全文获取类型
收费全文 | 11889篇 |
免费 | 819篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 70篇 |
综合类 | 5篇 |
化学工业 | 2401篇 |
金属工艺 | 101篇 |
机械仪表 | 284篇 |
建筑科学 | 432篇 |
矿业工程 | 20篇 |
能源动力 | 215篇 |
轻工业 | 1984篇 |
水利工程 | 68篇 |
石油天然气 | 20篇 |
无线电 | 683篇 |
一般工业技术 | 1739篇 |
冶金工业 | 3112篇 |
原子能技术 | 23篇 |
自动化技术 | 1561篇 |
出版年
2024年 | 35篇 |
2023年 | 140篇 |
2022年 | 114篇 |
2021年 | 325篇 |
2020年 | 270篇 |
2019年 | 270篇 |
2018年 | 347篇 |
2017年 | 354篇 |
2016年 | 464篇 |
2015年 | 419篇 |
2014年 | 545篇 |
2013年 | 989篇 |
2012年 | 859篇 |
2011年 | 646篇 |
2010年 | 468篇 |
2009年 | 465篇 |
2008年 | 490篇 |
2007年 | 423篇 |
2006年 | 392篇 |
2005年 | 244篇 |
2004年 | 226篇 |
2003年 | 197篇 |
2002年 | 191篇 |
2001年 | 121篇 |
2000年 | 120篇 |
1999年 | 165篇 |
1998年 | 866篇 |
1997年 | 502篇 |
1996年 | 367篇 |
1995年 | 224篇 |
1994年 | 209篇 |
1993年 | 217篇 |
1992年 | 50篇 |
1991年 | 63篇 |
1990年 | 52篇 |
1989年 | 56篇 |
1988年 | 64篇 |
1987年 | 49篇 |
1986年 | 43篇 |
1985年 | 54篇 |
1984年 | 23篇 |
1983年 | 17篇 |
1982年 | 32篇 |
1981年 | 30篇 |
1980年 | 47篇 |
1979年 | 23篇 |
1978年 | 18篇 |
1977年 | 103篇 |
1976年 | 218篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
The treatment of patients with uterine neoplasms may be significantly altered by the stage of disease at the time of diagnosis. A noninvasive and accurate means of staging these tumors is therefore desirable. This article discusses the magnetic resonance imaging techniques and findings that are essential for the accurate staging of uterine neoplasms. The imaging findings are presented following a discussion of the histopathologic findings, clinical presentation, diagnosis and staging, pathways of tumor spread, and treatment of each neoplasm. A comparison of magnetic resonance and other imaging techniques is also provided. 相似文献
22.
23.
OBJECTIVE: Microvascular pericytes may contract in two different ways: In the first, a circumferential or radial mechanical force applied at right angles to the long axis of the vessel may constrict the underlying vessel affecting blood flow and transmural pressure. Retraction and elongation of pericyte processes may also occur tangentially and at right angles to the vessel axis and alter microvessel permeability by changing the amount of ablumenal surface covered or the openness of interendothelial junctions. In this study, cultured pericytes were utilized as a model experimental system to determine if vasoactive stimulation changes their shape in a manner consistent with this hypothesis. METHODS: Pericytes cultured from isolated rate capillaries were subjected to angiotensin II and histamine. Their response was monitored by measuring the area of non-yielding substrate covered by the pericytes and the manner in which their shape changed. Shape changes were quantified by calculating the surface area: perimeter perimeter ratios. RESULTS: Histamine significantly reduced surface area covered and the surface area:perimeter ratio. The pericyte processes retracted, resulting in elongated, spindle-shaped cells. These effects were nullified by the H1 blocker diphenhydramine suggesting a receptor-specific response. Angiotensin II also elicited contraction and reduced surface area, but the cells contracted laterally and longitudinally. The surface area: perimeter ratios also decreased. CONCLUSIONS: These results indicate that pericytes are capable of two types of contractile responses in culture, depending on the specific vasoactive stimulus. 相似文献
24.
25.
26.
Rui A. S. Lapa José L. F. C. Lima 《Journal of Automated Methods and Management in Chemistry》1991,13(3):119-122
The construction of a microcomputer-controlled electrode switch for
use in potentiometric determinations is described. This can be coupled to most of the analytical equipment usually found in laboratories, to enable a setting up of automatic systems capable of performing sequential determinations with several ion-selective
electrodes. The assessment of its analytical usage and behaviour are discussed. 相似文献
27.
André Girard Pierre Dominique Lansard Bernard Liau Anne Marie Mongeon Jean Luc Thibault 《电信纪事》1991,46(5-6):335-350
Classical hierarchical routing in telephone networks is extended to a wider class called out-of-chain routing in such a way that some useful properties of hierarchical routing are retained. This new routing pattern offers more potential paths than the fixed hierarchical one and can be introduced as a dynamic routing where the fixed alternate sequences change at some predetermined instants during the day. The effect of this new routing pattern on the network performances is examined. The main topic of this paper is to present heuristic methods used to optimise such routings in large networks. We show on artificial networks that the throughput of a given network can be significantly improved by suitable routing choices. We demonstrate that the integration of routing changes within a multihour dimensioning process is possible but the lack of realistic data does not permit at this time to quantify the value of routing optimization on real networks. 相似文献
28.
29.
30.
Patrícia Carvalho de Souza André Salim Khayat Igor Chamon Seligmann Rommel Mario Rodríguez Burbano 《Biocell》2008,32(2):207-210
The collared peccary (Tayassu tajacu) is widely distributed over the American continent, being found from the south of the USA to the north of Argentina. In Brazil, it is spread all over the country, being one of the potential species to be raised in captivity. Therefore, the cytogenetic techniques could be a potential tool for reproductive monitoring of animals raised in captivity, mainly when destined for commercial purposes. This study had the objective of determining the chromosome number of two populations raised in captivity and characterizing them by GTG banding. For this purpose, an analysis was made of mitotic metaphases obtained from lymphocyte cultures made from blood samples of 11 animals, six of which from the Northeast and five from the North of Brazil. The results of this analysis showed the same karyotype pattern for the species (2n=30 chromosomes and NF=48), besides corresponding to the South American pattern of the species, i.e., without a translocation between autosomes 1 and 8, chromosome X acrocentric, and no differences were found between the two populations studied. However, chromosomal polymorphisms were observed compared to data from the literature on populations from North and South America. 相似文献