全文获取类型
收费全文 | 47730篇 |
免费 | 4821篇 |
国内免费 | 2401篇 |
专业分类
电工技术 | 2967篇 |
综合类 | 4949篇 |
化学工业 | 6411篇 |
金属工艺 | 1627篇 |
机械仪表 | 2549篇 |
建筑科学 | 6980篇 |
矿业工程 | 2035篇 |
能源动力 | 2300篇 |
轻工业 | 2350篇 |
水利工程 | 1958篇 |
石油天然气 | 2940篇 |
武器工业 | 625篇 |
无线电 | 4272篇 |
一般工业技术 | 3670篇 |
冶金工业 | 3115篇 |
原子能技术 | 706篇 |
自动化技术 | 5498篇 |
出版年
2024年 | 163篇 |
2023年 | 533篇 |
2022年 | 1021篇 |
2021年 | 1221篇 |
2020年 | 1385篇 |
2019年 | 1278篇 |
2018年 | 1208篇 |
2017年 | 1617篇 |
2016年 | 1864篇 |
2015年 | 1906篇 |
2014年 | 2787篇 |
2013年 | 2833篇 |
2012年 | 3349篇 |
2011年 | 3612篇 |
2010年 | 2721篇 |
2009年 | 2786篇 |
2008年 | 2631篇 |
2007年 | 3177篇 |
2006年 | 2940篇 |
2005年 | 2383篇 |
2004年 | 1970篇 |
2003年 | 1798篇 |
2002年 | 1525篇 |
2001年 | 1305篇 |
2000年 | 1029篇 |
1999年 | 853篇 |
1998年 | 608篇 |
1997年 | 557篇 |
1996年 | 449篇 |
1995年 | 416篇 |
1994年 | 372篇 |
1993年 | 244篇 |
1992年 | 224篇 |
1991年 | 150篇 |
1990年 | 153篇 |
1989年 | 112篇 |
1988年 | 82篇 |
1987年 | 74篇 |
1986年 | 52篇 |
1985年 | 164篇 |
1984年 | 254篇 |
1983年 | 289篇 |
1982年 | 210篇 |
1981年 | 323篇 |
1980年 | 125篇 |
1979年 | 45篇 |
1978年 | 40篇 |
1977年 | 13篇 |
1975年 | 23篇 |
1974年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Full-profile neutron powder diffraction structure refinements of dioxotrilead(II)tetraoxosulfate(VI) at 2 and 45K reveal that both the alpha- and the gamma-Pb3O2 (SO4) polymorphs have to be refined simultaneously at these temperatures. Accordingly, the paraelastic alpha phase is trapped in the ferroelastic gamma phase, yielding thus mixtures of both compounds in a nearly 1:1 molar ratio. Both structures are essentially similar. The slight variations of the lead-oxygen distances in the infinite edge-sharing tetrahedral (Pb3 O2)n double-chains force the sulfate group to adopt nearly C3v and C2v site symmetries respectively in the alpha and gamma phases. The present work is a good example of the behaviour of the DBW3.2 program (1) when mixtures of very similar structures are refined simultaneously (high correlation between some structural parameters). 相似文献
92.
指出当今建筑业良好的市场给建筑师们提供了展示自己作品的广大空间 ,但其精品却为之甚少。为此 ,对建筑业存在的一些问题及制约建筑师出精品的主、客观因素进行了分析 ,指出建筑师应提高自身素质 ,树立精品意识 ,增强市场竞争能力 相似文献
93.
土壤固化剂无侧限抗压强度试验研究 总被引:3,自引:0,他引:3
针对山西省长治市石子河河道处理问题 ,采用固化剂粘土进行了无侧限抗压强度试验 ,并与水泥土进行了比较。发现固化剂 2的无侧限抗压试验强度最佳 ,为工地现场试验及河道综合治理提供了更为有力的理论依据 相似文献
94.
boundary conditions. A cell structure which is independent to the nodes is used to evaluate the integrals of EFG 相似文献
95.
tific Experiment Center of Guangxi Medical University,Nanning 530021,China)Objective:To investigate the mutation pattern of adenomatous polyposis coli(APC),Kirsten-ras(K-ras) and p53 genes in sporadic colorectal cancer tissues.Meth 相似文献
96.
The equations for predicting the number-average molecular weight are derived on the basis of the three stage polymerization model (TSPM) in this paper. By applying the equations, a plotting approach is proposed to determine the apparent initiator efficiency defined as f[(αtd+1)/2] and the constant of chain transfer to monomer, where f is the initiator efficiency and αtd denotes the fraction of the termination rate constants by disproportionation. Using the approach to plot the experimental data in the literature, it is found that the chain transfer to monomer can be neglected for both methylmethacrylate (MMA) and styrene (St) polymerizations, but it can exert a significant effect on ethylmethacrylate (EMA) polymerization. In addition, the apparent initiator efficiency is found to be independent of reaction temperature and initiator concentration at each stage. The values of f[(αtd+1)/2] at gel effect stage are slightly reduced as compared with that at low conversion stage for MMA and EMA polymerizations. However, it decreases significantly at gel effect stage for St polymerization. Using the equations derived and the apparent initiator efficiencies obtained from TSPM plots, the number-average molecular weights at different conversions can be predicted. Comparisons show that the agreement between predictions and experimental data is satisfactory. 相似文献
97.
98.
Optimizing of laminar viscous flow through a pipe by two dimensionless values is investigated analytically. Dimensionless entropy generation and pumping power to heat transfer rate ratio are used as basis for constant viscous and the temperature dependence on the viscosity. For this matter we calculate entropy generation and pumping power for a fully developed in a pipe subjected to constant wall temperature for either constant viscosity and the variable viscosity. The variation entropy generation increase along the pipe length for viscous fluid is drawn, either the variation summation dimensionless entropy generation and the pumping power to heat transfer rate ratio are varying the fluid inlet temperature for fixed pipe length and are varying pipe length for fixed fluid inlet temperature are drawn. For low heat transfer conditions the entropy generation due to viscosity friction becomes dominant and the dependence of viscosity with the temperature becomes essentially important to be considered. 相似文献
99.
The 226Ra and 228Ra content of the lichens Umbilicaria cylindrica, U. deusta, U. murina and U. hirsuta has been determined as a function of the growth altitude above sea level, based on data derived from material collected from localities in southwest Poland. These data are interpreted as graphs and formulae to show the influence of environmental factors, particularly altitude, on the concentration of 226Ra and 228Ra, and the coefficients of accumulation calculated. 相似文献
100.
以Takens嵌入定理和影子定理为理论依据,提出一种能对混沌信号去噪的局部投影方法。该方法不需潜在动力学系统的先验知识,符合工程实用的要求。通过实验结果表明这种方法对混沌信号去噪很有效。 相似文献