全文获取类型
收费全文 | 2863篇 |
免费 | 167篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 29篇 |
技术理论 | 1篇 |
综合类 | 5篇 |
化学工业 | 407篇 |
金属工艺 | 22篇 |
机械仪表 | 32篇 |
建筑科学 | 44篇 |
能源动力 | 55篇 |
轻工业 | 91篇 |
水利工程 | 6篇 |
石油天然气 | 1篇 |
无线电 | 401篇 |
一般工业技术 | 479篇 |
冶金工业 | 1162篇 |
原子能技术 | 9篇 |
自动化技术 | 293篇 |
出版年
2023年 | 7篇 |
2022年 | 20篇 |
2021年 | 34篇 |
2020年 | 22篇 |
2019年 | 40篇 |
2018年 | 41篇 |
2017年 | 38篇 |
2016年 | 68篇 |
2015年 | 72篇 |
2014年 | 75篇 |
2013年 | 195篇 |
2012年 | 101篇 |
2011年 | 99篇 |
2010年 | 100篇 |
2009年 | 101篇 |
2008年 | 90篇 |
2007年 | 101篇 |
2006年 | 81篇 |
2005年 | 79篇 |
2004年 | 59篇 |
2003年 | 52篇 |
2002年 | 38篇 |
2001年 | 37篇 |
2000年 | 33篇 |
1999年 | 43篇 |
1998年 | 364篇 |
1997年 | 241篇 |
1996年 | 158篇 |
1995年 | 105篇 |
1994年 | 88篇 |
1993年 | 78篇 |
1992年 | 23篇 |
1991年 | 33篇 |
1990年 | 18篇 |
1989年 | 27篇 |
1988年 | 26篇 |
1987年 | 24篇 |
1986年 | 21篇 |
1985年 | 24篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 14篇 |
1980年 | 14篇 |
1979年 | 4篇 |
1978年 | 9篇 |
1977年 | 34篇 |
1976年 | 61篇 |
1975年 | 6篇 |
1973年 | 5篇 |
排序方式: 共有3037条查询结果,搜索用时 15 毫秒
81.
RS Hogg AE Weber KJ Craib AH Anis MV O'Shaughnessy MT Schechter JS Montaner 《Canadian Metallurgical Quarterly》1998,12(16):2203-2209
OBJECTIVE: To estimate the potential direct cost of making triple combination antiretroviral therapy widely available to HIV-positive adults and children living in countries throughout the world. METHODS: For each country, antiretroviral costs were obtained by multiplying the annual cost of triple antiretroviral therapy by the estimated number of HIV-positive persons accessing therapy. Per capita antiretroviral costs were computed by dividing the antiretroviral costs by the country's total population. The potential economic burden was calculated by dividing per capita antiretroviral costs by the gross national product (GNP) per capita. All values are expressed in 1997 US dollars. RESULTS: The potential cost of making triple combination antiretroviral therapy available to HIV-positive individuals throughout the world was estimated to be over US$ 65.8 billion. By far the greatest financial burden was on sub-Saharan Africa. The highest per capita drug cost in this region would be incurred in the subregions of Southern Africa (US$ 149) followed by East Africa (US$ 116), Middle Africa (US$ 44), and West Africa (US$ 42). In the Americas, subregional data indicated the highest per capita drug cost would be in the Latin Caribbean (US$ 22), followed by the Caribbean (US$ 17), Andean Area (US$ 7), the Southern Cone (US$ 6), North America (US$ 6), and Central American Isthmus (US$ 5). In Asia and Europe the percentage of the GNP necessary to finance drug therapy was less than 1% in most countries examined. CONCLUSION: Our results demonstrate that the cost of making combination antiretroviral therapy available worldwide would be exceedingly high, especially in countries with limited financial resources. 相似文献
82.
Simultaneous bleaching of vital teeth and an open-chamber nonvital tooth with 10% carbamide peroxide
OBJECTIVE: The purpose of this study was to evaluate the effectiveness of bleaching a nonvital tooth with an open pulp chamber while simultaneously bleaching the other vital teeth with 10% carbamide peroxide. METHOD AND MATERIALS: Ten discolored nonvital teeth were treated. Each nonvital tooth was prepared as in the conventional "walking bleaching" fashion, so that the gutta-percha was sealed from the pulp chamber. The 10% carbamide peroxide was injected into the chamber of the nonvital tooth and loaded into the custom-fitted tray for all teeth. The nonvital teeth were bleached from both the inside and the outside. The patient closed the orifice with a cotton pellet during the day and changed the cotton pellet after meals. The patient applied fresh solution nightly. RESULTS: All teeth were successfully lightened. The time required to lighten the nonvital tooth was related to the duration of the discoloration. CONCLUSION: With proper patient selection and education, this technique can provide an effective way to lighten nonvital and vital teeth simultaneously, especially where extended treatment time may be required for difficult discolorations. 相似文献
83.
Post-transcriptional gene silencing in plants 总被引:2,自引:0,他引:2
The author demands an introduction of quality assurance in biological research concerning human beings. He sketches systems which can be built into studies as a quality control. By the example of growth studies he illustrates the problems of theoretical considerations and practicability. He gives an overview of 7 questions arising in anthropometric growth studies: Why? Where? Whom? What? When? Who? and How? In connection with the final one, he discusses and analyzes the possibilities and the different ways of quality assurance in such studies. 相似文献
84.
LA Pérula de Torres J Martínez de la Iglesia J Espejo Espejo MV Rubio Cuadrado I Enciso Berge FJ Fonseca del Pozo JM Aranda Lara 《Canadian Metallurgical Quarterly》1997,20(8):425-434
OBJECTIVE: To describe the health status of a population over 60 years and to study their relationship with several socio-demographic variables. DESIGN: A cross-sectional study, population based. SETTINGS: A community. PARTICIPANTS: A randomized sample of 1,103 non institutionalized people over 60 years living in the city of Cordoba (Spain). MEASUREMENTS AND MAIN RESULTS: By mean of a personal interview at home we used the OARS-MFAQ-VE questionnaire. Low self-rated health was associated with the age, to be female sex, a low cultural background, and a low income. Only 5.2% of the study people do not suffered any illness and 56% state that their health problems are major problems for doing their current activities. 4.9% declared to have some degree of physical incapacity. 3.7% of elderly population has an important cognitive deficit. CONCLUSIONS: The majority of elderly people has good health. Age is related with a poor health. Women have more health problems than men. 相似文献
85.
RA Dickson MV Seeman 《Canadian Metallurgical Quarterly》1997,154(12):1792; author reply 1793-1792; author reply 1794
86.
MB Iarustovski? RG Grigor'iants VS Timokhov MV Abramian IL Mikha?lova SS Volkova IaV Banketov II Golenishchev II Iakovleva 《Canadian Metallurgical Quarterly》1997,(6):40-46
The efficacy of continuous methods of renal substitute therapy (RST) in patients with multiple organ failure is assessed. The patients were divided in 2 groups administered different types of PST. Group 1 were 16 patients subjected to RST by peritoneal dialysis, in group 2 (n = 16) GP and/or GDP were used. Hemodynamics, hematological and biochemical values, and clearance of inflammation mediators were monitored and hemohydrobalance and complications of therapy assessed in the course of RST. Both RST methods proved to be highly effective. The possibility of differentiated use of peritoneal dialysis and GP/GDP permits an individual approach to treatment, and equally high efficacy of both methods solves the problem of treating total renal insufficiency in the majority of patients with multiple organ failure following cardiovascular surgery. 相似文献
87.
Yuan‐Hsiang Yu Chien‐Chih Jen Hsiu‐Ying Huang Pei‐Chi Wu Chao‐Cheng Huang Jui‐Ming Yeh 《应用聚合物科学杂志》2004,91(6):3438-3446
A series of heterocyclically conjugated polymer–clay nanocomposite (PCN) materials that consisted of organic poly(3‐hexylthiophene) (P3HT) and inorganic montmorillonite (MMT) clay platelets were prepared by in situ oxidative polymerization with FeCl3 as an oxidant. The as‐synthesized PCN materials were characterized by Fourier transform infrared (FTIR) spectroscopy, wide‐angle powder X‐ray diffraction (WAXRD), and transmission electron microscopy (TEM). The effects of the material composition on the anticorrosion, gas barrier, thermal stability, flammability, mechanical strength, and electrical conductivity properties of the P3HT and PCN materials were studied by electrochemical corrosion measurements, gas‐permeability analysis (GPA), thermogrametric analysis (TGA), limiting oxygen index (LOI) measurements, dynamic mechanical analysis (DMA), and a four‐point probe technique, respectively. The molecular weights of extracted and bulk P3HT were determined by gel permeation chromatography (GPC) with THF as an eluant. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3438–3446, 2004 相似文献
88.
The present study aims to investigate the effect of suspended nanoparticles in base fluids, namely nanofluids, on the thermal resistance of a disk-shaped miniature heat pipe [DMHP]. In this study, two types of nanoparticles, gold and carbon, in aqueous solution are used respectively. An experimental system was set up to measure the thermal resistance of the DMHP with both nanofluids and deionized [DI] water as the working medium. The measured results show that the thermal resistance of DMHP varies with the charge volume and the type of working medium. At the same charge volume, a significant reduction in thermal resistance of DMHP can be found if nanofluid is used instead of DI water. 相似文献
89.
With an atomic-force microscope and a grazing-incidence small-angle X-ray scattering we studied ex situ the evolution of hierarchical structures in isothermally annealed ultrathin films of asymmetric polystyrene-block-poly(methyl methacrylate) P(S-b-MMA) that dewetted on polar substrates via a mechanism involving nucleation and growth. Film instability causes the surface to acquire an undulating thickness through incommensurability, producing not only the relief structures on a micrometer scale but also mesophase-separated domains on a nanometer scale. The dewetted morphologies strongly influence the ordering behavior of the nanoscale domains. The noncylindrical nanostructures become stable at the curved edges of the relief microstructures in the destabilized P(S-b-MMA) films, for which a preferential wetting of the PS block with the free surface is prohibited. Additionally, the shape of relief structures as result of film instability correlates with the formation of mesophase-separated nanodomains. At early stages of film instability, the formation of parallel-oriented PMMA cylindrical nanodomains increases the deformation energy and it further persists to force the shape of relief structures between irregular holes to have a facet-wedge shape. However, those relief structures are expected to be not at equilibrium. At high temperatures, the relief structures between irregular holes progressively developed to form hemispherical-cap drops accompanied by a transformation of cylindrical into noncylindrical nanodomains at curved surfaces. 相似文献
90.
Chi Wang Yong-Wen Cheng Chia-Hung Hsu Huan-Sheng Chien Shih-Yung Tsou 《Journal of Polymer Research》2011,18(1):111-123
Solutions of five different polymers, namely, polystyrene (PS), polyacrylonitrile (PAN), polyhydroxybutrate (PHB), poly(D-L-lactic
acid) (PLA), and Nylon6, were used to investigate their rheological properties on the electrospinnability. In order to effectively
reduce the diameter of electrospun fibers, polymers with higher molecular weights (MW) were needed to develop entangled solutions
at much lower concentrations and with viscosities as low as that of a pure solvent. A minimum polymer concentration 1.0–2.0
times larger than the entanglement concentration was required to prepare the bead-free fibers. Using this strategy, uniform
PS fibers with the lowest ever diameter of ∼15 nm were successfully obtained using an MW of 3 × 107 g/mol at a concentration of 0.1 vol.%. For a given electrospinning solution, processing variables of low flow-rate (Q) and high voltage (V) were desirable in obtaining fibers with small diameters. However, Q and V were correlated by a power law relation: V∼Q
a, wherein the exponent a had a value of 0.1–0.4, which was relevant with the solution types. Based on the finite element analysis (FEA), a significant
measure of electric field (E) occurred around the needle tip used in the experiment, and its magnitude decayed with increasing distance from the needle
end (z): E∼z
−n. The exponent n was 1.0–2.0, depending on the needle–plate geometry, i.e., needle length, needle diameter (D
o
), plate diameter, and tip-to-plate distance (H). According to FEA results, H exhibited negligible effects on the electric field in the region of interest, i.e., z/D
o
∼1 to 10. Due to the presence of high measures of E at the needle end, approaches to render a shorter and thinner straight jet issuing from the Taylor cone to yield thinner
fibers were sought because a more significant jet stretching in the “jet whipping region” can take place. A feasible route
to predict the as-spun fiber diameter produced by the manipulation of the electrified jet is provided by experimentally measuring
the jet diameter and numerically calculating the electric field for the jet whipping process. 相似文献