全文获取类型
收费全文 | 37905篇 |
免费 | 3185篇 |
国内免费 | 1558篇 |
专业分类
电工技术 | 1986篇 |
技术理论 | 2篇 |
综合类 | 2486篇 |
化学工业 | 6779篇 |
金属工艺 | 2290篇 |
机械仪表 | 2196篇 |
建筑科学 | 2830篇 |
矿业工程 | 1139篇 |
能源动力 | 983篇 |
轻工业 | 2198篇 |
水利工程 | 591篇 |
石油天然气 | 2789篇 |
武器工业 | 254篇 |
无线电 | 4404篇 |
一般工业技术 | 4637篇 |
冶金工业 | 1718篇 |
原子能技术 | 485篇 |
自动化技术 | 4881篇 |
出版年
2024年 | 187篇 |
2023年 | 647篇 |
2022年 | 1099篇 |
2021年 | 1570篇 |
2020年 | 1200篇 |
2019年 | 978篇 |
2018年 | 1179篇 |
2017年 | 1297篇 |
2016年 | 1078篇 |
2015年 | 1422篇 |
2014年 | 1817篇 |
2013年 | 2250篇 |
2012年 | 2340篇 |
2011年 | 2656篇 |
2010年 | 2160篇 |
2009年 | 2049篇 |
2008年 | 1966篇 |
2007年 | 1827篇 |
2006年 | 2011篇 |
2005年 | 1803篇 |
2004年 | 1214篇 |
2003年 | 1044篇 |
2002年 | 945篇 |
2001年 | 819篇 |
2000年 | 955篇 |
1999年 | 1122篇 |
1998年 | 875篇 |
1997年 | 773篇 |
1996年 | 731篇 |
1995年 | 604篇 |
1994年 | 496篇 |
1993年 | 368篇 |
1992年 | 279篇 |
1991年 | 216篇 |
1990年 | 155篇 |
1989年 | 134篇 |
1988年 | 116篇 |
1987年 | 72篇 |
1986年 | 55篇 |
1985年 | 26篇 |
1984年 | 22篇 |
1983年 | 20篇 |
1982年 | 31篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 2篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
In this paper, we propose a routing algorithm called minimum fusion Steiner tree (MFST) for energy efficient data gathering with aggregation (fusion) in wireless sensor networks. Different from existing schemes, MFST not only optimizes over the data transmission cost, but also incorporates the cost for data fusion, which can be significant for emerging sensor networks with vectorial data and/or security requirements. By employing a randomized algorithm that allows fusion points to be chosen according to the nodes' data amounts, MFST achieves an approximation ratio of 5/4log(k + 1), where k denotes the number of source nodes, to the optimal solution for extremely general system setups, provided that fusion cost and data aggregation are nondecreasing against the total input data. Consequently, in contrast to algorithms that only excel in full or nonaggregation scenarios without considering fusion cost, MFST can thrive in a wide range of applications 相似文献
42.
在cdma20001x前向信道中,要对一段信号进行传送,一般选用QPSK调制,因为QPSK调制比QAM更适合噪音环境。采用TI6000系列的TMS320C6711芯片处理前向信道信号,可以对复杂性和实时性较高的信号做采集、量化、编码、调制等实时处理,主要功能通过软件编程实现,从而使系统具有结构灵活、可靠性高、可扩展等优点。 相似文献
43.
44.
文章分析了影响地震采集系统延迟时间的因素,并根据系统延迟的理论对产生的原因进行了论证.同时对实际生产中的测试方法进行了阐述研究和分析,提出了新的测试方法,并结合实际生产提出了合理性建议. 相似文献
45.
Nanocrystalline Gd2O3:A (A=Eu3+, Dy3+, Sm3+, Er3+) phosphor films and their patterning were fabricated by a Pechini sol–gel process combined with a soft lithography. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy, UV/vis transmission and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 500 °C and that the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free non-patterned phosphor films were obtained by optimizing the composition of the coating sol, which mainly consisted of grains with an average size of 70 nm and a thickness of 550 nm. Using micro-molding in capillaries technique, we obtained homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths (5, 10, 20 and 50 μm). Significant shrinkage (50%) was observed in the patterned films during the heat treatment process. The doped rare earth ions (A) showed their characteristic emission in crystalline Gd2O3 phosphor films due to an efficient energy transfer from Gd2O3 host to them. Both the lifetimes and PL intensity of the rare earth ions increased with increasing the annealing temperature from 500 to 900 °C, and the optimum concentrations for Eu3+, Dy3+, Sm3+, Er3+ were determined to be 5, 0.25, 1 and 1.5 mol% of Gd3+ in Gd2O3 films, respectively. 相似文献
46.
47.
48.
针对加油站在油品进、销、存方面因管理和人为作弊而产生的损耗大问题,提出了解决办法:各环节交接手续要严密完备;发货方实施保量运输,选择信誉好的承运方;在销售、储存方面应加强管理,推行加油站计量员、账务员集中管理,主要账表电子表格化,及时上报主管部门,执行责任追究制并与效益工资挂钩。 相似文献
49.
50.
Laparoscopic retroperitoneal lymph node dissection is a new surgical procedure used to enhance staging in men with clinical stage I nonseminomatous germ cell tumors of the testis. The procedure has been performed in a limited number of patients at several centers with extensive laparoscopic experience. Laparoscopic retroperitoneal lymphadenectomy is a technically demanding procedure which can be successfully completed in the majority of patients. However, the risk of complications is greater than in patients who undergo standard open retroperitoneal lymph node dissection. The primary advantage of a laparoscopic approach is shortened hospitalization and rapid return to normal activity. The role of laparoscopy in the management of patients with testis malignancy has not been defined. The use of this staging procedure may help minimize the need for surveillance studies following surgery and may be best utilized in men with a lower likelihood of nodal metastases. Ultimately, prospective study in large groups of patients will be necessary to determine the role of laparoscopic retroperitoneal lymph node dissection in patients with testis cancer. 相似文献