全文获取类型
收费全文 | 35152篇 |
免费 | 792篇 |
国内免费 | 43篇 |
专业分类
电工技术 | 424篇 |
综合类 | 16篇 |
化学工业 | 6892篇 |
金属工艺 | 613篇 |
机械仪表 | 752篇 |
建筑科学 | 1357篇 |
矿业工程 | 360篇 |
能源动力 | 777篇 |
轻工业 | 2561篇 |
水利工程 | 328篇 |
石油天然气 | 259篇 |
无线电 | 2562篇 |
一般工业技术 | 5056篇 |
冶金工业 | 9230篇 |
原子能技术 | 368篇 |
自动化技术 | 4432篇 |
出版年
2022年 | 275篇 |
2021年 | 479篇 |
2020年 | 317篇 |
2019年 | 407篇 |
2018年 | 481篇 |
2017年 | 449篇 |
2016年 | 550篇 |
2015年 | 435篇 |
2014年 | 716篇 |
2013年 | 1948篇 |
2012年 | 1091篇 |
2011年 | 1428篇 |
2010年 | 1120篇 |
2009年 | 1192篇 |
2008年 | 1395篇 |
2007年 | 1290篇 |
2006年 | 1204篇 |
2005年 | 1090篇 |
2004年 | 908篇 |
2003年 | 900篇 |
2002年 | 893篇 |
2001年 | 644篇 |
2000年 | 548篇 |
1999年 | 641篇 |
1998年 | 1194篇 |
1997年 | 906篇 |
1996年 | 890篇 |
1995年 | 735篇 |
1994年 | 697篇 |
1993年 | 685篇 |
1992年 | 541篇 |
1991年 | 396篇 |
1990年 | 544篇 |
1989年 | 516篇 |
1988年 | 470篇 |
1987年 | 536篇 |
1986年 | 452篇 |
1985年 | 564篇 |
1984年 | 550篇 |
1983年 | 493篇 |
1982年 | 440篇 |
1981年 | 379篇 |
1980年 | 363篇 |
1979年 | 434篇 |
1978年 | 365篇 |
1977年 | 347篇 |
1976年 | 414篇 |
1975年 | 317篇 |
1974年 | 286篇 |
1973年 | 287篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Y Munakata JL McClelland MH Johnson RS Siegler 《Canadian Metallurgical Quarterly》1997,104(4):686-713
Infants seem sensitive to hidden objects in habituation tasks at 3.5 months but fail to retrieve hidden objects until 8 months. The authors first consider principle-based accounts of these successes and failures, in which early successes imply knowledge of principles and failures are attributed to ancillary deficits. One account is that infants younger than 8 months have the object permanence principle but lack means-ends abilities. To test this, 7-month-olds were trained on means-ends behaviors and were tested on retrieval of visible and occluded toys. Means-ends demands were the same, yet infants made more toy-guided retrievals in the visible case. The authors offer an adaptive process account in which knowledge is graded and embedded in specific behavioral processes. Simulation models that learn gradually to represent occluded objects show how this approach can account for success and failure in object permanence tasks without assuming principles and ancillary deficits. 相似文献
102.
Final-offer salary arbitration in major league baseball offers a unique institutional arrangement that creates a naturally occurring, non-equivalent-groups, repeated measures research design. The structural arrangements allow for examination of anticipatory expectancy effects and assessment of behavioral responses consistent with equity theory predictions. In addition, equity theory can be tested without the methodological problems inherent in defining the referent other. Performance and mobility were examined for major league baseball position players who won and lost their arbitration hearings. Prearbitration performance significantly predicted arbitration outcome. A significant relationship was noted between losing arbitration and postarbitration performance decline. Losers were significantly more likely to change teams and leave major league baseball. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
Human peripheral blood monocytes were examined for migration across an endothelial cell monolayer in an in vitro vessel wall construct. Few monocytes invaded in the absence of a chemotactic gradient, despite significant adhesion to the endothelial monolayer. However, the addition of zymosan-activated human plasma to the lower compartment, to create a chemotactic gradient across the vessel wall, resulted in significantly enhanced monocyte migration. Pretreatment of the monocytes with monoclonal antibodies to thrombospondin (TSP) dramatically inhibited monocyte diapedesis into the vessel wall. The same treatment inhibited monocyte adhesion to endothelial cells in two-dimensional monolayer cultures as well as in vessel wall constructs (no chemotactic gradient). Of interest, however, the monoclonal antibodies had no inhibitory effect on monocyte migration into collagen gels devoid of endothelial cells in response to the same chemotactic gradient, suggesting the importance of TSP in monocyte-endothelial cell interactions. Monoclonal antibodies to fibronectin and normal mouse immunoglobulin G did not inhibit migration in this model of a vessel wall. Furthermore, monoclonal antibodies to TSP showed no inhibition of human peripheral blood neutrophil migration. Previous studies have shown that monocytes synthesize TSP and express this moiety on their surface. The present data suggest that monocytes may utilize TSP to interact with endothelial cells lining the vessel wall during diapedesis. 相似文献
104.
Nestor Paul G.; Faux Steven F.; McCarley Robert W.; Penhune Virginia; Shenton Martha E.; Pollak Seth; Sands Stephen F. 《Canadian Metallurgical Quarterly》1992,101(4):682
M. I. Possner's 1980 reaction time (RT) paradigm was used to examine the engagement and disengagement operations of visual selective attention in patients with schizophrenia. In the 1st experiment 14 medicated, chronic schizophrenic Ss (diagnosed by criteria of the Diagnostic and Statistical Manual of Mental Disorders [DSM-I]), and 15 age-matched normal and control Ss made a speeded response to a target preceded by a valid, and invalid, or no cue. Control Ss showed the expected advantage and disadvantage in RT for valid and invalid cues, which suggests intact engagement and disengagement operations. For schizophrenic Ss, valid cues also enhanced RT, but invalid cues did not slow RT. Similar results were found in the 2nd experiment. The failure of unpredictable, invalid cues to inhibit RT in chronic schizophrenia may be related to an abnormality in the disengagement operation of selective attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
105.
Rats were trained on a spatial delayed-nonmatching-to-sample (DNMTS) task, matched for performance, and randomly assigned to treatment with dorsal noradrenergic bundle injections of either 6-hydroxydopamine, to deplete cortical norepinephrine (NE), or vehicle, to control for the effects of surgery. After recovery, there were no significant differences between the groups when retrained on the DNMTS task at retention intervals (RIs) from 0.1 to 15.0 sec. Furthermore, no differences were observed when rats were trained at a 6.0-sec RI filled with distracting stimuli or when dummy information runs were added to increase proactive interference. These results demonstrate that depletion of cortical NE cannot account for the DNMTS performance deficits observed in rats recovered from pyrithiamine-induced thiamine deficiency (R. L. Knoth and R. G. Mair, 1991; J. K. Robinson and Mair, 1992). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
106.
107.
Can a few seconds of high school teachers' nonverbal (NV) behavior predict students' ratings of these teachers (SRT)? Yes, but NV-SRT relations varied among various instructional situations. NV behaviors while administering the class and using the board were unrelated to SRT. Positive judgments of NV behavior while disciplining the class and interacting with students were positively related to SRT. NV behaviors in frontal teaching were negatively related to SRT. The most negative NV-SRT relations were found for teachers' differential NV behavior toward high- versus low-achieving students. Teacher differentiality and SRT have rarely been investigated in high school. The structure of SRT seems to differ between high school and college, and students' anger about teachers' differentiality strongly predicted their evaluations. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
108.
Existing NASA supported scientific databases are usually developed and managed by a team of database administrators whose main concern is the efficiency of the databases in terms of normalization and data search constructs. The populating of the database is usually done in a manual fashion by row and column as the data become available, and the data dictionary is usually defined by the same team (at times with little input from the end science user). This process is tedious, error prone and self-limiting in terms of what can be described in a relational Data Base Management System (DBMS). The next generation Earth remote sensing platforms [i.e., Earth Observing System (EOS)] will be capable of generating data at a rate of over 300 Megabits per second from a suite of instruments designed for different applications. What is needed is an innovative approach that creates object-oriented data-bases that segment, characterize, and catalog, and are manageable in a domain-specific context, and whose contents are available interactively and in near-real-time to the user community. This paper describes work in progress that utilizes an artificial neural net approach to characterize satellite imagery of undefined objects into high-level data objects. The characterized data is then dynamically allocated to an object-oriented database where it can be reviewed and accessed by a user. The definition, development, and evolution of the overall data system model are steps in the creation of an application-driven knowledge-based scientific information system. 相似文献
109.
Compared the frequency resolving power of 3 male budgerigar birds and 3 humans on several nonsimultaneous masking procedures in which one pure tone was used to mask another. Similar patterns of frequency selectivity were found for all 3 masking procedures (forward, backward, and combined forward/backward) for both species. Budgerigars showed considerably greater frequency resolving power on all 3 procedures than humans. Budgerigars also showed differences in frequency resolving power across masking conditions, but human Ss did not. Results indicate that the budgerigar auditory system may be even more highly tuned than was previously thought and suggest fundamental differences between the mechanisms of frequency selectivity of birds and humans. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
110.
We will analyze the economic sensitivity of new energy-saving technologies to weather, future energy price, and system lifetime uncertainties. Graphical rate of return analysis is employed. A representative residential solar water heating investment is analyzed to illustrate the impact of uncertainties. The wide range of reasonable rates of return found suggests some considerations for policy makers and some areas of future research. 相似文献