全文获取类型
收费全文 | 7328篇 |
免费 | 454篇 |
国内免费 | 16篇 |
专业分类
电工技术 | 226篇 |
综合类 | 34篇 |
化学工业 | 1699篇 |
金属工艺 | 226篇 |
机械仪表 | 209篇 |
建筑科学 | 232篇 |
矿业工程 | 35篇 |
能源动力 | 270篇 |
轻工业 | 1052篇 |
水利工程 | 62篇 |
石油天然气 | 41篇 |
武器工业 | 1篇 |
无线电 | 451篇 |
一般工业技术 | 1673篇 |
冶金工业 | 246篇 |
原子能技术 | 94篇 |
自动化技术 | 1247篇 |
出版年
2023年 | 61篇 |
2022年 | 59篇 |
2021年 | 186篇 |
2020年 | 150篇 |
2019年 | 172篇 |
2018年 | 290篇 |
2017年 | 272篇 |
2016年 | 309篇 |
2015年 | 241篇 |
2014年 | 369篇 |
2013年 | 737篇 |
2012年 | 481篇 |
2011年 | 589篇 |
2010年 | 466篇 |
2009年 | 376篇 |
2008年 | 298篇 |
2007年 | 269篇 |
2006年 | 174篇 |
2005年 | 185篇 |
2004年 | 117篇 |
2003年 | 131篇 |
2002年 | 152篇 |
2001年 | 117篇 |
2000年 | 100篇 |
1999年 | 73篇 |
1998年 | 104篇 |
1997年 | 86篇 |
1996年 | 78篇 |
1995年 | 60篇 |
1994年 | 58篇 |
1993年 | 58篇 |
1992年 | 49篇 |
1991年 | 38篇 |
1990年 | 39篇 |
1989年 | 40篇 |
1988年 | 27篇 |
1986年 | 24篇 |
1985年 | 52篇 |
1984年 | 63篇 |
1983年 | 53篇 |
1982年 | 48篇 |
1981年 | 70篇 |
1980年 | 57篇 |
1979年 | 51篇 |
1978年 | 43篇 |
1977年 | 37篇 |
1976年 | 51篇 |
1975年 | 35篇 |
1974年 | 25篇 |
1973年 | 38篇 |
排序方式: 共有7798条查询结果,搜索用时 484 毫秒
51.
52.
New inclusion methods for the simultaneous determination of the zeros of algebraic, exponential and trigonometric polynomials are presented. These methods are realized in real interval arithmetic and do not use any derivatives. Using Weierstrass' correction some modified methods with the increased convergence rate are constructed. Convergence analysis and numerical example are included. 相似文献
53.
In the initial part the change of microstructure for steel X20 CrMoV 121 is discussed in terms of the distribution of carbide precipitates and its effects on accelerated creep resistance and hardness are presented. In the following, experimental results of microstructure and accelerated creep resistance are presented for the steels X20CrMoV 121 and P91 annealed for up to 8760 hours at 650°C and 750°C before the testing. A similar evolution of the distribution of carbide particles of a size above 102 nm is found for both steels, while the accelerated creep resistance is diminished much stronger for the steel X20CrMoV 121. This difference is due to a greater stability of NbC than that of VC precipitates, both related to the evolution of the chemical composition of complex chromium, molybdenum and iron carbide particles. 相似文献
54.
P. Lobotka I. Vávra Š. Gaži A. Plecenik J. Dérer 《Journal of Low Temperature Physics》1997,106(3-4):381-386
A Josephson junction Nb/Si/Nb with a 10 nm thick amorphous silicon barrier is studied. The upper electrode contains a 2 nm
thick sublayer of amorphous phase adjacent to the barrier, as revealed by cross-sectional TEM. Thus, the junction can be considered
as a S-I-N-S system with the N layer represented by amorphous niobium. Peculiarities in the I–V and Δ(T) dependencies are
observed and explained as a consequence of a proximity effect present in the upper electrode. 相似文献
55.
Bojana Obrenić 《Theory of Computing Systems》1994,27(1):41-63
A technique foremulating multicomputer interconnection networks that are based onseparable graphs (graphs having bounded degree and sublinear multicolor recursive bisectors) is presented. Efficient emulations among interconnection networks are necessary for porting programs designed for one network to another.Emulations are formalized asgraph embeddings, where the nodes (processors) of theguest graph (emulated network) are assigned to nodes of thehost graph (emulator), while the edges (communication links) of the guest are routed via paths in the host. The communication slowdown in an emulation depens on thedilation (length of the longest routing path) and thecongestion (number of paths that contend for a host edge) of the embedding. Theexpansion of the embedding (the ratio of the sizes of the host to guest) determines the inefficiency of processor utilization.
Cell trees are introduced as interconnection networks whose special communication properties enable them to serve as intermediate devices in these emulations. Nodes in cell trees are organized into equinumerous parts calledcells; the cells are labeled by nodes of a complete binary tree. Communication in cell trees is restricted to two specific and distinct primitives:cell communication is confined within cells, whiletransfer communication occurs between adjacent cells. Rather than solved directly, the emulation problem for the original guest-host pair is decomposed into two independent parts: emulating the guest by the cell tree, and emulating the cell tree by the host.In emulations of separable graphs by cell trees, the node assignment that ensures small dilation is derived from the separator-based decomposition of guest graphs. The congestion-free edge routing is achieved by coordinatingglobal andlocal phases, which are based on two characteristic cell-tree communication primitives.The technique is instantiated by emulating cell trees on specific host graphs. Withshuffle-like hypercube-derivative networks as hosts new constant-expansion emulations are obtained that have both dilation and congestion logarithmic in the size of the multicolor bisector of guest graphs. These emulations are the first such to have optimal (up to constants)congestion; they provide the firstoptimal algorithm for emulating arbitrary separable graphs on shuffle-like networks. The application of the technique tohypercubes as hosts also produces optimal emulations that differ from those previously known by having smaller expansion constants.This research was supported in part by NSF Grants CCR-88-12567 and CCR-90-13184, and by the University of Massachusetts Graduate School Fellowship for the academic year 1991-92. A preliminary version of this paper was presented at the 3rd ACM Symposium on Parallel Algorithms and Architectures, July 22–24, 1991, in Hilton Head, South Carolina, USA. 相似文献
56.
F. Ditrói I. Mahunka 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1985,236(2):375-379
A computerised method is presented for the construction of the level scheme on the basis of measured energies of the gamma transitions without any previous knowledge of the observed isotope. The method and the steps of the algorithm are discussed. The calculated results are compared with the published schemes for the given isotopes. 相似文献
57.
OE Santana Rodríguez ML Malé Gil JF HernándezSantana JM Limi?ana Ca?al AM Martín Sánchez 《Canadian Metallurgical Quarterly》1998,14(6):555-561
Von Hippel-Lindau disease (VHL) is an autosomal dominant tumour syndrome caused by germline mutations of the VHL tumour suppressor gene located on chromosome 3p25-26. In VHL tumours may occur in 14 different target organs, including the eye. Retinal angiomas are considered the first manifestation of VHL disease in 43% of cases, and the cumulative probability of developing a retinal angioma in one or both eyes rises during each decade of life, reaching 80% for patients over 80 years old. Since 1976 patients with VHL at the University Hospital of Utrecht and their at-risk relatives have been screened periodically by a multidisciplinary team. Long-term follow-up ophthalmological data were analysed with special attention to natural course and results of treatment. In addition, we looked for a genotype-phenotype correlation. Retinal angiomas were found in all families. In one large family with a missense mutation (V170D) of the VHL gene, in which the complete spectrum of visceral- and central nervous system (CNS) features of VHL is present, macular, parapapillary, optic disc and ora serrata angiomas were also found. In general, however, a clear-cut genotype-phenotype correlation could not be found. Only early detection and treatment of peripheral retinal angiomas can be expected to decrease the percentage of patients with decreased visual acuity. Therefore, early detection and treatment of these tumours is of paramount importance. Ophthalmological screening of patients and persons at risk should start as early as possible. In patients with apparently sporadic retinal angiomas it is advisable to perform germline DNA analysis, since the risk of developing VHL is high, especially if the angiomas are bilateral, or unilateral and multifocal, if the patient is young, or if there is a family history suggestive of VHL. 相似文献
58.
The dependence of the magnetic momentm obtained from the hysteresis loops on the speed of the magnetic field sweep
=dH
ext/dt is explained on the basis of Anderson's interpretation of the magnetic flux creep. In addition, a phenomenological model is suggested which predicts a linear dependence ofm on ln
with the slope m/ ln
, numerically equal to the relaxation rate m/ ln(t) from the usual magnetic relaxation. Such linear relations betweenm and ln
were observed experimentally in single crystals of YBaCuO. Preliminary experiments on the complementary time dependent relaxation ofm after a simulated step change ofH
ext gave mostly relaxation rates close to the predicted values. The model here presented also enables one to compare the critical state in the superconductor at a field sweep rate
with the critical state at some timet
eff after a step change ofH
ext. The values of
analyzed in our experiments actually correspond to the critical state at timest
eff between0.04 and4 sec after an imaginary large step change ofH
ext. 相似文献
59.
B. Klaić 《Scientometrics》1990,19(1-2):11-24
The research activity of chemists from the Rugjer Bokovi Institute (RBI, Zagreb, Yugoslavia) was analyzed for the period 1976–1985, covering 2018 research years of scientific work, and 1149 SCI registered papers (0.57 publications per research year). At the average, one paper was published by 3.05 scientists. The papers were published in 235 different journals, most frequently is the nationalCroatica Chemica Acta (171 papers). The publications were divided into two groups: for the periods 1976–1980 and 1981–1985, and for each paper citations were collected in the respective time period. An average publication had 2.58 citations. Chemical papers from the second period had 2.73 citations per paper, which is 85% of the expected value, and this was considerably more than for Yugoslav papers (66%) in general. The papers were classified according to the subfields used in theJournal Citation Reports, and the results compared with the data published bySchubert, Glänzel andBraun. The distribution of citations was also analyzed. 相似文献
60.