全文获取类型
收费全文 | 47457篇 |
免费 | 3363篇 |
国内免费 | 19篇 |
出版年
2024年 | 52篇 |
2023年 | 175篇 |
2022年 | 566篇 |
2021年 | 912篇 |
2020年 | 568篇 |
2019年 | 682篇 |
2018年 | 1028篇 |
2017年 | 906篇 |
2016年 | 1478篇 |
2015年 | 2326篇 |
2014年 | 2670篇 |
2013年 | 2981篇 |
2012年 | 3942篇 |
2011年 | 3781篇 |
2010年 | 2392篇 |
2009年 | 2193篇 |
2008年 | 3034篇 |
2007年 | 2913篇 |
2006年 | 2544篇 |
2005年 | 2367篇 |
2004年 | 2163篇 |
2003年 | 1866篇 |
2002年 | 1614篇 |
2001年 | 1301篇 |
2000年 | 1229篇 |
1999年 | 991篇 |
1998年 | 393篇 |
1997年 | 339篇 |
1996年 | 246篇 |
1995年 | 209篇 |
1994年 | 209篇 |
1993年 | 172篇 |
1992年 | 326篇 |
1991年 | 295篇 |
1990年 | 266篇 |
1989年 | 227篇 |
1988年 | 174篇 |
1987年 | 163篇 |
1986年 | 131篇 |
1985年 | 105篇 |
1984年 | 78篇 |
1983年 | 84篇 |
1982年 | 66篇 |
1981年 | 53篇 |
1980年 | 55篇 |
1979年 | 69篇 |
1978年 | 51篇 |
1977年 | 50篇 |
1976年 | 43篇 |
1974年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
52.
53.
J Chae M J Kim J H Goo S Collier D Gubb J Charlton P N Adler W J Park 《Development (Cambridge, England)》1999,126(23):5421-5429
The tissue polarity genes control the polarity of hairs, bristles and ommatidia in the adult epidermis of Drosophila. We report here the identification of a new tissue polarity gene named starry night (stan). Mutations in this essential gene alter the polarity of cuticular structures in all regions of the adult body. The detailed polarity phenotype of stan on the wing suggested that it is most likely a component of the frizzled (fz) pathway. Consistent with this hypothesis, stan appears to be downstream of and required for fz function. We molecularly cloned stan and found that it encodes a huge protocadherin containing nine cadherin motifs, four EGF-like motifs, two laminin G motifs, and seven transmembrane domains. This suggests that Stan functions in signal reception, perhaps together with Fz. 相似文献
54.
55.
56.
Ryan K. Cheu Andrew T. Gustin Christina Lee Luca Schifanella Charlene J. Miller Avie Ha Casey Kim Violeta J. Rodriguez Margaret Fischl Adam D. Burgener Kelly B. Arnold Maria L. Alcaide Nichole R. Klatt 《PLoS pathogens》2020,16(12)
Despite the efficacy of antiretroviral-based pre-exposure prophylactics (PrEP) in men who have sex with men, studies in women have produced widely varying outcomes. Recent evidence demonstrates that vaginal microbial communities are associated with increased HIV acquisition risk and may impact PrEP efficacy. Here, we investigate the mechanisms underlying how vaginal bacteria alter PrEP drug levels and impact HIV infection rates ex vivo. Using cervicovaginal lavages (CVLs) from women with or without bacterial vaginosis (BV), we identified microbial metabolism of PrEP drugs in BV samples through LC-MS/MS analysis of soluble drug levels and metabolite formation in dual T-cell cultures. CVL samples were assessed for microbiome analysis using sequencing of bacterial 16S rRNA genes. We also observed non-Lactobacillus bacteria that are associated with BV may potentially impact PrEP efficacy through increased HIV infection rates in co-cultures containing Lactobacillus or BV bacteria, PrEP drugs, CEM-GFP cells, and HIV-1LAI virus. Finally, we used these data to develop a novel predictive mathematical simulation modeling system to predict these drug interactions for future trials. These studies demonstrate how dysbiotic vaginal microbiota may impact PrEP drugs and provides evidence linking vaginal bacteria to PrEP efficacy in women. 相似文献
57.
Two new beta-xylosyl derivatives of ginsenoside Re, 20(S)-protopanaxatriol 6-O-alpha-L-rhamnopyranosyl-(1 --> 2)-[beta-D-xylopyranosyl-(1 --> 4)]-beta-D-glucopyranosyl-20-O-beta-D-glucopyranoside and 20(S)-protopanaxatriol 6-O-alpha-L-rhamnopyranosyl-(1 --> 2)-[beta-D-xylopyranosyl-(1 --> 6)]-beta-D-glucopyranosyl-20-O-beta-D-glucopyranoside, were respectively synthesized from p-nitrophenyl beta-D-xylopyranoside and phenyl beta-D-xylopyranoside as donors and ginsenoside Re as the acceptor in 25% acetone and acetonitrile by a cellulase preparation from Trichoderma viride and a beta-galactosidase preparation from Aspergillus oryzae. The latter enzyme preparation also catalyzed the hydrolysis of ginsenoside Re to the minor saponin, ginsenoside Rg2. 相似文献
58.
59.
This study was undertaken to investigate the cryopreservation of Cryptosporidium parvum oocysts. Oocysts purified from mouse feces were suspended in distilled water, 10% glycerin, and 2.5% potassium dichromate. They were stored at -20 C and -80 C for 2, 7, and 30 days, respectively. In addition to the purified oocysts, the feces of C. parvum-infected mice were preserved under the same conditions described above. Purified and fecal oocysts were thawed at 4 C, and their viability was assessed by a nucleic acid stain, excystation test, tissue culture infectivity test, and infectivity to immunosuppressed adult mice. Oocysts purified from fecal material prior to cryopreservation lost most of their viability and all of their infectivity for tissue culture and mice. However, when oocysts were cryopreserved in feces, between 11.7 and 34.0% were judged to be viable and retained their infectivity for mice when stored at -20 C (but not -80 C) for 2, 7, and 30 days. Clearly, fecal material provides a cryoprotective environment for C. parvum oocysts stored at -20 C for at least 30 days. 相似文献
60.
Formation of secretory vesicles in the noncellular secretory cavity of glandular trichomes of Cannabis saliva L. was examined by transmission electron microscopy. Two patterns of vesicle formation occurred during gland morphogenesis. 1) During initial phases of cavity formation small hyaline areas arose in the wall near the plasma membrane of the disc cell. Hyaline areas of elongated shape and different sizes were distributed throughout the wall and adjacent to the secretory cavity. Hyaline areas increased in size, some possibly fusing with others. These hyaline areas, possessing a membrane, moved into the cavity where they formed vesicles. As membraned vesicles they developed a more or less round shape and their contents became electron-dense. 2) During development of the secretory cavity and when abundant secretions were present in the disc cells, these secretions passed through the wall to accumulate as membraned vesicles of different sizes in the cavity. As secretions emerged from the wall, a membrane of wall origin delimited the secretory material from cavity contents. Vesicles released from the wall migrated in the secretory cavity and contacted the sheath where their contents permeated into the subcuticular wall as large or diffused quantities of secretions. In the subcuticular wall these secretions migrated to the wall–cuticle interface where they contributed to structural thickening of the cuticle. This study demonstrates that the secretory process in glands of Cannabis involves not only secretion of materials from the disc cell, but that the disc cell somehow packages these secretions into membraned vesicles outside the cell wall prior to deposition into the secretory cavity for subsequent structural development of the sheath. 相似文献