全文获取类型
收费全文 | 4235篇 |
免费 | 189篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 26篇 |
综合类 | 2篇 |
化学工业 | 792篇 |
金属工艺 | 84篇 |
机械仪表 | 85篇 |
建筑科学 | 187篇 |
矿业工程 | 14篇 |
能源动力 | 130篇 |
轻工业 | 295篇 |
水利工程 | 46篇 |
石油天然气 | 29篇 |
无线电 | 319篇 |
一般工业技术 | 813篇 |
冶金工业 | 980篇 |
原子能技术 | 23篇 |
自动化技术 | 602篇 |
出版年
2023年 | 36篇 |
2022年 | 55篇 |
2021年 | 121篇 |
2020年 | 88篇 |
2019年 | 101篇 |
2018年 | 94篇 |
2017年 | 85篇 |
2016年 | 99篇 |
2015年 | 84篇 |
2014年 | 124篇 |
2013年 | 258篇 |
2012年 | 188篇 |
2011年 | 268篇 |
2010年 | 178篇 |
2009年 | 160篇 |
2008年 | 185篇 |
2007年 | 179篇 |
2006年 | 147篇 |
2005年 | 117篇 |
2004年 | 107篇 |
2003年 | 113篇 |
2002年 | 79篇 |
2001年 | 75篇 |
2000年 | 68篇 |
1999年 | 64篇 |
1998年 | 154篇 |
1997年 | 117篇 |
1996年 | 86篇 |
1995年 | 53篇 |
1994年 | 71篇 |
1993年 | 71篇 |
1992年 | 53篇 |
1991年 | 52篇 |
1990年 | 45篇 |
1989年 | 45篇 |
1988年 | 47篇 |
1987年 | 52篇 |
1986年 | 26篇 |
1985年 | 29篇 |
1984年 | 37篇 |
1983年 | 36篇 |
1982年 | 37篇 |
1981年 | 29篇 |
1980年 | 32篇 |
1979年 | 33篇 |
1978年 | 31篇 |
1977年 | 25篇 |
1976年 | 38篇 |
1975年 | 24篇 |
1973年 | 20篇 |
排序方式: 共有4427条查询结果,搜索用时 683 毫秒
21.
N. R. Bohidar Norman R. Bohidar Nicholas R. Bohidar 《Drug development and industrial pharmacy》1994,20(5):815-839
A discordant observation is a data point whose value is drastically different from that of the rest of the members in the data set. In the context of content uniformity experiments, however, a discordant observation arises in two ways: (i) when the value of an observation is markedly distant from that of the other data points even though it is within the required compendial range, and (ii) when the value of an observation is outside the permissible compendial range. Several statistical tests for detecting one or more discordant observations are presented. Since discordancy distorts the symmetricity of the data, several tests of symmetricity are provided. Tests for detection of group discordancy induced by discordant samples are also included. The compendial requirements are explained in statistical terms. The impact of discordant observations on compendial compliance requirements is assessed. The statistical basis of the construction of compendial limits as well as the assumptions implicit in the construction is elaborated. The results of the statistical analysis of three content uniformity studies are appropriately interpreted. 相似文献
22.
23.
Mulcahy Nicholas J.; Call Josep; Dunbar Robin I. M. 《Canadian Metallurgical Quarterly》2005,119(1):23
Two important elements in problem solving are the abilities to encode relevant task features and to combine multiple actions to achieve the goal. The authors investigated these 2 elements in a task in which gorillas (Gorilla gorilla) and orangutans (Pongo pygmaeus) had to use a tool to retrieve an out-of-reach reward. Subjects were able to select tools of an appropriate length to reach the reward even when the position of the reward and tools were not simultaneously visible. When presented with tools that were too short to retrieve the reward, subjects were more likely to refuse to use them than when tools were the appropriate length. Subjects were proficient at using tools in sequence to retrieve the reward. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
24.
25.
Remote sensing of species mixtures in conifer plantations using LiDAR height and intensity data 总被引:2,自引:0,他引:2
Daniel N.M. Donoghue Peter J. Watt Nicholas J. Cox Jimmy Wilson 《Remote sensing of environment》2007,110(4):509-522
In even-aged, single species conifer plantations LiDAR height data can be modelled to provide accurate estimates of tree height and volume. However, it is apparent that growth models developed for single species stands are not directly transferable to a more general situation of mixed species plantations. This paper evaluates the ability of small footprint, dual-return, pulsed airborne LiDAR data to estimate the proportion of the productive species when mixed with a nurse crop in closed canopy plantations. A study area located in Galloway Forest District in Scotland is used as an example of Lodgepole pine and Sitka spruce mixed plantation; this area contains good examples of a wide range of pure and mixed species plantation types. Three species groups are studied: areas of pure Sitka spruce, areas of pure Lodgepole pine and areas where the two species have been planted together. Two approaches are assessed for detection of plantation mixtures: the first uses LiDAR intensity data to separate spruce and pine species and the second uses LiDAR-derived canopy density measures, coefficient of variation, skewness, percent of ground returns (which provides a measure of canopy openness) and the mean canopy height, which enables areas with height variations to be identified. From analysis of LiDAR data extracted from 54 study plots using logistic regression, the coefficient of variation and LiDAR intensity data provide the most useful predictors of the proportion of spruce in a pine/spruce mixture with coefficients of determination (R2) of 0.914 and 0.930 respectively. The method could be developed as a mapping tool, which in combination with existing inventory data should help to improve timber volume forecasting for mixed species even-aged plantations. 相似文献
26.
Nicholas HOENICH 《Hemodialysis international. International Symposium on Home Hemodialysis》2007,11(Z1):S26-S31
The extracorporeal circuit in hemodialysis and related therapies facilitates passage of blood to and from the patient and forms an integral link with the safety systems of the proportioning system. Historically, elements of the circuit were subject to problems such as spallation introduced by the blood pump and plasticizer from the tubing sets leaching into the blood. Many of these early issues have been largely resolved, although there is still potential for further improvement and innovation. The introduction of such improvements and innovations into clinical practice is critically dependent upon their cost and benefit to patient and renal unit staff. 相似文献
27.
Nicholas Cravotta 《电子设计技术》2006,13(12):86-86,88,90
JTRS正致力于将可互换SDR(软件无线电)带入军用领域。但SDR对商业应用是否也是足够好的选择呢?SDR(软件无线电)并不是一种新技术。过去业界就已经尝试实现SDR,但都没有达到目标。最近激发起对SDR兴趣的是创新性软硬件技术的出现,这些技术能够以市场可承受的价格提供足够的灵活性、性能和功率效率。例如,宽带变换器现在可以工作在宽频率范围内,根据一种特定的位分辨率处理接收到的波形,而高频处理器可以直接与信号工作,从而省掉IF(中频)级,并降低成本。 相似文献
28.
The long‐term consequences of the sale of public sector dwellings to sitting tenants are under‐researched; in particular, the experience of tenant purchasers in the housing market subsequent to purchase is little known. This paper reports research designed to fill this gap in knowledge. Over 200 tenants who had bought their dwelling from the Scottish Special Housing Association and subsequently resold on the open market were traced using the Register fo Sasines and the Land Register and interviewed. Most had made considerable capital gains on resale and had used some of the realised capital to trade up in the housing market. They were, on average, slightly more affluent and younger than sitting tenant purchasers generally; they represented a group of households who were privileged within the public sector through living as tenants in the best stock and who were enabled by the Right to Buy to convert that good luck into hard cash and move into mainstream owner occupation. This good luck compounded the advantaged position vis‐à‐vis other tenants that they enjoyed in the labour market. 相似文献
29.
Managed care has become the dominant economic force in health care delivery and has challenged many of professional psychology's training concepts and cherished attitudes. Organized psychology has not kept pace with the rapid industrialization of health care during the past decade and has been overlooked as a participant in health economic decisions. A number of changes need to be made in professional education and training if psychology is to be a major player in the new health systems. Additionally, professional psychologists must reexamine some of their most generally accepted attitudes and beliefs if they are to survive. These are described with a number of recommendations for the survival of an embattled profession. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
30.