全文获取类型
收费全文 | 175436篇 |
免费 | 10232篇 |
国内免费 | 7846篇 |
专业分类
193514篇 |
出版年
2024年 | 377篇 |
2023年 | 2424篇 |
2022年 | 4497篇 |
2021年 | 5808篇 |
2020年 | 4638篇 |
2019年 | 5639篇 |
2018年 | 5097篇 |
2017年 | 3762篇 |
2016年 | 4328篇 |
2015年 | 6701篇 |
2014年 | 11453篇 |
2013年 | 12915篇 |
2012年 | 8553篇 |
2011年 | 10484篇 |
2010年 | 7665篇 |
2009年 | 8293篇 |
2008年 | 8533篇 |
2007年 | 8995篇 |
2006年 | 7374篇 |
2005年 | 6536篇 |
2004年 | 5514篇 |
2003年 | 4797篇 |
2002年 | 4395篇 |
2001年 | 3306篇 |
2000年 | 2903篇 |
1999年 | 2798篇 |
1998年 | 2650篇 |
1997年 | 2331篇 |
1996年 | 2273篇 |
1995年 | 2265篇 |
1994年 | 2051篇 |
1993年 | 1961篇 |
1992年 | 1831篇 |
1991年 | 1688篇 |
1990年 | 1416篇 |
1989年 | 1337篇 |
1988年 | 1276篇 |
1987年 | 1104篇 |
1986年 | 986篇 |
1985年 | 1330篇 |
1984年 | 1802篇 |
1983年 | 1180篇 |
1982年 | 1505篇 |
1981年 | 1318篇 |
1980年 | 1052篇 |
1979年 | 1006篇 |
1978年 | 695篇 |
1977年 | 591篇 |
1976年 | 547篇 |
1973年 | 382篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Summary We describe the in vitro influence of 3,5,3′-triiodo-l-thyronine (T3),l-thyroxine (T4), a thyroid-stimulating hormone (TSH), and/or estradiol (E2: chosen as the control of the methodology) on the cell kinetics (cell distribution in the S+G2+M phases) of mouse MXT and human MCF-7 mammary cancer cells. Experiments were performed by means of a cell image processor,
analyzing MCF-7 or MXT cells that had been grown on glass cover slips and whose nuclei had been stained by the Feulgen reaction,
which is selective and quantitative (stoichiometric) with respect to DNA. We show that T3, T4, and TSH at 0.01 μM dramatically stimulate the cell kinetics of the MXT mouse and the MCF-7 human mammary cancer cell lines. Indeed, the three
hormones bring about a significant transient increase in the S+G2+M fraction as does E2. Furthermore, our data indicate that E2 and TSH are antagonistic with regards to MXT or MCF-7 cell kinetics.
This work is supported by grants awarded by the IRSIA and the Fonds de la Recherche Scientifique Médicale (FRSM, Belgium). 相似文献
992.
993.
994.
N-hydroxy-2-naphthylamine (NOH-2NA). an active metabolite of human occupational bladder carcinogens, induced, in V79 Chinese hamster cells. chromosomal aberrations which were suppressed in the presence of catalase and/or superoxide dismutase. The induction of the aberrations was more efficient in a more basic pH in parallel with the generation of hydrogen peroxide from NOH-2NA. The possible role of the oxidation product of NOH-2NA in the induction of the aberrations is discussed. 相似文献
995.
James C. Beck Howard L. Hosick Bruce A. Watkins 《In vitro cellular & developmental biology. Plant》1989,25(5):409-418
Summary We investigated the effects of conditioned media derived from mouse mammary fat pads on the proliferation of CL-S1 cells,
an epithelial cell line originally isolated from a preneoplastic mammary outgrowth line. Cell proliferation in vitro in serum-free
defined medium was compared to that in this medium conditioned using intact mammary fat pad pieces or isolated fat pad adipocytes.
Culture medium was conditioned by incubating the conditioning material in defined culture medium for 24 h at 37°C. Conditioned
medium induced CL-S1 proliferation as much as 10- to 20-fold above the minimal levels of growth in control cultures after
13 d of culture. The growth-stimulatory factor(s) had an apparent molecular weight of greater than 10 kDa. This growth-stimulatory
activity was both heat and trypsin stable. Because the role of adipose tissue is to store and release lipids, we next tested
whether lipids are released during medium conditioning. The lipid composition of the fat pad conditioned medium was characterized
using both thin layer and gas liquid chromatography. These lipid analyses indicated that the fat pad pieces released significant
amounts of fatty acids and phospholipids into the medium during the conditioning period. The free fatty acid composition included
both saturated and unsaturated molecules, and about 80% of the total fatty acids consisted of palmitate, stearate, oleate,
and linoleate. These same fatty acids were a structural component of the majority of phospholipid found in the medium. The
addition of palmitate or stearate to defined medium had no effect or was inhibitory for CL-S1 proliferation, depending on
the concentration used. Defined medium supplemented with oleate, arachidonate, or linoleate induced CL-S1 proliferation, and
the inhibitory effects of palmitate and stearate were overcome by addition of oleate and linoleate. These data indicate that
both unsaturated and saturated fatty acids are released from intact adipose cells of the mouse mammary fat pad and that fatty
acids can influence the growth of prenoplastic mouse mammary epithelium. Thus, unsaturated fatty acids, perhaps in conjunction
with other substances released simultaneously, are candidate molecules for the substances that mediate the effect of adipose
tissue on growth of epithelium.
This work was supported in part by a grant from the American Institute for Cancer Research; grant CA 46885 from the National
Institutes of Health, Bethesda, MD; and by State of Washington initiative 171. 相似文献
996.
997.
998.
本文研究了人胃低分化粘液性腺癌细胞MGC 80-3不同周期时相中ConA受体的分布与侧向运动。MGc 80-3细胞经同步化培养,用F-ConA标记。被标记细胞中G_1、S和G_2期呈不连续的分布,但它们之间又存在显著的差异。M期呈较均匀的强荧光分布(与其它时相细胞比较)。荧光漂白恢复方法测定ConA受体复合物侧向运动表明:各个周期时相之间不仅运动方式不同,而且运动速率也有显著差异。M期与G_1期主要表现出扩散型运动;而S期与G_2期表现为流动型运动。G_1期的扩散系数大干M期的;S期的流动速率大于G_2期的。但可动分子百分比以G_2期最高。这些结果表明了ConA受体的动力学性质。它受到细胞周期的调节。 相似文献
999.
Growth factor modulation of melanoma growth stimulatory activity mRNA expression in human malignant melanoma cells correlates with cell growth 总被引:2,自引:0,他引:2
This report demonstrates that the expression of melanoma growth stimulatory activity (MGSA) mRNA can be modulated in a positive fashion in the Hs294T human melanoma cell line by PDGF and MGSA. There is close correlation between MGSA expression and the pattern of cell growth in Hs294T cells. 相似文献
1000.
Biosynthesis of lysosomal endopeptidases 总被引:6,自引:0,他引:6
A H Erickson 《Journal of cellular biochemistry》1989,40(1):31-41
Despite the clear differences between the amino acid sequence and enzymatic specificity of aspartic and cysteine endopeptidases, the biosynthetic processing of lysosomal members of these two families is very similar. With in vitro translation and pulse-chase analysis in tissue culture cells, the biosynthesis of cathepsin D, a aspartic protease, and cathepsins B, H and L, cysteine proteases, are compared. Both aspartic and cysteine endopeptidases undergo cotranslational cleavage of an amino-terminal signal peptide that mediates transport across the endoplasmic reticulum (ER) membrane. Addition of high-mannose carbohydrate also occurs cotranslationally in the lumen of the ER. Proteases of both enzyme classes are initially synthesized as inactive proenzymes possessing amino-terminal activation peptides. Removal of the propeptide generates an active single-chain enzyme. Whether the single-chain enzyme undergoes asymmetric cleavage into a light and a heavy chain appears to be cell type specific. Finally, late during their biosynthesis both classes of enzymes undergo amino acid trimming, losing a few amino acid residues at the cleavage site between the light and heavy chains and/or at their carboxyltermini. During biosynthesis these enzymes are also secreted to some extent. In most cells the secreted enzyme is the proenzyme bearing some complex carbohydrate. Under certain physiological conditions the inactive secreted enzymes may become activated as a result of a conformational change that may or may not result in autolysis. Analysis of the biochemical nature of the various processing steps helps define the cellular pathway followed by newly synthesized proteases targeted to the lysosome. 相似文献