全文获取类型
收费全文 | 699篇 |
免费 | 37篇 |
国内免费 | 21篇 |
专业分类
757篇 |
出版年
2023年 | 6篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 20篇 |
2019年 | 13篇 |
2018年 | 14篇 |
2017年 | 15篇 |
2016年 | 20篇 |
2015年 | 11篇 |
2014年 | 24篇 |
2013年 | 31篇 |
2012年 | 15篇 |
2011年 | 23篇 |
2010年 | 25篇 |
2009年 | 30篇 |
2008年 | 40篇 |
2007年 | 45篇 |
2006年 | 26篇 |
2005年 | 17篇 |
2004年 | 32篇 |
2003年 | 31篇 |
2002年 | 15篇 |
2001年 | 21篇 |
2000年 | 18篇 |
1999年 | 25篇 |
1998年 | 20篇 |
1997年 | 28篇 |
1996年 | 20篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 21篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1979年 | 1篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有757条查询结果,搜索用时 0 毫秒
751.
Archicupressus is a new genus of the Cupressaceae based on a permineralized conifer female cone from the Upper Cretaceous of Hokkaido. The
type species,Archicupressus nihongii sp. nov., is characterized by peltate bract-scale complexes consisting of a completely fused bract and scale bearing erect
seeds. Bract-scale complexes are arranged in whorls of three on the cone axis. Each complex has a bristle-like projection,
the bract apex, at the top. Affinities to some genera in the Cupressaceae are discussed.
Consecutive number from the previous paper (Ohsawaet al., 1992). Supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan
to Makoto Nishida, No. 02640533. 相似文献
752.
Mandibular cortical indices on cone‐beam computed tomography images in osteoporotic women on treatment with oral bisphosphonates 下载免费PDF全文
753.
BackgroundThis investigation focused on the clinical implications of the use of the Collapsed Cone Convolution algorithm (CCC) in breast radiotherapy and investigated the dosimetric differences as respect to Pencil Beam Convolution algorithm (PBC).Material and methods15 breast treatment plans produced using the PBC algorithm were re-calculated using the CCC algorithm with the same MUs. In a second step, plans were re-optimized using CCC algorithm with modification of wedges and beam weightings to achieve optimal coverage (CCCr plans). For each patient, dosimetric comparison was performed using the standard tangential technique (SWT) and a forward-planned IMRT technique (f-IMRT).ResultsThe CCC algorithm showed significant increased dose inhomogeneity. Mean and minimum PTV doses decreased by 1.4% and 2.8% (both techniques). Mean V95% decreased to 83.7% and 90.3%, respectively for the SWT and f-IMRT. V95% was correlated to the ratio of PTV and lung volumes into the treatment field. The re-optimized CCCr plans achieved similar target coverage, but high-dose volume was significantly larger (V107%: 7.6% vs 2.3% (SWT), 7.1% vs 2.1% (f-IMRT). There was a significantly increase in the ipsilateral lung volume receiving low doses (V5 Gy: 31.3% vs 26.2% in SWT, 27.0% vs 23.0% in f-IMRT). MUs needed for PTV coverage in CCCr plans were higher by 3%.ConclusionsThe PBC algorithm overestimated PTV coverage in terms of all important dosimetric metrics. If previous clinical experience are based on the use of PBC model, especially needed is discussion between medical physicists and radiation oncologists to fully understand the dosimetric changes. 相似文献
754.
Phosphatidic acid (PA) is the simplest phospholipid and is involved in the regulation of various cellular events. Recently, we developed a new PA sensor, the N-terminal region of α-synuclein (α-Syn-N). However, whether α-Syn-N can sense physiologically produced, endogenous PA remains unclear. We first established an inactive PA sensor (α-Syn-N-KQ) as a negative control by replacing all eleven lysine residues with glutamine residues. Using confocal microscopy, we next verified that α-Syn-N, but not α-Syn-N-KQ, detected PA in macrophagic phagosomes in which PA is known to be enriched, further indicating that α-Syn-N can be used as a reliable PA sensor in cells. Finally, because PA generated during neuronal differentiation is critical for neurite outgrowth, we investigated the subcellular distribution of PA using α-Syn-N. We found that α-Syn-N, but not α-Syn-N-KQ, accumulated at the peripheral regions (close to the plasma membrane) of neuronal growth cones. Experiments using a phospholipase D (PLD) inhibitor strongly suggested that PA in the peripheral regions of the growth cone was primarily produced by PLD. Our findings provide a reliable sensor of endogenous PA and novel insights into the distribution of PA during neuronal differentiation. 相似文献
755.
756.
I. Novales Flamarique C. W. Hawryshyn 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1998,182(3):331-341
Two families of fishes, the Cyprinidae and Salmonidae, exhibit ultraviolet sensitivity and polarization sensitivity (i.e.,
differential sensitivity to the orientation of the electric field of polarized light). Both of these families possess a square
arrangement of double cones and/or their dividing partitions in the centro-temporal retina, an area where polarization sensitivity
has been tested for and found. To correlate the presence of an ordered cone mosaic in the centro-temporal retina with polarization
sensitivity in ultraviolet-sensitive fishes, we examined the visual system of the common white sucker (Catostomus commersoni) and compared it to those of the above-mentioned families. We found that the common white sucker possesses four cone-mediated
neural mechanisms similar to those in cyprinids and salmonids, but it does not exhibit polarization sensitivity. In addition,
unlike cyprinids and salmonids, the common white sucker shows a random cone mosaic in the centro-temporal retina. These results
suggest that polarization sensitivity in ultraviolet-sensitive fishes requires an ordered double-cone mosaic in this area
of the retina.
Accepted: 19 July 1997 相似文献
757.
Dominance among fruits/sinks and the search for a correlative signal 总被引:14,自引:0,他引:14
Fritz Bangerth 《Physiologia plantarum》1989,76(4):608-614
The present problems with hormonal signals transferring dominance effects are reviewed and, as a new hypothesis, it is stated that the sequence of sink development may establish the dominance effect. 'Primigenic dominance' (PD) is suggested to describe this kind of correlative inhibition, in which the earlier developed sink inhibits later developed organs.
New results show that the polar IAA export of the earlier developed sink inhibits the IAA export of later developed sinks. This 'autoinhibition' occurs at 'junctions', where auxin streams from various sinks meet. It is suggested that this depressed IAA-export of the subordinated fruit/sink acts as the signal that leads to inhibited development.
This hypothesis avoids some of the problems related with other hypotheses, such as the requirement of a multidirectional signal. Primigenic dominance is a unifying hypothesis, which can be applied to most correlative dominance phenomena in the plant. Primigenic dominance is less complicated than the traditional 'apical dominance' (AD) hypothesis, because it does not require secondary messengers. 相似文献
New results show that the polar IAA export of the earlier developed sink inhibits the IAA export of later developed sinks. This 'autoinhibition' occurs at 'junctions', where auxin streams from various sinks meet. It is suggested that this depressed IAA-export of the subordinated fruit/sink acts as the signal that leads to inhibited development.
This hypothesis avoids some of the problems related with other hypotheses, such as the requirement of a multidirectional signal. Primigenic dominance is a unifying hypothesis, which can be applied to most correlative dominance phenomena in the plant. Primigenic dominance is less complicated than the traditional 'apical dominance' (AD) hypothesis, because it does not require secondary messengers. 相似文献