全文获取类型
收费全文 | 63669篇 |
免费 | 7057篇 |
国内免费 | 4257篇 |
专业分类
电工技术 | 5610篇 |
技术理论 | 4篇 |
综合类 | 5219篇 |
化学工业 | 8850篇 |
金属工艺 | 3714篇 |
机械仪表 | 4377篇 |
建筑科学 | 5349篇 |
矿业工程 | 2314篇 |
能源动力 | 1780篇 |
轻工业 | 4657篇 |
水利工程 | 1599篇 |
石油天然气 | 3146篇 |
武器工业 | 990篇 |
无线电 | 7768篇 |
一般工业技术 | 6047篇 |
冶金工业 | 2674篇 |
原子能技术 | 870篇 |
自动化技术 | 10015篇 |
出版年
2024年 | 378篇 |
2023年 | 1130篇 |
2022年 | 2402篇 |
2021年 | 3298篇 |
2020年 | 2385篇 |
2019年 | 1824篇 |
2018年 | 2030篇 |
2017年 | 2299篇 |
2016年 | 2036篇 |
2015年 | 3057篇 |
2014年 | 3683篇 |
2013年 | 4309篇 |
2012年 | 5198篇 |
2011年 | 5379篇 |
2010年 | 4862篇 |
2009年 | 4668篇 |
2008年 | 4518篇 |
2007年 | 4020篇 |
2006年 | 3757篇 |
2005年 | 3179篇 |
2004年 | 2091篇 |
2003年 | 1390篇 |
2002年 | 1305篇 |
2001年 | 1121篇 |
2000年 | 1025篇 |
1999年 | 830篇 |
1998年 | 491篇 |
1997年 | 440篇 |
1996年 | 407篇 |
1995年 | 357篇 |
1994年 | 241篇 |
1993年 | 195篇 |
1992年 | 179篇 |
1991年 | 106篇 |
1990年 | 92篇 |
1989年 | 62篇 |
1988年 | 55篇 |
1987年 | 37篇 |
1986年 | 35篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1959年 | 9篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
本文提出一种新的ATM交换排队结构——成组输入排队结构(GIQ),其基本思想是将输入端分组,同一组的输入端共享排队缓存。GIQ不仅能提高缓存的利用率和系统的吞吐率(达到96.2%),而且还能大大改善交换结构的抗突发能力。采用计算机仿真模拟的方法,分析了GIQ在均匀连续业务流和突发业务流下的性能,并与其它输入排队结构的性能进行了比较。 相似文献
43.
44.
Randomized trial of breast self-examination in Shanghai: methodology and preliminary results 总被引:3,自引:0,他引:3
DB Thomas DL Gao SG Self CJ Allison Y Tao J Mahloch R Ray Q Qin R Presley P Porter 《Canadian Metallurgical Quarterly》1997,89(5):355-365
BACKGROUND: The efficacy of breast self-examination in helping to reduce mortality from breast cancer has not been rigorously demonstrated. PURPOSE: To assess efficacy, a large, randomized trial was initiated in Shanghai, China. METHODS: From October 1989 to October 1991, 267040 current and retired female employees associated with 520 factories in the Shanghai Textile Industry Bureau were randomly assigned on the basis of factory to either a self-examination instruction group (133375 women) or a control group (133665 women). The women were born within the period from 1925 through 1958. Women in the instruction group were given intensive training in breast self-examination, including the use of silicone breast models and personalized instruction, plus two subsequent reinforcement sessions and multiple reminders to practice the technique. Women in the control group were asked to attend training sessions on the prevention of low back pain. All women have been followed for the development of breast diseases and for death from breast cancer. RESULTS: A high level of participation during the first 4-5 years of the trial was documented among women in the instruction group. Randomly sampled women in this group demonstrated greater proficiency in detecting lumps in breast models than did randomly sampled women in the control group. Approximately equal numbers of breast cancers were detected in the two groups (331 in the instruction group and 322 in the control group) through 1994, which is the last year for which case-finding efforts have been completed. The breast cancers detected in the instruction group were not diagnosed at an appreciably earlier stage or smaller size than those in the control group. More benign breast lesions were detected in the instruction group than in the control group (1457 versus 623, respectively), suggesting a higher index of suspicion for women who received training. Cumulative breast cancer mortality rates through 5 years from entry into the study were nearly equivalent for the two groups. CONCLUSIONS: Breast self-examination has not led to a reduction in mortality from breast cancer in this study cohort in the first several years since the trial began. A shift toward the diagnosis of disease at a less advanced stage in women given instruction has also not been demonstrated. Longer follow-up of participants in this trial is required before final assessment can be made of the efficacy of breast self-examination. IMPLICATIONS: At this time, there is insufficient evidence to recommend for or against the teaching of breast self-examination. 相似文献
45.
46.
47.
A modified transverse resonance method is presented for analyzing generalized multilayered, multiconductor quasiplanar structures with practical parameters such as finite conductor thickness and mounting grooves. Recurrence relations are obtained by using network theory for obtaining the overall transverse equivalent network. while the discontinuity involving the finite-thickness metal sheet and mounting groove is carried out by a field-theory-based multimodal variational formulation. The frequency behaviors of propagating, evanescent, and complex modes are obtained for several commonly used quasiplanar lines, showing good agreement with published results. Furthermore, a leaky-wave study is carried out for open structures, since the open condition can be included in this formulation without difficulties 相似文献
48.
49.
硅化腐植酸钠GFN-1的研制 总被引:1,自引:0,他引:1
针对目前生产腐植酸硅化产品原料受限的缺点,在大量试验的基础上,确定了一条以腐植酸和硅化剂为主要原料的生产工艺,合成了一种与有机硅腐植酸钾(OSAM-K)性能相当的硅化腐植酸钠产品GFN-1,对其常规性能指标和在清水及无固相聚合物钻井液体系中、在膨润土浆和低固相钻井液体系中应用指标,耐温性能进行了对比实验。实验结果表明,GFN-1作为钻井液添加剂,具有良好的降滤失、降黏、耐温及热稳定性,并兼有优良的控制页岩分散能力,其大多数应用性能相当于或略优于OSAM-K,作为替代品完全能够满足油田现场应用的需要。GFN-1的硅化原料性质稳定、来源广泛,生产工艺简单易行,产品质量稳定,具有较好的推广价值。 相似文献
50.