全文获取类型
收费全文 | 73286篇 |
免费 | 6411篇 |
国内免费 | 3464篇 |
专业分类
电工技术 | 3672篇 |
技术理论 | 10篇 |
综合类 | 3897篇 |
化学工业 | 14533篇 |
金属工艺 | 2119篇 |
机械仪表 | 2450篇 |
建筑科学 | 4558篇 |
矿业工程 | 6201篇 |
能源动力 | 6292篇 |
轻工业 | 4832篇 |
水利工程 | 1065篇 |
石油天然气 | 18052篇 |
武器工业 | 299篇 |
无线电 | 2835篇 |
一般工业技术 | 4929篇 |
冶金工业 | 3662篇 |
原子能技术 | 1111篇 |
自动化技术 | 2644篇 |
出版年
2024年 | 239篇 |
2023年 | 1003篇 |
2022年 | 1953篇 |
2021年 | 2635篇 |
2020年 | 2685篇 |
2019年 | 2247篇 |
2018年 | 1999篇 |
2017年 | 2192篇 |
2016年 | 2711篇 |
2015年 | 2547篇 |
2014年 | 4554篇 |
2013年 | 4587篇 |
2012年 | 5494篇 |
2011年 | 5738篇 |
2010年 | 3927篇 |
2009年 | 3891篇 |
2008年 | 3346篇 |
2007年 | 4105篇 |
2006年 | 4331篇 |
2005年 | 3560篇 |
2004年 | 3106篇 |
2003年 | 2718篇 |
2002年 | 2356篇 |
2001年 | 2119篇 |
2000年 | 1779篇 |
1999年 | 1395篇 |
1998年 | 1092篇 |
1997年 | 976篇 |
1996年 | 758篇 |
1995年 | 637篇 |
1994年 | 528篇 |
1993年 | 389篇 |
1992年 | 314篇 |
1991年 | 244篇 |
1990年 | 209篇 |
1989年 | 217篇 |
1988年 | 96篇 |
1987年 | 66篇 |
1986年 | 63篇 |
1985年 | 56篇 |
1984年 | 46篇 |
1983年 | 36篇 |
1982年 | 34篇 |
1981年 | 79篇 |
1980年 | 43篇 |
1979年 | 12篇 |
1976年 | 5篇 |
1973年 | 5篇 |
1959年 | 5篇 |
1951年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
A. Hofmann 《低温学》2004,44(3):159-165
An intermediate refrigeration with boil-off gas cooled shields using the boil-off gas stream is an alternative method to the conventional intermediate refrigeration with a cryogenic liquid.By using an analytical calculation method relations are derived, which enable complete predictions about the effectiveness of an intermediate refrigeration with boil-off gas cooled shields as a function of the number of shields for the different stored cryogenic liquids. For this theoretical derivation however, the restrictive assumption must be made that the thermal conductivity of the used insulation material has a constant value between the considered temperature boundaries.For purposes of a more exact calculation a numerical method is therefore suggested, which takes into consideration that the thermal conductivity is temperature-dependent. For a liquid hydrogen storage vessel with a perlite-vacuum insulation e.g., the effectiveness of one shield and its equilibrium temperature are given as a function of the position of the shield in the insulation space. 相似文献
43.
介绍了Shell渣油气化装置将渣油原料改为天然气时控制系统的改造方案。提出的改造思路不但可用于Shell渣油气化,也可用于德士古渣油气化的油改气工程中。 相似文献
44.
叙述了目前加油站在实行按任意温度下的体积交接,由于未考虑油品体积随温度、压力、密度的变化,出现了零售损耗很大的问题。建议加油站在现阶段采用“准标准体积”交接;在由体积转换为质量计算加油站损溢时,使用油库当月发出的平均密度;当财会核销损溢时,不使用盘存的体积和固定密度进行计算的方法,而使用实际盘点的质量数,以真实反映加油站的当期损溢。 相似文献
45.
The capacity to store water in a reservoir declines as it traps sediment. A river entering a reservoir forms a prograding delta. Coarse sediment (e.g., sand) deposits in the fluvial topset and avalanching foreset of the delta, and is typically trapped with an efficiency near 100%. The trap efficiency of fine sediment (e.g., mud), on the other hand, may be below 100%, because some of this sediment may pass out of the reservoir without settling out. Here, a model of trap efficiency of mud is developed in terms of the mechanics of a turbidity current that plunges on the foreset. The dam causes a sustained turbidity current to reflect and form a muddy pond bounded upstream by a hydraulic jump. If the interface of this muddy pond rises above any vent or overflow point at the dam, the trap efficiency of mud drops below 100%. A model of the coevolution of topset, foreset, and bottomset in a reservoir that captures the dynamics of the internal muddy pond is presented. Numerical implementation, comparison against an experiment, and application to a field-scale case provide the basis for a physical understanding of the processes that determine reservoir trap efficiency. 相似文献
46.
Critical Shear Stress of Bimodal Sediment in Sand-Gravel Rivers 总被引:1,自引:0,他引:1
A new model for the critical shear stress and the transport of graded sediment is presented. The model is based on the size distribution of the bed surface and can be used to compute sediment transport rates in numerical simulations with an active layer model. This model makes a distinction between unimodal and bimodal sediments. It is assumed that all size fractions of unimodal sediments have the same critical shear stress while there is selective transport for the gravel fractions of bimodal sediments. A recently published laboratory transport data set is used to calibrate our model. 相似文献
47.
48.
49.
N. Leclerc A. Michaud K. Sirois J.‐F. Morin M. Leclerc 《Advanced functional materials》2006,16(13):1694-1704
New electroactive and photoactive conjugated copolymers consisting of alternating 2,7‐carbazole and oligothiophene moieties linked by vinylene groups have been developed. Different oligothiophene units have been introduced to study the relationship between the polymer structure and the electronic properties. The resulting copolymers are characterized by UV‐vis spectroscopy, size‐exclusion chromatography, and thermal and electrochemical analyses. Bulk heterojunction photovoltaic cells from different copolymers and a soluble fullerene derivative, [6,6]‐phenyl‐C61 butyric acid methyl ester, have been fabricated, and promising preliminary results are obtained. For instance, non‐optimized devices using poly(N‐(4‐octyloxyphenyl)‐2,7‐carbazolenevinylene‐alt‐3″,4″‐dihexyl‐2,2′;5′,2″;5″,2″′;5″′,2″″‐quinquethiophenevinylene 1″,1″‐dioxide) as an absorbing and hole‐carrier semiconductor exhibit power conversion efficiency up to 0.8 % under air mass (AM) 1.5 illumination. These features make 2,7‐carbazolenevinylene‐based and related polymers attractive candidates for solar‐cell applications. 相似文献
50.
煤气吹扫时惰性气体抑爆用量的优选 总被引:1,自引:0,他引:1
运用惰性气体消防抑爆理论,采用数学积分法计算出吹扫煤气设施时抑爆所需最少惰性气体需要量. 相似文献