全文获取类型
收费全文 | 1164篇 |
免费 | 93篇 |
专业分类
1257篇 |
出版年
2021年 | 16篇 |
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 18篇 |
2017年 | 9篇 |
2016年 | 18篇 |
2015年 | 38篇 |
2014年 | 33篇 |
2013年 | 49篇 |
2012年 | 65篇 |
2011年 | 57篇 |
2010年 | 41篇 |
2009年 | 17篇 |
2008年 | 54篇 |
2007年 | 60篇 |
2006年 | 52篇 |
2005年 | 42篇 |
2004年 | 46篇 |
2003年 | 52篇 |
2002年 | 52篇 |
2001年 | 14篇 |
2000年 | 19篇 |
1999年 | 21篇 |
1998年 | 14篇 |
1996年 | 9篇 |
1995年 | 12篇 |
1992年 | 12篇 |
1991年 | 13篇 |
1990年 | 16篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 14篇 |
1982年 | 19篇 |
1981年 | 11篇 |
1980年 | 13篇 |
1979年 | 21篇 |
1978年 | 10篇 |
1977年 | 17篇 |
1976年 | 11篇 |
1975年 | 11篇 |
1974年 | 10篇 |
1973年 | 11篇 |
1971年 | 9篇 |
1970年 | 15篇 |
1969年 | 14篇 |
1968年 | 9篇 |
1967年 | 11篇 |
排序方式: 共有1257条查询结果,搜索用时 0 毫秒
1.
Compression wood (CW) contains higher quantities of β-1-4-galactan than does normal wood (NW). However, the physiological
roles and ultrastructural distribution of β-1-4-galactan during CW formation are still not well understood. The present work
investigated deposition of β-1-4-galactan in differentiating tracheids of Cryptomeria japonica during CW formation using an immunological probe (LM5) combined with immunomicroscopy. Our immunolabeling studies clearly
showed that differences in the distribution of β-1-4-galactan between NW (and opposite wood, OW) and CW are initiated during
the formation of the S1 layer. At this stage, CW was strongly labeled in the S1 layer, whereas no label was observed in the S1 layer of NW and OW. Immunogold labeling showed that β-1-4-galactan in the S1 layer of CW tracheids significantly decreased during the formation of the S2 layer. Most β-1-4-galactan labeling was present in the outer S2 region in mature CW tracheids, and was absent in the inner S2 layer that contained helical cavities in the cell wall. In addition, delignified CW tracheids showed significantly more labeling
of β-1-4-galactan in the secondary cell wall, suggesting that lignin is likely to mask β-1-4-galactan epitopes. The study
clearly showed that β-1-4-galactan in CW was mainly deposited in the outer portion of the secondary cell wall, indicating
that its distribution may be spatially consistent with lignin distribution in CW tracheids of Cryptomeria japonica. 相似文献
2.
3.
K Yoshida T Sakurada H Kitaoka H Fukazawa N Kaise K Kaise M Yamamoto S Saito K Yoshinaga 《Endocrinologia japonica》1983,30(2):211-217
Monodeiodination of T4 to T3 and rT3 in the intact cells of dog renal tubuli and glomeruli was investigated. The tubuli and glomeruli were obtained by a sieve method. T4 (2 micrograms/ml) was incubated in Tris-HCl buffer, pH 7.5, with renal cells (180 micrograms protein/ml) and 5 mM DTT for 1 h at 37 degrees C and the T3 and rT3 generated during incubation were measured by specific radioimmunoassays. In order of decreasing activity, dog renal cortical tubuli, cortical homogenate, glomeruli and medullary tubuli were capable of converting T4 to T3. Net rT3 production from T4 in cortical tubuli was also greater than that in cortical homogenate. The conversion of T4 to T3 and also to rT3 in cortical tubuli was enzymatic in nature, since the reactions showed dependence on time and protein concentration; instability to heating; temperature and pH optimum. The production of T3 and rT3 from T4 was maximum at pH 6.5 and at pH 9.5, respectively, indicating that two different enzymic systems, a 5- and a 5'-monodeiodinase, might be involved in the deiodination of the tyrosyl and the phenolic ring of T4 in dog kidney. 相似文献
4.
Alvin Sarachek 《Mycopathologia》1987,99(1):31-39
Heterokaryons (hets), but not monokaryons of Candida albicans die when grown anaerobically on minimal medium. Their rates of inactivation increase with decreases in growth temperatures from 37°C to 25°C. At 10°C, however, anaerobiosis is not lethal and suppresses the inactivation which normally occurs among hets cultured aerobically at that temperature. Killing of hets by anaerobiosis can be altered significantly by certain exogenously provided amino acids or intermediates of oxidative respiration. Aspartic acid alone promotes inactivation whereas alanine, glutamic acid or lysine individually have no effects. However, glutamate and lysine combined afford slight protection against inactivation while aspartate and glutamate combined, with or without lysine, are highly protective: the activity of the aspartate-glutamate combination is completely negated by the addition of alanine. Other common amino acids have no effects on het responses to anaerobiosis other than the ability, when combined, to relieve the antagonism of alanine for the aspartate-glutamate combination. Anaerobic survivals are also enhanced by oxalacetic acid or -ketoglutaric acid, and even more so by a combination of these two intermediates. The resistances to inactivation elicited by the oxalacetate -ketoglutarate or aspartate-glutamate combinations are not additive. These relationships are interpreted to signify that inactivation of hets by anaerobic growth is largely, if not exclusively, due to depletion of their oxalacetic acid and -ketoglutaric acid contents for amino acid biosyntheses, and the unique inability of het cells to replenish those keto acids upon subsequent return to aerobic conditions. The observations are consistent with previous indications that mitochondria formed by hets are functionally abnormal. 相似文献
5.
T Aoyagi T Wada F Kojima M Nagai S Harada T Takeuchi K Tsunoda K Abe K Yoshinaga 《Biotechnology and applied biochemistry》1990,12(3):258-263
The relation of plasma renin activity (PRA) and plasma levels of angiotensin I (AI) and II (AII) to those of various proteases, including eight endopeptidases and four aminopeptidases, was investigated in 51 normal control subjects. The multivariate study using factor analysis showed that the plasma proteases can be classified into three main components: the aminopeptidase, the plasmin, and the kinin-kallikrein. PRA and AI were related almost exclusively to the aminopeptidase component, while the AII level was related not only to the same component but also to the kallikrein-kinin component. This kind of multivariate study may help in the elucidation of the role of proteases and bioactive peptides, such as angiotensin derivatives, in essential hypertension through a comparison of multivariate relationships in controls and patients. 相似文献
6.
Requirement of c-kit for development of intestinal pacemaker system. 总被引:65,自引:0,他引:65
H Maeda A Yamagata S Nishikawa K Yoshinaga S Kobayashi K Nishi S Nishikawa 《Development (Cambridge, England)》1992,116(2):369-375
A discovery that the protooncogene encoding the receptor tyrosine kinase, c-kit, is allelic with the Dominant white spotting (W) locus establishes that c-kit plays a functional role in the development of three cell lineages, melanocyte, germ cell, and hematopoietic cell which are defective in W mutant mice. Recent analyses of c-kit expression in various tissues of mouse, however, have demonstrated that c-kit is expressed in more diverse tissues which are phenotypically normal in W mutant mice. Thus, whether or not c-kit expressed outside the three known cell lineages plays a functional role is one of the important questions needing answering in order to fully elucidate the role of c-kit in the development of the mouse. Here, we report that some of the cells in smooth muscle layers of developing intestine express c-kit. Blockade of its function for a few days postnatally by an antagonistic anti-c-kit monoclonal antibody (mAb) results in a severe anomaly of gut movement, which in BALB/c mice produces a lethal paralytic ileus. Physiological analysis indicates that the mechanisms required for the autonomic pacing of contraction in an isolated gut segment are defective in the anti-c-kit mAb-treated mice, W/Wv mice and even W/+ mice. These findings suggest that c-kit plays a crucial role in the development of a component of the pacemaker system that is required for the generation of autonomic gut motility. 相似文献
7.
K Hanew S Sato A Sasaki M Goh Y Shimizu O Murakami K Yoshinaga 《Endocrinologia japonica》1985,32(6):811-817
To evaluate the PRL secretory mechanism in patients with PRL-secreting adenoma (PRL-oma), plasma PRL responses to dopamine (DA) were studied in these cases and in normal subjects. Plasma PRL values showed clear decreases during the infusion of DA (5 micrograms/kg/min for 90 min) in both 6 normal and 7 PRL-oma subjects (%decrease: 43.8 +/- 3.9% vs. 53.9 +/- 5.6%; NS) and postinhibitory increases after the termination. However, the postinhibitory increase occurred more promptly and markedly in PRL-oma patients than in normal subjects, i.e. the postinhibitory increase exceeded the basal level 45 min after the termination of DA infusion in PRL-oma patients, whereas the increase in normal subjects did not exceed the basal level even 90 min after the infusion. When domperidone was injected at the termination of DA infusion, the postinhibitory increases were significantly enhanced in either PRL-oma or normal subjects. The maximal increments in plasma PRL in the combination test of DA plus domperidone were significantly larger in PRL-oma patients, but were almost the same in normal controls, compared to the single domperidone test. In contrast, TRH did not modify the postinhibitory rises in 9 PRL-oma patients. These results indicate that the secretory properties and the sensitivities of lactotrophs to decreasing action of DA might be different between PRL-oma patients and normal controls. Further, the postinhibitory rebound phenomenon in PRL-oma patients is possibly determined by an overshoot of PRL storage concomitantly with a decreasing DA action.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
8.
9.
10.
Alternative Developmental Pathways Determined by Environmental Conditions in the Cellular Slime Mold Dictyostelium discoideum 总被引:19,自引:3,他引:16 下载免费PDF全文
The cellular slime mold Dictyostelium discoideum grows in the soil as a population of independent, uninucleate amoebae. Upon entrance to the stationary phase, the amoebae collect in multicellular aggregates to form organized fruiting bodies composed of spores and stalk cells. Depending upon environmental conditions, the developing aggregate either constructs the fruiting body at the site of aggregation or transforms into a structure that can migrate to a more favorable location. Environmental conditions that favor migration are (i) the accumulation of metabolite(s) produced by the aggregate and (ii) a low ionic strength in the substratum. Conditions that prevent migration or that stop a migrating slug are (i) the presence of buffer and (ii) illumination by overhead light. 相似文献