全文获取类型
收费全文 | 10569篇 |
免费 | 816篇 |
国内免费 | 4篇 |
专业分类
11389篇 |
出版年
2023年 | 67篇 |
2022年 | 120篇 |
2021年 | 222篇 |
2020年 | 186篇 |
2019年 | 238篇 |
2018年 | 304篇 |
2017年 | 238篇 |
2016年 | 354篇 |
2015年 | 611篇 |
2014年 | 587篇 |
2013年 | 726篇 |
2012年 | 886篇 |
2011年 | 817篇 |
2010年 | 546篇 |
2009年 | 497篇 |
2008年 | 622篇 |
2007年 | 562篇 |
2006年 | 569篇 |
2005年 | 513篇 |
2004年 | 476篇 |
2003年 | 382篇 |
2002年 | 371篇 |
2001年 | 122篇 |
2000年 | 97篇 |
1999年 | 111篇 |
1998年 | 126篇 |
1997年 | 97篇 |
1996年 | 77篇 |
1995年 | 64篇 |
1994年 | 72篇 |
1993年 | 67篇 |
1992年 | 50篇 |
1991年 | 44篇 |
1990年 | 54篇 |
1989年 | 45篇 |
1988年 | 34篇 |
1987年 | 31篇 |
1986年 | 32篇 |
1985年 | 40篇 |
1984年 | 51篇 |
1983年 | 28篇 |
1982年 | 31篇 |
1981年 | 27篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1978年 | 17篇 |
1976年 | 16篇 |
1975年 | 22篇 |
1974年 | 13篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Francisco Gutirrez‐Corchero M. Victoria Arruga Lourdes Sanz Cristina García M. Angeles Hernndez Francisco Campos 《Molecular ecology resources》2002,2(1):75-77
FTA® cards were used for long‐term storage of avian blood samples. Blood DNA was extracted by a simple method and used in PCR for sex identification of adult and nestling Great Grey Shrikes Lanius excubitor. 相似文献
2.
3.
Abstract Resting cells of the fission yeast Schizosaccharomyces pombe , suspended in buffer with glucose, responded to the addition of asparagine by increasing trehalase activity. This response was preceded by a peak in cAMP concentration. The addition of the nitrogen source to resting cells, devoid of the catalytic subunit of cAMP-dependent protein kinase, produced the transient increase in cAMP but did not promote any change in trehalase activity. In the budding yeast Pachysolen iannophilus , the activation of trehalase by nitrogen source was also accompanied by a sharp peak in cAMP. These results suggest that in the two yeasts cAMP acts as a second messenger in the transduction of the nitrogen-source-induced signal causing the activation of trehalase. 相似文献
4.
A Shafiee M Vosooghi C G Francisco R Freire R Hernandez J A Salazar E Suarez S Sotheeswaran A A Gunatilaka 《Steroids》1987,49(4-5):397-402
The chemical synthesis and physical data of several new esters of testosterone (17 beta-hydroxyandrost-4-en-3-one), which contain either a halogeno or an alkoxy substituent in the acid chain, are reported. 相似文献
5.
Concentrations of human prolactin (hPrl) greater than or equal to 600 ng/ml produced inhibition of progestin production in cultures of granulosa cells pooled from follicles of women stimulated with clomiphene citrate-human chorionic gonadotropin (hCG). However, cells collected from follicles of human menopausal gonadotropin (HMG)-hCG-treated patients did not demonstrate a significant reduction in progestin secretion in response to hPrl. We conclude that high concentrations of hPrl can result in inhibition of steroidogenesis, but the expression of the inhibitory effects of Prl depends upon the hormonal treatments used to stimulate follicular growth. 相似文献
6.
Antonio Gomez Sanchez Manuel Mancera Francisco Rosado Manuel Rico 《Carbohydrate research》1984,134(1):75-82
3,4,5,6,7-Penta-O-acetyl-1,2-dideoxy-1-nitro-d-gluco-hept-1-enitol reacts with methyl acetoacetate in an unusual Michael reaction, giving the normal adduct (6), and a bicyclic derivative (9) that arises from quasi-dimerization of the former when a high concentration of the base is used. Acetylation of compound 9 gives the hydroxylamine O-acetate (10).From the reactions of 3,4,5,6,7-penta-O-acetyl-1,2-dideoxy-1-nitro-d-galacto-hept-1-enitol with ethyl and tert-butyl acetoacetate, the normal adducts (7 and 8) were isolated. The structures of compounds 6 to 10 were established on the basis of their spectral properties (u.v., i.r., mass, and 1H- and 13C-n.m.r.) 相似文献
7.
Antonio G. Gonzalez Jaime Bermejo Barrera Francisco J. Tolfdo Marante 《Phytochemistry》1983,22(4):1049-1050
The fruit bodies of the Basidiomycete Scleroderma polyrhizum have been shown to contain the steroids ergosta-4,6,8(14) 22-tetraen-3-one and 5α,8α-epidoxyergosta-6,22-dien-3β-ol and also palmitic and oleic acids. 相似文献
8.
9.
10.
Echevarra Fidel; Bautista Begoa; Guerrero Francisco; Rodrguez Valeriano 《Journal of plankton research》1994,16(10):1441-1447
Very short-term feeding activity of the cladoceran Ceriodaphniasp. was investigated in situ in a eutrophic reservoir in thesouth of Spain, using fluorimetric analysis of the gut pigmentcontent in periods when the water column was relatively mixedor strongly stratified. The results obtained in the mixed watercolumn showed a clear increase in gut pigment content at dawn,a period sampled with high frequency. The accumulation of thecladoceran at the depth of maximum concentration of phytoplankton,and the high gut pigment concentration in cladocerans at thatdepth just after dawn, suggested active feeding of Ceriodaphniaon phytoplankton at that time. During stratification, the abundanceof Ceriodaphnia was higher, but the gut pigment contents werevery low and they did not reflect any clear feeding patterns,with either time or depth. Changes in phytoplankton concentrationand composition between the relatively mixed and the stratifiedwater column suggest a shift in feeding activity from herbivorousto. 相似文献