全文获取类型
收费全文 | 2769篇 |
免费 | 30篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 26篇 |
综合类 | 5篇 |
化学工业 | 160篇 |
金属工艺 | 40篇 |
机械仪表 | 42篇 |
建筑科学 | 68篇 |
矿业工程 | 21篇 |
能源动力 | 22篇 |
轻工业 | 123篇 |
水利工程 | 7篇 |
石油天然气 | 6篇 |
无线电 | 120篇 |
一般工业技术 | 208篇 |
冶金工业 | 1815篇 |
原子能技术 | 10篇 |
自动化技术 | 128篇 |
出版年
2022年 | 11篇 |
2021年 | 13篇 |
2020年 | 8篇 |
2019年 | 16篇 |
2018年 | 16篇 |
2017年 | 16篇 |
2016年 | 22篇 |
2015年 | 13篇 |
2014年 | 31篇 |
2013年 | 67篇 |
2012年 | 28篇 |
2011年 | 48篇 |
2010年 | 35篇 |
2009年 | 49篇 |
2008年 | 50篇 |
2007年 | 45篇 |
2006年 | 37篇 |
2005年 | 35篇 |
2004年 | 34篇 |
2003年 | 36篇 |
2002年 | 21篇 |
2001年 | 25篇 |
2000年 | 27篇 |
1999年 | 72篇 |
1998年 | 526篇 |
1997年 | 320篇 |
1996年 | 188篇 |
1995年 | 118篇 |
1994年 | 99篇 |
1993年 | 132篇 |
1992年 | 27篇 |
1991年 | 49篇 |
1990年 | 43篇 |
1989年 | 43篇 |
1988年 | 36篇 |
1987年 | 46篇 |
1986年 | 26篇 |
1985年 | 32篇 |
1984年 | 9篇 |
1983年 | 26篇 |
1982年 | 21篇 |
1981年 | 22篇 |
1980年 | 21篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 56篇 |
1976年 | 107篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有2801条查询结果,搜索用时 0 毫秒
91.
ABSTRACTThe efficacy of climate-change mitigation policy within the building sector is examined in terms of how fragmentation can limit the extent of mitigation actions that can be achieved in a timely manner. The policy and regulatory context for the building industry is examined in relation to the policy context for solutions and recommendations that will work for all parties. Based on this analysis, two substantive recommendations are made for improved policy design. Firstly, a decoupling of policy objectives and policy mechanisms is needed so that the policy-taking stakeholders (in design, development and construction) can reduce energy use in buildings more effectively. Secondly, policy-taking stakeholders need an explicit and diverse system in order to advocate for policy objectives. The major aspect of this work is the development of a new conceptual framework that ties together these recommendations into a continuous process of policy-making and policy-taking. This framework demonstrates an idealized system that operates simultaneously top down and bottom up, and the development of policy objectives is influenced by stakeholders of all kinds to further the goals of an energy-efficient, low-carbon built environment. 相似文献
92.
Contact lens wear continues to be the highest single risk factor for microbial keratitis, particularly when worn in the extended wear modality. For microbial keratitis to occur, the presence of at least a bacterial load as well as a break in the corneal surface is required. One such break occurs in the case of a corneal erosion. These well-circumscribed areas of full thickness epithelial loss can occur both with and without contact lens wear, however the risk of infection is greater in the presence of a lens due to its capacity to provide a vector for the entry of bacterial pathogens. While erosions in non-contact lens wearers are thought to result from defective epithelial basement membrane anchoring, the underlying causes during contact lens wear are yet unknown. This article sets out to review corneal erosions associated with contact lens wear, their associated risk factors such as extended wear, the mechanisms that may be responsible for their formation and the factors that differentiate them from other contact lens related adverse events. Appropriate diagnosis and understanding of the relevant pathophysiology is important to the effective treatment and an understanding of the aetiological factors responsible for erosions is critical to the development of preventative strategies and effective clinical care. 相似文献
93.
Matthew O.T. Cole 《Automatica》2012,48(9):2377-2380
This paper describes the construction of low-pass FIR filters for application as command input shapers in motion control systems. The filters are designed to operate on an arbitrary command input signal to ensure a finite settling time for system modes with known natural frequency and damping ratio. In addition, the required roll-off rate of the filter frequency response may be prescribed in the design. Excitation of unmodeled high-frequency modes can thereby be reduced. The filters also produce an input-smoothing effect that is useful in situations where discontinuities in the input signal or its derivatives would be detrimental to system performance or function. Numerical case studies are presented to clarify these effects. 相似文献
94.
Dr. Samuel H. Henager Stephanie Henriquez Dr. Daniel R. Dempsey Prof. Philip A. Cole 《Chembiochem : a European journal of chemical biology》2020,21(1-2):64-68
The activity and localization of PTEN, a tumor suppressor lipid phosphatase that converts the phospholipid PIP3 to PIP2, is governed in part by phosphorylation on a cluster of four Ser and Thr residues near the C terminus. Prior enzymatic characterization of the four monophosphorylated (1p) PTENs by using classical expressed protein ligation (EPL) was complicated by the inclusion of a non-native Cys at the ligation junction (aa379), which may alter the properties of the semisynthetic protein. Here, we apply subtiligase-mediated EPL to create wt 1p-PTENs. These PTENs are more autoinhibited than previously appreciated, consistent with the role of Tyr379 in driving autoinhibition. Alkaline phosphatase sensitivity analysis revealed that these autoinhibited 1p conformations are kinetically labile. In contrast to the Cys mutant 1p-PTENs, which are poorly recognized by an anti-phospho-PTEN antibody, three of the four wt 1p-PTENs are recognized by a commonly used anti-phospho-PTEN antibody. 相似文献
95.
ABSTRACT: BACKGROUND: The food group intake patterns of low income Hispanic and African American preschool children are not well documented. The aim of this study was to perform a food group intake analysis of low income minority preschool children and evaluate how macronutrient and micronutrient intake compares to Dietary Reference Intakes (DRI). METHODS: A cross sectional study design using three-day food diaries analyzed by dietary analysis software (Nutrient Database System for Research) was used. Children were recruited from well-child clinics at Children's Healthcare of Atlanta at Hughes Spalding and North Dekalb Grady Satellite Clinic, Atlanta, GA. Low-income, African American and Hispanic preschool age children (n = 291) were enrolled. A total of 105 completed the 3-day food diaries were returned and analyzed. Chi-squared tests were used to assess demographic variables. The mean percentage of intake per day of specific food groups and sub-groups were obtained (servings of given food group/total daily servings). Food intake data and proportion of children meeting DRIs for macro- and micronutrients were stratified by race/ethnicity, nutritional status, and caloric intake, and were compared using t-tests. Regression models controlling for age, BMI and sex were obtained to assess the effect of total caloric intake upon the proportional intake of each studied food group. RESULTS: The mean age of African American children was 2.24 [PLUS-MINUS SIGN] 1.07 years and Hispanic children 2.84 [PLUS-MINUS SIGN] 1.12 years. African Americans consumed more kcal/kg/day than Hispanics (124.7 [PLUS-MINUS SIGN] 51 vs. 96.9 [PLUS-MINUS SIGN] 33, p < 0.05). Hispanics consumed more fruits (22.0 [PLUS-MINUS SIGN] 10.7% vs. 14.7 [PLUS-MINUS SIGN] 13.7%, p < 0.05), while African Americans consumed more grains (25.7 [PLUS-MINUS SIGN] 7.8% vs. 18.1 [PLUS-MINUS SIGN] 6.4%, p < 0.05), meats (20.7 [PLUS-MINUS SIGN] 9.0% vs. 15.4 [PLUS-MINUS SIGN] 6.1%, p < 0.05), fats (9.8 [PLUS-MINUS SIGN] 5.4% vs. 7.0 [PLUS-MINUS SIGN] 5.8%, p < 0.05), sweet drinks (58.7 [PLUS-MINUS SIGN] 17.1% vs. 41.3 [PLUS-MINUS SIGN] 14.8%, p < 0.05) and low-fat dairy products (39.5 [PLUS-MINUS SIGN] 19.3% vs. 28.9 [PLUS-MINUS SIGN] 12.6%, p < 0.05). Among Hispanics, the proportional intake of fruits, fats and grains varied by total caloric intake, while no difference by total caloric intake was found for the dietary patterns of African Americans. Micronutrient intake also differed significantly between African American and Hispanic children. CONCLUSIONS: Food group intake patterns among low-income children differ by ethnic group. There is a need for more research to guide program design and target nutritional interventions for this population. 相似文献
96.
97.
98.
Exact solutions are given for the transient temperature in flux-base fins with the method of Green’s functions (GF) in the form of infinite series for three different tip conditions. The speed of convergence is improved by replacing the steady part by a closed-form steady solution. For the insulated-tip case, a quasi-steady solution is presented. Numerical values are presented and the conditions under which the quasi-steady solution is accurate are determined. An experimental example is given for estimation of the heat transfer coefficient (HTC) on a non-rotating roller bearing, in which the outer bearing race is treated as a transient fin. 相似文献
99.
Guided by family interaction theory, this study examined the influences of psychological, peer, and familial processes on alcohol use among young adolescent girls and assessed the contributions of familial factors. An ethnically diverse sample of 1,187 pairs of girls (M age = 12.83 years), and their mothers completed surveys online. Questionnaires assessed girls’ lifetime and recent alcohol use, as well as girls’ demographic, psychological, peer, and family characteristics. Hierarchical logistic regression models showed that although girls’ drinking was associated with a number of psychological and peer factors, the contributions of family domain variables to girls’ drinking were above and beyond that of psychological and peer factors. The interaction analyses further highlighted that having family rules, high family involvement, and greater family communication may offset risks in psychological and peer domains. Study findings underscore the multifaceted etiology of drinking among young adolescent girls and assert the crucial roles of familial processes. Prevention programs should be integrative, target processes at multiple domains, and include work with parents. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
100.
Issa Ouedraogo Patrice Savadogo Mulualem Tigabu Roy Cole Per Christer Oden Jean-Marie Ouadba 《Landscape Research》2013,38(3):303-320
Forest cover decline is one of the most important environmental issues in the tropics. The present study was carried out in Burkina Faso, West Africa, and aimed at assessing the trajectories of forest cover change and measuring landscape metrics of the trajectory classes in order to better understand the processes of change. Landsat and ASTER images acquired over a period of 30 years were used for cover change detection and the Fragstats package was used to compute landscape metrics with five unifying change classes. Results showed a substantial increase in cropland with concurrent decline in forest cover. Deforestation represented 63% of the Percentage of Landscape (PLAND) in 2006, while reforestation accounted for only 28%. Both of these classes had high Normalized Landscape Shape Index (NLSI) values, indicating that they were present as scattered small patches. The old cultivation (30-year permanent cropland) was aggregated (IJI ≈ 0) while deforestation exhibited highly interspersed patches. The old forest and old cultivation presented lower Area Weighted Fractal Dimension Index (FRAC_AM), but deforestation and reforestation had the higher FRAC_AM. These results confirmed that there was a high level of deforestation and fragmentation in southern Burkina Faso and justify the need for a proper management plan to ensure the sustainable use of forest resources. 相似文献