全文获取类型
收费全文 | 47566篇 |
免费 | 4566篇 |
国内免费 | 2588篇 |
专业分类
电工技术 | 2912篇 |
技术理论 | 4篇 |
综合类 | 3952篇 |
化学工业 | 7801篇 |
金属工艺 | 2740篇 |
机械仪表 | 3028篇 |
建筑科学 | 3597篇 |
矿业工程 | 1645篇 |
能源动力 | 1367篇 |
轻工业 | 3514篇 |
水利工程 | 933篇 |
石油天然气 | 2351篇 |
武器工业 | 455篇 |
无线电 | 5336篇 |
一般工业技术 | 5623篇 |
冶金工业 | 2280篇 |
原子能技术 | 566篇 |
自动化技术 | 6616篇 |
出版年
2024年 | 217篇 |
2023年 | 781篇 |
2022年 | 1327篇 |
2021年 | 1894篇 |
2020年 | 1437篇 |
2019年 | 1282篇 |
2018年 | 1379篇 |
2017年 | 1540篇 |
2016年 | 1417篇 |
2015年 | 1944篇 |
2014年 | 2379篇 |
2013年 | 2926篇 |
2012年 | 3055篇 |
2011年 | 3166篇 |
2010年 | 2893篇 |
2009年 | 2653篇 |
2008年 | 2580篇 |
2007年 | 2450篇 |
2006年 | 2496篇 |
2005年 | 2163篇 |
2004年 | 1589篇 |
2003年 | 1832篇 |
2002年 | 2301篇 |
2001年 | 2076篇 |
2000年 | 1380篇 |
1999年 | 1168篇 |
1998年 | 859篇 |
1997年 | 670篇 |
1996年 | 561篇 |
1995年 | 546篇 |
1994年 | 419篇 |
1993年 | 270篇 |
1992年 | 254篇 |
1991年 | 198篇 |
1990年 | 128篇 |
1989年 | 111篇 |
1988年 | 97篇 |
1987年 | 60篇 |
1986年 | 44篇 |
1985年 | 30篇 |
1984年 | 21篇 |
1983年 | 15篇 |
1982年 | 19篇 |
1981年 | 11篇 |
1980年 | 29篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1959年 | 7篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
采用溶剂热法制备了硅基介孔分子筛材料,较系统地考察了晶化温度、晶化时间及焙烧温度等因素对其结构的影响,并利用N2吸附手段进行了表征.结果表明,晶化温度和晶化时间能明显影响硅基介孔材料的结构,而过高的焙烧温度易导致介孔结构的塌陷. 相似文献
2.
3.
燕皮传统加工工艺中碱液对肉糜特性的影响 总被引:1,自引:1,他引:0
燕皮是以猪肉和甘薯粉为原料,手工制成的薄如纸且经煮不烂的传统食品。在传统制作燕皮过程中添加山榉灰配制的碱液是影响肉糜品质的关键步骤。通过测定制作燕皮过程中各工序样品的氮溶解指数、持水性、乳化稳定性、pH值和粘度,利用SDS-PAGE分析样品中的蛋白质组分、利用光学显微镜观察它们的结构变化,证实植物碱液能够提高样品的氮溶解指数、持水性和乳化稳定性并且延迟了肉糜硬化。同时实验证明碳酸碱(Na2CO3或K2CO3)可替代传统工艺中的植物碱,为后续标准化、工业化生产提供可行条件。 相似文献
5.
6.
本文阐述了通过Friedel-Crafts反应合成邻-(4-乙基苯甲酰基)苯甲酸的方法.研究了影响产物质量的因素,提出了适宜的工艺条件. 相似文献
7.
The objectives of this study were to evaluate the possible mechanisms involved in prolongation of bleeding time in pre-eclamptic patients receiving a magnesium sulfate infusion to prevent convulsions. Eighteen pre-eclamptic patients near term or at term (4 cases 33 to 35 weeks; the remainder > 36 weeks) were studied. Fifteen of them received magnesium sulfate infusion; 3 did not and served as controls. Bleeding time (modified Ivy method with Surgicutt), platelet count, platelet aggregation pattern, as well as serum arachidonic acid metabolites [thromboxane B2 (TxB2) and 6-Keto-prostaglandin F1 alpha (6-Keto-PGF1 alpha)] werde done on admission to the labor floor (before magnesium infusion) and repeated at discontinuation of the infusion, 12-24 hours postpartum; the controls received the second test 24 hours postpartum. Thirteen of 15 patients receiving magnesium sulfate had an increase in bleeding time from an average of 6 minutes 31 seconds to 11 minutes 56 seconds, an 82% rise (p < 0.004). In 2 there was a decrease. Among the 3 controls the averages were 6 minutes 38 seconds and 6 minutes 3 seconds. The total magnesium given ranged from 52.5 to 145 grams. Platelet counts averaged 251,000/mm3 (range 145,000-519,000). Platelet aggregation pattern done in 11 patients and was normal and unchanged after magnesium in 10 of the patients with increased bleeding time and one control. TxB2 and 6-Keto-PGF1 alpha levels did not change significantly either after magnesium administration (688 and 135 pgm/ml, to 654 and 117) or in controls (695 and 230 pgm/ml, to 445 and 225). Likewise, the ratio of these 2 substances did not change in either group (6.3 to 6.6, and 4.2 to 2.2). There was no correlation between duration of infusion or total magnesium given and directions of small changes observed. This study confirms a prior preliminary observation that magnesium sulfate infusion, as currently used to prevent eclamptic convulsions, induces a significant prolongation of bleeding time. This effect is mediated neither by changes in platelets count or aggregation pattern, nor by changing the level or ratios of serum arachidonic acid metabolites (TxB2 and 6-Keto-PGF1 alpha). Further studies are needed to clarify the mechanism of this clinically important observation of increased bleeding following magnesium sulfate infusion. 相似文献
8.
温熙华 《电信工程技术与标准化》2002,(5):36-39
本主要介绍基于CDMA智能网平台的一种增值业务——“位置服务”,阐述这个业务的网络结构、涉及到的技术问题和解决方案,并将这个整体思路投入到开发业务中去。 相似文献
9.
Brian M. Louie Thomas Franaszek Tina Pho Wen Yen Chiu David S. Soong 《应用聚合物科学杂志》1985,30(9):3841-3856
Oxygen injection has been proposed and experimentally demonstrated as an effective control measure for limiting the rate of heat release and altering the rate of polymerization in emulsion processes. A detailed mathematical model has been previously developed to describe the system behavior with and without oxygen injection. A simple lab scale apparatus was constructed and run extensively. Only trace quantities of oxygen are needed to inhibit the reaction completely. The facile response makes this method attractive for fast temperature control. However, because of the rapid penetration of dissolved oxygen into the polymer particles, growing radical chains are terminated prematurely, lowering product molecular weights. To minimize this detrimental effect, pulsed oxygen control is used and extensive experimental work was performed to determine the effects of controller set points on molecular weight. Moderate oxygen flows and moderate set point temperatures are found to give the optimal response without significant lowering of the final molecular weight. Injected quantities agree well with the order-of-magnitude sparging calculations needed to completely stop initiation. However, complete agreement between model simulations and experimental results was not reached due to an unmeasured loss of monomer from the reactor. Chain transfer to monomer is found to be important in modeling the polymer molecular weight. It has, however, a negligible effect on the reaction rate. 相似文献
10.
中原大化集团公司尿素装置在操作上使用的是Snam公司提供的尿素操作手册 ,在运行过程中 ,发现有许多地方与实际状况出入很大 ,经过不断的总结经验 ,并在工艺操作中进行改进、优化 ,使装置达到安全、稳定、经济运行的目的。1 二氧化碳压缩机操作方式的改进二氧化碳压缩机自开车以来 ,防喘振系统一直未投用。由于Snam公司提供的防喘振曲线富裕度较大 ,操作人员对实际喘振点不清楚 ,正常生产中转速控制较高 ,操作盲目性很大 ,在 1 0 0 %负荷下 ,防喘振阀仍有 1 0 %左右的开度 ,造成蒸气消耗偏高。1 999- 0 3- 31 ,对二氧化碳压缩机各… 相似文献