全文获取类型
收费全文 | 1892篇 |
免费 | 96篇 |
专业分类
各国政治 | 167篇 |
工人农民 | 64篇 |
世界政治 | 193篇 |
外交国际关系 | 163篇 |
法律 | 753篇 |
中国政治 | 22篇 |
政治理论 | 604篇 |
综合类 | 22篇 |
出版年
2023年 | 10篇 |
2022年 | 6篇 |
2021年 | 16篇 |
2020年 | 33篇 |
2019年 | 59篇 |
2018年 | 55篇 |
2017年 | 73篇 |
2016年 | 98篇 |
2015年 | 56篇 |
2014年 | 70篇 |
2013年 | 335篇 |
2012年 | 59篇 |
2011年 | 53篇 |
2010年 | 57篇 |
2009年 | 65篇 |
2008年 | 67篇 |
2007年 | 78篇 |
2006年 | 78篇 |
2005年 | 70篇 |
2004年 | 52篇 |
2003年 | 71篇 |
2002年 | 66篇 |
2001年 | 34篇 |
2000年 | 49篇 |
1999年 | 33篇 |
1998年 | 48篇 |
1997年 | 28篇 |
1996年 | 32篇 |
1995年 | 31篇 |
1994年 | 22篇 |
1993年 | 15篇 |
1992年 | 21篇 |
1991年 | 7篇 |
1990年 | 20篇 |
1989年 | 6篇 |
1988年 | 22篇 |
1987年 | 15篇 |
1986年 | 5篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1975年 | 3篇 |
1970年 | 3篇 |
1965年 | 2篇 |
1964年 | 2篇 |
排序方式: 共有1988条查询结果,搜索用时 0 毫秒
271.
Anthony A. Braga David M. Hureau Andrew V. Papachristos 《Journal of Quantitative Criminology》2014,30(1):113-139
Objectives
The relatively weak quasi-experimental evaluation design of the original Boston Operation Ceasefire left some uncertainty about the size of the program’s effect on Boston gang violence in the 1990s and did not provide any direct evidence that Boston gangs subjected to the Ceasefire intervention actually changed their offending behaviors. Given the policy influence of the Boston Ceasefire experience, a closer examination of the intervention’s direct effects on street gang violence is needed.Methods
A more rigorous quasi-experimental evaluation of a reconstituted Boston Ceasefire program used propensity score matching techniques to develop matched treatment gangs and comparison gangs. Growth-curve regression models were then used to estimate the impact of Ceasefire on gun violence trends for the treatment gangs relative to comparisons gangs.Results
This quasi-experimental evaluation revealed that total shootings involving Boston gangs subjected to the Operation Ceasefire treatment were reduced by a statistically-significant 31 % when compared to total shootings involving matched comparison Boston gangs. Supplementary analyses found that the timing of gun violence reductions for treatment gangs followed the application of the Ceasefire treatment.Conclusions
This evaluation provides some much needed evidence on street gang behavioral change that was lacking in the original Ceasefire evaluation. A growing body of scientific evidence suggests that jurisdictions should adopt focused deterrence strategies to control street gang violence problems. 相似文献272.
Kristopher D. Wisniewski Ph.D. Nicholas Cooper M.Sc. Vivienne Heaton Ph.D. Colin Hope B.Sc.; M.Sc. Duncan Pirrie Ph.D. Andrew J. Mitten M.Geo. Jamie K. Pringle Ph.D. 《Journal of forensic sciences》2019,64(5):1530-1539
Police witness intelligence stated a murdered adult male “Fred” had been vertically buried in wooded hilly terrain 30 years ago in the Midlands, U.K. Conventional search methods were unsuccessful; therefore, the police requested a geophysical investigation to be undertaken to determine whether “Fred” could be detected. A multiphased geophysical approach was conducted, using bulk ground conductivity and metal detectors, then follow‐up magnetics and ground penetrating radar (GPR) survey profiles on electromagnetic (EM) anomalous areas. A tight grid pattern was used to account for the reduced target size. Relatively high‐resolution EM and GPR techniques were determined optimal for this terrain and sandy soil. Geophysical anomalies were identified and the most promising intrusively investigated, and this was found to be a large boulder and tree roots. Study implications suggest careful multiphase geophysical surveys are best practice and give confidence in cold case searches. This study yielded a no‐body result, effectively saving police time and costs from further investigations. 相似文献
273.
274.
275.
Organic impurity profiling of fentanyl samples associated with recent clandestine laboratory methods
Steven G. Toske PhD Jennifer R. Mitchell MS James M. Myslinski PhD Andrew J. Walz PhD David B. Guthrie PhD Elizabeth M. Guest PhD Charlotte A. Corbett PhD Emily D. Lockhart MS 《Journal of forensic sciences》2023,68(5):1470-1483
Nearly a decade ago, fentanyl reappeared in the United States illicit drug market. In the years since, overdose deaths have continued to rise as well as the amount of fentanyl seized by law enforcement agencies. Research surrounding fentanyl production has been beneficial to regulatory actions and understanding illicit fentanyl production. In 2017, the Drug Enforcement Administration (DEA) began collecting seized fentanyl samples from throughout the United States to track purity, adulteration trends, and synthetic impurity profiles for intelligence purposes. The appearance of a specific organic impurity, phenethyl-4-anilino-N-phenethylpiperidine (phenethyl-4-ANPP) indicates a shift in fentanyl production from the traditional Siegfried and Janssen routes to the Gupta-patent route. Through a collaboration between the DEA and the US Army's Combat Capabilities Development Command Chemical Biological Center (DEVCOM CBC), the synthesis of fentanyl was investigated via six synthetic routes, and the impurity profiles were compared to those of seized samples. The synthetic impurity phenethyl-4-ANPP was reliably observed in the Gupta-patent route published in 2013, and its structure was confirmed through isolation and structure elucidation. Organic impurity profiling results for illicit fentanyl samples seized in late 2021 have indicated yet another change in processing with the appearance of the impurity ethyl-4-anilino-N-phenethylpiperidine (ethyl-4-ANPP). Through altering reagents traditionally used in the Gupta-patent route, the formation of this impurity was determined to occur through a modification of the route as originally described in the Gupta patent. 相似文献
276.
Kayla E. Watson MSc Bailey J. Henwood MSc Katherine Hewins PhD Andrew Roberts MSc Rachael Hazael PhD 《Journal of forensic sciences》2023,68(4):1121-1132
Identifying failure mechanisms in skeletal tissue allows a deeper understanding of the effects of specific projectile impacts on bone. While ballistic trauma in flat bones is largely researched, knowledge of how long bones react to gunshot impacts is limited in the literature. The impacts of deforming ammunition appear to produce higher levels of fragmentation; however, these have not been studied in depth. This study compares the damage to femora bone by HP 0.357 and 9 mm projectiles constructed with both full and semi-metal jackets. Impact experiments were undertaken on a single-stage light gas gun involving the use of a high-speed video camera and full reconstruction of the bones to ascertain fracture patterns occurring in the femora. Higher degrees of fragmentation are likened to the presence of semi-jacketed HP projectiles than jacketed HP projectiles. The observations of external facing beveled edges are believed to be associated with the increased separation of the jacket and lead core of projectiles. Additionally, experimentation has shown that the amount of kinetic energy lost postimpact is likely related to the presence or the absence of a metal jacket on an HP projectile. The observed data, therefore, suggest that the composition, rather than the configuration, of a projectile affects the type and extent of the damage. 相似文献
277.
278.
279.
280.
AbstractDespite an overall decrease in residential mobility after the 2007 housing crisis, many households, particularly those that are low income, continue to move in pursuit of a better life. Traditional theories of residential mobility suggest that mobility will occur when housing and transportation costs are cumulatively greater than the cost of moving to a new location. At the same time, the influence of these factors is not likely to be uniform across geographic contexts or for moves up or down the metropolitan hierarchy. Our analysis examines how well affordability measures explain patterns of county-level residential mobility. Specifically, we contrast conventional measures of affordability focused on the ratio of income to housing expense with measures of location affordability that factor in both housing and transportation costs. We find that whereas households tend to move from lower to higher cost locations, transit affordability at the destination plays an important role in mobility decisions. 相似文献