全文获取类型
收费全文 | 6840篇 |
免费 | 497篇 |
国内免费 | 2篇 |
出版年
2023年 | 24篇 |
2022年 | 56篇 |
2021年 | 117篇 |
2020年 | 77篇 |
2019年 | 90篇 |
2018年 | 158篇 |
2017年 | 124篇 |
2016年 | 247篇 |
2015年 | 327篇 |
2014年 | 344篇 |
2013年 | 478篇 |
2012年 | 507篇 |
2011年 | 577篇 |
2010年 | 363篇 |
2009年 | 328篇 |
2008年 | 426篇 |
2007年 | 418篇 |
2006年 | 412篇 |
2005年 | 357篇 |
2004年 | 365篇 |
2003年 | 339篇 |
2002年 | 329篇 |
2001年 | 60篇 |
2000年 | 53篇 |
1999年 | 60篇 |
1998年 | 70篇 |
1997年 | 59篇 |
1996年 | 62篇 |
1995年 | 57篇 |
1994年 | 32篇 |
1993年 | 46篇 |
1992年 | 48篇 |
1991年 | 31篇 |
1990年 | 36篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1986年 | 18篇 |
1985年 | 25篇 |
1984年 | 26篇 |
1983年 | 11篇 |
1982年 | 15篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1975年 | 11篇 |
1974年 | 7篇 |
排序方式: 共有7339条查询结果,搜索用时 13 毫秒
111.
Manuel Rey Teresa Fernández Victoria González Roberto Rodriguez 《In vitro cellular & developmental biology. Plant》1992,28(3):148-152
Summary A profitable system for the establishment of morphogenic callus cultures and indirect shoot induction and development was
accomplished from nodal shoot segments obtained from adult and micropropagated plants of kiwifruit (Actinidia deliciosa [Chev.] Liang and Ferguson, var.deliciosa) cv. “Hayward”. The effects of medium composition, cytokinin levels, dilution of salts, and type of callus derived from the
cultured primary explants were studied. Medium composition as well as type of callus greatly affected organogenic responses. 相似文献
112.
Teresa M. Szopa 《Journal of insect physiology》1981,27(7):441-446
Allatectomy of adult female Schistocerca gregaria prevents the normal development of the accessory reproductive glands and no secretion is produced. Development of the glands can be restored by the administration of synthetic juvenile hormone and the response is dose-dependent. A continuous supply of hormone is required for maintenance of secretory activity. In the normal developmental sequence the total protein content of the glands remains constant until the time at which vitellogenesis occurs in the terminal oöcytes. As maturation proceeds there is a linear increase in protein content of the glands. The initial increase occurs as a result of cellular changes in the glands and is then followed by an increase due to an accumulation of secretion in the lumina. 相似文献
113.
Tight linkage of genes that encode the two glutamate synthase subunits of Escherichia coli K-12. 总被引:8,自引:7,他引:1 下载免费PDF全文
E Lozoya R Sanchez-Pescador A Covarrubias I Vichido F Bolivar 《Journal of bacteriology》1980,144(2):616-621
A hybrid deoxyribonucleic acid molecule, plasmid pRSP20, which was isolated from the Clarke and Carbon Escherichia coli gene bank, was shown to complement the gltB31 mutation, which affects the synthesis of glutamate synthase in E. coli strain PA340. We present evidence which demonstrates that plasmid pRSP20 carries an 8-megadalton E. coli chromosomal fragment, including the genes encoding the two unequal glutamate synthase subunits. Polypeptides with molecular weights of about 135,000 and 53,000, which comigrated with purified E. coli glutamate synthase subunit polypeptides and immunoprecipitated with antibodies to E. coli glutamate synthase, were synthesized by minicells carrying the pRSP20 plasmid. 相似文献
114.
Gary A. Griess Ph.D. Seymour Zigman Ph.D. Teresa Yulo 《Molecular and cellular biochemistry》1976,12(1):9-14
Summary Variations in size and charge of calf lens proteins, particularly gamma crystallins, were studied by polyacrylamide gel electrophoresis. Exposure of gamma crystallins to near-UV light in the presence of L-tryptophan produces species of higher electrophoretic mobility and higher retardation. Treatment with urea and sulfonation also produced changes in the retardation co-efficient. The increase of retardation co-efficient of gamma crystallin is interpreted to be a result of conformational changes. Gamma crystallins are particularly sensitive to photo-modification, and this process may be associated with age-related changes in the lens.Supported by research grants from the U.S.P.H.S. EY #00459, a FIGHT-FOR-SIGHT Postdoctoral Research Fellowship (FIGHT-FOR-SIGHT, INC., N.Y.C.) and The Rochester Eye and Human Parts Bank, Inc. 相似文献
115.
116.
Michel De Wilde Teresa Cabezón Raimundo Villarroel Albert Herzog Alex Bollen 《Molecular & general genetics : MGG》1975,142(1):19-33
Summary Two spontaneous mutants of Escherichia coli strain KMBL-146 selected for resistance to the aminoglycoside antibiotic neamine show severe restriction of amber suppressors in vivo. Purified ribosomes from the mutant strains exhibit low neamine-induced misreading in vitro and a decreased affinity for the related antibiotic streptomycin.Biochemical analysis shows that the mutants each have two modified 30S ribosomal proteins, S12 and S5. In agreement with these results, genetic analysis shows that two mutations are present, neither of which confers resistance to neamine by itself; the mutation located in gene rpxL (the structural gene for protein S12) confers streptomycin dependence but this dependence is suppressed in the presence of the second mutation, located in gene rpxE (the structural gene for protein S5). 相似文献
117.
118.
A new orthonaphthoquinone diterpene has been isolated from Salvia aethiopis and given the trivial name aethiopinone. The structure of this natural 相似文献
119.
The oldest known estuarine bivalve assemblage is documented from the Lower Ordovician (upper Arenig-lower Llanvirn) Alto del Cóndor Formation, which crops out in the Cordillera Oriental of northwestern Argentina. This unit displays most of the diagnostic sedimentary attributes of estuarine environments. Biotic components include low-diversity trace fossils and a peculiar bivalve fauna consisting of the new genera Konduria, Pseudoredonia, and Pucamya, and the new species Redonia condorensis. This constitutes the earliest known occurrence of bivalves in brackish waters, suggesting that the capability of this clade to colonize estuarine environments developed early in their radiation. 相似文献
120.
Catarina Macedo-Silva Vera Miranda-Gonalves Ana Lameirinhas Joana Lencart Alexandre Pereira Joo Lobo Rita Guimares Ana Teresa Martins Rui Henrique Isabel Bravo Carmen Jernimo 《Cell death & disease》2020,11(12)
Esophageal squamous cell carcinoma (ESCC), the most frequent esophageal cancer (EC) subtype, entails dismal prognosis. Hypoxia, a common feature of advanced ESCC, is involved in resistance to radiotherapy (RT). RT response in hypoxia might be modulated through epigenetic mechanisms, constituting novel targets to improve patient outcome. Post-translational methylation in histone can be partially modulated by histone lysine demethylases (KDMs), which specifically removes methyl groups in certain lysine residues. KDMs deregulation was associated with tumor aggressiveness and therapy failure. Thus, we sought to unveil the role of Jumonji C domain histone lysine demethylases (JmjC-KDMs) in ESCC radioresistance acquisition. The effectiveness of RT upon ESCC cells under hypoxic conditions was assessed by colony formation assay. KDM3A/KDM6B expression, and respective H3K9me2 and H3K27me3 target marks, were evaluated by RT-qPCR, Western blot, and immunofluorescence. Effect of JmjC-KDM inhibitor IOX1, as well as KDM3A knockdown, in in vitro functional cell behavior and RT response was assessed in ESCC under hypoxic conditions. In vivo effect of combined IOX1 and ionizing radiation treatment was evaluated in ESCC cells using CAM assay. KDM3A, KDM6B, HIF-1α, and CAIX immunoexpression was assessed in primary ESCC and normal esophagus. Herein, we found that hypoxia promoted ESCC radioresistance through increased KDM3A/KDM6B expression, enhancing cell survival and migration and decreasing DNA damage and apoptosis, in vitro. Exposure to IOX1 reverted these features, increasing ESCC radiosensitivity and decreasing ESCC microtumors size, in vivo. KDM3A was upregulated in ESCC tissues compared to the normal esophagus, associating and colocalizing with hypoxic markers (HIF-1α and CAIX). Therefore, KDM3A upregulation in ESCC cell lines and primary tumors associated with hypoxia, playing a critical role in EC aggressiveness and radioresistance. KDM3A targeting, concomitant with conventional RT, constitutes a promising strategy to improve ESCC patients’ survival.Subject terms: Predictive markers, Cancer 相似文献