全文获取类型
收费全文 | 34941篇 |
免费 | 2910篇 |
国内免费 | 1025篇 |
专业分类
38876篇 |
出版年
2024年 | 88篇 |
2023年 | 485篇 |
2022年 | 713篇 |
2021年 | 1117篇 |
2020年 | 1327篇 |
2019年 | 1685篇 |
2018年 | 1443篇 |
2017年 | 967篇 |
2016年 | 958篇 |
2015年 | 1272篇 |
2014年 | 2122篇 |
2013年 | 2244篇 |
2012年 | 1315篇 |
2011年 | 1736篇 |
2010年 | 1225篇 |
2009年 | 1596篇 |
2008年 | 1694篇 |
2007年 | 1660篇 |
2006年 | 1624篇 |
2005年 | 1399篇 |
2004年 | 1231篇 |
2003年 | 1021篇 |
2002年 | 880篇 |
2001年 | 641篇 |
2000年 | 602篇 |
1999年 | 452篇 |
1998年 | 497篇 |
1997年 | 481篇 |
1996年 | 510篇 |
1995年 | 504篇 |
1994年 | 479篇 |
1993年 | 429篇 |
1992年 | 446篇 |
1991年 | 383篇 |
1990年 | 372篇 |
1989年 | 326篇 |
1988年 | 282篇 |
1987年 | 279篇 |
1986年 | 228篇 |
1985年 | 281篇 |
1984年 | 273篇 |
1983年 | 143篇 |
1982年 | 245篇 |
1981年 | 197篇 |
1980年 | 182篇 |
1979年 | 176篇 |
1978年 | 115篇 |
1977年 | 115篇 |
1976年 | 108篇 |
1973年 | 81篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Jesper Hald Niels Rasmussen Mogens H. Claesson 《Cancer immunology, immunotherapy : CII》1995,41(4):243-250
Tumour-infiltrating lymphocytes (TIL) and tumours from six patients with squamous cell carcinomas of the head and neck (SCCHN) were investigated. The six tumours all expressed major histocompatibility complex (MHC) class I antigens both in vivo and as tumor cell lines grown in vitro. In addition, the cancer cells either overexpressed the tumour-suppressor gene product p53 or harboured human papilloma virus 16/18 (HPV). The TIL were expanded in vitro in the presence of interleukin-2, immobilised anti-CD3 mAb and soluble anti-CD28 mAb. Expanded TIL cultures contained both CD4+and CD8+T cells, but generally contained few CD56+CD3-cells of the natural killer (NK) phenotype. CD8+T cells dominated the individual TIL cultures from five of the six patients and showed significant autologous tumour cell lysis. In TIL cultures derived from four of these tumour-reactive TIL cultures, killing could be partially blocked by an anti-MHC class I mAb. TIL cultures reacting with autologous tumour cells also showed strong TCR/CD3-redirected cytotoxicity when assayed against hybridoma cells expressing anti-TCR/CD3 mAb as well as natural-killer(NK)-like activity. A number of TIL cultures devoid of autologous tumour cell lysis were capable of lysing the natural-killer(NK)-sensitive K562 cell line suggesting that the SCCHN cells themselves are resistant to NK-like lysis. In conclusion, TIL cultures from head and neck carcinomas contain T cells which, upon expansion in vitro, can lyse autologous tumour cells in a MHC-class-I-restricted fashion. Thus, the results of the present study document that carcinomas of the head and neck in some patients are infiltrated by cytotoxic T cell precursors potentially capable of rejecting the autologous tumour. 相似文献
102.
Mouse hybridoma cells cultured on the verge of starvation-induced apoptosis, i.e. in a medium diluted with saline, proved to serve as a sensitive screening system for apoptosis-suppressing activity of nutrient medium components. Conventional amino acid mixtures were found to suppress the starvation-induced apoptosis, whereas a vitamin mixture was ineffective. (Frank F (1995) Biotechnol. Bioeng. 45: 86–90). Recent experiments showed that suppression of apoptosis, and concurrent resumption of growth, could be achieved by addition of single substances at millimolar concentrations. The set of active substances included certain coded L-amino acids (glycine, alanine, serine, threonine, proline, asparagine, glutamine, histidine), non-coded amino acids (-alanine, taurine, 4-aminobutyric acid), and a non-metabolizable analogue (2-aminoisobutyric acid). This finding shows that some amino acids do not act solely as nutrients, but also as specific signal molecules. The specificity of the effect points to the involvement of adaptively regulated amino acid transport systems A and N in maintaining the balance between triggering and suppression of starvation-induced apoptosis. 相似文献
103.
Shinji Hosoi Mitsuo Satoh Hiromasa Miyaji Tatsunari Nishi Tamio Mizukami Mamoru Hasegawa Seiga Itoh Tatsuya tamaoki 《Cytotechnology》1995,19(1):1-10
Pro-UKS1 was designed as a thrombin-resistant derivative of pro-urokinase (pro-UK) by introducing a glycosylation site using site-directed mutagenesis. An expression plasmid for pro-UKS1, pMo1UKS1SEd1-5, was constructed and introduced into Namalwa KJM-1 cells (Hosoiet al., 1988), and cells resistant to G418 and Methotrexate (MTX) were obtained. Amongst them, the highest pro-UKS1 producer (resistant to 500 nM of MTX), clone 41-8, was selected and further characterized. Clone 41-8 was cultured in serum-free ITPSGF medium (Hosoiet al., 1988). Under the conventional conditions, the concentration of pro-UKS1 reached 26 g ml–1. Addition of glucose and tri-iodothyronine (T3) improved productivity, and the maximal productivity of pro-UKS1 was 67 g ml–1 day–1. In this conditioned medium, content of pro-UKS1 was above 80% of total proteins.Abbreviations BSA
bovine serum albumin
- dhfr
dihydrofolate reductase
- HEPES
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- kb
kilobase pairs
- kDa
kilodaltons
- MTX
Methotrexate
- PBS
phosphate buffered saline
- pro-UK
pro-urokinase
- SDS-PAGE
sodium dodecyl sulfate-polyacrylamide gel electrophoresis
- T3
tri-iodothyronine
- Tween-PBS
phosphate buffered saline containing 0.05% Tween 80 相似文献
104.
Massimo De Felici 《Molecular reproduction and development》1984,10(4):423-432
Fluorescent lectins were used to study the chemical nature of carbohydrate moieties present on the surface of female and male germ cells isolated from mouse gonads during fetal and early posnatal development. Concanavalin A (ConA), lens culinaris agglutinin (LCA), ricinus communis agglutinin (RCAI) and wheat germ agglutinin (WGA) bound intensely to the germ cell plasma membrane at all stages studied. Other lectins such as ulex europaeus agglutinin (UEAI) and agglutinin (SBA) did not bind or bound moderately (SBA to female germ cells only). Distinct developmental-related changes were observed when female germ cells were labeled with fluorescein-conjugated peanut agglutinin (PNA) or dolichos biflorus agglutinin (DBA). DBA and PNA binding was absent or weak in fetal female and male germ cells, but became intensely positive in oocytes in the immediate postnatal period. The percentage of oocytes stained with DBA increased during the first three days after birth, and from day 3–4 onwards all oocytes were strongly labeled. I suggest that these changes in lectin binding reflect changes in biochemical structure of the oocyte surface related to differentiative events occurring in the mouse ovary immediately after birth. 相似文献
105.
Taenia taeniaeformis: characterization of larval metabolic products and growth of host gastric cells in vitro 总被引:1,自引:0,他引:1
Development of larvae of the cestode parasite Taenia taeniaeformis in the liver of rats induces gross hyperplasia of the gastric mucosa and excessive mucus production in the stomach without any direct contact with the stomach. Because the taeniid larvae are known to elaborate excretory-secretory (E-S) product in vivo and in vitro, the product was analyzed further, and its effects on cultured rat and dog stomach cells were investigated. In vitro E-S product contained less negatively charged glycosaminoglycan than either heparin or chondroitin sulfate, and proteins of various molecular weights. It stimulated the growth of both rat and dog stomach cells at concentrations of 3-9 micrograms protein/ml culture medium. At a concentration of 30 micrograms protein/ml culture medium, it stimulated hexosamine production in the cells up to 20 times, and multiple intracytoplasmic granules were found in both rat and dog cultured cells by light and electron microscopy. These results suggest that larval E-S product may be involved in the induction of gastric hyperplasia and hypermucus secretion. 相似文献
106.
R. Evangelisti M. Bodo A. Caruso E. Becchetti Prof. P. Carinci 《Cell and tissue research》1984,238(2):241-245
Summary Administration of Concanavalin A (Con A) to cultured skin fibroblasts derived from chick embryos at two developmental stages produce variations in the relative concentration of individual glycosaminoglycan (GAG) secreted by the cells. This effect is different: at 7 days (increase of hyaluronic acid and dermatan sulphate and decrease of chondroitin sulphate) and at 14 days (dermatan sulphate is not detectable).All the cells bind the Con A specifically, but a different pattern of agglutination is present in fibroblasts of the two embryonic ages. Since Con A is well known to bind carbohydrate-containing surface proteins, the result suggests that the release of GAG by chick embryonic fibroblasts can be modulated by cell surface receptors. 相似文献
107.
Dr. Heidelinde Dürnberger Kurt Pohlhammer Gerhard Weinbörmair 《Cell and tissue research》1978,187(3):489-494
Summary Ovariectomy, performed immediately after the final hatch, caused a reduction of stainable (neurosecretory?) material in the paramedial neurosecretory cells (PNC) (A-type) of the suboesophageal ganglion in 10 day-old females of Teleogryllus commodus (Walk.). A concomitant increase in nuclear volume and in the incorporation of 35S-cysteine indicates increased synthesis of neurosecretory material. From these findings it is concluded that more stainable material is secreted in the cerebral neurohaemal organ after Ovariectomy. A functional relationship between the PNC and the ovaries is suggested. 相似文献
108.
R. J. J. Kanoza D. M. Brunette A. D. Purdon J. Sodek 《In vitro cellular & developmental biology. Plant》1978,14(9):746-753
Summary An operational criterion for the identification and isolation of epithelial-like (E) cells, based on their ability to cover
and protect, a collagen gel from the action of collagenase, has been developed. The E cells isolated by this collagenase-separation
technique (CST) exhibited the ultrastructural features, including desmosomes and abundant tonofilaments, that are considered
characteristic of this cell type. Unlike confluent cultures of fibroblast-like (F) cells, E cells were not found to have large
external transformation-sensitive (LETS) protein on their surface membranes. The CST provides a nondestructive, and efficient
means of identifying and isolating E cells from mixed populations. 相似文献
109.
The larval midgut of the silkmoth Hyalophora cecropia was examined using scanning electron microscopy. Goblet cells were observed to contain within their cavities a matrix plug. This matrix material was extruded onto the lumen side of the epithelium when the tissue was stretched. The rôle of this matrix material in maintenance of the capacity of the midgut to transport ions in vivo and in vitro is discussed. 相似文献
110.
A new cell culture microcarrier that can be covalently bonded by cell attachment proteins and can be thin-sectioned for electron microscopy was synthesized. It was easily made by sulfonating cross-linked polystyrene beads for a negative surface charge followed by covalent attachment of polyethylenimine for a positive charge. Cell attachment proteins, e.g. collagen, was covalently bonded directly to the microcarrier using a carbodiimide or after activating the microcarrier surface with glutaraldehyde. HeLa-S3 cells attached, spread and grew to confluence more efficiently on the positive microcarriers and those coated with collagen than on the negative ones. Endothelial cells grew best on those with a negative surface charge. The nature of the microcarrier surface was not the only aspect involved in cell adhesion but also the type of serum proteins adsorbed. Qualitatively different proteins coated the microcarriers depending upon whether the carrier was negative, positive or coated with collagen. Comparison of various types of available microcarriers indicated that the modified cross-linked polystyrene beads used here were best for transmission and scanning electron microscopy. Endothelial cells grown on the microcarriers had the same ultrastructure as cells grown in monolayers in culture dishes. Of a variety of microcarriers tested the modified cross-linked polystyrene beads were the only ones that could be used for both ultrastructural and biochemical techniques. 相似文献