全文获取类型
收费全文 | 374500篇 |
免费 | 29345篇 |
国内免费 | 15521篇 |
专业分类
电工技术 | 22297篇 |
技术理论 | 57篇 |
综合类 | 23106篇 |
化学工业 | 62229篇 |
金属工艺 | 20925篇 |
机械仪表 | 23943篇 |
建筑科学 | 29202篇 |
矿业工程 | 12466篇 |
能源动力 | 10958篇 |
轻工业 | 21832篇 |
水利工程 | 6453篇 |
石油天然气 | 24829篇 |
武器工业 | 3174篇 |
无线电 | 41844篇 |
一般工业技术 | 44047篇 |
冶金工业 | 19891篇 |
原子能技术 | 3628篇 |
自动化技术 | 48485篇 |
出版年
2024年 | 1615篇 |
2023年 | 6249篇 |
2022年 | 11026篇 |
2021年 | 15456篇 |
2020年 | 11867篇 |
2019年 | 9472篇 |
2018年 | 10664篇 |
2017年 | 12035篇 |
2016年 | 10798篇 |
2015年 | 14321篇 |
2014年 | 18368篇 |
2013年 | 22012篇 |
2012年 | 23471篇 |
2011年 | 25797篇 |
2010年 | 22109篇 |
2009年 | 21061篇 |
2008年 | 20660篇 |
2007年 | 19792篇 |
2006年 | 20397篇 |
2005年 | 18022篇 |
2004年 | 11512篇 |
2003年 | 10018篇 |
2002年 | 8952篇 |
2001年 | 8181篇 |
2000年 | 8626篇 |
1999年 | 10150篇 |
1998年 | 8484篇 |
1997年 | 7039篇 |
1996年 | 6604篇 |
1995年 | 5539篇 |
1994年 | 4550篇 |
1993年 | 3183篇 |
1992年 | 2574篇 |
1991年 | 2021篇 |
1990年 | 1552篇 |
1989年 | 1269篇 |
1988年 | 1049篇 |
1987年 | 702篇 |
1986年 | 561篇 |
1985年 | 353篇 |
1984年 | 249篇 |
1983年 | 206篇 |
1982年 | 204篇 |
1981年 | 135篇 |
1980年 | 140篇 |
1979年 | 78篇 |
1978年 | 33篇 |
1977年 | 39篇 |
1976年 | 55篇 |
1975年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
文章简要分析了我国目前在中硬岩石爆破中工业炸药的使用情况,介绍了山西兴安化学材料厂新研制的一种适用于硬岩爆破的高爆速、高威力水胶炸药新品种,对其性能、爆破效果、经济实用性和安全性等进行了阐述。 相似文献
72.
王小龙 《理化检验(物理分册)》1998,34(9):17-20
通过比较多种材料的光滑薄圆筒和切口薄壁圆筒试样的扭断裂曲线,测向两种试验的断裂韧性KIIC相同,从而间接证实了利用光滑薄壁筒测定延性金属断裂韧性KC方法的正确性。 相似文献
73.
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
74.
W. Lim C. K. Wang 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1996,370(2-3):568-572
The one-dimensional (1D) position-sensitive superheated-liquid-droplet dosimeter (SLDD) has been fabricated and tested in the laboratory. The 1D SLDD is fabricated from a 9.525-mm OD, 6.35-mm ID, 20-cm long, Plexiglas-walled tube filled with a mixture of superheated-liquid Freon droplets and host medium glycerol. Washer-shaped piezoelectric acoustic transducers are positioned at both ends of the tube; they determine the number and positions of the acoustic events when the superheated-liquid droplets evaporate upon neutron irradiation. The SLDD is irradiated with the 137Cs and 60Co γ-sources, as well as 252Cf neutron source to test for its radiation response and spatial resolution. The SLDD based on the Freon-134a superheated-liquid droplets operating at 20°C and 1 atm is found to be ideal for measuring absorbed neutron dose. This study also proves that the positions of the radiation-induced nucleation acoustic events can be linearly determined from the differences in the transmission times received by the acoustic transducers on the 1D SLDD. The spatial resolution of the neutron depth-dose is 1 mm due the finite response time (1 μs) of the piezoelectric acoustic transducers. 相似文献
75.
Simultaneous determination of six ephedrines in urine sample has been achieved by high performance liquid chromatography on a Lichrospher RP-18 column, using methylamphetamine as internal standard. The 6 ephedrines are well separated in 25 minutes with resolution better than 1.8. This method has high recovery, selectivity and reproducibility, and the linearity is satisfactory from 1.5 micrograms/ml to 25 micrograms/ml with correlation coefficients better than 0.999. 相似文献
76.
77.
In this study, the effect and side-effect of epidural injection with lappaconitine compound for post-operative analgesia was observed. One hundred and twenty patients were randomly divided into 4 groups. Lappaconitine compound (LB) consisted of 12 mg of lappaconitine and 22.5 mg of bupivacaine, was given to group A (the group of observation), and lappaconitine 12 mg, bupivacaine 22.5 mg and morphine 2 mg to group B, C and D respectively for control. All were given by epidural injection with single blind method during post-operative pain of incision operation. Result showed that the initiating of analgesia was quicker in group A and C than that in group B and D, and the efficacy was group D > A > C > B. There was significant difference between group A and B in the above two parameters, P < 0.01 and P < 0.05. The analgisia maintenence time of single injection was D > A > B > C, that of group D was significantly longer than that of group A (P < 0.01). It indicated that the epidural injection with LB was more rapid and potent than that with lappaconitine alone in post-operative analgesia, and the former had no side-effect, it was safer than morphine. 相似文献
78.
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
79.
Molecular basis of hypoxia-induced erythropoietin expression 总被引:1,自引:0,他引:1
80.
Using AuGeNiCr multilayered metals as the wafer bonding medium, long-wavelength GaInAsP/InP vertical cavity surface emitting lasers employing Al-oxide/Si as the upper and lower distributed Bragg reflectors were fabricated on Si substrate with the bonding interface formed outside the vertical cavity surface emitting laser cavity. Laser emission at 1.545 μm was measured under pulsed operations near room temperature. The low-temperature metallic bonding process demonstrates a great potential in device fabrication 相似文献