全文获取类型
收费全文 | 262篇 |
免费 | 19篇 |
国内免费 | 63篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 14篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 3篇 |
2015年 | 9篇 |
2014年 | 7篇 |
2013年 | 17篇 |
2012年 | 16篇 |
2011年 | 10篇 |
2010年 | 29篇 |
2009年 | 16篇 |
2008年 | 22篇 |
2007年 | 10篇 |
2006年 | 13篇 |
2005年 | 11篇 |
2004年 | 11篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 10篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 4篇 |
1967年 | 1篇 |
1958年 | 1篇 |
1956年 | 1篇 |
1954年 | 3篇 |
1953年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有344条查询结果,搜索用时 15 毫秒
61.
62.
63.
Biomass and production of phyto- and bacterio-plankton in eutrophic Lake Tystrup, Denmark 总被引:4,自引:0,他引:4
BO RIEMANN 《Freshwater Biology》1983,13(4):389-398
SUMMARY.
- 1 Phytoplankton primary production and biomass were compared with bacterial secondary production estimated by means of frequency of dividing cells (FDC) in eutrophic Lake Tystrup. Denmark.
- 2 In the upper part of the photic zone, bacterial secondary production constituted 12% of the carbon fixed by the phytoplankton. In vertical profiles, bacterial secondary production ranged from 7.6% (early spring) to 121% (during August) of the carbon fixed by the algae.
- 3 A close relationship was found between occurrence and activity of bacteria and algae, suggesting that released organic products are of primary importance to the bacteria.
- 4 The annual phytoplankton primary production was estimated as 227 g C m-2 compared to 102 g C m-2 assimilated by the bacteria, so 45% of the carbon fixed by the phytoplankton went through pelagic bacteria.
64.
十二指肠内胆盐对胃肌电和运动的影响及其神经机制探讨 总被引:1,自引:0,他引:1
本文观察了牛磺胆酸钠(ST)灌入小鼠十二指肠后胃肌电快波、慢波和胃收缩波的变化,并对其神经机制作了探讨。用胃壁双电极和胃内水囊-压力换能器法将胃电和胃运动信号输至放大器,然后由记录仪及电子计算机对该信号进行记录、采集、贮存和处理。以5min为单位,计算出灌注 ST 前、后胃电快波、慢波和收缩波频率与总幅度变化的百分数。结果为:十二指肠灌注 ST(n=10)后,胃电快波频率、幅度和收缩波幅度明显抑制。腹腔神经丛麻醉,利血平化和碳酰胆碱可消除 ST 引起的抑制效应。酚妥拉明不能去除该抑制效应,心得安可部分消除 ST 的抑制效应。上述结果表明,十二指肠灌注 ST 对胃电快波和胃运动有抑制效应,并提示该抑制效应的神经传出途径可能为交感肾上腺素能纤维,由β受体介导。 相似文献
65.
66.
67.
68.
69.
The endothelial cell receptor (EPCR) for protein C (PC)/activated protein C (APC) is a 221 amino-acid residues long transmembrane glycoprotein with unclear physiological function. To facilitate future studies and to rationalize recently reported experimental data about this protein, we have constructed three-dimensional models of human, bovine and mouse EPCR using threading and comparative model building. EPCR is homologous to CD1/MHC class I molecules. It consists of two domains, which are similar to the alpha1 and alpha2 domains of MHC class I molecules, whereas the alpha3 domain of MHC is replaced in EPCR by a transmembrane region followed by a short cytosolic tail. The alpha1 and alpha2 domains of CD1/MHC proteins form a groove, which binds short peptides. These domains are composed of an eight-stranded antiparallel beta-pleated sheet with two long antiparallel alpha-helices. The distance between the helical segments dictates the width of the groove. The cleft in EPCR appears to be relatively narrow and it is lined with hydrophobic/aromatic and polar residues with a few charged amino acids. Analysis of the human EPCR model predicts that (a) the protein does not contain any calcium binding pockets; (b) C101 and C169 form a buried disulphide bridge, while C97 is free, and buried in the core of the molecule; and (c) four potential glycosylation sites are solvent exposed. 相似文献
70.
Three new species of monogencans parasitizing hagfish are described: Myxinidocotyle californica gen. et sp.n., M. japonica sp.n. and Lophocotyle novaezeelandica sp.n. The pseudohaptor of Myxinidocotyle has 8+8 transverse ridges that never attain the radial arrangement characterizing Lophocotyle and Acanthocotyle . There are no sclerites in the pseudohaptoral ridges of Myxinidocotyle and Lophocotyle . The male reproductive system of Myxinidocotyle and Lophocotyle differs from that of Acanthocotyle in having a bilateral accessory gland apparatus and an armed copulatory organ. The femrle reproductive system has a large vaginal receptaculum scminis; in Myxinidocotyle with two vagino-intestinal canals. The uterine pore and the male genital pore are close together and the vaginal pore is situated posterior to them, on the left ventral side of the body. We conclude that Myxinidocotyle, Lophocotyle and Acunrkocotyle represent different levels of acanthocotylid evolution. Myxinidocotyle being the most primitive. The family Acanthocotylidac is divided into the subfamilies Myxinidoeutylinae subfam.n., Lophocotylinae and Acanthoeutylinae. 相似文献