全文获取类型
收费全文 | 177570篇 |
免费 | 16529篇 |
国内免费 | 9518篇 |
专业分类
电工技术 | 13994篇 |
技术理论 | 8篇 |
综合类 | 18145篇 |
化学工业 | 17789篇 |
金属工艺 | 7252篇 |
机械仪表 | 15996篇 |
建筑科学 | 20465篇 |
矿业工程 | 6778篇 |
能源动力 | 7868篇 |
轻工业 | 14026篇 |
水利工程 | 7579篇 |
石油天然气 | 8319篇 |
武器工业 | 2018篇 |
无线电 | 10141篇 |
一般工业技术 | 17178篇 |
冶金工业 | 7103篇 |
原子能技术 | 2540篇 |
自动化技术 | 26418篇 |
出版年
2024年 | 733篇 |
2023年 | 2178篇 |
2022年 | 4501篇 |
2021年 | 5223篇 |
2020年 | 5455篇 |
2019年 | 4578篇 |
2018年 | 4498篇 |
2017年 | 5486篇 |
2016年 | 6648篇 |
2015年 | 6988篇 |
2014年 | 11367篇 |
2013年 | 11405篇 |
2012年 | 13182篇 |
2011年 | 14517篇 |
2010年 | 10400篇 |
2009年 | 10607篇 |
2008年 | 9952篇 |
2007年 | 11940篇 |
2006年 | 10370篇 |
2005年 | 8725篇 |
2004年 | 7364篇 |
2003年 | 6297篇 |
2002年 | 5075篇 |
2001年 | 4185篇 |
2000年 | 3574篇 |
1999年 | 2987篇 |
1998年 | 2554篇 |
1997年 | 2172篇 |
1996年 | 1773篇 |
1995年 | 1469篇 |
1994年 | 1316篇 |
1993年 | 982篇 |
1992年 | 910篇 |
1991年 | 675篇 |
1990年 | 571篇 |
1989年 | 484篇 |
1988年 | 404篇 |
1987年 | 277篇 |
1986年 | 238篇 |
1985年 | 219篇 |
1984年 | 254篇 |
1983年 | 239篇 |
1982年 | 198篇 |
1981年 | 97篇 |
1980年 | 94篇 |
1979年 | 66篇 |
1978年 | 53篇 |
1977年 | 47篇 |
1976年 | 43篇 |
1959年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Poly(ethylene aspartate) [PEA] was synthesized by the melt condensation of D,L-aspartic acid and ethylene glycol. PEA containing pendent amino and carbonyl groups in its repeating chain was used as the polymeric ligand for complexation with transition metal ions, viz. Co(II), Ni(II), Cu(II), Mn(II), Zn(II), Cd(II), Ca(II), Mg(II), Pb(II) and Hg(II). Complexation was found to be most effective in DMSO. The resulting polyester-metal complexes were solid coloured materials which have been characterized by IR spectroscopy, elemental analysis and magnetic susceptibility measurements. The thermal stability of the polyester-metal complexes was investigated by thermogravimetric analysis (TGA). On the basis of the physico-chemical studies, an oxygen and nitrogen coordinated structure for the polyester-metal complexes is proposed. 相似文献
72.
Batch process industries are characterized by complex precedence relationships between operations, which renders the estimation
of an acceptable workload very difficult. A detailed schedule based model can be used for this purpose, but for large problems
this may require a prohibitive large amount of computation time. We propose a regression based model to estimate the makespan
of a set of jobs. We extend earlier work based on deterministic processing times by considering Erlang-distributed processing
times in our model. This regression-based model is used to support customer order acceptance. Three order acceptance policies
are compared by means of simulation experiments: a scheduling policy, a workload policy and a regression policy. The results
indicate that the performance of the regression policy can compete with the performance of the scheduling policy in situations
with high variety in the job mix and high uncertainty in the processing times.
Correspondence to: C.V. Ivanescu 相似文献
73.
柴油机低频排气噪声规律分析 总被引:4,自引:0,他引:4
针对柴油机(4-85)低频排气噪声,对其产生机理、规律及其影响因素等作了理论计算、分析及实验。对低频排气噪声信号进行频域分析后可知,其主要由一系列离散的谐波组成,是以柴油机点火频率为基频的一种类周期性噪声,有可能应用有源噪声控制技术。 相似文献
74.
Cluster analysis in industrial market segmentation through artificial neural network 总被引:6,自引:0,他引:6
Market segmentation has commonly applied cluster analysis. This study intends to make the comparison of conventional two-stage method with proposed two-stage method through the simulated data. The proposed two-stage method is the combination of self-organizing feature maps and K-means method. The simulation results show that the proposed scheme is better than the conventional two-stage method based on the rate of misclassification. 相似文献
75.
盖层封闭能力的灰聚类评价方法 总被引:5,自引:1,他引:4
提出灰聚类评价方法,用于盖层封闭能力定量评价。所有被评价对象构成聚类对象集,所有评价指标构成评价指标集,所划分的盖层封闭能力等级构成聚类的灰类集,按照最大聚类权确定对象所属的灰类,即盖层的封闭能力级别。评价流程是:确定指标灰类模式→数据预处理→利用聚类公式计算→利用最大聚类权准则抉择。这种方法避免了加法评分法要依靠人的主观经验划定总评分值的问题,而且由于把评价对象视为“灰”的,具有处理边缘信息的能力。以琼东南盆地3个主要探区的盖层封闭性评价为例,介绍了灰聚类评价的具体应用方法。灰聚类评价方法同样可用于储集层评价、圈闭评价等地质问题的定量研究。表2参3(王孝陵摘 相似文献
76.
中针对变井储试井分析问题,给出了确定变井储系数及计算续流量的方法,并用反褶积分析积分析方法解释了未出现径向流的早期测压数据,给出了解决早期试井资料分析问题的有效方法。 相似文献
77.
段群章 《有色金属材料与工程》1993,(1)
本文评述了近年来苯基荧光酮类试剂在金属及合金光度分析中应用的发展状况,显色反应的条件,以及相应光度分析方法的检测限和测定范围等。参考文献87篇。 相似文献
78.
本文提出了用一个标样进行系列试样 X 射线定量相分析的方法.它克服了一般 X 射线定量方法需要混合研磨和手续烦复的缺点以及无标样 X 射线定量方法存在病态方程不易解决的问题.该方法对常规 X 射线定量分析具有普遍的实用性. 相似文献
79.
Macroscopic analysis of design processes based on a scheme for coding designers' cognitive actions 总被引:1,自引:0,他引:1
We have devised a new scheme for coding designers' cognitive actions from video/audio design protocols. Designers' actions are coded into four cognitive levels; physical, perceptual, functional and conceptual. Relations between actions belonging to different levels, such as dependencies and triggering relations, are also coded. The present scheme has two benefits. First, we found that design actions are definable in a systematic way using the vocabulary of the scheme, and thus a designer's cognitive behaviours in each of local design stages is represented as a structure composed of defined primitive actions. This is expected to lay the foundation for microscopic analyses of how particular types of actions contribute to the formation of key design ideas. Second, this scheme is suitable for macroscopic analyses of how designers cognitively interact with their own sketches. We examined, for a practising architect, the ways in which drawing, inspection of drawings, perception, and functional thoughts correlated with one another in his design process. The findings suggest that design sketches serve not only as external memory or as a provider of visual cues for association of non-visual information, but also as a physical setting in which design thoughts are constructed on the fly. 相似文献
80.
The interaction of different metal oxides such as Co3O4, NiO, Al2O3, Cr2O3, Fe2O3 and SiO2 with Na2SO4 at a temperature of 1100 and 1200 K in flowing oxygen has been studied. The thermogravimetric studies for each system were
carried out as a function of Na2SO4 in the mixture. The presence of different constituents in the reaction products were identified by X-ray diffraction analysis
and the morphologies of the reaction products were characterized using metallography and scanning electron microscopy (SEM).
The formation of products was also investigated by thermodynamic computation of free energies of the reactions and the study
of relevant equilibrium phase diagrams. The soluble species in the aqueous solutions of the reaction products were determined
quantitatively using atomic absorption spectrophotometry.
The high temperature interaction products usually contain a 3-phase structure namely, Na2O·M2O
x
, M2O
x
and metal sulphide and/or metal sulphate. The formation of Na2O·M2O
x
depends upon the solid state solubility of metal oxide in the molten salt at high temperatures. Under limited solubility
conditions Na2O·M2O
x
is invariably formed, but as soon as this condition is relaxed the oxide. M2O
x
, precipitates and forms a separate phase. 相似文献