全文获取类型
收费全文 | 883篇 |
免费 | 14篇 |
专业分类
各国政治 | 15篇 |
工人农民 | 6篇 |
世界政治 | 76篇 |
外交国际关系 | 96篇 |
法律 | 569篇 |
中国共产党 | 13篇 |
中国政治 | 88篇 |
政治理论 | 16篇 |
综合类 | 18篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2018年 | 5篇 |
2014年 | 14篇 |
2013年 | 9篇 |
2012年 | 58篇 |
2011年 | 57篇 |
2010年 | 28篇 |
2009年 | 19篇 |
2008年 | 41篇 |
2007年 | 66篇 |
2006年 | 79篇 |
2005年 | 70篇 |
2004年 | 75篇 |
2003年 | 47篇 |
2002年 | 55篇 |
2001年 | 42篇 |
2000年 | 46篇 |
1999年 | 19篇 |
1998年 | 14篇 |
1997年 | 12篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 17篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 6篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1966年 | 1篇 |
1964年 | 5篇 |
1963年 | 6篇 |
1960年 | 1篇 |
1959年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有897条查询结果,搜索用时 15 毫秒
31.
3,4-methylenedioxyamphetamine (MDA) derivatives are increasingly abused central nervous system stimulants with neurotoxic properties. In recent years a number of controlled substance analogs (designer drugs) with high structural variety reached the illegal market making their identification an arduous task. The underivatized compounds give very similar or even virtually identical electron impact mass spectra containing mainly intense C(n)H(2n+2)N(+) immonium ions. Using tandem mass spectrometry (MS-MS) the additional structural information contained in the collision induced dissoziation (CID) mass spectra of molecular ions using electron impact (EI) and especially chemical ionization (CI) allowed an unequivocal differentiation of 18 studied regioisomeric 1-(methylenedioxyphenyl)-2-propanamines and 1-(methylenedioxyphenyl)-2-butanamines.Further synthetic methods are presented for 1-(3,4-methylenedioxyphenyl)-N-propyl-2-butanamine, N-isopropyl-1-(3,4-methylenedioxyphenyl)-2-butanamine and four 1-(2, 3-methylenedioxyphenyl)-2-butanamines. N-alkylated 1-(3, 4-methylenedioxyphenyl)-2-butanamine compounds (e.g. MBDB) are also known to be abused psychoactive agents (entactogenes) without the sympatomimetic effects of the 3,4-methylenedioxyamphetamines. 相似文献
32.
33.
发达国家的大多数人认为,“世界粮食问题”主要是指不发达国家还有很多人在忍饥挨饿.这个问题为什么会持续存在呢? 对世界各国的分析比较表明粮食充裕与人平收入之间有密切关系,在各个国家内部,对家庭消费的研究也表明存在这种密切的关系.这就说明,大多数饥民是贫穷国家的贫民.如此说来,世界粮食问题是贫穷导致的需求不足引起的. 但是,我们也可以从另一个角度来分析一些世界性的数据资料.在一些贫穷国家,没有足够的粮食满足公民的一般需要,许多国家粮食需求总量的增长快于供应总量的增长,过去 相似文献
34.
This article introduces the reader to present conditions and suicide prevention measures in Japan. The suicide rate has increased gradually since the early 1990s, reaching a postwar peak in 1998. The number of suicides has remained at about 30,000 every year since 1998. Middle-aged (55-59 years) and elderly men have especially high suicide rates. In 2002, The Council of Learned People on Measures Against Suicides (organized by the Japanese Ministry of Health, Labor, and Welfare) released its report on national suicide prevention strategies. Although national suicide prevention strategies have just begun to be established, some prefectures or regions have undertaken unique suicide prevention measures. 相似文献
35.
36.
37.
38.
De Greef S Claes P Mollemans W Loubele M Vandermeulen D Suetens P Willems G 《Journal of forensic sciences》2005,50(6):1282-1288
A mobile and fast, semi-automatic ultrasound (US) system was developed for facial soft tissue depth registration. The system consists of an A-Scan ultrasound device connected to a portable PC with interfacing and controlling software. For 52 cephalometric landmarks, the system was tested for repeatability and accuracy by evaluating intra-observer agreement and comparing ultrasound and CT-scan results on 12 subjects planned for craniofacial surgery, respectively. A paired t-test evaluating repeatability of the ultrasound measurements showed 5.7% (n = 3) of the landmarks being significantly different (p < 0.01). US and CT-scan results showed significant differences (p < 0.01) using a Wilcoxon signed rank test analysis for 11.5% (n = 6) of the landmarks. This is attributed to a difference in the volunteer's head position between lying (CT) and sitting (US). Based on these tests, we conclude that the proposed registration system and measurement protocol allows relatively fast (52 landmarks/20 min), non-invasive, repeatable and accurate acquisition of facial soft tissue depth measurements. 相似文献
39.
Jackowski C Römhild W Aebi B Bernhard W Krause D Dirnhofer R 《The American journal of forensic medicine and pathology》2005,26(4):355-359
We present a case of an accidental autoerotic death involving the inhalation of a propane-butane gas mixture, also known as LPG (liquefied petroleum gas). A 19-year-old male was found dead in supine position in his bed in a residential accommodation one day after he was last seen alive. On a personal computer at the end of the bed, a pornographic movie was still running. On his left shoulder, an empty rubber balloon and on the bedside 2 empty "Kisag-Gas" cartridges were found. Toxicologic investigations revealed an intoxication with propane and butane, together with a recent consumption of cannabis. This case report compares the toxicologic findings with other recently published cases, and the theories of the toxic effects are discussed. 相似文献
40.
This study was designed to compare the qualitative results and concentrations of methamphetamine (MA) and its metabolite amphetamine (AP) in head hair and hair collected from different parts of the body (axillae and pubis). Hair from subjects (N = 14) suspected MA users was simultaneously collected. Hair preparation involved washing step, fine cutting, overnight extraction, derivatization by the trifluoroacetic anhydride, and gas chromatography/mass spectrometry (GC/MS) using selective ion monitoring. In this study, we found a good correlation of the qualitative results for MA between head hair and hair on other parts of the body, but there were some differences in concentrations of MA and AP. Namely, the concentrations of MA and AP were higher in axillary and pubic hair than in head hair. 相似文献