全文获取类型
收费全文 | 18465篇 |
免费 | 807篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 217篇 |
综合类 | 18篇 |
化学工业 | 3913篇 |
金属工艺 | 339篇 |
机械仪表 | 406篇 |
建筑科学 | 1045篇 |
矿业工程 | 50篇 |
能源动力 | 514篇 |
轻工业 | 1753篇 |
水利工程 | 121篇 |
石油天然气 | 64篇 |
武器工业 | 1篇 |
无线电 | 1595篇 |
一般工业技术 | 3103篇 |
冶金工业 | 3081篇 |
原子能技术 | 188篇 |
自动化技术 | 2885篇 |
出版年
2023年 | 161篇 |
2022年 | 312篇 |
2021年 | 469篇 |
2020年 | 351篇 |
2019年 | 373篇 |
2018年 | 436篇 |
2017年 | 395篇 |
2016年 | 494篇 |
2015年 | 433篇 |
2014年 | 531篇 |
2013年 | 1091篇 |
2012年 | 873篇 |
2011年 | 1140篇 |
2010年 | 782篇 |
2009年 | 850篇 |
2008年 | 889篇 |
2007年 | 784篇 |
2006年 | 719篇 |
2005年 | 603篇 |
2004年 | 503篇 |
2003年 | 452篇 |
2002年 | 432篇 |
2001年 | 305篇 |
2000年 | 327篇 |
1999年 | 356篇 |
1998年 | 738篇 |
1997年 | 480篇 |
1996年 | 400篇 |
1995年 | 291篇 |
1994年 | 278篇 |
1993年 | 269篇 |
1992年 | 188篇 |
1991年 | 163篇 |
1990年 | 141篇 |
1989年 | 143篇 |
1988年 | 129篇 |
1987年 | 122篇 |
1986年 | 114篇 |
1985年 | 141篇 |
1984年 | 133篇 |
1983年 | 117篇 |
1982年 | 92篇 |
1981年 | 103篇 |
1980年 | 86篇 |
1979年 | 102篇 |
1978年 | 90篇 |
1977年 | 115篇 |
1976年 | 137篇 |
1975年 | 81篇 |
1974年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Memorializes Richard Solomon, one of the major learning theorists of the 2nd half of the 20th century. Solomon was named the 1st James M. Skinner University Professor of Science in 1975, was elected to the National Academy of Sciences, and was awarded, among other honors, the Warren Medal for research by the Society of Experimental Psychologists, the American Psychological Association Distinguished Scientific Contribution Award, and the American Psychological Foundation's Award for Distinguished Teaching in Experimental Psychology. He conducted research on a broad array of topics such as word frequency and perceptual defense, children's estimation of the size of tokens, hoarding behaviors in rats, and personality ratings and sociometric patterns. His work made a major contribution to the exploration of Pavlovian conditioning. Other topics of research focused on in Solomon's laboratories included avoidance learning, learned helplessness, punishment, and the opponent-process theory of acquired motivation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
92.
CJ Martin 《Canadian Metallurgical Quarterly》1997,68(12):775-781
BACKGROUND: The most common cause of a sudden onset of painful proptosis with diplopia in an otherwise healthy adult is orbital pseudotumor. However, there are other conditions that mimic this presentation and must be ruled out with laboratory testing and imaging studies. CASE REPORT: A 41-year-old Hawaiian man sought treatment for an acute, progressive, painful, left ophthalmoplegia without exophthalmos. During the next week, a loss of accommodation and associated pupillary reaction, decreased visual acuity, color vision deficits, and a paracentral scotoma developed. CT and MRI revealed a mass in the orbital apex. All systemic findings were negative, and high-dose systemic steroid therapy was initiated. Symptoms resolved within hours of the first dose, and signs were completely absent 1 month later. Follow-up MRI revealed complete absence of the previously noted mass. CONCLUSION: This is an atypical case of orbital pseudotumor, since there was no exophthalmos. It was diagnosed by clinical presentation, laboratory and imaging studies, and response to therapy. 相似文献
93.
Charles A. Bateman Lijie Zhang Helen M. Chan Martin P. Harmer 《Journal of the American Ceramic Society》1992,75(5):1281-1283
It is experimentally observed that the peritectic reaction, 211 + liquid → 123, can be driven essentially to completion in 1 h at an undercooling of only ∽30°C. The kinetic data, together with the observed microstructures, are inconsistent with the normal mechanism of the peritectic reaction. It is proposed that the mechanism of the reaction involves dissolution of 211 particles into the liquid and precipitation of solid 123. The aligned grain structure is explained through sympathetic nucleation of new 123 grains on existing grains. 相似文献
94.
Tucker Joan S.; Friedman Howard S.; Tsai Catherine M.; Martin Leslie R. 《Canadian Metallurgical Quarterly》1995,10(1):3
Models of the relations between contact with pets and better health are examined in an archival prospective study using data derived from the longitudinal study initiated by Terman in 1921 (current N?=?343 men, 300 women) . In survival analyses of documented longevity, playing with pets in 1977 (M age?=?67 years) was not associated with mortality risk through 1991 for the total sample nor for those who were unmarried or those who were less satisfied with their human relationships. Playing with pets was not associated with health-prone attributes or healthy behaviors such as personality, social ties, education, and smoking. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
95.
Multiresolution decompositions for video coding are reviewed. Both nonrecursive and recursive coding schemes are considered. In nonrecursive schemes, it is shown that pyramid structures have certain advantages over subband or wavelet techniques, and a specific spatiotemporal pyramid coding of HDTV is discussed in some detail. It is shown that recursive, DPCM like schemes will incur a slight loss of optimality due to a restricted form of prediction if multiresolution decomposition with compatible decoding is required. Compatibility and transmission issues are also discussed. Multiresolution transmission for digital broadcast TV is introduced. This, when combined with multiresolution source coding, achieves spectrum efficiency, robustness and graceful degradation under channel impairments.Invited PaperWork supported in part by the National Science Foundation under grants ECD-88-11111, MIP-90-14189 and Bell Communications Research.Work supported by the National Science Foundation under grants ECD-88-11111. K.M. Uz is now with David Sarnoff Research Center in Princeton, NJ 08543. 相似文献
96.
W Fries SA Grassi L Leone D Giacomin F Galeazzi R Naccarato A Martin 《Canadian Metallurgical Quarterly》1995,30(12):1221-1223
BACKGROUND: Common etiopathogenic factors may explain the association of systemic sarcoidosis with inflammatory bowel disease. METHODS: We report two cases of such an association: one of sarcoidosis that developed 2 years after proctocolectomy for ulcerative colitis and one of sarcoidosis and Crohn's colitis. Factors like increased cellular immunity or circulating immunocomplexes or autoantibodies may have a role. Exogenous agents or familiarity may also be involved. CONCLUSIONS: It is postulated that the association between sarcoidosis and inflammatory bowel disease (both ulcerative colitis and Crohn's disease) does not occur by chance alone and that the two conditions may share some genetic or immunologic alterations. The two diseases, however, follow an independent clinical course. 相似文献
97.
This article describes the development and validation of scales to measure clients' outcome optimism, perceived progress, and self-agency related to change in problems presented in therapy. In Study 1, initial confirmatory and subsequent exploratory factor analyses (N?=?257) identified effort and persistence as an additional unique factor and guided selection of items to measure the 4 constructs. In Study 2, confirmatory factor analysis of the revised scales with a new sample (N?=?93) confirmed the measurement model. Results of convergent and discriminant validity analyses generally were in the predicted directions. The Perceived Progress scale demonstrated criterion validity with changes in dyadic adjustment and family functioning. The Outcome Optimism and Self-Agency scales showed variability in their relationship to the Perceived Progress scale over the first 3 sessions of therapy. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
98.
The kinetics of cyclotrimerization and the thermal stability of bisphenol Abased cyanate ester resin systems were determined using Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetry. The bisphenol A dicyanate was cured with 4 phr nonylphenol and with the octoates of zinc and manganese, and cobalt acetylacetonate at concentrations ranging from 0 to 750 ppm metal. An empirical rate law was used to predict the cyanate concentration profiles. The observed reaction rate showed a first-order dependen?e on the initial metal concentration and a second-order dependence on the cyanate concentration in the kinetically controlled regime. For the uncatalyzed systems, the kinetics was described by a second-order autocatalytic model. The thermal stability of the network was found to be dependent on the catalyst concentration for the zinc catalysts. For the samples cured with manganese, no effect of concentration on the thermal stability was observed. 相似文献
99.
The typical inventory routing problem deals with the repeated distribution of a single product from a single facility with an unlimited supply to a set of customers that can all be reached with out-and-back trips. Unfortunately, this is not always the reality. We introduce the inventory routing problem with continuous moves to study two important real-life complexities: limited product availabilities at facilities and customers that cannot be served using out-and-back tours. We need to design delivery tours spanning several days, covering huge geographic areas, and involving product pickups at different facilities. We develop an innovative randomized greedy algorithm, which includes linear programming based postprocessing technology, and we demonstrate its effectiveness in an extensive computational study. 相似文献
100.
Potential applications of knowledge based expert systems in the area of construction project monitoring and control are described. Originally developed from research in artificial intelligence, these systems are computer programs that can undertake intelligent tasks currently performed by highly skilled people. While some project monitoring can be accomplished by algorithmic procedures, the capability of knowledge based expert systems to deal with illstructured problems and to be extensively modified over time make them desirable for application in this area. Sample applications and heuristic rules in scheduling and inventory control are provided. 相似文献