全文获取类型
收费全文 | 205710篇 |
免费 | 3092篇 |
国内免费 | 622篇 |
专业分类
电工技术 | 3530篇 |
综合类 | 159篇 |
化学工业 | 31728篇 |
金属工艺 | 8123篇 |
机械仪表 | 6153篇 |
建筑科学 | 5071篇 |
矿业工程 | 1339篇 |
能源动力 | 5282篇 |
轻工业 | 18212篇 |
水利工程 | 2335篇 |
石油天然气 | 4077篇 |
武器工业 | 8篇 |
无线电 | 23323篇 |
一般工业技术 | 40926篇 |
冶金工业 | 37596篇 |
原子能技术 | 5102篇 |
自动化技术 | 16460篇 |
出版年
2022年 | 1591篇 |
2021年 | 2365篇 |
2019年 | 1776篇 |
2018年 | 2816篇 |
2017年 | 2846篇 |
2016年 | 3029篇 |
2015年 | 2007篇 |
2014年 | 3338篇 |
2013年 | 9382篇 |
2012年 | 5413篇 |
2011年 | 7423篇 |
2010年 | 5860篇 |
2009年 | 6621篇 |
2008年 | 6717篇 |
2007年 | 6746篇 |
2006年 | 5792篇 |
2005年 | 5370篇 |
2004年 | 5148篇 |
2003年 | 4998篇 |
2002年 | 4622篇 |
2001年 | 4711篇 |
2000年 | 4629篇 |
1999年 | 4786篇 |
1998年 | 11434篇 |
1997年 | 8176篇 |
1996年 | 6455篇 |
1995年 | 4715篇 |
1994年 | 4312篇 |
1993年 | 4102篇 |
1992年 | 3253篇 |
1991年 | 3093篇 |
1990年 | 2894篇 |
1989年 | 2963篇 |
1988年 | 2846篇 |
1987年 | 2413篇 |
1986年 | 2317篇 |
1985年 | 2733篇 |
1984年 | 2523篇 |
1983年 | 2364篇 |
1982年 | 2096篇 |
1981年 | 2215篇 |
1980年 | 2042篇 |
1979年 | 2135篇 |
1978年 | 2124篇 |
1977年 | 2376篇 |
1976年 | 3201篇 |
1975年 | 1841篇 |
1974年 | 1765篇 |
1973年 | 1775篇 |
1972年 | 1445篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Raffael Ott Xenia Pawlow Andreas Weiß Anna Hofelich Melanie Herbst Nadine Hummel Cornelia Prehn Jerzy Adamski Werner Rmisch-Margl Gabi Kastenmüller Anette-G. Ziegler Sandra Hummel 《International journal of molecular sciences》2020,21(24)
Shared metabolomic patterns at delivery have been suggested to underlie the mother-to-child transmission of adverse metabolic health. This study aimed to investigate whether mothers with gestational diabetes mellitus (GDM) and their offspring show similar metabolomic patterns several years postpartum. Targeted metabolomics (including 137 metabolites) was performed in plasma samples obtained during an oral glucose tolerance test from 48 mothers with GDM and their offspring at a cross-sectional study visit 8 years after delivery. Partial Pearson’s correlations between the area under the curve (AUC) of maternal and offspring metabolites were calculated, yielding so-called Gaussian graphical models. Spearman’s correlations were applied to investigate correlations of body mass index (BMI), Matsuda insulin sensitivity index (ISI-M), dietary intake, and physical activity between generations, and correlations of metabolite AUCs with lifestyle variables. This study revealed that BMI, ISI-M, and the AUC of six metabolites (carnitine, taurine, proline, SM(-OH) C14:1, creatinine, and PC ae C34:3) were significantly correlated between mothers and offspring several years postpartum. Intergenerational metabolite correlations were independent of shared BMI, ISI-M, age, sex, and all other metabolites. Furthermore, creatinine was correlated with physical activity in mothers. This study suggests that there is long-term metabolic programming in the offspring of mothers with GDM and informs us about targets that could be addressed by future intervention studies. 相似文献
73.
László Lőrincz Máté Zsemberi György Bánsághi Tamás Sohajda Edit Székely 《化学工程与技术》2018,41(7):1466-1472
Chiral molecules, especially enantiomers and diastereomers of purity > 99 %, present a significant market share within the chemical, pharmaceutical, and flavor industries. Antisolvent precipitations, both batch and semicontinuous operations to serve the current trends in flow chemistry were demonstrated to be environmentally benign and efficient tools in achieving high optical purities. Although salts are known to be insoluble in supercritical CO2, instabilities of the nascent salts were detected and applied for increasing efficiency. Diastereomeric excess values of the crystalline products exceeded 99 % in maximum of three consecutive steps both by repeated resolution with half molar equivalent of the amine to the acid and by direct recrystallization of the salts. 相似文献
74.
Anna Enrico Wenjing Zhang Marie Lund Traulsen Elena Marzia Sala Paola Costamagna Peter Holtappels 《Journal of the European Ceramic Society》2018,38(7):2677-2686
Water-based sol-gel electrospinning is employed to manufacture perovskite oxide La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) nanofiber cathodes for intermediate-temperature solid oxide fuel cells. LSCF fibrous scaffolds are synthesized through electrospinning of a sol-gel solution employing water as the only solvent. Morphological characterizations demonstrate that the LSCF fibers have highly crystalline structure with uniform elemental distribution. After heat treatment, the average fiber diameter is 250 nm and the porosity of the nanofiber tissue is 37.5 %. The heat treated LSCF nanofibers are applied directly onto a Ce0.9Gd0.1O1.95 (CGO) electrolyte disk to form a symmetrical cell. Electrochemical characterization is carried out through electrochemical impedance spectroscopy (EIS) in the temperature range 550?°C–950?°C, and reproducibility of the electrochemical performance for a series of cells is demonstrated. At 650?°C, the average measured polarization resistance Rp is 1.0 Ω cm2. Measured performance decay is 1 % during the first 33?h of operation at 750?°C, followed by an additional 0.7 % over the subsequent 70?h. 相似文献
75.
Gina Cavaliere Giovanna Trinchese Nadia Musco Federico Infascelli Chiara De Filippo Vincenzo Mastellone Valeria Maria Morittu Pietro Lombardi Raffaella Tudisco Micaela Grossi Vincenzo Monda Monica I. Cutrignelli Antonietta Messina Serena Calabrò Heleena B. Moni Luigi Stradella Giovanni Messina Marcellino Monda Maria Pina Mollica 《Journal of dairy science》2018,101(3):1843-1851
Excessive energy intake may evoke complex biochemical processes characterized by inflammation, oxidative stress, and impairment of mitochondrial function that represent the main factors underlying noncommunicable diseases. Because cow milk is widely used for human nutrition and in food industry processing, the nutritional quality of milk is of special interest with respect to human health. In our study, we analyzed milk produced by dairy cows fed a diet characterized by a high forage:concentrate ratio (high forage milk, HFM). In view of the low n-6:n-3 ratio and high content of conjugated linoleic acid of HFM, we studied the effects of this milk on lipid metabolism, inflammation, mitochondrial function, and oxidative stress in a rat model. To this end, we supplemented for 4 wk the diet of male Wistar rats with HFM and with an isocaloric amount (82 kJ, 22 mL/d) of milk obtained from cows fed a diet with low forage:concentrate ratio, and analyzed the metabolic parameters of the animals. Our results indicate that HFM may positively affect lipid metabolism, leptin:adiponectin ratio, inflammation, mitochondrial function, and oxidative stress, providing the first evidence of the beneficial effects of HFM on rat metabolism. 相似文献
76.
An explicit extraction of the retinal vessel is a standout amongst the most significant errands in the field of medical imaging to analyze both the ophthalmological infections, for example, Glaucoma, Diabetic Retinopathy (DR), Retinopathy of Prematurity (ROP), Age-Related Macular Degeneration (AMD) as well as non retinal sickness such as stroke, hypertension and cardiovascular diseases. The state of the retinal vasculature is a significant indicative element in the field of ophthalmology. Retinal vessel extraction in fundus imaging is a difficult task because of varying size vessels, moderately low distinction, and presence of pathologies such as hemorrhages, microaneurysms etc. Manual vessel extraction is a challenging task due to the complicated nature of the retinal vessel structure, which also needs strong skill set and training. In this paper, a supervised technique for blood vessel extraction in retinal images using Modified Adaboost Extreme Learning Machine (MAD-ELM) is proposed. Firstly, the fundus image preprocessing is done for contrast enhancement and in-homogeneity correction. Then, a set of core features is extracted, and the best features are selected using “minimal Redundancy-maximum Relevance (mRmR).” Later, using MAD-ELM method vessels and non vessels are classified. DRIVE and DR-HAGIS datasets are used for the evaluation of the proposed method. The algorithm’s performance is assessed based on accuracy, sensitivity and specificity. The proposed technique attains accuracy of 0.9619 on the DRIVE database and 0.9519 on DR-HAGIS database, which contains pathological images. Our results show that, in addition to healthy retinal images, the proposed method performs well in extracting blood vessels from pathological images and is therefore comparable with state of the art methods. 相似文献
77.
78.
79.
The design of a microstrip‐fed annular‐ring slot antenna (ARSA) with circular polarization (CP) radiation is initially studied. To obtain CP radiation with broad 3‐dB axial ratio (AR) bandwidth that can cover the WiMAX 2.3 GHz (2305–2320 MHz, 2345–2360 MHz) and WLAN 2.4 GHz (2400–2480 MHz) bands, a novel technique of extending an inverted L‐shaped slot from the bottom section of the annular‐ring is proposed. To suppress the harmonic modes induced by the CP ARSA, the technique of integrating a defected ground structure into the annular‐ring slot is further introduced. From the measured results, 10‐dB impedance bandwidth and 3‐dB AR bandwidth of 44.86 and 9.68% were achieved by the proposed harmonic suppressed CP ARSA. Furthermore, average gain and radiation efficiency of ~4.7 dBic and 71%, respectively, were also exhibited across the bands of interest. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:337–345, 2015. 相似文献
80.