首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   19001篇
  免费   338篇
  国内免费   177篇
电工技术   247篇
综合类   23篇
化学工业   2310篇
金属工艺   592篇
机械仪表   276篇
建筑科学   621篇
矿业工程   31篇
能源动力   203篇
轻工业   775篇
水利工程   72篇
石油天然气   19篇
武器工业   1篇
无线电   898篇
一般工业技术   1537篇
冶金工业   1570篇
原子能技术   159篇
自动化技术   10182篇
  2023年   59篇
  2022年   120篇
  2021年   143篇
  2020年   105篇
  2019年   132篇
  2018年   173篇
  2017年   110篇
  2016年   191篇
  2015年   192篇
  2014年   456篇
  2013年   730篇
  2012年   1154篇
  2011年   3589篇
  2010年   1535篇
  2009年   1385篇
  2008年   1093篇
  2007年   991篇
  2006年   803篇
  2005年   876篇
  2004年   806篇
  2003年   795篇
  2002年   496篇
  2001年   176篇
  2000年   167篇
  1999年   177篇
  1998年   342篇
  1997年   215篇
  1996年   173篇
  1995年   142篇
  1994年   125篇
  1993年   138篇
  1992年   137篇
  1991年   80篇
  1990年   101篇
  1989年   85篇
  1988年   102篇
  1987年   72篇
  1986年   65篇
  1985年   85篇
  1984年   117篇
  1983年   71篇
  1982年   71篇
  1981年   89篇
  1980年   68篇
  1979年   85篇
  1978年   68篇
  1977年   67篇
  1976年   56篇
  1975年   58篇
  1973年   47篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Nickel molybdate catalysts used in several different upgrading reactions of coal-derived materials from low-rank Australian coals have been regenerated and their activity assessed using a number of physical and chemical techniques. Regeneration of spent coked catalysts for 20 hours in air at 450°C was sufficient to restore chemical hydrogenation activity to catalyst used for pre-asphaltene, asphaltene and oil upgrading, provided poisoning of the catalyst surface by other impurities, principally chlorine-containing molecules, had not occurred.  相似文献   
72.
This paper describes how SWoRD (scaffolded writing and rewriting in the discipline), a web-based reciprocal peer review system, supports writing practice, particularly for large content courses in which writing is considered critical but not feasibly included. To help students gain content knowledge as well as writing and reviewing skills, SWoRD supports the whole cycle of writing, reviews, back-reviews, and rewriting by scaffolding the journal publication process as its authentic practice model. In addition, SWoRD includes algorithms that compute individual reviewer’s review accuracy, which is in turn used to support the various drawbacks of reciprocal peer reviews (e.g., variation in motivation or ability of reviewers). Finally, this paper describes an empirical evaluation showing that the SWoRD approach is effective in improving writing quality in content classes.  相似文献   
73.
Soft sediments from the Detroit River were analyzed for the USEPA priority pollutants to generally characterize contaminant distribution. Forty-three were detected. Highest heavy metal concentrations were found in the Trenton Channel and immediately downstream of Grosse Ile. They ranged from an area mean (N = 2) of 0.19 mg/kg mercury to 338.7 mg/kg zinc (dry weight). Polynuclear aromatic hydrocarbons ranged from 0.1 mg/kg to 38.8 mg/kg (mean, N = 2) with the highest levels near Grosse Ile. PCBs ranged from 0.015 mg/kg to 1.7 mg/kg (mean, N = 2). Organochlorine pesticides were not detected except for a trace of heptachlor in one sample. Sediment contamination in the Detroit River is widespread with higher concentrations on the U.S. side downstream of the Rouge River and in the Trenton Channel. The significance of these in-place pollutants to biota and as a source to Lake Erie is still unknown.  相似文献   
74.
The estimate of the population correlation used in the formula for sampling error variance of a correlation is typically the observed correlation, but in meta-analysis the average of the observed correlations can be used. For the case in which there is no variation in the study population correlations or sample sizes and the number of studies is very large, the authors found that use of the average correlation estimator is more accurate than use of the traditional, individual correlation estimator, except in those rare cases in which the uncorrected population correlation is greater than .60. For typical sample sizes, when the uncorrected population correlation is between -.40 and .40, there is virtually no error in the meta-analysis credibility interval based on the average correlation estimator. On the other hand, the amount of the error in the individual correlation estimator is qualitatively important if the sample is 25 or less and the population correlation is less than .40. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
75.
Although the association between marital conflict and child adjustment problems has been well documented, there is no empirical evidence that conflict actually causes maladjustment. The investigation of causation requires theoretically and empirically informed longitudinal research. Two topics are addressed to facilitate such research. First, how marital conflict may lead to adjustment problems is outlined, with a focus on constructs that are likely to be critical to any theory on this topic. Second, several issues are identified that need to be addressed in longitudinal research on the mechanisms underlying the link between marital and child problems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
76.
77.
78.
Tension and vascular headache patients, initially treated with biofeedback and/or relaxation training in either a minimal therapist contact protocol (3 visits) or an intensive individual protocol (10 or 16 visits) were followed-up prospectively for 2 years. In the first study, for the first 6 months of follow-up, half of all patients continued to keep headache diaries and were seen monthly and the other half had only minimal contact. The results at 1-year follow-up, based on 4 weeks of daily headache diaries, revealed equally good maintenance from both treatment protocols and from both follow-up conditions. In Study 2, we found that patients remained improved over pretreatment baseline levels at the 2-year follow-up regardless of initial treatment intensity. Approximately three quarters of vascular patients who were initially improved at posttreatment remained improved at 2 years. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
79.
Frank G. Pagan 《Software》1988,18(6):509-527
There is an effective and quite general method of manually deriving compilers from programming-language interpreters without dealing directly with machine language. The method is an implementation of the largely theoretical and under-appreciated concept of partial computation, but can be understood on its own terms. It involves the translation of a source program's intermediate form into the interpreter's implementation language. This paper shows how the method can be used to transform both a sample iterative interpreter and a sample recursive interpreter into compilers. The result can be a large gain in program execution speed. Other advantages of the method, including the ease and practicality of applying it, are discussed.  相似文献   
80.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号