全文获取类型
收费全文 | 644篇 |
免费 | 54篇 |
专业分类
698篇 |
出版年
2021年 | 13篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2016年 | 20篇 |
2015年 | 17篇 |
2014年 | 27篇 |
2013年 | 26篇 |
2012年 | 33篇 |
2011年 | 29篇 |
2010年 | 18篇 |
2009年 | 16篇 |
2008年 | 24篇 |
2007年 | 28篇 |
2006年 | 28篇 |
2005年 | 25篇 |
2004年 | 22篇 |
2003年 | 28篇 |
2002年 | 24篇 |
2001年 | 19篇 |
2000年 | 6篇 |
1999年 | 13篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 11篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 12篇 |
1974年 | 8篇 |
1972年 | 8篇 |
1971年 | 6篇 |
1970年 | 16篇 |
1969年 | 4篇 |
1968年 | 8篇 |
1967年 | 9篇 |
1966年 | 9篇 |
1965年 | 4篇 |
排序方式: 共有698条查询结果,搜索用时 0 毫秒
81.
82.
83.
Jesús Olivero John E. Fa Miguel A. Farfán Jerome Lewis Barry Hewlett Thomas Breuer Giuseppe M. Carpaneto María Fernández Francesco Germi Shiho Hattori Josephine Head Mitsuo Ichikawa Koichi Kitanaishi Jessica Knights Naoki Matsuura Andrea Migliano Barbara Nese Andrew Noss Dieudonné Ongbwa Ekoumou Pascale Paulin Raimundo Real Mike Riddell Edward G. J. Stevenson Mikako Toda J. Mario Vargas Hirokazu Yasuoka Robert Nasi 《PloS one》2016,11(1)
Pygmy populations occupy a vast territory extending west-to-east along the central African belt from the Congo Basin to Lake Victoria. However, their numbers and actual distribution is not known precisely. Here, we undertake this task by using locational data and population sizes for an unprecedented number of known Pygmy camps and settlements (n = 654) in five of the nine countries where currently distributed. With these data we develop spatial distribution models based on the favourability function, which distinguish areas with favourable environmental conditions from those less suitable for Pygmy presence. Highly favourable areas were significantly explained by presence of tropical forests, and by lower human pressure variables. For documented Pygmy settlements, we use the relationship between observed population sizes and predicted favourability values to estimate the total Pygmy population throughout Central Africa. We estimate that around 920,000 Pygmies (over 60% in DRC) is possible within favourable forest areas in Central Africa. We argue that fragmentation of the existing Pygmy populations, alongside pressure from extractive industries and sometimes conflict with conservation areas, endanger their future. There is an urgent need to inform policies that can mitigate against future external threats to these indigenous peoples’ culture and lifestyles. 相似文献
84.
85.
86.
87.
Joerg Kotzerke Robert Punzet Roswitha Runge Sandra Ferl Liane Oehme Gerd Wunderlich Robert Freudenberg 《PloS one》2014,9(8)
99mTc is the standard radionuclide used for nuclear medicine imaging. In addition to gamma irradiation, 99mTc emits low-energy Auger and conversion electrons that deposit their energy within nanometers of the decay site. To study the potential for DNA damage, direct DNA binding is required. Plasmid DNA enables the investigation of the unprotected interactions between molecules and DNA that result in single-strand breaks (SSBs) or double-strand breaks (DSBs); the resulting DNA fragments can be separated by gel electrophoresis and quantified by fluorescent staining. This study aimed to compare the plasmid DNA damage potential of a 99mTc-labeled HYNIC-DAPI compound with that of 99mTc pertechnetate (99mTcO4
−). pUC19 plasmid DNA was irradiated for 2 or 24 hours. Direct and radical-induced DNA damage were evaluated in the presence or absence of the radical scavenger DMSO. For both compounds, an increase in applied activity enhanced plasmid DNA damage, which was evidenced by an increase in the open circular and linear DNA fractions and a reduction in the supercoiled DNA fraction. The number of SSBs elicited by 99mTc-HYNIC-DAPI (1.03) was twice that caused by 99mTcO4
− (0.51), and the number of DSBs increased fivefold in the 99mTc-HYNIC-DAPI-treated sample compared with the 99mTcO4
− treated sample (0.02 to 0.10). In the presence of DMSO, the numbers of SSBs and DSBs decreased to 0.03 and 0.00, respectively, in the 99mTcO4
– treated samples, whereas the numbers of SSBs and DSBs were slightly reduced to 0.95 and 0.06, respectively, in the 99mTc-HYNIC-DAPI-treated samples. These results indicated that 99mTc-HYNIC-DAPI induced SSBs and DSBs via a direct interaction of the 99mTc-labeled compound with DNA. In contrast to these results, 99mTcO4
− induced SSBs via radical formation, and DSBs were formed by two nearby SSBs. The biological effectiveness of 99mTc-HYNIC-DAPI increased by approximately 4-fold in terms of inducing SSBs and by approximately 10-fold in terms of inducing DSBs. 相似文献
88.
Purification of MEA, a mast cell growth-enhancing activity, to apparent homogeneity and its partial amino acid sequencing 总被引:3,自引:0,他引:3
J Moeller L Hültner E Schmitt M Breuer P D?rmer 《Journal of immunology (Baltimore, Md. : 1950)》1990,144(11):4231-4234
A novel growth factor for bone marrow derived murine mucosal type mast cells has been isolated from the conditioned medium of the Mlsa-reactive mouse Th cell line MLS-4.2. In proliferation assays this growth factor synergizes, like IL-4, with IL-3 on established mast cell lines and was therefore termed MEA: mast cell growth enhancing activity. MEA was characterized as a glycoprotein with a Mr range between 37,000 and 43,000. Apparent homogeneity was obtained by using a four-step purification scheme including cation exchange chromatography, Procion red affinity chromatography, IEF, and gel filtration. Inasmuch as MEA was N-terminally blocked during automated Edman-degradation, peptide fragments after digestion with trypsin were used for partial amino acid sequence determination. All evaluable MEA peptide fragments showed complete sequence homology to a recently purified and cloned novel T cell growth factor (P40/TCGF III), the mouse homologue of human IL-9. 相似文献
89.
90.