全文获取类型
收费全文 | 1052篇 |
免费 | 73篇 |
出版年
2023年 | 6篇 |
2022年 | 15篇 |
2021年 | 26篇 |
2020年 | 20篇 |
2019年 | 20篇 |
2018年 | 34篇 |
2017年 | 18篇 |
2016年 | 31篇 |
2015年 | 54篇 |
2014年 | 64篇 |
2013年 | 101篇 |
2012年 | 89篇 |
2011年 | 74篇 |
2010年 | 51篇 |
2009年 | 25篇 |
2008年 | 36篇 |
2007年 | 54篇 |
2006年 | 46篇 |
2005年 | 38篇 |
2004年 | 43篇 |
2003年 | 32篇 |
2002年 | 35篇 |
2001年 | 20篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 13篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 14篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1979年 | 9篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1972年 | 2篇 |
1970年 | 2篇 |
1967年 | 5篇 |
1925年 | 1篇 |
1921年 | 1篇 |
排序方式: 共有1125条查询结果,搜索用时 17 毫秒
41.
42.
43.
The α-d-galactosidases of six Streptomyces strains were examined on their inducer susceptibility, substate specificity, and inhibitor susceptibility. In all strains examined, α-d-galactosidase was induced by d-galactose, but neither by d-fucose nor by l-arabinose. α-d-Fucosidase activity was always induced accompanying with α-d-galactosedase activity. β-l-Arabinosidase activity, however, was never observed. These α-d-galactosidases were purified to electrophoretically pure degree by successive ammonium sulfate and ethanol precipitation, and ion exchange and gel filtration chromatography. The purified preparations from six strains were different from each other in their chromatographic behaviors and in some physical properties, but they all showed strong α-d-fucosidase activity as well. The α-d-galactosidase activities were strongly inhibited by d-galactose and l-arabinose, but scarcely by d-fucose. On the other hand, their α-d-fucosidase activities were inhibited by d-fucose as well as by d-galactose and l-arabinose. 相似文献
44.
Yuzo Yamada Kazuaki Iizuka Kô Aida Teijiro Uemura 《Bioscience, biotechnology, and biochemistry》2013,77(1):97-98
A crude inhibitor for pancreatic lipase was extracted from soybean seeds. The lipase activity decreased curvilinearly with an increase in inhibitor concentration. At a low inhibitor concentration, enhanced inhibition was observed by the co-existence of protein such as bovine serum albumin in the reaction mixture. The lipase activity was inhibited immediately after the addition of inhibitor which did not cause the significant destraction of substrate emulsion. The lipase activities of Aspergillus niger, Rhizopus delemar and castor bean seeds were also inhibited. The inhibition was observed when various oil substrates such as soybean oil, linseed oil, olive oil emulsions and Ediol were used, and the extent of inhibition varied among them. Column chromatography of inhibitor on Sephadex G–100 showed that the molecular weight of a main peak of inhibitor was estimated as about 80,000. 相似文献
45.
Mina Fujitani Takafumi Mizushige Keshab Bhattarai Asami Iwahara Ryojiro Aida 《Bioscience, biotechnology, and biochemistry》2013,77(7):1164-1171
We investigated the effect of daidzein feeding and estradiol treatment on food intake in cholecystokinin-1 receptor (CCK1R) deficiency, leptin receptor (ObRb) deficiency rats and their wild-type rats. These rats underwent an ovariectomy or a sham operation. For the 5 week experiment, each rat was divided in three groups: control, daidzein (150 mg/kg diet), and estradiol (4.2 μg/rat/day) groups. In both CCK1R+ and CCK1R? rats, daidzein feeding and estradiol treatment significantly decreased food intake. Daidzein feeding significantly reduced food intake in ovariectomized ObRb? rats, although not in ObRb+ rats. Estradiol treatment significantly lowered food intake in ovariectomized ObRb+ and ObRb? rats. In the ovariectomized rats, estradiol treatment significantly increases uterine weight, while daidzein feeding did not change it, suggesting that daidzein might have no or weak estrogenic effect in our experiment. These results suggest that CCK1R and ObRb signalings were not essential for the daidzein- and estradiol-induced anorectic action. 相似文献
46.
l-Glutamic acid was formed from d-, l-, and dl-PCA with cell-free extract of Pseudomonas alcaligenes ATCC-12815 grown in the medium containing dl-PCA as a sole source of carbon and nitrogen. The enzyme(s) involved in this conversion reaction was distributed in the soluble fraction within the cell and in 0.5 saturated fraction at the fractionation procedure with the saturation of ammonium sulfate. Optimum pH of this enzyme(s) lied at pH 8.5 and optimum temperature was 30°C. Cu (5 × 10?3 m) inhibited the reaction considerably while Ca or Fe accelerated it. PALP (1×10?3 m) also gave an enhanced activity to some extent. The enzyme preparation converted dextro-rotatory enan-thiomorph of PCA to its laevo-rotatory one which in turn was not converted to the opposite rotation direction by this enzyme. Furthermore, the preparation did not, if any, show d-glutamic acid racemase activity. Isotopic experiments with using dl-PCA-1-14C revealed that l-glutamic acid-1-14C was formed by the cleavage of –CO–NH– bond of pyrrolidone ring of PCA. It was concluded that dl-PCA when assimilated by the present bacterium is at first transformed to l-PCA by the optically isomerizing enzyme and subsequently is cleaved to l-glutamic acid probably by the PCA hydrolysing enzyme. 相似文献
47.
Background
Aging of the immune system, known as immunosenescence, is associated with profound changes in both innate and adaptive immune responses, resulting in increased susceptibility to infection and a decreased ability to respond to vaccination. The purpose of this study was to investigate the effect of age and menopause on the expression of 22 different cytokines/chemokines in both plasma and cervical lavage samples from female sex-worker cohort from Nairobi, Kenya (age range 20–65).Results
Cytokine/chemokine levels were measured using a Miliplex multiplex assay (Millipore). We found that age positively correlated with MCP-1 (p?=?0.0002) and IP-10 (p?=?0.03) systemic cytokine expression, and that women over 50 expressed the highest levels of these cytokines, but also had elevated expression of MIG (ANOVA p?=?0.0096) and MIP-3β(ANOVA p?=?0.0434). We also found that IL-8 (p?=?0.047) and sCD40L (p?=?0.01) systemic expression negatively correlated with age. Further, MIG (p?=?0.0081) and MCP-1 (p?=?0.0157) were present at higher levels in post-menopausal women suggesting a potential estrogen dependant systemic regulation of these cytokines. In cervical lavage samples, age did not directly correlate with the expression of any of the tested cytokines/chemokines, however sIL-2Rα (ANOVA p?=?0.0170) and IL-15 (ANOVA p?=?0.0251)were significantly higher in women over 50. Menopause was shown to have a more profound effect on cytokine expression in the cervical mucosa with MIG (p?=?0.0256), MIP-3α (p?=?0.0245), IL-1β (p?=?0.0261), IL-6 (p?=?0.0462), IL-8 (p?=?0.007), IP-10 (p?=?0.0357) and MCP-1 (p?=?0.0427) all significantly under-expressed in post-menopausal women.Conclusions
This study demonstrates that aging and menopause-associated hormonal changes are associated with significant changes in systemic and mucosal cytokine/chemokine expression, which may have implications for the age-related decline in the ability to fight against infections.48.
49.
Pathogens and the diseases they cause have been among the most important selective forces experienced by humans during their evolutionary history. Although adaptive alleles generally arise by mutation, introgression can also be a valuable source of beneficial alleles. Archaic humans, who lived in Europe and Western Asia for more than 200,000 years, were probably well adapted to this environment and its local pathogens. It is therefore conceivable that modern humans entering Europe and Western Asia who admixed with them obtained a substantial immune advantage from the introgression of archaic alleles. Here we document a cluster of three Toll-like receptors (TLR6-TLR1-TLR10) in modern humans that carries three distinct archaic haplotypes, indicating repeated introgression from archaic humans. Two of these haplotypes are most similar to the Neandertal genome, and the third haplotype is most similar to the Denisovan genome. The Toll-like receptors are key components of innate immunity and provide an important first line of immune defense against bacteria, fungi, and parasites. The unusually high allele frequencies and unexpected levels of population differentiation indicate that there has been local positive selection on multiple haplotypes at this locus. We show that the introgressed alleles have clear functional effects in modern humans; archaic-like alleles underlie differences in the expression of the TLR genes and are associated with reduced microbial resistance and increased allergic disease in large cohorts. This provides strong evidence for recurrent adaptive introgression at the TLR6-TLR1-TLR10 locus, resulting in differences in disease phenotypes in modern humans. 相似文献
50.