全文获取类型
收费全文 | 4998篇 |
免费 | 201篇 |
专业分类
各国政治 | 289篇 |
工人农民 | 126篇 |
世界政治 | 503篇 |
外交国际关系 | 314篇 |
法律 | 2196篇 |
中国政治 | 27篇 |
政治理论 | 1684篇 |
综合类 | 60篇 |
出版年
2021年 | 26篇 |
2020年 | 54篇 |
2019年 | 62篇 |
2018年 | 108篇 |
2017年 | 135篇 |
2016年 | 170篇 |
2015年 | 107篇 |
2014年 | 92篇 |
2013年 | 768篇 |
2012年 | 137篇 |
2011年 | 125篇 |
2010年 | 131篇 |
2009年 | 147篇 |
2008年 | 142篇 |
2007年 | 157篇 |
2006年 | 167篇 |
2005年 | 162篇 |
2004年 | 153篇 |
2003年 | 154篇 |
2002年 | 145篇 |
2001年 | 85篇 |
2000年 | 103篇 |
1999年 | 92篇 |
1998年 | 108篇 |
1997年 | 91篇 |
1996年 | 57篇 |
1995年 | 85篇 |
1994年 | 77篇 |
1993年 | 80篇 |
1992年 | 82篇 |
1991年 | 65篇 |
1990年 | 59篇 |
1989年 | 74篇 |
1988年 | 74篇 |
1987年 | 85篇 |
1986年 | 77篇 |
1985年 | 80篇 |
1984年 | 68篇 |
1983年 | 59篇 |
1982年 | 61篇 |
1981年 | 60篇 |
1980年 | 43篇 |
1979年 | 48篇 |
1978年 | 42篇 |
1977年 | 39篇 |
1976年 | 28篇 |
1975年 | 28篇 |
1974年 | 27篇 |
1973年 | 26篇 |
1969年 | 23篇 |
排序方式: 共有5199条查询结果,搜索用时 0 毫秒
271.
Dried, treated wood was sealed with Thompson's WaterSeal "Clear Multi-Surface Waterproofer" and exposed to outdoor, summer conditions. Sections of the sealed wood were then periodically tested and analyzed in accordance with ASTM methods. The WaterSeal contained a medium petroleum distillate (MPD) as a solvent for a wax. The treated lumber contained a background of aldehydes that could mimic a dearomatized MPD if not carefully investigated by the analyst. The MPD of the WaterSeal was detectable 14 days, but not 27 days after application with exposure to relatively hot, dry and sunny weather conditions. The test was repeated with the MPD detectable 16 days, but not 20 days after application with exposure to cooler and wetter weather conditions. The testing demonstrates the need for a thorough and complete investigation by the fire investigator and the submission of comparison samples to the laboratory. 相似文献
272.
Latkoczy C Becker S Dücking M Günther D Hoogewerff JA Almirall JR Buscaglia J Dobney A Koons RD Montero S van der Peijl GJ Stoecklein WR Trejos T Watling JR Zdanowicz VS 《Journal of forensic sciences》2005,50(6):1327-1341
Forensic analysis of glass samples was performed in different laboratories within the NITE-CRIME (Natural Isotopes and Trace Elements in Criminalistics and Environmental Forensics) European Network, using a variety of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) systems. The main objective of the interlaboratory tests was to cross-validate the different combinations of laser ablation systems with different ICP-MS instruments. A first study using widely available samples, such as the NIST SRM 610 and NIST SRM 612 reference glasses, led to deviations in the determined concentrations for trace elements amongst the laboratories up to 60%. Extensive discussion among the laboratories and the production of new glass reference standards (FGS 1 and FGS 2) established an improved analytical protocol, which was tested on a well-characterized float glass sample (FG 10-1 from the BKA Wiesbaden collection). Subsequently, interlaboratory tests produced improved results for nearly all elements with a deviation of < 10%, demonstrating that LA-ICP-MS can deliver absolute quantitative measurements on major, minor and trace elements in float glass samples for forensic and other purposes. 相似文献
273.
Ecke DJ Sampath R Willett P Samant V Massire C Hall TA Hari K McNeil JA Büchen-Osmond C Budowle B 《Journal of forensic sciences》2005,50(6):1380-1385
Infectious microorganisms are important to multiple communities engaged in biodefense and biosecurity, including the agencies responsible for health, defense, law enforcement, agriculture, and drug and food safety. Many agencies have created lists of high priority infectious microorganisms to prioritize research efforts or to formally control the possession and distribution of specific organisms or toxins. However, the biological classification of infectious microorganisms is often complex and ambiguous, leading to uncertainty and confusion for scientists involved in biosecurity work. To address this problem, we created a database, known as the Microbial Rosetta Stone, which resolves many of these ambiguities and includes links to additional information on the microbes, such as gene sequence data and scientific literature. Here we discuss the efforts to coordinate organism names from pathogen lists from various governmental agencies according to biological relatedness and show the overlap of high-priority organisms from multiple agencies. To our knowledge, this is the first comprehensive coordination of pathogens, synonyms, and correct taxonomic names. The organized tables and visual aids are freely available at http://www.microbialrosettastone.com. This website provides a single location where access to information on a broad range of disease-causing organisms and toxins is available to members of the biosecurity community. 相似文献
274.
There have long been calls for the reduction of coercion in treating civilly committed psychiatric patients. The present study assessed whether a minor procedural change intended to reduce the adversarial nature of the treatment process would have a positive impact. Results suggested that the change in procedure had a positive effect for the most direct outcome variables but results were more mixed for the indirect outcome variables. Nonetheless, overall indications were that the change of procedure affected patient outcome. 相似文献
275.
Four reality monitoring variables were used to discriminate suspect from foil identifications in 183 actual criminal cases. Four hundred sixty-one identification attempts based on five and six-person lineups were analyzed. These identification attempts resulted in 238 suspect identifications and 68 foil identifications. Confidence, automatic processing, eliminative processing and feature use comprised the set of reality monitoring variables. Thirty-five verbal confidence phrases taken from police reports were assigned numerical values on a 10-point confidence scale. Automatic processing identifications were those that occurred “immediately” or “without hesitation.” Eliminative processing identifications occurred when witnesses compared or eliminated persons in the lineups. Confidence, automatic processing and eliminative processing were significant predictors, but feature use was not. Confidence was the most effective discriminator. In cases that involved substantial evidence extrinsic to the identification 43% of the suspect identifications were made with high confidence, whereas only 10% of the foil identifications were made with high confidence. The results of a laboratory study using the same predictors generally paralleled the archival results. Forensic implications are discussed. 相似文献
276.
The solution parameters associated with gradient elution reversed phase high-performance liquid chromatography (HPLC) were characterized by evaluating the electrospray ionization mass spectrometry (ESIMS) response of selected smokeless powder additives. Using direct liquid infusion, the positive ion ESIMS responses were determined for three general classes of powder constituents: dialkylphthalate acid esters, N,N'-dialkyl-N,N'-diphenyl urea based stabilizers and nitroso-, nitro-, and dinitro- derivatives of diphenylamine. The relative ESIMS intensities of the powder components were investigated as a function of three solution parameters: ammonium acetate concentration, pH, and percent methanol. The effect of the ammonium acetate concentration demonstrates that the electrolyte is required for efficient ionization and the ESIMS intensity was optimal at a concentration of 2mM for the selected compounds, except 2,4'-dinitrodiphenylamine. The aqueous solution pH, corresponding to the available protons in solution, did not have a significant effect on the ESIMS intensity of the analytes. The percent methanol was evaluated with both decreasing and constant electrolyte concentrations to demonstrate the effects of droplet stability and ion transfer into the gas phase. These findings were applied to the analysis of the selected smokeless powder additives using HPLC-ESIMS to illustrate increased sensitivity for the protonated molecules. 相似文献
277.
278.
Public Choice - The tax rule suggested by Groves and Ledyard is certainly an ingenious one, although there is no indication as to how one might fall upon that specific scheme. If offers Pareto... 相似文献
279.
280.
Robert L. Llneberry 《政策研究评论》1985,4(3):407-411
Policy scientists can make important contributions to the study of policy distribution, a question that is likely to be among the most crucial national issues to be discussed throughout this decade. One aspect of this question that has been neglected is the theoretical assumption associated with public choice theory that politicians, once elected, will reward their supporters through the distribution of policy benefits. However, empirical research indicates that policy benefits seldom are distributed in this way. Instead, politicians follow the principle of universalism. In league with bureaucracies and policy communities, politicians define need and then ask bureaucracies to allocate benefits. This makes politicians roles as distributors of policy very different than simplistic models suggest. 相似文献