全文获取类型
收费全文 | 11074篇 |
免费 | 116篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 98篇 |
综合类 | 2篇 |
化学工业 | 1016篇 |
金属工艺 | 101篇 |
机械仪表 | 300篇 |
建筑科学 | 216篇 |
矿业工程 | 28篇 |
能源动力 | 129篇 |
轻工业 | 873篇 |
水利工程 | 107篇 |
石油天然气 | 15篇 |
无线电 | 864篇 |
一般工业技术 | 1022篇 |
冶金工业 | 5574篇 |
原子能技术 | 108篇 |
自动化技术 | 746篇 |
出版年
2021年 | 68篇 |
2020年 | 51篇 |
2019年 | 62篇 |
2018年 | 60篇 |
2017年 | 82篇 |
2016年 | 66篇 |
2015年 | 47篇 |
2014年 | 104篇 |
2013年 | 316篇 |
2012年 | 160篇 |
2011年 | 237篇 |
2010年 | 211篇 |
2009年 | 231篇 |
2008年 | 260篇 |
2007年 | 240篇 |
2006年 | 246篇 |
2005年 | 218篇 |
2004年 | 179篇 |
2003年 | 198篇 |
2002年 | 200篇 |
2001年 | 163篇 |
2000年 | 160篇 |
1999年 | 254篇 |
1998年 | 1522篇 |
1997年 | 934篇 |
1996年 | 689篇 |
1995年 | 482篇 |
1994年 | 353篇 |
1993年 | 401篇 |
1992年 | 131篇 |
1991年 | 154篇 |
1990年 | 157篇 |
1989年 | 151篇 |
1988年 | 157篇 |
1987年 | 163篇 |
1986年 | 122篇 |
1985年 | 139篇 |
1984年 | 94篇 |
1983年 | 105篇 |
1982年 | 79篇 |
1981年 | 116篇 |
1980年 | 88篇 |
1979年 | 79篇 |
1978年 | 74篇 |
1977年 | 191篇 |
1976年 | 346篇 |
1975年 | 77篇 |
1974年 | 71篇 |
1973年 | 65篇 |
1972年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
J Byrne S Kienzle D Johnson G Duke V Gannon B Selinger J Thomas 《Water science and technology》2006,53(10):327-334
Long-term trends in alpine and prairie snow pack accumulation and melt are affecting streamflow within the Oldman River Basin in southern Alberta, Canada. Unchecked rural and urban development also has contributed to changes in water quality, including enhanced microbial populations and increased waterborne pathogen occurrence. In this study we look at changing environment within the Oldman River Basin and its impact on water quality and quantity. The cumulative effects include a decline in net water supplies, and declining quality resulting in increased risk of disease. Our data indicates that decreases in the rate of flow of water can result in sedimentation of bacterial contaminants within the water column. Water for ecosystems, urban consumption, recreation and distribution through irrigation is often drawn from waterholding facilities such as dams and weirs, and concern must be expressed over the potential for contaminate build-up and disproportionate potential of these structures to pose a risk to human and animal health. With disruption of natural flow rates for water resulting from environmental change such as global warming and/or human intervention, increased attention needs to be paid to use of best management practices to protect source water supplies. 相似文献
12.
13.
Present-day computer-aided design (CAD) packages play only a small part in the area of mechanical engineering design, which involves the synthesis and embodiment of physical components to perform a pre-determined function without unwanted side effects. The computer cannot properly help the designer in this task until it is able to capture and process the function requirements of the design. This paper describes the computer system being developed for this purpose at the Engineering Design Centre at Cambridge University Engineering Department. The paper also explores some of the geometrical and programming implications raised. 相似文献
14.
Genetic algorithms in engineering electromagnetics 总被引:10,自引:0,他引:10
This paper presents a tutorial and overview of genetic algorithms for electromagnetic optimization. Genetic-algorithm (GA) optimizers are robust, stochastic search methods modeled on the concepts of natural selection and evolution. The relationship between traditional optimization techniques and the GA is discussed. Step-by-step implementation aspects of the GA are detailed, through an example with the objective of providing useful guidelines for the potential user. Extensive use is made of sidebars and graphical presentation to facilitate understanding. The tutorial is followed by a discussion of several electromagnetic applications in which the GA has proven useful. The applications discussed include the design of lightweight, broadband microwave absorbers, the reduction of array sidelobes in thinned arrays, the design of shaped-beam antenna arrays, the extraction of natural resonance modes of radar targets from backscattered response data, and the design of broadband patch antennas. Genetic-algorithm optimization is shown to be suitable for optimizing a broad class of problems of interest to the electromagnetic community. A comprehensive list of key references, organized by application category, is also provided 相似文献
15.
Applications of large-scale computer modeling and simulation to a class of bioelectric field problems in a variety of biomedical research areas, from single cells to full human structures, are described. The authors focus on a specific subset of bioelectric field problems that have applications in electrocardiography and electroencephalography. The physics and physiology of bioelectric volume conductors are introduced. A specific computational example and the authors' view on the future direction of computational medicine are presented 相似文献
16.
The Fusion program, a method for agile, flexible computer integrated manufacturing (CIM) at Motorola's Paging Products Group, is discussed. Fusion's CIM and automated assembly system can manufacture a wide variety of different products on the same production line. The development of the Fusion program and how it differs from its predecessor, the Bandit program, are described 相似文献
17.
We demonstrate multi-emitter Si/GexSi1-x n-p-n heterojunction bipolar transistors (HBT's) which require no base contact for transistor operation. The base current is supplied by the additional emitter contact under reverse bias due to the heavy doping of the emitter-base junction. Large-area HBT test structures exhibit good transistor characteristics, with current gain β≈400 regardless of whether the base current is supplied by a test base electrode or one of the emitter contacts. These devices have enhanced logic functionality because of emitter contact symmetry. Since device fabrication does not require base electrode formation, the number of processing steps can be reduced without significant penalty to HBT performance 相似文献
18.
This study demonstrates that the use of high field 1H NMR spectroscopy permits individual detection of phosphatidylcholine and sphingomyelin molecules at the surface of native low density lipoprotein (LDL) particles. Distinct behaviour was observed for the choline head group -N(CH3)3 resonances of these different phospholipids revealing preferential immobilisation for phosphatidylcholine. This suggests the existence of reversible and irreversible phosphatidylcholine-apolipoprotein B interactions and is consistent with microdomain formation at the surface monolayer of LDL. The novel resonance assignment and results show that 1H NMR can provide efficient and practical means for future studies on the structure and dynamics at the LDL surface. 相似文献
19.
This is the second in a series of articles provided to the readers of PENNSYLVANIA MEDICINE as an update from researchers and clinicians in this cutting-edge medical field. The series is partially sponsored through a grant from the Pennsylvania Department of Health to the University of Pittsburgh Department of Human Genetics. 相似文献
20.
D Cullinan F Johnson AP Grollman M Eisenberg C de los Santos 《Canadian Metallurgical Quarterly》1997,36(39):11933-11943
Vinyl chloride reacts with cellular DNA producing 3,N4-etheno-2'-deoxycytidine (epsilonC) along with other exocyclic adducts. The solution structure of an oligodeoxynucleotide duplex containing an epsilonC.dG base pair was determined by high-resolution NMR spectroscopy and molecular dynamics simulations. NMR data indicated that the duplex adopts a right-handed helical structure having all residues in anti orientation around the glycosylic torsion angle. The epsilonC adduct has a sugar pucker in the C3'-endo/C4'-exo region while the rest of the residues are in the C2'-endo/C3'-exo range. NOE interactions established Watson-Crick alignments for canonical base pairs of the duplex. The imino proton of the lesion-containing base pair resonated as a sharp signal that was resistant to water exchange, suggesting hydrogen bonding. Restrained molecular dynamics simulations generated three-dimensional models in excellent agreement with the spectroscopic data. The refined structures are slightly bent at the lesion site without major perturbations of the sugar-phosphate backbone. The adduct is displaced and shifted toward the major groove of the helix while its partner on the complementary strand remains stacked. The epsilonC(anti).dG(anti) base pair alignment is sheared and stabilized by the formation of hydrogen bonds. The biological implications of structures of epsilonC-containing DNA duplexes are discussed. 相似文献