全文获取类型
收费全文 | 8680篇 |
免费 | 474篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 117篇 |
综合类 | 38篇 |
化学工业 | 2194篇 |
金属工艺 | 227篇 |
机械仪表 | 185篇 |
建筑科学 | 601篇 |
矿业工程 | 20篇 |
能源动力 | 281篇 |
轻工业 | 838篇 |
水利工程 | 86篇 |
石油天然气 | 43篇 |
武器工业 | 1篇 |
无线电 | 656篇 |
一般工业技术 | 1452篇 |
冶金工业 | 553篇 |
原子能技术 | 58篇 |
自动化技术 | 1815篇 |
出版年
2023年 | 75篇 |
2022年 | 154篇 |
2021年 | 332篇 |
2020年 | 184篇 |
2019年 | 200篇 |
2018年 | 270篇 |
2017年 | 233篇 |
2016年 | 313篇 |
2015年 | 233篇 |
2014年 | 337篇 |
2013年 | 624篇 |
2012年 | 483篇 |
2011年 | 614篇 |
2010年 | 427篇 |
2009年 | 491篇 |
2008年 | 453篇 |
2007年 | 410篇 |
2006年 | 341篇 |
2005年 | 291篇 |
2004年 | 269篇 |
2003年 | 258篇 |
2002年 | 189篇 |
2001年 | 138篇 |
2000年 | 137篇 |
1999年 | 114篇 |
1998年 | 129篇 |
1997年 | 128篇 |
1996年 | 97篇 |
1995年 | 79篇 |
1994年 | 80篇 |
1993年 | 83篇 |
1992年 | 58篇 |
1991年 | 60篇 |
1990年 | 62篇 |
1989年 | 68篇 |
1988年 | 49篇 |
1987年 | 47篇 |
1986年 | 50篇 |
1985年 | 54篇 |
1984年 | 62篇 |
1983年 | 44篇 |
1982年 | 39篇 |
1981年 | 37篇 |
1980年 | 39篇 |
1979年 | 33篇 |
1978年 | 34篇 |
1977年 | 33篇 |
1976年 | 40篇 |
1975年 | 40篇 |
1973年 | 36篇 |
排序方式: 共有9165条查询结果,搜索用时 15 毫秒
991.
The melting of secondary-phase particles—or, more precisely, the melting of such particles together with the surrounding matrix—in
two ternary Al-Mg-Si alloys has been studied. In the quasi-binary Al-Mg2Si alloy, one melting reaction is found. In the alloy with an Si content in excess of that necessary to form Mg2Si, three different melting reactions are observed. At upquenching temperatures above the eutectic temperature, the reaction
rates are very high, and it is assumed that they are controlled by diffusion of the alloying elements in the liquid. Melting
is also observed after prolonged annealing at temperatures below the eutectic temperature in these alloys, which is explained
by the different diffusion rates of Mg and Si. The rate of the melting reaction is in this case assumed to be controlled by
diffusion of the alloying elements in the solid α-Al phase. It is shown that calculation of the particle/matrix interface
composition, which determines when melting is possible, cannot be made solely on the basis of the phase diagram, but must
also include the rate of diffusion of Mg and Si. The melting temperatures observed differ somewhat from the accepted eutectic
temperatures for these alloys. On prolonged annealing, the liquid droplets formed dissolve into the surrounding matrix and
their chemical composition is found to change during dissolution. The resulting eutectic structure after quenching of a droplet
is explained by the phase diagram and the different diffusion rates of Mg and Si as well as by the nucleation conditions of
the constituents involved. 相似文献
992.
We describe a female stillbirth with duplication of 3q21-->qter and deletion of 11q23-->qter resulting from an unbalanced segregation of a maternal t(3;11) reciprocal translocation. The proband had some of the clinical features consistent with those seen in patients with dup(3q) syndrome or distal del(11q) syndrome. Prenatal sonographic examination showed short limbs, intrauterine growth retardation, and an omphalocele containing the liver. 相似文献
993.
The effects of glyceryl nonivamide (GLNVA) on ionic currents were compared and examined in rat pituitary GH3 cells. Hyperpolarization-activated K+ currents in GH3 cells bathed in high-K+ Ca2+-free external solution were studied to assess effects of GLNVA on the an inwardly rectifying K+ current (I(K(IR))). GLNVA is very potent in blocking I(K(IR)) in a concentration-dependent manner, with a half maximal concentrations of 0.1 microM. The complete block of I(K(IR)) achieved with concentrations > or = 1 microM revealed the presence of a non-inactivating current. We also found that GLNVA at a concentration above 30 microM inhibited L-type voltage-dependent Ca2+ current and two components of K+ outward currents, while GLNVA (< or = 3 microM) did not have any effect on them. This study shows that GLNVA, in addition to retaining the capability of eliciting peptidergic neurons, is a selective block of I(K(IR)) in GH3 cells and will provide a useful tool for characterizing I(K(IR)) and understanding its physiological function. In addition, the carefulness should be taken about the interpretation of GLNVA-mediated responses in vivo or in vitro. 相似文献
994.
Wouter A. Serdijn Albert C. Van Der Woerd Jan Davidse Arthur H. M. Van Roermund 《Analog Integrated Circuits and Signal Processing》1995,8(2):131-143
This paper discusses the design of low-voltage low-power fully-integratable automatic gain controls. Four different AGCs are presented, all consisting of three elementary building blocks: a controlled amplifier, a comparator and a voltage follower. Their design is treated separately. As an example, the final section describes an automatic gain control for hearing instruments, realized in a bipolar process. 相似文献
995.
Jan Pejtersen 《Indoor air》1996,6(4):239-248
Abstract The sensory pollution load and microbial contamination of glass-fibre filters at high and low relative humidity were investigated in an experimental set-up in the laboratory. Dust and particles from the outdoor air were collected in two EU7 glass-fibre filters for a pre-conditioning period of 16–18 weeks during which there was a constant airflow with a velocity of 1.9 m/s through the filters. One of the filters was exposed to outdoor air of approximately 40% relative humidity and 10°C, the other to outdoor air of approximately 80% relative humidity and 5°C. The dust in ventilation filters can constitute a serious pollution source in the indoor environment, causing deterioration in the quality of the supply air even before it enters the ventilated spaces. The sensory pollution load from the used filters after the continuous operating time of 16–18 weeks was significantly higher than the sensory pollution load from new filters but the sensory load at 40% and 80% relative humidity did not differ. The microbial contamination of the supply air downstream of the filters, which on average had been exposed to outdoor air of 40% and 80% relative humidity, was negligible. 相似文献
996.
Recently there has been increased interest in the development of high-level architectural synthesis tools targeting power optimization. In this paper, we first present an overview of the various architecture synthesis tasks and analyze their influence on power consumption. A survey of previously proposed techniques is given, and areas of opportunity are identified. We next propose a new architecture synthesis technique for low-power implementation of real-time applications. The technique uses algorithm partitioning to preserve locality in the assignment of operations to hardware units. Preserving locality results in more compact layouts, reduced usage of long high-capacitance buses, and reduced power consumption in multiplexors and buffers. Experimental results show reductions in bus and multiplexor power of up to 80% and 60%, respectively, resulting in 10–25% reduction in total power. 相似文献
997.
In a series of 5 experiments, the allocation of attention prior to the execution of saccade sequences was examined by using a dual-task paradigm. In the primary task, participants were required to execute a sequence of 2 endogenous saccades. The secondary task was a forced-choice letter identification task. During the programming of the saccade sequences, letters were briefly presented at the saccade goals and at no-saccade locations. The results showed that performance was better for letters presented at any of the saccade goals than for letters presented at any of the no-saccade locations. The results support a spatial model that assumes that prior to the execution of a saccade sequence, attention is allocated in parallel to all saccade goals. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
998.
MohammadReza Mousavi Michel Reniers Jan Friso Groote 《Information Processing Letters》2005,93(5):217-223
Considering operators defined using Structural Operational Semantics (SOS), commutativity axioms are intuitive properties that hold for many of them. Proving this intuition is usually a laborious task, requiring several pages of boring and standard proof. To save this effort, we propose a syntactic SOS format which guarantees commutativity for a set of composition operators. 相似文献
999.
Frans M.M. Snijkers Anita Buekenhoudt Jan J. Luyten Jos Cooymans Myrjam Mertens 《Scripta materialia》2004,51(12):1129-1134
Yttria doped Ba-hafnates were prepared by solid state route and the proton conductivity of pressed samples of yttria doped barium hafnate was determined with impedance spectroscopy. The results are compared with existing data for cerates and zirconates. It was found that Ba-hafnates show a level of proton conduction that is comparable to that of doped Ba-zirconates at low and slightly higher at high temperatures. This is in agreement with the prediction based on the ionic radius of the tetravalent atom in the perovskite. 相似文献
1000.
A 90-nm logic technology featuring strained-silicon 总被引:10,自引:0,他引:10
Thompson S.E. Armstrong M. Auth C. Alavi M. Buehler M. Chau R. Cea S. Ghani T. Glass G. Hoffman T. Jan C.-H. Kenyon C. Klaus J. Kuhn K. Zhiyong Ma Mcintyre B. Mistry K. Murthy A. Obradovic B. Nagisetty R. Phi Nguyen Sivakumar S. Shaheed R. Shifren L. Tufts B. Tyagi S. Bohr M. El-Mansy Y. 《Electron Devices, IEEE Transactions on》2004,51(11):1790-1797
A leading-edge 90-nm technology with 1.2-nm physical gate oxide, 45-nm gate length, strained silicon, NiSi, seven layers of Cu interconnects, and low-/spl kappa/ CDO for high-performance dense logic is presented. Strained silicon is used to increase saturated n-type and p-type metal-oxide-semiconductor field-effect transistors (MOSFETs) drive currents by 10% and 25%, respectively. Using selective epitaxial Si/sub 1-x/Ge/sub x/ in the source and drain regions, longitudinal uniaxial compressive stress is introduced into the p-type MOSEFT to increase hole mobility by >50%. A tensile silicon nitride-capping layer is used to introduce tensile strain into the n-type MOSFET and enhance electron mobility by 20%. Unlike all past strained-Si work, the hole mobility enhancement in this paper is present at large vertical electric fields in nanoscale transistors making this strain technique useful for advanced logic technologies. Furthermore, using piezoresistance coefficients it is shown that significantly less strain (/spl sim/5 /spl times/) is needed for a given PMOS mobility enhancement when applied via longitudinal uniaxial compression versus in-plane biaxial tension using the conventional Si/sub 1-x/Ge/sub x/ substrate approach. 相似文献