全文获取类型
收费全文 | 15773篇 |
免费 | 393篇 |
国内免费 | 194篇 |
出版年
2023年 | 139篇 |
2022年 | 108篇 |
2021年 | 180篇 |
2020年 | 213篇 |
2019年 | 240篇 |
2018年 | 238篇 |
2017年 | 187篇 |
2016年 | 228篇 |
2015年 | 411篇 |
2014年 | 1194篇 |
2013年 | 1073篇 |
2012年 | 1044篇 |
2011年 | 1326篇 |
2010年 | 1054篇 |
2009年 | 660篇 |
2008年 | 706篇 |
2007年 | 721篇 |
2006年 | 646篇 |
2005年 | 517篇 |
2004年 | 557篇 |
2003年 | 416篇 |
2002年 | 276篇 |
2001年 | 163篇 |
2000年 | 195篇 |
1999年 | 260篇 |
1998年 | 236篇 |
1997年 | 201篇 |
1996年 | 199篇 |
1995年 | 204篇 |
1994年 | 236篇 |
1993年 | 173篇 |
1992年 | 212篇 |
1991年 | 171篇 |
1990年 | 149篇 |
1989年 | 161篇 |
1988年 | 158篇 |
1987年 | 144篇 |
1986年 | 126篇 |
1985年 | 130篇 |
1984年 | 155篇 |
1983年 | 93篇 |
1982年 | 153篇 |
1981年 | 116篇 |
1980年 | 132篇 |
1979年 | 125篇 |
1978年 | 79篇 |
1977年 | 87篇 |
1976年 | 51篇 |
1972年 | 24篇 |
1971年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
In Silene vulgaris (M.) G. cell culture three growth phases were distinguished, namely, a lag phase, an exponential phase and a stationary phase. Pectin termed silenan and an acidic arabinogalactan were isolated as cell wall polysaccharides of S. vulgaris callus at the different growth phases during culture. Production of silenan as the galacturonan (or rhamnogalacturonan) core was observed at the beginning of the exponential phase and at the stationary phase of the callus growth. Arabinogalactan, containing the galacturonic acid residues, is formed at the exponential phase followed by attachment to the core of silenan in the middle of the exponential phase. The arabinogalactan constituent of silenan appeared to be destroyed gradually at the stationary growth phase. The monosaccharide compositions of silenan and arabinogalactan were determined at various phases of the callus growth. Silenan was found to be formed in maximum amounts at the exponential phase of the cell growth. Insignificant alterations of the yields of acidic arabinogalactan were found during culture while total productivity per litre of medium and rate of production per day of arabinogalactan were found to be maximal at the exponential phase of growth. 相似文献
972.
Origin of two isoprenoid units in a lavandulyl moiety of sophoraflavanone G from Sophora flavescens cultured cells 总被引:2,自引:0,他引:2
Cell suspension cultures of Sophora flavescens produced large amounts of sophoraflavanone G, an 8-lavandulylated flavanone and lupalbigenin, a 6,3'-di-dimethylallylated isoflavone, by the simultaneous addition of cork tissues and methyl jasmonate. The labeling pattern of the isoprene units resulting after administration of [1-13C] glucose into the cell cultures in the presence of the above additives revealed that two isoprene units in the lavandulyl group of sophoraflavanone G and two dimethylallyl groups of lupalbigenin were biosynthesized via the 1-deoxy-D-xylulose-5-phosphate pathway. 相似文献
973.
Kiguchi K Ishiwata I Tokieda Y Iguchi M Ishiwata C Iwata M Ishizuka B Yoshikawa H Tachibana T Hashimoto H Ishikawa H 《Human cell》2002,15(2):97-102
A cell line designated HUUCLEC was established from a human uterine cervical lymphoepithelial carcinoma obtained from a 61-year-old Japanese woman. The cell line has grown slowly without interruption and serial passages were successively carried out 60 times within 3 years. The cultured cells were spindle or round in shape, showing anaplastic and pleomorphic features, a pavement cell arrangement and multilayering without contact inhibition. The population doubling time of the HUUCLEC line was 72 hours while the chromosomal number varied widely and showed aneuploidy. The modal chromosomal number was stable at the triploid range and marker chromosomes were present; the Ebstein-Barr virus was absent in the cultured cells. 相似文献
974.
Impact of genomics approaches on plant genetics and physiology 总被引:2,自引:0,他引:2
Tabata S 《Journal of plant research》2002,115(4):271-275
975.
The spatial and temporal patterns of post-embryonal cell growth and cell division were characterised in excised cotyledons
of vegetable marrow (Cucurbita pepo L. var. giromontia Alef.) incubated in water. The concurrent roles of these two processes in cotyledon growth were determined using paradermal
sections of the first palisade layer of developing cotyledons. Tissue specificity was observed in the pattern of cell division.
The daughter cells derived from an initial cell, which had already differentiated before imbibition of the seeds, were tightly
packed in a cluster, which enabled us to monitor cell division during early cotyledon development. Heterogeneity of cell size
was recognised during the process of cell proliferation in the cluster, suggesting that cell division is uncoupled from control
of cell size. There was significantly more cell division in the marginal part of the cotyledons than in other parts, suggesting
high activity of the marginal meristem. Light enhanced cell and cotyledon enlargement, but had no effect on the number of
divisions. This study elucidated the cellular basis of post-germinative Cucurbita cotyledon morphogenesis and development.
Electronic Publication 相似文献
976.
Chamras H Ardashian A Heber D Glaspy JA 《The Journal of nutritional biochemistry》2002,13(12):2783-716
Epidemiological studies suggest that dietary polyunsaturated fatty acids (PUFA) may influence breast cancer progression and prognosis. In order to study potential mechanisms of action of fatty acid modulation of tumor growth, we studied, in vitro, the influence of n-3 and n-6 fatty acids on proliferation, cell cycle, differentiation and apoptosis of MCF-7 human breast cancer cells. Both eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) inhibited the MCF-7 cell growth by 30% and 54%, respectively, while linoleic acid (LA) had no effect and arachidonic acid (AA) inhibited the cell growth by 30% (p < 0.05). The addition of vitamin E (10uM) to cancer cells slightly restored cell growth. The incubation of MCF-7 cells with PUFAs did not alter the cell cycle parameters or induce cell apoptosis. However, the growth inhibitory effects of EPA, DHA and AA were associated with cell differentiation as indicated by positive Oil-Red-O staining of the cells. Lipid droplet accumulation was increased by 65%, 30% and 15% in the presence of DHA, EPA and AA, respectively; (p < 0.05). These observations suggest that fatty acids may influence cellular processes at a molecular level, capable of modulating breast cancer cell growth. 相似文献
977.
Hemphill A Stettler M Walker M Siles-Lucas M Fink R Gottstein B 《Trends in parasitology》2002,18(10):445-451
This article reviews the use of an in vitro culture model for the maintenance and proliferation of Echinococcus multilocularis metacestodes and the formation of protoscoleces. This model has been used to identify and characterize parasite molecules involved in host-parasite interactions, and is a suitable tool to perform in vitro drug-screening assays. The development of a simple and easy-to-handle assay to determine the effects of drugs on parasite viability, without the need for time-consuming animal experimentation, has opened the way for larger-scale in vitro drug screening. 相似文献
978.
The maintenance of acidic pH in the digestive vacuole of the malaria parasite is thought to be crucial to the digestion of host cell haemoglobin and the subsequent process of heme detoxification. It may also be important in the mode of action of chloroquine and in the mechanism of resistance to the drug. Obtaining a definitive measurement of digestive vacuole pH has been surprisingly difficult. Some of the techniques for the measurement of pH in acid vesicles are outlined here along with some key aspects that are specific to malaria parasites. The use of acridine orange and dextran-tagged dyes as probes for the measurement of digestive vacuole pH has proved problematic, yet some surprising findings have emerged from work with these compounds. 相似文献
979.
Reconstruction of articular cartilage defects using adult osteochondral allografts is an established clinical procedure, whose
principal drawback is lack of lateral integration of the grafts to the surrounding tissue. Autologous chondrocytes transplantation
is a sophisticated technique requiring cell culture and a staged operation. Its main draw back is the lack of mechanical strength
early on. This study was conducted in order to evaluate the possibility of using embryonal epiphyses as a cartilage reconstruction
tissue. A xenogeneic human to rabbit sub-acute osteochondral defect model was designed to evaluate the possibility of allogeneic
implantation in humans. The following procedures were perfomed (n = 5): transplantation of 1. live epiphyses 2. live epiphyses
with autogeneic periosteum 3. de-vitalized epiphyses and 4. devitalized epiphyses with autogeneic articular chondrocytes.
A fifth control group did not receive any implant. Animals in groups 1 and 2 had a viable reconstruction of the articular
surface with little evidence of rejection and without pannus formation. Animals in groups 3 and 4 became severely arthritic
and the graft was resorbed. Nitric oxide synthase accumulation was reduced in group 1 and 2 as compared to groups 3, 4, and
5, indicating a joint preserving function of the epiphyseal grafts. Epiphyseal grafts appear to be a feasible procedure for
reconstruction of articular cartilage defects even in a xenogeneic model.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
980.