全文获取类型
收费全文 | 2773篇 |
免费 | 46篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 42篇 |
综合类 | 3篇 |
化学工业 | 559篇 |
金属工艺 | 162篇 |
机械仪表 | 70篇 |
建筑科学 | 148篇 |
矿业工程 | 10篇 |
能源动力 | 98篇 |
轻工业 | 226篇 |
水利工程 | 26篇 |
石油天然气 | 62篇 |
武器工业 | 1篇 |
无线电 | 205篇 |
一般工业技术 | 689篇 |
冶金工业 | 200篇 |
原子能技术 | 80篇 |
自动化技术 | 250篇 |
出版年
2021年 | 30篇 |
2020年 | 22篇 |
2019年 | 23篇 |
2018年 | 66篇 |
2017年 | 53篇 |
2016年 | 55篇 |
2015年 | 41篇 |
2014年 | 46篇 |
2013年 | 105篇 |
2012年 | 102篇 |
2011年 | 159篇 |
2010年 | 132篇 |
2009年 | 130篇 |
2008年 | 93篇 |
2007年 | 112篇 |
2006年 | 113篇 |
2005年 | 64篇 |
2004年 | 65篇 |
2003年 | 85篇 |
2002年 | 80篇 |
2001年 | 90篇 |
2000年 | 60篇 |
1999年 | 49篇 |
1998年 | 90篇 |
1997年 | 88篇 |
1996年 | 58篇 |
1995年 | 48篇 |
1994年 | 50篇 |
1993年 | 54篇 |
1992年 | 38篇 |
1991年 | 41篇 |
1990年 | 30篇 |
1989年 | 35篇 |
1988年 | 34篇 |
1987年 | 38篇 |
1986年 | 44篇 |
1985年 | 31篇 |
1984年 | 35篇 |
1983年 | 14篇 |
1982年 | 18篇 |
1981年 | 26篇 |
1980年 | 15篇 |
1979年 | 21篇 |
1978年 | 14篇 |
1977年 | 21篇 |
1976年 | 31篇 |
1975年 | 14篇 |
1974年 | 18篇 |
1973年 | 16篇 |
1971年 | 13篇 |
排序方式: 共有2831条查询结果,搜索用时 15 毫秒
81.
82.
A secondary battery of the type polyaniline/propylene carbonate-LiClO4/Li–Al is described. The polymer is made by aniline oxidation with ammonium persulphate in NH4F, 2.3 HF as solvent. The discharge capacity of the polymer is 100 Ah kg–1 at 25°C and 140 Ah kg–1 at 40°C for current densities of 0.5 mA cm–2 and for an amount of material giving a capacity of 10 mAh. The voltage in open circuit for the fully charged battery is 3.6 V. The average usable potential is 2.8–3 V. The energy density for the polymer lies between 280 and 420 Wh kg–1. The ratio of the amounts of electricity in discharge and charge is one for several hundred deep cycles. The behaviour with regard to self discharge and to constant applied voltage (floating life) is excellent. 相似文献
83.
Effect of a mixture of steam-flaked corn and soybeans on health, growth, and selected blood metabolism of Holstein calves 总被引:2,自引:0,他引:2
The objective of the experiment was to evaluate the effects of steam-flaked corn grains and soybeans on calf health, growth, and selected blood parameters. Holstein bull calves (n = 30, approximately 7 ± 3 d of age) were purchased from local dairy farms and offered milk, starter diets, and hay, and were then assigned to the experiment at 21 ± 3 d of age. Calves were blocked into 3 treatments by birth date and body weight and randomly assigned to receive fresh milk and a commercial pelleted starter containing extruded corn and soybeans (ECS), steam-flaked corn and soybeans (SFCS), or ground corn and soybeans (GCS). The experiment was conducted with calves from 3 to 13 wk of age. Body weight, calf starter intake, milk intake, total dry matter intake, and body structural growth were not significantly influenced by corn and soybean processing during the study; however, feed efficiency was significantly improved by the SFCS treatment. Average daily gain generally decreased during the weaning week for all treatments, but did not differ significantly among treatments. Health incidences for calves fed the SFCS starter were lower than those fed the other 2 treatments. The blood hematocrit was higher for calves fed the SFCS starter than for those fed the GCS and ECS starters during wk 6 to 11. The concentration of plasma β-hydroxybutyrate was higher for the calves fed the GCS and SFCS treatments than for those fed the ECS treatment during wk 6 to 13, but lower during wk 4 and 5. Plasma glucose concentrations decreased remarkably with increasing calf age but were not affected by corn and soybean processing. Plasma nonesterified fatty acids were influenced by calf age, and higher NEFA concentration was observed in the SFCS treatment than in the other 2 treatments during wk 5 to 9. Calves consuming the SFCS starter had similar average daily gain, milk intake, starter intake, total dry matter intake, and body structure, but had improved feed efficiency when compared with animals consuming the GCS and ECS starters. The SFCS starter decreased incidence of diarrhea during the postweaning period and required less veterinary treatment. These data suggest that the steam-flaking of corn and soybeans can influence the growth performance and the selected blood parameters of calves and that, in this study, the extrusion of corn and soybeans had no beneficial effect on the growth performance of calves. 相似文献
84.
Aprahamian M Bour G Akladios CY Fylaktakidou K Greferath R Soler L Marescaux J Egly JM Lehn JM Nicolau C 《Chembiochem : a European journal of chemical biology》2011,12(5):777-783
Myo-inositol trispyrophosphate (ITPP), a synthetic allosteric effector of hemoglobin, increases the regulated oxygen-releasing capacity of red blood cells (RBCs), leading to suppression of hypoxia-inducible factor 1α (HIF-1α) and to down-regulation of hypoxia-inducible genes such as vascular endothelial growth factor (VEGF). As a consequence, tumor growth is markedly affected. The effect of weekly intravenous injection of ITPP on an orthotopic, syngenic rat hepatocellular carcinoma (HCC) model was compared to that for untreated animals and animals subjected to conventional Doxorubicin chemotherapy. The longitudinal examination of HCC was performed by microCT imaging, and the cellular and molecular changes were evaluated by histology and Western blotting analysis of HIF-1α, VEGF, and caspase-3 gene expression in the tumor and in the surrounding liver. Hematologic impact was evaluated by blood cell-count measurement and determination of P50 (oxygen partial pressure for a 50 % oxygen saturation of hemoglobin). The HCC evaluation by microCT revealed a high potency of ITPP for tumor growth inhibition, thus allowing long-term survival and even cure of almost all the treated animals. The P50 value of hemoglobin in RBCs underwent a shift of 30 % following ITPP injection. Under these conditions, HIF-1α activity was strongly decreased, VEGF expression was down-regulated, and apoptosis was induced in HCC and surrounding liver cells, as indicated by Caspase-3 expression. ITPP did not affect hematologic parameters during treatment. The observations of in vivo tumor eradication suggest a significant clinical potential for ITPP in cancer therapy. 相似文献
85.
Composites of phenolic resin of novolac type as matrix, with metal particles of Zn as conducting filler, without or with 15% v/v carbon fibers were manufactured by hot pressing. The porosity ratio, the hardness, the flexural and shear strength, and the electrical conductivity of the composites were determined. The percolation threshold was determined based on two models of electrical conductivity versus the content of metal particles of Zn, namely, an analogous to polymer gelation model and the other based on the power law. The composites of carbon fibers combined with Zn particles have higher electrical conductivity than the corresponding without carbon fibers and high strength, lower than that of the composite reinforced with carbon fibers without Zn particles, but still acceptable. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
86.
Cytotoxic Activity and Structure–Activity Relationship of Triazole‐Containing Bis(Aryl Ether) Macrocycles 下载免费PDF全文
Dr. Eduardo Hernández‐Vázquez Dr. Alejandra Chávez‐Riveros Dr. Adriana Romo‐Pérez María Teresa Ramírez‐Apán Dr. Alma D. Chávez‐Blanco Dr. Rocío Morales‐Bárcenas Dr. Alfonso Dueñas‐González Dr. Luis D. Miranda 《ChemMedChem》2018,13(12):1193-1209
Cancer continues to be a worldwide health problem. Certain macrocyclic molecules have become attractive therapeutic alternatives for this disease because of their efficacy and, frequently, their novel mechanisms of action. Herein, we report the synthesis of a series of 20‐, 21‐, and 22‐membered macrocycles containing triazole and bis(aryl ether) moieties. The compounds were prepared by a multicomponent approach from readily available commercial substrates. Notably, some of the compounds displayed interesting cytotoxicity against cancer (PC‐3) and breast (MCF‐7) cell lines, especially those bearing an aliphatic or a trifluoromethyl substituent on the N‐phenyl moiety (IC50<13 μm ). Additionally, some of the compounds were able to induce apoptosis relative to the solvent control; in particular, (Z)‐N‐cyclohexyl‐7‐oxo‐6‐[4‐(trifluoromethyl)phenyl]‐11H‐3,10‐dioxa‐6‐aza‐1(4,1)‐triazola‐4(1,3),9(1,4)‐dibenzenacyclotridecaphane‐5‐carboxamide ( 12 f ) was the most potent in this regard (22.7 % of apoptosis). 相似文献
87.
The effect of storage conditions (light, temperature, container types) and time on the quality of natural olive oils from different cultivars and Australian regions were studied. The oils’ changing quality was monitored through several physico-chemical methods (free fatty acids, peroxide value, UV-spectrometry (K232, K 270 and ΔK), induction time, total polyphenol content, bitterness, pyropheophytin a and 1,2-diacyl-glycerol content) and sensory analysis over 24 months. Pyropheophytins a and 1,2-diacyl-glycerols criteria showed very good performance as indicators of overall olive oil quality and freshness as well as highlighting any problems during the storage of the product. Pyropheophytin a increment averaged 7 % per year and the 1,2-diacyl-glycerols decreased at an average of 23 % per year at normal storage conditions over time. 相似文献
88.
89.
Léa Gauthier Vessela Atanasova-Penichon Sylvain Chéreau Florence Richard-Forget 《International journal of molecular sciences》2015,16(10):24839-24872
Fusarium graminearum is the causal agent of Fusarium head blight (FHB) and Gibberella ear rot (GER), two devastating diseases of wheat, barley, and maize. Furthermore, F. graminearum species can produce type B trichothecene mycotoxins that accumulate in grains. Use of FHB and GER resistant cultivars is one of the most promising strategies to reduce damage induced by F. graminearum. Combined with genetic approaches, metabolomic ones can provide powerful opportunities for plant breeding through the identification of resistant biomarker metabolites which have the advantage of integrating the genetic background and the influence of the environment. In the past decade, several metabolomics attempts have been made to decipher the chemical defense that cereals employ to counteract F. graminearum. By covering the major classes of metabolites that have been highlighted and addressing their potential role, this review demonstrates the complex and integrated network of events that cereals can orchestrate to resist to F. graminearum. 相似文献
90.
E. J. PODLAHA A. BO¨GLI Ch. BONHO^TE D. LANDOLT 《Journal of Applied Electrochemistry》1997,27(7):805-814
An alternative electrode design to existing inverted rotating disc electrode configurations is presented which eliminates the need for a special cell. A thin, insulated, conducting shaft is mounted in the centre of an electroactive disc. The resulting electrode, an inverted rotating shaft-disc electrode (IRSDE), can be mounted on any conventional disc rotator. Ferricyanide and copper reduction were used to characterize the mass transfer behaviour for different size disc electrodes with a constant shaft diameter. The limiting current was found to vary linearly with the square root of rotation rate for all sizes. The Levich equation was valid for a small shaft to disc radius. A maximum in the thickness of deposited copper near the central shaft was observed resulting from the combined effect of a radial component to mass transport and the shaft wall. An empirical expression for the average limiting current density at the IRSDE taking into account the shaft to disc radius ratio is presented. 相似文献