全文获取类型
收费全文 | 5956篇 |
免费 | 320篇 |
国内免费 | 18篇 |
专业分类
电工技术 | 107篇 |
综合类 | 17篇 |
化学工业 | 1178篇 |
金属工艺 | 110篇 |
机械仪表 | 144篇 |
建筑科学 | 200篇 |
矿业工程 | 35篇 |
能源动力 | 154篇 |
轻工业 | 365篇 |
水利工程 | 81篇 |
石油天然气 | 24篇 |
武器工业 | 8篇 |
无线电 | 481篇 |
一般工业技术 | 1026篇 |
冶金工业 | 1335篇 |
原子能技术 | 37篇 |
自动化技术 | 992篇 |
出版年
2023年 | 36篇 |
2022年 | 63篇 |
2021年 | 106篇 |
2020年 | 100篇 |
2019年 | 96篇 |
2018年 | 111篇 |
2017年 | 107篇 |
2016年 | 136篇 |
2015年 | 126篇 |
2014年 | 198篇 |
2013年 | 344篇 |
2012年 | 308篇 |
2011年 | 406篇 |
2010年 | 295篇 |
2009年 | 321篇 |
2008年 | 334篇 |
2007年 | 343篇 |
2006年 | 264篇 |
2005年 | 216篇 |
2004年 | 202篇 |
2003年 | 189篇 |
2002年 | 176篇 |
2001年 | 131篇 |
2000年 | 127篇 |
1999年 | 109篇 |
1998年 | 127篇 |
1997年 | 116篇 |
1996年 | 107篇 |
1995年 | 92篇 |
1994年 | 86篇 |
1993年 | 89篇 |
1992年 | 54篇 |
1991年 | 48篇 |
1990年 | 59篇 |
1989年 | 73篇 |
1988年 | 54篇 |
1987年 | 47篇 |
1986年 | 41篇 |
1985年 | 50篇 |
1984年 | 52篇 |
1983年 | 40篇 |
1982年 | 32篇 |
1981年 | 46篇 |
1980年 | 34篇 |
1979年 | 27篇 |
1978年 | 41篇 |
1977年 | 31篇 |
1976年 | 29篇 |
1975年 | 15篇 |
1974年 | 19篇 |
排序方式: 共有6294条查询结果,搜索用时 187 毫秒
181.
Texture analysis provides a means to quantify complex changes in microscope images. We previously showed that cytoplasmic poly-adenylated mRNAs form mRNA granules in post-ischemic neurons and that these granules correlated with protein synthesis inhibition and hence cell death. Here we utilized the texture analysis software MaZda to quantify mRNA granules in photomicrographs of the pyramidal cell layer of rat hippocampal region CA3 around 1 h of reperfusion after 10 min of normothermic global cerebral ischemia. At 1 h reperfusion, we observed variations in the texture of mRNA granules amongst samples that were readily quantified by texture analysis. Individual sample variation was consistent with the interpretation that animal-to-animal variations in mRNA granules reflected the time-course of mRNA granule formation. We also used texture analysis to quantify the effect of cycloheximide, given either before or after brain ischemia, on mRNA granules. If administered before ischemia, cycloheximide inhibited mRNA granule formation, but if administered after ischemia did not prevent mRNA granulation, indicating mRNA granule formation is dependent on dissociation of polysomes. We conclude that texture analysis is an effective means for quantifying the complex morphological changes induced in neurons by brain ischemia and reperfusion. 相似文献
182.
传统遗传算法在求解Job Shop调度问题时存在收敛速度慢,易于早熟的缺点。在病毒遗传算法(VEGA)和灾变遗传算法的基础上提出了一种带有灾变因子的病毒遗传算法(IVEGA-C)。该算法在传统遗传算法的基本结构上加入了病毒感染操作和灾变操作,病毒感染操作实现了同代个体之间横向传递进化信息,灾变操作采用灭绝操作。正是这种改进加快了遗传算法的收敛速度,避免了早熟现象和陷入局部最优解。通过仿真实验验证了IVEGA-C算法在解决Job Shop调度问题中的性能优于传统GA算法和VEGA算法。最后给出了应用该算法的一个实例。 相似文献
183.
电控气型地面防喷器控制装置远控系统采用先进的SIEMENS S7-300系列PLC和PROFIBUS总线技术,使得地面防喷器控制装置对防喷器的控制时间大大缩短,提高了整个控制系统的安全、可靠性;通过电气按钮实现对防喷器的控制,通过增加声、光报警系统、控制状态指示灯、压力显示数码管,提高了作业人员的可操作性,使得整个控制系统更加人性化。 相似文献
184.
Hooshang Hemami Kamran Barin Yi-Chung Pai 《IEEE transactions on neural systems and rehabilitation engineering》2006,14(4):470-480
The ankle strategy is one of the postural adjustment maneuvers humans utilize when the support platform is disturbed. This paper presents a quantitative analysis of the ankle strategy. A three-link sagittal biped model is considered. The first link represents the two legs locked together. The second link represents the two thighs locked together. The third link represents the hip, the torso, the upper limbs, the neck, and the head. The dynamics, control, and stability of the three-link biped, under platform translation, are considered. The disturbance of the platform is represented as an input and the effect of the muscular system is reduced to a set of torques applied to the joints and across the joints. Two digital computer simulations are presented to demonstrate the behavior of the biped under backward or forward platform disturbance. The simulations are compared with experimental measurements of humans subjected to postural disturbances. It is shown that the effect of a horizontal disturbance at the ankle appears to be about 40 times that of the effect of the disturbance at the knees and at least a few hundred times larger than the effect of a disturbance at the hip. This means that, under translational platform disturbance, the ankle angle is subjected to the largest excursion. The knee and the hip angle excursions are relatively minor. Consequently, the biped, as a whole, appears to move as a single inverted pendulum. Major postural corrections are initiated by the ankle excursion. Further, when the available ankle torque is limited or nonexistent, the stability requires resorting to the knee or hip strategies. 相似文献
185.
Bayen Ute J.; Erdfelder Edgar; Bearden J. Neil; Lozito Jeffrey P. 《Canadian Metallurgical Quarterly》2006,32(5):1003
Hindsight bias is the phenomenon that after people are presented with the correct answer to a question, their judgment regarding their own past answer to this question is biased toward the correct answer. In three experiments, younger and older adults gave numerical responses to general-knowledge questions and later attempted to recall their responses. For some questions, the correct answer was provided during recall (Experiment 1) or before recall (Experiments 2 and 3). Multinomial model-based analyses show age differences in both recollection bias and reconstruction bias when the correct judgment was in working memory during the recall phase. The authors discuss implications for theories of cognitive aging and theories of hindsight bias. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
186.
Robert H. Clarke Diana Twede Jeffrey R. Tazelaar Kenneth K. Boyer 《Packaging Technology and Science》2006,19(1):45-54
The objective of this research was to determine the relationship between different product types and tag orientations on the readability of RFID tags on shipping containers in a palletload that is driven through a portal type reader. This research finds that the content of packages can dramatically reduce the read rate. Only 25% of the tags on shipping containers containing water‐filled bottles could be read. Rice‐filled jars had a higher read rate (80.6%). Even empty boxes did not have a 100% read rate. For the variables without appreciable package contents, only 74–79% of loads had all of their tags read. The orientation of the tag does make a difference, especially when coupled with a filled package between it and the reader antennae. Tags facing outwards, towards the reader antennae, had the highest likelihood of a successful read. When tags for the boxes of water‐filled bottles were all facing downwards, no tags were read. Supply chain managers need to understand these limitations of the technology and find ways to overcome them before RFID can be successfully implemented in supply chains. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
187.
Lahey Benjamin B.; Loeber Rolf; Burke Jeffrey D.; Applegate Brooks 《Canadian Metallurgical Quarterly》2005,73(3):389
It is essential to identify childhood predictors of adult antisocial personality disorder (APD) to target early prevention. It has variously been hypothesized that APD is predicted by childhood conduct disorder (CD), attention-deficit/hyperactivity disorder (ADHD), or both disorders. To test these competing hypotheses, the authors used data from a single childhood diagnostic assessment of 163 clinic-referred boys to predict future APD during early adulthood. Childhood Diagnostic and Statistical Manual of Mental Disorders (3rd ed., rev.; American Psychiatric Association, 1987) CD, but not ADHD, significantly predicted the boys' subsequent APD. An interaction between socioeconomic status (SES) and CD indicated that CD predicted APD only in lower SES families, however. Among children who met criteria for CD, their number of covert but not overt CD symptoms improved prediction of future APD, controlling for SES. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
188.
Parker Jeffrey G.; Low Christine M.; Walker Alisha R.; Gamm Bridget K. 《Canadian Metallurgical Quarterly》2005,41(1):235
Children's vulnerability to jealousy surrounding their best friends was explored in 2 studies. Study 1 involved 94 adolescents who reported on their friendship jealousy on a newly created measure. Results indicated that the jealousy measure had sound psychometric properties and produced individual differences that were robust over time and free from socially desirable responding. As expected, girls and adolescents with low self-worth reported the greatest friendship jealousy. Study 2 involved 399 young adolescents and extended the measurement of self-report jealousy to a broader age range. In addition, Study 2 included assessments of jealousy provided by friends and other peers. Self- and peer-reported jealousy were only modestly associated and had somewhat distinct correlates. Structural modeling revealed that young adolescents' reputation for friendship jealousy was linked to behaving aggressively and to broader peer adjustment difficulties. Both self- and peer-reported jealousy contributed to loneliness. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
189.
Often quantitative data in the social sciences have only ordinal justification. Problems of interpretation can arise when least squares multiple regression (LSMR) is used with ordinal data. Two ordinal alternatives are discussed, dominance-based ordinal multiple regression (DOMR) and proportional odds multiple regression. The Q2 statistic is introduced for testing the omnibus null hypothesis in DOMR. A simulation study is discussed that examines the actual Type I error rate and power of Q2 in comparison to the LSMR omnibus F test under normality and non-normality. Results suggest that Q2 has favorable sampling properties as long as the sample size-to-predictors ratio is not too small, and Q2 can be a good alternative to the omnibus F test when the response variable is non-normal. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
190.
Peter Revesz Jeffrey A. White 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2005,540(2-3):470-479
A new method for white beam position monitoring for both bend magnet and wiggler synchrotron X-ray radiation has been developed. This method utilizes visible light luminescence generated as a result of ionization by the intense X-ray flux. In video beam position monitors (VBPMs), the luminescence of helium gas at atmospheric pressure is observed through a view port using a CCD camera next to the beam line. The beam position, profile, integrated intensity and FWHM are calculated from the distribution of luminescence intensity in each captured image by custom software. Misalignment of upstream apertures changes the image profile making VBPMs helpful for initial alignment of upstream beam line components. VBPMs can thus provide more information about the X-ray beam than most beam position monitors (BPMs). A beam position calibration procedure, employing a tilted plane-parallel glass plate placed in front of the camera lens, has also been developed. The accuracy of the VBPM system was measured during a bench-top experiment to be better than 1 μm. The He-luminescence-based VBPM system has been operative on three CHESS beam lines (F hard-bend and wiggler, A-line wiggler and G-line wiggler) for about a year. The beam positions are converted to analog voltages and used as feedback signals for beam stabilization. In our paper we discuss details of VBPM construction and describe further results of its performance. 相似文献