全文获取类型
收费全文 | 12278篇 |
免费 | 539篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 122篇 |
综合类 | 5篇 |
化学工业 | 2390篇 |
金属工艺 | 181篇 |
机械仪表 | 239篇 |
建筑科学 | 676篇 |
矿业工程 | 30篇 |
能源动力 | 393篇 |
轻工业 | 972篇 |
水利工程 | 121篇 |
石油天然气 | 47篇 |
无线电 | 908篇 |
一般工业技术 | 2315篇 |
冶金工业 | 2284篇 |
原子能技术 | 63篇 |
自动化技术 | 2092篇 |
出版年
2023年 | 85篇 |
2022年 | 152篇 |
2021年 | 259篇 |
2020年 | 205篇 |
2019年 | 241篇 |
2018年 | 264篇 |
2017年 | 263篇 |
2016年 | 274篇 |
2015年 | 253篇 |
2014年 | 379篇 |
2013年 | 733篇 |
2012年 | 618篇 |
2011年 | 847篇 |
2010年 | 565篇 |
2009年 | 533篇 |
2008年 | 664篇 |
2007年 | 585篇 |
2006年 | 498篇 |
2005年 | 444篇 |
2004年 | 385篇 |
2003年 | 371篇 |
2002年 | 321篇 |
2001年 | 199篇 |
2000年 | 205篇 |
1999年 | 196篇 |
1998年 | 389篇 |
1997年 | 301篇 |
1996年 | 277篇 |
1995年 | 213篇 |
1994年 | 183篇 |
1993年 | 154篇 |
1992年 | 115篇 |
1991年 | 106篇 |
1990年 | 117篇 |
1989年 | 103篇 |
1988年 | 89篇 |
1987年 | 96篇 |
1986年 | 79篇 |
1985年 | 107篇 |
1984年 | 86篇 |
1983年 | 91篇 |
1982年 | 83篇 |
1981年 | 69篇 |
1980年 | 56篇 |
1979年 | 61篇 |
1978年 | 52篇 |
1977年 | 68篇 |
1976年 | 75篇 |
1975年 | 38篇 |
1974年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
Delapasse J.S. Behbehani K. Kuangchung Tsui Klein K.W. 《IEEE transactions on bio-medical engineering》1994,41(11):1083-1091
A new self-tuning regulator for control of mean arterial blood pressure using sodium nitroprusside is presented. In addition to adapting to various patient response gains and time constants, the controller can accommodate variations in pure time delays, a problem that has not been addressed fully in previously proposed controllers. The control algorithm derivation is based on incorporating a self-turning controller with an adaptive discrete time delay compensator. The derivation, however, is general and can potentially be applied to other pharmacological agents in addition to sodium nitroprusside. The a priori information required for implementation of the controller is the estimate of the order of the patient response transfer function and the range of the pure time delay. An attractive feature of the controller is its capability to optimize the level of the infused drug during the transient phase of the control without creating an output offset. This feature tends to reduce the overall level of the infused drug. Hence, it may be useful when the cost of a drug or its long-term administration side effects is of concern, such as in the case of sodium nitroprusside 相似文献
75.
Part 1 concerns representation: Pop-out for a target that can be distinguished from the distractors only by the relative position of its components was demonstrated, thereby showing that simple shape information is represented preattentively. Findings are discussed in terms of early- vs late-selection debate and in terms of theories of search and texture segregation. Part 2 concerns selection: Strong learning in a varied-mapping paradigm was demonstrated, and it was shown that preattentive shape information can be used for selection. Finally, an account of the learning, namely the group scale hypothesis, is suggested and a final experiment to test it is presented. Results confirm and extend the emphasis placed by J. Duncan and G. W. Humphreys's (1989) attentional engagement theory on grouping processes in visual search. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
76.
Montmorillinite clays, modified with either Zn(II) or Fe(III) chlorides have been used to catalyze the Friedel-Crafts alkylation of thiophene. High yields (ca. 80%) of 2- and 3-benzylthiophene mixtures were obtained using either catalyst in chlorobenzene or nitrobenzene solvent at 80°C. The ratio of 2–3-products was found to be controlled by their relative stability. Reactions were most rapid in nitrobenzene solution (<5 min) and resulted in formation of the 2-isomer as the only mono-substituted product. This is believed to be the first example in which an alkylation of thiophene has been limited to one regio-isomer. 相似文献
77.
Steven S Fu Miles McFall Andrew J Saxon Jean C Beckham Timothy P Carmody Dewleen G Baker Anne M Joseph 《Nicotine & tobacco research》2007,9(11):1071-1084
We conducted a systematic review of what is known about the relationship between post-traumatic stress disorder (PTSD) and smoking to guide research on underlying mechanisms and to facilitate the development of evidence-based tobacco treatments for this population of smokers. We searched Medline, PsychINFO, and the Cochrane Central Register of Controlled Trials and identified 45 studies for review that presented primary data on PTSD and smoking. Smoking rates were high among clinical samples with PTSD (40%-86%) as well as nonclinical populations with PTSD (34%-61%). Most studies showed a positive relationship between PTSD and smoking and nicotine dependence, with odds ratios ranging between 2.04 and 4.52. Findings also suggest that PTSD, rather than trauma exposure itself, is more influential for increasing risk of smoking. A small but growing literature has examined psychological factors related to smoking initiation and maintenance and the overlapping neurobiology of PTSD and nicotine dependence. Observational studies indicate that smokers with PTSD have lower quit rates than do smokers without PTSD. Yet a few tobacco cessation treatment trials in smokers with PTSD have achieved quit rates comparable with controlled trials of smokers without mental disorders. In conclusion, the evidence points to a causal relationship between PTSD and smoking that may be bidirectional. Specific PTSD symptoms may contribute to smoking and disrupt cessation attempts. Intervention studies that test behavioral and pharmacological interventions designed specifically for use in patients with PTSD are needed to reduce morbidity and mortality in this population. 相似文献
78.
The paper presents a case study of the development of an expert decision support system which uses simple heuristic methods for fast determination of routes for simultaneous signals in a transmission network of limited capacity. It illustrates how heuristic solutions can be embodied in a model-based DSS and how the standard decision support literature, although intuitively appealing, provides little practical assistance in system construction or classification 相似文献
79.
Fast algorithms for single frequency estimation 总被引:2,自引:0,他引:2
In this paper, some new estimators of the frequency of a single complex sinusoid are presented. The rotate-add-decimate (RAD) method of Crozier is first refined to more closely approach the Cramer-Rao Bound (CRB). An additional modification yields an unbiased estimator (ERAD) that essentially achieves the CRB above a signal-to-noise ratio (SNR) threshold comparable to that of RAD. In addition, this estimator is proven to achieve the CRB for high SNR. The ERAD method requires approximately 2N complex multiply-adds and log/sub 2/N arctangents. A modified ERAD (MERAD) is proposed that matches the SNR threshold and computational complexity of the RAD method (approximately 3N complex multiply-adds and log/sub 2/N arctangents) but achieves the CRB for high SNR. 相似文献
80.