全文获取类型
收费全文 | 264096篇 |
免费 | 4933篇 |
国内免费 | 1821篇 |
专业分类
电工技术 | 5453篇 |
技术理论 | 5篇 |
综合类 | 1169篇 |
化学工业 | 43115篇 |
金属工艺 | 11085篇 |
机械仪表 | 7845篇 |
建筑科学 | 6779篇 |
矿业工程 | 1666篇 |
能源动力 | 5736篇 |
轻工业 | 26246篇 |
水利工程 | 2912篇 |
石油天然气 | 6009篇 |
武器工业 | 243篇 |
无线电 | 28035篇 |
一般工业技术 | 49815篇 |
冶金工业 | 47319篇 |
原子能技术 | 5660篇 |
自动化技术 | 21758篇 |
出版年
2021年 | 2679篇 |
2019年 | 2224篇 |
2018年 | 3524篇 |
2017年 | 3482篇 |
2016年 | 3854篇 |
2015年 | 2897篇 |
2014年 | 4726篇 |
2013年 | 11629篇 |
2012年 | 7935篇 |
2011年 | 10499篇 |
2010年 | 8311篇 |
2009年 | 8893篇 |
2008年 | 9684篇 |
2007年 | 9751篇 |
2006年 | 8615篇 |
2005年 | 7524篇 |
2004年 | 6756篇 |
2003年 | 6294篇 |
2002年 | 6283篇 |
2001年 | 6373篇 |
2000年 | 5961篇 |
1999年 | 5924篇 |
1998年 | 12892篇 |
1997年 | 9564篇 |
1996年 | 7307篇 |
1995年 | 5560篇 |
1994年 | 5099篇 |
1993年 | 4969篇 |
1992年 | 3951篇 |
1991年 | 3765篇 |
1990年 | 3833篇 |
1989年 | 3780篇 |
1988年 | 3537篇 |
1987年 | 3026篇 |
1986年 | 3058篇 |
1985年 | 3417篇 |
1984年 | 3331篇 |
1983年 | 3078篇 |
1982年 | 2714篇 |
1981年 | 2911篇 |
1980年 | 2648篇 |
1979年 | 2847篇 |
1978年 | 2741篇 |
1977年 | 2845篇 |
1976年 | 3696篇 |
1975年 | 2458篇 |
1974年 | 2290篇 |
1973年 | 2323篇 |
1972年 | 1981篇 |
1971年 | 1785篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
Solar refrigeration projects both national and international with sorption and other refrigeration systems have been developed in Mexico and other Latin American countries in the last 15 years. A review of the main projects, both for solar cooling and refrigeration and the results obtained are presented in this paper. A methodology where 19 solar technologies for cooling were identified is also presented. Although solar cooling is still not an economically viable technology, the advances made and the experience gained in the projects described and the improved systems envisaged, will make solar refrigeration systems play an important role in the future. 相似文献
933.
Bond Gary R.; Dietzen Laura L.; McGrew John H.; Miller Larry D. 《Canadian Metallurgical Quarterly》1995,40(2):75
Tested the hypothesis that Ss with severe mental illnesses would achieve better vocational outcomes with an accelerated approach to supported employment (AASE), as compared to gradual approaches (GA) with prevocational training. 86 Ss (mean age 35.1 yrs) with a diagnosis of a serious mental illness, were randomly assigned to either the AASE, or the GA, which included a minimum of 4 mo prevocational training. Data were obtained on indicators of vocational outcomes over 2 yrs, and for a limited number of Ss (n=36), during the 4th yr of inception into the program. Initially, only 5% of Ss preferred prevocational training. After 1 yr, AASE Ss showed better outcomes for a range of indicators, including achievement of competitive employment, duration of employment and mean earnings. During the 4th yr, 59% of these Ss were competitively employed, as compared to only 6% of GA Ss. Rehabilitation is more effective using AASE than GA. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
934.
Socially amoral economic forces now drive health system change. The authors, assisted by a panel of experts on employers, health plans, providers, and consumers, discuss current drivers such as (1) employers' price-focused purchasing, without good quality/value measures; (2) health plans' growing successes and market clout; (3) providers declining prospects and fears about their future; and (4) consumers' worries about less choice. Future influences will include Medicare reforms, better information, and pro-consumer regulation of managed care, as well as rising social distress. The health system's future is now open for resolution in an evolving, imperfect market. 相似文献
935.
936.
N Rizzo MC Pittalis G Pilu A Perolo C Banzi A Visentin L Bovicelli 《Canadian Metallurgical Quarterly》1996,16(2):159-163
The participation of sarcoplasmic reticulum Ca2+ release channels in the activation of Ca(2+)-sensitive K+ currents (IK(Ca)) by cyclic dibutyryl GMP was investigated in smooth muscle cells from the circular layer of guinea-pig gastric fundus. All experiments were performed in the presence of 3 microM nicardipine into the bath and low Ca2+ buffering capacity of the pipette-filling solution (pCa 7.4). Ruthenium red (10 microM) as well as its combination with 10 microM heparin abolished the cyclic GMP-induced activation of IK(Ca), while 10 microM heparin remained ineffective. Ryanodine (10 microM) and the subsequently added 1 microM thapsigargin induced a relatively small increase in IK(Ca) amplitudes. The addition of 10 microM ryanodine to 1 microM thapsigargin-containing bath solution caused a vast increase in IK(Ca). It is hypothesyzed that protein kinase G-induced vectorial Ca2+ flux from the cell bulk and sarcoplasmic reticulum Ca2+ stores toward the plasma membrane is realized by a spontaneous Ca(2+)-induced Ca2+ release from a superficially situated Ca2+ store. 相似文献
937.
Neusser S. Nijhuis J. Spaanenburg L. Hoefflinger B. Franke U. Fritz H. 《Micro, IEEE》1993,13(1):57-66
A solution to autonomous lateral vehicle guidance using a neurocontroller that can learn from measured human-driving data without knowledge of the physical car parameters is discussed. Simulations and practical tests confirm that a small-size feedforward autonomous neural network (21 neurons) can learn to steer a vehicle at high speeds only from looking at human-driving examples. In this way, the network learns the total closed-loop behavior, including the nonlinear dynamics of the vehicle and the driver's individual driving style. The main result of practical investigations is that the neutral controller trained on human-driving examples exhibits an aperiodic behavior that does not vanish at higher speeds (tests performed up to 130 km/h) and produces fewer lateral deviations than the linear state controller 相似文献
938.
Following two years operation of the 100 kW grid-connected installation N13 near Domat/Ems, Switzerland, considerable data are available. The yield of the installation was calculated on the basis of long-term meteorological data and of the Meteonorm model. The findings show a close correlation between the forecast and the measured yields. With 100% availability of the inverter in 1991, the performance of the installation rose from 59% in 1990 to 79% in 1991. With standardized analysis of the data, the performance of the grid-connected installation N13 can be compared with other grid-connected installations irrespective of size and location. 相似文献
939.
Dennis L. Nielson 《Geothermics》1996,25(4-5)
The exploration for a geothermal resource on Ascension Island utilized a strategy that initially employed geologic mapping. On the basis of this, subsurface faults were mapped using an aeromagnetic survey. The faults were then explored using electrical resistivity surveys to define areas of potential hydrothermal fluid up-welling. The results of all of these techniques were used to site temperature gradient holes. A deep geothermal exploration well was then drilled in the area with highest heat flow adjacent to a rhyolite-to-trachyte volcanic complex. 相似文献
940.
Experiments conducted at ground stations of the Quasar satellite communication network using both a null base as well as a
base of around 2000 km is described. In experiments with a null base, the time scale transmission error was 1 nsec. Comparison
of the results of collocation with data cbtained by the GLONASS system in the course of experiments using a 2100-km base demonstrated
a divergence of the results of from 5 to 25 nsec.
Translated from Izmeritel'naya Tekhnika, No. 4, pp. 35–38, April, 1996. 相似文献