全文获取类型
收费全文 | 29334篇 |
免费 | 3049篇 |
国内免费 | 1573篇 |
专业分类
电工技术 | 1677篇 |
综合类 | 3109篇 |
化学工业 | 3812篇 |
金属工艺 | 1185篇 |
机械仪表 | 1629篇 |
建筑科学 | 5018篇 |
矿业工程 | 1149篇 |
能源动力 | 1568篇 |
轻工业 | 2255篇 |
水利工程 | 1006篇 |
石油天然气 | 1942篇 |
武器工业 | 279篇 |
无线电 | 2779篇 |
一般工业技术 | 2335篇 |
冶金工业 | 1525篇 |
原子能技术 | 541篇 |
自动化技术 | 2147篇 |
出版年
2024年 | 103篇 |
2023年 | 360篇 |
2022年 | 736篇 |
2021年 | 875篇 |
2020年 | 980篇 |
2019年 | 895篇 |
2018年 | 804篇 |
2017年 | 1061篇 |
2016年 | 1169篇 |
2015年 | 1219篇 |
2014年 | 1687篇 |
2013年 | 1856篇 |
2012年 | 2259篇 |
2011年 | 2339篇 |
2010年 | 1740篇 |
2009年 | 1679篇 |
2008年 | 1636篇 |
2007年 | 2046篇 |
2006年 | 1819篇 |
2005年 | 1444篇 |
2004年 | 1187篇 |
2003年 | 1043篇 |
2002年 | 872篇 |
2001年 | 727篇 |
2000年 | 593篇 |
1999年 | 520篇 |
1998年 | 366篇 |
1997年 | 346篇 |
1996年 | 291篇 |
1995年 | 266篇 |
1994年 | 233篇 |
1993年 | 154篇 |
1992年 | 144篇 |
1991年 | 101篇 |
1990年 | 86篇 |
1989年 | 73篇 |
1988年 | 51篇 |
1987年 | 39篇 |
1986年 | 24篇 |
1985年 | 33篇 |
1984年 | 24篇 |
1983年 | 14篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1959年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
261.
通过对焦煅烧回窑的一些设计和运行参数的讨论,论述了锥形回转窑的设计及其使用的可行性和优越性。 相似文献
262.
263.
固相接枝共聚法制备PP—g—PS 总被引:4,自引:0,他引:4
用固相接枝共聚方法制备了聚丙烯接枝苯乙烯(PP-g-PS),详细地考察了聚丙烯与引发剂的品种、反应温度、苯乙烯及引发剂的浓度等因素对接枝率和接枝效率的影响。研究结果表明:PP-g-PS具有较高的接技率,应用于聚丙烯/聚苯乙烯(PP/PS)共混物中,能降低分散相PS的粒径,提高PP/PS的相容性。 相似文献
264.
This paper presents a mathematical model based on the reaction rate expressions to describe the displacement of methane conversion in the steam reforming. The effect of several parameters including weight hourly space velocity (WHSV), load-to-surface ratio, reaction pressure, hydrogen partial pressure in permeate side and reaction temperature were investigated. Simulation and experimental results showed that a conversion higher than 80% could be achieved in a palladium membrane reactor at reaction temperature of 500 °C relative to 850 °C in a conventional fixed bed reactor (FBR). Besides, the yield of CO (<2%) in membrane reactor was much lower than that (>50%) in the FBR, which indicated the significant depression of CO production in use of membrane reactor. 相似文献
265.
为了合理判别软弱破碎围岩隧道的二衬施作时机,结合工程实践,通过洞室拱顶沉降和边墙变形收敛的现场监控量测,提出了利用围岩-初支系统变形实测数据判别软弱破碎围岩隧道二衬施作合理时机的考虑支护是否保守的五级速率比值法并研发了相应的软件,并通过工程实例进行了成功验证。研究表明:1研制的软件操作具有界面简洁、友好,以及操作简单易用的特点,具有测点围岩-初支系统位移和收敛的现场监测数据的录入、储存、修改和管理等功能,能方便地进行软弱破碎围岩隧道的二衬合理时机判别;2通过工程实例验证分析表明,提出的方法是可行的,与现行的二衬时机选择的方法本质上是相同的,但更加具有可操作性,研究成果可以为同类型隧道的二衬时机选择提供可资借鉴的方法。 相似文献
266.
Budimir Popovic 《Nutrient Cycling in Agroecosystems》1985,6(2):139-147
The effect of fertilization with urea and ammonium nitrate on nitrogen mineralization was studied in a series of laboratory incubation experiments. The samples (humus layer) were collected from field experiments with different applications of fertilizers during a period of 11–14 years. The nitrogen fertilization influenced some chemical properties of the humus layer such as pH, N-Kjeldahl content and the content of inorganic nitrogen, especially in the samples from North Sweden. Nitrate nitrogen was formed in humus samples classified as non-nitrifying in several cases, usually after urea fertilization. 相似文献
267.
针对隐写分析中特征维数过高的问题,提出一种特征加权支持向量机音频隐写分析算法.利用特征相关性对原始特征进行优化选择,利用增益比率法计算特征权重,提出了改进特征加权支持向量机.与常用的C-SVM进行的对比实验表明,该方法能够有效提高检测率,降低时间复杂度. 相似文献
268.
269.
控制燃煤硫的污染与动力煤全硫比价划分 总被引:7,自引:0,他引:7
讨论了中国煤炭资源中全硫分布的特点,指出加强动力煤洗选,降低硫含量的重要性;采用IGCC工艺和热煤气脱硫技术,可以实现高硫煤的有效利用。并提出制定合理的动力煤全硫比价问题。 相似文献
270.
Granular S, finely-ground S, iron sulphate and aluminium sulphate were added at two rates to the surface (0–6 cm) of a soil and acidification and leaching of nutrients were measured over 12 months in a laboratory study. Iron and aluminium sulphate both rapidly lowered soil pH in the top 0–6 cm of the soil. There was little difference in soil pH after 3 and 12 months reaction of these two amendments. In contrast, for granular S and finely-ground S there were clear decreases in soil pH between 3 and 12 months reaction with the soil. Finely-ground S was oxidized in the soil faster than granular S and therefore had a more acidifying effect. The top 0–6 cm of the soil was acidified by all the agents used but the deeper soil was less affected. The only treatments which lowered the pH of the 12–18 cm layer below pH 6 were the high rates of iron and aluminium sulphate. Soil acidification resulted in a decrease in exchangeable Ca, Mg and K, an increase in exchangeable Al and a decrease in effective CEC in the acidified soil layers.At both levels of addition, total ionic strength of percolates from the soil followed the order: aluminium sulphate = iron sulphate > finely gound S > granular S > control and was higher at the higher rate of addition. The pH values of percolates followed the order: control > granular S > finely ground S > iron sulphate = aluminium sulphate and were lower at the higher rate of addition. For the amended soils there was a very close relationship between the pattern and total amounts of SO
4
2-
and Ca2+ leached.It was concluded that granular S is not an effective acidifying agent since it is oxidized very slowly in the soil and that acidfying agents should be incorporated to the depth that acidification is required. 相似文献