全文获取类型
收费全文 | 2466篇 |
免费 | 261篇 |
出版年
2016年 | 22篇 |
2015年 | 43篇 |
2014年 | 44篇 |
2013年 | 60篇 |
2012年 | 85篇 |
2011年 | 96篇 |
2010年 | 57篇 |
2009年 | 52篇 |
2008年 | 78篇 |
2007年 | 47篇 |
2006年 | 72篇 |
2005年 | 81篇 |
2004年 | 59篇 |
2003年 | 69篇 |
2002年 | 57篇 |
2001年 | 77篇 |
2000年 | 75篇 |
1999年 | 78篇 |
1998年 | 27篇 |
1997年 | 26篇 |
1996年 | 33篇 |
1995年 | 33篇 |
1994年 | 27篇 |
1993年 | 21篇 |
1992年 | 68篇 |
1991年 | 71篇 |
1990年 | 61篇 |
1989年 | 59篇 |
1988年 | 59篇 |
1987年 | 69篇 |
1986年 | 66篇 |
1985年 | 67篇 |
1984年 | 60篇 |
1983年 | 54篇 |
1982年 | 45篇 |
1981年 | 48篇 |
1980年 | 47篇 |
1979年 | 65篇 |
1978年 | 53篇 |
1977年 | 51篇 |
1976年 | 45篇 |
1975年 | 52篇 |
1974年 | 56篇 |
1973年 | 35篇 |
1972年 | 34篇 |
1971年 | 25篇 |
1970年 | 25篇 |
1969年 | 25篇 |
1968年 | 24篇 |
1966年 | 20篇 |
排序方式: 共有2727条查询结果,搜索用时 156 毫秒
991.
HMG CoA reductase: a negatively regulated gene with unusual promoter and 5' untranslated regions 总被引:132,自引:0,他引:132
G A Reynolds S K Basu T F Osborne D J Chin G Gil M S Brown J L Goldstein K L Luskey 《Cell》1984,38(1):275-285
992.
Photosynthetic properties of photoautotrophic suspensions cultured in a minimal growth medium have been evaluated to determine whether changes have occurred in ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity, phosphoenol-pyruvate (PEP) carboxylase activity, chlorophyll content, or culture growth. Five photoautotrophic lines Amaranthus powellii, Datura innoxia, Glycine max, Gossypium hirsutum, and a Nicotiana tabacum-Nicotiana glutinosa fusion hybrid were grown in a medium without organic carbon other than phytohormones, and without vitamins. These photoautotrophic lines had total Rubisco activities ranging from 85 to 266 micromoles CO2 fixed per milligram chlorophyll hour−1, with percent activation of Rubisco ranging from 16 to 53%. Inclusion of protease inhibitors in the homogenization buffer did not result in higher Rubisco activity. PEP carboxylase activity for cells cultured in minimal medium was found to range from 16 to 146 micromoles CO2 per milligram chlorophyll hour−1, with no higher activity in the C4Amaranthus cells compared with PEP carboxylase activity in the C3 species assayed. Rubisco-to-PEP carboxylase ratios ranged from 2.2 to 1 up to 9.4 to 1. Chlorophyll contents increased in all but the Nicotiana cell line, and all of the photoautotrophic culture lines were capable of growth in vitamin-free medium with the exception of SB-P, which requires thiamine. 相似文献
993.
994.
L S Goldstein D M Gersten A K Bruce 《International journal of radiation biology and related studies in physics, chemistry, and medicine》1978,34(4):375-380
An agent extracted from the radioresistant bacterium M. radiodurans was found to protect several strains of E. coli from X-radiation. Optimal radioprotection was observed when the repair-proficient B/r strain was irradiated in the presence of the agent under hypoxic conditions. It is proposed that this agent acts to modify damage incurred in the presence of reduced oxygen concentrations so that this damage might be subsequently repaired. 相似文献
995.
996.
R W Steele J W Eichberg R L Heberling J J Eller A L Goldstein S S Kalter W T Kniker 《Journal of medical primatology》1977,6(3):163-171
E (erythrocyte) and EAC (erythrocytes coated with antibody and complement) rosettes were quantitated in baboons, cebus monkeys and cotton-topped marmosets. There was poor correlation between E rosette levels and other parameter of T-lymphocyte function. In nonhuman primates, E rosettes were increased in the presence of thymosin fraction V, while human E rosettes were not affected. 相似文献
997.
Matteo M. Trucco Ola Awad Breelyn A. Wilky Seth D. Goldstein Ruili Huang Robert L. Walker Preeti Shah Varalakshmi Katuri Naheed Gul Yuelin J. Zhu Edward F. McCarthy Ido Paz-Priel Paul S. Meltzer Christopher P. Austin Menghang Xia David M. Loeb 《PloS one》2013,8(11)
Chordoma is a rare primary bone malignancy that arises in the skull base, spine and sacrum and originates from remnants of the notochord. These tumors are typically resistant to conventional chemotherapy, and to date there are no FDA-approved agents to treat chordoma. The lack of in vivo models of chordoma has impeded the development of new therapies for this tumor. Primary tumor from a sacral chordoma was xenografted into NOD/SCID/IL-2R γ-null mice. The xenograft is serially transplantable and was characterized by both gene expression analysis and whole genome SNP genotyping. The NIH Chemical Genomics Center performed high-throughput screening of 2,816 compounds using two established chordoma cell lines, U-CH1 and U-CH2B. The screen yielded several compounds that showed activity and two, sunitinib and bortezomib, were tested in the xenograft. Both agents slowed the growth of the xenograft tumor. Sensitivity to an inhibitor of IκB, as well as inhibition of an NF-κB gene expression signature demonstrated the importance of NF-κB signaling for chordoma growth. This serially transplantable chordoma xenograft is thus a practical model to study chordomas and perform in vivo preclinical drug testing. 相似文献
998.
Jisun Paik Michael Haenisch Charles H. Muller Alex S. Goldstein Samuel Arnold Nina Isoherranen Thea Brabb Piper M. Treuting John K. Amory 《The Journal of biological chemistry》2014,289(21):15104-15117
Knowledge of the regulation of testicular retinoic acid synthesis is crucial for understanding its role in spermatogenesis. Bisdichloroacetyldiamines strongly inhibit spermatogenesis. We reported previously that one of these compounds, WIN 18,446, potently inhibited spermatogenesis in rabbits by inhibiting retinoic acid synthesis. To understand how WIN 18,446 inhibits retinoic acid synthesis, we characterized its effects on human retinal dehydrogenase ALDH1A2 in vitro as well as its effects on retinoid metabolism in vivo using mice. WIN 18,446 strongly and irreversibly inhibited ALDH1A2 in vitro. In vivo, WIN 18,446 treatment completely abolished spermatogenesis after 4 weeks of treatment and modestly reduced adiposity in mice fed a chow diet. Effects of WIN 18,446 on retinoid concentrations were tissue-dependent. Although lung and liver retinyl ester concentrations were lower in WIN 18,446-treated animals, adipose retinyl ester levels were increased following the treatment. Interestingly, animals treated with WIN 18,446 had significantly higher circulating retinol concentrations compared with control mice. The effect on spermatogenesis by WIN 18,446 was not prevented by simultaneous treatment with retinoic acid, whereas effects on other tissues were partially or completely reversed. Cessation of WIN 18,446 treatment for 4 weeks reversed most retinoid-related phenotypes except for inhibition of spermatogenesis. Our data suggest that WIN 18,446 may be a useful model of systemic acquired retinoic acid deficiency. Given the effects observed in our study, inhibition of retinoic acid biosynthesis may have relevance for the treatment of obesity and in the development of novel male contraceptives. 相似文献
999.
1000.
This paper presents new demographic findings for a high altitude Himalayan population residing in Ladakh, India, and reviews problematic issues regarding the hypothesized relationship between fertility/fecundity and altitude in the Himalayas in light of these findings. It concludes that the low completed fertility ratio reported for the Sherpas of Khumbu, Nepal, is not caused by hypoxia-induced low fecundity, but is the product of cultural factors affecting the exposure of females to the risk of intercourse, a critical confounding factor that has not received adequate consideration in previous studies. Contrary to earlier reports, the present study demonstrates that all high altitude Himalayan populations for which published data exist exhibit moderately high fertility and fecundity, and do not differ significantly in their fertility levels. Furthermore, it argues that the claims for a statistically significant difference in fertility between high, moderate, and low altitude Himalayan populations are groundless, and suggests that a parallel reevaluation of Andean findings is required. [fertility, fecundity, hypoxia, Himalayas, Andes] 相似文献