全文获取类型
收费全文 | 5101篇 |
免费 | 426篇 |
国内免费 | 2篇 |
出版年
2023年 | 21篇 |
2022年 | 38篇 |
2021年 | 73篇 |
2020年 | 56篇 |
2019年 | 86篇 |
2018年 | 75篇 |
2017年 | 91篇 |
2016年 | 154篇 |
2015年 | 236篇 |
2014年 | 260篇 |
2013年 | 322篇 |
2012年 | 385篇 |
2011年 | 361篇 |
2010年 | 246篇 |
2009年 | 198篇 |
2008年 | 284篇 |
2007年 | 248篇 |
2006年 | 256篇 |
2005年 | 242篇 |
2004年 | 262篇 |
2003年 | 234篇 |
2002年 | 225篇 |
2001年 | 68篇 |
2000年 | 56篇 |
1999年 | 73篇 |
1998年 | 59篇 |
1997年 | 64篇 |
1996年 | 62篇 |
1995年 | 42篇 |
1994年 | 26篇 |
1993年 | 47篇 |
1992年 | 37篇 |
1991年 | 41篇 |
1990年 | 35篇 |
1989年 | 35篇 |
1988年 | 40篇 |
1987年 | 27篇 |
1986年 | 39篇 |
1985年 | 34篇 |
1984年 | 29篇 |
1983年 | 32篇 |
1982年 | 23篇 |
1981年 | 24篇 |
1980年 | 15篇 |
1979年 | 28篇 |
1978年 | 23篇 |
1977年 | 28篇 |
1976年 | 23篇 |
1974年 | 18篇 |
1973年 | 27篇 |
排序方式: 共有5529条查询结果,搜索用时 109 毫秒
51.
Summary Most of the specific monoamine fluorescence of the fowl neurohypophysis is found in the eminentia mediana and the infundibular stem. The densest accumulation of fluorescent structures is located to the zona externa and the subependymal layer, whereas generally only scattered fluorescence is demonstrable in the fiber layer. The neural lobe tissue is provided with very fine smooth fibers often difficult to distinguish. Spectrofluorimetric determinations have shown that noradrenaline is the major catecholamine in the chick neurohypophysis. From the embryological studies it is evident that the monoamine fluorescence first appears in the subependymal layer, the fiber layer and the neural lobe (after about 15 days of incubation). The zona externa fluorescence is not visible until just before hatching. 10 days after hatching the fluorescence intensity of the chick neurohypophysis is similar to that of the adult. Some comparisons are also made with the appearance of monoamines in the mouse.The authors take great pleasure in expressing their warmest thanks for laboratory facilities and good advice provided by Dr. Bengt Falck at the Institute of Histology, Lund, Sweden.This work was supported by grants from the Swedish Natural Science Research Council (project no. 99-35 and 2180-16), from the United States Public Health Service (NB-06701-02) and from the Swedish Medical Research Council (B-69-14 x -56-05 C). 相似文献
52.
From a previously published theory (Israelsson and Johnsson 1967) for circumnutations in Helianthus annuus it is possible to predict the geotropical curvatures of the hypocotyls. This extension of the theory is given in the present paper and some geotropical experiments are performed and discussed. The agreement between the theory and the experiments has been verified in the case of gravitational stimulation during relatively short stimulation periods, in the case of continuous gravitational stimulation, etc. Restrictions in the proposed model are discussed. 相似文献
53.
54.
55.
56.
Summary By means of a highly sensitive and specific histochemical method for the demonstration of certain biogenic monoamines a plexus of nerves containing a primary catecholamine has been demonstrated in the pars intermedia of the toad, Bufo arenarum. These nerves are restricted in distribution to the part of the gland which contains colloid vesicles (stored MSH ?) in the cells. The view is put forward, based on the results of pharmacological and surgical experiments, that the adrenergic nerves inhibit the release of the MSH from the pars intermedia. The origin of the nerves in the brain is unknown, but experiments with lesions have shown that it is not to be found in the nucleus periventricularis arcuatus.The research reported in this document has been sponsored by the Swedish Medical Research Council and by the Swedish Natural Science Research Council.Research fellow of the Commission of Scientific Research of the Province of Buenos Aires, Argentina. 相似文献
57.
58.
59.
In Vivo Substitution of Choline for Sodium Evokes a Selective Osmoinsensitive Increase of Extracellular Taurine in the Rat Hippocampus 总被引:1,自引:0,他引:1
Recent investigations have demonstrated that taurine and phosphoethanolamine (PEA) are the amino acids most sensitive to microdialysis-perfusion with reduced concentrations of NaCl. The aim of the present work was to assess the importance of Na+ deficiency in evoking this response. Further, the previously described selectivity of replacement of Cl- with acetate with respect to amino acid release was reinvestigated. The hippocampus of urethane-anesthetized rats was dialyzed with Krebs-Ringer bicarbonate buffer, and amino acid concentrations of the perfusate were determined. Choline chloride was then stepwise substituted for NaCl, and, in some cases, mannitol (122 mM) was included in low sodium-containing media. In other experiments, NaCl was replaced with sodium acetate. The dialysate levels of taurine increased selectively in response to Na+ substitution. The elevation of taurine was linearly related to the increase in choline chloride, and maximal levels amounted to 335% of basal levels. The increase in extracellular taurine was not inhibited by perfusion with medium made hyperosmotic with mannitol. Replacement of Cl- with acetate stimulated the release of taurine to 652% of resting levels. In addition, PEA levels increased to 250% of control concentration. Other amino acids were unaffected by Cl- substitution. The results show that taurine transport is considerably more sensitive to Na+ depletion than glutamate transport, which also is known to be Na+ dependent. The taurine increase evoked by low Na+ is not caused by cellular swelling as it was unaffected by hyperosmolar medium. Finally, substitution of acetate for Cl- causes a specific elevation of extracellular taurine and PEA, possibly as a result of cytotoxic edema. 相似文献
60.
M Stemler T Weimer Z X Tu D F Wan M Levrero C Jung G R Pape H Will 《Journal of virology》1990,64(6):2802-2809
The immune response to the X protein of human hepatitis B virus (HBV) was studied by epitope mapping by using a set of MS2-HBx fusion proteins and synthetic peptides. Antibodies in sera of patients with acute and chronic HBV infection showed a multispecific immune response. Each serum contained antibodies to a different set of epitopes, which taken together cover most of the HBx sequence. Some of the epitopes were detectable only by immunoblotting with fusion proteins; others were detectable only by an enzyme-linked immunosorbent assay (ELISA) with synthetic peptides. The carboxy-terminal half of the HBx protein was preferentially recognized by antibodies from patients with chronic hepatitis and contained a short immunodominant antigenic region with at least two major nonoverlapping epitopes. Anti-HBx antibody titers as revealed by peptide ELISAs were highest and most frequent in patients with chronic hepatitis and usually low in acutely infected patients and asymptomatic carriers. The data demonstrate a remarkable qualitative and quantitative heterogeneity of the humoral HBx immune response which can be monitored by HBx-specific peptide ELISAs. Such tests may become useful diagnostic tools. 相似文献