全文获取类型
收费全文 | 13989篇 |
免费 | 353篇 |
国内免费 | 54篇 |
专业分类
电工技术 | 212篇 |
综合类 | 12篇 |
化学工业 | 3105篇 |
金属工艺 | 251篇 |
机械仪表 | 303篇 |
建筑科学 | 647篇 |
矿业工程 | 98篇 |
能源动力 | 385篇 |
轻工业 | 975篇 |
水利工程 | 130篇 |
石油天然气 | 164篇 |
武器工业 | 1篇 |
无线电 | 855篇 |
一般工业技术 | 2069篇 |
冶金工业 | 3315篇 |
原子能技术 | 158篇 |
自动化技术 | 1716篇 |
出版年
2022年 | 127篇 |
2021年 | 170篇 |
2020年 | 148篇 |
2019年 | 161篇 |
2018年 | 184篇 |
2017年 | 186篇 |
2016年 | 211篇 |
2015年 | 172篇 |
2014年 | 238篇 |
2013年 | 833篇 |
2012年 | 469篇 |
2011年 | 645篇 |
2010年 | 416篇 |
2009年 | 455篇 |
2008年 | 585篇 |
2007年 | 558篇 |
2006年 | 545篇 |
2005年 | 458篇 |
2004年 | 366篇 |
2003年 | 371篇 |
2002年 | 384篇 |
2001年 | 245篇 |
2000年 | 237篇 |
1999年 | 252篇 |
1998年 | 217篇 |
1997年 | 236篇 |
1996年 | 238篇 |
1995年 | 243篇 |
1994年 | 245篇 |
1993年 | 294篇 |
1992年 | 248篇 |
1991年 | 186篇 |
1990年 | 210篇 |
1989年 | 217篇 |
1988年 | 169篇 |
1987年 | 215篇 |
1986年 | 206篇 |
1985年 | 250篇 |
1984年 | 223篇 |
1983年 | 203篇 |
1982年 | 182篇 |
1981年 | 192篇 |
1980年 | 163篇 |
1979年 | 183篇 |
1978年 | 182篇 |
1977年 | 137篇 |
1976年 | 142篇 |
1975年 | 172篇 |
1974年 | 134篇 |
1973年 | 133篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
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
82.
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
83.
Joo-Sik Yoo William W. Schultz 《International Journal of Heat and Mass Transfer》2003,46(24):4747-4750
This study considers a small Rayleigh number thermal convection in a fluid-saturated porous medium between two infinite-horizontal walls. The lower and upper walls have sinusoidal temperature distributions with a wave number and a phase difference, and the effect of the parameters on the flow and heat transfer characteristics is investigated. For a given wave number, an out-of-phase configuration yields minimum heat transfer at the walls. Maximum heat transfer occurs at the wave number of 2.286 with an in-phase configuration. 相似文献
84.
Carels Robert A.; Cacciapaglia Holly; Pérez-Benítez Carlos I.; Douglass Olivia; Christie Samantha; O'Brien William H. 《Canadian Metallurgical Quarterly》2003,71(4):753
Reports an error in the original article by R. A. Carels et al (Journal of Consulting & Clinical Psychology, 2003[Jun], Vol 71[3], 613-618). On page 615, Lines 18, 20, 22, of Table 1, the data in the rows that read "Tachycardia in min per hr," "Repetitive PVCs per hr," and "PVCs per hr" are incorrectly reported in the n and % columns. They should have been reported in the M and SD columns. The corrected table is provided. (The following abstract of this article originally appeared in record 2003-00756-023.) Ventricular arrhythmia exhibits considerable within-subject variability that cannot be attributed to clinical status alone. This investigation examined the extent to which cardiac arrhythmia was associated with psychological and physical factors assessed during the hour preceding arrhythmic or nonarrhythmic activity. Approximately twice hourly, 46 patients randomly completed a diary assessing mood and physical symptoms during 24-hr electrocardiographic monitoring. Greater negative emotion was associated with increased arrhythmia. Additionally, greater negative emotion was significantly associated with increased arrhythmia among participants in a low left ventricular ejection fraction group (LVEF). However, this relationship between negative emotion and arrhythmia was not... (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
85.
Abstract The whole DNA of soybean was implanted into four varieties of wheat of Zhongyu5, Huaiyin 9628, Wenyou 1, Jimai 5 respectively via ion-beam mediation. There were 5 plantsobtained whose protein content was higher than 18.5%, the highest one was 21.44%. There were 3plants obtained whose protein content was lower than 11.5%, the lowest one was 10.96%. We cansee that the whole DNA of soybean transformed into wheat via ion beam implantation can inducethe increase in wheat protein content dramatically. The result also shows that the transformationefficiency of different gene types of wheat receptor varies greatly that the implanting time has acertain effect on the efficiency of transformation. 相似文献
86.
87.
Jodi E Williams Susan E. Duncan Robert C. Williams Kumar Mallikarjunan William N. Eigel III Sean F. O'Keefe 《Journal of food science》2006,71(3):S265-S269
ABSTRACT: Flavor characteristics of roasted peanuts over short-term storage were explored through sensory and chemical analyses. The volatiles from freshly roasted peanuts were evaluated over short-time (21 d) storage using gas chromatography, chemosensory techniques, and a sensory panel to quantify and identify pyrazines and hexanal over a 21-d storage period. A significant decrease ( P < 0.05) was noted in 2,3-diethylpyrazine, 2-methoxypyrazine, 2,3-dimethylpyrazine, 2-ethyl-3-methylpyrazine, and 2,3,5-trimethylpyrazine concentrations over a 21-d period. No significant difference ( P > 0.05) was noted in the 2-methylpyrazine and 2-ethylpyrazine concentrations. The hexanal concentration significantly increased ( P < 0.05) over the 21-d period. The peroxide values and sensory analysis agreed with these results. A significant increase ( P < 0.05) in peroxide value was seen at days 14 and 21, and a significant decrease ( P < 0.05) in fresh roasted peanuty flavor from day 0 to 21 and significant increases ( P < 0.05) in painty, cardboardy, and bitter flavors from day 7 to 21 with the sensory analysis. The electronic nose successfully separated day 0 and 21 samples from day 7 and 14 samples, which were also separated but with some overlap. 相似文献
88.
89.
This naver analvzes the surface emission coefficient corresponding to anv diffusion coefficient expressed as an exponential function of the concentration diffusing substance in capillary porous solids. Theoretical equations for surface emission coefficient for both sorption and desorption are presented. Procedures to derive the diffusion coefficient and to verify the corresponding surface emission coefficient are made using experimental sorption data of aspen (Populur sp.) wood. It is of interest to note that the theoretical models for diffusion and surface emission coefficients can be established and/or evaluated using the same set of experimental dara. 相似文献
90.
Trimethylpentane diol (TMPD) dibenzoate use in vinyl as a plasticizer is not well recognized, and little has been published on vinyl performance characteristics. To assess new applications for vinyl, a basic evaluation was conducted. Based on the results of the screen and other considerations an evaluation for utility in plastisol silk screen ink was conducted. The results indicated that the TMPD dibenzoate performed very well in white ink, requiring good fabric dye bleed resistance compared to polymeric and phthalates currently being used for non-bleed ink. Non-bleed characteristics are important for colored tee shirt printing. The benzoate is a good solvator and has excellent extraction resistance. 相似文献