全文获取类型
收费全文 | 23420篇 |
免费 | 3243篇 |
国内免费 | 2436篇 |
专业分类
电工技术 | 2757篇 |
综合类 | 2692篇 |
化学工业 | 1337篇 |
金属工艺 | 1397篇 |
机械仪表 | 1694篇 |
建筑科学 | 3310篇 |
矿业工程 | 1331篇 |
能源动力 | 610篇 |
轻工业 | 263篇 |
水利工程 | 1063篇 |
石油天然气 | 1040篇 |
武器工业 | 714篇 |
无线电 | 2820篇 |
一般工业技术 | 3122篇 |
冶金工业 | 796篇 |
原子能技术 | 362篇 |
自动化技术 | 3791篇 |
出版年
2024年 | 105篇 |
2023年 | 340篇 |
2022年 | 693篇 |
2021年 | 872篇 |
2020年 | 876篇 |
2019年 | 835篇 |
2018年 | 709篇 |
2017年 | 974篇 |
2016年 | 1028篇 |
2015年 | 1101篇 |
2014年 | 1582篇 |
2013年 | 1734篇 |
2012年 | 1841篇 |
2011年 | 1981篇 |
2010年 | 1525篇 |
2009年 | 1526篇 |
2008年 | 1372篇 |
2007年 | 1513篇 |
2006年 | 1401篇 |
2005年 | 1151篇 |
2004年 | 921篇 |
2003年 | 835篇 |
2002年 | 725篇 |
2001年 | 565篇 |
2000年 | 479篇 |
1999年 | 395篇 |
1998年 | 333篇 |
1997年 | 292篇 |
1996年 | 207篇 |
1995年 | 206篇 |
1994年 | 175篇 |
1993年 | 136篇 |
1992年 | 110篇 |
1991年 | 89篇 |
1990年 | 75篇 |
1989年 | 74篇 |
1988年 | 60篇 |
1987年 | 33篇 |
1986年 | 18篇 |
1985年 | 35篇 |
1984年 | 19篇 |
1983年 | 24篇 |
1982年 | 11篇 |
1980年 | 14篇 |
1979年 | 17篇 |
1963年 | 7篇 |
1961年 | 7篇 |
1960年 | 8篇 |
1959年 | 7篇 |
1955年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Quantitative analyses of flow and stage data, remote sensing and geographic information systems analysis, and field studies were used to assess the impact of dams and diversions on the point bar habitat of the Sacramento Valley Tiger Beetle (Cicindela hirticollis abrupta). The reaches of interest include sites of known historic populations of C. h. abrupta along the Sacramento River from approximately 8 km north of Colusa southward to the confluence with the Feather River and along the Feather River between Yuba City and its confluence with the Sacramento River. The results from this study show that construction of two major dams has altered flows such that prolonged and increased flows during summer, fall, and early winter have most likely disrupted life cycles, flooded larvae, drowned overwintering adults and led to high mortality. Additionally, habitat availability has decreased over time because point bars have decreased in number and area causing increased distances between populations and isolation of populations. Moreover, point bar armouring, channel scouring, altered flows, redirected flows through weirs, and lithologic controls have produced a bimodal distribution of mean grain sizes in the Sacramento River in which the more northern bars contain gravel deposits and more southern bars possess fine sands. These conditions negatively alter moisture retention and sediment compaction and, consequently, burrowing conditions needed by this tiger beetle. Additionally, more stabilized flows (reduced variability) and increased fine‐grained deposition have enabled development and encroachment of vegetation onto the sand bars. Finally, human stresses, such as foot traffic and vehicular traffic may have interfered with burrowing, ovipositing, and foraging. The combination of these stress factors has most likely led to a reduction in source populations and, ultimately, the apparent extirpation of the entire metapopulation. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
32.
33.
Andrew Davenport 《Hemodialysis international. International Symposium on Home Hemodialysis》2003,7(4):348-352
Continuous renal replacement therapy (CRRT) is becoming the treatment of choice for critically ill patients with acute renal failure around the world. In particular, CRRT is used for patients with combined liver and acute renal failure, because they are often hemodynamically unstable. The question arises as to whether the use of CRRT should be extended to those patients with acute and chronic liver failure who do not have dialysis-dependent renal failure. CRRT could potentially allow some detoxification by removing water-soluble toxins and also allow regulation of intravascular volume and correction of sodium and other electrolyte and acid–base imbalances. By providing homeostatic control, CCRT could potentially help support patients by bridging to liver transplantation and managing those who eventually recover with hepatic regeneration. 相似文献
34.
Melissa Kurtz 《Journal of Failure Analysis and Prevention》2007,7(3):175-178
Fuel system assemblies used on recreational watercraft failed after a short time in service in a seawater environment. Examination
of the assemblies revealed significant degradation of the polyacetal connectors of the wire subassemblies. Optical and microscopic
evaluations indicated the complete loss of connector material implying decomposition of the resin, along with mud-cracking
and a rough surface morphology signifying chemical attack. An elemental analysis performed on both an intact connector and
degraded connector suggested a potential chemical agent in the form of zinc chloride. At elevated temperatures, concentrated
zinc chloride solutions are known to decompose polyacetal resins. The source of the zinc chloride was established as corrosion
products that resulted during the dezincification of the internal brass connector through exposure to saltwater in the application. 相似文献
35.
介绍沙角发电C厂2号发电机转子接地检测装置的基本原理和在装置发出报警信号后的分析和判断过程。对该装置出现故障后ALSTOM公司提出的临时检测方案作了分析,指出了该方案的不足之处,提出并实施改进后的临时检测方案。 相似文献
36.
M. K. Karthikeyan R. K. Gupta V. Rajesh B. R. Ghosh P. P. Sinha 《Journal of Failure Analysis and Prevention》2007,7(6):429-433
17-4 PH stainless steel is used as internal drive shaft material in liquid engine pumps. One of the drive shafts failed during
operation. The shaft pieces were in contact for short duration after failure, which has resulted in abrasion of fractured
surfaces. Samples from the location of failure were taken, and investigation of the failure was carried out using optical
and scanning electron microscopy. The microstructural analysis of the material and fractographic analysis of the fractured
surface show that the failure was caused by excessive torsion. 相似文献
37.
介绍了阳泉市煤矿采空区对公路建设所造成的危害,对其上覆岩层变形破坏的地质因素及其破坏机理作了分析,指出应该采取各种措施减少对公路的破坏。 相似文献
38.
39.
40.