226篇 |
力学 | 751篇 |
综合类 | 126篇 |
数学 | 1171篇 |
物理学 | 4087篇 |
无线电 | 6209篇 |
出版年
2024年 | 44篇 |
2023年 | 339篇 |
2022年 | 494篇 |
2021年 | 662篇 |
2020年 | 644篇 |
2019年 | 641篇 |
2018年 | 567篇 |
2017年 | 609篇 |
2016年 | 738篇 |
2015年 | 870篇 |
2014年 | 1007篇 |
2013年 | 1307篇 |
2012年 | 1468篇 |
2011年 | 1440篇 |
2010年 | 1124篇 |
2009年 | 1090篇 |
2008年 | 1137篇 |
2007年 | 991篇 |
2006年 | 857篇 |
2005年 | 777篇 |
2004年 | 592篇 |
2003年 | 477篇 |
2002年 | 410篇 |
2001年 | 353篇 |
2000年 | 280篇 |
1999年 | 281篇 |
1998年 | 170篇 |
1997年 | 166篇 |
1996年 | 172篇 |
1995年 | 143篇 |
1994年 | 110篇 |
1993年 | 118篇 |
1992年 | 92篇 |
1991年 | 77篇 |
1990年 | 66篇 |
1989年 | 55篇 |
1988年 | 26篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 26篇 |
1984年 | 15篇 |
1983年 | 20篇 |
1982年 | 15篇 |
1981年 | 8篇 |
1980年 | 13篇 |
1977年 | 5篇 |
1976年 | 10篇 |
1975年 | 9篇 |
1973年 | 8篇 |
1972年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 855 毫秒
91.
§ 1 IntroductionConsiderthefollowingnonlinearoptimizationproblem :minimizef(x)subjecttoC(x) =0 , a≤x≤b ,( 1 .1 )wheref(x) :Rn→R ,C(x) =(c1(x) ,c2 (x) ,...,cm(x) ) T:Rn→Rm aretwicecontinuouslydifferentiable,m≤n ,a ,b∈Rn.Trustregionalgorithmsareveryeffectiveforsolvingnonlinearoptimi… 相似文献
92.
93.
The dendrite growth process of transparent NaBi(WO4)2 with small prandtl and high melting point was studied by using the in-situ observation system. According to the dynamic images and detailed information, there are two kinds of restriction effect on
the dendrite growth, the competition between arms and branches and the convection in the melt. The dendrite growth rate was
time dependent, and the rate of arm growth reached the maximum 5.8 mm/s in the diffusive-advective region and rapidly decreased
in the diffusive-convective region. The growth rate of branch had the same change trends as the arm’s. Based on the EPMA-EDS
data of solidification structure of quenched NaBi(WO4)2 melt, it was found that there were component differences from stoichiometric concentration in the melt near the interface
during the growth process.
Supported by the National Natural Science Foundation of China (Grant No. 50331040) and the Innovation Funds from Shanghai
Institute of Ceramics, Chinese Academy of Sciences (Grant No. SCX0623) 相似文献
94.
Crosslinking behaviors of acrylonitrile butadiene rubber (NBR)/poly (vinyl chloride) (PVC) alloy, filled with anhydrous copper sulfate (CuSO4) particles, were investigated for the first time by dynamic mechanical analysis (DMA) under hetero and isothermal modes, respectively. In the heterothermal testing, (NBR/PVC)/CuSO4 compound showed two marked increases in the storage modulus (E′), corresponding to coordination crosslinking of NBR-CuSO4 and self-crosslinking of NBR and PVC respectively. During the isothermal testing, a dramatic increase in E′ was found at the initial stage while that of original NBR/PVC alloy was not detected. The marked increase in E′ of (NBR/PVC)/CuSO4 compound was mainly due to the crosslinking induced by coordination between CN and Cu2+. The increasing extent of E′ increased with the rise of CuSO4 content, suggesting the formation of a greater number of crosslinks. Moreover, the activation energy (Ea) of crosslinking process was about 139 kJ/mol. In this work, fourier transform infrared spectrum (FT-IR) and equilibrium swelling method were also performed for the characterization of the compound. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 41–51, 2007 相似文献
95.
艾滋病防治资源投入的效果分析 总被引:1,自引:1,他引:0
基于GOALS模型的基本思想,建立了效果分析模型,并针对两种不同的资金分配方案,模拟了两种方案对2006—2010年某地艾滋病流行的影响,并对模拟结果进行了分析. 相似文献
96.
97.
p型未掺杂富锌ZnO薄膜的形成和性能研究 总被引:1,自引:1,他引:0
以高纯ZnO为靶材,氩气为溅射气体,利用射频磁控溅射技术在石英衬底上生长出纤锌矿结构的富锌ZnO薄膜.薄膜沿(002)择优取向生长,厚约为1.2μm,呈现电绝缘特性.将溅射的ZnO薄膜在10-3Pa,510~1 000 K的温度范围等温退火1 h,室温Hall测量结果表明ZnO薄膜的导电性能经历了由绝缘—n型—p型—n型半导体的变化.XPS测试表明ZnO薄膜的Zn/O离子比随退火温度的升高而降低,但一直是富锌ZnO,说明未掺杂的富锌ZnO也可以形成p型导电.p型未掺杂富锌ZnO薄膜的形成可归因于VZn受主浓度可以克服VO和Zni本征施主的补偿效应. 相似文献
98.
本主要介绍原木经销商在周期内原木变价销售情况下的最佳期初贮存量的决策方法,在建立期望机会成本的数学模型基础上,探讨原木随机存贮策略的最优化问题。 相似文献
99.
Tian Le LIN Bao Zhen YAN Gao Fei HU Mei WANG 《中国化学快报》2006,17(7):937-940
Complex formation between aluminium and quercetin(Q) in methanol was investigated by means of 27^Al solid-state, 13^C and 1^H NMR and MS(ESI), UV and IR spectra. Formation of the 1:2 complex was favored in methanol relative to all other solvent and the predominant species observed of Al(Ⅲ) has a 1:2 stoichiometry. The fine structure of 1:2 aluminum complex of quercetin was that the aluminum central atom chelated with two quereetin molecules and two methoxyl groups between two five membered rings, its coordination is six, the chelated site was 3-hydroxy-4-carbonyl. 相似文献
100.
Howel Tong 《应用数学学报(英文版)》2002,18(2):177-184
Abstract I reflect upon the development of nonlinear time series analysis since 1990 by focusing on five majorareas of development. These areas include the interface between nonlinear time series analysis and chaos,thenonparametric/semiparametric approach,nonlinear state space modelling,financial time series and nonlinearmodelling of panels of time series. 相似文献