全文获取类型
收费全文 | 36795篇 |
免费 | 4415篇 |
国内免费 | 10篇 |
出版年
2021年 | 400篇 |
2019年 | 332篇 |
2018年 | 401篇 |
2017年 | 367篇 |
2016年 | 643篇 |
2015年 | 1048篇 |
2014年 | 1163篇 |
2013年 | 1500篇 |
2012年 | 1815篇 |
2011年 | 1727篇 |
2010年 | 1139篇 |
2009年 | 1088篇 |
2008年 | 1560篇 |
2007年 | 1558篇 |
2006年 | 1429篇 |
2005年 | 1378篇 |
2004年 | 1367篇 |
2003年 | 1335篇 |
2002年 | 1290篇 |
2001年 | 995篇 |
2000年 | 971篇 |
1999年 | 870篇 |
1998年 | 544篇 |
1997年 | 457篇 |
1996年 | 441篇 |
1995年 | 393篇 |
1994年 | 398篇 |
1993年 | 407篇 |
1992年 | 737篇 |
1991年 | 686篇 |
1990年 | 682篇 |
1989年 | 708篇 |
1988年 | 618篇 |
1987年 | 655篇 |
1986年 | 515篇 |
1985年 | 624篇 |
1984年 | 534篇 |
1983年 | 443篇 |
1982年 | 457篇 |
1981年 | 415篇 |
1980年 | 387篇 |
1979年 | 479篇 |
1978年 | 422篇 |
1977年 | 377篇 |
1976年 | 361篇 |
1975年 | 351篇 |
1974年 | 419篇 |
1973年 | 406篇 |
1972年 | 318篇 |
1971年 | 305篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Three species of blackflies were found in emergence-trap samples taken overa period of 8 months from a second-order, forested, cold-stenothermal stream in southern Ontario. The emergence phenologies of the two common species, Prosimulium mixtum and Stegopterna mutata, are described and compared with their phenologies in other streams in North America. Hypotheses are presented for the poor faunal diversity and prolonged emergence of the two species in the stream studied. Emergence data are used to describe the pupal distribution in the stream.Wing-length measurements showed a distinct dimorphism in P. mixtum: females were larger than males. Adult size (except of P. mixtum females) varied among sampling sites in the stream and, in the case of S. mutata, this variation was time dependent. 相似文献
12.
Ann McElroy 《Medical anthropology quarterly》1998,12(4):512-515
Evolution of Sickness and Healing. Horacio Fábrega Jr. Berkeley: University of California Press, 1997 (cloth), xv. 364pp. 相似文献
13.
Rebecca R. Sharitz Susan A. Wineriter Michael H. Smith Edwin H. Liu 《American journal of botany》1980,67(9):1297-1303
Biochemical phenotsypes of four taxa of Typha from the eastern United States were determined by starch gel electrophoresis. The isozyme banding patterns of T. latifolia, T. angustifolia and T. domingensis are distinct and allow unambiguous species identification when morphological characters are inadequate or unsuitable. The fourth form, T. glauca, is not an F1 hybrid, but it does appear to be intermediate between T. latifolia and T. angustifolia. The status of T. glauca and evolutionary relationships among the four forms may now be clarified by additional sampling because of the distinct and relatively invariant isozyme banding patterns which are described. 相似文献
14.
15.
16.
Hemopexin-mediated heme uptake by liver. Characterization of the interaction of heme-hemopexin with isolated rabbit liver plasma membranes 总被引:6,自引:0,他引:6
Plasma membranes isolated from rabbit liver retain the ability to interact specifically with heme-hemopexin. In this system, apohemopexin does not compete effectively with heme-hemopexin for binding. The membranes bind heme-hemopexin complexes with high affinity (KD = 6.8 X 10(-7) M) and with an apparent capacity of 2.3 pmol/mg of membrane protein. These membranes also retain the ability to remove heme from heme-hemopexin. The release of heme reaches a plateau after 15-30 min at 30 degrees C and does not involve metabolic energy, proteolysis of hemopexin or pH gradients. The apohemopexin formed is rapidly released from the membranes. The accumulation of heme is saturable and is affected by pH and temperature with maximum uptake occurring between pH 5.5 and 6.5 and at 30 degrees C. Interestingly, much more heme (approximately 25 pmol/mg of membrane protein) is accumulated than hemopexin at saturation, implying that the receptor can turn over several times and that a heme-binding component exists in the rabbit liver plasma membrane. 相似文献
17.
18.
R Smith 《BMJ (Clinical research ed.)》1987,295(6612):1547-1550
19.
Treatment of cut-throat trout broodfish Salmo clarki (Richardson) with Sulphamerazine at 220 mg/kg (10 g/100 1b) of fish/day for 14 days resulted in severe kidney histopathology and increased mortality among males. Experimental data presented showed that cut-throat trout broodfish were extremely sensitive to Sulphamerazine toxicity. Hydropic degeneration of renal tubule epithelium and haemorrhage into tubule lumens were observed in kidneys of both male and female trout, but was more severe in the former. Death, which occurred only in males, was correlated with spawning stress and impaired renal function. 相似文献
20.