全文获取类型
收费全文 | 1046008篇 |
免费 | 121882篇 |
国内免费 | 553篇 |
出版年
2016年 | 11855篇 |
2015年 | 17266篇 |
2014年 | 19954篇 |
2013年 | 28415篇 |
2012年 | 32109篇 |
2011年 | 32342篇 |
2010年 | 21881篇 |
2009年 | 20578篇 |
2008年 | 29388篇 |
2007年 | 30216篇 |
2006年 | 28504篇 |
2005年 | 27267篇 |
2004年 | 27054篇 |
2003年 | 26057篇 |
2002年 | 25406篇 |
2001年 | 44569篇 |
2000年 | 45046篇 |
1999年 | 36290篇 |
1998年 | 14030篇 |
1997年 | 14674篇 |
1996年 | 14058篇 |
1995年 | 13208篇 |
1994年 | 13147篇 |
1993年 | 12924篇 |
1992年 | 30874篇 |
1991年 | 30010篇 |
1990年 | 29508篇 |
1989年 | 28941篇 |
1988年 | 26574篇 |
1987年 | 25969篇 |
1986年 | 23965篇 |
1985年 | 24182篇 |
1984年 | 20145篇 |
1983年 | 17536篇 |
1982年 | 13845篇 |
1981年 | 12389篇 |
1980年 | 11851篇 |
1979年 | 19526篇 |
1978年 | 15509篇 |
1977年 | 13958篇 |
1976年 | 13346篇 |
1975年 | 14541篇 |
1974年 | 15502篇 |
1973年 | 15332篇 |
1972年 | 13742篇 |
1971年 | 12663篇 |
1970年 | 10925篇 |
1969年 | 10346篇 |
1968年 | 9370篇 |
1967年 | 8450篇 |
排序方式: 共有10000条查询结果,搜索用时 70 毫秒
931.
A face fly (Musca autumnalis) population near Wetaskiwin, central Alberta, Canada, was sampled 9 times from 26 July to 29 September 1988 for the early larval stages of Thelazia spp. Of 426 female flies examined, 159 (37%) contained Thelazia spp. (almost exclusively T. skrjabini), with an average worm burden of 4.2 larvae per infected fly. Prevalence ranged from 17 to 56% over 9 collections. This is the first report of Thelazia skrjabini in flies from western North America and the highest Thelazia prevalence in face flies yet reported in North America. The face fly population was also parasitized by Heterotylenchus autumnalis, with a prevalence of 5.5%. 相似文献
932.
933.
Biophysics - A change in the content of energy substrates in myocardial mitochondria depending upon the vibration frequency and the duration of the total vertical vibration exposure was studied... 相似文献
934.
Plant and Soil - Perennial plants play important roles in maintaining ecosystem functions by forming fertile islands beneath their canopies. Little is known about how the fertile island effect... 相似文献
935.
Jin Wei Mia Madel Alfajaro Peter C. DeWeirdt Ruth E. Hanna William J. Lu-Culligan Wesley L. Cai Madison S. Strine Shang-Min Zhang Vincent R. Graziano Cameron O. Schmitz Jennifer S. Chen Madeleine C. Mankowski Renata B. Filler Neal G. Ravindra Victor Gasque Fernando J. de Miguel Ajinkya Patil Huacui Chen Craig B. Wilen 《Cell》2021,184(1):76-91.e13
- Download : Download high-res image (212KB)
- Download : Download full-size image
936.
N P Veselkin I V Batueva 《Rossi?skii fiziologicheski? zhurnal imeni I.M. Sechenova / Rossi?skaia akademiia nauk》1999,85(6):743-750
Glycine and GABA play the role of inhibitory transmitters in the lamprey spinal cord. The mechanisms of action of both amino acids to the membrane receptors producing the postsynaptic inhibition as well as role and mechanism of GABA action producing the presynaptic inhibition are considered in this paper. The data concerned with morphological substrates of both type inhibitions are discussed. 相似文献
937.
938.
Pigment epithelium-derived factor (PEDF) has neuronal differentiation and survival activity on retinoblastoma and cerebellar granule (CG) cells. Here, we investigated the presence of PEDF receptors on retinoblastoma Y-79 and CG cells. PEDF radiolabeled with (l25)I remained biologically active and was used for radioligand binding analysis. The binding was saturable and specific to a single class of receptors on both cells and with similar affinities (K(d) = 1.7-3.6 nM, B(max) = 0.5-2.7 x 10(5) sites/Y-79 cell; and K(d) = 3.2 nM, B(max) = 1.1 x 10(3) sites/CG cell). A polyclonal antiserum to PEDF, previously shown to block the PEDF neurotrophic activity, prevented the (125)I-PEDF binding. We designed two peptides from a region previously shown to confer the neurotrophic property to human PEDF, synthetic peptides 34-mer (positions 44-77) and 44-mer (positions 78-121). Only peptide 44-mer competed for the binding to Y-79 cell receptors (EC(50) = 5 nM) and exhibited neuronal differentiating activity. PEDF affinity column chromatography of membrane proteins from both cell types revealed a PEDF-binding protein of approximately 80 kDa. These results are the first demonstration of a PEDF-binding protein with characteristics of a PEDF receptor and suggest that the region comprising amino acid positions 78-121 of PEDF might be involved in ligand-receptor interactions. 相似文献
939.
940.