全文获取类型
收费全文 | 523207篇 |
免费 | 5309篇 |
国内免费 | 1073篇 |
专业分类
电工技术 | 8981篇 |
综合类 | 319篇 |
化学工业 | 81269篇 |
金属工艺 | 28058篇 |
机械仪表 | 18713篇 |
建筑科学 | 11167篇 |
矿业工程 | 5104篇 |
能源动力 | 10446篇 |
轻工业 | 34556篇 |
水利工程 | 7050篇 |
石油天然气 | 16785篇 |
武器工业 | 36篇 |
无线电 | 51335篇 |
一般工业技术 | 116941篇 |
冶金工业 | 78737篇 |
原子能技术 | 15797篇 |
自动化技术 | 44295篇 |
出版年
2021年 | 4349篇 |
2019年 | 4146篇 |
2018年 | 12839篇 |
2017年 | 13148篇 |
2016年 | 11679篇 |
2015年 | 5216篇 |
2014年 | 8524篇 |
2013年 | 20180篇 |
2012年 | 14242篇 |
2011年 | 21058篇 |
2010年 | 17943篇 |
2009年 | 18571篇 |
2008年 | 19303篇 |
2007年 | 20090篇 |
2006年 | 12812篇 |
2005年 | 13463篇 |
2004年 | 12356篇 |
2003年 | 11888篇 |
2002年 | 11145篇 |
2001年 | 10442篇 |
2000年 | 10193篇 |
1999年 | 9596篇 |
1998年 | 20553篇 |
1997年 | 15684篇 |
1996年 | 12064篇 |
1995年 | 9438篇 |
1994年 | 8644篇 |
1993年 | 8689篇 |
1992年 | 6950篇 |
1991年 | 7007篇 |
1990年 | 6940篇 |
1989年 | 6816篇 |
1988年 | 6623篇 |
1987年 | 6021篇 |
1986年 | 5937篇 |
1985年 | 6637篇 |
1984年 | 6399篇 |
1983年 | 5980篇 |
1982年 | 5644篇 |
1981年 | 5807篇 |
1980年 | 5685篇 |
1979年 | 5798篇 |
1978年 | 6044篇 |
1977年 | 6490篇 |
1976年 | 7927篇 |
1975年 | 5458篇 |
1974年 | 5389篇 |
1973年 | 5481篇 |
1972年 | 4832篇 |
1971年 | 4447篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
ABSTRACT: Physical aging of amorphous anhydrous fructose at temperature 5 °C and at 22 °C was studied using differential scanning calorimetry (DSC). The dynamic glass transition temperature, Tg0 for unaged samples was 16 °C and 13.3 °C for heating rate of 10 °C/min and 1 °C/min, respectively. The fictive temperature, Tf0 for unaged samples calculated by Richardson and Savill method was 12 °C, which is close to the dynamic value obtained from the lower DSC heating rate. The fictive temperature Tf of the aged fructose glasses at temperatures both below and above the transition region was fitted well by a non-exponential decay function (Williams-Watts form). Aging above the transition region (22 °C) for 18 d increased both the dynamic glass transition temperature Tg and the fictive temperature Tf . However, aging below the transition region (5 °C) for 1 d increased the dynamic glass transition temperature Tg but decreased the fictive temperature Tf . 相似文献
952.
V. Psota I. Boha
enko J. Hartmann M. Budinsk J. Chmelík 《Journal of the Institute of Brewing》2002,108(2):200-203
A newly developed method GFFF (Gravitational Field‐Flow Fractionation) and the well known method LALLS (Low Angle Laser Light Scattering) were used to assess starch granule size distribution of ten varieties of spring barley. As a distribution criterion, the ratio of starch granule content larger than 8 μm (type A) and smaller than 8 μm (type B) was chosen. Both methods divided the observed set in a similar way. Varieties Akcent, Forum and Atribut formed a variety set with the highest ratio of large and small starch granules. Varieties Scarlet and Kompakt had intermediate ratios. The remaining five varieties Amulet, Novum, Olbram, Tolar and Krona had the lowest ratios of large and small starch granules. Statistical analysis showed that there was a highly significant correlation between the GFFF and LALLS methods. 相似文献
953.
The possible application of adaptive antennas in microcellular operational environments is studied in this paper with the help of a site-specific ray-tracing propagation model. First are examined the statistics of propagation parameters that play an important role for the performance of adaptive antennas. Particular emphasis is put on the spatial characteristics of the radio channel under line-of-sight (LOS) and non-LOS conditions. For this reason, area statistics are produced for a typical small-cell environment for parameters such as the number of multipath clusters, number of rays, angular size, and excess delay of each impulse response, as well as the number of rays, angular size and power of the multipath clusters. Results show that contrary to the common belief for such environments, the signal is not "almost" uniformly distributed in the spatial domain, instead is contained in a few narrow clusters. Then the effect of the microcellular environment on the uplink performance of some well-known techniques like conventional beamforming, maximum entropy, switched beams, maximum ratio and optimum combining, and beam-space optimum combining is examined . The results show that for typical time-division multiple-access (TDMA) scenarios with one and two users, the beam space optimum combining (strongest eigenvalue version) and the switched beams methods, offer the best performance 相似文献
954.
Portable system for data acquisition and transmission based on handheld PC technology 总被引:1,自引:0,他引:1
A portable system is developed to monitor physical activity by acquiring and storing data from body-mounted sensors; a handheld PC is used for managing data acquisition and storage, including radio-transmission to a remote host. An application related to the use of a gyro-accelerometric sensor for determining walking distance is discussed. 相似文献
955.
V.R. Velasco 《Microelectronics Journal》2002,33(4):361-364
We study the electronic states of different GaAs-AlAs Fibonacci quasi-perodic heterostructures grown along the (001) direction. We employ an empirical tight-binding Hamiltonian including spin-orbit coupling together with the surface Green function matching method. We present results for the eighth Fibonacci generation formed from different building blocks. We compare these results with those of the constituent quantum wells and with those of heterostructures containing the same number of GaAs and AlAs slabs after periodic repetition of the building blocks. No Fibonacci spectrum is found in the energy regions near the conduction and valence band edges of GaAs. A selective localization of the local density of states in the GaAs layers is found for many electronic states. 相似文献
956.
Low-loss (<6 dB), flat-top, 16-wavelength, 100-GHz channel spacing DWDM (de)multiplexers are reported. The bulk-optics architecture used allows excellent thermal stability for operating temperature [-10, 60°C] 相似文献
957.
Tonchev V.D. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2002,48(4):975-977
It is proved that a class of q-ary (2n,n) formally self-dual codes obtained from symmetric matrices over GF (q), contains codes that meet the Varshamov-Gilbert bound. The codes are self-dual with respect to the symplectic inner product and yield quantum codes encoding one state with n q-ary qubits and having minimum distance proportional to n 相似文献
958.
The stability of the reactive interface during the solid-state displacement reaction, Cu2O+Co1−X
Fe
X
=2Cu+(Co1−X
Fe
X
)O, is studied as a function of Co-Fe alloy composition at 1223 K. For X≤0.03, the reaction zone has a layered structure, and the cation diffusion in (Co, Fe)O is the rate-limiting step. The interface
is unstable in the early stages of the reaction; the instability decreases with time as the oxide thickness increases, and
the interface becomes planar at long times. The time required for the attainment of interface planarity increases with the
value of X. The reaction kinetics are consistent with the available cation-diffusion data in (Co, Fe)O. For X≥0.045, the product zone is a composite of Cu+(Co, Fe)O, and the rate is limited by the oxygen transport in copper. The transition
to interface instability occurs when the oxide can support a cation flux that exceeds the maximum possible oxygen flux in
copper. During the reaction, composition gradients develop in (Co, Fe)O because of higher diffusion rates for iron than for
cobalt. 相似文献
959.
本文设计了用于千兆以太网基带铜缆接收器均衡的甚高频自适应连续时间Gm-C二阶带通滤波器。基于最陡梯度下降算法,带通滤波器的零点在57-340MHz的频率范围内可以自适应地调节,中心频率为1.278GHz。通过外接电阻伺服环路,滤波器中跨导转换器的跨导值不受工艺偏差和温度变化的影响,采用CSMC-HJ0.6μm CMOS工艺器件模型,用Cadence Spectres仿真器仿真了设计的自适应滤波器电路,仿真结果验证了设计原理和设计的电路。系统的最长学习时间为880个参考时钟周期。 相似文献
960.