全文获取类型
收费全文 | 2248篇 |
免费 | 122篇 |
专业分类
2370篇 |
出版年
2022年 | 13篇 |
2021年 | 27篇 |
2020年 | 16篇 |
2019年 | 14篇 |
2018年 | 29篇 |
2017年 | 36篇 |
2016年 | 42篇 |
2015年 | 66篇 |
2014年 | 70篇 |
2013年 | 113篇 |
2012年 | 124篇 |
2011年 | 149篇 |
2010年 | 89篇 |
2009年 | 96篇 |
2008年 | 125篇 |
2007年 | 170篇 |
2006年 | 140篇 |
2005年 | 166篇 |
2004年 | 166篇 |
2003年 | 139篇 |
2002年 | 163篇 |
2001年 | 19篇 |
2000年 | 15篇 |
1999年 | 29篇 |
1998年 | 44篇 |
1997年 | 30篇 |
1996年 | 31篇 |
1995年 | 15篇 |
1994年 | 17篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 18篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1971年 | 4篇 |
1970年 | 7篇 |
排序方式: 共有2370条查询结果,搜索用时 15 毫秒
991.
Ito C Itoigawa M Onoda S Hosokawa A Ruangrungsi N Okuda T Tokuda H Nishino H Furukawa H 《Phytochemistry》2005,66(5):567-572
Isolation and structure elucidation of three coumarins, murrayacoumarins A, B, and C, together with eight known coumarins, from the leaves of Murraya siamensis Craib collected in Thailand are described. Results of a primary screening of inhibitory effects of seven of these compounds on 12-O-tetradecanoylphorbol-13-acetate-induced Epstein-Barr virus early antigen activation in Raji cells are also presented. 相似文献
992.
Matsumoto K Akao Y Ohguchi K Ito T Tanaka T Iinuma M Nozawa Y 《Bioorganic & medicinal chemistry》2005,13(21):6064-6069
We investigated the antiproliferative effects of four structurally similar prenylated xanthones, alpha-mangostin, beta-mangostin, gamma-mangostin, and methoxy-beta-mangostin, in human colon cancer DLD-1 cells. These xanthones differ in the number of hydroxyl and methoxy groups. Except for methoxy-beta-mangostin, the other three xanthones strongly inhibited cell growth at 20 microM and their antitumor efficacy was correlated with the number of hydroxyl groups. Hoechst 33342 nuclear staining and nucleosomal DNA-gel electrophoresis revealed that the antiproliferative effects of alpha- and gamma-mangostin, but not that of beta-mangostin, were associated with apoptosis. It was also shown that their antiproliferative effects were associated with cell-cycle arrest by affecting the expression of cyclins, cdc2, and p27; G1 arrest was by alpha-mangostin and beta-mangostin, and S arrest by gamma-mangostin. These findings provide a relevant basis for the development of xanthones as an agent for cancer prevention and combination therapy with anti-cancer drugs. 相似文献
993.
Using novel variations of traditional methods, report in the December 29(th) issue of Cell that diverse genes involved in neural biology (particularly those critical in development) show higher rates of protein evolution in primates than in rodents-particularly in the lineage leading to humans. 相似文献
994.
995.
Nobuko Watanabe Kumiko Nagamatsu Toshiyuki Mizuno Masakatsu Matsumoto 《Luminescence》2005,20(2):63-72
Bicyclic dioxetanes bearing 5-(t-butyldimethylsiloxy)inden-2-yl, 3, or 5-(t-butyldimethylsiloxy)benzo(b)thiazol-2-yl, 4, were synthesized. On treatment with large excess of tetrabutylammonium fluoride in DMSO, dioxetane, 3, decomposed rapidly with accompanying emission of red (vermilion) light (lambda(max) (CL) = 637 nm). Comparing the chemiluminescent properties for 3 with those for related dioxetane, 1, in which pi-conjugation system is not fixed in plane, both CIEEL-decay rate and chemiluminescent efficiency were found to be improved for 3. Chemiluminescent decomposition of dioxetane, 4, was similarly induced to emit crimson light (lambda(max) (CL) = 725 nm), though the chemiluminescent efficiency was low. 相似文献
996.
997.
Cell wall regeneration and cell division in isolated tobacco mesophyll protoplasts 总被引:21,自引:3,他引:18
Summary Protoplasts were isolated from palisade tissue of tobacco leaves by treatment with pectinase and cellulase under aseptic conditions, and were cultured in a synthetic liquid medium. Calcofluor, a fluorescent brightener, was found to be an excellent stain for plant cell walls and was used to demonstrate regeneration of cell walls in these protoplasts. The cultured protoplasts regenerated cell walls by the 3rd day of culture, giving rise to spherical cells. The majority of the protoplasts regenerating cell walls underwent mitosis and cell division. The cycle of mitosis and cell division was repeated 2–3 times during 2 weeks of culture. Some of the nutritional conditions affecting division in the cultured protoplasts were studied. 相似文献
998.
Moso bamboo (Phyllostachys edulis) groves have been expanding in Japanese forests, thus an assessment of the rate of bamboo grove expansion is a critical issue. Previous studies used time-series data which span typically more than a few years in order to determine the expansion of bamboo groves. This method cannot be used when time-series data were not available. In this study, we developed and tested a simple indicator based on one-time measurement of spatial distribution of culms to estimate the rate of bamboo grove expansion. Among 19 locations at four sites, the distribution patterns of culms from the pure bamboo stands to the expanding front were highly correlated with the actual edge expansion rate (E) based on the aerial photographs collected over ca. 15- and 30-year periods. In contrast, the culm density in the original stand itself was not correlated with E. These results suggest that one-time measurement of the distribution patterns of living culms (but not stand density) could be a useful indicator for estimating the expansion rates of bamboo groves. 相似文献
999.
Toshimi Matsuno Nobuo Kobayashi Fumio Hariguchi Toshiyuki Yamazaki Kin-ichi Imai Hiroshi Onaga 《Experimental parasitology》1984,57(1):55-61
The anticoccidial activity of an orotic acid analog, 1,6-dihydro-6-oxo-2-pyrazinecarboxylic acid 4-oxide (carboxyemimycin), was tested in battery experiments, utilizing 9-day-old Single-Comb White Leghorn cockerels. Carboxyemimycin, at 125 ppm and more in feed, exhibited marked anticoccidial activities against Eimeria tenella, E. necatrix, E. acervulina, and E. maxima. High doses of carboxyemimycin—up to 1000 ppm—did not cause any reduction in weight gains. The battery and in vitro studies with delayed and restricted medications revealed that carboxyemimycin affected the development of E. tenella in first and second generation schizogony and in gametogony. 相似文献
1000.
Kaoru Seike Michiko Nakazato Hisashi Hanazawa Toshiyuki Ohtani Tomihisa Niitsu Shin-ichi Ishikawa Atsuko Ayabe Ryoko Otani Kentaro Kawabe Fumie Horiuchi Shizuo Takamiya Ryoichi Sakuta 《BioPsychoSocial medicine》2016,10(1):28