全文获取类型
收费全文 | 5391篇 |
免费 | 13篇 |
专业分类
电工技术 | 13篇 |
化学工业 | 151篇 |
金属工艺 | 23篇 |
机械仪表 | 33篇 |
建筑科学 | 47篇 |
矿业工程 | 6篇 |
能源动力 | 30篇 |
轻工业 | 91篇 |
水利工程 | 7篇 |
石油天然气 | 5篇 |
无线电 | 123篇 |
一般工业技术 | 164篇 |
冶金工业 | 4564篇 |
原子能技术 | 25篇 |
自动化技术 | 122篇 |
出版年
2021年 | 10篇 |
2018年 | 11篇 |
2017年 | 8篇 |
2016年 | 21篇 |
2015年 | 7篇 |
2014年 | 15篇 |
2013年 | 46篇 |
2012年 | 28篇 |
2011年 | 40篇 |
2010年 | 27篇 |
2009年 | 27篇 |
2008年 | 37篇 |
2007年 | 26篇 |
2006年 | 33篇 |
2005年 | 23篇 |
2004年 | 21篇 |
2003年 | 38篇 |
2002年 | 24篇 |
2001年 | 28篇 |
2000年 | 19篇 |
1999年 | 145篇 |
1998年 | 1343篇 |
1997年 | 835篇 |
1996年 | 510篇 |
1995年 | 296篇 |
1994年 | 246篇 |
1993年 | 288篇 |
1992年 | 66篇 |
1991年 | 65篇 |
1990年 | 75篇 |
1989年 | 70篇 |
1988年 | 81篇 |
1987年 | 66篇 |
1986年 | 54篇 |
1985年 | 69篇 |
1984年 | 20篇 |
1983年 | 20篇 |
1982年 | 38篇 |
1981年 | 48篇 |
1980年 | 51篇 |
1979年 | 10篇 |
1978年 | 14篇 |
1977年 | 136篇 |
1976年 | 272篇 |
1975年 | 18篇 |
1974年 | 7篇 |
1972年 | 8篇 |
1970年 | 5篇 |
1968年 | 5篇 |
1955年 | 5篇 |
排序方式: 共有5404条查询结果,搜索用时 15 毫秒
11.
A pulsed singly resonant optical parametric oscillator (OPO) has been constructed which can provide tunable coherent radiation over the entire wavelength range extending from 354 nm in the near ultraviolet, throughout the visible, to 2.370 μm in the near infrared using a single β-BaB2O4 crystal. The oscillator is pumped at 308 nm by a pulsed narrow band injection-seeded XeCl excimer laser in a near-field pumping configuration, and energy conversion efficiencies (optical-to-optical) in excess of 10% have been obtained in a 12-nm-long crystal across the OPO tuning range. The requirements placed upon the spectral and spatial coherence of the pump laser for optimum OPO operation are discussed. Experimental results on several oscillator parameters, including tuning range, oscillation threshold, energy conversion efficiency, and spatial and temporal characteristics, are presented 相似文献
12.
13.
D Gianola J L Foulley R L Fernando C R Henderson K A Weigel 《Journal of dairy science》1992,75(10):2805-2823
Procedures are described to estimate variances when heterogeneity of genetic and residual dispersion parameters exists for some criterion. Genetic and residual variances are considered to follow distributions with either known or unknown parameters. The estimates of variances obtained are weighted averages of the corresponding parameter and of a data-based statistic. Although the techniques presented are largely inspired by Bayesian ideas, the procedures can be given a frequentist interpretation, and the parameters of the prior distributions can be estimated from the data at hand. Techniques are described and illustrated for situations in which animals are related or unrelated across herds. We conjecture that the proposed estimators have smaller mean squared error than those obtained by grouping observations in some way and then applying REML within each group. 相似文献
14.
15.
16.
Studied self-monitoring of eyeblink responses in 80 undergraduate volunteers to test hypotheses that (a) the direction of reactive effects is a function of the perceived value of the target behavior; (b) neither the behavior's value nor self-monitoring alone is sufficient to produce significant effects but that both are necessary; (c) self-monitoring is more reactive than monitoring by the E; (d) multiple reports of monitoring are more reactive than a single report of monitoring; and (e) self-monitoring effects are more reactive than a single report of merely attending to a particular behavior. Results provide general support for the 1st 2 hypotheses and suggestive support for the 3rd. Results pertaining to the 4th and 5th hypotheses took an unexpected twist and suggest the need for further study. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
17.
Based on the hitherto published population data of the human red cell PGM1 and acid phosphatase polymorphisms, the geographical distributions of their gene frequencies were analyzed. As far as the acid phosphatase alleles are concerned, a marked geographical gradient was found as the Pa and Pb alleles showed significant correlations with the mean annual temperatures of the various human biotopes (Pa:r = -0.706; Pb:r = +0.812). Against that, the world distribution of the PGM1 alleles did not show a comparable correlation (PGM1 1:R = +0.063; PGM2 1:R = -0.063). The possible reasons for the distribution pattern of the acid phosphatase alleles are discussed. 相似文献
18.
19.
Hemodynamic effects of vasodilator agents in dogs with experimental ventricular septal defects 总被引:1,自引:0,他引:1
The ratio of pulmonary to systemic vascular resistance (Rp/Rs) largely determines the amount of left-to-right shunting and pulmonary to systemic flow rat (Qp/Qs) in the presence of a large isolated ventricular septal defect. The possibility that pharmacologic reduction of systemic vascular resistance with alpha-adrenergic receptor blockade or beta-adrenergic receptor stimulation would increase the ratio Rp/Rs, and therefore reduce the ratio Qp/Qs, was studied in dogs in which ventricular septal defects had been surgically created. Administration of phentolamine and phenoxybenzamine caused a 42% reduction in Rs and no reduction in Rp. Qs was unchanged and Qp declined by 24% and the ratio Qp/Qs fell by 32%. Infusion of the beta-adrenergic receptor stimulant isoproterenol also reduced Qp/Qs. However, this was accomplished as a result of an increase in Qs and at the expense of an increase in heart rate. As a decline in the ratio Qp/Qs has been shown to be beneficial to patients with large left-to-right shunts, pharmacologic reduction of systemic vascular resistance may prove to be helpful in treating congestive heart failure in those patients with large left-to-right shunts at the ventricular level who are refractory to the usual decongestive measures. 相似文献
20.
Bulling among yearling feedlot steers 总被引:1,自引:0,他引:1
RE Pierson R Jensen PM Braddy DP Horton RM Christie 《Canadian Metallurgical Quarterly》1976,169(5):521-523
The effect of ingestion of 250 ml X-ray contrast medium on resting gastrooesophageal sphincter pressure was studied in 10 normal human subjects. Twenty minutes after initiated intake of the contrast medium, a significant fall in sphincter pressure was recorded. In the light of studies on the neurogenic and hormonal regulation of the sphincter pressure it is attempted to account for this effect, and it is concluded that it must be a manifestation of a reflectory relaxation of the sphincter region. From a clinical point of view the consequence must be a demand for standardized conditions with regard to composition and pH of the contrast medium, time schedule and degree of abdominal compression in those cases in which radiological evaluation of the resistance against reflux is called for. 相似文献