全文获取类型
收费全文 | 8188篇 |
免费 | 175篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 85篇 |
综合类 | 3篇 |
化学工业 | 1253篇 |
金属工艺 | 168篇 |
机械仪表 | 158篇 |
建筑科学 | 267篇 |
矿业工程 | 16篇 |
能源动力 | 145篇 |
轻工业 | 728篇 |
水利工程 | 49篇 |
石油天然气 | 48篇 |
无线电 | 762篇 |
一般工业技术 | 1132篇 |
冶金工业 | 2633篇 |
原子能技术 | 95篇 |
自动化技术 | 826篇 |
出版年
2021年 | 57篇 |
2020年 | 61篇 |
2019年 | 65篇 |
2018年 | 77篇 |
2017年 | 84篇 |
2016年 | 108篇 |
2015年 | 63篇 |
2014年 | 87篇 |
2013年 | 412篇 |
2012年 | 155篇 |
2011年 | 242篇 |
2010年 | 186篇 |
2009年 | 203篇 |
2008年 | 222篇 |
2007年 | 224篇 |
2006年 | 212篇 |
2005年 | 194篇 |
2004年 | 215篇 |
2003年 | 197篇 |
2002年 | 187篇 |
2001年 | 185篇 |
2000年 | 163篇 |
1999年 | 191篇 |
1998年 | 595篇 |
1997年 | 388篇 |
1996年 | 280篇 |
1995年 | 205篇 |
1994年 | 206篇 |
1993年 | 222篇 |
1992年 | 142篇 |
1991年 | 122篇 |
1990年 | 141篇 |
1989年 | 120篇 |
1988年 | 107篇 |
1987年 | 116篇 |
1986年 | 125篇 |
1985年 | 129篇 |
1984年 | 99篇 |
1983年 | 119篇 |
1982年 | 120篇 |
1981年 | 96篇 |
1980年 | 77篇 |
1979年 | 105篇 |
1978年 | 99篇 |
1977年 | 118篇 |
1976年 | 193篇 |
1975年 | 65篇 |
1974年 | 72篇 |
1973年 | 73篇 |
1972年 | 53篇 |
排序方式: 共有8368条查询结果,搜索用时 750 毫秒
81.
82.
Conlon P.J. Tong Y.P. French P.M.W. Taylor J.R. Shestakov A.V. 《Electronics letters》1994,30(9):709-710
Sub-100 fs pulse generation from a Kerr lens modelocked Cr4+ :YAG laser has been demonstrated for the first time, yielding femtosecond pulses tunable from 1.49 to 1.56 μm with pulses as short as 90 fs obtained at 1.53 μm 相似文献
83.
Expected value judgments of 5-, 6-, 8-, and 10-yr-olds were studied by using an information integration approach. Children saw roulette-type games with prizes of crayons. They made judgments in a continuous scale of how happy a puppet playing the game would be. In one task, probability and value of a single winning outcome were varied factorially. All ages took both cues into account. Young children used an additive integration rule, whereas children 8 yrs and older used the multiplying rule as predicted by mathematical theory. A 2nd task contained games with both 1 and 2 alternative prizes. At all ages, data patterns were similar to the normative predictions. Even young children showed some understanding of probability dependence. A serial version of the addition strategy may contribute to advanced performance in the 2-prize task. These results are consistent with conceptual understanding of expected value. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
84.
Banaji and Crowder (see record 1990-00387-001) contend "that the movement to develop an ecologically valid psychology of memory has proven itself largely bankrupt" (p. 1185). The authors have two primary concerns. First, they believe that it is rare for studies of real-world cognition to support conclusions that generalize broadly. Second, they are concerned that such studies may be inherently incapable of making significant theoretical or methodological contributions. The research program outlined here can be viewed as a response (in the form of a case study) to the Banaji and Crowder position. Specifically, this project has adopted both theoretical and methodology perspectives from the study of real-world memory to address a long-standing issue in the mainstream memory literature. The project itself was designed to characterize the strategies used to estimate event frequency and the conditions that foster the use of these strategies. A valid model of the estimation process is necessary in order to understand the encoding and representation of event frequency. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
85.
AIMS: This study was designed to assess the efficacy of low dose methotrexate, 15 mg weekly, as a steroid-sparing agent in asthmatic patients requiring long-term oral prednisone treatment. METHODS: The study was a randomised, double blind, placebo controlled, cross over study of 48 weeks duration. Eleven patients with severe steroid-dependent asthma were included. A successful outcome was defined as a reduction in mean prednisone requirements of 7 mg daily compared to baseline requirements, during active treatment. RESULTS: Two patients were required to be withdrawn owing to methotrexate-related adverse effects. The mean prednisone dose for patients who completed the study was 14.4 mg per day (95% CI; 13.6, 15.1) during active treatment, and 12.9 mg per day (95% CI: 12.2, 13.6) during placebo treatment (NS). Only one patient reduced his individual dose requirements by more than 7 mg per day, whereas in three patients prednisone requirements actually increased during active treatment. There were no significant differences in symptom scores, pulmonary function data, and exacerbations between active and placebo treatments. CONCLUSION: No significant steroid-sparing effect was obtained using low dose methotrexate in this study. This negative outcome may be attributable to the small population of patients studied, low baseline FEV1, and the omission of a steroid minimisation run-in period. Our results highlight the importance of careful patient selection and a painstaking approach in the management of patients with steroid-dependent asthma. 相似文献
86.
The exact distributions associated with the current compendial test requirements are generated by resorting to the well known Computer Intensive Algorithm method to establish the exact percentage point (limit) for RSD, corresponding to each selected cut-off probability level (confidence level) for each of the four possible experimental outcomes based on the USP-NF test requirements. A table is constructed to present the two-dimensional power function. The similarities between these tabular values and the current compendial RSD limits for 10 and 30 dosage units are extremely remarkable.
Minor differences exist, however. It is suggested that both the theoretical as well as the numerical approaches should be carried out to arrive at a comprehensive solution. 相似文献
Minor differences exist, however. It is suggested that both the theoretical as well as the numerical approaches should be carried out to arrive at a comprehensive solution. 相似文献
87.
88.
89.
Reports the death of L. E. Tyler, who served as the 81st president of the American Psychological Association. Her view was that the purpose of counseling was to encourage natural, life-long developmental processes as distinguished from psychotherapy, which she felt was more appropriate to clinicians' dealings with disturbances of personality. It is noted that Tyler's concern for clarifying the human puzzle of personal change moved, over time, from individual differences to individuality and from a psychometric perspective to a systems–ecological view of real-world choices. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
90.
A study of eight deaths involving the benzodiazepine flunitrazepam was performed to assess the contribution of this drug to the fatalities. Coronial deaths in Victoria in the 2-year period to mid-1991 were selected in which either flunitrazepam or flunitrazepam and ethanol were the principal toxicological findings. All bodies were subject to a full autopsy by forensic pathologists, and a full toxicological examination. No significant pathology was found at autopsy in any case. Very high concentrations of 7-aminoflunitrazepam, a metabolite of flunitrazepam, were present in all cases. In four cases no other significant drug was detected, whereas in the other four cases there were significant concentrations of ethanol (mean 1.6 g/L). In these two groups of cases the concentrations of 7-aminoflunitrazepam were 0.45 mg/L and 0.16 mg/L, respectively. Only moderate levels of flunitrazepam were detected, suggesting that 7-aminoflunitrazepam is produced postmortem and may be an important marker of flunitrazepam usage. The causes of death in these eight cases were probably either flunitrazepam toxicity or a combination of flunitrazepam and ethanol toxicity. Only one case appeared likely to have been a suicide. Our observations in these cases suggest that flunitrazepam may cause death in the absence of other drugs or significant disease. The presence of ethanol reduces the amount of flunitrazepam needed to cause death. 相似文献