全文获取类型
收费全文 | 4633篇 |
免费 | 543篇 |
国内免费 | 300篇 |
出版年
2024年 | 22篇 |
2023年 | 131篇 |
2022年 | 106篇 |
2021年 | 321篇 |
2020年 | 313篇 |
2019年 | 504篇 |
2018年 | 276篇 |
2017年 | 152篇 |
2016年 | 149篇 |
2015年 | 174篇 |
2014年 | 339篇 |
2013年 | 344篇 |
2012年 | 249篇 |
2011年 | 271篇 |
2010年 | 175篇 |
2009年 | 196篇 |
2008年 | 184篇 |
2007年 | 190篇 |
2006年 | 179篇 |
2005年 | 128篇 |
2004年 | 126篇 |
2003年 | 102篇 |
2002年 | 94篇 |
2001年 | 81篇 |
2000年 | 77篇 |
1999年 | 56篇 |
1998年 | 48篇 |
1997年 | 46篇 |
1996年 | 44篇 |
1995年 | 54篇 |
1994年 | 48篇 |
1993年 | 43篇 |
1992年 | 46篇 |
1991年 | 33篇 |
1990年 | 35篇 |
1989年 | 14篇 |
1988年 | 19篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 17篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 2篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有5476条查询结果,搜索用时 31 毫秒
91.
Lun He Kurt J. Isselbacher Jack R. Wands Howard M. Goodman Chiaho Shih Andrea Quaroni 《In vitro cellular & developmental biology. Plant》1984,20(6):493-504
Summary A human hepatocellular carcinoma cell line (FOCUS—Friendship of China and United States) was derived from a patient with primary
hepatocellular carcinoma. This cell line has been in continuous culture over an 18-mo period. The morphological and ultrastructural
features of FOCUS are consistent with its neoplastic hepatocellular orgin. FOCUS cells contain aspartate aminotransferase
and glucose-6-phosphatase activity. In addition, α1-antitrypsin, fibrinogen, alpha fetoprotein, and carcinoembryonic antigens were detectble in the cytoplasm of the cultured
cells by immunochemical staining techniques. The karyotype of the FOCUS cell is human in origin and it contains human DNA
sequences as detected by molecular hybridization analysis. The FOCUS cells do not show evidence of density-dependent inhibition
of growth under confluent conditions. Repeated growth curves over an 18-mo period were identical, revealing a doubling time
of 42 to 48 h. The malignant potential of FOCUS cells was further demonstrated by their ability to lead to gross tumor formation
after subcutaneous infection into nude mice. From one of the solid tumors grown in nude mice, recultured cell lines have been
established and found to have properties identical to the original FOCUS cell line. This FOCUS cell line represents an additional
model for further investigation of tumor specific antigens and the relationship between hepatitis B virus (HBV) and hepatocellular
carcinoma. Preliminary molecular characterization has indicated the existence of integrated HBV sequences within the FOCUS
genome. 相似文献
92.
The mucin-associated antigens Tn, sialosyl-Tn (STn), T and sialosyl-T (STAg) antigens accumulate through aberrant and incomplete glycosylation in malignant epithelial cells. Their diagnostic and prognostic significance in tumours of the colon and cervix has been described, and a possible role for Tn antigen in cell-to-cell adhesion has been suggested. These antigens have been demonstrated through peanut agglutinin (PNA) lectin binding and more recently using specific monoclonal antisera. Differences between the two methods have been described, which may be due to fixation schedules and/or specificity. We have investigated the effect of fixation on the binding of biotinylated PNA lectin and compared its reactivity with the immunoreactivity of monoclonal antisera to Tn, STn, T and STAg antigens in benign and malignant epithelium of the gall bladder, extrahepatic bile ducts and ampulla of Vater. We found that short-term fixation in formol sublimate resulted in poor PNA binding. All other tested fixation schedules showed strong perinuclear binding, similar to that found on cryostat sections. When compared with monoclonal antisera, PNA binding demonstrated the lowest specificity in benign epithelium. In both benign and malignant epithelium, the two methods cannot substitute for each other. STn and STAg antigens were found to be oncodevelopmental throughout the extrahepatic biliary tract. When used in a panel, they are useful as diagnostic markers of malignancy in gall bladder epithelium. 相似文献
93.
Shashi Shrivastav Yousuf Sharief John Day Charles F. Reich Robert A. Bonar 《In vitro cellular & developmental biology. Plant》1981,17(12):1117-1124
Summary A new cell line, SS78, was established from a primary renal cell carcinoma of a Caucasian male. The tissue was dispersed with
collagenase, and viable cells were separated by flotation on a Ficoll-Hypaque gradient. In culture, the SS78 cells retained
a distinct epithelial morphology, and no fibroblastlike cells were seen. The cultured cells were aneuploid with a modal chromosome
number of 80 and had several marker chromosomes. Inoculation of the cultured cells into athymic nude mice caused tumors at
the sites of inoculation.
This research was supported in part by Grants CA 15972 and CA 14930 from the National Cancer Institute through the National
Bladder Cancer Project and by the Medical Research Service of the Veterans Administration. 相似文献
94.
Summary The palate epithelium of the frog was examined by scanning electron microscopy, light microscopy and high speed cine micrography. The cilia remain stationary for much of the time in the end-of-effective stroke position. Each beat cycle begins with a forwardly-directed recovery stroke lasting about 60 ms, followed by an effective stroke towards the oesophagus lasting about 12 ms. Activity can often be correlated with the presence of mucus, which is carried as strands on the tips of the ciliary effective strokes whilst the recovery strokes move beneath the mucus. Coordination of ciliary activity was very variable; local antiplectic metachrony of the recovery strokes could almost always be seen, and on very active epithelia effective strokes were associated with approximately diaplectic waves (either to left or right), but any particular pattern of coordinated activity was transient and quickly transformed to another pattern. Beating and coordination of these short cilia were compared with those of cilia propelling water. 相似文献
95.
急性病毒性肝炎的发病率慢性肝炎患病率和肝病死亡率的研究 总被引:15,自引:0,他引:15
1984~1987年,在黑龙江、河北、河南、湖南、上海五个省市城乡10.08855人口中进行急性肝炎发病率、慢性肝炎患病率、与病毒性肝炎有关的肝病死亡率的研究。急性肝炎标化发病率为152.19/10万,主要发生在20~50岁组人群;因无甲肝暴发流行,除上海外各点季节发病率分布均衡。慢性肝炎标化患病率为158.25/10万(诊断标准为6个月前有明确急性肝炎病史,现有明显的临床症状或体征,肝功能异常,故实际慢肝患病率要高于此数字);与病毒性肝炎有关的肝病死亡(包括肝癌)标化率为22.65/10万,其中肝病为 13.14/10万。男性死亡率显著高于女性。 相似文献
96.
Ken-ichiro Fukuchi Samir S. Deeb† Kouzin Kamino† Charles E. Ogburn Alan D. Snow Raymond T. Sekiguchi Thomas N. Wight Henri Piussan† George M. Martin 《Journal of neurochemistry》1992,58(5):1863-1873
Expression of the genes encoding the beta/A4 amyloid protein precursor (APP) and microtubule-associated protein tau was studied in an embryonal carcinoma cell line (P19) that differentiates in vitro into cholinergic neurons after treatment with retinoic acid. Expression of APP increased 34- (mRNA) and 50-fold (protein) during neuronal differentiation; APP-695 accounted for most of this increase. These remarkable increases in APP expression coincided with a proliferation of neuronal processes and with an increase in content of tau mRNA. Moreover, subsequent decreases in the levels of APP and tau mRNA coincided with the onset of the degeneration of the neuronal processes. Immunocytochemical staining suggested that greater than 85% of the P19-derived neurons are cholinergic and that APP is present in the neuronal processes and cell bodies. These results suggest that APP may play an important role in construction of neuronal networks and neuronal differentiation and also indicate that this embryonal carcinoma cell line provides an ideal model system to investigate biological functions of APP and the roles of APP and tau protein in development of Alzheimer's disease in cholinergic neurons. 相似文献
97.
Breast Carcinoma With Osteoclast-Like Giant Cells 总被引:1,自引:0,他引:1
The cytological and histological findings of a case of breast carcinoma with osteoclast-like giant cells are presented. A fine needle aspiration specimen demonstrated the characteristic combination of malignant epithelium and reactive multinucleated cells and enabled identification of this rare variant of breast cancer. Immunocytochemical studies using the monoclonal antibody KP1[CD68] support a histiocytic origin for the osteoclast-like cells. 相似文献
98.
Ming-Chi Wu Grace K. Arimura John S. Holcenberg Adel A. Yunis 《In vitro cellular & developmental biology. Plant》1982,18(9):750-754
Summary Cultured human pancreatic carcinoma cells (MIA PaCa-2) have been shown previously to be very sensitive toE. coli
l-asparaginase (EC II). The present studies have demonstrated that another enzyme,Acinetobacter glutaminase-asparaginase (AGA) is much more effective in inhibiting cell growth. At the concentration of 0.0025 U/ml of AGA
activity the enzyme totally inhibited cell growth, whereas the EC II with the same concentration did not show any effect.
The inhibition of cell growth correlated well with inhibition of protein and glycoprotein synthesis. The addition ofl-glutamine at the concentration of 1 mM completely reversed the inhibition of protein synthesis. Similarly, the addition ofl-glutamine at the concentration of 3 mM daily on 3 successive days after adding AGA resulted in significant reversal of growth inhibition. The results of this study
indicate that the action of AGA on MIA PaCa-2 is, to a great extent, exerted through itsl-glutaminase activity.
This work was supported in part by USPHS Grant CA 19182. Dr. Wu is recipient of Research Career Development Award Grant CA00686
and Dr. Yunis is a Howard Hughes Investigator. 相似文献
99.
Angie Rizzino Victor Terranova David Rohrbach Craig Crowley Heather Rizzino 《Journal of cellular biochemistry》1980,13(2):243-253
In this paper we have examined the growth and differentiation of the embryonal carcinoma cell line, F9, in the defined medium EM-3 at low density. We show that the growth of F9 and their differentiated cells (F9-diff) in EM-3 is strongly density dependent. At low cell densities the growth of both cell types is severely limited and most of the cells do not survive. Although this poses a problem for working with F9 and F9-diff in EM-3, it provides a convenient assay for identifying molecules that support their growth at low density. Using this assay, we have determined that laminin, a newly isolated glycoprotein of basement membranes, significantly improves the growth and short-term survival of both F9 and F9-diff. However, addition of laminin to EM-3 is insufficient to promote the clonal growth of these cell types. Our findings also indicate that laminin promotes the attachment of F9 and F9-diff in defined media. On the basis of our results, we propose an attachment function for laminin during the early stages of mammalian development. 相似文献
100.
Bombesin production by human small cell carcinoma of the lung 总被引:5,自引:0,他引:5
G D Sorenson S R Bloom M A Ghatei S A Del Prete C C Cate O S Pettengill 《Regulatory peptides》1982,4(2):59-66
A series of continuous cell lines of human small cell carcinoma of the lung (SCCL) have been evaluated for the production of bombesin (BN). In early established cultures BN was detected in the medium of 9 out of 11 cell lines and in 6 out of 7 cell homogenates examined. Levels in the medium were frequently higher in cultures of later passages compared to earlier passages of the same line and low levels developed in the two previously negative cell lines. Plasma concentrations were greater than 80 pmol/l in 2 out of 27 (7%) randomly selected patients with SCCL. A culture (DMS 406) established from the tumor of a patient with the highest plasma level (1240 pmol/l) was the highest producer in vitro. The results indicate that BN, which has been demonstrated immunocytochemically to be present in normal bronchial mucosal cells, is frequently produced by SCCL in vitro but elevated plasma levels are infrequently found in patients with this neoplasm. 相似文献