全文获取类型
收费全文 | 5305篇 |
免费 | 130篇 |
国内免费 | 3篇 |
学科分类
工业技术 | 5438篇 |
出版年
2021年 | 77篇 |
2020年 | 47篇 |
2019年 | 58篇 |
2018年 | 69篇 |
2017年 | 72篇 |
2016年 | 79篇 |
2015年 | 67篇 |
2014年 | 112篇 |
2013年 | 297篇 |
2012年 | 145篇 |
2011年 | 234篇 |
2010年 | 206篇 |
2009年 | 179篇 |
2008年 | 213篇 |
2007年 | 194篇 |
2006年 | 199篇 |
2005年 | 164篇 |
2004年 | 154篇 |
2003年 | 158篇 |
2002年 | 128篇 |
2001年 | 97篇 |
2000年 | 97篇 |
1999年 | 103篇 |
1998年 | 184篇 |
1997年 | 132篇 |
1996年 | 127篇 |
1995年 | 113篇 |
1994年 | 113篇 |
1993年 | 106篇 |
1992年 | 101篇 |
1991年 | 53篇 |
1990年 | 72篇 |
1989年 | 63篇 |
1988年 | 67篇 |
1987年 | 62篇 |
1986年 | 57篇 |
1985年 | 92篇 |
1984年 | 88篇 |
1983年 | 77篇 |
1982年 | 60篇 |
1981年 | 57篇 |
1980年 | 52篇 |
1979年 | 58篇 |
1978年 | 62篇 |
1977年 | 67篇 |
1976年 | 66篇 |
1975年 | 50篇 |
1974年 | 43篇 |
1973年 | 35篇 |
1972年 | 30篇 |
排序方式: 共有5438条查询结果,搜索用时 15 毫秒
1.
This article, the first of three articles on the synthesis of rice processing plants, focuses on the development of simplified mathematical models necessary for use in optimizing rice processing plants. The second concentrates on the optimal synthesis of a rice plant and the third on the sensitivity of the optimization to uncertainty in model parameters. Existing models for rice processing unit operations are not suitable for flowsheet optimization and new models need to be developed to overcome numerical difficulties that occur in optimization applications, specifically in mixed integer nonlinear programming (MINLP) applications. Simplified models of the drying, cooling, and tempering units are developed. In addition head rice yield models, used as a quality indicator, energy consumption, and economic models were also developed. Naturally, the new models exhibit some mismatch with respect to the existing models from which they were developed. However, a sensitivity analysis, presented in Part III, has shown that the optimal flowsheet structure was not sensitive to a lack of fit between the simplified and complex models. The simplified models were found adequate to be appropriate for use at the synthesis stage. 相似文献
2.
Douglas W. Cooper 《Particulate Science and Technology》1989,7(4):371-380
Aerogels are highly porous materials made by removing the liquid phase of a dilute suspension of solids by taking off the vapor under super-critical temperature and pressure conditions. The aerogel structure has a skeleton of nanometer-size elements forming pores that are tens of nanometers in dimension. In some cases the structure of the aerogel arises from clusters having fractal geometry. The collection efficiency and pressure drop for such material is predicted here from models in the literature. A quality factor is used to compare aerogel material with other filter materials. The quality factor relating gas filtration efficiency with pressure drop is predicted to be unusually high for these materials in comparison with other common fibrous filter media, predicting lower flow resistance for aerogels at equivalent particle collection efficiency levels. 相似文献
3.
Cathy Lawson Douglas C. Montgomery 《Quality and Reliability Engineering International》2006,22(8):971-984
Variation exists in all processes. Significant work has been done to identify and remove sources of variation in manufacturing processes resulting in large returns for companies. However, business process optimization is an area that has a large potential return for a company. Business processes can be difficult to optimize due to the nature of the output variables associated with them. Business processes tend to have output variables that are binary, nominal or ordinal. Examples of these types of output include whether a particular event occurred, a customer's color preference for a new product and survey questions that assess the extent of the survey respondent's agreement with a particular statement. Output variables that are binary, nominal or ordinal cannot be modeled using ordinary least‐squares regression. Logistic regression is a method used to model data where the output is binary, nominal or ordinal. This article provides a review of logistic regression and demonstrates its use in modeling data from a business process involving customer feedback. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
4.
This study tested a partial version of R. W. Lent, S. D. Brown, and G. Hackett's (1994) social-cognitive career theory model. Among 204 high school girls who attended science, math, and engineering (SME) career conferences, the authors used a 4-year longitudinal design to predict the choice of an SME college major and SME self-efficacy and outcome expectations in college. In addition, among students who had declared SME majors, variables assessed in high school and college were used to predict aspirations to become leaders in SME fields. The results generally provided empirical validation of the model. Regression analyses revealed that college SME outcome expectations were associated with plans to become a leader in an SME field. Implications for research and interventions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
5.
Douglas E. Chandler 《Microscopy research and technique》1991,17(3):266-293
Fertilization of the sea urchin egg is accompanied by a sequence of structural changes in the egg cortex that include exocytosis, endocytosis, and microvillar growth. This architectural reorganization is coordinated by two intracellular signals: a rapid, transient rise in cyto-solic free calcium and a slower, longer lasting increase in cytoplasmic pH. In this report we provide ultrastructural views of these events in quick-frozen eggs and discuss their relationship to the calcium and pH signals. 相似文献
6.
PI Lobo C Spencer MT Douglas WC Stevenson TL Pruett 《Canadian Metallurgical Quarterly》1993,55(5):1063-1066
Recent reports indicate a higher incidence of both acute and chronic liver allograft rejection when, at the time of transplantation, the recipients serum contains donor-specific anti-HLA antibodies. From 9/89 to 5/91, 133 liver allografts were performed at our institution. Thirteen liver recipients had donor-specific IgG anti-HLA antibodies (complement-fixing) at the time of transplantation. In eleven patients, antibodies reacted to donor class I antigens while in 1 patient the donor-specific antibody had class II reactivity. Twelve patients have been followed for a minimum of 12 months (median 18 months, range 28-12 months). No hyperacute rejection was seen in any of the cases and four patients had acute rejections. Thus far only one of the twelve patients has biopsy evidence suggestive of chronic liver injury. The remaining have normal liver enzymes and bilirubin. Three of these twelve patients died (one from a myocardial infarction and the others from sepsis) accounting for a one-year graft survival of 75%. There was no significant statistical difference in the one-year graft survival in those recipients without donor-specific antibodies (i.e., 80.5%). In eight of the twelve patients, pretransplant preformed antibody level (PRA) was > 50%. In six of the thirteen patients donor-specific antibody was present at dilutions greater than 1:64. As previously reported, the donor-specific antibody disappeared from the serum posttransplant within hours and did not reappear. In vitro studies demonstrated no factor in portal or hepatic artery blood that could inhibit rabbit complement mediated lysis of anti-HLA antibodies. We conclude that it is not a contraindication to do liver transplants in the presence of donor-specific anti-HLA antibodies. 相似文献
7.
In a survey of the practical wind energy resource present in the Tayside Region of Scotland it was estimated that over 1500 km2 of land is suitable for wind energy development in the Region after consideration of a range of physical, technical and institutional factors. Wind speed data for this survey was obtained from the Energy Technology Support Unit (ETSU) UK Wind Speed Data Package. To verify the wind speeds obtained from the ETSU package a representative sample of sites in and around the identified areas of potential in Tayside were modelled for mean annual wind speed using the Wind Atlas Analysis and Application Program (WAsP). The wind speeds for the sites obtained from the WAsP analysis were compared with those obtained from the ETSU UK Wind Speed Data Package and conclusions drawn as to the reliability of the Tayside wind energy survey and the general applicability of the ETSU package for broad wind energy resource assessment. 相似文献
8.
Previous work on condition monitoring of induction machines has focused on steady-state speed operation. Here, a new concept is introduced based on an analysis of transient machine currents. The technique centers around the extraction and removal of the fundamental component of the current and analyzing the residual current using wavelets. Test results of induction machines operating both as a motor and a generator shows the ability of the algorithm to detect broken rotor bars. 相似文献
9.
Douglas Harman 《Cities》1985,2(3):218-222
Despite the opportunities for increased efficiency and cost savings offered by recent technological developments, many local governments have failed to capitalize on such advances. In the USA, some local governments have joined together in loose associations to share their experiences with new technologies and to develop strategies to take full advantage of developments in information and other technologies. The Virginia Innovation Group is one such group and represents a systematic effort to help local governments fulfil their potential as creative environments for aggressive adaptation of available technologies. As a result, the Virginia Innovation Group and its related groups should serve as a useful example to local governments elsewhere. 相似文献
10.
Reports the death of Roger Todd Davis (1926-2002) and how he contributed to the post-WWII development of primatology and primate laboratories, which are important precursors to the study of modern cognition and cognitive neuroscience. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献