全文获取类型
收费全文 | 68682篇 |
免费 | 5822篇 |
国内免费 | 2982篇 |
专业分类
电工技术 | 3893篇 |
技术理论 | 10篇 |
综合类 | 4553篇 |
化学工业 | 11539篇 |
金属工艺 | 3592篇 |
机械仪表 | 3894篇 |
建筑科学 | 5398篇 |
矿业工程 | 1832篇 |
能源动力 | 1917篇 |
轻工业 | 5312篇 |
水利工程 | 1289篇 |
石油天然气 | 3687篇 |
武器工业 | 530篇 |
无线电 | 8255篇 |
一般工业技术 | 8536篇 |
冶金工业 | 3424篇 |
原子能技术 | 716篇 |
自动化技术 | 9109篇 |
出版年
2024年 | 312篇 |
2023年 | 1182篇 |
2022年 | 2096篇 |
2021年 | 2875篇 |
2020年 | 2249篇 |
2019年 | 1784篇 |
2018年 | 2054篇 |
2017年 | 2142篇 |
2016年 | 2091篇 |
2015年 | 2689篇 |
2014年 | 3349篇 |
2013年 | 3899篇 |
2012年 | 4310篇 |
2011年 | 4718篇 |
2010年 | 3890篇 |
2009年 | 3710篇 |
2008年 | 3690篇 |
2007年 | 3450篇 |
2006年 | 3288篇 |
2005年 | 2862篇 |
2004年 | 2142篇 |
2003年 | 1894篇 |
2002年 | 1735篇 |
2001年 | 1549篇 |
2000年 | 1691篇 |
1999年 | 2016篇 |
1998年 | 1712篇 |
1997年 | 1397篇 |
1996年 | 1378篇 |
1995年 | 1149篇 |
1994年 | 1007篇 |
1993年 | 699篇 |
1992年 | 545篇 |
1991年 | 393篇 |
1990年 | 342篇 |
1989年 | 309篇 |
1988年 | 219篇 |
1987年 | 154篇 |
1986年 | 111篇 |
1985年 | 81篇 |
1984年 | 62篇 |
1983年 | 41篇 |
1982年 | 52篇 |
1981年 | 33篇 |
1980年 | 34篇 |
1979年 | 13篇 |
1977年 | 9篇 |
1976年 | 13篇 |
1974年 | 11篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
A novel series of temperature‐sensitive poly[(N‐isopropylacrylamide)‐co‐(ethyl methacrylate)] (p(NIPAM‐co‐EMA)) microgels was prepared by the surfactant‐free radical polymerization of N‐isopropylacrylamide (NIPAM) with ethyl methacrylate (EMA). The shape, size dispersity and volume‐phase transition behavior of the microgels were investigated by transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis) spectroscopy, dynamic light scattering (DLS) and differential scanning calorimetry (DSC). The transmission electron micrographs and DLS results showed that microgels with narrow distributions were prepared. It was shown from UV–Vis, DLS and DSC measurements that the volume‐phase transition temperature (VPTT) of the p(NIPAM‐co‐EMA) microgels decreased with increasing incorporation of EMA, but the temperature‐sensitivity was impaired when more EMA was incorporated, causing the volume‐phase transition of the microgels to become more continuous. It is noteworthy that incorporation of moderate amounts of EMA could not only lower the VPTT but also enhance the temperature‐sensitivity of the microgels. The reason for this phenomenon could be attributed to changes in the complicated interactions between the various molecules. Copyright © 2004 Society of Chemical Industry 相似文献
72.
J.A. Bakken L. Barone D. Braun M. Caillat C. Dionisi C. Dor H. Elmamouni F. Ferroni G.L. Grazer J.T. He R. Herbiet B. Ille P. Lecomte E. Longo P.F. Loverre Y.S. Lu J.P. Martin U. Micke R.P. Mount P.A. Pirou H.-G. Sander D. Schmitz M. Schneegans D.P. Stickland R.L. Sumner K.L. Tung E. Valente M. Vivargent 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1985,228(2-3):294-302
A calorimeter of 25 bismuth germanate (BGO) crystals equipped with silicon photodiode readout has been tested at the CERN SPS in the energy range 1–50 GeV. The response for electrons has been shown to be linear in this energy range and the rms resolution obtained (
) is approximately 1%, for E > 4 GeV. The electron/pion separation was found to be better than 1:500 in the energy range 1–20 GeV. Data on lateral and longitudinal shower development were compared with the results of a Monte Carlo simulation using the SLAC-EGS program and found to be in good agreement. 相似文献
73.
Dongming Peng Mi Lu 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2005,13(1):106-125
Although the notion of the parallelism in multidimensional applications has existed for a long time, it is so far unknown what the bound (if any) of inter-iteration parallelism in multirate multidimensional digital signal processing (DSP) algorithms is, and whether the maximum inter-iteration parallelism can be achieved for arbitrary multirate data flow algorithms. This paper explores the bound of inter-iteration parallelism within rate-balanced multirate multidimensional DSP algorithms and proves that this parallelism can always be achieved in hardware system given the availability of a large number of processors and the interconnections between them. 相似文献
74.
Most algorithms on receiver autonomous integrity monitoring (RAIM) are under the assumption of a single-satellite fault, because there is an extremely small probability that significant simultaneous multiple-satellite faults may occur. However, after the implementation of the Galileo system in a few years, there will be more satellites in view for the user to utilise together with GPS satellites, and a combination of them will bring better performance for RAIM. On the other hand, with the help of wide area augmentation system and the use of dual-frequency operation, pseudo-range errors will be reduced greatly. Thus, tighter alert limits are required for RAIM, and formerly `small' errors should not be neglected. All of those factors make it necessary to consider simultaneous multiple-satellite faults. A detailed theoretical analysis of RAIM under the condition of two-satellite faults for both vertical and horizontal directions is presented. The characteristic/max slopes for every pair of satellites are then deduced in order to calculate the tighter vertical/horizontal protection level for RAIM 相似文献
75.
The solid solutions of Ba-doped SrBi2Ta2O9 layered perovskite ceramic powders have been successfully prepared via a two-step process using BiTaO4 as a precursor. The lattice constants of the solid solutions monotonically increase with increasing barium-ion content. The sinterability of (Sr1–xBax)Bi2Ta2O9 powders is significantly improved by increasing the barium-ion content. When the specimens with high barium-ion contents are sintered at 1100°C, they thermally decompose to form rod-like grains and the matrix expands, leading to a lower density. The addition of barium ions to SrBi2Ta2O9 also results in significant variation in the morphology of the sintered specimens and the occurrence of c-axis preferred orientation which is ascribed to the anisotropic growth of plate-like grains. The precise control of the barium-ion content as well as the sintering conditions is critical for obtaining densified barium-ion doped SrBi2Ta2O9 ceramics with a pure, layered perovskite structure. 相似文献
76.
77.
A novel finger‐sensing nanocomposite with remarkable and reversible piezoresistivity is successfully fabricated by dispersing homogeneously conductive graphite nanosheets (GNs) in a silicone rubber (SR) matrix. Because of the high aspect ratio of the graphite nanosheets, the nanocomposite displays a very low percolation threshold. The SR/GN nanocomposite with a volume fraction of conductive nanosheets closest to that for the percolation threshold presents a sharp positive‐pressure coefficient effect of the resistivity under very low pressure, namely, in the finger‐pressure range (0.3–0.7 MPa), whereby the abrupt transition could be attributed to compressive‐stress‐induced deformation of the conducting network. The super‐sensitive piezoresistive behavior of the nanocomposite is accounted for by an extension of the tunneling conduction theory which provides a good approximation to the piezoresistive effect. 相似文献
78.
Enhancing echo cancellation via estimation of delay 总被引:2,自引:0,他引:2
Youhong Lu Fowler R. Tian W. Thompson L. 《Signal Processing, IEEE Transactions on》2005,53(11):4159-4168
The advent of packetized audio transmission, such as voice over IP (VoIP), has resulted in challenging requirements for echo cancellation technology. One key aspect of this technology is the need to characterize, quickly and accurately, the echo paths in the transmission media. Echo paths consist of a constant time delay with no echo signal and active regions in which the echo signal is present. When an adaptive filter echo cancellation algorithm is used, its performance can be greatly increased, and its complexity can be reduced if it is only applied to the active regions. This requires an algorithm to estimate the constant delay and locate the active regions. Traditionally, delay estimation has been based on direct application of cross-correlation. This method has poor performance because the input signals are highly correlated and has a high implementation cost because many cross-correlation lags have to be computed for longer time delays. The delay estimation addressed in this paper has two major advantages over the traditional methods. The first is that it has improved performance because the input signals are processed to have less correlation. The second is that the implementation cost is significantly reduced because fewer cross-correlation lags are computed, and an efficient method to estimate lags is created. 相似文献
79.
80.