全文获取类型
收费全文 | 151121篇 |
免费 | 6965篇 |
国内免费 | 4138篇 |
专业分类
电工技术 | 5371篇 |
技术理论 | 6篇 |
综合类 | 8342篇 |
化学工业 | 21996篇 |
金属工艺 | 9111篇 |
机械仪表 | 7654篇 |
建筑科学 | 7124篇 |
矿业工程 | 2662篇 |
能源动力 | 2890篇 |
轻工业 | 9192篇 |
水利工程 | 2845篇 |
石油天然气 | 3919篇 |
武器工业 | 706篇 |
无线电 | 16331篇 |
一般工业技术 | 23103篇 |
冶金工业 | 5695篇 |
原子能技术 | 1043篇 |
自动化技术 | 34234篇 |
出版年
2024年 | 202篇 |
2023年 | 751篇 |
2022年 | 1571篇 |
2021年 | 2214篇 |
2020年 | 1657篇 |
2019年 | 1380篇 |
2018年 | 15906篇 |
2017年 | 14983篇 |
2016年 | 11508篇 |
2015年 | 3108篇 |
2014年 | 3381篇 |
2013年 | 4213篇 |
2012年 | 7833篇 |
2011年 | 14405篇 |
2010年 | 12989篇 |
2009年 | 10134篇 |
2008年 | 11640篇 |
2007年 | 12454篇 |
2006年 | 4779篇 |
2005年 | 5210篇 |
2004年 | 4017篇 |
2003年 | 3447篇 |
2002年 | 2686篇 |
2001年 | 1972篇 |
2000年 | 1800篇 |
1999年 | 1537篇 |
1998年 | 1095篇 |
1997年 | 980篇 |
1996年 | 834篇 |
1995年 | 667篇 |
1994年 | 614篇 |
1993年 | 386篇 |
1992年 | 342篇 |
1991年 | 248篇 |
1990年 | 169篇 |
1989年 | 161篇 |
1988年 | 130篇 |
1987年 | 66篇 |
1986年 | 43篇 |
1968年 | 43篇 |
1967年 | 34篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1960年 | 30篇 |
1959年 | 41篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
The magnetization of a melt-texture growth (MTG) HTSC ring has been studied. It is shown that the magnetic field inside the ring is larger than the external field under a certain range of external magnetic fields. We have also investigated the magnetic field dependence of the response of a detective coil near a rotating superconducting ring. The responses of the MTG sample are different for different cooling methods. 相似文献
103.
Certain new sulfide-smelting processes and coal-gasification processes generate high-strength sulfur dioxide streams, for
which a new process for converting sulfur dioxide to elemental sulfur needs to be developed because no process exists that
is generally and economically applicable to the treatment of such streams. A thermodynamic and experimental investigation
to develop a new process for converting sulfur dioxide to elemental sulfur by a cyclic process involving calcium sulfide and
calcium sulfate without generating secondary pollutants was carried out. In this process, the starting raw material, calcium
sulfate, is reduced by a suitable reducing agent, such as hydrogen, to produce calcium sulfide, which is used to reduce sulfur
dioxide to elemental sulfur vapor and calcium sulfate. The latter is, in turn, reduced to regenerate calcium sulfide. In this
Part I, detailed experimental results are presented on the kinetics of the reaction between sulfur dioxide and calcium-sulfide
pellets, which produces elemental sulfur and calcium sulfate. The experiments were carried out at temperatures between 1023
and 1088 K and sulfur-dioxide partial pressures between 9 and 60 kPa by the use of a thermogravimetric analysis (TGA) technique.
The rate of this reaction was demonstrated by the conversion of 40 pct calcium-sulfide pellets obtained from the hydrogen
reduction of fresh calcium sulfate in 10 minutes at 1073 K under a sulfur-dioxide partial pressure of 43 kPa. The reactivity
decreased somewhat during the first three cycles but remained largely unchanged thereafter up to the tenth cycle. This characteristic
of the pellets is important because the solids must be reusable for repeated cycles to avoid generating secondary pollutants.
A pore-blocking model was found to fit the reaction rate. The reaction is first order with respect to sulfur-dioxide partial
pressure and has an activation energy of 101 to 134 kJ/mol (24 to 32 kcal/mol) for calcium-sulfide pellets reacted and regenerated
several different times. Sulfur dioxide-containing streams from certain sources, such as the regenerator off-gas from an integrated-gasification,
combined-cycle, desulfurization unit and new sulfide-smelting plants, contain much higher partial pressures of SO2. In these cases, the rate of the first reaction is expected to be proportionally higher than in the test conditions reported
in this article. The reduction kinetics of calcium-sulfate pellets with hydrogen gas is reported in the accompanying Part
II. 相似文献
104.
简单介绍了碳氧比测井的原理及通常的数据处理方法。分析了由常规数据处理所得曲线仍然存在的问题及可能的成因 ,并给出了可行的修正办法。讨论了另一种可行的曲线异常数据的检测、剔除方法。实践表明 :文章讨论的两点建议都是可行的 ,并且在提高测量曲线质量的同时也提高了地层含油饱和度的解释精度。 相似文献
105.
Microbiological denitrification of red beet juice 总被引:1,自引:0,他引:1
Dorota Walkowiak-Tomczak 《European Food Research and Technology》2002,215(5):401-406
The purpose of study was the determination of optimal conditions for red beet juice denitrification by Paracoccus denitrificans bacteria as well as the evaluation of the usefulness of microbiologically treated juice for the production of a natural colouring preparation for foods. Total reduction of nitrates was found during bacterial culturing at 25 and 30 °C, at an initial pH of 7.0-8.0 and juice osmotic pressure of 900-1100 mOsm/kg. Microbiological denitrification procedure affected colour, taste and aroma of the juice. However, the use of juice as food colouring and component was made feasible by acidification and partial evaporation of water together with volatile substances. 相似文献
106.
当成千上万的农民远离穷困的村落,视而不见地掠过小城镇,径奔大城市寻梦或淘金,一个显见的事实是,大城市里有更多的就业机会,有更多的钱赚——从生存的角度看,只要条件具备,没有谁不愿意趋利避害。 站在政府的角度,秩序则是重要的。任何政府都担心刑事案件随着它的城市人口的暴涨而剧增,而且,这还不是惟一的,因为与“月黑风高夜,杀人放火天”的刑事案件相伴的至少还有贫民窟。杀人、放火、贫民窟等等一系列大城市综合症,恰恰是西方国家城市化道路的“遗产”,是发展中国家快速城市化的特产。 相似文献
107.
现有的虚拟专用网(VPN)方案大多基于IP协议,这种结构的VPN在数据包转发速度、扩展性、服务质量等方面都存在欠缺,所以本文提出了基于多协议标记交换(MPLS)骨干网络的VPN解决方案.由于MPLS和IPSec在身份认证方面都没有定义,所以我们在方案中把认证中心(CA)的证书管理引入进来.该方案的核心思想是:利用MPLS在传输效率上的优势,通过CA进行身份认证、IKE协议[1]进行密钥协商以及IPSec协议[2]进行数据包加密,从而在MPLS骨干网络上建立一个安全高效的VPN.本文对实现MPLS VPN的每个关键部件都做了进一步的描述. 相似文献
108.
Liang Y.C. Wenjiang Zeng Pick Hong Ong Zhaoxia Gao Jun Cai Balasubramanian N. 《Electron Device Letters, IEEE》2002,23(12):700-703
In this letter, a concise process technology is proposed for the first time to enable the fabrication of good quality three-dimensional (3-D) suspended radio frequency (RF) micro-inductors on bulk silicon, without utilizing the lithography process on sidewall and trench-bottom patterning. Samples were fabricated to demonstrate the applicability of the proposed process technology. 相似文献
109.
110.
环境友好阻燃环氧树脂覆铜板研究进展 总被引:15,自引:0,他引:15
论述了环境友好阻燃环氧树脂覆铜板研究开发的意义。提出通过开发并使用含氮、磷或硅的非卤阻燃型环氧树脂,含磷、氮或磷-氮的功能性阻燃固化剂和在体系中添加有机磷阻燃剂、氢氧化铝等无机阻燃剂等途径来开发环境友好阻燃环氧树脂覆铜板。并对我国在今后该领域的研究作了展望。 相似文献