全文获取类型
收费全文 | 4721篇 |
免费 | 213篇 |
国内免费 | 28篇 |
专业分类
电工技术 | 56篇 |
综合类 | 34篇 |
化学工业 | 724篇 |
金属工艺 | 86篇 |
机械仪表 | 182篇 |
建筑科学 | 93篇 |
矿业工程 | 5篇 |
能源动力 | 111篇 |
轻工业 | 300篇 |
水利工程 | 15篇 |
石油天然气 | 16篇 |
无线电 | 414篇 |
一般工业技术 | 554篇 |
冶金工业 | 2019篇 |
原子能技术 | 52篇 |
自动化技术 | 301篇 |
出版年
2024年 | 3篇 |
2023年 | 37篇 |
2022年 | 73篇 |
2021年 | 115篇 |
2020年 | 74篇 |
2019年 | 82篇 |
2018年 | 98篇 |
2017年 | 110篇 |
2016年 | 104篇 |
2015年 | 100篇 |
2014年 | 125篇 |
2013年 | 170篇 |
2012年 | 181篇 |
2011年 | 223篇 |
2010年 | 180篇 |
2009年 | 166篇 |
2008年 | 163篇 |
2007年 | 102篇 |
2006年 | 104篇 |
2005年 | 82篇 |
2004年 | 83篇 |
2003年 | 75篇 |
2002年 | 77篇 |
2001年 | 71篇 |
2000年 | 51篇 |
1999年 | 105篇 |
1998年 | 707篇 |
1997年 | 404篇 |
1996年 | 236篇 |
1995年 | 163篇 |
1994年 | 132篇 |
1993年 | 123篇 |
1992年 | 43篇 |
1991年 | 51篇 |
1990年 | 35篇 |
1989年 | 43篇 |
1988年 | 35篇 |
1987年 | 37篇 |
1986年 | 25篇 |
1985年 | 19篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 15篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 24篇 |
1976年 | 80篇 |
1914年 | 2篇 |
排序方式: 共有4962条查询结果,搜索用时 359 毫秒
1.
2.
Ha ABDEL MAKSOUD Mk MAHFOUZ Mi SOLIMAN Mohamed G ELHARRIF M ABBASS Ma EL-BADRY 《Biocell》2020,44(1):111-115
Pyrethroid esters are widely used as insecticides worldwide. In this study, we aimed to evaluate the harmful
effect of deltamethrin on the male reproductive system through the assessment of reproductive hormones, inflammatory
markers, and testicular function. To achieve our aim, eighty male 7-9-week-old, Wistar rats were taken, weighed, and
divided into four experimental groups. The first group was kept as a control group, and the other three groups were
given deltamethrin orally at different concentrations (0.87, 8.7, and 17.4 mg/kg body weight) for nine weeks. The results
indicated that deltamethrin administration associated with a significant decrease in reproductive hormones, especially
FSH, LH, and significant elevation in the interleukin 2 (IL2), interleukin 6 (IL6), histamine, and cortisol levels. Also, the
significance of inhibition of sperm motility and viability, decreased testis weights, sperm count, and fructose in semen
were noted. These findings clarify the harmful effect of deltamethrin on the male reproductive system by producing a
significant alteration in reproductive hormones, inflammatory markers as well as testicular function. 相似文献
3.
Effect of Supports and Promoters on the Performance of Ni-Based Catalysts in Ethanol Steam Reforming
Thanh Khoa Phung Thong Le Minh Pham Anh-Nga T. Nguyen Khanh B. Vu Ha Ngoc Giang Tuan-Anh Nguyen Thanh Cong Huynh Hong Duc Pham 《化学工程与技术》2020,43(4):672-688
Ethanol steam reforming (ESR) is one of the potential processes to convert ethanol into valuable products. Hydrogen produced from ESR is considered as green energy for the future and can be an excellent alternative to fossil fuels with the aim of mitigating the greenhouse gas effect. The ESR process has been well studied, using transition metals as catalysts coupled with both acidic and basic oxides as supports. Among various reported transition metals, Ni is an inexpensive material with activity comparable to that of noble metals, showing promising ethanol conversion and hydrogen yields. Additionally, different promoters and supports were utilized to enhance the hydrogen yield and the catalyst stability. This review summarizes and discusses the influences of the supports and promoters of Ni-based catalysts on the ESR process. 相似文献
4.
Jeong-Soo Lee Yang-Kyu Choi Daewon Ha Balasubramanian S. Tsu-Jae King Bokor J. 《Electron Device Letters, IEEE》2003,24(3):186-188
The hydrogen annealing process has been used to improve surface roughness of the Si-fin in CMOS FinFETs for the first time. Hydrogen annealing was performed after Si-fin etch and before gate oxidation. As a result, increased saturation current with a lowered threshold voltage and a decreased low-frequency noise level over the entire range of drain current have been attained. The low-frequency noise characteristics indicate that the oxide trap density is reduced by a factor of 3 due to annealing. These results suggest that hydrogen annealing is very effective for improving device performance and for attaining a high-quality surface of the etched Si-fin. 相似文献
5.
Lead content of rice collected from various areas in the world 总被引:1,自引:0,他引:1
ZW Zhang CS Moon T Watanabe S Shimbo M Ikeda 《Canadian Metallurgical Quarterly》1996,191(1-2):169-175
Rice samples consumed by local populations were collected between 1990 and 1995 in 17 areas in the world, mostly from Asia (10 areas), but also from 7 areas outside of Asia. In total, 1528 samples were obtained (about one half from Japan) and were analyzed for lead (Pb) by electrothermal atomic absorption spectrometry. When the Pb contents in rice samples were classified into 10 areas in Asia, the highest and the lowest geometric means (GMs) were for Indonesia (38 ng/g) and Australia (2 ng/g), respectively. Among 7 regions outside Asia, the GM was highest for Spain (58 ng/g) and the lowest for the USA. (3 ng/g). Moreover, inter-regional differences were significant, when more than 100 samples from one area were divided into 3-9 regions and GMs for regions were compared. There was a marked difference in Pb contents in rice by areas and regions in the world. Nevertheless, comparison by area of the present results with those reported in literature show that there has been no substantial reduction in Pb in rice in the past decade either in Japan or elsewhere in the world. 相似文献
6.
7.
Semi‐Markovian processes (SMP) serve as a versatile means to model various traffic types generated by sources or superposed
from links in ATM networks. An efficient discrete time analysis method is proposed for SMP/G/1 queueing systems to evaluate
ATM switches with non‐renewal input. Some basic results are derived for the autocorrelation function of semi‐Markovian processes
and for the effect of state space reduction on autocorrelation, which show how to represent correlated traffic with given
characteristic by an adequate SMP model of limited size.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Anna Hać 《Journal of Network and Systems Management》1994,2(1):49-62
This paper analyzes the performance of a switching architecture. The performance measures include the elapsed time of packet transfer and the waiting time to begin transfer. The architecture is partitioned depending on the type of network used and the expected traffic in the network. Every partition has a switch with a buffer that can absorb surges of bursty traffic within the network partition. The buffer size depends on the type of the network and incoming traffic. The partition size depends on the network bandwidth, network traffic, packet size and buffer size. Examples of different networks are used to show the applications of the model. The results show that the elapsed time of packet switch transfer depends exponentially on the number of partitions in the network. 相似文献
9.
Pre-transplant nephrectomy was done in a 25-year-old man for calculous pyelonephritis using a retroperitoneal laparoscopic approach with a newly devised ligature applicator-dissector- kidney retractor. 相似文献
10.
E Bazopoulou-Kyrkanidou P Neou CS Bartsocas S Kyrkanides I Fanourakis 《Canadian Metallurgical Quarterly》1995,6(3):227-232
PURPOSE: To select ideal radiologic projections for mapping and ablation of tachycardias of right ventricular outflow tract (RVOT). METHODS: Ten hearts from human corpses were studied utilizing radiopaque material to identify the pulmonary valve and three distinct sites on this valve: septal anterior (A), septal posterior (P) and free-wall (L). Next, the hearts were filmed in the frontal plane and in oblique projections with 15 degrees increments to the right and to the left. The projections in which the sites were lateralized on the valve, eased radiologic interpretation and were considered ideal for mapping and ablation. Depending on the proximity of the sites to the lateral extremes of the pulmonary valve, the projections were considered ideal ( ), intermediary (++) and inadequate (+). RESULTS: Projections [table: see text] CONCLUSION: The A site of RVOT was best indicated in the 60 and 45 degrees left anterior oblique projections; the 0 degree postero anterior projection was best for mapping the P site; the L region was best explored in the 60 degrees right anterior oblique projection. 相似文献