全文获取类型
收费全文 | 1520128篇 |
免费 | 143374篇 |
国内免费 | 1524篇 |
出版年
2021年 | 16216篇 |
2019年 | 16214篇 |
2018年 | 18267篇 |
2017年 | 17043篇 |
2016年 | 28567篇 |
2015年 | 42917篇 |
2014年 | 51153篇 |
2013年 | 77468篇 |
2012年 | 41597篇 |
2011年 | 30884篇 |
2010年 | 45058篇 |
2009年 | 45900篇 |
2008年 | 28755篇 |
2007年 | 27528篇 |
2006年 | 31890篇 |
2005年 | 32695篇 |
2004年 | 31762篇 |
2003年 | 29310篇 |
2002年 | 27656篇 |
2001年 | 46147篇 |
2000年 | 44064篇 |
1999年 | 39872篇 |
1998年 | 25335篇 |
1997年 | 25280篇 |
1996年 | 24502篇 |
1995年 | 24105篇 |
1994年 | 23889篇 |
1993年 | 22990篇 |
1992年 | 34737篇 |
1991年 | 32934篇 |
1990年 | 31179篇 |
1989年 | 31631篇 |
1988年 | 29304篇 |
1987年 | 27678篇 |
1986年 | 26285篇 |
1985年 | 28072篇 |
1984年 | 26509篇 |
1983年 | 23191篇 |
1982年 | 22582篇 |
1981年 | 21429篇 |
1980年 | 19963篇 |
1979年 | 22825篇 |
1978年 | 20646篇 |
1977年 | 19532篇 |
1976年 | 18538篇 |
1975年 | 18777篇 |
1974年 | 19574篇 |
1973年 | 19823篇 |
1972年 | 17312篇 |
1971年 | 15522篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Irvin M. Modlin 《The Yale journal of biology and medicine》1992,65(5):393-Oct;65(5):393
992.
993.
994.
Rodney A. Bray 《Systematic parasitology》1990,16(3):195-200
A new species, Pseudopecoelus sewelli, is described from the deep-sea fish Hoplostethus atlanticus from off southeastern Australia. It is an elongate form with considerable variation in such important characters as the anterior vitelline extent, the sucker ratio and the egg-size. The features distinguishing this species from five related forms are combinations of the sucker ratio, egg-size, lobation of gonads, presence or absence of a cirrus-sac and the position of the genital pore. 相似文献
995.
996.
Observations on the floral biology of Luculia gratissima (Rubiaceae)showed that this species is distylous with complementary positioningof anthers and stigmas in the two floral forms. Unusual featuresof distyly in this species include the larger size of the corolla,the stigma surface and the stigmatic papillae in the thrum flowerscompared to the pin ones. Stigmatic surfaces have similar secretionsbut they appear more copious in thrum than pin. The floral dimorphismwas accompanied by a very effective self-incompatibility systemand no seed was set on selfing. Seed number per capsule on crossingwas significantly greater in thrum flowers compared to pin.Incompatible pollen tubes were inhibited within 24 h at thebase of the stigma/top of the style in both morphs. Amputationof this region of the gynoecium removed the self-incompatibilityreaction in thrum but not pin flowers. Pollination with a mixtureof compatible and incompatible pollen and sequential pollinationwith self followed by cross pollen showed that there were interactionsbetween the two types of pollen tube. The presence of compatibletubes was found to cause the excessive swelling of the pollen-tubetip of the incompatible ones. The incompatible tubes did notappear to have any effect on the growth of compatible ones. Luculia gratissima, distyly, floral biology, self-incompatibility, pollen-tube interactions 相似文献
997.
998.
Peculiarities of the axons growth in the culture of 14-day old chick embryo spinal cord after 24, 48 hr, 3, 5 and 7 days in the Maximov's chamber were observed. For the stimulation of axon growth the spinal cord was cultivated simultaneously with the explants of the muscle tissue and in the medium after the addition of supernatant of the somatic muscle. It has been demonstrated that the growth of the axons stimulated with the muscle explants or muscle supernatant takes place through the growth cones, while in the absence of growth stimulation effect glial cells can take part in the axons growth. It is supposed that the glial cells are capable of playing the role of the cells, which direct axons growth in the absence of influence of specific target factor. 相似文献
999.
1000.