全文获取类型
收费全文 | 26816篇 |
免费 | 3407篇 |
国内免费 | 2222篇 |
专业分类
电工技术 | 1908篇 |
技术理论 | 1篇 |
综合类 | 3603篇 |
化学工业 | 1385篇 |
金属工艺 | 733篇 |
机械仪表 | 2371篇 |
建筑科学 | 4486篇 |
矿业工程 | 1501篇 |
能源动力 | 577篇 |
轻工业 | 826篇 |
水利工程 | 1102篇 |
石油天然气 | 916篇 |
武器工业 | 472篇 |
无线电 | 3103篇 |
一般工业技术 | 2229篇 |
冶金工业 | 1148篇 |
原子能技术 | 256篇 |
自动化技术 | 5828篇 |
出版年
2024年 | 122篇 |
2023年 | 420篇 |
2022年 | 726篇 |
2021年 | 814篇 |
2020年 | 915篇 |
2019年 | 738篇 |
2018年 | 736篇 |
2017年 | 842篇 |
2016年 | 1002篇 |
2015年 | 1051篇 |
2014年 | 1748篇 |
2013年 | 1610篇 |
2012年 | 2089篇 |
2011年 | 2121篇 |
2010年 | 1711篇 |
2009年 | 1724篇 |
2008年 | 1725篇 |
2007年 | 1992篇 |
2006年 | 1663篇 |
2005年 | 1549篇 |
2004年 | 1245篇 |
2003年 | 1043篇 |
2002年 | 832篇 |
2001年 | 749篇 |
2000年 | 639篇 |
1999年 | 509篇 |
1998年 | 384篇 |
1997年 | 325篇 |
1996年 | 243篇 |
1995年 | 215篇 |
1994年 | 235篇 |
1993年 | 137篇 |
1992年 | 100篇 |
1991年 | 81篇 |
1990年 | 67篇 |
1989年 | 67篇 |
1988年 | 49篇 |
1987年 | 32篇 |
1986年 | 26篇 |
1985年 | 28篇 |
1984年 | 28篇 |
1983年 | 10篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1961年 | 6篇 |
1959年 | 8篇 |
1956年 | 5篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
Saudino Kimberly J.; Wertz Annie E.; Gagne Jeffrey R.; Chawla Sonia 《Canadian Metallurgical Quarterly》2004,87(5):698
Twin studies suggest that parent ratings of temperament exaggerate differences between twins. The present study examined whether such contrast effects also operate for nontwin siblings. The activity level (AL) and shyness of 95 nontwin sibling pairs (ages 3 to 8 years) were assessed via parent ratings and objective measures (actigraph and observer ratings). Siblings showed no resemblance in either parent-rated AL or shyness; however, sibling resemblance for actigraph AL and observer-rated shyness was substantial. Thus, parents do contrast their nontwin siblings when rating these 2 temperament dimensions. Moreover, the importance of sibling differences in temperament to the sibling relationship and differential maternal treatment varied across the different measures of AL and shyness, suggesting that parent perceptions may play a role in these associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
24.
The role of Nb2O5 and γ-Al2O3 oxide supports on the ammoxidation of propane on supported mixed Sb–V oxide at different Sb+V surface coverages is studied. Sb and V oxide species on alumina and on niobia support show different structural features that reflect in different performance during the ammoxidation of propane to acrylonitrile. Niobia-supported catalysts are much more selective to acrylonitrile than alumina-supported ones. Alumina interacts weakly with the supported oxides while niobia forms new phases through solid state reactions with the supported oxides during catalytic operation that must account for its higher selectivity values towards acrylonitrile and higher specific rate of acrylonitrile formation per vanadium site. 相似文献
25.
The scale along the coordinate axes in the equations of motion hitherto used for an H-maser (in relative units) is shown to depend on Q as the quality factor for an H-maser. This hinders both analysis of the operation of the H-maser and optimization of its parameters. The modified equations of motion proposed here do not have that shortcoming. We determine the atomic flux into the bulb that gives the H-maser the best metrological characteristics. 相似文献
26.
通过对减振器结构设计的理论分析,建立了减振器的数学模型,同时通过设计的模拟装置对减振效果进行了实测,效果良好。 相似文献
27.
用保角变换法对共面波导金属厚度效应进行了理论分析,编制了相应的计算机程序,给出了数值解,并对此进行了多元曲线拟合,导出了考虑金属厚度后的形状比k、有效介电常数、特征阻抗、损耗的闭定表达式。用此修正表达式求得特征阻抗及损耗的数值解,并与K.C.格普塔的修正值及实验测量值进行了详细比较,结果表明此修正公式与实验值相符较好。 相似文献
28.
S V Bhat 《Bulletin of Materials Science》1994,17(7):1271-1285
When examined using continuous wave electron paramagnetic resonance and nuclear magnetic resonance spectrometers, the highT
c superconductors give rise to intense, low field, ‘non-resonant’ absorption signals in the superconducting state. This phenomenon
can be used as a highly sensitive, contactless technique for the detection and characterization of superconductivity even
in samples containing only minute amounts of the superconducting phase. Further, it can also be applied to the determination
of material parameters of interest such asJ
c andH
c2 in addition to being a powerful way of distinguishing between weak-link superconductivity and bulk superconductivity. The
details of these aspects are discussed. 相似文献
29.
30.
Estimating the state of a nonlinear stochastic system (observed through a nonlinear noisy measurement channel) has been the goal of considerable research to solve both filtering and control problems. In this paper, an original approach to the solution of the optimal state estimation problem by means of neural networks is proposed, which consists in constraining the state estimator to take on the structure of a multilayer feedforward network. Both non-recursive and recursive estimation schemes are considered, which enable one to reduce the original functional problem to a nonlinear programming one. As this reduction entails approximations for the optimal estimation strategy, quantitative results on the accuracy of such approximations are reported. Simulation results confirm the effectiveness of the proposed method. 相似文献