全文获取类型
收费全文 | 823篇 |
免费 | 31篇 |
专业分类
854篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 9篇 |
2020年 | 11篇 |
2019年 | 6篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 16篇 |
2015年 | 18篇 |
2014年 | 28篇 |
2013年 | 48篇 |
2012年 | 57篇 |
2011年 | 53篇 |
2010年 | 33篇 |
2009年 | 34篇 |
2008年 | 60篇 |
2007年 | 67篇 |
2006年 | 59篇 |
2005年 | 61篇 |
2004年 | 71篇 |
2003年 | 56篇 |
2002年 | 44篇 |
2001年 | 7篇 |
2000年 | 12篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 11篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 1篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有854条查询结果,搜索用时 0 毫秒
841.
842.
Most surveys of large wood in streams are conducted by counting and measuring every piece of large wood within a reach, a
technique that is effective but time-consuming. In this study we evaluated an alternative method that takes less time and
can be employed in studies in which an estimate of total large wood volume along a stream reach is the primary metric of interest.
In first- through third-order streams we estimated in-stream large wood volume and large wood frequency, comparing large wood
census estimates to those from a modified a line-intercept technique that has been commonly used in terrestrial forest surveys.
Estimates of large wood volume from line transects located in the geographic center of the stream (parallel to stream axis
and equidistant from bankfull margins) were highly correlated with those from the wood census (P < 0.001, r
2 = 0.88, Pearson’s r = 0.935), but produced slightly greater estimates of large wood volume (regression slope = 1.28, SE = 0.16). Line-intercept
estimates of large wood frequency (number per 100 m of stream) were significantly correlated to the wood census counts, but
the line-intercept method underestimated frequency by about 50% (P = 0.016). Differences in the estimated large wood volume between line-intercept and wood census surveys were associated with
variability in the diameter of the large wood, but unrelated to stream bankfull width, for the range of stream sizes evaluated
in this study (≈ 2 to 11 m). Our results suggest that in small constrained streams, line-intercept surveys are an effective
method for estimating in-stream large wood volume and that these estimates better approximate results from whole-stream census
techniques where the diameter of in-stream wood is relatively consistent.
Handling editor: K. Martens 相似文献
843.
Motoko Ohata Lanxi Zhou Yukihiro Yada Issei Yokoyama Keizo Arihara 《Bioscience, biotechnology, and biochemistry》2020,84(9):1894-1902
ABSTRACT This study investigated the effect of the odors generated by the glycine/glucose Maillard reaction and the potent odorants 2,3-dimethylpyrazine (3DP) and 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF) on the human mood and integrative physiological activity. The score of certain subjective moods, especially anger-hostility, and tension-anxiety were decreased significantly after inhalation of the Maillard reaction sample and DMHF, and fatigue-inertia mood was also significantly decreased by DMHF, suggesting a sedative effect of these odors on mood, while 3DP had no effect. Miosis rate and fingertip temperature increased significantly following inhalation of the odor from the Maillard reaction sample and both potent odorants, suggesting that the parasympathetic nervous system dominates through suppression of the sympathetic activity. The physiological relaxing effect of these odors was also confirmed by decreased flicker frequency value and decreased oxyhemoglobin in the prefrontal cortex. 相似文献
844.
845.
Kaoru Wada Shinichi Mizuno Hirotoshi Ohta Yukihiro Nishiyama 《Microbiology and immunology》1997,41(10):841-845
Antigenic domain 1 (AD-1), located between amino acids 608 and 625 of human cytomegalovirus (CMV) gB protein, is the major domain recognized by neutralizing antibodies. Amino acids 552 to 630 are essential for the binding of neutralizing antibodies. We developed an enzyme-linked immunosorbent assay (ELISA) to detect antibodies against a fusion protein containing amino acid residues 549 to 644 of the gB polypeptide and maltose binding protein (MBP). Of 180 seropositive samples, 106 (58.9%) showed positive immuno-reactivity against the fusion protein. None of the seronegative samples reacted with the fusion protein. Among 57 seropositive individuals typed for HLA, subjects with HLA-DR9 had a higher positive rate against the fusion protein (13/14=92.9%) than those without HLA-DR9 (25/43=58.1%). In addition, subjects with HLA-DR15 had a lower positive rate against the fusion protein (7/16=43.3%) than those without HLA-DR15 (31/41 = 75.6%). Mean OD values of HLA-DR15-positive individuals were significantly lower than those of HLA-DR15-negative individuals. Thus, among CMV-infected individuals, HLA-DR9 may be associated with responders for neutralizing antibodies and HLA-DR15 may be associated with non/low-responders. 相似文献
846.
Ayako Yajima Yumiko Urano-Tashiro Kisaki Shimazu Eizo Takashima Yukihiro Takahashi Kiyoshi Konishi 《Microbiology and immunology》2008,52(2):69-77
Bacterial recognition of host sialic acid-containing receptors plays an important role in microbial colonization of the human oral cavity. The aggregation of human platelets by Streptococcus gordonii DL1 is implicated in the pathogenesis of infective endocarditis. In addition, we consider that hemagglutination of this organism may act as an additive factor to increase the severity of this disease. We previously reported that this interaction requires the bacterial expression of a 203-kDa protein (Hsa), which has sialic acid-binding activity. In the present study, we confirmed that erythrocyte surface sialoglycoproteins are the receptors for Hsa. We examined the effects of proteinase K, chymotrypsin, phospholipase C, and α(2-3) or α(2-3, 6, 8) neuraminidase on hemagglutination activity and found that the interaction occurs between Hsa and α2-3-linked sialic acid-containing proteins of erythrocytes. We expressed recombinant NR2, which is the putative binding domain of Hsa, fused with GST in Escherichia coli BL21. Dot-blot analysis demonstrated that GST-HsaNR2 binds both glycophorin A (GPA) and band 3. Moreover, GPA and a small amount of band 3 were detected by GST pull-down assays. These findings indicate that S. gordonii Hsa specifically binds to GPA and band 3, α2-3-linked sialic acid membrane glycoproteins. 相似文献
847.
Yukihiro Chiba 《Ecological Research》1991,6(1):21-28
Ramification in tree structure was investigated by the main axis cutting method, which differs from the ordinary stratified
clipping method. An axis running from the arbitrary terminal leader of the shoot to the stem base was termed the “main axis”.
Cutting the main axis into pieces of constant length gives the “segment layer”, which consists of segments of the main axis
and all branches and leaves diverging from the respective segments. There was a linear relationship between the weight of
a main axis segment (in the range where leaves exist) of constant length and that of all the parts above the segment. Since
plant form is determined by branches diverging regularly from the mother branch or stem, this linear relationship is considered
to support the concept of the pipe model theory. It is also suggested that the proportionality constant of the linear relationship
may specify the branching structure or ramifications of plant form. 相似文献
848.
Malonic acid, mevalonic acid, geraniol and nerol were incorporated into tetrahydrocannabinolic acid and cannabichromenic acid in Cannabis sativa. The pathway from cannabigerolic acid to tetrahydrocannabinolic acid via cannabidiolic acid was established by feeding labelled cannabinoid acids. Cannabichromenic acid was shown to be formed on a side pathway from cannabigerolic acid. 相似文献
849.
Yukihiro Akeda Kanna Okayama Tomomi Kimura Rikard Dryselius Toshio Kodama Kazunori Oishi Tetsuya Iida & Takeshi Honda 《FEMS microbiology letters》2009,296(1):18-25
Vibrio parahaemolyticus causes human gastroenteritis. Genomic sequencing of this organism has revealed that it has two sets of type III secretion systems, T3SS1 and T3SS2, both of which are important for its pathogenicity. However, the mechanism of protein secretion via T3SSs is unknown. A characteristic of many effectors is that they require specific chaperones for efficient delivery via T3SSs; however, no chaperone has been experimentally identified in the T3SSs of V. parahaemolyticus . In this study, we identified candidate T3SS1-associated chaperones from genomic sequence data and examined their roles in effector secretion/translocation and binding to their cognate substrates. From these experiments, we concluded that there is a T3S-associated chaperone, VecA, for a cytotoxic T3SS1-dependent effector, VepA. Further analysis using pulldown and secretion assays characterized the chaperone-binding domain encompassing the first 30–100 amino acids and an amino terminal secretion signal encompassing the first 5–20 amino acids on VepA. These findings will provide a strategy to clarify how the T3SS1 of V. parahaemolyticus secretes its specific effectors. 相似文献
850.