全文获取类型
收费全文 | 4515篇 |
免费 | 299篇 |
出版年
2021年 | 48篇 |
2020年 | 23篇 |
2019年 | 33篇 |
2018年 | 50篇 |
2017年 | 40篇 |
2016年 | 66篇 |
2015年 | 97篇 |
2014年 | 129篇 |
2013年 | 230篇 |
2012年 | 198篇 |
2011年 | 201篇 |
2010年 | 127篇 |
2009年 | 119篇 |
2008年 | 172篇 |
2007年 | 207篇 |
2006年 | 196篇 |
2005年 | 187篇 |
2004年 | 203篇 |
2003年 | 211篇 |
2002年 | 198篇 |
2001年 | 189篇 |
2000年 | 204篇 |
1999年 | 158篇 |
1998年 | 73篇 |
1997年 | 69篇 |
1996年 | 56篇 |
1995年 | 43篇 |
1994年 | 38篇 |
1993年 | 33篇 |
1992年 | 84篇 |
1991年 | 105篇 |
1990年 | 96篇 |
1989年 | 95篇 |
1988年 | 81篇 |
1987年 | 82篇 |
1986年 | 78篇 |
1985年 | 78篇 |
1984年 | 60篇 |
1983年 | 63篇 |
1982年 | 34篇 |
1981年 | 25篇 |
1980年 | 16篇 |
1979年 | 41篇 |
1978年 | 26篇 |
1977年 | 30篇 |
1976年 | 22篇 |
1975年 | 21篇 |
1974年 | 24篇 |
1973年 | 30篇 |
1970年 | 17篇 |
排序方式: 共有4814条查询结果,搜索用时 187 毫秒
81.
Mutants of Group D1Salmonella Carrying the Somatic Antigen of Group A Organisms: Evidence for the Lack of Cytidine Diphosphate Paratose-2-Epimerase Activity 总被引:3,自引:3,他引:0 下载免费PDF全文
The mutant strains of Salmonella durban that possessed O antigen 2, 12 of group A Salmonella were defective in the cytidine diphosphate paratose-2-epimerase activity. The enzyme preparation of the mutant strains catalyzed the conversion of cytidine diphosphate glucose into cytidine diphosphate paratose but not into cytidine diphosphate tyvelose. The defect in the epimerase activity was also confirmed by the use of purified cytidine diphosphate paratose as a substrate. The specificity of dideoxyhexosyl transferase catalyzing the formation of the group-specific determinant is discussed. 相似文献
82.
T Suda N Horiuchi S Sasaki E Ogata I Ezawa 《Biochemical and biophysical research communications》1973,54(2):512-518
Kidney mitochondria were isolated from rachitic chicks and their activity in the metabolism of 25-OH-D3 was studied in relation to the amount of calcium added . The addition of 0.050.2 mM calcium to a mitochondrial suspension caused a marked and dose-related stimulation of 1-hydroxylation. A sharp decline in the activity was induced by higher concentrations (0.3-0.5 mM) of calcium. The rate of 24-hydroxylation was not influenced by calcium. In these effects, calcium was relatively specific among various divalent cations. These data strongly suggest that calcium is directly involved in the regulation of the vitamin D activation in kidney mitochondria. 相似文献
83.
84.
85.
86.
87.
88.
The meiotic chromosomes of man 总被引:4,自引:0,他引:4
Summary Information was obtained on the chromosome number, and the behavior of autosomes as well as of the sex chromosomes in meiosis in human male germ cells derived from 25 Japanese patients, 4 to 79 years in age, who were hospitalized mostly due to epididymitis, prostate cancer, undescended testes or infertility.In 16 out of the 25 specimens, the chromosome numbers, 46 in 2n and 23 in n, were consistently established together with an XY sex-determining mechanism based on spermatogonial and spermatocyte divisions. No reliable counts were obtained from the remaining 9 cases, because of that they provided no cells for precise investigation.The X and Y chromosomes during the leptotene stage were observed as two separate heteropycnotic bodies lying along the inner wall of the nucleus, while at pachytene they formed a sex-vesicle after homologous pairing. At the diplotene, diakinesis and first metaphase the X and the Y appeared as an isopycnotic bivalent showing an end-to-end association, though there were some cells in which they remained as two separate entities free from contact. Evidence was presented that the X and the Y seemed to associate with each other at the distal end of the short arm of each element.One or sometimes two smallest autosomal bivalents tended to show rather precociously a chiasma-terminalization at the first metaphase.The metaphase chromosomes of the second spermatocytes were evident by the haploid number as well as by their widely diverged chromatids with a characteristic spiral configuration.The testicular materials under study contained in most cases polyploid cells with a considerable frequency in spermatogonia as well as in first and second spermatocytes. Giant sperm heads were observed not infrequently, mostly being abnormal in shape. No significant correlation was obtained between the frequency of polyploid cells and the age of patients so far studied.Contribution No. 679 from the Zoological Institute, Faculty of Science, Hokkaido University, Sapporo. — It is our pleasure to dedicate this paper to Professor Dr. Hans Bauer, Max-Planck-Institut für Meeresbiologie, Tübingen, in honor of his sixtieth birthday. 相似文献
89.
Since Fasciola sp. contained proteolytic enzyme(s), it was confirmed that degradation took place in protein components in extracts of the liver flukes, which resulted in lack of clarity of sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Degradation was shown to occur mostly during a heating process of the extract samples. The proteolytic activity in the extracts was completely blocked and electrophoretic patterns were improved only by the use of cysteine proteinase inhibitor N-[N-(L-3-trans-carboxyoxiran-2-carbonyl)-L-leucyl]-agmatine (E-64). Great improvement was also noted in electrophoretic patterns of the extracts of other trematodes, such as Paragonimus westermani, P. miyazakii and Clonorchis sinesis, when their extracts were treated with E-64. 相似文献
90.