全文获取类型
收费全文 | 4471篇 |
免费 | 218篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 36篇 |
综合类 | 1篇 |
化学工业 | 1022篇 |
金属工艺 | 50篇 |
机械仪表 | 61篇 |
建筑科学 | 206篇 |
矿业工程 | 8篇 |
能源动力 | 77篇 |
轻工业 | 744篇 |
水利工程 | 58篇 |
石油天然气 | 26篇 |
无线电 | 171篇 |
一般工业技术 | 575篇 |
冶金工业 | 1203篇 |
原子能技术 | 16篇 |
自动化技术 | 436篇 |
出版年
2024年 | 9篇 |
2023年 | 45篇 |
2022年 | 117篇 |
2021年 | 197篇 |
2020年 | 102篇 |
2019年 | 126篇 |
2018年 | 137篇 |
2017年 | 114篇 |
2016年 | 144篇 |
2015年 | 77篇 |
2014年 | 142篇 |
2013年 | 306篇 |
2012年 | 240篇 |
2011年 | 304篇 |
2010年 | 215篇 |
2009年 | 214篇 |
2008年 | 219篇 |
2007年 | 221篇 |
2006年 | 190篇 |
2005年 | 165篇 |
2004年 | 110篇 |
2003年 | 101篇 |
2002年 | 108篇 |
2001年 | 71篇 |
2000年 | 71篇 |
1999年 | 79篇 |
1998年 | 84篇 |
1997年 | 59篇 |
1996年 | 68篇 |
1995年 | 52篇 |
1994年 | 56篇 |
1993年 | 53篇 |
1992年 | 42篇 |
1991年 | 19篇 |
1990年 | 36篇 |
1989年 | 41篇 |
1988年 | 39篇 |
1987年 | 26篇 |
1986年 | 28篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 20篇 |
1981年 | 23篇 |
1980年 | 13篇 |
1979年 | 18篇 |
1978年 | 16篇 |
1976年 | 11篇 |
1975年 | 14篇 |
1974年 | 11篇 |
排序方式: 共有4690条查询结果,搜索用时 15 毫秒
21.
X-ray photoelectron spectroscopy (XPS) applied to the study of fluorinated polymer surfaces presents several problems related both to peak assignment and to degradation. In this work, we analyse extensively the question of XPS peak assignments in this kind of surfaces. We conclude that in this kind of surfaces using binding energy differences between fluorine and carbon is better than using absolute binding energies. Also a useful relation between fluorine photoelectron energy vs. polymer composition expressed through the atomic ratio fluorine/carbon (F/C) was found. A protocol for data treatment is proposed and applied to a XPS study of the degradation induced by X-ray on high-density polyethylene surfaces modified by direct fluorination. Results obtained for the degradation, namely the atomic ratio F/C obtained by two different methods, combined with angle resolved X-ray photoelectron spectroscopy (ARXPS) were used to study the fluorine concentration profile in depth, producing self-consistent results. 相似文献
22.
Reports an error in the original article by E. A. Maylor (Psychology and Aging, 1993[Sep], Vol 8[3], 420–428). There is an error in the picture recognition data. This was one of the tasks administered in an earlier group testing session (see page 421). The number of false positives for an older S was incorrectly entered onto the data sheet as 31 instead of only 13. (The following abstract of this article originally appeared in record 1994-01191-001.) Ss (aged 52–83 yrs) named 30 famous people 4 times over the course of an hour and responded to 2 targets (a beard and a pipe) by marking the trial number on the response sheet. Initial performance in the prospective memory task was related only to a measure of incidental learning. Subsequent forgetting (i.e., success followed by failure) occurred more often for older Ss than for younger Ss, but there was no difference between the age groups in recovery (i.e., failure followed by success). Forgetting was predicted by age, even after a composite measure of general ability was included in the regression. Recovery was related to general ability alone. Results both replicate and extend those from a reanalysis of a previous study (E. A. Maylor, 1990). They provide a striking contrast with the effect of age on retrospective memory.… (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
23.
24.
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
25.
Elizabeth Andrews 《河流研究与利用》1989,4(2):199-202
The British otter Lutra lutra L. requires good water quality, an adequate supply of fish and certain types of vegetation or cavities (holts) adjacent to water bodies for resting and breeding sites. In the U.K. otters and their holts are legally protected. Trained surveyors are needed to confirm the presence of otters on a river as the animals are rarely seen, but their tracks and droppings (spraints) may be detected. To evaluate a river for otters, information is required on water quality, fish species and biomass, as well as available habitat. Pioneer evaluation work based on the River Corridor Survey techniques has been done on Welsh rivers with good otter populations. Riparian vegetation, especially trees, is shown to be particularly important. This work is now being extended to areas on the margins of otter distribution such as the lower river Wye in England and Wales. Such surveys provide important management information for water authorities and give opportunities for enhancement work to benefit this animal. 相似文献
26.
Adolescents' desire and need for autonomy may have a significant impact on the therapeutic relationship. The implications of this idea are examined, both theoretically and empirically. First, adolescent autonomy is conceptualized in relational terms, and some of the conditions for the growth of autonomy are outlined. Then, this conceptualization is applied to a study of the therapeutic relationship in adolescent psychotherapy where it is shown how some of therapists' and adolescents' interactions and reactions can be understood by recognizing the influence of adolescent autonomy. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
27.
Reviews the book, Language in the Americas by Joseph H. Greenberg (1987). Greenberg's work on universals of language has crossed disciplinary boundaries to become known to many psychologists interested in language. His equally important work in language classification, of which Language in the Americas is one part, remains unfamiliar to psychologists. This book is a pioneering work in that it is the first genetic classification of the indigenous languages of both North and South America. Greenberg maintains that all of the languages of the Americas belong to three families: Eskimo-Aleut, Na-Dene, and a family that he has named Amerind. This assertion is both important and controversial; the controversy lies in the grouping of most of the languages including all of those of South and Central America into the Amerind family. Most of Language in the Americas consists of the Amerind etymological dictionary, arranged so that the reader can assess lexical similarities within and between subgroups. Greenberg's discussion is informed, articulate, profound, and to the point. He draws on relevant sources and examples from diverse fields of knowledge. The depth and breadth of his scholarship and the clarity of his presentation create a work that is an intellectual pleasure to read. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
28.
Self-efficacy expectations predict survival for patients with chronic obstructive pulmonary disease.
Kaplan Robert M.; Ries Andrew L.; Prewitt Lela M.; Eakin Elizabeth 《Canadian Metallurgical Quarterly》1994,13(4):366
Evaluated the validity of self-efficacy expectations as predictors of mortality for 119 patients with chronic obstructive pulmonary disease. Ss completed 4 physiological measures that represent common clinical indicators of disease severity: forced expiratory volume in 1 s(FEV1.0), arterial blood gas measurement of resting partial pressure of oxygen (PaO?), single-breath diffusing capacity (DLCO), and maximum oxygen uptake (V02max) during exercise. In addition, self-reported self-efficacy expectation for walking on a treadmill was measured. Self-efficacy was a significant univariate predictor of 5-yr survival. However, when controlling for FEV1.0 in multivariate survival analysis, self-efficacy had only a marginal effect. Simple self-report scales may provide significant information about health status. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
29.
Troyer Angela K.; Cullum C. Munro; Smernoff Eric N.; Kozora Elizabeth 《Canadian Metallurgical Quarterly》1994,8(1):95
Qualitative performance features and extended-time effects on the Block Design subtest of the Wechsler Adult Intelligence Scale—Revised (WAIS—R) were examined in 145 healthy Ss (aged 50–95 yrs). Raw scores were calculated at standard and extended time limits; error types and starting points were recorded for a subgroup of Ss. In Ss age 60 yrs and older, there was a consistent decline with age in overall scores at both time limits. Extra time allotments resulted in modest but significant increases in scores. Older and younger Ss benefited equally from the extra time, indicating that the age-related decline on this task cannot be accounted for by general age-related psychomotor slowing. Single- and multiblock rotation errors were relatively common, whereas stimulus boundedness and broken configurations were rare. Despite some potential limitations in generalizability, the results suggest that the incorporation of qualitative scoring procedures in the assessment of visuoconstructional skills may enhance understanding of normal and abnormal brain–behavior relationships. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
30.
Twenty-one 15- to 17-year-olds attempted to purchase cigarettes in 232 stores in the manner that confederates typically do in access studies, as well as in the manipulative ways (e.g., lying about their ages) that youth smokers do, thereby modeling youth access to tobacco within versus outside of studies, respectively. Youth typical-research versus manipulative behavior was contrasted with clerk behavior (requests for youth ID cards) to examine the relative contributions of both to youth access to tobacco for the 1st time. Results revealed that clerk behavior was the strongest predictor of cigarette sales to youth and hence underscore the need for interventions with merchants. Sales nonetheless were higher under youth-manipulative conditions and thereby highlight the low ecological validity of access research. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献