全文获取类型
收费全文 | 11135篇 |
免费 | 1119篇 |
国内免费 | 394篇 |
专业分类
电工技术 | 291篇 |
综合类 | 934篇 |
化学工业 | 3928篇 |
金属工艺 | 456篇 |
机械仪表 | 431篇 |
建筑科学 | 1347篇 |
矿业工程 | 611篇 |
能源动力 | 394篇 |
轻工业 | 633篇 |
水利工程 | 386篇 |
石油天然气 | 776篇 |
武器工业 | 29篇 |
无线电 | 318篇 |
一般工业技术 | 565篇 |
冶金工业 | 848篇 |
原子能技术 | 230篇 |
自动化技术 | 471篇 |
出版年
2024年 | 38篇 |
2023年 | 142篇 |
2022年 | 317篇 |
2021年 | 362篇 |
2020年 | 436篇 |
2019年 | 366篇 |
2018年 | 327篇 |
2017年 | 374篇 |
2016年 | 399篇 |
2015年 | 440篇 |
2014年 | 661篇 |
2013年 | 728篇 |
2012年 | 919篇 |
2011年 | 852篇 |
2010年 | 688篇 |
2009年 | 708篇 |
2008年 | 551篇 |
2007年 | 726篇 |
2006年 | 645篇 |
2005年 | 530篇 |
2004年 | 430篇 |
2003年 | 386篇 |
2002年 | 306篇 |
2001年 | 249篇 |
2000年 | 217篇 |
1999年 | 169篇 |
1998年 | 123篇 |
1997年 | 115篇 |
1996年 | 83篇 |
1995年 | 65篇 |
1994年 | 49篇 |
1993年 | 35篇 |
1992年 | 36篇 |
1991年 | 31篇 |
1990年 | 24篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 24篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 20篇 |
1983年 | 10篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
91.
Local‐scale Benefits of River Connectivity Restoration Planning Beyond Jurisdictional Boundaries 下载免费PDF全文
A. W. Milt P. J. Doran M. C. Ferris A. T. Moody T. M. Neeson P. B. McIntyre 《河流研究与利用》2017,33(5):788-795
Conservation planning aims to optimize outcomes for select species or ecosystems by directing resources toward high‐return sites. The possibility that local benefits might be increased by directing resources beyond the focal area is rarely considered. We present a case study of restoring river connectivity for migratory fish of the Great Lakes Basin by removing dams and road crossings within municipal jurisdictions versus their broader watersheds. We found that greater river connectivity could often be achieved by considering both intra‐jurisdictional and extra‐jurisdictional barriers. Focusing on jurisdictional barriers alone generally forfeited <20% (median = 0%) of habitat gains for those who value solely habitat gains within the jurisdiction, but >75% (median = 100%) for planners who value larger‐scale habitat gains. Similarly, cost savings tended to be between ?50% and +50%, but in some cases were very negative. Our study underscores the local‐scale benefits of broadening restoration investments, especially for decision makers of the Great Lakes Basin and contributes to a discussion of appropriate and efficient scales of conservation planning. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
92.
针对一分加污垢的特点,通过实验,研制了以有机酸为主要成份的尿素分解加热器清洗剂及清洗工艺,并进行了4台次加热器的清洗,取得了较好的效果。此清洗方法具有工艺简单、安全、分析控制容易、费用低廉的特点。 相似文献
93.
94.
95.
96.
金属离子掺杂二氧化钛及水体光催化脱氮研究 总被引:2,自引:1,他引:2
采用溶胶-凝胶法制备了掺杂Ce^3+、La^3+、Ag^+、Fe^3+的TiO2光催化剂,以考察其薄膜和粉体形式对水中无机氮的光催化去除效果和活性.用所制备的催化剂对含氨氮-亚硝酸氮的混合液进行了光催化脱氮研究.本文利用UV—Vis吸收光谱、XRD和TEM对催化剂进行了表征.同时,对影响TiO2光催化效率的因素:如掺杂金属离子的种类、浓度、涂膜层数、反应液中有无Fe^2+、不锈钢和玻璃载体、反应器的构型等进行了探讨,并对今后的研究进行展望.经过2h紫外光照射反应,实验最佳脱氮效果:金属离子掺杂TiO2薄膜型催化剂总氮去除率在30%左右,金属离子掺杂粉末型催化剂光催化最高总氮去除率可达41.7%. 相似文献
97.
98.
A method has been developed for calculating hydraulic pressures induced by thermal expansion of liquid binders early in the removal cycle, when evaporative losses are negligible and fully saturated conditions prevail. Specific results were obtained for flat compacts containing a common wax binder, mixed with varying amounts of low-density polyethylne. In general, these results show how the risk of hydraulic fracture increases with heating rate and compact thickness. Although pressures are minimal when the binder consists entirely of wax, the continual addition of polyethylene eventually gives rise to unacceptable risk levels, even for relatively thin compacts. Binder removal at elevated temperatures is considered subsequently. In this case, vapor pressures eventually approach a critical level, thereby allowing mass removal by evaporation to overcome the effect of thermal expansion in maintaining full saturation. With the onset of void formation, the developing capillary pressure supersedes hydraulic pressure as the driving force in liquid transport. Besides representing capillary flow, the present formulation also accounts for thermal degradation of the binder during removal. The resulting system of equations was solved numerically for a variety of representative debinding conditions. Predictions for flat compact containing a balanced wax/polyethylene binder indicate that thermal degradation of the polyethylene can give rise to a marked improvement in debinding rates. It turns out, however, that this enhancement is far more effective in thinner compacts. 相似文献
99.
100.