全文获取类型
收费全文 | 30115篇 |
免费 | 2716篇 |
国内免费 | 1548篇 |
专业分类
电工技术 | 2555篇 |
技术理论 | 2篇 |
综合类 | 2569篇 |
化学工业 | 3763篇 |
金属工艺 | 964篇 |
机械仪表 | 1571篇 |
建筑科学 | 3046篇 |
矿业工程 | 1321篇 |
能源动力 | 3864篇 |
轻工业 | 1202篇 |
水利工程 | 722篇 |
石油天然气 | 1808篇 |
武器工业 | 285篇 |
无线电 | 3813篇 |
一般工业技术 | 2318篇 |
冶金工业 | 1284篇 |
原子能技术 | 529篇 |
自动化技术 | 2763篇 |
出版年
2024年 | 103篇 |
2023年 | 447篇 |
2022年 | 786篇 |
2021年 | 979篇 |
2020年 | 1042篇 |
2019年 | 904篇 |
2018年 | 849篇 |
2017年 | 1052篇 |
2016年 | 1192篇 |
2015年 | 1276篇 |
2014年 | 2031篇 |
2013年 | 2028篇 |
2012年 | 2325篇 |
2011年 | 2394篇 |
2010年 | 1847篇 |
2009年 | 1846篇 |
2008年 | 1718篇 |
2007年 | 1821篇 |
2006年 | 1669篇 |
2005年 | 1310篇 |
2004年 | 1103篇 |
2003年 | 983篇 |
2002年 | 812篇 |
2001年 | 716篇 |
2000年 | 589篇 |
1999年 | 496篇 |
1998年 | 336篇 |
1997年 | 309篇 |
1996年 | 301篇 |
1995年 | 221篇 |
1994年 | 199篇 |
1993年 | 133篇 |
1992年 | 101篇 |
1991年 | 100篇 |
1990年 | 68篇 |
1989年 | 63篇 |
1988年 | 41篇 |
1987年 | 36篇 |
1986年 | 33篇 |
1985年 | 21篇 |
1984年 | 22篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 15篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1959年 | 3篇 |
1956年 | 2篇 |
1955年 | 3篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
介绍了中国石油化工股份有限公司高桥分公司 1.4Mt/a同轴式重油催化裂化装置的特点和生产情况。为了满足市场需求 ,提高经济效益 ,几年来在该装置上又采用了一些新技术 ,使装置的运转水平进一步提高。如应用降烯烃催化剂GOR Q ,与使用MLC 5 0 0催化剂相比 ,汽油烯烃体积含量约 30 % ,下降 8~ 10个百分点 ;汽油辛烷值基本不变 ;产品分布改善 ;液体收率增加 ;柴油性质变化不大。又如最大量烷烃异构化 (MIP)新型提升管反应系统的应用 ,与常规催化裂化相比 ,产品分布相当 ,汽油的烯烃体积含量下降至 30 %~ 35 % ,MON增加 0 .5~ 0 .8个单位 ,RON下降幅度不大于 0 .5个单位 相似文献
102.
Da SHU Baode SUN Ke LI Jun WANG Yaohe ZHOUState Key Laboratory of Metal Matrix Composites Shanghai Jiao Tong University Shanghai China 《材料科学技术学报》2003,19(3):221-225
The continuous separation of inclusions from aluminum melt flowing in a circular pipe using a high frequency magneticfield was investigated both theoretically and experimentally The separation efficiency was calculated based on thetrajectory method and compared with experimental results. It is found that the separation efficiency is a functilnondimensional parameters t_i·d_p~2B_e~2/μ_fμ_eα~2 and α/δ.The effective way to improve the separation efficiency is to increasethe effective magnetic flux density and decrease the pipe radius. and the value of α/δ should be kept about 2 in orderto obtain the optimum separation efficiency. 相似文献
103.
104.
105.
106.
Suitability of sweet sorghum in Greece, where irrigation supply during crop development is limited as rainfall is scarce and
evapotranspiration loss is high, is examined in relation with radiation availability. A two-year field experiment was conducted,
in central Greece, imposing four soil water regimes via different irrigation treatments: (1) Highly irrigated, (2) Highly
irrigated till anthesis when irrigation stopped, (3) Medium irrigated, and (4) Low irrigated. It was found that above-ground
dry biomass production from non-water-stressed sweet sorghum plants suggests a high productivity potential among C4 crops. Under water shortage, radiation use efficiency may be significantly lower. Radiation use efficiency seems to be linearly
related to water consumption. Stressed plants (probably except severely stressed) seem to use available water more efficiently
than unstressed plants. The slope of the line relating dry matter produced and water evapotranspired increases the sooner
the stress is sensed. Yield reduction resulting from post-anthesis irrigation stopage is very little. High water use efficiency
values tend to be related with low radiation use efficiency values. 相似文献
107.
建立了热采注汽系统热效率的计算模型。根据XX油田数据计算了2个注汽系统的热效率。提出了提高注汽系统热效率的三项措施:(1)降低锅炉的过剩空气系数;(2)按最大允许热损失设计地面输汽管线的保温层厚度;(3)使用视导热系数小的隔热油管,按箍增加隔热结构,防止热封隔器的泄漏等。 相似文献
108.
通过对工作面端面冒顶原因及支护系统的分析得出,加大液压支架的流量可以加快移架速度,降低冒顶事故率,提高生产效率。 相似文献
109.
The smooth fractionator 总被引:8,自引:0,他引:8
H. J. G. Gundersen 《Journal of microscopy》2002,207(3):191-210
A modification of the general fractionator sampling technique called the smooth fractionator is presented. It may be used in almost every situation in which sampling is performed from distinct items that are uniquely defined, often they are physically separated items or clusters like pieces, blocks, slabs, sections, etc. To each item is associated a ‘guesstimate’ or an associated variable with a more‐or‐less close – and possibly biased ? relationship to the content of the item. The smooth fractionator is systematic sampling among the items arranged according to the guesstimates in a unique, symmetric sequence with one peak and minimal jumps. The smooth fractionator is both very simple to implement and so efficient that it should probably always be used unless the natural sequence of the sampling items is equally smooth. So far, there is no theory for the prediction of the efficiency of smooth fractionator designs in general, and their properties are therefore illustrated with a range of real and simulated examples. At the cost of a slightly more elaborate sampling scheme, it is, however, always possible to obtain an unbiased estimate of the real precision and of some of the variance components. The only real practical problem for always obtaining a high precision with the smooth fractionator is specimen inhomogeneity, but that is detectable at almost no extra cost. With careful designs and for sample sizes of about 10, the sampling variation for the primary, smooth fractionator sampling step may in practice often be small enough to be ignored. 相似文献
110.
本文介绍利用LotusNotes软件平台的电子邮件、复合文档数据库、工作流和完全的Client/Server技术 ,建立一个以开放、先进的Intranet/web及消息传递和工作流管理技术为核心的新一代全方位网络办公自动化系统。 相似文献