全文获取类型
收费全文 | 3805篇 |
免费 | 264篇 |
出版年
2023年 | 18篇 |
2022年 | 57篇 |
2021年 | 101篇 |
2020年 | 48篇 |
2019年 | 64篇 |
2018年 | 100篇 |
2017年 | 75篇 |
2016年 | 126篇 |
2015年 | 210篇 |
2014年 | 232篇 |
2013年 | 281篇 |
2012年 | 325篇 |
2011年 | 320篇 |
2010年 | 206篇 |
2009年 | 170篇 |
2008年 | 244篇 |
2007年 | 235篇 |
2006年 | 204篇 |
2005年 | 187篇 |
2004年 | 173篇 |
2003年 | 177篇 |
2002年 | 156篇 |
2001年 | 31篇 |
2000年 | 27篇 |
1999年 | 22篇 |
1998年 | 29篇 |
1997年 | 19篇 |
1996年 | 21篇 |
1995年 | 14篇 |
1994年 | 17篇 |
1993年 | 15篇 |
1992年 | 23篇 |
1991年 | 9篇 |
1990年 | 18篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1982年 | 6篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1970年 | 8篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有4069条查询结果,搜索用时 31 毫秒
1.
2.
Francesca Passaretta Domenico Bosco Lucia Centurione Maria Antonietta Centurione Fabio Marongiu Roberta Di Pietro 《Journal of cellular and molecular medicine》2020,24(7):4350-4355
Human Amniotic Epithelial Cells (hAEC) isolated from term placenta are a promising source for regenerative medicine. However, it has long been debated whether the hAEC population consists of heterogeneous or homogeneous cells. In a previous study, we investigated the characteristics of hAEC isolated from four different regions of the amniotic membrane finding significant heterogeneity. The aim of this study was to evaluate the hepatic differentiation capability of hAEC isolated from these four regions. Human term placentae were collected after caesarean section and hAEC were isolated from four regions of the amniotic membrane (R1-R4, according to their relative distance from the umbilical cord) and treated in hepatic differentiation conditions for 14 days. hAEC-derived hepatocyte-like cells showed marked differences in the expression of hepatic markers: R4 showed higher levels of Albumin and Hepatocyte Nuclear Factor (HNF) 4α whereas R1 expressed higher Cytochrome P450 enzymes, both at the gene and protein level. These preliminary results suggest that hAEC isolated from R1 and R4 of the amniotic membrane are more prone to hepatic differentiation. Therefore, the use of hAEC from a specific region of the amniotic membrane should be taken into consideration as it could have an impact on the outcome of therapeutic applications. 相似文献
3.
4.
M Martelli G Cotte G Goyet 《Comptes rendus des séances de la Société de biologie et de ses filiales》1975,169(5):1245-1248
An experimental study in pregnant mice shows no statistically significative teratogenic influence of ultrasounds. 相似文献
5.
S Papa S Capitani A Matteucci M Vitale P Santi A M Martelli N M Maraldi F A Manzoli 《Cytometry》1987,8(6):595-601
The development of hepatocyte polyploidy in rats aged up to 4 months was analyzed by flow cytometry using both scatter and fluorescent parameters to distinguish DNA diploid and DNA tetraploid populations and to discriminate between parenchymal and non-parenchymal compartments. The precise origin of each class of nuclei was assessed in whole liver homogenate using purified hepatocytes, obtained by liver perfusion followed by separation on Percoll gradient, and identifying the peaks corresponding to parenchymal nuclei. The results indicate that preparative procedures involving homogenization of the rat liver tissue caused loss of the DNA octaploid population. Data on the relative proportion of the different DNA ploidy elements during rat liver development, which are in good agreement with those observed by cell analysis by means of microspectrophotometry, indicate the usefulness of flow cytometry as a choice method for the analysis of ploidy distribution. 相似文献
6.
A Martelli F Mattioli G Pastorino L Robbiano A Allavena G Brambilla 《Mutation research》1991,260(1):65-72
The results of this work, carried out to extend the limited information at present available on the genotoxic potential of chloramphenicol (CAP), indicate that in millimolar concentrations this antibacterial agent produced a minimal amount of DNA fragmentation in both V79 cells and metabolically competent rat hepatocytes. Moreover, a level of DNA-repair synthesis indicative of a weak but positive response was detected in primary cultures of liver cells obtained from 2 of 3 human donors, and a borderline degree of repair was present in those prepared from rats. The promutagenic character of CAP-induced DNA lesions was confirmed by a low but significant increase in the frequency of 6-thioguanine-resistant clones of V79 cells, which, however, was absent when the exposure was done in the presence of co-cultured rat hepatocytes. Finally, oral administration to rats of 1/2 LD50 CAP did not increase the incidence of either micronucleated polychromatic erythrocytes or micronucleated hepatocytes. Taken as a whole these findings suggest that CAP should be considered a compound intrinsically capable of producing a very weak genotoxic effect, but only at concentrations about 25 times higher than those occurring in patients treated with maximal therapeutic dosages. 相似文献
7.
On the association of DNA polymerase alpha activity with the nuclear matrix in HeLa cells 总被引:1,自引:0,他引:1
The association of DNA polymerase alpha activity with the nuclear matrix has been reinvestigated in HeLa cells. Isolated nuclei were extracted with 2M NaCl and then digested with Dnase I and the final structures were recovered by centrifugation through a sucrose cushion. Typically over 98% of the total DNA synthesized in the matrix fraction on either endogenous matrix-associated DNA or activated calf thymus DNA was due to DNA polymerase alpha as defined by inhibition to n-ethylmaleimide or aphidicolin. DNA polymerase beta activity was absent or recovered in only trace amounts. Matrix-bound DNA polymerase alpha activity demonstrated a remarkable degree of stability: DNA synthesis was essentially linear up to 3 hours at 37 degrees C. Overall, these results substantiate previous findings from regenerating rat liver, unlike other data obtained from tissue culture cells. 相似文献
8.
Claudio Nicolini Andrew S. Belmont Antonietta Martelli 《Cell biochemistry and biophysics》1986,8(2):103-117
Using HeLa S-3 cells synchronized by selective detachment, in this paper we report a parallel study of nuclear morphology
and autoradiography grain patterns between middle G1 and middle S phases: Our results show two distinct [3H]-thymidine labeling patterns. The first “peripheral” labeling pattern has a characteristic nuclear size distribution, in
contrast to the heterogeneous and varying size distributions of Feulgen-stained nuclei, and apparently is characteristic of
very early S phase. The sizes of the second labeling pattern—homogeneous or inhomogeneous grain distribution throughout the
nucleus—are equal or larger than the first and vary with S phase progression. Together, the corresponding nuclear sizes of
the labeled nuclei represent the larger extreme of nuclear areas, and the labeling index closely parallels the fraction of
nuclei with areas larger than the minimum size of the labeled nuclei. These results suggest a characteristic nuclear size
(reflecting unique intranuclear DNA distribution) as a necessary, if not sufficient, requirement for S phase initiation. Parallel
experimentation with rat liver cells—synchronized in vivo by partial hepatectomy and analyzed by thin section autoradiography—confirms
the existence of a peripheral labeling pattern in both the very early part and the very late part of S phase, which reconciles
our data with previous results and points to the fact that both initiation and termination sites for DNA replication are near
the nuclear periphery. 相似文献
9.
A Martelli L Robbiano L Giuliano A Pino G Angelini G Brambilla 《Mutation research》1985,144(3):209-211
The ability of N-nitrosodimethylamine (DMN) and methyl methanesulfonate (MMS) to induce DNA damage in primary cultures of human hepatocytes was examined by the alkaline elution technique. Both the agents induced a dose-dependent increase in DNA elution rate, but appreciable differences in the degree of response to the procarcinogen DMN were observed among cultures obtained from the livers of four patients. A comparative analysis of DNA fragmentation indicated a substantial similarity between human and concurrently studied rat hepatocytes in their response to both DMN and MMS. 相似文献
10.
Nicholas C. Nicolaides Fabio Palombo Kenneth W. Kinzler Bert Vogelstein Josef Jiricny 《Genomics》1996,31(3):395
Defects in mismatch repair genes cause the genetic instability characteristic of hereditary nonpolyposis colorectal cancer and a subset of sporadic colon tumors. The newest member of the mismatch repair gene family,GTBP, has recently been identified as a partial cDNA. Here, we describe the isolation of its 5′ terminus, allowing definition of the entire coding region. Several polymorphisms within the 5′ end were identified and are presented. 相似文献