全文获取类型
收费全文 | 26159篇 |
免费 | 1833篇 |
国内免费 | 62篇 |
专业分类
电工技术 | 381篇 |
综合类 | 27篇 |
化学工业 | 6227篇 |
金属工艺 | 1010篇 |
机械仪表 | 1546篇 |
建筑科学 | 468篇 |
矿业工程 | 9篇 |
能源动力 | 1124篇 |
轻工业 | 2280篇 |
水利工程 | 101篇 |
石油天然气 | 19篇 |
无线电 | 4380篇 |
一般工业技术 | 5730篇 |
冶金工业 | 1652篇 |
原子能技术 | 362篇 |
自动化技术 | 2738篇 |
出版年
2024年 | 25篇 |
2023年 | 320篇 |
2022年 | 483篇 |
2021年 | 826篇 |
2020年 | 576篇 |
2019年 | 666篇 |
2018年 | 861篇 |
2017年 | 843篇 |
2016年 | 1009篇 |
2015年 | 799篇 |
2014年 | 1217篇 |
2013年 | 1712篇 |
2012年 | 1787篇 |
2011年 | 2218篇 |
2010年 | 1600篇 |
2009年 | 1617篇 |
2008年 | 1450篇 |
2007年 | 1126篇 |
2006年 | 995篇 |
2005年 | 837篇 |
2004年 | 785篇 |
2003年 | 706篇 |
2002年 | 706篇 |
2001年 | 614篇 |
2000年 | 523篇 |
1999年 | 495篇 |
1998年 | 772篇 |
1997年 | 458篇 |
1996年 | 432篇 |
1995年 | 286篇 |
1994年 | 186篇 |
1993年 | 163篇 |
1992年 | 128篇 |
1991年 | 106篇 |
1990年 | 83篇 |
1989年 | 100篇 |
1988年 | 80篇 |
1987年 | 69篇 |
1986年 | 55篇 |
1985年 | 45篇 |
1984年 | 39篇 |
1983年 | 28篇 |
1982年 | 31篇 |
1981年 | 27篇 |
1980年 | 29篇 |
1979年 | 13篇 |
1977年 | 24篇 |
1976年 | 36篇 |
1975年 | 18篇 |
1974年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Hong Jeong Jeong‐Ho Park 《International Journal of Adaptive Control and Signal Processing》2002,16(1):1-23
Tracking targets of interest is one of the major research areas in radar surveillance systems. We formulate the problem as incomplete data estimation and apply EM to the MAP estimate. The resulting filter has a recursive structure analogous to the Kalman filter. The advantage is that the measurement‐update deals with multiple measurements in parallel and the parameter‐update estimates the system parameters on the fly. Experiments tracking separate targets in parallel show that tracking maintenance ratio of the proposed system is better than that of NNF and RMS position error is smaller than that of PDAF. Also, the system parameters are correctly obtained even from incorrect initial values. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
62.
Nanocomposites based on poly(butylene terephthalate) (PBT) and an organoclay (Cloisite 30B) were prepared by melt blending using a twin‐screw extruder. Two kinds of PBTs, ie PBT‐A and PBT‐B, with different inherent viscosities (ηinh), were used for this study (ηinh of PBT‐A and PBT‐B were 0.74 and 1.48, respectively). Dispersion of the clay layers in the PBT nanocomposites was characterized by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile and dynamic mechanical properties and non‐isothermal crystallization temperatures of the nanocomposites were also examined. Nanocomposites based on the higher‐viscosity PBT (PBT‐B) showed a higher degree of exfoliation of the clay and a higher reinforcing effect when compared to the composites based on the lower‐viscosity PBT (PBT‐A). The clay nanolayers dispersed in PBT matrices lead to increases in the non‐isothermal crystallization temperatures of the PBTs, with such increases being more significant for the PBT‐B nanocomposites than for the PBT‐A nanoocomposites. Copyright © 2004 Society of Chemical Industry 相似文献
63.
Existing location-based routing protocols are not versatile enough for a large-scale ad hoc environment to simultaneously meet all of the requirements of scalability, bandwidth efficiency, energy efficiency, and quality-of-service routing. To remedy this deficiency, we propose an optimal tradeoff approach that: 1) constructs a hybrid routing protocol by combining well-known location-update schemes (i.e., proactive location updates within nodes' local regions and a distributed location service), and 2) derives its optimal configuration, in terms of location-update thresholds (both distance and time-based), to minimize the overall routing overhead. We also build a route-discovery scheme based on an Internet-like architecture, i.e., first querying the location of a destination, then applying a series of local-region routing until finding a complete route by aggregating the thus-found partial routes. To find the optimal thresholds for the hybrid protocol, we derive the costs associated with both location updates and route discovery as a function of location-update thresholds, assuming a random mobility model and a general distribution for route request arrivals. The problem of minimizing the total cost is then cast into a distributed optimization problem. We first prove that the total cost is a convex function of the thresholds, and then derive the optimal thresholds. Finally, we show, via simulation, that our analysis results indeed capture the real behavior. 相似文献
64.
Han-Kyu Lim Deog Kyoon Jeong KyungTae Kim JunMo Park Han-gyoo Kim 《Communications Magazine, IEEE》2005,43(5):141-148
Network direct attached storage (NDAS) is a network storage architecture that allows direct attachment of existing ATA/ATAPI devices to Ethernet without a separate server. Unlike other architectures such as NAS, SAN, and USB mass storage, no server computer intervenes between the storage and the client hosts. We describe an NDAS disk controller (NDC) amenable to low-cost single-chip implementation that processes a simplified L3/L4 protocol and converts commands between ATA/ATAPI and Ethernet, while the remaining complex tasks are performed by remote hosts. Unlike NAS architectures that use TCP/IP, NDAS uses a TCP-like lean protocol that lends itself well to high-performance hardware realization. Thanks to the simple NDAS architecture and protocol, an NDC implemented on a single 4 mm /spl times/ 4 mm chip in 0.18 /spl mu/m CMOS technology achieves a maximum throughput of 55 Mbytes/s on gigabit Ethernet, which is comparable to that of a high-performance disk locally attached to a host computer. 相似文献
65.
66.
67.
68.
69.
LiFePO4 is a potential candidate for the cathode material of the lithium secondary batteries. A co-precipitation method was adopted to prepare LiFePO4 because it is simple and cheap. Nitrogen gas was needed to prevent oxidation of Fe2+ in the aqueous solution. The co-precipitated precursor shows the high reactivity with the reductive gas, and the single phase of LiFePO4 is successfully synthesized with the aid of carbon under less reductive conditions. LiFePO4 fine powder prepared by co-precipitation method shows high rate capability, impressive specific capacity and cycle property. 相似文献
70.
H. M. Park M. C. Sung 《International journal for numerical methods in engineering》2004,60(12):1949-1968
The Karhunen–Loève Galerkin procedure is employed to solve an inverse radiation problem of determining the time‐varying strength of a heat source, which mimics flames in a furnace, from temperature measurements in three‐dimensional participating media where radiation and conduction occur simultaneously. The inverse radiation problem is solved through the minimization of a performance function, which is expressed by the sum of square residuals between calculated and observed temperature, using a conjugate gradient method. Through the Karhunen–Loève Galerkin procedure, one can represent the system dynamics with a minimum degree of freedom, and consequently the amount of computation required in the solution of the inverse problem is reduced drastically when the present technique is adopted. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献