全文获取类型
收费全文 | 53041篇 |
免费 | 3056篇 |
国内免费 | 54篇 |
专业分类
电工技术 | 390篇 |
综合类 | 39篇 |
化学工业 | 10770篇 |
金属工艺 | 928篇 |
机械仪表 | 1100篇 |
建筑科学 | 1629篇 |
矿业工程 | 198篇 |
能源动力 | 1008篇 |
轻工业 | 9269篇 |
水利工程 | 567篇 |
石油天然气 | 198篇 |
武器工业 | 7篇 |
无线电 | 2173篇 |
一般工业技术 | 8938篇 |
冶金工业 | 11358篇 |
原子能技术 | 208篇 |
自动化技术 | 7371篇 |
出版年
2024年 | 121篇 |
2023年 | 506篇 |
2022年 | 560篇 |
2021年 | 1317篇 |
2020年 | 1138篇 |
2019年 | 1233篇 |
2018年 | 2218篇 |
2017年 | 2213篇 |
2016年 | 2316篇 |
2015年 | 1769篇 |
2014年 | 2074篇 |
2013年 | 4430篇 |
2012年 | 3192篇 |
2011年 | 2902篇 |
2010年 | 2504篇 |
2009年 | 2109篇 |
2008年 | 2147篇 |
2007年 | 1994篇 |
2006年 | 1306篇 |
2005年 | 1098篇 |
2004年 | 1023篇 |
2003年 | 967篇 |
2002年 | 909篇 |
2001年 | 672篇 |
2000年 | 611篇 |
1999年 | 659篇 |
1998年 | 3508篇 |
1997年 | 2343篇 |
1996年 | 1492篇 |
1995年 | 884篇 |
1994年 | 688篇 |
1993年 | 749篇 |
1992年 | 273篇 |
1991年 | 260篇 |
1990年 | 203篇 |
1989年 | 206篇 |
1988年 | 233篇 |
1987年 | 195篇 |
1986年 | 167篇 |
1985年 | 206篇 |
1984年 | 184篇 |
1983年 | 134篇 |
1982年 | 167篇 |
1981年 | 205篇 |
1980年 | 213篇 |
1979年 | 112篇 |
1978年 | 108篇 |
1977年 | 356篇 |
1976年 | 744篇 |
1973年 | 95篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
V Gattás Zaror M Fisberg G Barrera Acevedo R U Dagach-Imbarack 《Archivos latinoamericanos de nutrición》1987,37(2):239-249
To evaluate the effect of dietary factors on plasma zinc levels, dietary zinc intake was estimated and plasma levels were measured in 37 healthy young adults of low and middle socioeconomic status. Our study included 16 males aged 29 +/- 7 and 21 females aged 26 +/- 6 years. Dietary intake of zinc and protein was determined from a 24-hour dietary recall survey. Plasma zinc was measured by atomic absorption spectrophotometry. Alkaline phosphatase (AP) in plasma was also measured and the weight/height percentage for each subject calculated according to Jelliffe's standards. The average diet was composed of cereals, legumes, eggs, bread and noodles, caloric intake was 2051 +/- 154 kcal/day for men and 1767 +/- 158 (x +/- SD) kcal/day for women. The daily intake of zinc was 8.3 +/- 3.0 mg/day for males, and 9.7 +/- 2.0 mg/day for females. Cereals were the main source of zinc for men, while egg and dairy products were for women. Plasma zinc values were 82 +/- 22 micrograms/dl for men and 94 +/- 19 micrograms/dl for women (p less than 0.01). For the whole group plasma zinc concentration was 89 +/- 21 micrograms/dl. Seven males and two females had low plasma zinc values (70 micrograms/dl or less). Alkaline phosphatase (AP) levels were 110 +/- 10 IU for males and 71 +/- 4 IU for females (p less than 0.001). These values did not correlate with the zinc levels. Average weight/height was 99 +/- 18 for men, and 108 +/- 18 for females. Results indicate that on the average, in our study group plasma zinc levels were within the normal range, although they were significantly lower in men. Dietary intake of zinc was below the recommendations, being higher for women as related to values presented by men. The observed low plasma levels of zinc may be caused by a low intake, and/or poor bioavailability. 相似文献
92.
J. Hrivňák L. Soják J. Krupčík Y. P. Duchesne 《Journal of the American Oil Chemists' Society》1973,50(3):68-71
The influence of temperature on the gas chromatographic separation ofcis-trans isomers of the methyl esters of some monounsaturated fatty acids was studied on capillary columns coated with Apiezon L,
BDS and DEGS. As far as methyl oleate and methyl elaidate are concerned, the separation is better at lower temperatures on
Apiezon L (180–210 C) and at higher temperatures on polyester phases (BDS, DEGS; 150–180 C). The influence of temperature
on the separation ofcis-trans isomers on the three stationary phases under study is explained by the higher values of δECL/δt forcis isomers. The variation of the equivalent carbon chain length with temperature can be used for the identification ofcis-trans isomers in natural mixtures. 相似文献
93.
González RJ Torres R De Greef D Bonaldo A Robutti J Borrás F 《Archivos latinoamericanos de nutrición》2005,55(4):354-360
Knowledge of the association between cooking properties and endosperm hardness may help nutritionist and processors to select raw materials for preparing maize based food products, particularly those eaten as cooked dispersions. Seven commercial maize cultivars differing in hardness were selected to evaluate endosperm hardness on the kernels and some characteristics such as composition and hydration and cooking properties on the grits obtained from those maizes. Results show that the differences in endosperm hardness (directly related to grits protein content) can explain the differences in swelling and amylographic consistencies values. Cultivars with the hardest endosperm show the lowest values at high temperature. They also show the lowest amylographic consistencies. On the other hand softer endosperms present the highest swelling power and the highest amylographic consistencies. These differences are attributed to the restriction for starch swelling caused by the protein matrix. Endosperm hardness measurements and swelling power at 95 degrees C, can be useful to select cultivars that are going to be used to prepare maize based foods like atoles, polenta, etc. 相似文献
94.
We propose a new entropy coding scheme, denoted in this paper as the UVLC (universal variable length coding). It is universal in the sense that its efficiency is close to one for a large class of images. The UVLC, when it is applied to block orthogonal transforms, processes groups of blocks at the bit level, using universal codes designed for binary memoryless sources. It can be used for every video coding application, from high definition TV (HDTV) to high quality videotelephony (above 2 Mbit/s) for transform or subband coding. Last but not least, its implementation is very regular and can be realized in a single chip for the encoding oftv at theccir 601 format. 相似文献
95.
96.
We study the problem of minimizing the sum of a smooth convex function and a convex block-separable regularizer and propose a new randomized coordinate descent method, which we call ALPHA. Our method at every iteration updates a random subset of coordinates, following an arbitrary distribution. No coordinate descent methods capable to handle an arbitrary sampling have been studied in the literature before for this problem. ALPHA is a very flexible algorithm: in special cases, it reduces to deterministic and randomized methods such as gradient descent, coordinate descent, parallel coordinate descent and distributed coordinate descent—both in nonaccelerated and accelerated variants. The variants with arbitrary (or importance) sampling are new. We provide a complexity analysis of ALPHA, from which we deduce as a direct corollary complexity bounds for its many variants, all matching or improving best known bounds. 相似文献
97.
98.
Balderas-López JA Díaz-Reyes J Zelaya-Angel O 《The Review of scientific instruments》2011,82(12):124901
A photoacoustic (PA) methodology, in the transmission configuration, for simultaneous measurements of thermal effusivity and molar absorption coefficient (absorptivity) for pigments in liquid solution is introduced. The analytical treatment involves a self-normalization procedure for the PA signal, as a function of the modulation frequency, for a strong absorbing material in the thermally thin regime, when the light travels across the sample under study. Two fitted parameters are obtained from the analysis of the self-normalized PA amplitude and phase, one of them proportional to the sample's optical absorption coefficient and from which, taking it for a series of samples at different concentrations, the pigment's absorptivity in liquid solution can be measured, the other one yields the sample's thermal effusivity. Methylene blue's absorptivity in distilled water was measured with this methodology at 658 nm, finding good agreement with the corresponding one reported in the literature. 相似文献
99.
E. Castillo D.P. Morales G. Botella A. García L. Parrilla A.J. Palma 《Digital Signal Processing》2013,23(6):1897-1909
This paper describes a novel model for fetal heart rate (FHR) monitoring from single-lead mother?s abdomen ECG (AECG) measurements. This novel method is divided in two stages: the first step consists on a one-step wavelet-based preprocessing for simultaneous baseline and high-frequency noise suppression, while the second stage efficiently detects fetal QRS complexes allowing FHR monitoring. The presented structure has been simplified as much as possible, in order to reduce computational cost and thus enable possible custom hardware implementations. Moreover, the proposed scheme and its fixed-point modeling have been tested using real abdominal ECG signals, which allow the validation of the presented approach and provide high accuracy. 相似文献
100.
The vehicle routing problem with deliveries and pickups is one of the main problems within reverse logistics. This paper focuses on an important assumption that divides the literature on the topic, namely the restriction that all deliveries must be completed before pickups can be made. A generalised model is presented, together with a mathematical formulation and its resolution. The latter is carried out by adopting a suitable implementation of the reactive tabu search metaheuristic. Results show that significant savings can be achieved by allowing a mixture of delivery and pickup loads on-board and yet not incurring delays and driver inconvenience. 相似文献