全文获取类型
收费全文 | 13661篇 |
免费 | 339篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 191篇 |
综合类 | 12篇 |
化学工业 | 3014篇 |
金属工艺 | 224篇 |
机械仪表 | 283篇 |
建筑科学 | 643篇 |
矿业工程 | 97篇 |
能源动力 | 375篇 |
轻工业 | 966篇 |
水利工程 | 130篇 |
石油天然气 | 162篇 |
武器工业 | 1篇 |
无线电 | 828篇 |
一般工业技术 | 2001篇 |
冶金工业 | 3309篇 |
原子能技术 | 138篇 |
自动化技术 | 1647篇 |
出版年
2022年 | 116篇 |
2021年 | 168篇 |
2020年 | 143篇 |
2019年 | 159篇 |
2018年 | 179篇 |
2017年 | 178篇 |
2016年 | 203篇 |
2015年 | 164篇 |
2014年 | 225篇 |
2013年 | 805篇 |
2012年 | 440篇 |
2011年 | 617篇 |
2010年 | 398篇 |
2009年 | 434篇 |
2008年 | 560篇 |
2007年 | 546篇 |
2006年 | 536篇 |
2005年 | 444篇 |
2004年 | 360篇 |
2003年 | 357篇 |
2002年 | 370篇 |
2001年 | 235篇 |
2000年 | 229篇 |
1999年 | 247篇 |
1998年 | 212篇 |
1997年 | 228篇 |
1996年 | 237篇 |
1995年 | 240篇 |
1994年 | 243篇 |
1993年 | 290篇 |
1992年 | 245篇 |
1991年 | 184篇 |
1990年 | 201篇 |
1989年 | 214篇 |
1988年 | 169篇 |
1987年 | 214篇 |
1986年 | 203篇 |
1985年 | 247篇 |
1984年 | 223篇 |
1983年 | 201篇 |
1982年 | 180篇 |
1981年 | 189篇 |
1980年 | 161篇 |
1979年 | 179篇 |
1978年 | 180篇 |
1977年 | 136篇 |
1976年 | 142篇 |
1975年 | 172篇 |
1974年 | 133篇 |
1973年 | 132篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Sausen Kenneth P.; Lovallo William R.; Pincomb Gwendolyn A.; Wilson Michael F. 《Canadian Metallurgical Quarterly》1992,11(1):55
Examined hemodynamic responses to systematic variations in occupational stress using ambulatory blood pressure monitors. Heart rate, systolic blood pressure, diastolic blood pressure, rate–pressure product, and mood states were measured before, during, and after low-stress (lecture) and high-stress (examination) work in 44 healthy White male medical students. The lecture day was characterized by stable patterns of cardiovascular activity across all 3 periods. Hemodynamic activity and reports of activation and distress were greater on the examination day than on the lecture day. Cardiovascular activity during the pre-examination period was as high as that seen during the examination period itself, indicating an anticipatory stress effect. Pressor activity decreased after the examination, although some residual chronotropic activity was seen. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
72.
Grossman Frances K.; Pollack William S.; Golding Ellen 《Canadian Metallurgical Quarterly》1988,24(1):82
This study looked at the quality and quantity of interactions between fathers and their firstborn 5-year-olds from the perspective of the family as a developmental interdependent system. The goals were to identify predictors of men's parenting from men's own adaptation (direct effects) and from their wives' characteristics (indirect effects), both measured during the expectancy. Twenty-three families from the Boston University Pregnancy and Parenthood Project made up the sample. Measures included self-report scales, observations, and semistructured interviews. Several of men's psychological characteristics, particularly their autonomy and job satisfaction, predicted their play time and the quality of their interactions with their children. Women's autonomy, occupation, and age in the expectancy predicted men's caretaking and weekday time involvement with their 5-year-olds. We suggest that the findings can best be explained by the concepts of complementarity and identification. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
73.
74.
Vandermonde and resultant matrices: An abstract approach 相似文献
75.
76.
Coating of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (PMN–PT) relaxor ferroelectrics by a sol–gel method is followed by growth of epitaxial SrRuO3 (SRO) metallic oxide electrodes on SrTiO3 (STO) single-crystal substrate by pulsed laser deposition. High-quality PMN–PT films on SRO with preferred growth orientation were successfully fabricated by controlling the operation parameters. Structural properties of relaxor ferroelectric PMN–PT thin films on SRO/STO substrates have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). In-plane and out-of-plane alignments of the heterostructure are confirmed and the structural twinning of the materials are also revealed. 相似文献
77.
The technology to create secure digital signatures is proven and workable on PC-level hardware, as well as on mainframes. the issues currently restraining widespread use of digital signatures are primarily legal. This tutorial survey first identifies the functions a digital signature should ideally perform by tracing an example Internet-based electronic business transaction. After an overview of the technology that provides the required functionality, this article presents the current legal status of digital signature use, including a number of unresolved liability issues, and summarizes some precautions for digital signature use. 相似文献
78.
William E. Mustain Hyea Kim Tyler Osborn Paul A. Kohl 《Israel journal of chemistry》2008,48(3-4):251-257
Platinum-ruthenium electrodes (PtxRu1-x) have been prepared by electrochemical and electroless deposition and investigated as catalysts for the oxidation of methanol in acidic solutions. PtxRu1-x deposits were electrochemically deposited from acidic chloride electrolytes at potentials between −0.46 and 0.34 V (vs. NHE). The composition of the electrodeposit was estimated by energy dispersive X-ray spectroscopy and is a strong function of the electrode potential. An empirical model for the deposition process is presented and kinetic parameters are estimated and discussed. Also, the methanol oxidation activity of the PtxRu1-x catalysts was characterized by cyclic voltammetry in 1.0 M CH3OH, 1.0 M H2SO4 solutions. Electroless PtxRu1-x samples were prepared in a modified Leaman bath with hydrazine dihydrochloride as the reducing agent. The kinetic results for the electrochemical deposition of PtxRu1-x were directly applied and the deposition potential was estimated as approximately 0.40 V. 相似文献
79.
Chronis Andrea M.; Lahey Benjamin B.; Pelham William E. Jr.; Williams Stephanie Hall; Baumann Barbara L.; Kipp Heidi; Jones Heather A.; Rathouz Paul J. 《Canadian Metallurgical Quarterly》2007,43(1):70
Children with attention-deficit/hyperactivity disorder (ADHD) are at risk for adverse outcomes such as substance abuse and criminality, particularly if they develop conduct problems. Little is known about early predictors of the developmental course of conduct problems among children with ADHD, however. Parental psychopathology and parenting were assessed in 108 children who first met Diagnostic and Statistical Manual of Mental Disorders (4th ed.) criteria for ADHD at 4-7 years old. When demographic variables and baseline ADHD and conduct problems were controlled, maternal depression predicted conduct problems 2-8 years following the initial assessment, whereas positive parenting during the structured parent- child interaction task predicted fewer future conduct problems. These findings suggest that maternal depression is a risk factor, whereas early positive parenting is a protective factor, for the developmental course of conduct problems among children with ADHD. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
80.
Norman Fenton Martin Neil William Marsh Peter Hearty Łukasz Radliński Paul Krause 《Empirical Software Engineering》2008,13(5):499-537
Standard practice in building models in software engineering normally involves three steps: collecting domain knowledge (previous
results, expert knowledge); building a skeleton of the model based on step 1 including as yet unknown parameters; estimating
the model parameters using historical data. Our experience shows that it is extremely difficult to obtain reliable data of
the required granularity, or of the required volume with which we could later generalize our conclusions. Therefore, in searching
for a method for building a model we cannot consider methods requiring large volumes of data. This paper discusses an experiment
to develop a causal model (Bayesian net) for predicting the number of residual defects that are likely to be found during
independent testing or operational usage. The approach supports (1) and (2), does not require (3), yet still makes accurate
defect predictions (an R
2 of 0.93 between predicted and actual defects). Since our method does not require detailed domain knowledge it can be applied
very early in the process life cycle. The model incorporates a set of quantitative and qualitative factors describing a project
and its development process, which are inputs to the model. The model variables, as well as the relationships between them,
were identified as part of a major collaborative project. A dataset, elicited from 31 completed software projects in the consumer
electronics industry, was gathered using a questionnaire distributed to managers of recent projects. We used this dataset
to validate the model by analyzing several popular evaluation measures (R
2, measures based on the relative error and Pred). The validation results also confirm the need for using the qualitative factors
in the model. The dataset may be of interest to other researchers evaluating models with similar aims. Based on some typical
scenarios we demonstrate how the model can be used for better decision support in operational environments. We also performed
sensitivity analysis in which we identified the most influential variables on the number of residual defects. This showed
that the project size, scale of distributed communication and the project complexity cause the most of variation in number
of defects in our model. We make both the dataset and causal model available for research use. 相似文献