全文获取类型
收费全文 | 2354篇 |
免费 | 108篇 |
出版年
2021年 | 12篇 |
2020年 | 14篇 |
2019年 | 27篇 |
2018年 | 28篇 |
2017年 | 22篇 |
2016年 | 38篇 |
2015年 | 55篇 |
2014年 | 59篇 |
2013年 | 240篇 |
2012年 | 153篇 |
2011年 | 153篇 |
2010年 | 78篇 |
2009年 | 106篇 |
2008年 | 150篇 |
2007年 | 131篇 |
2006年 | 137篇 |
2005年 | 131篇 |
2004年 | 148篇 |
2003年 | 140篇 |
2002年 | 134篇 |
2001年 | 17篇 |
2000年 | 27篇 |
1999年 | 26篇 |
1998年 | 30篇 |
1997年 | 33篇 |
1996年 | 25篇 |
1995年 | 30篇 |
1994年 | 30篇 |
1993年 | 25篇 |
1992年 | 24篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1985年 | 8篇 |
1984年 | 17篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 23篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 10篇 |
1971年 | 5篇 |
1966年 | 5篇 |
排序方式: 共有2462条查询结果,搜索用时 15 毫秒
971.
Reversing-pulse electric birefringence (RPEB) was measured for the first time for four fractionated poly(γ-benzyl-L -glutamate), [Glu(OBzl)]n, samples in N,N-dimethylformamide (DMF) at 20°C and at 535 nm. The RPEB signal showed a deep minimum for each sample on reversal of an applied electric field. The profiles of the reverse-transient signal were analyzed by taking into account the polydispersity for the continuous distribution of molecular lengths. The best set of three quantities (lw, lw/ln, (βw)2/2γw), which determine a signal profile, was evaluated for each sample. By combining the experimental data of intrinsic viscosity and RPEB, the diameter of a cylinder, which is assumed for the [Glu(OBzl)]n helix, was found to be 17 Å. The value (βw)2/2γw, which is related to the ratio of weight-average permanent dipole moment μw, and electric polarizability anisotropy Δαw, was found to be in the range of 20–45. This indicates that the former contributes predominantly to electric field orientation, but the latter also should not be ignored. With the three parameters from the reverse portion, the rise and decay curves were regenerated theoretically in excellent agreement with experimental signals. 相似文献
972.
Changes in the protein synthesis of Xenopus hepatocytes caused by insulin, estradiol-17β (estradiol) and dexamethasone were studied by using a primary culture in serum-free medium. All of these hormones stimulated the synthesis of secretory and intracellular proteins. Dexamethasone induced or stimulated the synthesis of many proteins (though limited in number), whereas estradiol induced or stimulated relatively few proteins, including the yolk precursor protein vitellogenin. The majority of these proteins differed in molecular weight and/or isoelectric point. When hepatocytes were treated with both steroids, most of the proteins were synthesized at the rates expected from the single treatment of the respective steroids. Thus, each steroid selectively stimulated the synthesis of its specific proteins. However, exceptional proteins were observed, whose syntheses were stimulated only by double treatment. In contrast, insulin seemed to cause an overall increase in individual secretory protein synthesis. 相似文献
973.
Kanji Ohyama Yuko Uchida Norihiko Misawa Tohru Komano Minoru Fujita Tamio Ueno 《Plant cell reports》1984,3(1):21-22
The culture of cells of Euphorbia tirucalli L. resulted in the formation of intracellular particles which osmium tetroxide staining and electron microscopy indicated to be oil bodies. Chemical analysis (TLC, HPLC, GLC and GC-MS) disclosed steroids, triterpenoids, and diterpenoids as the major oil components of the cultured cells. 相似文献
974.
Toshio Omori Minoru Matsubara Susumu Masuda Tohru Kodama 《Applied microbiology and biotechnology》1991,35(4):431-435
Summary
Pseudomonas testosteroni M4-1, capable of using phthalate as the sole carbon and energy source, was isolated. Tn5 mutagenesis using pSUP2021 yielded mutant strains of M4-1 that are defective in phthalate metabolism and produce a dihydrodiol compound. The dihydrodiol compound produced by mutant strain M4-122 was isolated and identified as 4,5-dihydro-4,5-dihydroxyphthalate (DDP) by elementary analysis, mass analysis and nuclear magnetic resonance. Various conditions to increase the yield of DDP from phthalate were examined for mutant strain M4-122. With resting cells 6 g DDP/1 were produced. The additional of ethanol to the resting-cell reaction mixture enhanced DDP production and 10 g DDP/1 was produced from 8.3 g/1 of phthalate.
Offprint requests to: T. Omori 相似文献
975.
Yasuyuki Sasaguri Hidetaka Yanagi Hideaki Nagase Ryuji Nakano Shyuichi Fukuda Minoru Morimatsu 《Virchows Archiv. B, Cell pathology including molecular pathology》1991,60(1):91-97
Human aortic endothelial cells, isolated at autopsy from a 52-year-old male dying from lung cancer, were treated with simian
virus 40 (SV40). One colony was isolated from the infected endothelial cell culture 4 weeks after infection. The cells expressed
SV40 large T antigen and p53 protein (p53) in their nuclei but lacted the characteristics of a transformed phenotype. The
cells grew well in a monolayer over the 97th passage and exhibited Factor Vlll-related antigen, Ulex europaeus 1 agglutinin
(UEA-1) as endothelial cell markers, and a well-developed fibronectin network. The amount of prostacyclin synthesized by the
cells was less than the amount synthesized by normal aortic or umbilical cord vein endothelial cells. The cells produced relatively
large amounts of procollagenase, and 12-o-tetradecanoyl-phorbol-13-acetate (TPA) augmented the ability of the cells to produce
this enzyme. These immortalized human aortic endothelial cells, which have some characteristics of normal endothelial cells
and, like capillary endothelial cells, have the ability to produce collagenase, will probably prove useful for studies of
atherosclerosis and angiogenesis. 相似文献
976.
When aromatic hydrocarbon (Ah)-responsive and -non-responsive strains of mice were pretreated with 3-methylcholanthrene (MC) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), vitamin C reduced the microsomal aryl hydrocarbon hydroxylase (AHH) activity. The AHH inhibitors 7,8-benzoflavone (7,8-BF) and 3-methylsulfonyl-3′,4,4′,5-tetrachlorobiphenyl (3-MSF-3′,4,4′,5-tetraCB) showed various inhibitory effects depending upon the types of microsomes, whereas vitamin C exhibited inhibition irrespective of the types of microsomes. 7,8-BF and 3-MSF-3′,4,4′,5-tetraCB as well as vitamin C suppressed the reverse mutation of the Salmonella typhimurium tester strains TA98 and TA100 induced by benzo[a]pyrene. 相似文献
977.
Minoru Morikawa Naoki Harada Gen-Ichiro Soma Takeshi Yoshida 《In vitro cellular & developmental biology. Plant》1990,26(7):682-690
Summary The human leukemic cells HL-60, U937, KG-1 and THP-1 incubated with transforming growth factor-β1 (TGF-β1) were studied by
examining cell surface antigens and macrophage-specific activities. The addition of 0.5 ng/ml (20 pM) of TGF-β1 with 1α,25-dihydroxyvitamin D3 [1α, 25(OH)2D3] induced more Leu-M3 (CD14)-positive cells (approximately 80%) than 5×10−8
M 1α,25(OH)2D3 alone did (30 to 50%), although original HL-60 cells did not express any Leu-M3 antigen at all. Tumor necrosis factor-α (TNF-α)
with TGF-β1 and 1α,25(OH)2D3 was found to potentiate the expression of these surface antigens. Furthermore, the phagocytic activity was also induced strongly.
The expression of CR3 (CD11b) antigen was also increased, and all Leu-M3-positive cells were found CR3-positive when HL-60,
U937, and THP-1 cells were treated with these stimulants. In contrast, CR3 but not Leu-M3 was induced in KG-1 cells after
the same treatment. This may indicate that the responsiveness of leukemic cells to TGF-β1 and 1α,25(OH)2D3 might vary depending on a differentiation stage of the target cells. Furthermore, K562 cells originated from a more undifferentiated
precursor, were not able to respond to these two inducers. These results suggested that some of TGF-β superfamily proteins
might represent potent modulators in hematopoiesis, especially in the development of monocytes-macrophages or their precursors. 相似文献
978.
Release by Electrical Stimulation of Endogenous Glutamate, γ-Aminobutyric Acid, and Other Amino Acids from Slices of the Rat Medulla Oblongata 总被引:2,自引:2,他引:0
Evidence was obtained for the release of amino acids by electrical stimulation of slices of regions of the rat medulla oblongata: rostral ventrolateral, caudal ventrolateral and caudal dorsomedial. There was a Ca2+-dependent, tetrodotoxin-sensitive increase in the efflux of aspartate, glutamate, gamma-aminobutyric acid (GABA), glycine, and beta-alanine in all regions examined. There were distinct regional differences in the relative amounts of amino acids released. These results provide evidence for the possible neurotransmitter role of aspartate, glutamate, GABA, glycine, and beta-alanine in these regions of the rat medulla oblongata. 相似文献
979.
The complexes of the three BrCN-cleaved fragments of sperm whale apomyoglobin with hemin were studied by circular dichroism (CD). In native myoglobin, the heme is located in the middle fragment; the isolated peptide (residues 56–131), however, produces little extrinsic Cotton effects by the addition of hemin, although about four molecules of hemin are bound to this peptide. In marked contrast, the COOH-terminal peptide (residues 132–153), which binds three hemin molecules, shows strong Cotton effects in the Soret bands and drastically changes its conformation from unordered to highly helical. The Arg-modified or Lys-deaminated peptide no longer undergoes conformational changes by the addition of hemin, suggesting that the two propionic acid groups of one hemin molecule interact with the Arg residue and one of the Lys residues, which stabilizes the induced helical conformation. The NH2-terminal peptide (residues 1–55) binds one hemin molecules, and the helicity of this fragment is slightly enhanced by the addition of hemin. Both the CD and difference absorption spectra indicate that the mode of interaction between the peptides and hemin are different for the three apomyoglobin fragments. 相似文献
980.
Activities of aminopropyltransferases (spermidine synthase and spermine synthase) were inhibited by aurintricarboxylic acid (ATA). Spermidine synthase was slightly more sensitive to the inhibitor than spermine synthase. These inhibitions were not prevented by 0.15 M NaCl. Inhibition by ATA of spermidine synthase was ‘uncompetitive’ with respect to putrescine and that of spermine synthase was ‘non-competitive’ with respect to spermidine. When the amount of spermidine synthase or spermine synthase was varied, inhibition ratio hardly changed on either case implying no appreciable interaction between ATA and these enzymes. 相似文献