全文获取类型
收费全文 | 537686篇 |
免费 | 39270篇 |
国内免费 | 13066篇 |
学科分类
工业技术 | 590022篇 |
出版年
2025年 | 1142篇 |
2024年 | 10950篇 |
2023年 | 10250篇 |
2022年 | 14689篇 |
2021年 | 20534篇 |
2020年 | 17301篇 |
2019年 | 14386篇 |
2018年 | 14401篇 |
2017年 | 16094篇 |
2016年 | 15042篇 |
2015年 | 19364篇 |
2014年 | 24602篇 |
2013年 | 29602篇 |
2012年 | 31535篇 |
2011年 | 34722篇 |
2010年 | 30374篇 |
2009年 | 29318篇 |
2008年 | 29044篇 |
2007年 | 27995篇 |
2006年 | 28540篇 |
2005年 | 25105篇 |
2004年 | 16581篇 |
2003年 | 14227篇 |
2002年 | 12732篇 |
2001年 | 11669篇 |
2000年 | 12011篇 |
1999年 | 13696篇 |
1998年 | 11454篇 |
1997年 | 9598篇 |
1996年 | 8927篇 |
1995年 | 7459篇 |
1994年 | 6156篇 |
1993年 | 4406篇 |
1992年 | 3595篇 |
1991年 | 2784篇 |
1990年 | 2156篇 |
1989年 | 1800篇 |
1988年 | 1459篇 |
1987年 | 1013篇 |
1986年 | 770篇 |
1985年 | 533篇 |
1984年 | 386篇 |
1983年 | 298篇 |
1982年 | 300篇 |
1981年 | 209篇 |
1980年 | 201篇 |
1979年 | 110篇 |
1978年 | 59篇 |
1977年 | 65篇 |
1976年 | 96篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
对在实际组网中选择合理的ASON架构和保护方式作了相应分析,并为搭建可向ASON平滑演进的传统网络时需注意的问题提供了参考意见, 相似文献
6.
We propose and evaluate a medium-access control (MAC) protocol for synchronous cellular packet direct-sequence code-division multiple-access (DS/CDMA). The protocol is designed for handling a variety of multimedia traffic types in an integrated wireless-access network (IWAN). For instance, the protocol is suited for carrying multiple traffic types of different priorities. An analytical model for the equilibrium state has been developed for the proposed protocol. A comparative evaluation of the protocol is done for three different radio frequency bandwidths currently under consideration for personal communication services (PCS), i.e., 1.25 MHz, 5 MHz, and 10 MHz. Our results demonstrate that the proposed protocol is both robust and flexible for the intended IWAN applications. It offers a significant multiplexing gain as the bandwidth increases 相似文献
7.
通过对相变增韧陶瓷及一种可切削玻璃-陶瓷动态疲劳(恒应力速率)试验中高应力速率区断裂应力下降现象的理论分析,发现这种现象与材料的阻力特性(R-curve)密切相关。确立的σ_f-σ理论关系能够很好地描述整个应力速率区间内的动态疲劳试验结果。高应力速率区σ_f-σ在双对数坐标下为负斜率直线,直线斜率为(m为阻力曲线KR=k(△a)~m的指数),断裂主要由材料阻力行为控制;低应力速率区,σ_f-σ在双对数坐标下为正斜率直线,直线斜率为 (n为应力腐蚀指数),断裂主要由材料应力腐蚀行为控制。建立了测定材料阻力特性的一种新方法,分别用这种方法及压痕/弯曲方法对一种可切削玻璃-陶瓷的阻力特性进行了实验测定,两种方法所得结果有很好的一致性。 相似文献
8.
Introduction
Owing to long-time running, more facilities including stations, pipelines, vessels have become corrosive and aged ,some process has grown old, it has exert more burden for the maintenance and repair.Simultaneously, the fluid production rate, oil production rate and water injection rate has changed greatly so that the inflicts and problems from the established surface systems will become more obvious. Energy cost of production and running has increasing continuously. Capacity has been unbalance in systems and areas.
…… 相似文献
9.
In this work, a quantitative analysis is applied to resolve the newly reported polarity-dependent charge-to-breakdown (Q/sub BD/) data from thick oxides of 6.8 nm down to ultrathin oxides of 1.9 nm. Three independent sets of Q/sub BD/ data, i.e., n/sup +/poly/NFET stressed under inversion and accumulation, and p/sup +/ poly/PFET under accumulation are carefully investigated. The Q/sub BD/ degradation observed for p-type anodes, either poly-Si or Si-substrate, can be nicely understood with the framework of maximum energy released by injected electrons. Thus, this work provides a universal and quantitative account for a variety of experimental observations in the time-to-breakdown (T/sub BD/) and Q/sub BD/ polarity-dependence of oxide breakdown. 相似文献
10.
Nitrification is a key step for reliable biological nitrogen removal. In order to enhance nitrification in the activated sludge (AS) process, membrane-attached biofilm (MAB) was incorporated in a conventional activated sludge tank. Simultaneous organic carbon removal and nitrification of the MAB incorporated activated sludge (AS + MAB) process was investigated with continuous wastewater treatment. The effluent TOC concentration of AS and the AS + MAB processes were about 6.3 mg/L and 7.9 mg/L, respectively. The TOC removal efficiency of both AS and AS + MAB were above 95% during the wastewater treatment, indicating excellent organic carbon removal performance in both processes. Little nitrification occurred in the AS process. On the contrary, successful nitrification was obtained with the AS + MAB process with nitrification efficiency of about 90%. The volumetric and surface nitrification rates were about 0.14 g/Ld and 6.5 g/m2d, respectively. The results clearly demonstrated that nitrification in the conventional AS process was boosted by MAB. Furthermore, the microfaunal population in the AS + MAB process was different from that in the AS process. The high concentration of rotifers in the AS + MAB process was expected to decrease the generation of excess sludge in the process. 相似文献