全文获取类型
收费全文 | 4742篇 |
免费 | 470篇 |
专业分类
5212篇 |
出版年
2021年 | 41篇 |
2019年 | 39篇 |
2018年 | 35篇 |
2017年 | 38篇 |
2016年 | 55篇 |
2015年 | 102篇 |
2014年 | 137篇 |
2013年 | 167篇 |
2012年 | 200篇 |
2011年 | 214篇 |
2010年 | 162篇 |
2009年 | 141篇 |
2008年 | 191篇 |
2007年 | 207篇 |
2006年 | 215篇 |
2005年 | 183篇 |
2004年 | 207篇 |
2003年 | 208篇 |
2002年 | 186篇 |
2001年 | 120篇 |
2000年 | 107篇 |
1999年 | 114篇 |
1998年 | 96篇 |
1997年 | 55篇 |
1996年 | 69篇 |
1995年 | 53篇 |
1994年 | 55篇 |
1993年 | 60篇 |
1992年 | 72篇 |
1991年 | 86篇 |
1990年 | 80篇 |
1989年 | 47篇 |
1988年 | 79篇 |
1987年 | 49篇 |
1986年 | 48篇 |
1985年 | 74篇 |
1984年 | 58篇 |
1983年 | 48篇 |
1982年 | 56篇 |
1981年 | 47篇 |
1980年 | 46篇 |
1979年 | 40篇 |
1977年 | 47篇 |
1976年 | 42篇 |
1975年 | 36篇 |
1974年 | 48篇 |
1972年 | 41篇 |
1971年 | 35篇 |
1969年 | 32篇 |
1968年 | 37篇 |
排序方式: 共有5212条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Arnold N. Onyango 《Chemistry and physics of lipids》2012,165(7):777-786
Small reactive carbonyl compounds (RCCs) such as formaldehyde, acetaldehyde, acrolein, crotonaldehyde, glyoxal, methylglyoxal, glycolaldehyde, glycidaldehyde, and 2-butene-1,4-dial are involved in carbonyl and oxidative stress-related physiological disorders. While some evidence indicates that lipid oxidation could be an important source of these compounds in vivo, this has sometimes been doubted because the mechanisms of their formation thereby are poorly understood. Here, representative literature supporting the significant formation of these compounds during lipid oxidation under physiologically relevant conditions are highlighted, and the strengths and weaknesses of previously proposed mechanisms of their formation thereby are considered. In addition, based on the current understanding of lipid oxidation chemistry, some new pathways of their formation are suggested. The suggested pathways also generate 4-hydroxy-2-butenal, a precursor of the carcinogen furan, whose endogenous formation in tissues has hitherto not been seriously considered. 相似文献
5.
6.
D. W. T. Crompton S. E. Arnold D. E. Walters A. E. Keymer R. W. Marrs 《Journal of Zoology》1988,214(2):313-324
Aspects of the reproductive performance of Moniliformis moniliformis were investigated in rats allowed to feed ad libitum on a purified diet containing 1% (w/w) fructose as an energy source for the worms. The rats were infected with either 10, 20, 40 or 80 cystacanths each with the intention of investigating density-dependent effects on worm fecundity. The establishment of the worms in the gut was independent of dose, but survival, growth and reproductive performance generally were shown to be related to the infective dose given to the rats. The effects could not be related to the absolute numbers of worms present in the small intestine at post-mortem examination. In general, some unidentified regulatory process appeared to operate to create severe density-dependence in survival so that surviving parasites were not present in numbers expected to generate competition. Attainment of sexual maturity, growth and the production of mature eggs by worms from rats given doses of 80 cystacanths each were delayed compared with worms from rats given the other doses, but eventually the performance of the high-dose worms caught up. Worms attached more anteriorly in the small intestine grew bigger and produced more mature eggs. Possible mechanisms responsible for the observed effects are discussed. 相似文献
7.
Cytogenetic studies were done on bone marrow cells and peripheral lymphocytes of four patients (three with acute nonlymphocytic leukemia, one with aplastic anemia) at various intervals up to 861 days after total-body X irradiation (TBI) at doses between 4.5 and 10 Gy (450-1000 rad) followed by syngeneic or allogeneic bone marrow transplantation. Whereas no radiation-induced aberrations could be found in the bone marrow, apart from a transient finding in the patient with the lowest radiation dose, aberrant metaphases were seen in the peripheral lymphocytes of three patients in the range from 2.5 to 46% even at 861 days after the exposure. There were no demonstrable aberrations related to TBI in the only patient developing graft-versus-host disease. The dicentric yield as determined in the aberrant metaphases with 46 centromeres ranged between 3.4 +/- 1.3 and 4.9 +/- 0.4. In one patient it was demonstrated by BUdR-labeling that after 10 Gy (1000 rad) TBI the surviving and heavily damaged lymphocytes can go into cell cycle and reach at least the third mitosis. The percentage of aberrant cells diminished by about 25% at each mitotic division. 相似文献
8.
9.
Arnold Simanowitz 《BMJ (Clinical research ed.)》1988,297(6641):133-134
10.
Arnold ten Thoren und Hans-Heiner Bergmann 《Journal of Ornithology》1987,128(2):181-207
Zusammenfassung Das Lautrepertoire von sechs handaufgezogenen Graugänsen wurde in individuellen Längsschnitten vom Schlüpfen bis zum Alter von 100 Tagen mit sonagraphischer Methode analysiert. Die Einteilung des Repertoires erfolgte nach drei verschiedenen Kriterien: Klang, Sonagramm und Kontext. Im jugendlichen Repertoire ließen sich 4 Rufklassen voneinander trennen. Im Laufe der Jugendentwicklung veränderten sich vor allem die phonetischen Parameter der Rufe, während die syntaktischen weitgehend konstant blieben. Nach einem Anstieg in der ersten Woche fiel die Tonhöhe der Rufe bei allen untersuchten Individuen und Rufklassen gleichmäßig ab. Der Stimmbruch, meßbar an der Zunahme geräuschhafter Komponenten, war ein kontinuierlicher, langfristiger Prozeß. Die Individualität war nicht in einem einzelnen, wohl aber in der Kombination mehrerer Merkmale faßbar. Die Geschlechter waren schon früh an Unterschieden in der Tonhöhe erkennbar. An sonstigen ontogenetischen Veränderungen innerhalb des Untersuchungszeitraumes konnten die Erweiterung des Repertories durch Aufspaltung und Reifung sowie ein möglicher Verlust von Rufklassen beobachtet werden.
Herrn Dr. Hans Löhrl zum 75. Geburtstag gewidmet 相似文献
Juvenile development of vocalizations in Greylag Geese (Anser anser)
Summary The juvenile vocal development of six Greylag Geese from hatching up to the age of 100 days was analysed by using sonagraphic methods. The calls were classified by means of the acoustic phenomenon, sonagrams, and context criteria. The juvenile repertoire included four main call types. During ontogeny, changes of call parameters mainly referred to phonetic characteristics, whereas syntactic parameters remained more or less constant. The frequency pitch of calls changed to higher levels during the first week of development while in older goslings this parameter decreased constantly. This held true for each individual and call type. Breaking of the voice, defined as an increment of noisy parts in the vocalizations, is described as a continuous long term process. Structural individuality of calls apparently was not based on one single parameter, but on the combination of several ones. Sex differences were found in the pitch of vocalizations, correlating with different body weights of male and female geese. Additional developmental processes of the vocal repertoire included differentiation, maturation of new call types, and apparent suppression of juvenile ones. The functional organization of the juvenile call system in Greylags is discussed.
Herrn Dr. Hans Löhrl zum 75. Geburtstag gewidmet 相似文献