全文获取类型
收费全文 | 1127篇 |
免费 | 11篇 |
专业分类
电工技术 | 5篇 |
综合类 | 1篇 |
化学工业 | 62篇 |
金属工艺 | 6篇 |
机械仪表 | 11篇 |
建筑科学 | 16篇 |
矿业工程 | 1篇 |
能源动力 | 12篇 |
轻工业 | 39篇 |
水利工程 | 7篇 |
石油天然气 | 3篇 |
无线电 | 59篇 |
一般工业技术 | 54篇 |
冶金工业 | 796篇 |
原子能技术 | 10篇 |
自动化技术 | 56篇 |
出版年
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 8篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2014年 | 4篇 |
2013年 | 15篇 |
2012年 | 12篇 |
2011年 | 17篇 |
2010年 | 21篇 |
2009年 | 9篇 |
2008年 | 13篇 |
2007年 | 19篇 |
2006年 | 18篇 |
2005年 | 22篇 |
2004年 | 15篇 |
2003年 | 17篇 |
2002年 | 15篇 |
2001年 | 14篇 |
2000年 | 9篇 |
1999年 | 40篇 |
1998年 | 196篇 |
1997年 | 125篇 |
1996年 | 91篇 |
1995年 | 53篇 |
1994年 | 41篇 |
1993年 | 43篇 |
1992年 | 10篇 |
1991年 | 21篇 |
1990年 | 19篇 |
1989年 | 18篇 |
1988年 | 26篇 |
1987年 | 17篇 |
1986年 | 18篇 |
1985年 | 18篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 10篇 |
1977年 | 25篇 |
1976年 | 33篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1971年 | 7篇 |
1970年 | 3篇 |
排序方式: 共有1138条查询结果,搜索用时 31 毫秒
91.
Timothy J Wilt Dennis Niewoehner Robert L Kane Roderick MacDonald Anne M Joseph 《Nicotine & tobacco research》2007,9(1):21-32
Obtaining spirometric testing and providing those results to individuals who smoke has been advocated as a motivational tool to improve smoking cessation. However, its effectiveness is not known. We conducted a systematic review to determine if this approach improves rates of smoking cessation. Data sources included MEDLINE (1966 to October 2005), the Cochrane Library, and experts in the field. Eligible randomized controlled trials (RCTs) enrolled at least 25 smokers per arm, evaluated spirometry with associated counseling or in combination with other treatments, followed subjects at least 6 months, and provided smoking abstinence rates. Results from nonrandomized studies also were summarized. The primary outcome was patient-reported long-term (at least 6 months) sustained abstinence with biological validation. Additional outcomes included self-reported abstinence and point-prevalence abstinence. Seven RCTs (N = 6,052 subjects) met eligibility criteria. Follow-up duration ranged from 9 to 36 months. In six trials, the intervention group received concomitant treatments previously demonstrated to increase cessation independently. The range of abstinence was 3%-14% for control subjects and 7%-39% among intervention groups, statistically significantly in favor of intervention in four studies. The only RCT that assessed the independent contribution of spirometry in combination with counseling demonstrated a nonsignificant 1% improvement in patient-reported point-prevalence abstinence at 12 months in the group that received spirometry plus counseling versus counseling alone (6.5% versus 5.5%). Findings from observational studies were mixed, and the lack of controls makes interpretation problematic. Available evidence is insufficient to determine whether obtaining spirometric values and providing that information to patients improves smoking cessation compared with other smoking cessation methods. Spirometric values are of limited benefit as a predictor of smoking cessation or as a tool to "customize" smoking cessation strategies. 相似文献
92.
Solid-rotor turbine-generators have commonly been derived from the fitting of curves to terminal characteristics obtained by measurement or from finite element simulations. The paper presents a new method to represent the open-circuit operational inductances of a large turbogenerator of 150 MVA. The method differs from current estimation techniques because the lumped model and its parameters are determined simultaneously. It is based on a finite-element electromagnetic linear analysis of the solid-rotor machine cross section in the frequency domain. Network theory is used to characterise the quadrature-axis model where the problems of model structure and parameter determination are treated. A q-axis equivalent circuit with one damper winding and frequency dependent parameters is found. In addition, an analysis of the machine d-axis is presented. It is based in an electromagnetic study of the “black box” two-port network, where the open-circuit operational inductances are represented by frequency dependent parameters 相似文献
93.
94.
Canada is considering the development of a new standard for infant/child life jackets. Eight currently available (approved and non-approved) infant/child life jackets were procured for evaluation. Fifty-six participants were chosen as a sample of convenience from the general public for testing. The life jackets were divided into two groups of four, which were donned on a soft infant manikin procured from the Red Cross. In 224 attempts at donning, only 43 (19%) attempts resulted in the life jacket being donned correctly in less than 1 min. Only one life jacket came close to a good design and passed the life jacket standard for donning time and accuracy. Failure rates were observed across all the participants irrespective of age, gender, experience with children and experience with recreational marine equipment. Accuracy and speed of donning the life jacket were hampered as the number of donning sub-tasks increased. It was concluded that it is possible to design a life jacket that can be donned correctly in under 1 min. The life jacket must be of simple, intuitive design and fall naturally into the anatomical shape of the child. A minimum number of ties, zips and clips should be used in the design, and if such connectors are used they should be color coded or of different shapes and sizes to avoid confusion. 相似文献
95.
B Kachar F Liang U Lins M Ding XR Wu D Stoffler U Aebi TT Sun 《Canadian Metallurgical Quarterly》1999,285(2):595-608
The luminal surface of mouse urothelium in contact with the urine is almost entirely covered with plaques consisting of uroplakin-containing particles that form p6 hexagonal crystals with a center-to-center distance of 16 nm. A combination of quick-freeze/deep-etch images and our previous negative staining data indicate that the head domain of the uroplakin particle, which is exposed without an extensive glycocalyx shield, interacts closely with the head domains of the neighboring particles, while the membrane-embedded tail domains are farther apart; and that urothelial particles and plaques are not rigid structures as they can change their configuration in response to mechanical perturbations. Based on these data, we have constructed three-dimensional models depicting the structural organization of urothelial particles and plaques. Our models suggest that the head-to-head interaction may play a key role in determining the shape and size of the urothelial plaques. These models can explain many properties of urothelial plaques including their unique shape, detergent-insolubility, and morphological changes during vesicle maturation. 相似文献
96.
本文将重点介绍低价Delphi控件中的几个有趣的工具。涉及的内容有:异常处理,实现拖放,以及如何在应用程序申加入“每日一帖”对话框。 相似文献
97.
Kagel John H.; MacDonald Don N.; Battalio Raymond C.; White Steven; Green Leonard 《Canadian Metallurgical Quarterly》1986,100(2):95
Five male Wistar rats chose between a certain prospect and an uncertain prospect having equal expected value under varying levels of resource (water) availability. In contrast to results found with granivorous birds and common shrews (Sorex araneus), the rats did not switch from risk aversion (choosing the certain prospect) to risk preference (choosing the uncertain prospect) as resource availability varied from surplus to deficit, even though deficits were maintained for extended periods of time. Rather, Ss displayed an approximately constant level of risk aversion throughout. Explanations for these differences are offered in terms of procedural differences between this and earlier studies and in terms of differential behavioral patterns of relatively large organisms with large internal resource stores relative to their daily resource requirements. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
98.
The effects of 12 hourly 5-micrograms injections of luteinizing hormone-releasing hormone on luteinizing hormone release, were examined in 18 prepubertal Holstein heifers at 4, 7, or 10 mo of age. During a 6-h pretreatment period, mean serum luteinizing hormone concentrations and mean number of endogenous luteinizing hormone episodes per hour were not influenced by age. The 12-h treatment regimen induced a pulsatile release of luteinizing hormone in all heifers. The magnitude, pattern, and total amount of luteinizing hormone released were not influenced by age. However, in the 4 and 10-mo-old age groups, magnitude of luteinizing hormone response to the 3rd hourly injection of luteinizing hormone-releasing hormone was greater than the response to the second injection. Magnitudes of luteinizing hormone responses decreased with time after the 4th hourly injection through the 12th injection and patterns of decline appeared similar among the three age groups. The pituitary of the prepubertal dairy heifer is able to respond to an hourly pulsatile administration of luteinizing hormone-releasing hormone and this treatment regimen appears to produce a self-priming effect on luteinizing hormone release. 相似文献
99.
100.
We have investigated the effect of the anticancer compound, camptothecin on Jurkat T-cells, a lymphoblastoid leukemic cell-line. Exposure to low concentrations led to rapid cessation of DNA (more than 95%) and RNA (more than 75%) synthesis. Perturbations to the cell cycle were observed following exposure which caused a significant accumulation of cells within G1 (P = 0.03) with a concomitant decrease in G2/M (P = 0.025). Concentrations below 0.1 microM could inhibit DNA synthesis but not induce apoptosis. Induction of apoptosis was dose dependent and could be detected as early as 3 h post exposure. The apoptotic population appeared to be derived from G1 and S-phase cells but not G2/M, coinciding with the cell cycle compartments in which DNA and RNA polymerases function. However, direct inhibition of DNA polymerase alone was not shown to be associated the induction of apoptosis or with a decrease in susceptibility to camptothecin-induced cell death. The effects of camptothecin on Jurkat T-cells and the potential mechanisms involved are discussed in the context of observations made in other transformed cell lines. 相似文献