全文获取类型
收费全文 | 52907篇 |
免费 | 980篇 |
国内免费 | 179篇 |
专业分类
电工技术 | 530篇 |
综合类 | 634篇 |
化学工业 | 4694篇 |
金属工艺 | 588篇 |
机械仪表 | 867篇 |
建筑科学 | 854篇 |
矿业工程 | 391篇 |
能源动力 | 419篇 |
轻工业 | 2178篇 |
水利工程 | 609篇 |
石油天然气 | 50篇 |
武器工业 | 4篇 |
无线电 | 1840篇 |
一般工业技术 | 3509篇 |
冶金工业 | 31061篇 |
原子能技术 | 185篇 |
自动化技术 | 5653篇 |
出版年
2024年 | 58篇 |
2023年 | 196篇 |
2022年 | 121篇 |
2021年 | 119篇 |
2019年 | 61篇 |
2018年 | 480篇 |
2017年 | 702篇 |
2016年 | 1087篇 |
2015年 | 785篇 |
2014年 | 431篇 |
2013年 | 484篇 |
2012年 | 2167篇 |
2011年 | 2470篇 |
2010年 | 696篇 |
2009年 | 779篇 |
2008年 | 624篇 |
2007年 | 643篇 |
2006年 | 585篇 |
2005年 | 3348篇 |
2004年 | 2570篇 |
2003年 | 2072篇 |
2002年 | 846篇 |
2001年 | 741篇 |
2000年 | 288篇 |
1999年 | 894篇 |
1998年 | 9277篇 |
1997年 | 5622篇 |
1996年 | 3612篇 |
1995年 | 2075篇 |
1994年 | 1564篇 |
1993年 | 1701篇 |
1992年 | 305篇 |
1991年 | 427篇 |
1990年 | 406篇 |
1989年 | 392篇 |
1988年 | 421篇 |
1987年 | 319篇 |
1986年 | 283篇 |
1985年 | 226篇 |
1984年 | 73篇 |
1983年 | 93篇 |
1982年 | 178篇 |
1981年 | 223篇 |
1980年 | 256篇 |
1979年 | 63篇 |
1978年 | 117篇 |
1977年 | 794篇 |
1976年 | 1770篇 |
1975年 | 110篇 |
1971年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Instructional texts rewritten by five expert teams: Revisions and retention improvements. 总被引:1,自引:0,他引:1
Britton Bruce K.; Van Dusen Lani; Gulg?z Sami; Glynn Shawn M. 《Canadian Metallurgical Quarterly》1989,81(2):226
700 undergraduates were tested in 3 experiments on original or rewritten versions of 52 instructional texts about Army job tasks, general science, philosophy, and history. Five experts had rewritten various sets of the texts and stated hypotheses about the efficacious features of their revisions. We tested their hypotheses and several others. Recall and recognition tests were given immediately and after a 24-hr delay. Results showed that revisions made by 3 of the 5 experts improved retention of text information. The kind and number of revisions and improvements varied across the text sets. Most expert hypotheses were not supported, and they made many revisions they were declaratively unaware of. Some of our hypotheses about the revision features were supported, but different features were effective for different sets of texts. It was concluded that some experts have effective knowledge about improving instructional text, but it exists primarily in procedural form. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
102.
There are some foods that contain mutagenic or carcinogenic agents, some of which occur naturally and others that may be formed during preparation or cooking. Several foods such as legumes, also contain natural antimutagens and/or anticarcinogens. Lupine is one such legume that contains high amounts of protein (40%) and oils (14%). About 90 species of lupine have been reported throughout Mexico. However, the use of this crop as a source of food has been limited by the presence of antinutritional agents such as phenolic compounds (PC), carbohydrates (CH) and quinolizidinic alkaloids (Qas). It has also been suggested that consuming these compounds can affect human health and may even reduce the risk of disease. The objective of this work was to determine the effect of PC, CH and Qas, isolated and quantified from Lupinus campestris on the mutagenicity of 1-nitropyrene (1-NP) as a model mutagen and we used the Salmonella typhimurium tester strain YG1024 by the Kado microsuspension method. The results indicate that L. campestris seeds have 11 mg (+)catechin equivalent g(-1) seed coat; 120.3 mg g(-1) seeds and 2.13 mg g(-1) seeds of PC, CH and Qas, respectively. 1-NP mutagenicity was inhibited by 86% for PC, 76% for CH and 75% for Qas at concentrations of 200, 512 and 13.6 microg/tube, respectively. 相似文献
103.
The hydrolysis and condensation reactions of γ-APS have been studied in different acid content aqueous solution by using Fourier
Transform infrared (FT-IR) spectroscopy. The hydrolysis of γ-APS under the studied conditions can be followed by the increase
of the ethanol band located at 882 cm−1 and the decrease of the band due to the ρ(CH3) of γ-APS molecules located at 959 cm−1. Hydrolysis reaction is faster by increasing both H2O and acid concentrations, and it is completed when 3 moles of H2O per mole of γ-APS are used. The increase of the vibrational band located at 1146 cm−1 shows that condensation of the hydrolysed γ-APS molecules take place forming linear chains in poorly cross-linked structures.
Besides, both 8-membered cyclic siloxane formations and poorly cross-linked structures are formed and increase as the water
and acid content are increased. On the other hand, highly connected cross-linked structures do not appear due to the steric
hindrance of the non-hydrolysable aminopropyl group. The silanol band shows that hydrolysis is faster than condensation except
for samples with the lowest H2O content. 相似文献
104.
Mg-Al hydrotalcites intercalated with five different interlayer anions—CO32−, SO42−, Cl−, HPO42− or terephthalate—were synthesized by either the coprecipitation or ion-exchange method. The structure of the as-synthesized samples and the presence of intended anions in the interlayer gallery of hydrotalcites were determined by X-ray diffraction and FTIR spectroscopy. On calcination at 600 °C the materials were transformed into mixed metal oxides. The kind of the counterbalancing anions present in the parent hydrotalcite influences strongly textural parameters of the obtained Mg-Al oxides. Both temperature-programmed desorption of NH3 and CO2, and test reaction of 2-methyl-3-butyn-2-ol (MBOH) conversion were used to determine the acidity and basicity of the samples. The hydrotalcite derived mixed Mg-Al oxides showed the presence of Brønsted and Lewis acid and base sites. However, the strong basic character of the solids caused that acetone and acetylene were observed as the major products of MBOH conversion. 相似文献
105.
E St?lberg S St?lberg M Melander K Arimura 《Computer methods and programs in biomedicine》1991,34(2-3):219-227
Programs for rule based electromyography (EMG) interpretation and reporting are described. A number of parameters are obtained during an EMG investigation. The combination of these data leads to a neurophysiological conclusion. Knowledge from the literature, research and experience is the basis for rule development. Rules have been developed for 14 of the most commonly used classifications of an EMG. The syntax is relatively easy and the user may change the rules, add rules or apply the system for other types of data. The results are displayed in a new graphical way. The system presented here is part of an integrated EMG laboratory with administrative routines, distributed databases for storage of results and routines for automatic report generation. 相似文献
106.
Cristina Ca?ero Nikolaos Thomos George A Triantafyllidis George C Litos Michael Gerassimos Strintzis 《IEEE transactions on information technology in biomedicine》2005,9(1):44-49
Ultrasound imaging allows the evaluation of the degree of emergency of a patient. However, in some instances, a well-trained sonographer is unavailable to perform such echography. To cope with this issue, the Mobile Tele-Echography Using an Ultralight Robot (OTELO) project aims to develop a fully integrated end-to-end mobile tele-echography system using an ultralight remote-controlled robot for population groups that are not served locally by medical experts. This paper focuses on the user interface of the OTELO system, consisting of the following parts: an ultrasound video transmission system providing real-time images of the scanned area, an audio/video conference to communicate with the paramedical assistant and with the patient, and a virtual-reality environment, providing visual and haptic feedback to the expert, while capturing the expert's hand movements. These movements are reproduced by the robot at the patient site while holding the ultrasound probe against the patient skin. In addition, the user interface includes an image processing facility for enhancing the received images and the possibility to include them into a database. 相似文献
107.
Pulkki-R?back Laura; Elovainio Marko; Kivim?ki Mika; Raitakari Olli T.; Keltikangas-J?rvinen Liisa 《Canadian Metallurgical Quarterly》2005,24(3):307
This study examined associations of temperament at ages 6 to 12 with body-mass index (BMI) and waist circumference (WC) at ages 24 to 30 years. The participants were 619 men and women derived from the population-based Cardiovascular Risk in Young Finns Study. Temperament was operationalized as (negative) emotionality, sociability, and activity. High emotionality predicted increased BMI, independently of WC, and independently of childhood and adulthood risk factors for adult obesity. None of the temperament dimensions had any associations with WC after controlling for BMI. The findings suggest that temperamental difficulty in childhood may be a useful risk indicator for general body mass in adulthood, and the mechanisms relating temperament with body mass should be further explored. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
108.
Motivated by a study of similar problems stated for factors of words, we study forbidden subwords of a language or a word. A procedure for obtaining the set of all words avoiding a given set of subwords is presented. On the other hand, an algorithm for computing the set of minimal forbidden subwords for a word is given. The case of a two-letter alphabet appears to be particularly interesting and it is considered separately. 相似文献
109.
110.
E Persson M Ljunggren J la Cour Jansen R Strube L J?nsson 《Water science and technology》2006,53(12):139-147
A Discfilter with 10 and 18 microm filter openings, respectively, was placed in parallel to a flotation plant for separation of biological flocs from a post-denitrifying Kaldnes Moving Bed Process, the last treatment step at the municipal wastewater treatment plant at Sj?unda, Malm?, Sweden. The effluent concentrations from the 10 and 18 microm filter were 2-5 and 2-8 mg SS L(-1), respectively, which is comparable to, or better than, the flotation plant. Comparison with experiences from activated sludge plants shows that the Discfilter works especially well after the Kaldnes process. Particle size distribution (PSD) studies show that particles larger than the filter openings of 10 and 18 microm are separated with approximately 90% efficiency, whereas most of the smaller particles pass the filter. This fact indicates that the major particle separation mechanism is physical blocking. These findings point to the possibility of improving the prediction of the separation efficiency by combining measurements of turbidity and suspended solids with particle size analysis. 相似文献