全文获取类型
收费全文 | 23149篇 |
免费 | 2939篇 |
国内免费 | 2467篇 |
专业分类
电工技术 | 2034篇 |
技术理论 | 2篇 |
综合类 | 3007篇 |
化学工业 | 1852篇 |
金属工艺 | 2300篇 |
机械仪表 | 1441篇 |
建筑科学 | 1547篇 |
矿业工程 | 1003篇 |
能源动力 | 523篇 |
轻工业 | 530篇 |
水利工程 | 452篇 |
石油天然气 | 513篇 |
武器工业 | 249篇 |
无线电 | 2593篇 |
一般工业技术 | 2761篇 |
冶金工业 | 1276篇 |
原子能技术 | 169篇 |
自动化技术 | 6303篇 |
出版年
2024年 | 42篇 |
2023年 | 336篇 |
2022年 | 576篇 |
2021年 | 784篇 |
2020年 | 849篇 |
2019年 | 721篇 |
2018年 | 629篇 |
2017年 | 792篇 |
2016年 | 839篇 |
2015年 | 985篇 |
2014年 | 1591篇 |
2013年 | 1634篇 |
2012年 | 1766篇 |
2011年 | 1889篇 |
2010年 | 1405篇 |
2009年 | 1412篇 |
2008年 | 1338篇 |
2007年 | 1626篇 |
2006年 | 1435篇 |
2005年 | 1209篇 |
2004年 | 997篇 |
2003年 | 864篇 |
2002年 | 704篇 |
2001年 | 631篇 |
2000年 | 577篇 |
1999年 | 428篇 |
1998年 | 368篇 |
1997年 | 347篇 |
1996年 | 286篇 |
1995年 | 276篇 |
1994年 | 267篇 |
1993年 | 169篇 |
1992年 | 157篇 |
1991年 | 150篇 |
1990年 | 118篇 |
1989年 | 108篇 |
1988年 | 68篇 |
1987年 | 26篇 |
1986年 | 16篇 |
1985年 | 20篇 |
1984年 | 20篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1976年 | 3篇 |
1959年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
81.
According to the definition of spectral integral,a new spectral characteristic parameter,with the name Reversed Spectral Absorption Integral(RSAI),is proposed and used to retrieve the chromium content based on the Partial Least Squares Regression(PLSR) model.The contrastive study with other traditional spectral characteristic parameters,including differential transformation,inverse transformation,absorption area,etc.indicates that(1) the first derivation of square root transformed model can predict the chromium content quantitatively in terms of spectral transformations.(2) the stability of the absorption area model is slightly poor,and the chromium content of samples can only be estimated roughly.(3) However,as to the inversed spectral absorption integral model,the adjustment determination coefficient(Ad-R2) of the modeling and verification is 0.73 and 0.77,while the Root Mean Squared Error(RMSE) is 2.63 mg/kg and 2.36 mg/kg respectively with Relative Percent Deviation(RPD) being 3.21,which shows that the RSAI model has excellent prediction ability.So,the inversed spectral absorption integral new model can improve the accuracy and stability used to retrieve the chromium content,which provides a new idea for monitoring the chromium contamination in soil. 相似文献
82.
83.
目前网络上的服装图像数量增长迅猛,对于大量服装图像实现智能分类的需求日益增加。将基于区域的全卷积网络(Region-Based Fully Convolutional Networks,R-FCN)引入到服装图像识别中,针对服装图像分类中网络训练时间长、形变服装图像识别率低的问题,提出一种新颖的改进框架HSR-FCN。新框架将R-FCN中的区域建议网络和HyperNet网络相融合,改变图片特征学习方式,使得HSR-FCN可以在更短的训练时间内达到更高的准确率。在模型中引入了空间转换网络,对输入服装图像和特征图进行了空间变换及对齐,加强了对多角度服装和形变服装的特征学习。实验结果表明,改进后的HSR-FCN模型有效地加强了对形变服装图像的学习,且在训练时间更短的情况下,比原来的网络模型R-FCN平均准确率提高了大约3个百分点,达到96.69%。 相似文献
84.
85.
为获得高性能NiTi基记忆合金复合材料,通过熔炼、锻造、拔丝等手段获得一种NiTi-W原位复合材料。利用SEM扫描电镜观察材料显微组织;DSC测试材料的马氏体相变行为;利用WDT II-20万能拉伸试验机测试材料的力学性能。SEM分析结果显示,拔丝加工使W纤维直径细化至几微米,甚至亚微米级别,在NiTi基体中沿拔丝方向一致排布。DSC测试结果显示,材料经不同温度退火后展现出复杂的可逆马氏体相变行为,在某些升、降温曲线上出现多个吸放热峰现象。拉伸测试结果显示,600 ℃退火样品经适当的预拉伸变形后,屈服强度会大大增加,由~200 MPa提升到~800 MPa,断裂应力超过1 GPa,断裂应变高达40%,材料展现出优秀的线性超弹性,是一种集高强度、高塑性、高线性超弹性于一身的高性能材料。 相似文献
86.
Jing Ji Suping Fang Zhengyuan Shi Qing Xia Yibao Li 《Color research and application》2020,45(6):1023-1039
A well-known color characterization method is to take an image of a color chart and then to find the mapping matrix from the digital RGBs to the corresponding known CIEXYZs. However, the prediction errors are generally large in CIELAB color space because of the nonlinear transformation from CIEXYZs to CIELABs. In this article, we propose an efficient and simple nonlinear method for the color characterization of input devices. The approach for deriving a colorimetric mapping between digital RGB signals and CIELAB tristimulus values uses the polynomial modeling by considering the interrelations among the standard CIE color spaces. Furthermore, to improve the accuracy of solution, we take the polynomial root terms extension. Our algorithm is simple to implement because only a least-squares mapping should be solved. Various computational results are given to demonstrate the efficiency and capability of the proposed method. 相似文献
87.
《Ceramics International》2020,46(5):5968-5975
Using constant pressure ab initio calculations, we probe the high-pressure modifications in amorphous boron suboxide (B6O) consisting of glassy boron trioxide (B2O3) and boron (B) domains up to a theoretical pressure of 100 GPa. At this pressure, the structure remains amorphous. We find a steady increase in the average coordination of both B and oxygen (O) atoms. O atoms mostly attain threefold coordination as in B2O3 glass at high pressures. On the other hand, the mean coordination number of B-atoms reaches six at high pressures and the structural changes in B-rich regions are perceived to be quite analogous to those of amorphous B. B12 clusters are found to persevere during the pressurizing process and the high-pressure modifications occur predominantly around O-atoms and the regions that connect the pentagonal pyramid-like motifs to each other. Upon pressure release, some high-pressure configurations persist in the model and another noncrystalline structure being about 10% denser than the original state is recovered, suggesting a permanent densification and a possible irreversible amorphous-to-amorphous phase transformation in B6O. The recovered network shows slightly better mechanical properties than the uncompressed model. During the compression and decompression processes, amorphous B6O remains semiconducting. The delocalization of some band tail states is seen at high pressures. 相似文献
88.
Kevin J. Hanley 《International journal for numerical methods in engineering》2020,121(21):4865-4877
An algorithm is presented for discrete element method simulations of energy-conserving systems of frictionless, spherical particles in a reversed-time frame. This algorithm is verified, within the limits of round-off error, through implementation in the LAMMPS code. Mechanisms for energy dissipation such as interparticle friction, damping, rotational resistance, particle crushing, or bond breakage cannot be incorporated into this algorithm without causing time irreversibility. This theoretical development is applied to critical-state soil mechanics as an exemplar. It is shown that the convergence of soil samples, which differ only in terms of their initial void ratio, to the same critical state requires the presence of shear forces and frictional dissipation within the soil system. 相似文献
89.
《Calphad》2020
The sodium pyrovanadate (Na4V2O7) powder was synthesized by solid-state reaction using sodium carbonate (Na2CO3) and vanadium pentoxide (V2O5) as raw materials. X-ray powder diffraction (XRD), scanning electron microscope (SEM), and differential scanning calorimeter (DSC) were used to accurately characterize the synthesized sample. The solid-state phase transformation from α-Na4V2O7 to β-Na4V2O7 occurs at the temperature 696 K and the enthalpy is equals to 1.03 ± 0.01 kJ/mol, the endothermic effect at 931 K and the enthalpy is equals to 31.35 ± 0.31 kJ/mol, which is related to the melting of Na4V2O7. The high-temperature heat capacity of Na4V2O7 was measured using a Multi-high temperature calorimeter 96 line and DSC. The obtained high-temperature heat capacity of Na4V2O7, as a function of temperature, was modeled as: Cp=314.62+0.05T-5494390T-2 J·mol-1·K-1 (298.15-873 K). The temperature dependence on heat capacity was then used for computing changes in the enthalpy, entropy, and Gibbs free energy at the specific temperature internal. 相似文献
90.
The kinetics of lath martensite formation in Fe–17·3 wt-%Cr–7·1 wt-%Ni–1·1 wt-%Al–0·08 wt-%C stainless steel was investigated with magnetometry and microscopy. Lath martensite forms during cooling, heating and isothermally. For the first time, it is shown by magnetometry during extremely slow isochronal cooling that transformation rate maxima occur, which are interrupted by virtually transformation free temperature regions. Microscopy confirms martensite formation after athermal nucleation of clusters followed by their time dependent growth. The observations are interpreted in terms of time dependent autocatalytic lath martensite formation followed by mechanical stabilisation of austenite during the transformation process. 相似文献