全文获取类型
收费全文 | 541篇 |
免费 | 13篇 |
国内免费 | 1篇 |
专业分类
555篇 |
出版年
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 9篇 |
2016年 | 11篇 |
2015年 | 22篇 |
2014年 | 24篇 |
2013年 | 27篇 |
2012年 | 40篇 |
2011年 | 22篇 |
2010年 | 23篇 |
2009年 | 32篇 |
2008年 | 26篇 |
2007年 | 30篇 |
2006年 | 19篇 |
2005年 | 26篇 |
2004年 | 31篇 |
2003年 | 26篇 |
2002年 | 25篇 |
2001年 | 11篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1982年 | 3篇 |
1979年 | 5篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1970年 | 5篇 |
1969年 | 2篇 |
1965年 | 1篇 |
1964年 | 2篇 |
1963年 | 1篇 |
1961年 | 3篇 |
1958年 | 1篇 |
排序方式: 共有555条查询结果,搜索用时 22 毫秒
131.
CHANGES OF THYMIDINE KINASE IN THE DEVELOPING RAT BRAIN 总被引:4,自引:1,他引:3
Abstract— Thymidine kinase (ATP: thymidine-5'-phosphotransferase EC 2.7.1.21) of the supernatant fraction from 6-day-old rat brain possessed a pH optimum of 8.0 and required the presence of 5mM-ATP and 2.5 mM-MgCl2 for maximum activity. The activity was completely inhibited by addition of 1.8 mM-TTP. The enzyme activity was lost if the same supernatant fraction was refrozen and thawed. Km was 2.8 × 10−6 M for [6-3 H]thymidine.
Following subcellular fractionation of rat brain, the greatest proportion and highest specific activity of thymidine kinase was found in the supernatant fraction. Thymidine kinase activities reached a maximum at 6 days of age and then dropped sharply during maturation. Comparative studies of thymidine kinase activities of cerebrum, cerebellum and the remainder of the brain during growth indicated that the activity in the cerebellum was usually higher than those in the cerebrum and the remainder, and the biggest differences obtained at 6 days after birth corresponded with the peak in cerebellar activity. 相似文献
Following subcellular fractionation of rat brain, the greatest proportion and highest specific activity of thymidine kinase was found in the supernatant fraction. Thymidine kinase activities reached a maximum at 6 days of age and then dropped sharply during maturation. Comparative studies of thymidine kinase activities of cerebrum, cerebellum and the remainder of the brain during growth indicated that the activity in the cerebellum was usually higher than those in the cerebrum and the remainder, and the biggest differences obtained at 6 days after birth corresponded with the peak in cerebellar activity. 相似文献
132.
THYMIDINE METABOLISM AND DEOXYRIBONUCLEIC ACID SYNTHESIS IN THE DEVELOPING RAT BRAIN 总被引:3,自引:0,他引:3
—In growing rat brain, the specific activity of DNA at 12 h after the subcutaneous injection of [3H]thymidine underwent a sharp rise during the first 6 days of life, dropping just as precipitously by 15 days, thereafter continuing to decrease with increasing age. When [3H]thymidine was given to 6-day-old rats, a considerable amount was taken up immediately into the brain. Thymidine taken up into the acid-soluble fraction was readily phosphorylated to its nucleotides, thymidine mono-, di-, and triphosphate (TMP, TDP and TTP) within only 30 min following injection. The highest specific activity was found in TTP. The incorporation of of [3H]thymidine into DNA took place over a longer period of time after injection. 相似文献
133.
Masaru Nakano Hiroto Umehara Yoshihiro Hara Motohide Makino Mika Igarashi Mutsumi Nakada Toru Nakamura Yoichiro Hoshino Akira Kanno 《Molecular breeding : new strategies in plant improvement》2007,20(4):425-429
The class B genes, which belong to the MADS-box gene family, play important roles in regulating petal and stamen development
in flowering plants. These genes exist in two different types termed DEF- and GLO-like genes, and the B-function is provided by heterodimers of a DEF- and a GLO-like gene product. In the present study, dicot (tobacco and lettuce) and monocot (Tricyrtis hirta) plants were transformed with the GLO-like gene of Agapanthus praecox ssp. orientalis
ApGLO alone or in combination with the DEF-like gene of the same plant ApDEF. In two out of 10 transgenic tobacco plants containing ApGLO, sepals partially converted into petaloid organs. For lettuce, ray florets of four out of nine transgenic plants containing
ApGLO also developed additional petaloid organs. In two out of five transgenic T. hirta plants containing both ApGLO and ApDEF, organs developed in whorl 4 showed noticeable morphological alteration: they were much longer compared with carpels of non-transgenic
plants, and had purple spots overall on the surface as filaments of non-transgenic plants. No morphological alterations were
observed in vegetative organs between transgenic and non-transgenic plants for all the three species. The results obtained
in the present study indicate a possibility of molecular breeding for flower form alteration by genetic transformation with
the class B MADS-box gene(s) of heterologous plant species. 相似文献
134.
135.
Mutsumi Fukuda Seiji Watanabe Jun Kaneko Yoshifumi Itoh Yoshiyuki Kamio 《Journal of bacteriology》2009,191(5):1641-1649
136.
Honda A Yamashita K Hara T Ikegami T Miyazaki T Shirai M Xu G Numazawa M Matsuzaki Y 《Journal of lipid research》2009,50(2):350-357
We describe a highly sensitive and specific method for the quantification of key regulatory oxysterols in biological samples. This method is based upon a stable isotope dilution technique by liquid chromatography-tandem mass spectrometry (LC-MS/MS). After alkaline hydrolysis of human serum (5 microl) or rat liver microsomes (1 mg protein), oxysterols were extracted, derivatized into picolinyl esters, and analyzed by LC-MS/MS using the electrospray ionization mode. The detection limits of the picolinyl esters of 4beta-hydroxycholesterol, 7alpha-hydroxycholesterol, 22R-hydroxycholesterol, 24S-hydroxycholesterol, 25-hydroxycholesterol, 27-hydroxycholesterol, and 24S,25-epoxycholesterol were 2-10 fg (5-25 amol) on-column (signal-to-noise ratio = 3). Reproducibilities and recoveries of these oxysterols were validated according to one-way layout and polynomial equation, respectively. The variances between sample preparations and between measurements by this method were calculated to be 1.8% to 12.7% and 2.9% to 11.9%, respectively. The recovery experiments were performed using rat liver microsomes spiked with 0.05 ng to 12 ng of oxysterols, and recoveries of the oxysterols ranged from 86.7% to 107.3%, with a mean recovery of 100.6%. This method provides reproducible and reliable results for the quantification of oxysterols in small amounts of biological samples. 相似文献
137.
Yusuke Yamanoue Masaki Miya Keiichi Matsuura Harumi Sakai Masaya Katoh Mutsumi Nishida 《Molecular phylogenetics and evolution》2009,50(1):179-189
Balistoid fishes have a unique and reduced pelvic fin structure, which does not exhibit paired structures. The pelvic complex exhibits reductive trends, but its rudimentary structure was retained among balistoids, and its unidirectional and parsimonious reduction in more derived lineages has been hypothesized based on morphology. We investigated the evolution of pelvic complex reduction in balistoids using whole mitochondrial genome (mitogenome) data from 33 species (27 newly determined during the study) that represent the entire morphological diversity of balistoids. Partitioned maximum likelihood and Bayesian analyses were conducted with two datasets that comprised concatenated nucleotide sequences from 13 protein-coding genes (all positions included; third codon positions converted into purine [R] and pyrimidine [Y] [RY-coding]) plus 22 transfer RNA and two ribosomal RNA genes. The resultant trees were well resolved and largely congruent, with most internal branches having high support values. The mitogenomic datasets strongly supported monophylies of both balistids and monacanthids, but rejected previous hypotheses on the intra-relationships in each family. The present tree topology revealed that highly reduced pelvic complexes had multiple origins, and optimization of the traits on the resultant tree strongly suggested the non-unidirectional and independent reduction of pelvic complexes in balistoids. The evolution of balistoid pelvic structure is very different among fishes that exhibit its reductive trends, and this uniqueness in pelvic evolution may be a link to their reproductive behaviors. 相似文献
138.
Mutsumi Takagi 《Biotechnology and Bioprocess Engineering》2010,15(1):54-60
The noninvasive quality estimation of adherent mammalian cells for transplantation is reviewed. The quality and heterogeneity
of cells should be estimated before transplantation because cultured cells are not homogeneous but heterogeneous. The estimation
of cell quality should be performed noninvasively because most protocols of regenerative medicine are autologous cell system.
The differentiation level and contamination of other cell lineage could be estimated by two-dimensional cell morphology analysis
and tracking using a conventional phase contrast microscope. The noninvasive determination of the laser phase shift of a cell
using a phase-shifting laser microscope, which might be more noninvasive, and more useful than the atomic force microscope
and digital holographic microscope, was carried out to determine the three-dimensional cell morphology, and the estimation
of the cell cycle phase of each adhesive cell and the mean proliferation activity of a cell population. Chemical analysis
of the culture supernatant by conventional analytical methods such as ELISA was also useful to estimate the differentiation
level of a cell population. Chemical analysis of cell membrane and intracellular components using a probe beam, an infrared
beam, and Raman spectroscopy was useful for diagnosing the viability, apoptosis, and differentiation of each adhesive cell. 相似文献
139.
Cardinalfishes of the genus Apogon (Apogonidae) are one of the most speciose (>200 species) and numerically dominant fishes in coral reefs. Although the genus is divided into 10 subgenera, more than 70% of the species are included in the subgenus Ostorhinchus, most having either horizontal or vertical lines on the body. The phylogenetic relationship among 32 species of subgenus Ostorhinchus and 11 species of four other subgenera of Apogon, based on mitochondrially encoded 12S and 16S ribosomal genes and intervening tRNA(Val) gene, were investigated, using two species of the apogonid genus Fowleria as outgroups. The analyses demonstrated that Ostorhinchus (the most speciose subgenus) was polyphyletic, comprising at least three lineages, Ostorhinchus I, II, and III. Ostorhinchus I included two species, A. (O.) amboinensis and A. (O.) sangiensis, being a sister group to subgenus Zoramia. Ostorhinchus II and III included species with horizontal and vertical lines on the body, respectively. The respective monophylies of the latter two groups, together with a molecular clock calibration, indicated that in the evolutionary history of the genus, basic stripe patterns evolved first (more than 20 million years BP), with subsequent pattern diversification and modification. 相似文献
140.
Mutsumi Watanabe Dirk Walther Yoshiaki Ueda Katsuhiko Kondo Satoru Ishikawa Takayuki Tohge Asdrubal Burgos Yariv Brotman Alisdair R Fernie Rainer Hoefgen Matthias Wissuwa 《Plant, cell & environment》2020,43(9):2066-2079
Utilizing phosphate more efficiently is crucial for sustainable crop production. Highly efficient rice (Oryza sativa) cultivars have been identified and this study aims to identify metabolic markers associated with P utilization efficiency (PUE). P deficiency generally reduced leaf P concentrations and CO2 assimilation rates but efficient cultivars were reducing leaf P concentrations further than inefficient ones while maintaining similar CO2 assimilation rates. Adaptive changes in carbon metabolism were detected but equally in efficient and inefficient cultivar groups. Groups furthermore did not differ with respect to partial substitutions of phospholipids by sulfo- and galactolipids. Metabolites significantly more abundant in the efficient group, such as sinapate, benzoate and glucoronate, were related to antioxidant defence and may help alleviating oxidative stress caused by P deficiency. Sugar alcohols ribitol and threitol were another marker metabolite for higher phosphate efficiency as were several amino acids, especially threonine. Since these metabolites are not known to be associated with P deficiency, they may provide novel clues for the selection of more P efficient genotypes. In conclusion, metabolite signatures detected here were not related to phosphate metabolism but rather helped P efficient lines to keep vital processes functional under the adverse conditions of P starvation. 相似文献