全文获取类型
收费全文 | 945篇 |
免费 | 90篇 |
出版年
2022年 | 8篇 |
2021年 | 17篇 |
2020年 | 12篇 |
2019年 | 13篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 16篇 |
2015年 | 30篇 |
2014年 | 24篇 |
2013年 | 42篇 |
2012年 | 43篇 |
2011年 | 45篇 |
2010年 | 26篇 |
2009年 | 31篇 |
2008年 | 35篇 |
2007年 | 47篇 |
2006年 | 37篇 |
2005年 | 31篇 |
2004年 | 24篇 |
2003年 | 33篇 |
2002年 | 29篇 |
2001年 | 30篇 |
2000年 | 23篇 |
1999年 | 36篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1993年 | 7篇 |
1992年 | 22篇 |
1991年 | 14篇 |
1990年 | 8篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 10篇 |
1984年 | 15篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 17篇 |
1978年 | 11篇 |
1977年 | 10篇 |
1976年 | 20篇 |
1975年 | 13篇 |
1973年 | 27篇 |
1972年 | 9篇 |
1969年 | 8篇 |
1968年 | 8篇 |
1967年 | 6篇 |
1966年 | 10篇 |
排序方式: 共有1035条查询结果,搜索用时 31 毫秒
991.
992.
993.
Thioester-containing protein 1 (TEP1) is a central component in the innate immune response of Anopheles gambiae to Plasmodium infection. Two classes of TEP1 alleles, TEP1*S and TEP1*R, are found in both laboratory strains and wild isolates, related by a greater or lesser susceptibility, respectively to both P. berghei and P. falciparum infection. We report the crystal structure of the full-length TEP1*S1 allele which, while similar to the previously determined structure of full-length TEP1*R1, displays flexibility in the N-terminal fragment comprising domains MG1-MG6. Amino acid differences between TEP1*R1 and TEP1*S1 are localized to the TED-MG8 domain interface that protects the thioester bond from hydrolysis and structural changes are apparent at this interface. As a consequence cleaved TEP1*S1 (TEP1*S1cut) is significantly more susceptible to hydrolysis of its intramolecular thioester bond than TEP1*R1cut. TEP1*S1cut is stabilized in solution by the heterodimeric LRIM1/APL1C complex, which preserves the thioester bond within TEP1*S1cut. These results suggest a mechanism by which selective pressure on the TEP1 gene results in functional variation that may influence the vector competence of A. gambiae towards Plasmodium infection. 相似文献
994.
Peter J Baxter 《BMJ (Clinical research ed.)》1987,294(6578):1020
995.
Barbara Dowds Lesley Baxter Michael McKillen 《Biochimica et Biophysica Acta (BBA)/General Subjects》1978,541(1):18-34
The d-gluconate transport system of Bacillus subtilis is optimally induced by exposure of cells for 2 h to 5 mM d-gluconate in the growth medium. d-gluconate transport is subject to catabolite repression, as distinct from inducer exclusion or catabolite inhibition, in a manner parallel to the repression of inducible histidase synthesis, suggesting that the repression is not specific to this transport system. Maximum repression with the repressing carbon source (10 mM) added to cells grown in either casein hydrolysate or amino acid medium is achieved within two doubling times. Urea, the only non-carbon source tested for a repressing effect, was found to act solely by inducer exclusion. The ability of a sugar carbon source to evoke catabolite repression appears to be unrelated to its suitability as a substrate for the sugar: phosphoenolpyruvate phosphotransferase system but nonetheless the conversion to a phosphorylated derivative of the sugar seems essential. Repressed cells fail to synthesize, or do so to a more limited extent, an as yet unidentified phosphorylated compound (probably a highly phosphorylated nucleotide) which is accumulated in the medium of non-repressed cells. Mutant studies imply that inosinic acid synthesis is necessary for catabolite repression whereas the adenosine highly phosphorylated nucleotides required for spurulation are not. 相似文献
996.
It is frequently assumed that nitrogen (N2) fixation and denitrification do not co-occur in streams because each process should be favored under different concentrations of dissolved inorganic nitrogen (DIN), and therefore these processes are rarely quantified together. We asked if these processes could co-exist by conducting a spatial survey of N2 fixation using acetylene reduction and denitrification using acetylene block [with and without amendments of carbon (C) as glucose and nitrogen (N) as nitrate]. Rates were measured on rocks and sediment in 8 southeastern Idaho streams encompassing a DIN gradient of 26–615 µg L?1. Sampling at each site was repeated in summer 2015 and 2016. We found that both denitrification and N2 fixation occurred across the gradient of DIN concentrations, with N2 fixation occurring primarily on rocks and denitrification occurring in sediment. N2 fixation rates on rocks significantly decreased 100× across the DIN gradient in 1 year of the study, and amended (with N and C) denitrification rates increased 10× across the DIN gradient in both years. Multiple linear regression and partial least squares models with environmental characteristics measured at the scale of entire stream reaches showed that C and phosphorus were positive predictors of amended and unamended denitrification rates, but no significant model could explain N2 fixation rates across all streams and years. This, coupled with the observation that detectable rates of N2 fixation occurred primarily on rocks and denitrification occurred primarily on sediment, suggests that microhabitat scale factors may better predict the co-occurrence of these processes within stream reaches. Overlooking the potential co-occurrence of N2 fixation and denitrification in stream ecosystems will impede understanding by oversimplifying the contribution of each process to the N cycle. 相似文献
997.
Giles E. Hardingham Rickie Patani Paul Baxter David J. Wyllie Siddharthan Chandran 《Molecular neurobiology》2010,42(1):97-102
The capacity to generate myriad differentiated cell types, including neurons, from human embryonic stem (hES) cell lines offers
great potential for developing cell-based therapies and also for increasing our understanding of human developmental mechanisms.
In addition, the emerging development of this technology as an experimental tool represents a potential opportunity for neuroscientists
interested in mechanisms of neuroprotection and neurodegeneration. Potentially unlimited generation of well-defined functional
neurons from hES and patient-specific induced pluripotent cells offers new systems to study disease mechanisms, signalling
pathways and receptor pharmacology within a human cellular environment. Such systems may help in overcoming interspecies differences.
Far from replacing rodent in vivo and primary culture systems, hES and induced disease-specific pluripotent stem cell-derived
neurons offer a complementary resource to overcome issues of interspecies differences, accelerate drug discovery, study of
disease mechanism and provide basic insight into human neuronal physiology. 相似文献
998.
999.
L L Conrad D J Baxter 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1975,150(2):371-373
The intracellular distribution of 45Ca in the rat heart was studied following separate and combined administration of quinidine and propranolol. Both drugs caused an increased uptake of 45Ca in the nuclear-cell membrane fraction but quinidine suppressed the uptake in mitochondrial and microsomal fractions whereas propranolol did not affect the uptake of 45Ca in these fractions. In addition, there was an increase in serum radioactivity noted with quinidine which was not observed with propranolol. Combined treatment resulted in restoration of normal values for blood and mitochondrial fractions and an increased uptake of 45Ca in the microsomal fraction. 相似文献
1000.