全文获取类型
收费全文 | 3992篇 |
免费 | 218篇 |
出版年
2022年 | 28篇 |
2021年 | 53篇 |
2020年 | 24篇 |
2019年 | 36篇 |
2018年 | 50篇 |
2017年 | 49篇 |
2016年 | 77篇 |
2015年 | 107篇 |
2014年 | 121篇 |
2013年 | 241篇 |
2012年 | 223篇 |
2011年 | 224篇 |
2010年 | 142篇 |
2009年 | 150篇 |
2008年 | 248篇 |
2007年 | 255篇 |
2006年 | 230篇 |
2005年 | 221篇 |
2004年 | 279篇 |
2003年 | 201篇 |
2002年 | 224篇 |
2001年 | 114篇 |
2000年 | 98篇 |
1999年 | 79篇 |
1998年 | 49篇 |
1997年 | 45篇 |
1996年 | 25篇 |
1995年 | 27篇 |
1994年 | 20篇 |
1993年 | 37篇 |
1992年 | 71篇 |
1991年 | 51篇 |
1990年 | 33篇 |
1989年 | 35篇 |
1988年 | 37篇 |
1987年 | 28篇 |
1986年 | 34篇 |
1985年 | 30篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 15篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1976年 | 12篇 |
1975年 | 13篇 |
1974年 | 10篇 |
1972年 | 10篇 |
1968年 | 10篇 |
排序方式: 共有4210条查询结果,搜索用时 906 毫秒
51.
Summary The evolutionary relation of vertebrate myoglobin and the hemoglobin chains including the agnathan hemoglobin chain is investigated on the basis of a new view of amino acid changes that is developed by canonical discriminant analysis of amino acid residues at individual sites. In contrast to the clear discrimination of amino acid residues between myoglobin, hemoglobin a chain, and hemoglobin chain in warm-blood vertebrates, the three types of globins in the lower class of vertebrates show so much variation that they are not well discriminated. This is seen particularly at the sites that are ascertained in mammals to carry the amino acid residues participating in stabilizing the monomeric structure in myoglobin and the residues forming the subunit contacts in hemoglobin. At these sites, agnathan hemoglobin chains are evaluated to be intermediate between the myoglobin and hemoglobin chains of gnathostomes. The variation in the phylogenetically lower class of globins is also seen in the internal region; there the amino acid residues of myoglobin and hemoglobin chains in the phylogenetically higher class exhibit an example of parallel evolution at the molecular level. New quantities, the distance of sequence property between discriminated groups and the variation within each group, are derived from the values of discriminant functions along the peptide chain, and this set of quantities simply describes an overall feature of globins such that the distinction between the three types of globins has been clearer as the vertebrates have evolved to become jawed, landed, and warm-blooded. This result strongly suggests that the functional constraint on the amino acid sequence of a protein is changed by living conditions and that severe conditions constitute a driving force that creates a distinctive protein from a less-constrained protein.Offprint requests to: J. Otsuka 相似文献
52.
Tsuyoshi Kihara Masato Ikeda Hiroshi Miyazaki Akira Matsushita 《Journal of neurochemistry》1993,61(5):1859-1864
Abstract: The in vivo microdialysis method was used to study the effect of the cholecystokinin-related peptide, ceruletide, on extracellular levels of dopamine (DA) in the striatum following perfusion with various K+ concentrations. Increasing the K+ concentration in the perfusate from 4 to 15 or 17.5 m M did not change basal DA release or release evoked by electrical stimulation of the medial forebrain bundle (MFB). However, when the perfusing solution contained 20 or 30 m M K+ , dose-dependent reductions of both basal and MFB-stimulated DA release occurred. Subcutaneous administration of ceruletide at 160 μg/kg had no influence on the basal or MFB-stimulated DA release with 4 or 15 m M K+ in the perfusate. However, after perfusion with 17.5 m M K+ , ceruletide significantly attenuated the basal and MFB-stimulated DA release. Carbachol (10 μ M ) locally applied via the dialysis probe also attenuated MFB-stimulated DA release after perfusion with 17.5 m M K+ . From these results, we conclude that under appropriate depolarization of striatal DA terminals, ceruletide induces further depolarization and inactivation of nigrostriatal DA terminals. The present data suggest that this effect may be mediated via intrinsic cholinergic neurons in the striatum. 相似文献
53.
Mayumi Nishikata Aki Nakai Hitomi Fushida Keishiro Miyake Takaichi Arita Ken Iseki Katsumi Miyazaki Akikazu Nomura 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1993,612(2)
A method is described for the simultaneous determination of (+)- and (−)-homochlorcyclizine (HCZ) in human urine by high-performance liquid chromatography on a chiral stationary phase of ovomucoid-bonded silica. The pH of the buffer and organic modifier in the mobile phase markedly affected the chromatographic separation. A mobile phase of methanol—0.02 M acetate buffer (pH 4.7) (25:75, v/v) at a flow-rate of 1.0 ml/min was used for the urine assays. The ultraviolet absorption was monitored at 240 nm, and diphenhydramine was employed as the internal standard for the quantitation. (+)-HCZ, (−)-HCZ and the internal standard were eluted at retention times of 15, 25 and 8 min, respectively. The limit of determination for HCZ enantiomers was ca. 50 ng/ml of urine. One of the metabolites in human urine, which was a quaternary ammonium-linked glucuronide, could also be determined in a manner similar to unchanged HCZ after β-glucuronidase hydrolysis. A pharmacokinetic study was conducted with three healthy volunteers, who each received a single oral dose of racemic HCZ (20 mg). Distinct differences were found between the two enantiomers, particularly in the metabolic process, that is, the urinary excretion as (−)-HCZ-glucuronide within 48 h was ca. four times higher than that of the (+)-isomer. This method should be very useful for enantioselective pharmacokinetic studies of HCZ. 相似文献
54.
A. Kotake T. Arai M. Ohji S. Yamane N. Miyazaki K. Tsukamoto 《Zeitschrift fur angewandte Ichthyologie》2004,20(2):150-153
The age and migratory history of the Japanese eel, Anguilla japonica Temminck & Schlegel, collected in Miyako Bay along the Sanriku coast of Japan, was examined using the otolith microstructure and analysis of strontium (Sr) and calcium (Ca) concentrations conducted with wavelength dispersive X‐ray spectrometry by an electron microprobe. The line analysis of Sr : Ca ratios along the life history transect of each otolith showed a peak (ca. 15–17 × 10?3) which corresponded with the period of their leptocephalus and early glass eel stages in the ocean. The mean Sr : Ca ratios from the elver mark to the otolith edge indicated that there were eels with several general categories of migratory history, including sea eels that never entered freshwater (average Sr : Ca ratios, ≥6.0 × 10?3), and others that entered freshwater for brief periods but returned to the estuary or bay. This evidence of the occurrence of sea eels in this northern area indicates that Japanese eels of the Sanriku coast do not necessarily migrate into freshwater rivers during recruitment as do glass eels at the beginning of their growth phase; even those that do enter freshwater may later return to the marine environment. Thus, anguillid eel migrations into freshwater are clearly not an obligatory migratory pathway, but rather a facultative catadromy with seawater or estuarine residents as an ecophenotype. 相似文献
55.
Yamato Kikkawa Kotaro Akaogi Hiroto Mizushima Naoki Yamanaka Makoto Umeda Kaoru Miyazaki 《In vitro cellular & developmental biology. Animal》1996,32(1):46-52
Summary Ladsin is a laminin-like cell-adhesive scatter factor with potent cell motility-stimulating ability and was purified from
serum-free conditioned medium of a malignant human gastric adenocarcinoma cell line STKM-1. To test its possible role in tumor
angiogenesis, we investigated its effect on primary culture of endothelial cells (human umbilical vein endothelial cells)
and endothelial cell line ECV304 in this study. Cell adhesion and motility effects of ladsin were observed in both types of
endothelial cells. In cell-attachment assay, ladsin interacted with integrin α3β1 that was expressed on the endothelial cell
surface. In Boyden chambers, ladsin stimulated both directed and random migration of ECV304 cells. Ladsin induced repair of
artificial wounds generated in ECV304 cell monolayers by stimulating cell migration. Ladsin did not affect the growth rate
of ECV304 cells at a low cell density but significantly increased the saturation cell density. These results suggest that
ladsin may be involved in the adhesion and migration of endothelial cells under some physiological and pathological conditions. 相似文献
56.
57.
Akihiro Yoshida Kuniaki Takata Toshiko Kasahara Toshio Aoyagi Shozo Saito Hiroshi Hirano 《The Histochemical journal》1995,27(5):420-426
Summary Glucose is actively absorbed in the intestine by the action of the Na+-dependent glucose transporter. Using an antibody against the rabbit intestinal Na+-dependent glucose transporter (SGLT1), we examined the localization of SGLT1 immunohistochemically along the rat digestive
tract (oesophagus, stomach, duodenum, jejunum, ileum, colon and rectum). SGLT1 was detected in the small intestine (duodenum,
jejunum and ileum), but not in the oesophagus, stomach, colon or rectum. SGLT1 was localized at the brush border of the absorptive
epithelium cells in the small intestine. Electron microscopical examination showed that SGLT1 was localized at the apical
plasma membrane of the absorptive epithelial cells. SGLT1 was not detected at the basolateral plasma membrane. Along the crypt-villus
axis, all the absorptive epithelial cells in the villus were positive for SGLT1, whose amount increased from the bottom of
the villus to its tip. On the other hand, cells in the crypts exhibited little or no staining for SGLT1. Goblet cells scattered
throughout the intestinal epithelium were negative for SGLT1. These observations show that SGLT1 is specific to the apical
plasma membrane of differentiated absorptive epithelial cells in the small intestine, and suggest that active uptake of glucose
occurs mainly in the absorptive epithelial cells in the small intestine. 相似文献
58.
Ken Lee Akihiro Ito †Kunio Koshimura †Tetsuya Ohue †Yasutaka Takagi †Soichi Miwa 《Journal of neurochemistry》1995,64(2):874-882
Abstract: Hypoxia is known to disturb neuronal signal transmission at the synapse. Presynaptically, hypoxia is reported to suppress the release of neurotransmitters, but its postsynaptic effects, especially on the function of neurotransmitter receptors, have not yet been elucidated. To clarify the postsynaptic effects, we used cultured bovine adrenal chromaffin cells as a model of postsynaptic neurons and examined specific binding of l -[3 H]nicotine (an agonist for nicotinic acetylcholine receptors: nAChRs) and 22 Na+ flux under control and hypoxic conditions. Experiments were performed in media preequilibrated with a gas mixture of either 21% O2 /79% N2 (control) or 100% N2 (hypoxia). Scatchard analysis of the specific binding to the cells revealed that the KD under hypoxic conditions was twice as large as that under control conditions, whereas the B max was unchanged. When the specific [3 H]nicotine binding was kinetically analyzed, the association constant ( k 1 ) but not the dissociation constant ( k −1 ) was decreased to 40% of the control value by hypoxia. When the binding assay was performed using the membrane fraction, these changes were not observed. Nicotine-evoked 22 Na+ flux into the cells was suppressed by hypoxia. In contrast, specific [3 H]quinuclidinyl benzilate binding to the intact cells was unaffected by hypoxia. These results demonstrate that hypoxia specifically suppresses the function of nAChRs (and hence, neuronal signal transmission through nAChRs), primarily by acting intracellularly. 相似文献
59.
Souichi Satoh †Tatsuo Kimura †Masahiro Toda †Mutuko Maekawa †Satoshi Ono †Hirokazu Narita Hiroyuki Miyazaki Toshihiko Murayama Yasuyuki Nomura 《Journal of neurochemistry》1997,69(5):2197-2205
Abstract: Nitrogen oxides, such as nitric oxide, have been shown to regulate neuronal functions, including neurotransmitter release. We investigated the effect of S-nitroso-l -cysteine (SNC) on noradrenaline (NA) release in the rat hippocampus in vivo and in vitro. SNC stimulated [3H]NA release from prelabeled hippocampal slices in a dose-dependent manner. SNC stimulated endogenous NA release within 30 min to almost five times the basal level in vivo (microdialysis in freely moving rats). In a Na+-containing Tyrode's buffer, SNC-stimulated [3H]NA release was inhibited 30% by the coaddition of l -leucine. In the Na+-free, choline-containing buffer, SNC-stimulated [3H]NA release, which was similar to that in the Na+-containing buffer, was inhibited markedly by l -leucine, l -alanine, l -methionine, l -phenylalanine, and l -tyrosine. The effects of the other amino acids examined were smaller or very limited. The effect of l -leucine was stronger than that of d -leucine. A specific inhibitor of the L-type amino acid transporter, 2-aminobicyclo[2.2.1]-heptane-2-carboxylate (BCH), inhibited the effects of SNC on [3H]NA release in the Na+-free buffer. Uptake of l -[3H]leucine into the slices in the Na+-free buffer was inhibited by SNC, BCH, and l -phenylalanine, but not by l -lysine. The effect of SNC on cyclic GMP accumulation was not inhibited by l -leucine, although SNC stimulated cyclic GMP accumulation at concentrations up to 25 µM, much less than the concentration that stimulates NA release. These findings suggest that SNC is incorporated into rat hippocampus via the L-type-like amino acid transporter, at least in Na+-free conditions, and that SNC stimulates NA release in vivo and in vitro in a cyclic GMP-independent manner. 相似文献
60.
S Nakamura S Sakata T Komaki N Kojima K Kamikubo S Miyazaki K Yasuda H Tsukada S Shiraki K Miura 《Endocrinologia japonica》1984,31(6):675-679
We measured the levels of serum thyroglobulin (Tg) in 52 pregnant females at various stages and compared them with those of 15 age-matched nonpregnant females. Serum Tg was measured by a solid-phase immunoradiometric assay. In pregnant females, mean serum Tg levels at the first, second, early third, and late third trimesters were 8.4 (range; 1.3-18.0), 9.2 (1.7-25.6), 10.1 (1.8-22.8), and 12.1 ng/ml (5.3-25.2), respectively. The statistical comparison was made after logarithmic transformation of the data. The mean value only at the late third trimester was significantly higher than that of controls (mean; 6.0 ng/ml, range; 1.5-23.6), but each value was within the normal range. Although serum Tg levels have been reported to be high at the end of pregnancy, our results indicate that the Tg levels in females could be clinically interpreted without regard to the coexistence of pregnancy. 相似文献