全文获取类型
收费全文 | 9997篇 |
免费 | 1100篇 |
国内免费 | 938篇 |
专业分类
12035篇 |
出版年
2024年 | 40篇 |
2023年 | 140篇 |
2022年 | 347篇 |
2021年 | 518篇 |
2020年 | 364篇 |
2019年 | 505篇 |
2018年 | 433篇 |
2017年 | 384篇 |
2016年 | 443篇 |
2015年 | 599篇 |
2014年 | 696篇 |
2013年 | 809篇 |
2012年 | 875篇 |
2011年 | 786篇 |
2010年 | 485篇 |
2009年 | 444篇 |
2008年 | 504篇 |
2007年 | 413篇 |
2006年 | 407篇 |
2005年 | 318篇 |
2004年 | 249篇 |
2003年 | 253篇 |
2002年 | 203篇 |
2001年 | 168篇 |
2000年 | 164篇 |
1999年 | 154篇 |
1998年 | 90篇 |
1997年 | 62篇 |
1996年 | 69篇 |
1995年 | 73篇 |
1994年 | 67篇 |
1993年 | 53篇 |
1992年 | 64篇 |
1991年 | 68篇 |
1990年 | 49篇 |
1989年 | 54篇 |
1988年 | 41篇 |
1987年 | 47篇 |
1986年 | 40篇 |
1985年 | 47篇 |
1984年 | 45篇 |
1983年 | 43篇 |
1982年 | 29篇 |
1979年 | 27篇 |
1976年 | 23篇 |
1975年 | 19篇 |
1974年 | 27篇 |
1973年 | 29篇 |
1972年 | 20篇 |
1971年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Genetic relationship between Treponema pallidum and Treponema pertenue, two noncultivable human pathogens. 总被引:15,自引:1,他引:14 下载免费PDF全文
Genetic relationships among two strains of Treponema pallidum (Nichols and KKJ) and a strain of T. pertenue were determined by measuring the degree of deoxyribonucleic acid sequence homology. The results in indicated that these three virulent, noncultivable treponemes were genetically indistinguishable. Like T. pallidum (Nichols), T. pertenue (Gauthier) had no detectable deoxyribonucleic acid sequence homology with T. phagedenis (biotype Reiter), T. refringens (biotype Noguchi), or with salmon sperm. 相似文献
42.
43.
44.
In order to correlate and compare the antigenic relationships observed between nine yeast strains, we have studied their major antigenic determinant represented by the mannans. This material is a constituent of their cell.The compounds that we have isolated are, in reality, glycopeptides. All their polysaccharide fractions consist of mannose only — except for those of the compounds that we have isolated of R. glutinis and C. lipolytica. All these polysaccharides have very close ramified structures; the only one that seems to be very different is that of R. glutinis, and this is in agreement with the antigenic properties of that yeast.The peptidic fractions of these glycopeptides are rich in threonine, serine and aspartic acid and it is very likely that these amino acids make the link with the polysaccharide fraction. The quantity of these amino acids seem to be affected by the conditions of culture of the yeasts, but not their presence or absence. 相似文献
45.
The genetics of cell-mediated lympholysis. 总被引:1,自引:0,他引:1
M A Long B S Handwerger D B Amos E J Yunis 《Journal of immunology (Baltimore, Md. : 1950)》1976,117(6):2092-2099
The role of HLA antigens in the generation of cytotoxic cells in CML has been investigated. Cytotoxic effector cells were generated in MLC among HLA-A or HLA-A and HLA-B disparate, HLA-D identical siblings, and among HLA-A and HLA-B disparate, MLC identical (%RR less than or equal to 2 3.6) unrelated individual. The data indicate that HLA-D differences and poliferative MLC responses as measured by 3H-thymidine incorporation are not requisite for the in vitro generation of cytotoxic cells and suggest the existence of a CML-S locus (loci) distinct from HLA-A, HLA-B and HLA-D. The degree of cytotoxicity generated in a proliferative versus a "nonproliferative" MLC was comparable. In addition, these studies demonstrate that antigens other than the currently definable HLA-A, HLA-B, HLA-C, and HLA-D can serve as target determinants in cell-mediated lympholysis. 相似文献
46.
Jiaming Tian Bingxin Dai Li Gong Pingping Wang Han Ding Siwei Xia Weice Sun Cuiping Ren Jijia Shen Miao Liu 《PLoS neglected tropical diseases》2022,16(8)
Schistosomiasis is a serious and widespread parasitic disease caused by infection with Schistosoma. Because the parasite’s eggs are primarily responsible for schistosomiasis dissemination and pathogenesis, inhibiting egg production is a potential approach to control the spread and severity of the disease. The bromodomain and extra-terminal (BET) proteins represent promising targets for the development of epigenetic drugs against Schistosoma. JQ-1 is a selective inhibitor of the BET protein family. In the present study, JQ-1 was applied to S. japonicum in vitro. By using laser confocal scanning microscopy and EdU incorporation assays, we showed that application of JQ-1 to worms in vitro affected egg laying and the development of both the male and female reproductive systems. JQ-1 also inhibited the expression of the reproductive-related genes SjPlk1 and SjNanos1 in S. japonicum. Mice infected with S. japonicum were treated with JQ-1 during egg granuloma formation. JQ-1 treatment significantly reduced the size of the liver granulomas and levels of serum alanine aminotransferase and aspartate aminotransferase in mice and suppressed both egg laying and the development of male and female S. japonicum reproductive systems in vivo. Moreover, the mRNA expression levels of some proinflammatory cytokines were decreased in the parasites. Our findings suggest that JQ-1 treatment attenuates S. japonicum egg–induced hepatic granuloma due at least in part to suppressing the development of the reproductive system and egg production of S. japonicum. These findings further suggest that JQ-1 or other BET inhibitors warrant additional study as a new approach for the treatment or prevention of schistosomiasis. 相似文献
47.
XiaoLong Lin Zheng Liu LiPing Yan Xin Duan WenJun Bu XinHua Wang ChenGuang Zheng 《Ecology and evolution》2022,12(5)
Mitogenomes have been widely used for phylogenetic reconstruction of various Dipteran groups, but specifically for chironomid, they have not been carried out to resolve the relationships. Diamesinae (Diptera: Chironomidae) are important bioindicators for freshwater ecosystem monitoring, but its evolutionary history remains uncertain for lack of information. Here, coupled with one previously published and 30 new mitogenomes of Diamesinae, we carried out comparative mitogenomic analysis and phylogenetic analysis. Mitogenomes of Diamesinae were conserved in structure, and all genes arranged in the same order as the ancestral insect mitogenome. All protein‐coding genes in Diamesinae were under stronger purifying selection than those of other nonbiting midge species, which may exhibit signs of adaptation to life at cold living conditions. Phylogenetic analyses strongly supported the monophyly of Diamesinae, with Boreheptagyiini deeply nested within Diamesini. In addition, phylogenetic relationship of selected six genera was resolved, except Sympotthastia remained unstable. Our study revealed that the mitogenomes of Diamesinae are highly conserved, and they are practically useful for phylogenetic inference. 相似文献
48.
Yi Tan Lingchao Miao Jianbo Xiao Wai San Cheang 《Current issues in molecular biology》2022,44(5):2175
The potential anti-diabetic effect of resveratrol derivative, 3,3′,4,5′-tetramethoxy-trans-stilbene (3,3′,4,5′-TMS) and its underlying mechanism in high glucose (HG) and dexamethasone (DXMS)-stimulated insulin-resistant HepG2 cells (IR-HepG2) were investigated. 3,3′,4,5′-TMS did not reduce the cell viability of IR-HepG2 cells at the concentrations of 0.5–10 µM. 3,3′,4,5′-TMS increased the potential of glucose consumption and glycogen synthesis in a concentration-dependent manner in IR-HepG2 cells. 3,3′,4,5′-TMS ameliorated insulin resistance by enhancing the phosphorylation of glycogen synthase kinase 3 beta (GSK3β), inhibiting phosphorylation of insulin receptor substrate-1 (IRS-1), and activating phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway in IR-HepG2 cells. Furthermore, 3,3′,4,5′-TMS significantly suppressed levels of reactive oxygen species (ROS) with up-regulation of nuclear factor erythroid 2-related factor 2 (Nrf2) expression. To conclude, the beneficial effect of 3,3′,4,5′-TMS against insulin resistance to increase glucose consumption and glycogen synthesis was mediated through activation of IRS/PI3K/Akt signaling pathways in the IR-HepG2 cells, accomplished with anti-oxidative activity through up-regulation of Nrf2. 相似文献
49.
磨盘山天然次生林凋落物数量及动态 总被引:2,自引:0,他引:2
以磨盘山5.76hm2天然次生林群落固定监测样地为平台,均匀布设144个凋落物收集器,于2006年每月末(4—11月)连续收集其凋落物,用以分析群落尺度上的凋落物产量、组成及时空变化。结果表明,天然次生林年凋落量为3039.6 kg/hm2,以凋落叶(2499.2 kg/hm2)所占的比例最大,占年凋落量的82.22%,而凋落枝仅占年凋落量的9.92%,花果皮等所占比例更小,占总量的5%以下。1a内,凋落物收集器内共收集到42种树木的凋落叶,占样地内树种总数(46种)的91.30%,其中花曲柳(Fraxinus rhynchophylla)、核桃楸(Juglans mandshurica)和蒙古栎(Quercus mongolica)3个树种的凋落叶占落叶总量的82.97%,为叶凋落量的主要来源。不同收集器之间凋落量存在较大差异,99个收集器的年凋落量在200—400 g,2个收集器超过600 g;单个收集器全年最多可收集到19种树种的凋落叶,收集到凋落叶种数12种的收集器最多(29个)。凋落量月动态呈单峰型,69.78%的凋落量产生于9—10月份,叶凋落量月动态与凋落总量变化相同。落叶以秋季为主,但树种间叶凋落节律存在差异,其中核桃楸叶的凋落高峰集中在8—9月,花曲柳和春榆(Ulmus japonica)集中在9—10月,色木槭(Acer mono)为10月,蒙古栎叶为10—11月。 相似文献
50.