全文获取类型
收费全文 | 9637篇 |
免费 | 201篇 |
国内免费 | 12篇 |
学科分类
工业技术 | 9850篇 |
出版年
2022年 | 85篇 |
2021年 | 113篇 |
2020年 | 69篇 |
2019年 | 104篇 |
2018年 | 107篇 |
2017年 | 114篇 |
2016年 | 135篇 |
2015年 | 121篇 |
2014年 | 150篇 |
2013年 | 459篇 |
2012年 | 260篇 |
2011年 | 360篇 |
2010年 | 340篇 |
2009年 | 309篇 |
2008年 | 348篇 |
2007年 | 314篇 |
2006年 | 268篇 |
2005年 | 287篇 |
2004年 | 213篇 |
2003年 | 235篇 |
2002年 | 227篇 |
2001年 | 175篇 |
2000年 | 187篇 |
1999年 | 160篇 |
1998年 | 681篇 |
1997年 | 506篇 |
1996年 | 359篇 |
1995年 | 287篇 |
1994年 | 249篇 |
1993年 | 255篇 |
1992年 | 119篇 |
1991年 | 108篇 |
1990年 | 121篇 |
1989年 | 126篇 |
1988年 | 119篇 |
1987年 | 90篇 |
1986年 | 82篇 |
1985年 | 109篇 |
1984年 | 120篇 |
1983年 | 91篇 |
1982年 | 75篇 |
1981年 | 74篇 |
1980年 | 85篇 |
1979年 | 82篇 |
1978年 | 93篇 |
1977年 | 127篇 |
1976年 | 209篇 |
1975年 | 61篇 |
1974年 | 63篇 |
1973年 | 58篇 |
排序方式: 共有9850条查询结果,搜索用时 15 毫秒
11.
Socially amoral economic forces now drive health system change. The authors, assisted by a panel of experts on employers, health plans, providers, and consumers, discuss current drivers such as (1) employers' price-focused purchasing, without good quality/value measures; (2) health plans' growing successes and market clout; (3) providers declining prospects and fears about their future; and (4) consumers' worries about less choice. Future influences will include Medicare reforms, better information, and pro-consumer regulation of managed care, as well as rising social distress. The health system's future is now open for resolution in an evolving, imperfect market. 相似文献
12.
The relationship between office size and noise level is one of the most significant, yet least investigated, factors affecting software productivity. According to Tom DeMarco and Tim Lister (1992), US programmers with more than 80 square feet of private, noise-free office space consistently outperform programmers who occupy two- or three-person cubicles. The result was the Santa Teresa Programming Laboratory in San Jose, California, which opened in 1978. The author discusses some requirements of an optimal programming office environment. He considers the effectiveness of home working 相似文献
13.
14.
Text search is a type of strategic reading that involves locating specific goal-relevant information. Previous research has indicated that college and high school students often exhibit inefficient or unsuccessful text-search performance. Consequently, the effects of 2 manipulations on text-search performance were investigated: (1) the presence of indexed terms in a text-search task and (2) the use of a planning prompt before beginning a task. 34 college students engaged in 6 text-search tasks. Half of these tasks contained terms that could be used in an index; half required that a search term be generated. Half of the subjects were randomly assigned to a prompt condition in which they were prompted to plan their search before beginning each task. The results indicated that a planning prompt raised the success level of search performance, as did the presence of terms that were searchable in the textbook's index. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
15.
Abstract: Environmental justice advocates have recently focused attention on cumulative exposure in minority neighborhoods due to multiple sources of pollution. This article uses U.S. EPA's National Air Toxics Assessment (NATA) for 1996 to examine environmental inequality in California, a state that has been a recent innovator in environmental justice policy. We first estimate potential lifetime cancer risks from mobile and stationary sources. We then consider the distribution of these risks using both simple comparisons and a multivariate model in which we control for income, land use, and other explanatory factors, as well as spatial correlation. We find large racial disparities in California's “riskscape” as well as inequalities by other factors and suggest several implications for environmental and land use policy. 相似文献
16.
17.
Nitrification kinetics are important for process design, optimization, and capacity rating of activated sludge wastewater treatment plants. A Water Environment Research Foundation (WERF) project on Methods for Wastewater Characterization in Activated Sludge Modeling (WERF, 2003) focused significantly on the development of procedures for measuring the nitrifier maximum specific growth rate, micro(AUT). In addition, the importance of (and lack of data for) the nitrifier decay rate, b(AUT), was identified. This paper describes three bench-scale methods for measuring micro(AUT): the Low F/M SBR, Washout and High F/M methods. During the WERF project, the importance of pH and temperature control was investigated briefly; this paper summarizes further experimental work performed to address these issues. A summary of micro(AUT) measurements in a number of locations and using the different measurement techniques is provided. 相似文献
18.
RM Bionta G Blewitt CB Bratton D Casper A Ciocio R Claus M Crouch ST Dye S Errede GW Foster W Gajewski KS Ganezer M Goldhaber TJ Haines TW Jones D Kielczewska WR Kropp JG Learned JM LoSecco J Matthews HS Park LR Price F Reines J Schulz S Seidel E Shumard D Sinclair HW Sobel JL Stone L Sulak R Svoboda G Thornton van der Velde JC C Wuest 《Canadian Metallurgical Quarterly》1987,36(1):30-36
19.
Samuel L. Manzello Richard G. Gann Scott R. Kukuck Kuldeep Prasad Walter W. Jones 《火与材料》2007,31(5):297-310
A gypsum wall assembly was exposed to an intense real‐scale compartment fire. For the wall assembly, temperatures were measured at the exposed face, within the stud cavity, and at the unexposed face during the fire exposure. Total heat flux gauges were used to measure the temporal variation of the energy incident on the walls, and cameras, both visual and infrared, were used to image the unexposed face of the wall assembly during the fire exposure. The behaviour of the wall assembly under the fire load is discussed as are current model results for a simulation of the fire test. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
20.
V. Elliott Smith John M. Spurr John C. Filkins Jody J. Jones 《Journal of Great Lakes research》1985,11(3):231-246
Organochlorine analysis was performed on carcasses of 13 diving ducks from a 1981 wintering population that foraged on contaminated sediments in the lower Detroit River. Mean total PCB concentrations were 10 mg/kg for seven lesser scaups (Aythya affinis), 11 mg/kg for three greater scaups (A. marila), and 7.6 mg/kg for three goldeneyes (Bucephala clangula). Highest mean levels of other residues were measured for hexachlorobenzene (1.7 mg/kg) in goldeneyes, and transnonachlor (0.33 mg/kg) and 4,4’-DDE (1.3 mg/kg) in greater scaup. Quantitative analysis of 72 PCB congeners also was applied to water, seston, sediment, benthie oligochaetes, and carp from the same site. Principal congeners in most of the samples included some of the more toxic and persistent PCBs. Results of a multivariate analysis indicated that ratios of more conservative to less conservative PCBs did not vary significantly among ducks (α = .05), but differed from those in carp, oligochaetes, and sediment. For the February through March period of fat mobilization, concentrations of total PCB in lipid were inversely correlated with percent lipid (r = 0.76) in ducks. The percentage of conservative PCBs increased slightly. The distribution and partitioning of organochlorines, including toxic PCB congeners, varied considerably within this water column-sediment-fauna ecosystem. Estimates of toxic exposure based on total PCB values may be unreliable. 相似文献