全文获取类型
收费全文 | 213016篇 |
免费 | 27299篇 |
国内免费 | 24672篇 |
专业分类
电工技术 | 18871篇 |
技术理论 | 8篇 |
综合类 | 15090篇 |
化学工业 | 50300篇 |
金属工艺 | 9023篇 |
机械仪表 | 12225篇 |
建筑科学 | 10550篇 |
矿业工程 | 2632篇 |
能源动力 | 8953篇 |
轻工业 | 16393篇 |
水利工程 | 2863篇 |
石油天然气 | 5790篇 |
武器工业 | 2135篇 |
无线电 | 28914篇 |
一般工业技术 | 23357篇 |
冶金工业 | 5198篇 |
原子能技术 | 3748篇 |
自动化技术 | 48937篇 |
出版年
2024年 | 770篇 |
2023年 | 3787篇 |
2022年 | 6251篇 |
2021年 | 8205篇 |
2020年 | 7684篇 |
2019年 | 6957篇 |
2018年 | 6411篇 |
2017年 | 8514篇 |
2016年 | 9189篇 |
2015年 | 10494篇 |
2014年 | 10619篇 |
2013年 | 13986篇 |
2012年 | 15907篇 |
2011年 | 17905篇 |
2010年 | 12918篇 |
2009年 | 12846篇 |
2008年 | 13907篇 |
2007年 | 15687篇 |
2006年 | 14864篇 |
2005年 | 12722篇 |
2004年 | 10808篇 |
2003年 | 8592篇 |
2002年 | 6671篇 |
2001年 | 5148篇 |
2000年 | 4344篇 |
1999年 | 3633篇 |
1998年 | 2990篇 |
1997年 | 2421篇 |
1996年 | 1942篇 |
1995年 | 1623篇 |
1994年 | 1476篇 |
1993年 | 1091篇 |
1992年 | 870篇 |
1991年 | 690篇 |
1990年 | 586篇 |
1989年 | 431篇 |
1988年 | 330篇 |
1987年 | 227篇 |
1986年 | 186篇 |
1985年 | 253篇 |
1984年 | 226篇 |
1983年 | 153篇 |
1982年 | 208篇 |
1981年 | 96篇 |
1980年 | 107篇 |
1979年 | 25篇 |
1977年 | 24篇 |
1959年 | 22篇 |
1957年 | 21篇 |
1951年 | 24篇 |
排序方式: 共有10000条查询结果,搜索用时 749 毫秒
991.
高温延缓型有机硼OB-200交联压裂液的性能与应用 总被引:7,自引:2,他引:5
报道了实验考察高温延缓型有机硼交联剂OB 200在5g/L羟丙基瓜尔胶水基压裂液中的各项性能及其影响因素的结果,简述了在7口井上应用该压裂液的情况。OB 200/HPG压裂液在pH=11.5、温度5~35(40)℃时交联时间长达4.7~5.6min;不加破胶剂的压裂液在温度115~135℃时,8h内可完全破胶液化,讨论了OB 200体系的自动破胶机制;在135℃、170s-1条件下剪切2h,压裂液粘度>120mPa·s;高速(500s-1)剪切后,在低速下(80s-1)粘度可恢复到初始值的94.5%(95℃下)或70.0%(135℃下);在95~135℃滤失小,滤失系数为6.93×10-4~9.81×10-4m/(min)1/2;残渣含量低,135℃下破胶20h后为319mg/L,而对比硼酸盐压裂液(90℃)和有机钛压裂液(135℃)分别为364和457mg/L;在人造岩心上测得渗透率伤害率在5.74%~9.66%,平均7.32%,而对比有机钛压裂液为24.07%~29.98%,平均27.09%。在中原油田桥口和户部寨地区7口井2706~3769m井段用该压裂液压裂,施工成功率100%,获得了油、气增产效果。图5表4参3。 相似文献
992.
铸型尼龙改性的研究进展 总被引:4,自引:0,他引:4
铸型尼龙产品广泛地用于各种机械零件,改性后的铸型尼龙,可克服其自身的缺点,满足工业应用的要求。文章就我国近年来在铸型尼龙改性研究方面的情况及不同的改性方法做了详细的介绍。 相似文献
993.
Charles A. Bateman Lijie Zhang Helen M. Chan Martin P. Harmer 《Journal of the American Ceramic Society》1992,75(5):1281-1283
It is experimentally observed that the peritectic reaction, 211 + liquid → 123, can be driven essentially to completion in 1 h at an undercooling of only ∽30°C. The kinetic data, together with the observed microstructures, are inconsistent with the normal mechanism of the peritectic reaction. It is proposed that the mechanism of the reaction involves dissolution of 211 particles into the liquid and precipitation of solid 123. The aligned grain structure is explained through sympathetic nucleation of new 123 grains on existing grains. 相似文献
994.
The synthesis of rare-earth perovskite-type composition thin films of LaNiO3 by means of the inorganic-sol-gel (ISG) method was studied. The structural stability under high temperature in reducing atmospheres and the oxygen-sensitivity mechanism of the LaNiO3 thin films were examined. It is shown that under the experimental conditions, LaNiO3 decomposes and the valance states of nickel are +2 and +3. 相似文献
995.
研究了ZnCl_2对几种不同类型的、有工业应用价值的环加成反应的催化作用。结果表明,ZnCl_2对具有含氧基团底物的Diels-Alder反应催化效果显著。 相似文献
996.
Algebraic properties of cryptosystem PGM 总被引:2,自引:0,他引:2
In the late 1970s Magliveras invented a private-key cryptographic system calledPermutation Group Mappings (PGM). PGM is based on the prolific existence of certain kinds of factorization sets, calledlogarithmic signatures, for finite permutation groups. PGM is an endomorphic system with message space ℤ|G| for a given finite permutation groupG. In this paper we prove several algebraic properties of PGM. We show that the set of PGM transformations ℐ
G
is not closed under functional composition and hence not a group. This set is 2-transitive on ℤ|G| if the underlying groupG is not hamiltonian and not abelian. Moreover, if the order ofG is not a power of 2, then the set of transformations contains an odd permutation. An important consequence of these results
is that the group generated by the set of transformations is nearly always the symmetric group ℒ|G|. Thus, allowing multiple encryption, any permutation of the message space is attainable. This property is one of the strongest
security conditions that can be offered by a private-key encryption system.
S. S. Magliveras was supported in part by NSF/NSA Grant Number MDA904-82-H0001, by U.S. West Communications, and by the Center
for Communication and Information Science of the University of Nebraska. 相似文献
997.
黄运平 《武汉理工大学学报(材料科学英文版)》2002,17(1)
The topological index F* is defined and obtained by the method of a non-dimensional unit calculation in which three matrices multiply with each other. These matrices represent the connective cases of atoms in a molecule, the structural features of atoms on top and the bonded cases of the adjacent atoms respectively. The standard formation enthalpies of ABn(g) molecules were correlated with F'* (A = C, Al, Si, Ti, Zr, B = F, Cl, Br, I, H, n=1 -4) and these correlation coefficients are all more than 0.96. Some molecules (e.g CH4, SiH4,etc. )can be preferably handled by F* but can not be dealt with by other topological indices. By contrast to traditional hydrogen suppressed graph, the contribution of hydrogen atoms to structures and properties of molecules is considered. 相似文献
998.
A two-dimensional model was applied to simulate the liquid core reduction(LCR) technology of bloom CC using ANSYS software.The deformation characteristics of bloom under different liquid fraction and reducing amount are obtained.The results indicate that the main deformation condition of bloom shell is compressive strain,mainly undertaken by the liquid core,which increases with the enhancement of reducing amount.Solidified shell takes minor deformation.The longitudinal section of bloom appears sunken and the narrow side bulges,which grow serious when the liquid fractionincreases. 相似文献
999.
1000.
本文介绍了利用工作于Bragg衍射的Ge晶体声光调制器作为外差系统中的频移器来测量外差系统的噪声等效功率(NEP)的方法。该方法具有测试系统简单、信号光功率、偏频可调的优点。实验测试与理论分析吻合。 相似文献