全文获取类型
收费全文 | 125612篇 |
免费 | 3126篇 |
国内免费 | 461篇 |
专业分类
电工技术 | 1056篇 |
综合类 | 2347篇 |
化学工业 | 21091篇 |
金属工艺 | 5500篇 |
机械仪表 | 3864篇 |
建筑科学 | 3513篇 |
矿业工程 | 642篇 |
能源动力 | 2363篇 |
轻工业 | 11567篇 |
水利工程 | 1653篇 |
石油天然气 | 548篇 |
武器工业 | 3篇 |
无线电 | 10923篇 |
一般工业技术 | 22468篇 |
冶金工业 | 10589篇 |
原子能技术 | 482篇 |
自动化技术 | 30590篇 |
出版年
2024年 | 85篇 |
2023年 | 395篇 |
2022年 | 836篇 |
2021年 | 1308篇 |
2020年 | 964篇 |
2019年 | 1083篇 |
2018年 | 15627篇 |
2017年 | 14557篇 |
2016年 | 11372篇 |
2015年 | 1924篇 |
2014年 | 1887篇 |
2013年 | 3492篇 |
2012年 | 5642篇 |
2011年 | 11949篇 |
2010年 | 10244篇 |
2009年 | 7430篇 |
2008年 | 8538篇 |
2007年 | 9296篇 |
2006年 | 1406篇 |
2005年 | 2323篇 |
2004年 | 2160篇 |
2003年 | 2097篇 |
2002年 | 1368篇 |
2001年 | 709篇 |
2000年 | 745篇 |
1999年 | 691篇 |
1998年 | 2845篇 |
1997年 | 1820篇 |
1996年 | 1251篇 |
1995年 | 670篇 |
1994年 | 565篇 |
1993年 | 563篇 |
1992年 | 199篇 |
1991年 | 200篇 |
1990年 | 131篇 |
1989年 | 155篇 |
1988年 | 166篇 |
1987年 | 148篇 |
1986年 | 117篇 |
1985年 | 154篇 |
1984年 | 114篇 |
1983年 | 79篇 |
1982年 | 89篇 |
1981年 | 107篇 |
1980年 | 108篇 |
1977年 | 192篇 |
1976年 | 368篇 |
1973年 | 61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 15 毫秒
11.
Identification of Lophius budegassa(black‐bellied angler) and L. piscatorius(angler) (Lophiiformes) was carried out on the amplification of a 486 bp tRNAGlu/cytochrome b segment using the polymerase chain reaction (PCR). Direct DNA sequencing of 6 PCR products was carried out. Six restriction endonucleases (AluI, CfoI, HaeIII, HinfI, Mae, and ScrFI) with different species‐specific restriction fragment length polymorphism (RFLP) were selected. Digestions of PCR products from 30 individuals showed no intraspecific polymorphism. Double digestions (CfoI and HinfI, and HaeIII and ScrFI) were simpler and more rapid than single digestions. This technique is suitable for distinguishing tails of both Lophius species. 相似文献
12.
ML Martínez-Frías E Bermejo Sánchez E Rodríguez Pinilla A Villa 《Canadian Metallurgical Quarterly》1997,46(6):593-596
INTRODUCTION: Even though there are few epidemiological studies evaluating the birth weights of different groups of malformed babies with chromosomal abnormalities, it is widely known that infants with trisomy 18, and to a lesser degree those with trisomy 13 and other chromosomal alterations, have low birth weights. PATIENTS AND METHODS: In this study we present the analysis of the birth weights and gestational ages of a large sample of babies (23,155 malformed and a similar number of nonmalformed babies), separating the different groups of chromosomal anomalies and comparing the weight in the clinical groups of malformed infants. RESULTS: Most of the groups with chromosomal abnormalities present lower birth weights in comparison to the other groups. CONCLUSIONS: The results of our study support the conclusion that the relationship between chromosomal alterations and low birth weight is sufficiently important that such a low birth weight in children with minor or major anomalies should be considered as one more indication to perform chromosomal analysis. 相似文献
13.
SA Khotimchenko VM Kodentsova IA Alekseeva SG Vlaskina OA Vrzhesinskaia AA Sokol''nikov LA Kharitonchik IP Aleshko-Ozhevskií LV Sheviakova 《Canadian Metallurgical Quarterly》1997,43(3):158-164
Gamma delta T-Cells represent a minor subpopulation of T-lymphocytes in man and their role in normal and diseased human skin is unknown. This article is a comprehensive review of T-lymphocytes bearing the gamma delta T-cell receptor in normal and pathological human skin. Firstly, we have documented the occurrence of gamma delta T-cells in normal skin and in a range of reactive and malignant skin conditions. We have then discussed the experimental findings regarding the repertoire used by gamma delta T-cells in normal human skin and in cutaneous disorders with an increased percentage of gamma delta T-cells. 相似文献
14.
15.
The purpose of this paper is to evaluate two methods of assessing the productivity and quality impact of Computer Aided Software Engineering (CASE) and Fourth Generation Language (4GL) technologies: (1) by the retrospective method; and (2) the cross-sectional method. Both methods involve the use of questionnaire surveys. Developers' perceptions depend on the context in which they are expressed and this includes expectations about the effectiveness of a given software product. Consequently, it is generally not reliable to base inferences about the relative merits of CASE and 4GLs on a cross-sectional comparison of two separate samples of users. The retrospective method that requires each respondent to directly compare different products is shown to be more reliable. However, there may be scope to employ cross-sectional comparisons of the findings from different samples where both sets of respondents use the same reference point for their judgements, and where numerical rather than verbal rating scales are used to measure perceptions. 相似文献
16.
17.
孙维銮 《自动化与仪器仪表》1994,(3):31-34,38
从理论上和实践上对武钢1700、鞍钢1700改造前后、本钢1700改造前后和攀钢1450精轧机组的电动压下机构在带钢压下时的动特性进行计算和探讨,得出有说服力的结论。主题词: 相似文献
18.
Jan van Eijck 《Formal Aspects of Computing》1994,6(1):766-787
Presuppositions of utterances are the pieces of information you convey with an utterance no matter whether your utterance is true or not. We first study presupposition in a very simple framework of updating propositional information, with examples of how presuppositions of complex propositional updates can be calculated. Next we move on to presuppositions and quantification, in the context of a dynamic version of predicate logic, suitably modified to allow for presupposition failure. In both the propositional and the quantificational case, presupposition failure can be viewed as error abortion of procedures. Thus, a dynamic assertion logic which describes the preconditions for error abortion is the suitable tool for analysing presupposition. 相似文献
19.