全文获取类型
收费全文 | 67875篇 |
免费 | 5399篇 |
国内免费 | 558篇 |
出版年
2023年 | 264篇 |
2022年 | 681篇 |
2021年 | 1451篇 |
2020年 | 953篇 |
2019年 | 1174篇 |
2018年 | 1573篇 |
2017年 | 1347篇 |
2016年 | 2136篇 |
2015年 | 3292篇 |
2014年 | 3744篇 |
2013年 | 4301篇 |
2012年 | 5512篇 |
2011年 | 5193篇 |
2010年 | 3250篇 |
2009年 | 3003篇 |
2008年 | 4038篇 |
2007年 | 3820篇 |
2006年 | 3375篇 |
2005年 | 3108篇 |
2004年 | 2911篇 |
2003年 | 2509篇 |
2002年 | 2214篇 |
2001年 | 1788篇 |
2000年 | 1674篇 |
1999年 | 1372篇 |
1998年 | 608篇 |
1997年 | 552篇 |
1996年 | 435篇 |
1995年 | 386篇 |
1994年 | 390篇 |
1993年 | 350篇 |
1992年 | 591篇 |
1991年 | 566篇 |
1990年 | 504篇 |
1989年 | 458篇 |
1988年 | 385篇 |
1987年 | 365篇 |
1986年 | 318篇 |
1985年 | 281篇 |
1984年 | 218篇 |
1983年 | 201篇 |
1982年 | 169篇 |
1981年 | 164篇 |
1980年 | 150篇 |
1979年 | 185篇 |
1978年 | 172篇 |
1976年 | 131篇 |
1975年 | 145篇 |
1974年 | 163篇 |
1973年 | 128篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The effect of carbohydrate depletion on procoagulant activity and in vivo survival of highly purified human factor VIII 总被引:1,自引:0,他引:1
P J Fay S I Chavin J E Malone D Schroeder F E Young V J Marder 《Biochimica et biophysica acta》1984,800(2):152-158
Human factor VIII procoagulant protein (factor VIII) was purified using a modification of our previously described method, in which Sephacryl S-400 elution, rather than QAE-cellulose chromatography, served as the final purification step. The protein had a specific activity of more than 2500 U/mg and consisted of a single polypeptide (Mr 100 000) when analyzed by SDS-polyacrylamide gel electrophoresis. Factor VIII was shown to be a glycoprotein by staining with periodic acid-Schiff's reagent following electrophoresis. Treatment of factor VIII with a mixture of exo- and endoglycosidases caused a reduction by about 50% in the intensity of periodic acid-Schiff staining, as determined by scanning densitometry, and an increase in electrophoretic mobility (equivalent to a new Mr 95 000). Removal of this portion of the total carbohydrate had no significant effect on factor VIII clotting activity or on thrombin potentiation of clotting activity. The in vivo survival curves of a native and sugar-depleted 125I-labeled factor VIII both showed similar patterns of initial rapid decay to 60 and 40% activity, respectively, followed by a one-half decay time of 4 h for both. These results suggest that the carbohydrate portion of human factor VIII does not contribute significantly to either clotting function in vitro or to biological turnover in vivo. 相似文献
2.
Plant somatic cells have the capability to switch their cell fates from differentiated to undifferentiated status under proper
culture conditions, which is designated as totipotency. As a result, plant cells can easily regenerate new tissues or organs
from a wide variety of explants. However, the mechanism by which plant cells have such remarkable regeneration ability is
still largely unknown. In this study, we used a set of meristem-specific marker genes to analyze the patterns of stem cell
differentiation in the processes of somatic embryogenesis as well as shoot or root organogenesis in vitro. Our studies furnish preliminary and important information on the patterns of the de novo stem cell differentiation during various types of in vitro organogenesis. 相似文献
3.
4.
Cristian A. Acevedo Elizabeth Y. Sanchez Juan G. Reyes Manuel E. Young 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2010,878(3-4):449-455
It is known that skin releases volatile organic compounds to the environment, and also that its emission pattern changes with aging of the skin. It could be considered, that these compounds are intermediaries in cell metabolism, since many intermediaries of metabolic pathways have a volatile potential. In this work, a simple and non-destructive method consisting of SPME sampling and GC/MS analysis was developed to identify volatile organic emanations from cell cultures. This technique, applied to skin cells culture, indicates that the cells or cell metabolism produce several skin emissions. Chemometric analysis was performed in order to explore the relationship between a volatile profile and the senescence of cell cultures. Volatile profiles were different for cell cultures in different degrees of senescence, indicating that volatile compound patterns could be used to provide information about the age of skin cells. 相似文献
5.
6.
7.
8.
9.
K. H. Jang J. W. Seo K. B. Song C. H. Kim S. K. Rhee 《Bioprocess and biosystems engineering》1999,21(5):453-458
Secretion of levansucrase from Zymomonas mobilis in Escherichiacoli by glycine supplement was investigated. A significant amount of levansucrase (about 25% of total activity) was found in intact whole-cells. Cell fractionation experiments showed that levansucrase was found both in the periplasmic space and in the cytoplasmic fraction of E. coli. None or only trace amounts of levansucrase was detected in the extracellular culture broth at 24 h of cultivation and it accrued with the increasing concentration of glycine in the culture medium and duration of the culture period. Optimal glycine concentration for the maximum secretion of levansucrase was in the range of 0.8-1%, in which approximately 20-50% of levansucrase was released into the extracellular fraction at 24 h of cultivation, although glycine retarded the bacterial growth. 相似文献
10.
A recombinant cell line (NIH3T3:pLtkSN) was made by infecting parental cells (NIH3T3) with a recombinant retrovirus (pLtkSN) encoding herpes simplex virus thymidine kinase (HSVtk) gene. The cells expressing HSVtk (NIH3T3:pLtkSN) grew 2.3 times more than the parental cells (NIH3T3) in Dulbecco's Modified Eagles Media containing 10% (v/v) horse serum. The NIH3T3:pLtkSN cells also showed a significant enhancement in the maximal cell concentration and the specific growth rate even at 2.5% serum concentration. The specific O2 uptake rate of NIH3T3 was 2.1 times greater than that of NIH3T3:pLtkSN. Under both O2-limited and O2-unlimited conditions, it appears that HSVtk plays an important role in enhancing the growth characteristics of animal cells. 相似文献