全文获取类型
收费全文 | 10331篇 |
免费 | 489篇 |
国内免费 | 181篇 |
专业分类
11001篇 |
出版年
2023年 | 111篇 |
2022年 | 152篇 |
2021年 | 230篇 |
2020年 | 212篇 |
2019年 | 276篇 |
2018年 | 287篇 |
2017年 | 160篇 |
2016年 | 208篇 |
2015年 | 242篇 |
2014年 | 451篇 |
2013年 | 595篇 |
2012年 | 261篇 |
2011年 | 370篇 |
2010年 | 363篇 |
2009年 | 450篇 |
2008年 | 540篇 |
2007年 | 469篇 |
2006年 | 401篇 |
2005年 | 367篇 |
2004年 | 340篇 |
2003年 | 305篇 |
2002年 | 248篇 |
2001年 | 182篇 |
2000年 | 181篇 |
1999年 | 168篇 |
1998年 | 185篇 |
1997年 | 158篇 |
1996年 | 143篇 |
1995年 | 144篇 |
1994年 | 151篇 |
1993年 | 132篇 |
1992年 | 134篇 |
1991年 | 106篇 |
1990年 | 99篇 |
1989年 | 104篇 |
1988年 | 84篇 |
1987年 | 86篇 |
1986年 | 89篇 |
1985年 | 105篇 |
1984年 | 104篇 |
1982年 | 98篇 |
1981年 | 91篇 |
1980年 | 112篇 |
1979年 | 124篇 |
1978年 | 146篇 |
1977年 | 139篇 |
1976年 | 191篇 |
1974年 | 101篇 |
1973年 | 254篇 |
1972年 | 135篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
23.
Walter Malorni Pietro L. Indovina Giuseppe Arancia Stefania Meschini Maria T. Santini 《In vitro cellular & developmental biology. Plant》1990,26(4):399-410
Summary This paper describes the microscopic evidence supporting a cesium-induced delay in the fusion of chick embryo myoblast membranes
during in vitro myogenic differentiation. We have recently demonstrated that the sharp decrease in the conductivity and permittivity
of the membranes of these myogenic cells at the time of fusion is delayed 30 h by the addition of cesium to the culture medium
(Santini et al., Biochim. Biophys. Acta 945:56–64; 1988). We report here that this delay in fusion is substantiated by direct
microscopic observation and that cesium also induces ultrastructural changes in the myoblast cells themselves. Possible mechanisms
by which cesium may cause both the delay in fusion as well as the ultrastructural changes observed are discussed.
This investigation was partially supported by an Italian Consiglio Nazionale delle Ricerche grant 85.00.304.02 (to P. L. I.). 相似文献
24.
C.G. Rodriguez N. Makori M. A. Cukierski A. G. Hendrickx 《Journal of medical primatology》1996,25(2):122-132
Abstract: Formation of the definitive kidney in Macaca fascicularis embryos was investigated using light and electron microscopy. Appearance of the definitive kidney at stage 14 was indicated by the ureteric bud invading the metanephrogenic blastema. Glomerular capillaries originate from the connective tissue that surrounds the developing renal vesicle. At 46–100 days gestational age the more developed glomeruli show thinning of the capillary endothelium, thickening of the basal membrane, and presence of pedicels, suggesting a capability of renal function. 相似文献
25.
Multidrug resistance evaluation by confocal microscopy in primary urothelial cancer explant colonies
Alan J. Cooper Matthew C. Hayes Peter M. Duffy Claire L. Davies Christopher J. Smart 《Cytotechnology》1996,19(3):181-186
Assessing functional multidrug resistance (MDR) status in clinical biopsy material using drug autofluorescence has potential applications to clinical management. The small size of many cystoscopy specimens has led us to develop, as an alternative to flow cytometry, a protocol for studying epirubicin accumulation in adherent colonies of primary bladder cancer cells viewed live andin situ by confocal microscopy. The limitations to quantitation inherent in this technique are compensated for by preservation of cellular organisation and the elimination of non-malignant cells. Biopsy material is disaggregated and explanted into culture-grade petri dishes. After incubation for three to seven days plaques of epithelial cells have developed. Classical patterns of sensitive and resistant drug distribution are observed. Cells of the rolled edges of the colony accumulate more drug than those of the inner epithelial monolayer. Some central areas of larger colonies give the appearance of drug arrested at the intercellular junctions to give a fenestrated pattern. These observations contribute to the understanding of mechanisms in MDR as well as forming the basis for a clinical urological MDR evaluation protocol. 相似文献
26.
Cultured steroidogenic cells derived from the adrenal glands of duck embryos were used to study changes in the distribution of actin associated with the corticotropic responsiveness. Actin-containing components were identified by rhodamine-phalloidin staining. The actin in most of the unstimulated cells occurred as stress fibers that either ran parallel throughout the cell or were present as domains of parallel fibers at angles to one another. When incubated in Krebs-Henseleit buffer containing 1–24 ACTH, the cells released approximately equal amounts of corticosterone and aldosterone. Incubation of the cells in buffer containing cytochalasin D caused the cells to lose their stress fibers, and the actin became distributed at the periphery in what appeared to be fragments of stress fibers and clumps of fibrous material in the central cytoplasm. Although cytochalasin D did not affect the basal output of corticosterone and aldosterone, the 1–24 ACTH-induced rates of both hormones were suppressed significantly. After the cells had been washed in unadulterated buffer, the normal distribution of actin stress fibers was restored and the cells responded normally when incubated in buffer containing 1–24 ACTH. These results suggest that the actin components of the cytoskeleton are important determinants of corticotropin-induced steroidogenic responsiveness. 相似文献
27.
I. W. Gibson D. S. Gardiner I. Downie T. T. Downie I. A. R. More G. B. M. Lindop 《Cell and tissue research》1994,277(2):385-390
The peripolar cell is a glomerular epithelial cell situated within Bowman's capsule at its vascular pole. It is believed to be a secretory cell which forms part of the juxtaglomerular apparatus. Scanning electron microscopy was used to perform a comparative study of the morphology and number of peripolar cells in twelve mammalian species. The number of renin-secreting cells in kidney sections stained by renin antibodies and immunocytochemistry was counted. There was a marked inter-species variation in the number, size and appearance of peripolar cells. They were largest and most abundant in sheep and goat and fewest in dog, cow and human. There was no correlation between the numbers of peripolar cells and renin-secreting cells. This does not support the view that the peripolar cell is part of the juxtaglomerular apparatus. 相似文献
28.
Isolation of glucosinolate degrading microorganisms and their potential for reducing the glucosinolate content of rapemeal 总被引:1,自引:0,他引:1
Abstract K88ab fimbriae are filamentous protein structures at the surface of certain enterotoxigenic Escherichia coli strains. Electron microscopy analysis of K88ab fimbriae showed that these structures have different morphological appearances dependent on the medium in which cells expressing these fimbriae or in which purified fimbriae were suspended. Thin and curled structures, thin and flexible fimbriae, a wider and rigid form of the fimbriae, and, in addition, paracrystalline structures were detected. Optical diffraction analysis of the paracrystalline structures indicated a helical conformation of K88ab fimbriae. 相似文献
29.
Martin M. Lee Francis H.Y. Green W.Michael Schoel Samuel Schürch 《生物化学与生物物理学报:疾病的分子基础》1994,1226(2):151-162
Cell-substrate adhesion was quantified for two cultured mesothelioma cell lines (epitheliomatus and sarcomatous) on glass, fibronectin and laminin substrates. Interference reflection microscopy (IRM) was used to image the adhesion patterns of cells and a grey level analysis was employed to quantify adhesion. Sarcomatous cells demonstrated marked adhesion to glass and fibronectin-coated substrates but not to laminin-coated substrate, with the greatest adhesion occurring on the fibronectin-coated surface. This adhesion was accompanied by cytoplasmic spreading. By contrast, epitheliomatous cells showed little tendency to adhere to any of the substrates and only showed significant spreading when in contact with the laminin substrate (P < 0.01). A bioassay was used to determine the metastatic potential of each of the cell lines. Via the intravenous route, the sarcomatous cells killed the host rats in 24.7 ± 1.5 (S.D.) days compared to 27.3 ± 0.9 (S.D.) days for the epitheliomatous cells (P < 0.01). After subcutaneous inoculation of tumour cells, the sarcomatous cells killed the host rats in 54.7 ± 0.7 (S.D.) days compared to 48.5 ± 0.5 (S.D.) days for the epitheliomatous cells (P < 0.01). We conclude that the results of the metastasis bioassays were consistent with the predicted behavior of these cell lines based on their ability to adhere to substrates in the in vitro adhesion assays. 相似文献
30.
Recombinant human kidney epithelial 293 cells were cultivated as aggregates in suspension. The concentration calcium ion, in the range of 100 muM to 1mM, affected the rate of aggregate formation. During the course of cultivation the size distribution of aggregates shifted and the fraction of larger aggregates increased. This effect was more profound in cultures with a high calcium concentration. Scanning and transmission microscopic examination of the aggregates revealed that cell packing was greater in the high calcium cultures and that ultrastructural integrity was retained in aggregates from both low and high calcium cultures. Confocal microscopy was applied to examine the viability of cells in the interior of the aggregates. High viability was observed in the aggregates obtained from exponentially growing cultures. Aggregates from the high calcium culture in the stationary phase exhibited lower viability in the interior. With its ease of retention in a perfusion bioreactor, aggregate cultures offer an alternative choice for large-scale operation. (c) 1993 John Wiley & Sons, Inc. 相似文献