全文获取类型
收费全文 | 1410篇 |
免费 | 85篇 |
专业分类
电工技术 | 25篇 |
化学工业 | 351篇 |
金属工艺 | 19篇 |
机械仪表 | 31篇 |
建筑科学 | 50篇 |
矿业工程 | 1篇 |
能源动力 | 30篇 |
轻工业 | 143篇 |
水利工程 | 7篇 |
石油天然气 | 5篇 |
武器工业 | 1篇 |
无线电 | 164篇 |
一般工业技术 | 221篇 |
冶金工业 | 143篇 |
原子能技术 | 8篇 |
自动化技术 | 296篇 |
出版年
2023年 | 7篇 |
2022年 | 57篇 |
2021年 | 59篇 |
2020年 | 36篇 |
2019年 | 37篇 |
2018年 | 41篇 |
2017年 | 23篇 |
2016年 | 53篇 |
2015年 | 49篇 |
2014年 | 43篇 |
2013年 | 88篇 |
2012年 | 75篇 |
2011年 | 99篇 |
2010年 | 61篇 |
2009年 | 75篇 |
2008年 | 54篇 |
2007年 | 62篇 |
2006年 | 55篇 |
2005年 | 50篇 |
2004年 | 40篇 |
2003年 | 42篇 |
2002年 | 36篇 |
2001年 | 28篇 |
2000年 | 20篇 |
1999年 | 23篇 |
1998年 | 40篇 |
1997年 | 28篇 |
1996年 | 25篇 |
1995年 | 23篇 |
1994年 | 24篇 |
1993年 | 10篇 |
1992年 | 11篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1975年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有1495条查询结果,搜索用时 9 毫秒
171.
F Paolieri M Battifora AM Riccio G Ciprandi A Scordamaglia C Morelli M Bagnasco GW Canonica 《Canadian Metallurgical Quarterly》1997,52(9):935-943
Inhaled corticosteroids in the treatment of asthma have been shown to produce marked reductions in the number of inflammatory cells (mainly mast cells and eosinophils) and their products at bronchial level (such as cytokines). Recently, it has been demonstrated that epithelial cells express ICAM-1/CD54 in allergic patients both during natural allergen exposure and after allergen challenge. We have previously demonstrated that deflazacort (a systemic steroid) reduces the expression of ICAM-1 on conjunctival epithelial cells. The present study aimed to evaluate the effects exerted by budesonide on adhesion molecule expression by a human epithelial cell line (lung carcinoma: DM) and on soluble ICAM-1. Budesonide was added at concentrations corresponding to 10(-8), 10(-7), and 10(-6) mol/l in cultured epithelial cells, either in the absence of any stimulus or in the presence of interferon-gamma (IFN-gamma) at 500 U/ml. After 24 h of incubation, cytofluorometric analysis was performed for ICAM-1 and CD29/VLA beta 1. The 24-h supernatants of the same cultures were collected and then evaluated for soluble ICAM-1 (sICAM-1). The results showed that budesonide inhibits ICAM-1 and CD29 basal expression on the cells studied (P < 0.05): budesonide was effective in a dose-dependent manner. In addition, budesonide reduced surface ICAM-1 upregulation induced by IFN-gamma at 500 U/ml (P < 0.05). Finally, cell cultures with budesonide showed decreased levels of soluble ICAM-1 in basal condition, but not after IFN-gamma stimulation. 相似文献
172.
S Salminen A von Wright L Morelli P Marteau D Brassart WM de Vos R Fondén M Saxelin K Collins G Mogensen SE Birkeland T Mattila-Sandholm 《Canadian Metallurgical Quarterly》1998,44(1-2):93-106
Probiotics are commonly defined as viable microorganisms (bacteria or yeasts) that exhibit a beneficial effect on the health of the host when they are ingested. They are used in foods, especially in fermented dairy products, but also in pharmaceutical preparations. The development of new probiotic strains aims at more active beneficial organisms. In the case of novel microorganisms and modified organisms the question of their safety and the risk to benefit ratio have to be assessed. Lactic acid bacteria (LAB) in foods have a long history of safe use. Members of the genera Lactococcus and Lactobacillus are most commonly given generally-recognised-as-safe (GRAS) status whilst members of the genera Streptococcus and Enterococcus and some other genera of LAB contain some opportunistic pathogens. Lactic acid bacteria are intrinsically resistant to many antibiotics. In many cases resistances are not, however, transmissible, and the species are also sensitive to many clinically used antibiotics even in the case of a lactic acid bacteria- associated opportunistic infection. Therefore no particular safety concern is associated with intrinsic type of resistance. Plasmid-associated antibiotic resistance, which occasionally occurs, is another matter because of the possibility of the resistance spreading to other, more harmful species and genera. The transmissible enterococcal resistance against glycopeptide antibiotics (vancomycin and teicoplanin) is particularly noteworthy, as vancomycin is one of the last effective antibiotics left in the treatment of certain multidrug-resistant pathogens. New species and more specific strains of probiotic bacteria are constantly identified. Prior to incorporating new strains into products their efficacy should be carefully assessed, and a case by case evaluation as to whether they share the safety status of traditional food-grade organisms should be made. The current documentation of adverse effects in the literature is reviewed. Future recommendations for the safety of already existing and new probiotics will be given. 相似文献
173.
Experimental investigation of coupled conduction and laminar convection in a circular tube 总被引:2,自引:0,他引:2
Giovanni S. Barozzi Giorgio Pagliarini 《International Journal of Heat and Mass Transfer》1984,27(12):2321-2329
Wall heat conduction effects on laminar flow heat transfer are experimentally investigated. The steady flow of water through a uniformly heated copper pipe is considered in the experiment, which covers a range of Reynolds numbers from 500 to 1900. The thermal behaviour of the test section is simulated numerically and the influence of conduction along the pipe wall is therefore accounted for in the reduction of the data. Fully developed flow results satisfactorily compare with predictions by a theoretical method previously developed by the authors [Heat Technol. 2,72 (1984)]. Results are also reported for the case where the velocity profile is partially developed at the inlet of the heat transfer section. The combined effects on heat transfer of flow development and of wall axial heat conduction are discussed. 相似文献
174.
175.
Anil Mital Paul T. Kemmerling Robert D. Dryden Tom B. Leamon Donald L. Morelli Bahador Ghahramani 《IIE Transactions》1993,25(3):99-104
There is a growing concern in die labor sector to reduce stresses in the work place and the associated strains and adverse effects on health which result from newer forms of tasks that workers are increasingly called upon to perform. One approach to reducing stresses is to reduce the work-week (fewer hours per week). Social expectation of longer vacations and leisure time, demographic changes, and changes in the nature of die work and attitudes towards work also support this trend. The objective of this position paper is to consider the implication of such a move and the feasibility of this approach. Specifically, we consider the effects of a shorter work-week on productivity and economy and discuss the various patterns of shorter work-week. Finally, we present our position on die pattern of the shorter work-week in the United States in the future. 相似文献
176.
Alberto Milani Matteo Tommasini Giuseppe Zerbi Giorgio Canil Francesco Triulzi 《Polymer》2008,49(7):1812-1822
Amorphous fluorinated optical polymers, characterized by high transparency in the visible and near infrared spectra, high glass transition temperature and very good resistance to chemical environment, have been developed by co-polymerisation of tetrafluoroethylene (TFE) and 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxole (TTD). In this work we study at molecular level the effect of the introduction of the bulky TTD unit in a perfluoroalkyl chain.In particular the effect on the molecular structure and chain flexibility is investigated and spectroscopic markers correlated to chemical and structural defects are identified. The study includes a thorough experimental spectroscopic analysis (infrared and Raman spectra) of several different copolymer samples and a modelling based on Density Functional Theory calculations and semiempirical calculations on suitable model molecules. 相似文献
177.
Glulio D. Guerra Maurizio Palla Glovanna Pfzzirani Giorgio Soldani 《Polymer Bulletin》1988,20(2):123-130
Summary Grafting of polystyryl and copoly(styrene-b-isopren)yl maorocarbanions onto ethylene-maleic anhydride alternating copolymer was carried out under reaction conditions such as to obtain copolymers with middle-low grafting degree and long lateral chains. In order to ascertain the absence of secondary reactions, the coupling of n-BuLi with succinic anhydride vas investigated, and no secondary reaction vas observed. The graft copolymers, wich have molecular weights and elemental composition in good agreement with those expected, were studied by IR spectroscopy and DSC. Both spectra and calorimetric curves confirm the structures assigned to the copolymers. The tensile properties of the copolymers with copoly(styrene-b-isoprene) lateral chains were also investigated, The properties appear very dependent on the degree of grafting, on the solvent (benzene or THF) from which the specimens were deposited, and on their thermal history. 相似文献
178.
Giorgio Giorgi 《Calcolo》1984,21(4):307-316
Summary The paper by S. Mititelu [8] is revisited, giving correct proofs of both necessary and sufficient conditions for the existence
of solutions to a quasi-convex mathematical programming problem. The usual constraint qualifications established for such
a problem, are then further weakened.
I thank two anonymous referees for some useful suggestions on the first version of the present paper; any responsibility is
however solely mine. 相似文献
179.
A Giorgio L Tarantino N Mariniello G de Stefano A Perrotta V Aloisio A Voza L Finizia A Alaia L Del Viscovo 《Canadian Metallurgical Quarterly》1998,8(3):201-206
OBJECTIVE: The aim of this study was to determine whether the expression of thymidine phosphorylase by ovarian cancer cells correlates with the density of microvessels within the tumor, and with ultrasound-derived indices of blood flow. METHODS: Transvaginal ultrasonography with color Doppler imaging and pulsed Doppler spectral analysis was used to scan patients with an overt ovarian mass immediately before laparotomy. Sections of malignant tumors were analyzed for the cellular expression of thymidine phosphorylase and the intratumoral density of microvessels by immunohistochemistry using monoclonal antibodies to thymidine phosphorylase and factor VIII-related antigen, respectively. The main outcome measures were the histological classification of the tumor, the stage of the disease, whether or not the tumor cells were positive or negative for thymidine phosphorylase, the microvessel count and the peak systolic velocity (PSV). RESULTS: Forty-two tumors were studied (three of low malignant potential, 29 epithelial, four granulosa cell, two germ cell and four metastatic); 18 were stage I, six stage II, 11 stage III and three stage IV. Twenty-seven tumors (64%) were classified as thymidine phosphorylase-positive. The proportion of stage I tumors that was thymidine phosphorylase-positive (44%) was significantly lower (p = 0.022) than the corresponding value for stages II-IV (85%), but the values for microvessel count and PSV were similar. The microvessel count in thymidine phosphorylase-positive tumors was significantly higher than in thymidine phosphorylase-negative tumors (p = 0.005). Similarly, the PSV was significantly higher in thymidine phosphorylase-positive tumors (p = 0.009). There was a significant correlation between the microvessel count and the PSV (r = 0.354, p = 0.022). CONCLUSIONS: The expression of thymidine phosphorylase by malignant tumor cells is associated with an increase in microvessel density and PSV in patients with ovarian cancer. 相似文献
180.
Alberto Ballistreri Giorgio Montaudo Concetto Puglisi Emilio Scamporrino Daniele Vitalini 《应用聚合物科学杂志》1982,27(9):3369-3377
The influence of ammonium polyphosphate (APP) on the smoke emission of poly(acrylonitrile) (PAN) has been examined, and its mechanism of action as a smoke suppressant agent has been investigated. Smoke density and corresponding residual char data, as a function of temperature, were obtained in order to characterize the smoke propensity of PAN. The amount of generated smoke, both in smoldering and flaming conditions, was considerably lowered by the presence of APP, and higher char yields were obtained. Beside the smoke suppression, flame inhibition effect of APP on PAN was evidenced. Thermogravimetry (TG), oxygen index (OI), and nitrous oxide index (NOI) experiments were also performed. On the basis of our data, APP appears to act as a char-forming agent in PAN combustion. Both smoke suppression and flame inhibition effects can be considered a consequence of this action. 相似文献