全文获取类型
收费全文 | 142884篇 |
免费 | 6487篇 |
国内免费 | 3506篇 |
专业分类
电工技术 | 5069篇 |
技术理论 | 5篇 |
综合类 | 6430篇 |
化学工业 | 20509篇 |
金属工艺 | 8320篇 |
机械仪表 | 6512篇 |
建筑科学 | 7428篇 |
矿业工程 | 2112篇 |
能源动力 | 2879篇 |
轻工业 | 7378篇 |
水利工程 | 2346篇 |
石油天然气 | 3557篇 |
武器工业 | 508篇 |
无线电 | 16526篇 |
一般工业技术 | 23438篇 |
冶金工业 | 5188篇 |
原子能技术 | 1032篇 |
自动化技术 | 33640篇 |
出版年
2024年 | 326篇 |
2023年 | 1126篇 |
2022年 | 1836篇 |
2021年 | 2650篇 |
2020年 | 1894篇 |
2019年 | 1572篇 |
2018年 | 15967篇 |
2017年 | 15125篇 |
2016年 | 11556篇 |
2015年 | 2974篇 |
2014年 | 3103篇 |
2013年 | 3700篇 |
2012年 | 6894篇 |
2011年 | 13340篇 |
2010年 | 11829篇 |
2009年 | 8841篇 |
2008年 | 10205篇 |
2007年 | 11060篇 |
2006年 | 3475篇 |
2005年 | 4051篇 |
2004年 | 3138篇 |
2003年 | 2968篇 |
2002年 | 2440篇 |
2001年 | 1799篇 |
2000年 | 1662篇 |
1999年 | 1648篇 |
1998年 | 1226篇 |
1997年 | 1066篇 |
1996年 | 1048篇 |
1995年 | 824篇 |
1994年 | 690篇 |
1993年 | 509篇 |
1992年 | 455篇 |
1991年 | 348篇 |
1990年 | 218篇 |
1989年 | 182篇 |
1988年 | 166篇 |
1987年 | 100篇 |
1986年 | 66篇 |
1985年 | 56篇 |
1984年 | 34篇 |
1968年 | 43篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1959年 | 37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 9 毫秒
101.
We present some sufficient and necessary conditions for convergent splitting of a non-Hermitian indefinite matrix. Some sufficient
conditions to determinate a matrix with a (strongly) dominant symmetric part for a class of boundary value problem are also
obtained. These results are applicable to identify the convergence of iterative methods for solving large sparse systems of
linear equations. 相似文献
102.
用于生产甲基丙烯酸的杂多酸催化剂的研究 总被引:4,自引:0,他引:4
以异丁烯为原料的两段直接氧化生产甲基丙烯酸最新工艺有许多优点。其技术关键在于研制出高效的甲基丙烯醛选择性氧化催化剂。本文报道P-Mo-As-Cu杂多化合物催化剂的组成、制备条件对催化剂活性的影响。经优化后获得高选择性、高活性的二段氧化催化剂,其甲基丙烯酸收率达60%以上。 相似文献
103.
���þ��ܰ�ȫ�Բ������������� 总被引:1,自引:1,他引:0
本文通过对在用钻机井架的现场实际测试,建立数据库、测评模型,对实测的数据用计算机技术进行分析,提出了初始弯曲应力;数据正态分布检验——x~2检验;建立回归方程;在给定置信度下测评当前承载能力的技术概念。解决了在用钻机A型井架的安全性评估问题,是一种较为合理、可靠、科学的测评技术和方法。 相似文献
104.
We studied the molecular basis of protein C deficiency in a family with a history of thromboembolic disease. An approximately 50% reduction in anticoagulant activity despite normal levels of protein C amidolytic activity and antigen was detected in plasma from the proband. All the exons and intron/exon junctions of the protein C gene were studied using a strategy that combined polymerase chain reaction amplification with DNA sequencing of the amplified fragments. We identified a C-to-A change at nucleotide number 1387 of the protein C gene in the proband and his mother, and this mutant was designated protein C Osaka 10. The C-to-A change resulted in the substitution of Ser for Arg at position -1, which is the processing protease cleavage site. The mutant protein C was partially purified from plasma of the patient's mother using barium adsorption followed by ion-exchange column chromatography. It eluted at the same sodium chloride concentration as normal protein C, and thus gamma-carboxylation of the mutant protein appeared to be normal. The apparent molecular weight of this mutant protein C was the same as that of the normal protein on immunoblotting. Amino-terminal sequence analysis showed that the light chain of the mutant protein C had an additional Ser at position-1. Thus, the loss of anticoagulant activity of protein C Osaka 10 can be explained by alteration of the conformation of the Gla domain by the additional Ser in the mutant molecule. 相似文献
105.
Carboxymethyl-2-diethylaminoethylcellulose (CM-DEAE cellulose) was prepared by etherification of carboxymethylcellulose with diethylaminoethyl chloride in a NaOH solution. The behaviour of CM-DEAE cellulose in aqueous solution was studied by viscosity and GPC measurements. The degree of substitution (DS) and existing states of DEAE substituents were examined by the use of proton NMR, and those of the CM substituents were observed with FT-IR. The results reveal that the reduced viscosity and apparent molecular size of CM-DEAE cellulose vary with the concentration of sodium chloride and changes in pH and DS. These phenomena can be explained in terms of inter- and intra-molecular ionic interactions. 相似文献
106.
The crystallization behaviour of three amorphous alloys, Co50Ni25Si15B10, Ni50Co25Si15B10 and Ni50Co25P15B10, was studied by means of differential thermal analysis in conjunction with scanning transmission electron microscopy. Isochronal annealing showed a strong dependence of crystallization on scan rate over the range of 1.99 to 20.70 K min–1. At high Co/Ni ratios, a sequential two-stage crystallization process involving primary MS-I phase followed by MS-II phase precipitation was observed. At low Co/Ni ratios MS-I and MS-II crystallization were concurrent and inseparable. Replacement of the metalloid Si with P as the glass-former dramatically reduced the activation energy for crystallization as well as the crystallization temperature. A mechanistic understanding of these findings was pursued in light of TEM/STEM microanalysis 相似文献
107.
Keng Siau 《Requirements Engineering》2007,12(4):199-201
108.
109.
Phase-change read-and-write memory (PRAM) is a promising memory that can solve the problems of conventional memory—scalability, read/write speed, and reliability. We will review the opportunities and technical challenges of PRAM. The most important challenge of PRAM is the reduction of the writing current. Various approaches to reduce the writing current will be reviewed and the prospects of PRAM are discussed. 相似文献
110.