全文获取类型
收费全文 | 252103篇 |
免费 | 3773篇 |
国内免费 | 1046篇 |
专业分类
电工技术 | 4327篇 |
综合类 | 201篇 |
化学工业 | 37133篇 |
金属工艺 | 8222篇 |
机械仪表 | 7263篇 |
建筑科学 | 6785篇 |
矿业工程 | 541篇 |
能源动力 | 7243篇 |
轻工业 | 28643篇 |
水利工程 | 2120篇 |
石油天然气 | 1852篇 |
武器工业 | 5篇 |
无线电 | 33398篇 |
一般工业技术 | 46187篇 |
冶金工业 | 46463篇 |
原子能技术 | 3368篇 |
自动化技术 | 23171篇 |
出版年
2021年 | 1800篇 |
2020年 | 1346篇 |
2019年 | 1667篇 |
2018年 | 2571篇 |
2017年 | 2594篇 |
2016年 | 2875篇 |
2015年 | 2163篇 |
2014年 | 3657篇 |
2013年 | 11958篇 |
2012年 | 6756篇 |
2011年 | 9667篇 |
2010年 | 7447篇 |
2009年 | 8397篇 |
2008年 | 8918篇 |
2007年 | 8932篇 |
2006年 | 8281篇 |
2005年 | 7488篇 |
2004年 | 7212篇 |
2003年 | 7093篇 |
2002年 | 6592篇 |
2001年 | 7020篇 |
2000年 | 6324篇 |
1999年 | 6826篇 |
1998年 | 16382篇 |
1997年 | 11371篇 |
1996年 | 8583篇 |
1995年 | 6547篇 |
1994年 | 5707篇 |
1993年 | 5566篇 |
1992年 | 3998篇 |
1991年 | 3774篇 |
1990年 | 3548篇 |
1989年 | 3369篇 |
1988年 | 3277篇 |
1987年 | 2589篇 |
1986年 | 2487篇 |
1985年 | 3159篇 |
1984年 | 2797篇 |
1983年 | 2559篇 |
1982年 | 2344篇 |
1981年 | 2390篇 |
1980年 | 2202篇 |
1979年 | 2048篇 |
1978年 | 1879篇 |
1977年 | 2177篇 |
1976年 | 2724篇 |
1975年 | 1585篇 |
1974年 | 1489篇 |
1973年 | 1558篇 |
1972年 | 1148篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Continuous simulation is performed using the US Environmental Protection Agency (USEPA) Storm Water Management Model (SWMM) to evaluate regional differences around the United States in hydrologic and water quality performance of wet-weather controls. Controls are characterised as being limited by peak inflow rate (i.e. any device with little or no storage, such as screens, filters and some proprietary devices) or by storage capacity (e.g., ponds, tanks). For flow-limited devices, results are presented in the form of percentage of annual runoff volume captured (passing through the device) for a given inflow capacity. For storage-limited devices, results are presented in two forms: percentage of annual runoff volume captured as a function of unit basin size and drawdown (drain) time, and as a percentage of total suspended solids captured, for the same two variables. Regional differences are apparent, driven mainly by variations in rainfall patterns around the country. 相似文献
92.
93.
Pilot simplex experiments for improving the tablet strength of three aspirin tablet formulations based on precompression and compression forces were presented. As each simplex moved towards the direction of the optimum, the friability was being minimized and the crushing strength was concomittantly being maximized. Because it followed a systematic direction, simplex process would locate a local optimum rapidly. The appropriate levels of precompression and compression forces that produced tablets with the desired strength were attained in five trials. By contrast, random search for this force combination required at least ten trials. Simplex technique is a cost and time effective means for determining the precompression and compression forces that will reduce the friability or increase the hardness of a tablet formulation. Results appeared to also indicate that crushing strength might be a more reliable measure of tablet strength than friability. 相似文献
94.
R. Morena P. E. Lockwood L. Evans C. W. Fairhurst 《Journal of the American Ceramic Society》1986,69(4):75-C-
The effect on mechanical behavior of ZrO2 additions to a dental porcelain was investigated. The ZrO2 was introduced into the glassy matrix phase of the porcelain by refritting the all-glass porcelain constituent. X-ray diffraction indicated that a sizeable fraction of the ZrO2 was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance. 相似文献
95.
Indoor body-area channel model for narrowband communications 总被引:1,自引:0,他引:1
Fort A. Desset C. Wambacq P. Biesen L.V. 《Microwaves, Antennas & Propagation, IET》2007,1(6):1197-1203
Using wireless sensors placed on a person to continuously monitor health information is a promising new application. At the same time, new low-power wireless standards such as Bluetooth and Zigbee have been proposed for short range, low data-rate communication matching the requirements of these bio-medical applications. However, there are currently few measurements or models describing propagation around the body. To address this problem, electromagnetic waves near the torso are measured and a statistical model is derived for communication in the 915 MHz and 2.45 GHz industrial, scientific and medical bands associated with Zigbee and Bluetooth. Measurement setup and statistical analysis are described. 相似文献
96.
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
97.
R. Oliva A. L. Gemal A. W. N brega A. C. P. Araú jo 《Food Additives & Contaminants》2003,20(8):758-763
The structure of the recently introduced Brazilian government programme for monitoring pesticide residues in six major agricultural products is described. Residues found from the analysis of samples of tomatoes and strawberries are discussed in detail. The much greater frequency of detection of pesticide residues, many of which are not approved for use in Brazil, in produce being sold on the domestic market, as opposed to that produced for export, is of major concern. It is perceived that this new monitoring programme will become permanent and be used to underpin enforcement actions that will need to be taken to reduce the numbers of incidents of illegal residues occurring, particularly in fresh fruits and vegetables. 相似文献
98.
Neutron-irradiated quartz crystal is one of the interesting materials for the study of the glassy dynamics. The temperature and frequency dependence of the sound velocity in amorphous materials at temperatures above the low-temperature maximum is not well understood. In this paper we present the results of our measurements of the variation of the ultrasound velocity (270 – 650 MHz) in neutron-irradiated quartz crystals with different irradiation doses in temperature range 5 - 35 K. We have found that the temperature dependence of the ultrasound velocity is linear in the sample with a dose < 10 19 n/cm2 and is sublinear in samples with a dose > 10 19 n/cm2 . We discuss our results in the framework of the different theoretical approaches. PACS numbers: 61.43. j, 62.65.+k, 63. 相似文献
99.
100.