全文获取类型
收费全文 | 53046篇 |
免费 | 6177篇 |
国内免费 | 4230篇 |
学科分类
工业技术 | 63453篇 |
出版年
2024年 | 315篇 |
2023年 | 996篇 |
2022年 | 1982篇 |
2021年 | 2509篇 |
2020年 | 1860篇 |
2019年 | 1341篇 |
2018年 | 1457篇 |
2017年 | 1721篇 |
2016年 | 1521篇 |
2015年 | 2366篇 |
2014年 | 3106篇 |
2013年 | 3549篇 |
2012年 | 4295篇 |
2011年 | 4476篇 |
2010年 | 4216篇 |
2009年 | 3993篇 |
2008年 | 4126篇 |
2007年 | 4042篇 |
2006年 | 3386篇 |
2005年 | 2754篇 |
2004年 | 1989篇 |
2003年 | 1516篇 |
2002年 | 1503篇 |
2001年 | 1437篇 |
2000年 | 1013篇 |
1999年 | 531篇 |
1998年 | 287篇 |
1997年 | 209篇 |
1996年 | 189篇 |
1995年 | 154篇 |
1994年 | 143篇 |
1993年 | 83篇 |
1992年 | 84篇 |
1991年 | 51篇 |
1990年 | 55篇 |
1989年 | 48篇 |
1988年 | 24篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 22篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1959年 | 9篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 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.
稠油微生物开采技术现状及进展 总被引:2,自引:0,他引:2
综述了用微生物方法开采稠油的技术现状与进展,论题如下。①概述。②基本方法:异源微生物采油,包括微生物吞吐和微生物驱;本源微生物采油压大港孔店油田的实例。③主要机理,包括产表面活性剂,降解稠油中重质组分及其他。④技术研究,包括机理性、可行性及经济效益研究,列举了国内外6个实例。⑤现场应用,包括国外1个、国内6个实例。⑥该技术的优势及问题。参22。 相似文献
3.
储层泥浆侵入深度预测方法研究 总被引:4,自引:0,他引:4
泥浆侵入半径的确定尚缺乏严格的验证标准.以油水两相渗流理论和离子扩散方程为基础,结合储集层特点,研究了不同储层参数下泥浆滤液对地层的侵入特性.数值模拟侵入时间选取10 d和20 d.数值模拟结果表明,侵入半径在渗透率不变的情况下随孔隙度的增大而减小,在孔隙度不变的情况下随渗透率的增大而增大;当渗透率和孔隙度都发生变化时,泥浆侵入半径一般随孔隙度的增加呈幂函数增加.依据这种关系对测井资料约束处理,得到的泥浆侵入半径较客观地反映了地层的真实情况. 相似文献
4.
5.
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.
In the present study, attempts are made to extend the application of the mechanical model for the fatigue crack initiation (FCI) and the FCI life formula of metallic notched elements in laboratory air to those in the corrosive environment. The test results and analysis of the corrosion FCI (CFCI) life of aluminum alloys and Ti---6A1---4V show that the expression of the CFCI life obtained by modifying the FCI life formula in laboratory air can give a good fit to the test results of the CFCI life. The salt water (3.5% NaCl) environment has no effects on the CFCI resistant coefficient compared with the FCI resistant coefficient in laboratory air. However, 3.5% NaCl environment greatly decreases the CFCI threshold of aluminum alloy, but has little effect on the CFCI threshold of Ti---6A1---4V. The loading frequency ranging from 1 Hz to 10 Hz has no appreciable effect on the CFCI life, and thus, the CFCI threshold of aluminum alloys investigated. Hence, the expression for the CFCI life of metallic notched elements proposed in this study is a better one, which reveals a correlation between the CFCI life and the governing parameters, such as, the geometry of the notched elements, the nominal stress range, the stress ratio, the tensile properties and the CFCI threshold. However, this new expression of the CFCI life needs to be verified by more test results. 相似文献
10.
制作压力传感器时,在二氧化硅层上淀积多晶硅膜,既可利用优良的机械特性,又可保证压敏电阻与衬底间具有良好的绝缘性,由此可大大提高器件的温度特性。介绍了一种多晶硅压力传感器的原理和设计。实验结果表明,这类传感器具有灵敏度好,精度高等特点,电路工作范围为0-250℃,且具有良好的温度稳定性。 相似文献