全文获取类型
收费全文 | 2171篇 |
免费 | 149篇 |
国内免费 | 2篇 |
出版年
2022年 | 14篇 |
2021年 | 44篇 |
2020年 | 16篇 |
2019年 | 22篇 |
2018年 | 31篇 |
2017年 | 29篇 |
2016年 | 48篇 |
2015年 | 80篇 |
2014年 | 99篇 |
2013年 | 140篇 |
2012年 | 152篇 |
2011年 | 134篇 |
2010年 | 94篇 |
2009年 | 100篇 |
2008年 | 97篇 |
2007年 | 119篇 |
2006年 | 101篇 |
2005年 | 82篇 |
2004年 | 88篇 |
2003年 | 76篇 |
2002年 | 53篇 |
2001年 | 51篇 |
2000年 | 59篇 |
1999年 | 33篇 |
1998年 | 23篇 |
1997年 | 24篇 |
1996年 | 13篇 |
1995年 | 19篇 |
1994年 | 19篇 |
1993年 | 25篇 |
1992年 | 26篇 |
1991年 | 40篇 |
1990年 | 16篇 |
1989年 | 19篇 |
1988年 | 21篇 |
1987年 | 23篇 |
1986年 | 13篇 |
1985年 | 22篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1979年 | 17篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 17篇 |
1974年 | 11篇 |
1973年 | 24篇 |
1972年 | 13篇 |
1971年 | 16篇 |
1967年 | 14篇 |
1966年 | 12篇 |
排序方式: 共有2322条查询结果,搜索用时 15 毫秒
1.
2.
Nitrous oxide (N2O) decreased in vivo oxidation of histidine in rats fed a basal diet marginally deficient in methionine, although hepatic levels of S-adenosylmethionine (AdoMet) were not significantly altered. Excess dietary methionine increased hepatic levels of AdoMet and increased histidine oxidation. However, it did not protect histidine oxidation when the rats were treated with N2O. Parenteral administration of methionine greatly increased hepatic levels of AdoMet and increased histidine oxidation in normal and N2O treated rats. This indicates that when hepatic levels of AdoMet are greatly elevated by administration of methionine, N2O does not affect in vivo histidine oxidation. 相似文献
3.
Summary Maximum lipase production byAspergillus foetidus was obtained from cultures grown in the medium of 2% olive oil and 0.5% sucrose. The optimal conditions for the production of lipases in the Multigen fermenters were found to be at 500rpm with an airflow of 1.5 liter per mimute. Immobilization of the fungal source was found to be infeasible in natural polymers. 相似文献
4.
It is shown for the first time that the content of ubiquinone of liver increases (2.5 fold) on dietary administration of the
widely-used industrial Plasticizer diethylhexyl Phthalate to the rat. The increase is localized almost entirely in mitochondria
in which the concentration of the quinone Per mg Protein is 1.7 times the control. IncorPoration of the radioactive Precursor
(acetate) reveals that the biosynthesis of ubiquinone is increased in the livers of Plasticizer-administered animals. The
rate of degradation is not altered. 相似文献
5.
Lectins, the divalent or polyvalent (glyco) proteins of non-immune origin of the cells agglutinate cells or other materials,
that display more than one saccharide of sufficient complementarity. Lectins considered ‘identical’ in terms of mono-and disaccharide
specificity can be differentiated by their ability to recognise the fine differences in more complex structures. The present
review discusses the interaction of lectins with various oligosaccharides and their resultant separations due to structural
variations. 相似文献
6.
The development of sclerotia of Botrytis cinerea was examined at four stages during their maturation. The surface structure developed a network of profusely branched hyphae through their coalescence to a compact sclerotial body which was maturated by the deposition of melanin pigment. A characteristic feature of the hyphal cells of B. cinerea during the later stages of development was the presence of paramural bodies (plasmalemmasomes and lomasomes). Electrondense bodies with a limiting double-membrane congregated against the transverse septa of hyphal cells as sclerotia matured and may migrate from cell to cell through septal pores. We suggest that these and the lipid bodies found in hyphal cells may have a storage function in the resting sclerotia. 相似文献
7.
The -galactosidase (EC 3.2.1.32) of Corynebacterium murisepticum (inducible by lactose and galactose) was purified by successive column chromatography on Sephadex G-200, DEAE-Sephadex A-50 and DEAE-cellulose (DE52). The enzyme was found to be a dimer of identical subunits of molecular mass 100,000 daltons. The K
m values of the enzyme for the substrates lactose and o-nitrophenyl--d-galactopyranoside (ONPG) are 16.7 mM and 4.4 mM, respectively, indicating, its low affinity for the substrates. The Ouchterlony immunodiffusion method exhibited immunological homogeneity of the enzyme preparation. The catalytic site of the enzyme does not take part in antigen-antibody reaction. 相似文献
8.
P R Taylor M H Schiffman D Y Jones J Judd A Schatzkin P P Nair R Van Tassell G Block 《Mutation research》1988,206(1):3-9
Correlation studies suggest that fecal mutagenicity is increased in groups eating high-fat diets, the same groups who are often found to have high colorectal cancer incidence and mortality. The fecapentaenes are the best characterized class of fecal mutagens, but the relationship of dietary fat intake to the excretion of these potent genotoxins is unknown. We studied the effect of changes in amount and type of dietary fat on fecapentaene levels in 31 premenopausal women 20-40 years of age who participated in a controlled feeding study. After a pre-diet free-living period lasting 1 menstrual cycle, women were placed on a high-fat (40% energy from fat) diet for 4 menstrual cycles and then switched to a low-fat (20% energy from fat) diet for an additional 4 menstrual cycles. One-half the subjects were maintained throughout the study at a ratio of polyunsaturated-to-saturated fatty acids (P/S ratio) of 1.0, the other half at 0.3; body weight was constant. All meals during the controlled diet periods were prepared at the Human Study Facility of the Beltsville Human Nutrition Research Center. Fecapentaene and fecapentaene precursor levels were measured in acetone extracts from 3-day pooled stool samples collected during the study. No differences in fecapentaene or precursor levels were observed between the high- and low-fat diets at either P/S ratio. Fecapentaene and precursor levels were higher while on controlled diets than during the pre-diet free-living period, and levels declined again in the post-diet free-living period. We conclude that dietary fat has no significant effect on fecapentaene or precursor levels in acetone extracts of stool in premenopausal women. The effect of other dietary or non-dietary factors on fecapentaenes remains unknown. 相似文献
9.
Effect of saffron on thymocyte proliferation, intracellular glutathione levels and its antitumor activity. 总被引:1,自引:0,他引:1
S C Nair M J Salomi C D Varghese B Panikkar K R Panikkar 《BioFactors (Oxford, England)》1992,4(1):51-54
Liposome encapsulation of saffron effectively enhanced its antitumor activity towards Sarcoma-180 (S-180) and Ehrlich ascites carcinoma solid tumors in mice. Significant inhibition (P < 0.001) in the growth of these tumors was observed as compared with vehicle (control) mice. In the presence of phytohemagglutinin (PHA), a T cell mitogen, saffron stimulated non-specific proliferation of lymphocytes in vitro. The intracellular reduced glutathione and related enzymes, i.e. glutathione reductase and glutathione-S-transferase, of S-180 tumor cells were significantly elevated when incubated with saffron, possibly acting to maintain functional levels of other antioxidants. Our studies indicate the antioxidant activity of saffron. 相似文献
10.
A sucrose density gradient analysis of3H-uridine pulse-labelled RNA from the first postirradiation mitotic cycle ofPhysarum polycephalum shows that all the density classes of RNA synthesized during this period are resistant to the peptide-antibiotic, actinomycin
D. In fact, the synthesis is found to be greater in the presence of the drug. The heterogenously sedimenting synthetic activity
here may represent a single species of RNA and its precursors or more than one kind of RNA. Further characterization of this
RNA is meaningful in view of the actinomycin insensitivity of the postirradiation mitotic cycle itself to this antibiotic. 相似文献