全文获取类型
收费全文 | 45096篇 |
免费 | 5698篇 |
国内免费 | 4355篇 |
专业分类
电工技术 | 3538篇 |
技术理论 | 3篇 |
综合类 | 7587篇 |
化学工业 | 1927篇 |
金属工艺 | 936篇 |
机械仪表 | 3277篇 |
建筑科学 | 3070篇 |
矿业工程 | 952篇 |
能源动力 | 847篇 |
轻工业 | 2676篇 |
水利工程 | 1161篇 |
石油天然气 | 984篇 |
武器工业 | 536篇 |
无线电 | 6240篇 |
一般工业技术 | 4336篇 |
冶金工业 | 973篇 |
原子能技术 | 519篇 |
自动化技术 | 15587篇 |
出版年
2024年 | 218篇 |
2023年 | 638篇 |
2022年 | 1142篇 |
2021年 | 1238篇 |
2020年 | 1325篇 |
2019年 | 1155篇 |
2018年 | 1183篇 |
2017年 | 1425篇 |
2016年 | 1577篇 |
2015年 | 1698篇 |
2014年 | 2504篇 |
2013年 | 2770篇 |
2012年 | 3175篇 |
2011年 | 3416篇 |
2010年 | 2757篇 |
2009年 | 2903篇 |
2008年 | 3036篇 |
2007年 | 3434篇 |
2006年 | 3034篇 |
2005年 | 2652篇 |
2004年 | 2241篇 |
2003年 | 1879篇 |
2002年 | 1511篇 |
2001年 | 1286篇 |
2000年 | 1138篇 |
1999年 | 940篇 |
1998年 | 775篇 |
1997年 | 667篇 |
1996年 | 636篇 |
1995年 | 541篇 |
1994年 | 469篇 |
1993年 | 330篇 |
1992年 | 310篇 |
1991年 | 239篇 |
1990年 | 224篇 |
1989年 | 196篇 |
1988年 | 127篇 |
1987年 | 83篇 |
1986年 | 44篇 |
1985年 | 49篇 |
1984年 | 29篇 |
1983年 | 42篇 |
1982年 | 25篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1965年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
A scheme to randomly generate dust points on the surface of a three-dimensional (3D) object is proposed. This scheme will potentially eliminate the bias of a density of points which are approximately equally spaced on the surface, as well as eliminate possible weighting requirements for areas of higher density. This method has the potential to reduce computational effort, as fewer points might be required to define the surface area. The global trial function vector can be assigned to these dust points and then entered into the complex variable boundary element method (CVBEM) commercial code. This scheme can be applied to each piece of a system that is comprised of a connected multiple geometry. A noticeable benefit of this approach is that the same problem can be studied several times, using a new random distribution of surface points each time. The smallest error can then be determined and that run selected. The Mathematica code used to generate the scheme is attached as an appendix. 相似文献
112.
山东改造工程旧房质量检测 总被引:5,自引:4,他引:1
结合某成品仓库改作商业用房的工程实例,对该建筑进行了详细的检测与分析,并根据结果提出了针对性的加固方案,并对加固效果进行了探讨,为工程改造提供了依据,可供类似工程借鉴。 相似文献
113.
H9000 V4.0计算机监控系统技术特点概要 总被引:8,自引:3,他引:5
为了满足三峡右岸电站的应用需要,在H9000 V3.0计算机监控系统的基础上研制开发了H9000 V4.0系统,改进和完善了原系统已有功能,开发了新功能,进一步提高了系统的性能指标和可靠性指标。文中主要介绍H9000 V4.0系统的设计原则,以及数据采集、人机联系、报表定制、Web信息发布、历史数据管理等主要新功能。 相似文献
114.
115.
U. Reimer
H. -J. Schek
《Data & Knowledge Engineering》1989,4(4):321-352The first part of this paper introduces the basic constructs of a frame representation model and gives a formal definition for them. Subsequently the nested relational model (NF2) is described as an extension of the classical relational model to support relation-valued attributes. In the second part of this paper both models are compared with each other and a mapping of frame representation structures to NF2 structures is specified. The structural similarities between frames and NF2 relations are made clear and it is shown that their main difference is due to the type polymorphism introduced by the concept hierarchy of the frame model. This causes type collisions to occur in the strictly typed NF2 model when frames are directly mapped to NF2 structures. Two solutions to this problem are suggested and compared. The paper concludes with a reformulation of query operations of the frame model in terms of NF2 algebra operations. 相似文献
116.
During the 1997 winter season, shipborne polarimetric backscatter measurements of Great Lakes (freshwater) ice types using the Jet Propulsion Laboratory C-band scatterometer, together with surface-based ice physical characterization measurements and environmental parameters, were acquired concurrently with Earth Resource Satellite 2 (ERS-2) and RADARSAT Synthetic Aperture Radar (SAR) data. This polarimetric data set, composed of over 20 variations of different ice types measured at incident angles from 0° to 60° for all polarizations, was processed to radar cross-section to establish a library of signatures (look-up table) for different ice types. The library is used in the computer classification of calibrated satellite SAR data. Computer analysis of ERS-2 and RADARSAT ScanSAR images of Great Lakes ice cover using a supervised classification technique indicates that different ice types in the ice cover can be identified and mapped, and that wind speed and direction can have an influence on the classification of water as ice based on single frequency, single polarization data. Once satellite SAR data are classified into ice types, the ice map provides important and necessary input for environmental protection and management, ice control and ice breaking operations, and ice forecasting and modeling efforts. 相似文献
117.
Abstract— Recent commercial liquid‐crystal‐display (LCD) televisions are larger and brighter than traditional televisions, thus impacting the viewing conditions in which they are viewed. These changes in viewing conditions may require different electro‐optical transfer functions (EOTFs) for LCD TVs than those for conventional TVs. Here, the way various EOTFs affect the preferred image quality of test images with changes in brightness and surround illumination conditions are examined. The first method used a gain, offset, and gamma (GOG) function with a range of gamma values, and the second method altered the intrinsic EOTFs. Image preference for the simulated EOTFs was determined using a paired‐comparison experiment for ten images. The first experiment took place in a darkened room at two display luminance levels. The results indicated that a gamma of 1.6 was most preferred overall although more so at a lower screen luminance level. In a second experiment, the procedure was repeated with a dim surround of 10% of the display's white point. With this surround, preference for a gamma value of around 1.6 at both screen luminance levels was more enhanced. These results indicated that image preference for different EOTFs is dependent on display luminance and that this dependence is maintained with a dim surround. 相似文献
118.
Fumio Negoro 《Knowledge》2003,16(7-8):383-397
The purpose of our study is to build up relationships between requirement and source programs with our originally thought-out rules. When other rules to be derived from these original rules are applied to software development, even a single instruction in a programming language could be determined, and the program would satisfy the requirement. More specifically speaking, these rules will turn into a formula or a prototype of software programs. Hence, when the variables in the requirement are placed in the formula, we can get a required program in an automatic way. 相似文献
119.
An optimal control problem with nonsmooth performance criterion described by a system of ordinary differential equations is considered. Necessary first-order optimality conditions are obtained. 相似文献
120.
Herbert S. Bennett 《Journal of research of the National Institute of Standards and Technology》2007,112(4):209-221
In this paper, we present the theory for calculating Raman line shapes as functions of the Fermi energy and finite temperatures in zinc blende, n-type GaAs for donor densities between 1016 cm−3 and 1019 cm−3. Compared to other theories, this theory is unique in two respects: 1) the many-body effects are treated self-consistently and 2) the theory is valid at room temperature for arbitrary values of the ratio R = (Q2/α), where Q is the magnitude of the normalized wave vector and α is the normalized frequency used in the Raman measurements. These calculations solve the charge neutrality equation self-consistently for a two-band model of GaAs at 300 K that includes the effects of high carrier concentrations and dopant densities on the perturbed densities of states used to calculate the Fermi energy as a function of temperature. The results are then applied to obtain the carrier concentrations from Fermi energies in the context of line shapes in Raman spectra due to the coupling between longitudinal optical phonons and plasmons. Raman measurements have been proposed as a non-destructive method for wafer acceptance tests of carrier density in semiconductor epilayers. The interpretation of Raman spectra to determine the majority electron density in n-type semiconductors requires an interdisciplinary effort involving experiments, theory, and computer-based simulations and visualizations of the theoretical calculations. 相似文献