全文获取类型
收费全文 | 75394篇 |
免费 | 6988篇 |
国内免费 | 42篇 |
专业分类
82424篇 |
出版年
2022年 | 569篇 |
2021年 | 1129篇 |
2020年 | 691篇 |
2019年 | 846篇 |
2018年 | 1022篇 |
2017年 | 944篇 |
2016年 | 1562篇 |
2015年 | 2598篇 |
2014年 | 2903篇 |
2013年 | 3828篇 |
2012年 | 4687篇 |
2011年 | 4774篇 |
2010年 | 3104篇 |
2009年 | 2716篇 |
2008年 | 3932篇 |
2007年 | 4158篇 |
2006年 | 3919篇 |
2005年 | 3789篇 |
2004年 | 3673篇 |
2003年 | 3452篇 |
2002年 | 3342篇 |
2001年 | 1081篇 |
2000年 | 925篇 |
1999年 | 1077篇 |
1998年 | 1054篇 |
1997年 | 815篇 |
1996年 | 726篇 |
1995年 | 650篇 |
1994年 | 644篇 |
1993年 | 670篇 |
1992年 | 811篇 |
1991年 | 714篇 |
1990年 | 719篇 |
1989年 | 666篇 |
1988年 | 658篇 |
1987年 | 638篇 |
1986年 | 584篇 |
1985年 | 655篇 |
1984年 | 711篇 |
1983年 | 626篇 |
1982年 | 714篇 |
1981年 | 708篇 |
1980年 | 596篇 |
1979年 | 546篇 |
1978年 | 551篇 |
1977年 | 473篇 |
1976年 | 502篇 |
1975年 | 401篇 |
1974年 | 465篇 |
1973年 | 449篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The effects of 5-methoxy-N, N-dimethyltryptamine (5-MeODMT), a serotonin agonist with a preferential action on presynaptic autoreceptors, on prolactin release in male rats was determined. Basal serum prolactin levels were not altered after administration of 1.0, 2.0, 5.0, 10.0 or 20.0 mg/kg of 5-MeODMT.Pretreatment with 5-MeODMT reduced prolactin release by agents that depend on serotonergic neurotransmission for part of their prolactin release stimulation. Prolactin release in response to L-5-hydroxytryptophan (5-HTP) or morphine was significantly reduced by pretreatment of the rats with 5-MeODMT.The results of this experiment indicate that 5-MeODMT act as a presynaptic serotonin autoreceptor stimulant and not as a postsynaptic serotonin agonist on the neuronal systems that control prolactin release. 相似文献
2.
Puerto Rican populations of two species of sea anemones (Bunodosoma cavernata and B. granulifera) which had previously been considered one were assayed electrophoretically for enzymes encoded by 12 loci. The two species shared no common allozymes at 6 of the 12 loci. Genetic distance and identity values based on these allozymes were computed for the Puerto Rican populations and for B. cavernata from Florida and B. granulifera from Panama. The Puerto Rican populations of both species had much higher genetic identities for their geographically distant conspecifics than for each other. These results indicate that the two species are reproductively isolated and should be considered as separate valid species. Average heterozygosities are presented which are the first published for coelenterate species. 相似文献
3.
4.
5.
6.
7.
James B. Reid 《Animal behaviour》1982,30(4):1212-1216
A young captive rook, Corvus frugilegus, inserted a plug into a plug-hole in its aviary floor so that a pool of water formed, which was used by all four rooks in the aviary for drinking and bathing. The bird was selective about which, of six holes, it chose for insertion of the tool, choosing the appropriate one with respect to the water source. Days on which attempted or successful tool-use occurred were drier than other days, and days of successful tool-uses were also warmer. Availability of fresh water to the birds did not influence the occurrence of tool-use. 相似文献
8.
9.
10.
Frank J. Turano Kenneth Glade Wilson 《In vitro cellular & developmental biology. Plant》1985,21(3):135-139
Summary The feasibility of using plant cell culture to measure toxicity was determined by investigating the toxicological effects
of three chemical compounds, allyl alcohol, propargylglycine, and cadmium chloride, on cell cultures ofCatharanthus roseus G. Don (Madagascar periwinkle). Suspension cultures ofC. roseus were maintained in modified B5 medium and transferred every 5 d. Five-day-old cell cultures were exposed to various concentrations
(10,3,1,0.3,0.1,0.03,0.01,0.003,0.001,0.0003,0.0001, 0.00003, and 0.0 mM) of the toxicants in both acute and chronic toxicity tests.
In the acute test, cells were exposed to the toxicant for 24 h, washed three times with sterile medium, and plated in petri
plates with an equal volume of 1.4% agar medium. Cells in the chronic test were plated with an equal volume of 1.4% agar medium
containing various concentrations of the toxicant. Cells were incubated 28 d at 30°C in the dark. The colonies were counted
and the results plotted as percent survival versus toxicant concentration. The results indicate, at the concentrations tested,
thatC. roseus assay may be feasible in that it fulfills the criteria for a practical assay (e.g., rapid, simple, quantifiable, and reproducible).
This work was submitted to the faculty of Miami University in partial fulfillment of the requirements for the degree of Master
of Environmental Science, Institute of Environmental Sciences. 相似文献