全文获取类型
收费全文 | 475713篇 |
免费 | 4408篇 |
国内免费 | 1530篇 |
专业分类
电工技术 | 8104篇 |
综合类 | 602篇 |
化学工业 | 72044篇 |
金属工艺 | 23332篇 |
机械仪表 | 16350篇 |
建筑科学 | 9964篇 |
矿业工程 | 4617篇 |
能源动力 | 10080篇 |
轻工业 | 30161篇 |
水利工程 | 6476篇 |
石油天然气 | 16023篇 |
武器工业 | 68篇 |
无线电 | 49117篇 |
一般工业技术 | 105856篇 |
冶金工业 | 76063篇 |
原子能技术 | 15625篇 |
自动化技术 | 37169篇 |
出版年
2021年 | 4369篇 |
2019年 | 4214篇 |
2018年 | 7813篇 |
2017年 | 8150篇 |
2016年 | 8624篇 |
2015年 | 4943篇 |
2014年 | 8496篇 |
2013年 | 20071篇 |
2012年 | 12822篇 |
2011年 | 16858篇 |
2010年 | 13404篇 |
2009年 | 15242篇 |
2008年 | 15603篇 |
2007年 | 15318篇 |
2006年 | 12866篇 |
2005年 | 11676篇 |
2004年 | 11544篇 |
2003年 | 11250篇 |
2002年 | 10878篇 |
2001年 | 10818篇 |
2000年 | 10413篇 |
1999年 | 10161篇 |
1998年 | 22041篇 |
1997年 | 16257篇 |
1996年 | 12452篇 |
1995年 | 9799篇 |
1994年 | 8797篇 |
1993年 | 8955篇 |
1992年 | 6963篇 |
1991年 | 6895篇 |
1990年 | 6806篇 |
1989年 | 6703篇 |
1988年 | 6339篇 |
1987年 | 5916篇 |
1986年 | 5841篇 |
1985年 | 6345篇 |
1984年 | 5962篇 |
1983年 | 5669篇 |
1982年 | 5271篇 |
1981年 | 5423篇 |
1980年 | 5401篇 |
1979年 | 5353篇 |
1978年 | 5555篇 |
1977年 | 5879篇 |
1976年 | 7167篇 |
1975年 | 4912篇 |
1974年 | 4968篇 |
1973年 | 5014篇 |
1972年 | 4350篇 |
1971年 | 3945篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Formulation of the problem of designing the optimal structure of an active system was considered within the framework of the game-theoretical model of interaction of its participants. Solution and the results of studying the control mechanisms in applications such as in-house management and multiagent systems were presented. 相似文献
992.
An analytical expression for both band-to-band and band-trap-band indirect tunnelings is used to study the gate-induced drain leakage (GIDL) current of MOSFETs measured before and after hot-carrier stress. The voltage and temperature dependence of GIDL are characterized. Both results show that interface traps situated near the midgap participate in the conduction of GIDL, and band-trap-band indirect tunneling could be the major mechanism. This is further supported by the fact that the percentage increase in GIDL induced by hot-carrier stress is about the same as the corresponding increase in interface-trap density. On the other hand, under low-field conditions, trap-assisted Poole–Frenkle emission dominates over tunneling for temperatures even well below room temperature. 相似文献
993.
994.
This prospective study evaluates the results of extracorporal shock-wave piezoelectric lithotripsy in 52 patients, 41 with radiolucent and 11 with calcified shell gallstones. The fragmentation rate was above 90% and the complication rate 31% particularly with pains or intolerance to the adjuvant dissolution therapy. At the end of the treatment, seven cholecystectomies were carried out among the 31 patients for who lithotripsy failed. After 18 months, the success rate was 23% and 12 patients only remained stone free. Nowadays, thanks to the new laparoscopic therapy, extracorporal shock-wave lithotripsy is no longer judged appropriate, especially because of its poor cost-effectiveness and high recurrence ratio. 相似文献
995.
Ferrara K.W. Algazi V.R. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1994,41(2):185-198
In order to determine the limiting velocity resolution that can be achieved using ultrasound, and to provide a model which can be generalized for the analysis of disturbed flow, a theoretical and experimental evaluation of the statistics of the received signal from laminar flow following the transmission of a train of short pulses is presented. The authors derive the autocorrelation function and determine the length of the correlated signal for various flow rates, comparing experimental measurements to theoretical predictions. High resolution experimental RF M-mode images are used to verify the theoretical model. Using a fluid with a density, viscosity, volume concentration, particle size, and speed of sound which is similar to that of blood, the authors show that the signal remains correlated for a long interval under many conditions of clinical interest. Including a comparison with experimental data, the effect of the lateral transit time through the sample volume and the axial velocity spread within the sample volume on the correlation of the received signal is evaluated. When a significant range of velocity components is present within the sample volume, this range is the limiting factor in the length of the correlated signal interval. Therefore, the use of a wideband signal, which reduces the sample volume size, produces a returned signal that may be correlated for a larger number of pulses, or for a longer time 相似文献
996.
V. Carelli G. Di Colo E. Nannipieri M. F. Serafini 《Drug development and industrial pharmacy》1994,20(9):1673-1681
The enhancement effects of some chemicals on the percutaneous absorption of alprazolam through human skin was investigated in vitro. Linoleic acid, oleic acid, Comperlan F® (linoleic acid diethanolamide), Comperlan KD® (coconut fatty acid diethanolamide) and Ethomeen C12® (bis-(2-hydroxyethyl)cocamine) were evaluated for their enhancing effect either as neat solvents or combined with propylene glycol. The effects of skin pretreatment with the enhancers on the percutaneous absorption of alprazolam from a drug suspension in an aqueous gel were also investigated: skin pretreatment with some enhancers has shown potentially interesting aspects. The determination of alprazolam partitioning into untreated and pretreated horny layer supported the idea that, with oleic and linoleic acid, a contribution to the modification of the diffusional resistance of the skin was given by an increase of the drug solubility in the stratum coraeum. 相似文献
997.
G. Staccioli R. Seraglia P. Traldi G. Menchi U. Matteoli 《Holz als Roh- und Werkstoff》1994,52(1):39-41
A specimen fromt he fossil forest of Dunarobba (Central Italy) attributed toTaxodioxylon gypsaceum was chemically analyzed particularly for its terpene content. Main chemical constituents show variations related to ageing and carbonization process, while terpene content exhibits a drop of mono- and sesquiterpenes in favour of diterpenes and higher MW compounds. All components are exclusively hydrocarbons and represent alicyclic or partially aromatic structures. The identified families include abietane, phyllocladane, norabietane and norpimarane among diterpenes and traces of cadinane and selinane among sesquiterpenes. 相似文献
998.
999.
1000.
Lee I. Bremond-Gregoire P. Gerber R. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1994,82(1):158-171
Recently, significant progress has been made in the development of timed process algebras for the specification and analysis of real-time systems. This paper describes a timed process algebra called ACSR, which supports synchronous timed actions and asynchronous instantaneous events. Timed actions are used to represent the usage of resources and to model the passage of time. Events are used to capture synchronization between processes. To be able to specify real systems accurately, ACSR supports a notion of priority that can be used to arbitrate among timed actions competing for the use of resources and among events that are ready for synchronization. The paper also includes a brief overview of other timed process algebras and discusses similarities and differences between them and ACSR 相似文献