全文获取类型
收费全文 | 16670篇 |
免费 | 1024篇 |
国内免费 | 33篇 |
专业分类
电工技术 | 184篇 |
综合类 | 43篇 |
化学工业 | 3698篇 |
金属工艺 | 329篇 |
机械仪表 | 344篇 |
建筑科学 | 721篇 |
矿业工程 | 52篇 |
能源动力 | 546篇 |
轻工业 | 1543篇 |
水利工程 | 137篇 |
石油天然气 | 61篇 |
无线电 | 1209篇 |
一般工业技术 | 3099篇 |
冶金工业 | 2362篇 |
原子能技术 | 135篇 |
自动化技术 | 3264篇 |
出版年
2023年 | 186篇 |
2022年 | 413篇 |
2021年 | 648篇 |
2020年 | 424篇 |
2019年 | 452篇 |
2018年 | 550篇 |
2017年 | 530篇 |
2016年 | 571篇 |
2015年 | 503篇 |
2014年 | 639篇 |
2013年 | 1145篇 |
2012年 | 1037篇 |
2011年 | 1245篇 |
2010年 | 874篇 |
2009年 | 814篇 |
2008年 | 845篇 |
2007年 | 815篇 |
2006年 | 620篇 |
2005年 | 535篇 |
2004年 | 397篇 |
2003年 | 396篇 |
2002年 | 353篇 |
2001年 | 233篇 |
2000年 | 204篇 |
1999年 | 217篇 |
1998年 | 251篇 |
1997年 | 209篇 |
1996年 | 215篇 |
1995年 | 190篇 |
1994年 | 173篇 |
1993年 | 156篇 |
1992年 | 128篇 |
1991年 | 82篇 |
1990年 | 126篇 |
1989年 | 121篇 |
1988年 | 84篇 |
1987年 | 94篇 |
1986年 | 104篇 |
1985年 | 100篇 |
1984年 | 88篇 |
1983年 | 80篇 |
1982年 | 96篇 |
1981年 | 92篇 |
1980年 | 71篇 |
1979年 | 72篇 |
1978年 | 63篇 |
1977年 | 74篇 |
1976年 | 67篇 |
1975年 | 46篇 |
1974年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Daniel Bouche 《电信纪事》1992,47(9-10):400-412
We study the creeping waves propagating on a convex object, whose surface impedance is Z. To this end, we seek, by using an asymptotic expansion method, a solution of Maxwell equations, propagating along a geode sic, and satisfying Silver-Müller radiation condition at infinity, and the impedance boundary condition at the surface of the body. By using a geodesic coordinate system suited to the problem, we obtain a closed form solution. The electric and magnetic fields are given in term of the components of these fields along the binormal to the geodesic. We show that two types of creeping waves exist: the electric (resp. magnetic) type, with a non zero binormal component of the electric (resp magnetic) field. They are uncoupled, except in the vicinity of Z = 1, where a rotation of the polarization, similar to Rytov’s law, is evidenced. 相似文献
92.
Allen Daniel N.; Strauss Gregory P.; Kemtes Karen A.; Goldstein Gerald 《Canadian Metallurgical Quarterly》2007,21(6):713
Hemispheric involvement in reasoning abilities has been debated for some time, and it remains unclear whether the right hemisphere's involvement in problem solving is modality specific or dependent on the type of spatial reasoning required. In the current study, 2 types of nonverbal reasoning abilities were examined, spatial reasoning and proportional reasoning, in 109 patients with cerebrovascular disease that was confined to either the right or the left hemisphere or was diffuse in nature. Results indicated that no lateralizing effects were present based on type of spatial reasoning. Findings are consistent with the suggestion that higher order cognitive processes involved in nonverbal abstraction and problem solving are not strongly lateralized to the right hemisphere but rather are more generally distributed throughout the cortex. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
93.
Adding environments as first-class entities to a language can greatly enhance its expressiveness. But first-class environments rely on identifiers, the syntax of variables, and thus do not mesh well with lexically-scoped languages. We present first-class extents as an alternative. First-class extents are founded upon lexical variables with dynamic extent. They are defined directly on the variables themselves rather than on their syntax. They therefore do not cause variable name capturing problems that plague first-class environments. Moreover, distinguishing variables from locations allows first-class extents to be orthogonal to imperative and control features. 相似文献
94.
Daniel C. Mattis 《Journal of Superconductivity and Novel Magnetism》1995,8(4):479-481
We study a 3-band model of CuO2 with “bare bones” interactions: hopping from copper ions to nearest-neighbor oxygenst pd only, a two-body interaction on the copper ionsU dd only, and an overlap copper-oxygen parameter λpd. In the limitt pd ∝U dd 1/2→∞, t*=t pd 2/2U dd is the unit of energy with 8λpd 2 as the only parameter of significance. If the two-body interaction is invariant under particle-hole interchange, the low-lying states (energy O(t*)) can be described by conserved particles and can all be classified. They are quite distinct from the high-lying states (energies O(U dd)). The dynamics of the conserved fermion-like elementary particles are well described by a modifiedt-J model with extended hopping and nearest-neighbor superexchange attraction. This is a scenario known to be favorable to high-temperature superconductivity, but it must be noted that both the hopping range and the exchange are functions of 8λpd 2. Moreover, if the Hamiltonian isnot invariant under particle-hole interchange the dynamics becomes much more complex and possibly more inimical to high-temperature superconductivity. This may provide an explanation for the deleterious effect on superconductivity of very small concentrations of certain impurities. 相似文献
95.
Giuseppe G. G. Manzardo Sandra Kürsteiner-Laube und Daniel Perrin 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1996,203(6):501-506
In diethyl ether extracts from celeriac (Apium graveolens L. var.rapaceum) all four stereoisomers of (3a–7a)-cis-3-butylhexahydrophthalide were found to be present. The analyses were carried out by means of GC, enantioselective GC and GC-MS. The assignment of the relative configuration of the diastereomers3 and4 was accomplished by NOE difference spectroscopy. 相似文献
96.
The authors present an original analysis of an aperture-coupled microstrip antenna. The theory is based on the segmentation method, which considers the patch as a multiport network whose impedance matrix is deduced from a hybrid matrix, and the use of analytical expressions of the cavity admittance at the slot centre. The theory is presented for the first time, and the theoretical results are in good agreement with previous published measurements 相似文献
97.
This second article deals with using the Comsis software for a particular application. Simulation is used to determine the maximum channel density in presence of crosstalk. In a first part, the modelling of the system is described. The simulation parameters of different optical elements are given. The results show that in the case of channels modulated at 500 Mbitls using fsk modulation format, and a direct detection operation at 1,5 μm, a minimum spacing of 6 GHz can be obtained with a 2 dB penalty. Thus if only the bandwidth of the erbium doped fibre amplifier is taken into account, the maximum number of channels which can be used is 250. However if the fsr (free spectral range) of optical filter is taken into account, the maximun number of channels is limited to 30. 相似文献
98.
99.
Daniel G. Swanson 《国际射频与微波计算机辅助工程杂志》1995,5(1):4-12
A 22.5-GHz microstrip bandpass filter is analyzed using three different circuit analysis techniques. Circuit theory modeling fails to provide an accurate prediction when compared to measured data. But a hybrid analysis, which uses electromagnetic field solver computations and circuit theory models, provides good agreement with measured data. A more complete field solver analysis of the filter also shows good agreement when compared to measurements. In the later two cases, the electromagnetic analysis captures the actual current distribution on the filter that circuit theory fails to predict. © 1995 John Wiley & Sons, Inc. 相似文献
100.
Ashmead Daniel H.; Davis DeFord L.; Northington Anna 《Canadian Metallurgical Quarterly》1995,21(2):239
Of the several sources of acoustic information for distance perception, those arising from motion of the listener or sound source have received little attention. This motion-related information (recently called acoustic tau) is described, and experiments evaluating its utilization are presented. Accuracy and consistency at walking to the locations of briefly presented sounds were better when people listened while walking than while standing still. Manipulations of the sound to simulate shorter or longer target distances produced appropriate undershooting but not overshooting. The results indicate that people use motion-related acoustic information about distance to guide their locomotor actions, although they do not take full advantage of this information. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献