全文获取类型
收费全文 | 5646篇 |
免费 | 252篇 |
国内免费 | 816篇 |
出版年
2024年 | 16篇 |
2023年 | 92篇 |
2022年 | 116篇 |
2021年 | 170篇 |
2020年 | 151篇 |
2019年 | 188篇 |
2018年 | 201篇 |
2017年 | 167篇 |
2016年 | 186篇 |
2015年 | 186篇 |
2014年 | 285篇 |
2013年 | 399篇 |
2012年 | 301篇 |
2011年 | 266篇 |
2010年 | 228篇 |
2009年 | 285篇 |
2008年 | 290篇 |
2007年 | 267篇 |
2006年 | 218篇 |
2005年 | 215篇 |
2004年 | 206篇 |
2003年 | 163篇 |
2002年 | 204篇 |
2001年 | 171篇 |
2000年 | 182篇 |
1999年 | 130篇 |
1998年 | 121篇 |
1997年 | 101篇 |
1996年 | 88篇 |
1995年 | 90篇 |
1994年 | 87篇 |
1993年 | 97篇 |
1992年 | 92篇 |
1991年 | 78篇 |
1990年 | 60篇 |
1989年 | 32篇 |
1988年 | 35篇 |
1987年 | 38篇 |
1986年 | 29篇 |
1985年 | 58篇 |
1984年 | 45篇 |
1983年 | 39篇 |
1982年 | 60篇 |
1981年 | 45篇 |
1980年 | 43篇 |
1979年 | 33篇 |
1978年 | 36篇 |
1977年 | 37篇 |
1976年 | 36篇 |
1975年 | 23篇 |
排序方式: 共有6714条查询结果,搜索用时 15 毫秒
171.
Part of a large capitosaurid skull, similar to that of Cyclotosaurus posthumus from the Upper Triassic of Germany, has been discovered in the upper part of the Huai Hin Lat Formation near Chulabhorn (Nam Phrom) Dam. This discovery is consistent with the presumed Norian age of this formation. Although the phylogeny of the Capitosauridae is still unclear, the group of Upper Triassic Cyclotosaurus species to which C. posthumus belongs is monophyletic and seems to be known only from Laurasia or Northwestern Gondwana (Morocco). The occurrence of C. cf. posthumus in Thailand is consistent with the hypothesis previously put forward, that this part of Southeast Asia was bound to Laurasia in Mesozoic times. 相似文献
172.
Patrick De Wever 《Geobios》1981,14(1):5-15
Studies of skeleton elements of several jurassic species of Saitoum allow to compare them with Poulpus from Trias. The sub-family Poulpinae is introduced, caracterised by three cephalic arcs and the collar position of the cephalic structure. Among the jurassic forms, 4 species are newly described: S. corniculum, S. elegans, S. levium and S. trichylum. 相似文献
173.
The first mammalian remain ever found in NewCaledonia is an upper tooth found by golddiggers in the Plio-Pleistocene terrace from the Diahot river. This tooth, given to the Muséum national d'Histoire naturelle (Paris) in 1876, was determined as a rhinoceros tooth and then completely forgotten. Its detailed study shows that it belongs to Zygomaturus, a large marsupial diprotodontid genus whose story is rather complicated. The Diahot tooth represents a new species of Zygomaturus, Z. diahotensis nov. sp., close to Z. trilobus from the Australian Pleistocene. That kinship suggests a Plio-Pleistocene land connection between Australia and New Caledonia, whereas till now New Caledonia was supposed to be separated from Australia since the end of the Cretaceous, because of the total absence of indigenous mammals, fossil or recent, in New Caledonia. The latest geological studies in the East Pacific do not contradict our hypothesis. 相似文献
174.
Neonatal rats injected with either thyroxine (T4) or vehicle (NaOH) on postnatal Days 1, 2, and 3 were given classical-conditioning pairings of an odor with footshock when 7, 9, or 11 days of age. In accord with the conventional acceleration of other indices of maturation following the T4 treatment, 24-hr retention of the conditioned odor aversion was substantially enhanced among the 11 day-old rats given the earlier T4 treatment. This effect was marginally significant among 9-day olds but not among 7-day olds. 相似文献
175.
A lot of Stringocephalidae have been discovered,for the first time, in the Givetian of Afghanistan. Among these we have identified: Stringocephalus aff. burtini (Defrance)), St. (Parastringocephalus) dewalense n. sp., Rensselandia aff. circularis (Holzapfel)). The locality is situated in Hazarajat, in a Devonian sequence which is more than one thousand meters thick and the age of which ranges from Gedinnian (probable) to Frasnian. 相似文献
176.
The study of imprints of fossil plants collected in the Permian from the country of Hammanskraal (Namibia) leads to the following identifications: Glossopteris sp., Gangamopteris sp., Noegerrathiopsis sp., Gondwanidium sp., Asterotheca sp. and Lycopodiopsis derbyiB. Renault, Lycopodiopsis costilatus n. sp., Brasilodendron pedroanum(W. Carruthers) W.G. Chaloner & alii, Brasilodendron africanum n. sp. This flora has affinities with some fossil floras from South Africa and from Brazil, and is, probably, of upper Permian age. 相似文献
177.
A fluorinated vitamin D3 analog with biopotency greater than 1 alpha, 25-dihydroxy vitamin D3 总被引:2,自引:0,他引:2
R A Corradino H F DeLuca Y Tanaka N Ikekawa Y Kobayashi 《Biochemical and biophysical research communications》1980,96(4):1800-1803
Vitamin D metabolites and analogs induce synthesis of a specific calcium-binding protein in embryonic chick duodenum maintained in organ culture. Using calcium-binding protein biosynthesis as a specific and sensitive biochemical indicator of intrinsic biopotency, 24,24-difluoro-1α,25-dihydroxy vitamin D3 was found to be approximately four times more potent on a molar basis than the most active, naturally occurring metabolite, 1α,25-dihydroxy vitamin D3. 相似文献
178.
179.
The effects of prostaglandin E1 (PGE1) and indomethacin on isolated fetal and neonatal lamb mesenteric artery responses to norepinephrine were investigated. PGE1 (1.5μM) significantly reduced vasoconstriction responses to 0.5 to 5μM norepinephrine. Indomethacin (1μM) markedly potentiated the constrictor effects of 0.5 to 10μM norepinephrine. PGE1 prevented the potentiating effect of indomethacin. Neither PGE1 nor indomethacin altered basal muscle tension. These results suggest that endogenous PGs modify adrenergic responses in the isolated mesenteric arteries of preterm and newborn lambs. 相似文献
180.
The study of approximately twenty three thousand otoliths from Plio-Pleistocene sites in the harbour region of Antwerp, as well as a critical revision of already published material allowed us to identify a teleostean fauna with fourty seven species (including two subspecies and seven species in open nomenclature). Two of these, Ophidion springeri and Uranoscopus septentrionalis are new to science. The fauna is typical for coastal waters slightly warmer than those of the actual North Sea and caracterized by the predominance of Gadidae. Biostratigraphically this fauna is well individualized with respect to preceeding ones (only seven species in common with the Miocene fauna) and those following twenty-three species in common with the extant fauna). The following biostratigraphical subdivision has been recognized in the Upper Miocene and the Plio-Pleistocene of the Antwerp region: (1) an association with «genus? Macrouridarum labiatus, Trisopterus sculptus, Gadiculus benedeni and Trisopterus luscus spectabilis, in the Sands of Deurne (Upper Miocene); (2) an association with Gadiculus benedeni and Merlangius pseudaeglephinus, in the Formation of Kattendijk (Pliocene); (3) an association with Gadiculus verticalis and Merlangius pseudaeglefinus in the Formation of Lillo (Plio-Pleistocene); (4) an association with Gadus morhua and Merlangius pseudaeglefinus in the so called «Icenian deposits not present in Belgium but found in the Netherlands. 相似文献