全文获取类型
收费全文 | 902篇 |
免费 | 48篇 |
出版年
2022年 | 6篇 |
2021年 | 12篇 |
2020年 | 8篇 |
2019年 | 20篇 |
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 19篇 |
2015年 | 19篇 |
2014年 | 36篇 |
2013年 | 59篇 |
2012年 | 42篇 |
2011年 | 42篇 |
2010年 | 20篇 |
2009年 | 35篇 |
2008年 | 39篇 |
2007年 | 59篇 |
2006年 | 42篇 |
2005年 | 34篇 |
2004年 | 35篇 |
2003年 | 44篇 |
2002年 | 38篇 |
2001年 | 28篇 |
2000年 | 39篇 |
1999年 | 24篇 |
1998年 | 11篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 19篇 |
1991年 | 16篇 |
1990年 | 21篇 |
1989年 | 19篇 |
1988年 | 16篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 3篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 5篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1966年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有950条查询结果,搜索用时 15 毫秒
21.
22.
Summary Paternal age distribution for 1279 cases of Down's syndrome born in 1952–1968 was compared with the corresponding distribution for the general population, corrected for the maternal age as well as for the year of birth of the patients. Although there was no difference in the mean paternal age, the two distributions differed significantly, largely due to the excess of fathers aged 55 years and over and to the deficit of those aged 40–44 years in the patients born to mothers aged 30 years and over. The overall pattern of the relative incidence of Down's syndrome with advancing paternal age, with maternal age controlled, seems consistent with the hypothesis proposed by Stene et al. (1977). It increased from 0.8 for fathers aged 20–24 years slowly up to 1.2 for those aged 45–49 years, though with an intermediate drop to 0.8 at the age of 40–44 years, and then sharply to 2.4 for those aged 55 years and over. This rising pattern of the relative incidence with paternal age was essentially the same for the patients born in 1952–1960 and for those born in 1961–1968, although the slope was less steep in the latter than in the former group.This paper is dedicated to Professor Heinrich Schade in honor of his 70th birthday 相似文献
23.
Occurrence of a factor(s) which can selectively inhibit ribosomal RNA synthesis in isolated neurula cells of Xenopus laevis was examined in oocytes, unfertilized eggs, and embryos of Xenopus laevis. It was found that acid-soluble materials from full-sized oocytes, white-banded mature oocytes, unfertilized eggs, and pregastrular embryos were all active in significantly reducing the relative ratio of the [3H]uridine incorporation into 18S and 28S ribosomal RNA to that into 4S RNA from the control value. These results suggest that the inhibitor appears in the terminal step of oogenesis and, hence, may be assumed as a maternal regulator. 相似文献
24.
25.
H Shimoi T Kawahara K Suzuki Y Iwasaki A Y Jeng Y Nishikawa 《European journal of biochemistry》1992,209(1):189-194
The C-terminal amide structure of peptide hormones and neurotransmitters is synthesized via a two-step reaction catalyzed by peptidylglycine alpha-hydroxylating monooxygenase (PHM) and peptidylhydroxyglycine N-C lyase. A Xenopus laevis PHM expressed in insect-cell culture by the baculovirus-expression-vector system was purified to homogeneity and characterized. Using a newly established assay system for PHM, the kinetic features of this enzyme were investigated. As expected, the enzyme required copper ions, L-ascorbate and molecular oxygen for turnover. Salts like KI and KCl, and catalase stabilized the enzyme in the presence of L-ascorbate. The optimum pH value for the enzyme reaction was around six when Mes buffer was used and around seven when phosphate buffer was used under the same assay condition. Below pH 6, acetate, iodide and chloride ions activated the reaction. The kinetic analysis is consistent with a ping-pong mechanism with respect to peptide and L-ascorbate, and the peptide showed substrate inhibition. The substrate specificity of the enzyme at the penultimate position was examined by competitive assay using tripeptides with glycine at the C-termini and the inhibitory potency of these peptides in descending order was methionine > aromatic > non-polar amino acids. 相似文献
26.
Mechanisms of somatic embryogenesis in cell cultures: Physiology,biochemistry, and molecular biology
A. Komamine R. Kawahara M. Matsumoto S. Sunabori T. Toya A. Fujiwara M. Tsukahara J. Smith M. Ito H. Fukuda K. Nomura T. Fujimura 《In vitro cellular & developmental biology. Plant》1992,28(1):11-14
Summary One of the most characteristic cell functions in plants is totipotency. Somatic embryogenesis can be regarded as a model system
for the investigation of mechanisms of totipotency, because a high frequency and synchronous embryogenic system from single
somatic cells has been established in carrot suspension cultures. Four phases are recognized in this process, and several
molecular markers, viz. polypeptides, mRNAs, antigens against monoclonal antibodies, can be detected during the expression
of totipotency, but they disappear during its loss. Four organ-specific genes have been isolated from hypocotyls and roots
by differential screening. They were expressed preferentially after the globular-heart stages of embryogenesis, and were strongly
suppressed by auxin. A CEM 1 gene was isolated by differential screening of embryogenic cell clusters. This gene was expressed
strongly and transiently during the proglobular and globular stages. The sequence of CEM 1 was found to encode a polypeptide
showing high homology to the elongation factor isolated from eucaryotic cells. Thus good progress is being made in understanding
the basic mechanisms of somatic embryogenesis.
Presented in the Session-in-Depth Developmental Biology of Embryogenesis at the 1991 World Congress on Cell and Tissue Culture,
Anaheim, California, June 16–20, 1991. 相似文献
27.
Ei Matsunaga 《Human genetics》1980,54(1):127-128
Summary Centrometric fission of chromosome 10 is reported in a 25-year-old psychiatric patient and his 51/2-year-old normal daughter. The relevant literature on this subject is briefly reviewed. 相似文献
28.
Y Takai A Kishimoto Y Iwasa Y Kawahara T Mori Y Nishizuka A Tamura T Fujii 《Journal of biochemistry》1979,86(2):575-578
A new multifunctional protein kinase, which normally exists as an inactive form in the soluble fraction in mammalian tissues, attaches to membranes to exhibit full enzymatic activity. A low concentration of Ca2+ is absolutely necessary for this activation. This process is reversible. cAMP shows no effect. The active factors in membranes are phosphatidylinositol, phosphatidylserine, phosphatidic acid, diphosphatidylglycerol, and phosphatidylethanolamine in that order. Phosphatidylcholine and sphingomyelin are far less effective. Cytoplasmic as well as other membrane fractions from various tissues are active in supporting the enzymatic activity. A possible role of this Ca2+ and phospholipid-activated protein kinase system in transmembrane control is proposed. 相似文献
29.
Yoshio Kawahara Tsuyoshi Ohsumi Yasuhiko Yoshihara Shigeho Ikeda 《Bioscience, biotechnology, and biochemistry》2013,77(9):2475-2479
Osmoregulation in Brevibacterium lactofermentum was studied. Proline was accumulated up to approximately 35mg/g dry cell weight in the cells of a wild strain of the bacterium grown under osmotic stress. The osmotic tolerance of a proline auxotroph mutant obtained from the bacterium was lower than that in the wild strain. The activity of pyrroline-5-carboxylate reductase, one of the enzymes in the proline biosynthetic pathway, increased about 3-fold when the cells of B. lactofermentum were grown under osmotic stress. These data indicated that proline is important in osmoregulation in the bacterium. 相似文献
30.