全文获取类型
收费全文 | 46272篇 |
免费 | 4225篇 |
国内免费 | 2637篇 |
专业分类
电工技术 | 2953篇 |
技术理论 | 5篇 |
综合类 | 3632篇 |
化学工业 | 7357篇 |
金属工艺 | 2582篇 |
机械仪表 | 2820篇 |
建筑科学 | 3574篇 |
矿业工程 | 1210篇 |
能源动力 | 1207篇 |
轻工业 | 5006篇 |
水利工程 | 875篇 |
石油天然气 | 2168篇 |
武器工业 | 417篇 |
无线电 | 5574篇 |
一般工业技术 | 4988篇 |
冶金工业 | 2026篇 |
原子能技术 | 544篇 |
自动化技术 | 6196篇 |
出版年
2024年 | 247篇 |
2023年 | 863篇 |
2022年 | 1538篇 |
2021年 | 2016篇 |
2020年 | 1532篇 |
2019年 | 1317篇 |
2018年 | 1414篇 |
2017年 | 1573篇 |
2016年 | 1378篇 |
2015年 | 1950篇 |
2014年 | 2541篇 |
2013年 | 2817篇 |
2012年 | 3183篇 |
2011年 | 3154篇 |
2010年 | 2985篇 |
2009年 | 2833篇 |
2008年 | 2783篇 |
2007年 | 2635篇 |
2006年 | 2449篇 |
2005年 | 2021篇 |
2004年 | 1556篇 |
2003年 | 1662篇 |
2002年 | 1948篇 |
2001年 | 1638篇 |
2000年 | 1148篇 |
1999年 | 927篇 |
1998年 | 591篇 |
1997年 | 483篇 |
1996年 | 444篇 |
1995年 | 361篇 |
1994年 | 295篇 |
1993年 | 202篇 |
1992年 | 165篇 |
1991年 | 117篇 |
1990年 | 114篇 |
1989年 | 77篇 |
1988年 | 53篇 |
1987年 | 24篇 |
1986年 | 27篇 |
1985年 | 9篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 14篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1959年 | 3篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
宁东供水工程供水水泵共有卧式和立式离心泵2种方案可供选择,也是工程论证时争论的焦点,经综合比较及主机设备的国际招标,最终确定了奥地利安德里兹公司的卧式双吸中开式离心泵为宁东供水工程的供水水泵。 相似文献
2.
3.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献
4.
5.
The catalytic activities of alumina prepared from an Al alkoxide-amine adduct monomer for the reaction of cyclopentene oxide with piperidine was determined after various pretreatments, including calcination and exposure to moisture. They were compared with the activity of alumina prepared by the conventional hydrolysis method. It was found that the as-prepared sample from the alkoxide-amine monomer preparation was five times more active than a conventional preparation, suggesting that it has a higher density of surface Lewis acid sites. However, its activity was much more severely suppressed by exposure to moisture. 相似文献
6.
Disciplinary and linguistic considerations for academic Web linking: An exploratory hyperlink mediated study with Mainland China and Taiwan 总被引:4,自引:0,他引:4
The Web has become an important means of academic information exchange and can be used to give new insights into patterns
of informal scholarly communication. This study develops new methods to examine patterns of university Web linking, focusing
on Mainland China and Taiwan, and including language considerations. Multiple exploratory investigations into Web links were
conducted between universities in these two places. Firstly, inlinks were counted to each university Web site from its national
peers using four alternative Web document models. The results were shown to correlate significantly with research productivity
in Taiwan but not in the Mainland, although in the latter case less reliable institutional data could have been the cause.
For Taiwan, this is the first evidence of a scholarly association with academic linking for a non-English speaking region.
It was then ascertained that the same link counts associated more strongly with scientific than social scientific research
productivity in Taiwan. This confirms the general assumption of greater Web use by the hard sciences. We then investigated
Taiwan-Mainland university cross-links, and found that although English is extensively used on the Web, there was no evidence
that it was the language of preference for informal scholarly communication between the two areas.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
8.
9.
10.
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