全文获取类型
收费全文 | 39201篇 |
免费 | 4592篇 |
国内免费 | 3768篇 |
专业分类
电工技术 | 3317篇 |
技术理论 | 2篇 |
综合类 | 6831篇 |
化学工业 | 1721篇 |
金属工艺 | 817篇 |
机械仪表 | 2692篇 |
建筑科学 | 2654篇 |
矿业工程 | 813篇 |
能源动力 | 787篇 |
轻工业 | 2410篇 |
水利工程 | 1063篇 |
石油天然气 | 857篇 |
武器工业 | 499篇 |
无线电 | 5252篇 |
一般工业技术 | 3783篇 |
冶金工业 | 925篇 |
原子能技术 | 488篇 |
自动化技术 | 12650篇 |
出版年
2024年 | 167篇 |
2023年 | 519篇 |
2022年 | 938篇 |
2021年 | 1018篇 |
2020年 | 1063篇 |
2019年 | 987篇 |
2018年 | 1004篇 |
2017年 | 1222篇 |
2016年 | 1324篇 |
2015年 | 1394篇 |
2014年 | 2098篇 |
2013年 | 2354篇 |
2012年 | 2738篇 |
2011年 | 2947篇 |
2010年 | 2331篇 |
2009年 | 2525篇 |
2008年 | 2633篇 |
2007年 | 3011篇 |
2006年 | 2665篇 |
2005年 | 2365篇 |
2004年 | 1977篇 |
2003年 | 1639篇 |
2002年 | 1356篇 |
2001年 | 1147篇 |
2000年 | 1002篇 |
1999年 | 839篇 |
1998年 | 683篇 |
1997年 | 590篇 |
1996年 | 539篇 |
1995年 | 474篇 |
1994年 | 415篇 |
1993年 | 290篇 |
1992年 | 262篇 |
1991年 | 219篇 |
1990年 | 195篇 |
1989年 | 173篇 |
1988年 | 116篇 |
1987年 | 69篇 |
1986年 | 38篇 |
1985年 | 35篇 |
1984年 | 29篇 |
1983年 | 36篇 |
1982年 | 24篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1964年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
李振涛 《导弹与航天运载技术》1993,(5):16-26
本文给出了一组不仅能用于卫星轨道计算,同时也能用于导弹自由飞行轨道的中间轨道计算公式。引组公式的解与二体问题解有很好的可比性。由于导弹轨道与卫星轨道有很大不同,故计算中的各使用常数的取值范围也有很大不同。 相似文献
32.
33.
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
34.
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
35.
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
36.
37.
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
38.
Interventions for a variety of emotional and behavioral problems are commonly delivered in the context of treatment groups, with many using rolling admission to sustain membership (i.e., admission, dropout, and discharge from group are perpetual and ongoing). The authors present an overview of the analytic challenges inherent in rolling group data and outline commonly used (but flawed) analytic and design approaches to addressing (or sidestepping) these issues. Moreover, the authors propose use of latent class pattern mixture models (LCPMMs) as a statistically and conceptually defensible approach for modeling treatment data from rolling groups. The LCPMM approach is illustrated with rolling group data from a group-based alcoholism pilot treatment trial (N = 128). Different inferences were made with regard to treatment efficacy under LCPMM vs. the commonly used standard group-clustered latent growth model (LGM); coupled with other preliminary findings in this area, inferences from LGMs may be overly liberal when applied to data from rolling groups. Continued work on data analytic difficulties in groups with membership turnover is critical for furthering the ecological validity of research on behavioral treatments. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
39.
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
40.
The paper considers vulnerable multi-state series-parallel systems operating under influence of external impacts. Both the external impacts and internal failures affect system survivability, which is determined as the probability of meeting a given demand. The external impacts are characterized by several destructive factors affecting the system or its parts simultaneously.In order to increase the system's survivability a multilevel protection against the destructive factors can be applied to its subsystems. In such systems, the protected subsystems can be destroyed only if all of the levels of their protection are destroyed.The paper presents an algorithm for evaluating the survivability of series-parallel systems with arbitrary configuration of multilevel protection against multiple destructive factor impacts. The algorithm is based on a composition of Boolean and the Universal Generating Function techniques.Illustrative examples are presented. 相似文献