全文获取类型
收费全文 | 3856篇 |
免费 | 287篇 |
国内免费 | 15篇 |
出版年
2022年 | 40篇 |
2021年 | 65篇 |
2020年 | 48篇 |
2019年 | 70篇 |
2018年 | 97篇 |
2017年 | 82篇 |
2016年 | 103篇 |
2015年 | 181篇 |
2014年 | 177篇 |
2013年 | 256篇 |
2012年 | 292篇 |
2011年 | 267篇 |
2010年 | 155篇 |
2009年 | 165篇 |
2008年 | 200篇 |
2007年 | 216篇 |
2006年 | 188篇 |
2005年 | 185篇 |
2004年 | 184篇 |
2003年 | 153篇 |
2002年 | 144篇 |
2001年 | 73篇 |
2000年 | 61篇 |
1999年 | 67篇 |
1998年 | 39篇 |
1997年 | 39篇 |
1996年 | 30篇 |
1995年 | 28篇 |
1994年 | 31篇 |
1993年 | 18篇 |
1992年 | 29篇 |
1991年 | 29篇 |
1990年 | 27篇 |
1989年 | 30篇 |
1988年 | 20篇 |
1987年 | 18篇 |
1986年 | 37篇 |
1985年 | 25篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 20篇 |
1979年 | 18篇 |
1978年 | 15篇 |
1977年 | 18篇 |
1974年 | 13篇 |
1973年 | 15篇 |
1968年 | 11篇 |
1967年 | 19篇 |
排序方式: 共有4158条查询结果,搜索用时 15 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.
Summary The stability and gene expression of plasmid pBR322 in a chemostat with complex non-selective medium at different dilution rates were studied. It was observed that pBR322 was eventually lost from the population after a long lag period. The rate of plasmid loss decreases with decreasing dilution rate. This result is different from those obtained with cells grown in defined medium, where plasmid loss was observed to decrease with increasing dilution rate. In addition, it was observed that the -lactamase activity per ml per optical density of cell culture, independent of the dilution rates, increases with time and reaches a maximum around 4.5 units after 100 hrs of continuous culture. 相似文献
5.
6.
J Stachura M Pietroń K Nowak Z Rudzki W Nowak 《Folia histochemica et cytobiologica / Polish Academy of Sciences, Polish Histochemical and Cytochemical Society》1989,27(4):227-231
DAKO quick staining kits were used to immunostainings for Epithelial Membrane Antigen (EMA) Neuron Specific Enolase (NSE) and S-100 protein (S-100) in 18 carcinoid tumors of the gastrointestinal tract classified according to Soga and Tazawa. EMA was always absent in carcinoid tumors, being at the same time present within glandular epithelium. 88% of cases showed positive immunostaining for NSE. S-100 immunostaining showed immunopositive stellate cells present within the tumor especially within type A carcinoids. In addition in one carcinoid tumor thick, strongly S-100 positive bundles were noticed at the periphery of nests of tumor cells. Combined immunohistochemical and ultrastructural studies are needed to elucidate interrelation of neoplastic and neural elements within carcinoid tumorsa. 相似文献
7.
Giuseppe Familiari M.D. Stefania A. Nottola Antonio Familiari Pietro M. Motta 《Cell and tissue research》1989,257(2):247-253
Summary The present study provides further details on the fine-structural three-dimensional architecture of the zona pellucida (ZP) in growing and atretic follicles of mice by use of ruthenium red in combination with the detergents Triton X100 and saponin. These detergents were used for extraction of the soluble fraction of the zonal proteins in an attempt to expose the structural zonal glycoproteins, which in turn can be viewed as minute three-dimensional networks upon transmission- and scanning electron-microscopic examination. By use of these methods, the ZP of growing follicles appeared to be formed by interconnected filaments which also bind to globular structures building up a three-dimensional lattice. In contrast, the ZP of stage I as well as other (II and III) stages of atretic follicles showed a structure characterized by the presence of closely packed granules connected with short filaments to form a close-mesh reticulum. This structural change of the ZP, which in the present study is also associated with the disappearance of gap junctions within the granulosa and cumulus cell population, might represent one of the early events involved in the onset of atresia. These changes, most probably depending on an altered secretory activity of both oocytes and follicle cells, might lead to a degradation of the ZP network structure and to its subsequent increased density (condensation). All these morphodynamic events eventually contribute to a sequestration of the oocyte in the early stage of atresia. 相似文献
8.
Dynamics of plasmid maintenance in a CSTR upon square-wave perturbations in the dilution rate 总被引:1,自引:0,他引:1
The effects of forced oscillations in the dilution rate on a population of Escherichia coli K12 harboring the plasmid pBR322 in a chemostat with a nonselective medium were studied. In the constant dilution rate control experiments, the percentage of plasmid-containing cells decreased after a long lag time. Eventually, the culture approached a population consisting of 100% plasmid-free ells. However, under forced perturbations of the dilution rate, the culture maintained a mixed population of plasmid-free and plasmid-carrying cells for a longer period of ime. An unstructured model was developed to describe the above observations. Our results indicate that transient conditions created by dilution-rate perturbations provide a favorable environment for the plasmid-carrying population. In addition, experiments with different cycling frequencies suggest that adaptation by the culture to these transient conditions will reduce or totally eliminate such an advantage. 相似文献
9.
I De Dios J J Calvo J I San Roman M A Plaza M A Lopez 《Archives internationales de physiologie et de biochimie》1989,97(1):37-43
The effect of Dobutamine (a beta 1-adrenergic agonist) and Terbutaline (a beta 2-adrenergic agonist) on exocrine pancreatic secretion was studied in anaesthetized rabbits, simultaneously controlling pancreatic blood flow and blood pressure. The secretion of fluid and ions (bicarbonate, sodium and potassium) was unaffected by the infusion of Dobutamine (8 micrograms.kg-1.min-1) or Terbutaline (10 micrograms.kg-1.min-1). Neither were pancreatic blood flow or mean blood pressure altered. Dobutamine or Terbutaline depress the function of the acinar cells, amylase secretion being more affected by the action of Terbutaline. The results show that beta 1 and beta 2-adrenergic stimulation has no effect on the ductular cells but does decrease the secretion by the acinar cells. 相似文献
10.
Fiorenzo A. Peverali Maurizio D'Esposito Dario Acampora Giuseppe Bunone Mario Negri Antonio Faiella Anna Stornaiuolo Maria Pannese Enrica Migliaccio Antonio Simeone Giuliano Della Valle Edoardo Boncinelli 《Differentiation; research in biological diversity》1990,45(1):61-69
Mammalian genes containing a class-I homeobox (HOX genes) are highly expressed in the embryonic nervous system. As a first step towards the molecular analysis of the role these genes play in neural cells, we studied the expression of four human HOX genes in five neuroblastoma (NB) cell lines - SK-N-BE, CHP-134, IMR-32, SK-N-SH and LAN-1 - during the process of differentiation induced by treatment with retinoic acid (RA). The four genes, HOX1D, 2F, 3E and 4B, located at corresponding positions in the four HOX loci, share a high degree of sequence similarity with the Drosophila Deformed homeotic gene and constitute a homology group, group 10. One of these genes, HOX1D, is not expressed in the cells used, whereas the other three are highly expressed in untreated and RA-induced NB cells, even though the expression pattern in the various lines is slightly different for the three genes. Our analysis reveals a complex and specific expression pattern in these lines, paving the way to an identification of different NB-cell populations by means of specific HOX gene expression schemes. On the other hand, in every line studied, morphological maturation toward a neuronal differentiated phenotype appears to be associated with increased HOX gene expression. 相似文献