全文获取类型
收费全文 | 343514篇 |
免费 | 20197篇 |
国内免费 | 13447篇 |
专业分类
电工技术 | 17739篇 |
综合类 | 17634篇 |
化学工业 | 48355篇 |
金属工艺 | 19204篇 |
机械仪表 | 17305篇 |
建筑科学 | 16894篇 |
矿业工程 | 7531篇 |
能源动力 | 8987篇 |
轻工业 | 38305篇 |
水利工程 | 6514篇 |
石油天然气 | 7492篇 |
武器工业 | 2508篇 |
无线电 | 39455篇 |
一般工业技术 | 50122篇 |
冶金工业 | 36783篇 |
原子能技术 | 5638篇 |
自动化技术 | 36692篇 |
出版年
2023年 | 2882篇 |
2022年 | 6937篇 |
2021年 | 9097篇 |
2020年 | 6684篇 |
2019年 | 5019篇 |
2018年 | 5873篇 |
2017年 | 6892篇 |
2016年 | 6245篇 |
2015年 | 8702篇 |
2014年 | 11467篇 |
2013年 | 18935篇 |
2012年 | 17153篇 |
2011年 | 19573篇 |
2010年 | 17683篇 |
2009年 | 18131篇 |
2008年 | 18715篇 |
2007年 | 18419篇 |
2006年 | 15855篇 |
2005年 | 13341篇 |
2004年 | 11049篇 |
2003年 | 8785篇 |
2002年 | 8495篇 |
2001年 | 8213篇 |
2000年 | 7181篇 |
1999年 | 5377篇 |
1998年 | 8787篇 |
1997年 | 6866篇 |
1996年 | 5876篇 |
1995年 | 4701篇 |
1994年 | 4114篇 |
1993年 | 3962篇 |
1992年 | 3367篇 |
1991年 | 3264篇 |
1990年 | 3179篇 |
1989年 | 3123篇 |
1988年 | 2833篇 |
1987年 | 2581篇 |
1986年 | 2485篇 |
1985年 | 2926篇 |
1984年 | 2623篇 |
1983年 | 2507篇 |
1982年 | 2364篇 |
1981年 | 2298篇 |
1980年 | 2230篇 |
1979年 | 2231篇 |
1978年 | 2058篇 |
1977年 | 2478篇 |
1976年 | 3150篇 |
1975年 | 1883篇 |
1973年 | 1758篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
T P?usa P Górski H Frank-Piskorska M Kowalski J Kruszewski P Kuna M Kurek R Kurzawa W Silny E Zawisza 《Canadian Metallurgical Quarterly》1996,1(4):292-293
A review of isolates of Neisseria meningitidis and other laboratory evidence of meningococcal infection was carried out for the period 1990-1995. Thirty-three patients with evidence of meningococcal disease were identified over the six year period. Group B organisms were the most commonly identified, but an increase in Group C has occurred and is almost equal in number. Data from clinical, laboratory and public health sources should be centralized in a National Surveillance Centre. 相似文献
82.
R Gollamudi Z Feng EO Dillingham SE Bond G Han S Salgia 《Canadian Metallurgical Quarterly》1993,69(4):361-367
This investigation retrospectively examined changes in marital satisfaction following stroke. The relationship between such changes and other pertinent factors were also examined, including severity of aphasia, knowledge of aphasia, number of months after stroke, and length of the marriage. The subjects were 40 spouses of patients with aphasia grouped according to severity of the aphasia (mild, moderate, severe). Spouses completed two different measures of marital satisfaction--the Marital Satisfaction Scale (MSS) and the Marital Comparison Level Index (MCLI). These measures were completed in both a prestroke (retrospective reporting) and a poststroke format to allow for change to be assessed. In addition, a Knowledge of Aphasia questionnaire was completed by the normal spouses to evaluate their understanding of the disorder of aphasia. There was a significant difference between prestroke and poststroke scores on both the MSS and the MCLI, indicating a lower level of satisfaction following the stroke. The amount of change between prestroke and poststroke MSS and MCLI scores was not related to either number of months poststroke or number of years married. Although there was no relationship between changes in prestroke and poststroke scores on the MCLI and Knowledge of Aphasia scores, there was a significant correlation between changes in these scores on the MSS and Knowledge of Aphasia scores. Hence, the more knowledge spouses had regarding aphasia, the less the negative impact the stroke had on marital satisfaction, as measured by the MSS. Results are discussed in terms of the interdisciplinary treatment needs of aphasic patients and the implications for future investigations. 相似文献
83.
14 medicated hypertensive, 15 nonmedicated mild hypertensive, 39 normotensive, and 13 hypotensive adults participated in a 1–2 hr laboratory experiment that assessed each S's symptoms, moods, and estimates of systolic blood pressure (SBP) relative to actual SBP levels. Several self-reports and autonomic measures were collected during and after each of 22 tasks. Within-S correlations indicated that all Ss could estimate SBP at levels greater than chance. Further, 68% of the Ss evidenced at least 1 significant symptom–SBP correlation. Although medicated hypertensives believed they could estimate their BP more accurately than other groups, they were actually no more accurate than the other Ss. They also evidenced far fewer empirically derived symptom–SBP and emotion–SBP correlations than any other group. Overall, blood pressure (BP) beliefs were largely inaccurate. If these erroneous beliefs can be eliminated, Ss may be able to estimate BP fluctuations more accurately. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
84.
85.
Croon J.A. Rosmeulen M. Decoutere S. Sansen W. Maes H.E. 《Solid-State Circuits, IEEE Journal of》2002,37(8):1056-1064
In this paper, a physics-based mismatch model is presented. It is demonstrated on a 0.18-/spl mu/m technology that a simple mismatch model can still be used to characterize deep-submicron technologies. The accuracy of the model is examined and found to be within 20% in the strong inversion region. Bulk bias dependence is modeled in a physical way. To extract the mismatch parameters, a weighted fit is introduced. It is shown that the width and length dependence of the mismatch parameters is given by the Pelgrom model. 相似文献
86.
Steinwandt R. Geiselmann W. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2002,48(11):2990-2991
An attack on the public key cryptosystem Polly Cracker is described, that reveals the complete secret key σ ∈ Fq n by means of n (nonadaptively) chosen "fake" ciphertexts 相似文献
87.
Using AuGeNiCr multilayered metals as the wafer bonding medium, long-wavelength GaInAsP/InP vertical cavity surface emitting lasers employing Al-oxide/Si as the upper and lower distributed Bragg reflectors were fabricated on Si substrate with the bonding interface formed outside the vertical cavity surface emitting laser cavity. Laser emission at 1.545 μm was measured under pulsed operations near room temperature. The low-temperature metallic bonding process demonstrates a great potential in device fabrication 相似文献
88.
Wang J.R. Racette P. Tiesky M.E. Manning W. 《Geoscience and Remote Sensing, IEEE Transactions on》2002,40(6):1220-1229
The airborne Millimeter-wave Imaging Radiometer (MIR) measurements conducted over the Midwest region of the continental United States during January/February 1997 and over the Alaska-Arctic region during May 1998 are used to estimate column water vapor W<0.8 g/cm/sup 2/ under a clear sky. On board the same aircraft are two other instruments, the Cloud Lidar System (CLS) and MODerate-resolution Imaging Spectrometer (MODIS) Airborne Simulator (MAS), which provide cloud cover information and independent measurements of W, respectively. The MIR-estimated W values are compared and found to be in very good agreement with those measured by rawinsondes at near concurrence. A close correlation is found between the MIR-estimated W and that estimated from the MAS near-IR reflectance ratios. Water surface emissivities at several MIR frequencies are obtained in the process of the W retrieval from several flights over the Midwest lakes. These estimated emissivities compared favorably with values calculated for a calm water surface, which are based on a di-electric permittivity model and MAS-measured surface temperatures. The results from all comparisons strongly demonstrate the soundness of the technique for estimating W. 相似文献
89.
Development of a recurrent Sigma-Pi neural network rainfall forecasting system in Hong Kong 总被引:1,自引:1,他引:0
At the moment, weather forecasting is still an art — the experience and intuition of forecasters play a significant role in determining the quality of forecasting. This paper describes the development of a new approach to rainfall forecasting using neural networks. It deals with the extraction of information from radar images and an evaluation of past rain gauge records to provide shortterm rainfall forecasting. All of the meteorological data were provided by the Royal Observatory of Hong Kong (ROHK). Preprocessing procedures were essential for this neural network rainfall forecasting. The forecast of the rainfall was performed every half an hour so that a storm warning signal can be delivered to the public in advance. The network architecture is based on a recurrent Sigma-Pi network. The results are very promising, and this neural-based rainfall forecasting system is capable of providing a rain storm warning signal to the Hong Kong public one hour ahead. 相似文献
90.
J DiRuggiero N Santangelo Z Nackerdien J Ravel FT Robb 《Canadian Metallurgical Quarterly》1997,179(14):4643-4645
We investigated the capacity of the hyperthermophile Pyrococcus furiosus for DNA repair by measuring survival at high levels of 60Co gamma-irradiation. The P. furiosus 2-Mb chromosome was fragmented into pieces ranging from 500 kb to shorter than 30 kb at a dose of 2,500 Gy and was fully restored upon incubation at 95 degrees C. We suggest that recombination repair could be an extremely active repair mechanism in P. furiosus and that it might be an important determinant of survival of hyperthermophiles at high temperatures. 相似文献