全文获取类型
收费全文 | 22565篇 |
免费 | 2073篇 |
国内免费 | 11篇 |
出版年
2022年 | 190篇 |
2021年 | 330篇 |
2020年 | 238篇 |
2019年 | 261篇 |
2018年 | 397篇 |
2017年 | 383篇 |
2016年 | 578篇 |
2015年 | 978篇 |
2014年 | 1042篇 |
2013年 | 1291篇 |
2012年 | 1547篇 |
2011年 | 1548篇 |
2010年 | 1012篇 |
2009年 | 838篇 |
2008年 | 1245篇 |
2007年 | 1248篇 |
2006年 | 1221篇 |
2005年 | 1165篇 |
2004年 | 1127篇 |
2003年 | 1023篇 |
2002年 | 1039篇 |
2001年 | 254篇 |
2000年 | 225篇 |
1999年 | 263篇 |
1998年 | 250篇 |
1997年 | 206篇 |
1996年 | 198篇 |
1995年 | 186篇 |
1994年 | 171篇 |
1993年 | 180篇 |
1992年 | 180篇 |
1991年 | 157篇 |
1990年 | 184篇 |
1989年 | 158篇 |
1988年 | 143篇 |
1987年 | 151篇 |
1986年 | 138篇 |
1985年 | 160篇 |
1984年 | 151篇 |
1983年 | 165篇 |
1982年 | 178篇 |
1981年 | 162篇 |
1980年 | 131篇 |
1979年 | 108篇 |
1978年 | 132篇 |
1977年 | 101篇 |
1976年 | 94篇 |
1975年 | 90篇 |
1974年 | 113篇 |
1973年 | 91篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
32.
33.
We have analysed the lineage of olfactory receptor neurons usinga replication-incompetent retrovirus injected beneath the olfactoryepithelium of young rats. There are two major types of clustersof infected cells seen at 540 days after infection: (i)horizontal basal cells (HBCs); (ii) variable numbers of globosebasal cells (GBCs), and immature and mature sensory neurons.Olfactory nerve lesion increased the frequency of the globose/sensoryneuron clusters, as well as the number of cells/cluster, butdid not change the number of HBC clusters or cells/cluster.No clusters contained sustentacular cells. These data indicatethat, at least in young rats: (i) HBCs are not precursors ofolfactory neurons; (ii) there is a lineage path from GBCs tomature neurons; and (iii) sustentacular cells arise from a separatelineage. 相似文献
34.
35.
36.
Hideaki Naoe Tatsuyuki Chiyoda Jo Ishizawa Kenta Masuda Hideyuki Saya Shinji Kuninaka 《Biochemical and biophysical research communications》2013,430(2):757-762
Differentiation of placental trophoblast stem (TS) cells to trophoblast giant (TG) cells is accompanied by transition from a mitotic cell cycle to an endocycle. Here, we report that Cdh1, a regulator of the anaphase-promoting complex/cyclosome (APC/C), negatively regulates mitotic entry upon the mitotic/endocycle transition. TS cells derived from homozygous Cdh1 gene-trapped (Cdh1GT/GT) murine embryos accumulated mitotic cyclins and precociously entered mitosis after induction of TS cell differentiation, indicating that Cdh1 is required for the switch from mitosis to the endocycle. Furthermore, the Cdh1GT/GT TS cells and placenta showed aberrant expression of placental differentiation markers. These data highlight an important role of Cdh1 in the G2/M transition during placental differentiation. 相似文献
37.
An electron histochemical study was undertaken to localize calcium with ammonium oxalate precipitation technique in soleus muscle of rat in normal cases and in myopathy induced experimentally by a prolonged treatment of 2,4-dichlorophenoxyacetate (2,4-D). The calcium content of precipitates was detected by energy-dispersive X-ray microanalysis. In normal cases, the electron dense precipitates containing calcium were mainly found in the vesicles of sarcoplasmic reticulum, whereas in 2,4-D induced myopathy the deposits were shifted near the Z line into the myofibrils. Calcium, because the uptake into sarcoplasmic vesicles was inhibited by 2,4-D, could attach to other binding sites, such as to the troponin-C.A long-lasting binding of calcium might lead to a prolonged activation of the actin-myosin system. 相似文献
38.
39.
A new species,Acanthocephaloides cyrusi, is described from the fishesSolea bleekeri andPomadasys commersoni from Lake St. Lucia, Natal, South Africa. It is distinguished from the other species in the genus by the more marked sexual dimorphism in length, the arrangement of hooks, the proboscis with the longest hooks at the anterior-most extremity and the greater size of the proboscis hooks and body spines. An acanthella, which may represent this species, was found in the tanaidApseudes digitalis. 相似文献
40.