全文获取类型
收费全文 | 17015篇 |
免费 | 1364篇 |
国内免费 | 16篇 |
出版年
2022年 | 105篇 |
2021年 | 230篇 |
2020年 | 142篇 |
2019年 | 162篇 |
2018年 | 277篇 |
2017年 | 288篇 |
2016年 | 476篇 |
2015年 | 738篇 |
2014年 | 789篇 |
2013年 | 976篇 |
2012年 | 1282篇 |
2011年 | 1321篇 |
2010年 | 806篇 |
2009年 | 681篇 |
2008年 | 981篇 |
2007年 | 1007篇 |
2006年 | 945篇 |
2005年 | 903篇 |
2004年 | 791篇 |
2003年 | 761篇 |
2002年 | 734篇 |
2001年 | 231篇 |
2000年 | 220篇 |
1999年 | 218篇 |
1998年 | 141篇 |
1997年 | 121篇 |
1996年 | 106篇 |
1995年 | 111篇 |
1994年 | 87篇 |
1993年 | 90篇 |
1992年 | 123篇 |
1991年 | 100篇 |
1990年 | 79篇 |
1989年 | 107篇 |
1988年 | 102篇 |
1987年 | 85篇 |
1986年 | 80篇 |
1985年 | 95篇 |
1984年 | 104篇 |
1983年 | 93篇 |
1982年 | 97篇 |
1981年 | 89篇 |
1980年 | 83篇 |
1979年 | 65篇 |
1978年 | 72篇 |
1977年 | 64篇 |
1976年 | 72篇 |
1975年 | 66篇 |
1974年 | 74篇 |
1973年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
11.
A group of captive chimpanzees, consisting of one adult male and three mother/infant pairs, was systematically observed over a 15-month period. Over 200 hr of data were collected, using both sequential and time sampling techniques, and compared to the available data on wild chimps. Unlike many captive groups, most behavior patterns were remarkably similar, both qualitatively and quantitatively, to that of wild chimpanzees including: play, grooming, infant sexual development, tool use, food sharing, prosocial partner preferences, and aggressive displays. 相似文献
12.
A. Klockow-Beck A. Nick St. Geisshuesler D. Schaufelberger 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1998,720(1-2):141-151
A capillary electrophoresis (CE) method has been developed as an alternative method for the determination of the inorganic degradation products sulfate and sulfamate in topiramate drug product and drug substance, currently performed by ion chromatography. The anions are separated in a background electrolyte containing potassium chromate and boric acid, followed by indirect UV detection. By adding tetradecyltrimethylammonium bromide to the electrolyte, analysis is performed under co-electroosmotic flow conditions. Variations in injection volumes and migration times are compensated for by use of an internal standard. The validation of the method, which was performed according to ICH guidelines (International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use) [1], comprises specificity, accuracy, linearity, precision, sensitivity and robustness. In addition, the results of an actual tablet sample analysis obtained by this CE method are statistically shown to be in close agreement with those obtained by an ion chromatographic method. 相似文献
13.
Two methods were used to radioiodinate sea urchin sperm: lactoperoxidase-glucose oxidase and Iodo-Gen. Following iodination the sperm are viable, they undergo the acrosome reaction, and they fertilize eggs. Of the radioactivity associated with the labeled sperm, 28–50% is presumed to be free 125I?, 37–47% is incorporated in lipid, and 8–15% is in trypsin-digestible material believed to be protein. Digestion of the labeled, living sperm with trypsin removes 95.6–99.5% of the macromolecular label (the cells are alive after digestion) suggesting that almost all the protein label is on the external surface of the cell. Thin-layer chromatography of the lipid fraction shows that the major membrane phospholipids and cholesterol are labeled. SDS-PAGE analysis shows the protein-incorporated 125I is distributed among four glycoproteins of >250K, 84K, 64K, and 52K dalton apparent molecular weight. Twenty-eight percent of the total protein (trypsin-digestible) label is in the 84K component and 46% in the 64K band. Although both molecules contain much of the label, they are relatively minor components of the TX-100 extract of sperm. The methods outlined will be useful in determining the role of sperm surface components in fertilization. 相似文献
14.
15.
In this paper we propose an instrument for collecting sensitive data that allows for each participant to customize the amount of information that she is comfortable revealing. Current methods adopt a uniform approach where all subjects are afforded the same privacy guarantees; however, privacy is a highly subjective property with intermediate points between total disclosure and non-disclosure: each respondent has a different criterion regarding the sensitivity of a particular topic. The method we propose empowers respondents in this respect while still allowing for the discovery of interesting findings through the application of well-known inferential procedures. 相似文献
16.
17.
18.
Household‐level correlates of children's physical activity levels in and across 12 countries 下载免费PDF全文
Deirdre M. Harrington Fiona Gillison Stephanie T. Broyles Jean‐Philippe Chaput Mikael Fogelholm Gang Hu Rebecca Kuriyan Anura Kurpad Allana G. LeBlanc Carol Maher Jose Maia Victor Matsudo Timothy Olds Vincent Onywera Olga L. Sarmiento Martyn Standage Mark S. Tremblay Catrine Tudor‐Locke Pei Zhao Peter T. Katzmarzyk for the ISCOLE Research Group 《Obesity (Silver Spring, Md.)》2016,24(10):2150-2157
19.
Risk assessment is part of the risk analysis process as it is used in veterinary medicine to estimate risks related to international trade and food safety. Data from monitoring and surveillance systems (MO&SS) are used throughout the risk assessment process for hazard identification, release assessment, exposure assessment and consequence assessment. As the quality of risk assessments depends to a large extent on the availability and quality of input data, there is a close relationship between MO&SS and risk assessment. In order to improve the quality of risk assessments, MO&SS should be designed according to minimum quality standards. Second, recent scientific developments on state-of-the-art design and analysis of surveys need to be translated into field applications and legislation. Finally, knowledge about the risk assessment process among MO&SS planners and managers should be promoted in order to assure high-quality data. 相似文献
20.