全文获取类型
收费全文 | 31197篇 |
免费 | 4076篇 |
国内免费 | 2066篇 |
专业分类
电工技术 | 3832篇 |
技术理论 | 6篇 |
综合类 | 3243篇 |
化学工业 | 3199篇 |
金属工艺 | 1505篇 |
机械仪表 | 2328篇 |
建筑科学 | 3071篇 |
矿业工程 | 1876篇 |
能源动力 | 2501篇 |
轻工业 | 1715篇 |
水利工程 | 853篇 |
石油天然气 | 1583篇 |
武器工业 | 489篇 |
无线电 | 3303篇 |
一般工业技术 | 3176篇 |
冶金工业 | 1895篇 |
原子能技术 | 703篇 |
自动化技术 | 2061篇 |
出版年
2024年 | 72篇 |
2023年 | 482篇 |
2022年 | 912篇 |
2021年 | 1118篇 |
2020年 | 1128篇 |
2019年 | 1014篇 |
2018年 | 966篇 |
2017年 | 1131篇 |
2016年 | 1191篇 |
2015年 | 1218篇 |
2014年 | 1959篇 |
2013年 | 1804篇 |
2012年 | 2482篇 |
2011年 | 2755篇 |
2010年 | 2023篇 |
2009年 | 2092篇 |
2008年 | 1827篇 |
2007年 | 2215篇 |
2006年 | 1967篇 |
2005年 | 1570篇 |
2004年 | 1310篇 |
2003年 | 1044篇 |
2002年 | 883篇 |
2001年 | 762篇 |
2000年 | 676篇 |
1999年 | 494篇 |
1998年 | 366篇 |
1997年 | 361篇 |
1996年 | 273篇 |
1995年 | 246篇 |
1994年 | 217篇 |
1993年 | 162篇 |
1992年 | 149篇 |
1991年 | 109篇 |
1990年 | 73篇 |
1989年 | 77篇 |
1988年 | 49篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 11篇 |
1984年 | 16篇 |
1983年 | 2篇 |
1982年 | 33篇 |
1981年 | 15篇 |
1980年 | 6篇 |
1979年 | 18篇 |
1978年 | 3篇 |
1959年 | 8篇 |
1957年 | 1篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
E. Stenitzer H. Diestel Th. Zenker R. Schwartengräber 《Water Resources Management》2007,21(9):1567-1584
The performance of the water balance and crop growth model SIMWASER to estimate the water supply of a lawn by capillary rise
from shallow ground water was investigated by using lysimeter measurements with a sandy and a clayey soil. Moreover the robustness
of the model was evaluated by running it either with measured hydraulic soil parameters or with estimated pedotransfer functions
(PTFs) derived from texture and bulk density. Simulations were performed for the years 1996–1998 with input data from the
lysimeter station Berlin-Dahlem (Germany) for lysimeters containing undisturbed sandy or clayey soil monoliths, with groundwater
at 135 cm depth. Simulated evapotranspiration and percolation/capillary rise were in good agreement with the measured data
for all variants, while simulated soil water storage was acceptable only for the variants using hydraulic soil data based
on laboratory measurements or using PTFs derived from known soil class and bulk density. PTFs based on mean total pore volume
of the respective soil classes yielded soil water storages which were evidently too high; therefore they should be used with
care and must be avoided at all in simulating the soil water balance of arid sites with shallow groundwater. 相似文献
102.
我们于1985年对我院1984年开展肝单光子发射计算机断层以来的52例肝病人进行了分析总结。结果表明,肝单光子发射断层在诊断肝内占位性病变方面比普通肝静态γ照相有许多优点。需要指出的是,肝单光予发射断层的若干优点及诊断的准确性是与物理条件的正确选择和应用密切相关的。本文根据至今积累的近100例断层经验,从技术方面介绍了影响单 相似文献
103.
Power devices with high capability have been developed. 8‐kV/3.5‐kA‐class light‐triggered thyristors have the highest capability among power devices. These devices are used in the Kii Channel HVDC transmission system in Japan. In this paper, we report the extracted problems of conventional testing methods of 8‐kV/3.5‐kA‐class light‐triggered thyristors among manufacturers, and the proposed unified testing methods on the basis of element characteristics and operating conditions in the Kii Channel HVDC system. Furthermore, we propose a figure of merit for power devices for the practical use, and try to extract elements used at the Kii Channel HVDC system with small margins and low withstand capabilities. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 61–70, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10024 相似文献
104.
MV2000T智能变送器 总被引:1,自引:0,他引:1
较全面地介绍了ABB公司MV2 0 0 0T智能变送器的市场开发背景、工作原理、技术规格、性能特点及设计选型要点 相似文献
105.
In this paper, we consider the classical equations of the positive real lemma under the sole assumption that the state matrix A has unmixed spectrum: σ(A)∩σ(−A)=. Without any other system-theoretic assumption (observability, reachability, stability, etc.), we derive a necessary and sufficient condition for the solvability of the positive real lemma equations. 相似文献
106.
Acoustic Emission (AE) signals, which are electrical version of acoustic emissions, are usually analysed using a set of signal
parameters. The major objective of signal analysis is to study the characteristics of the sources of emissions. Peak amplitude(P
a
) and rise time(R
t
) are two such parameters used for source characterization. In this paper, we theoretically investigate the efficiency ofP
a
andR
t
to classify and characterize AE sources by modelling the input stress pulse and transducer. Analytical expressions obtained
forP
a
andR
t
clearly indicate their use and efficiency for source characterization. It is believed that these results may be of use to
investigators in areas like control systems and signal processing also 相似文献
107.
石英砂脱水性能的研究 总被引:1,自引:0,他引:1
通过大量试验结果 ,研究了各种粒度范围的石英砂的脱水性能 ,包括沉降特性、过滤性能、极限压缩浓度等 ,为进行此类产品的固液分离提供了重要的参考数据 相似文献
108.
109.
110.
F. D. McDaniel B. L. Doyle C. H. Seager D. S. Walsh G. Vizkelethy D. K. Brice C. Yang P. Rossi M. Nigam M. El Bouanani G. V. Ravi Prasad J. C. Schwartz L. T. Mitchell J. L. Duggan 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2002,190(1-4):1-10
A new ion beam analysis-based, single ion technique called the time to first photon has been developed to measure the decay of the luminescence signal of phosphors. Such measurements are currently needed to study luminescence decay mechanisms following high-density excitations and to identify strongly luminescent phosphor coatings with short lifetimes for ion photon emission microscopy (IPEM). The samples for this technique consist of thin phosphor layers placed or coated on the surface of PIN diodes. Single ions from an accelerator strike this sample and simultaneously create ion beam induced luminescence (IBIL) from the phosphor that is measured by a single-photon-detector, and an ion beam induced charge collection (IBICC) signal in the PIN diode. In this case, the IBICC signal provides the start pulse and the IBIL signal the stop pulse to a time to amplitude converter. It is straightforward to show that this approach also measures a signal proportional to activity versus time with an accuracy of 5% as long as the number of detected photons per ion is less than 0.1, which usually requires the use of absorbers for the IBIL detector or electronic discrimination for the IBIL signals. Details of the new analysis are given together with examples of luminescence decay measurements of several ceramic phosphors being considered to coat IPEM samples. IPEM is currently being developed at Sandia National Laboratory (SNL), the University of North Texas in Denton, and the Universities and INFN of Padova and Torino. 相似文献