全文获取类型
收费全文 | 20386篇 |
免费 | 1749篇 |
国内免费 | 6篇 |
专业分类
22141篇 |
出版年
2022年 | 181篇 |
2021年 | 338篇 |
2020年 | 162篇 |
2019年 | 266篇 |
2018年 | 223篇 |
2017年 | 259篇 |
2016年 | 462篇 |
2015年 | 761篇 |
2014年 | 878篇 |
2013年 | 1080篇 |
2012年 | 1463篇 |
2011年 | 1516篇 |
2010年 | 986篇 |
2009年 | 830篇 |
2008年 | 1267篇 |
2007年 | 1319篇 |
2006年 | 1129篇 |
2005年 | 1127篇 |
2004年 | 1095篇 |
2003年 | 1076篇 |
2002年 | 971篇 |
2001年 | 283篇 |
2000年 | 250篇 |
1999年 | 246篇 |
1998年 | 267篇 |
1997年 | 211篇 |
1996年 | 162篇 |
1995年 | 165篇 |
1994年 | 151篇 |
1993年 | 162篇 |
1992年 | 196篇 |
1991年 | 149篇 |
1990年 | 171篇 |
1989年 | 152篇 |
1988年 | 137篇 |
1987年 | 115篇 |
1986年 | 115篇 |
1985年 | 152篇 |
1984年 | 140篇 |
1983年 | 116篇 |
1982年 | 107篇 |
1981年 | 128篇 |
1980年 | 119篇 |
1979年 | 108篇 |
1978年 | 97篇 |
1977年 | 108篇 |
1976年 | 81篇 |
1974年 | 73篇 |
1973年 | 61篇 |
1972年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
G. Becker 《Biological cybernetics》1977,26(1):41-44
Building of vertical galleries (runways) by termites of the species Heterotermes indicola (Wasmann) is suppressed in the interior area of arrangements of plastic containers with equal groups of termites and takes place preferably at the periphery. This reaction is not induced by chemical, vibrational or thermal influences. Shielding separation by plates of glass, plastic foam or various metals demonstrated, that the influence on activity and directional behaviour is caused by fields produced by the termites. They are most probably alternating electric fields. These biofields act together or, if the direction of the gradients differs, in competition with a weak alternating magnetic field in the air-conditioned experimental room. The centrifugal reaction of the termites to the biofields which do not influence the feeding activity, induces gallery building at the periphery of the nesting area.This paper was presented at the International Congress of Entomology in Washington (D.C.), USA, on August 23, 1976. —Experiments with support by the Deutsche Forschungsgemeinschaft 相似文献
72.
73.
74.
The occurrence of larval Anisakis in North Sea herring was examined during the period 1965-1972 using a sampling method which yielded comparable data for all eight years. Data on abundance of infestation in several herring stocks pointed to remarkable fluctuations over the study period with an increase in the period 1966-1968 followed by a decrease in the period 1968-1972. Of various hypotheses that may explain this situation, it is concluded that changes in the migration behaviour of the herring may be responsible. Other data and statistics are discussed with special reference to variations in infestation level in different samples and to the occurrence of adult nematodes in marine mammals. 相似文献
75.
Y Becker 《Journal of theoretical biology》1978,75(3):339-347
A model is presented for intramolecular recombination of herpesvirus DNA. It is proposed that the terminal repeat sequences of the viral DNA contain insertion sequences which may integrate with homologous repeat sequences between the long (L) and short (S) components. In class 2 herpes-virus DNA (as defined by Honess &; Watson, 1977) in which the repeat sequences flank the S component only, circular-linear DNA molecules can be formed as an intermediate step. Reorientation of the S component leads to the formation of two DNA isomers. In class 3 herpesvirus DNA in which repeat sequences flank both the L and S components, either circular-linear or 8-shaped DNA molecules are proposed as intermediates leading to the formation of four DNA isomers. Fragmentation of the S component could lead to the formation of small circular DNA molecules. 相似文献
76.
Summary Mark-release-recapture experiments performed with natural populations of Drosophila at Mather, California show that flies tend to return to their area of original capture or an area ecologically similar to it. Such habitat choice explains the microgeographic genetic differentiation we observed in the population. This behavioral difference between the flies may have a genetic component or may be environmentally induced. Either way, the results help explain how high levels of genetic variation are maintained by natural selection in these species. 相似文献
77.
78.
Gerard N. Burrow Jeffrey Hopkins Yeshi Dhonden Lobsang Dolma 《The Yale journal of biology and medicine》1978,51(4):441-447
The visit of two Tibetan physicians provided a unique opportunity to gain insight into a practice of medicine very different from that of Western civilization. Initial discussions indicated that the practice of medicine and mysticism were inextricably interwoven in the Tibetan culture. Accordingly, the focus of the study was directed to goiter, which is both common in the Himalayas and easy to define.In Tibetan medical practice, illness is considered to be derived from both proximate and distant causes. Three humors, “wind,” “bile,” and “phlegm” are thought to be responsible for normal mental and physical functions when in balance, but disease when out of balance. Goiter was thought to be due to an imbalance of these humors. The Western discovery that endemic goiter in the Himalayas was due to iodine deficiency explained the proximate cause but did not explain why some individuals have goiter and others do not in the same iodine deficient village. 相似文献
79.
80.