首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6348篇
  免费   113篇
各国政治   476篇
工人农民   172篇
世界政治   660篇
外交国际关系   455篇
法律   2589篇
中国政治   40篇
政治理论   1995篇
综合类   74篇
  2023年   29篇
  2021年   26篇
  2020年   79篇
  2019年   114篇
  2018年   140篇
  2017年   160篇
  2016年   176篇
  2015年   125篇
  2014年   167篇
  2013年   982篇
  2012年   162篇
  2011年   183篇
  2010年   153篇
  2009年   155篇
  2008年   198篇
  2007年   262篇
  2006年   202篇
  2005年   187篇
  2004年   203篇
  2003年   197篇
  2002年   192篇
  2001年   118篇
  2000年   128篇
  1999年   105篇
  1998年   132篇
  1997年   106篇
  1996年   114篇
  1995年   88篇
  1994年   79篇
  1993年   91篇
  1992年   86篇
  1991年   96篇
  1990年   82篇
  1989年   73篇
  1988年   78篇
  1987年   90篇
  1986年   90篇
  1985年   57篇
  1984年   77篇
  1983年   76篇
  1982年   69篇
  1981年   52篇
  1980年   48篇
  1979年   48篇
  1978年   44篇
  1977年   51篇
  1976年   29篇
  1975年   29篇
  1974年   32篇
  1973年   37篇
排序方式: 共有6461条查询结果,搜索用时 0 毫秒
111.
Innovative handheld technologies are changing the possibilities for public health interventions. The present research describes a preliminary examination of the iPhone? when used as an assessment tool and an enhancement to an evidence-based, in-home child safety intervention. Three families with young children received an augmented version of the Safety module of SafeCare, a home-visiting child maltreatment prevention program. Specifically, parents were trained to use an iPhone to video rooms in their homes, as well as communicate feedback, logistics, and safety content between the home visitor and parent. The effectiveness of iPhone and video was examined using a multiple baseline design across in-home settings replicated across families. Home hazards were reduced dramatically across rooms and across participants. Face-to-face time of the home visitor was progressively reduced and replaced by video data collection. These data suggest smartphones are promising for data collection and for augmenting face-to-face interactions. Implications for reducing costs as smartphones become increasingly ubiquitous and for engaging and retaining participants are discussed.  相似文献   
112.
In this paper we examine the legal aspects of corporate computer usage policies including their creation, management, and their relevance to corporate computer forensic investigations. Misuse of corporate computing facilities cannot only lead to a reduction in employee productivity and network bandwidth, but can also increase the risk of infection of such facilities by computer viruses and other malicious code. Moreover, it may lead to the risk of liability and legal action.  相似文献   
113.
Abstract: Anyone with a computer, scanner, and color printer has the capability for creating documents such as identification cards, passports, and counterfeit currency. Laser desorption mass spectrometry (LDMS) has been demonstrated as a powerful tool for colorant analysis. Inkjet printers are now moving largely toward the use of pigments as colorants; their insolubility makes analysis by simpler methods such as thin‐layer chromatography no longer an option. Recent developments in pigmented inkjet printer inks, such as gloss optimizers that coat pigment particles, may prohibit colorant analysis by LDMS. We demonstrate here that pigments used in inks from two Epson printers can be detected and analyzed by LDMS. Also, LDMS spectra of various colors created using a 4‐cartridge (cyan/magenta/yellow/black, CMYK) inkset are evaluated, to begin to develop an approach for unraveling LDMS data from real samples, to determine the number of inks used by a printer, and the chemical composition of the colorants.  相似文献   
114.
Abstract: A procedure for automated bullet signature identification is described based on topography measurements using confocal microscopy and correlation calculation. Automated search and retrieval systems are widely used for comparison of firearms evidence. In this study, 48 bullets fired from six different barrel manufacturers are classified into different groups based on the width class characteristic for each land engraved area of the bullets. Then the cross‐correlation function is applied both for automatic selection of the effective correlation area, and for the extraction of a 2D bullet profile signature. Based on the cross‐correlation maximum values, a list of top ranking candidates against a ballistics signature database of bullets fired from the same model firearm is developed. The correlation results show a 9.3% higher accuracy rate compared with a currently used commercial system based on optical reflection. This suggests that correlation results can be improved using the sequence of methods described here.  相似文献   
115.
116.
117.
With increasing frequency, relatively small, fragmentary evidence thought to be osseous or dental tissue of human origin is submitted to the forensic laboratory for DNA analysis with the request for positive identification. Prior to performing DNA analysis, however, it is prudent to first perform a presumptive test or "screen" to determine whether the questioned material may be eliminated from further consideration. When material is shown not to be consistent with bone/teeth, DNA testing is not performed. When such determinations cannot be made from gross morphological features, elemental analysis can be indicative. This presumptive test is made possible by applying scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) in conjunction with an X-ray spectral database recently developed by the FBI laboratory. This database includes spectra for many different materials including known examples of bone and tooth from many different contexts and representing the full range of taphonomic conditions. Results of SEM/EDS analysis of evidence can be compared to these standards to determine if they are consistent with bone and/or tooth and, if not, then what the material might represent. Analysis suggests that although the proportions and amounts of calcium and phosphorus are particularly important in differentiating bone and tooth from other materials, other minor differences in spectral profile can also provide significant discrimination. Analysis enables bone and tooth to be successfully distinguished from other materials in most cases. Exceptions appear to be ivory, mineral apatite, and perhaps some types of corals.  相似文献   
118.
119.
Laser desorption mass spectrometry (LDMS) may be used for the detection and identification of dyes found in inks. Naturally-aged and artificially-aged blue and black ballpoint pen inks containing the cationic dye methyl violet were analyzed on paper. The average molecular weight of the dye sample was calculated from LD mass spectral data and plotted versus time. The resulting aging curves demonstrate that, as dye degradation increases, the average molecular weight of the dye decreases. Typical variables involved in ink aging, such as the type of paper and ink formulation, were investigated. Results show that these variables influence the rate of dye degradation. Furthermore, UV accelerated aging has been developed and tested as an alternative to thermal approaches.  相似文献   
120.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号