全文获取类型
收费全文 | 1408篇 |
免费 | 54篇 |
专业分类
1462篇 |
出版年
2023年 | 10篇 |
2022年 | 13篇 |
2021年 | 38篇 |
2020年 | 24篇 |
2019年 | 31篇 |
2018年 | 37篇 |
2017年 | 29篇 |
2016年 | 35篇 |
2015年 | 55篇 |
2014年 | 75篇 |
2013年 | 105篇 |
2012年 | 139篇 |
2011年 | 112篇 |
2010年 | 102篇 |
2009年 | 69篇 |
2008年 | 81篇 |
2007年 | 83篇 |
2006年 | 56篇 |
2005年 | 73篇 |
2004年 | 65篇 |
2003年 | 49篇 |
2002年 | 47篇 |
2001年 | 11篇 |
2000年 | 5篇 |
1999年 | 15篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 12篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有1462条查询结果,搜索用时 0 毫秒
101.
In vitro anti-mycobacterial activities of several 5-substituted acyclic pyrimidine nucleosides containing 1-(2-hydroxyethoxy)methyl and 1-[(2-hydroxy-1-(hydroxymethyl) ethoxy)methyl] acyclic moieties are investigated against three mycobacteria viz. Mycobacterium tuberculosis, Mycobacterium bovis, and Mycobacterium avium, which cause serious infections and mortality in healthy people as well as patients with AIDS. 1-(2-Hydroxyethoxy)methyl-5-(1-azido-2-haloethyl or 1-azidovinyl) analogs (4-7), 1-[(2-hydroxy-1-(hydroxymethyl)ethoxy)methyl]-5-decynyluracil (37), and 1-[(2-hydroxy-1-(hydroxymethyl)ethoxy)methyl]-5-dodecynyluracil (38) exhibited significant in vitro anti-tubercular activity against these mycobacteria. 相似文献
102.
Rakesh Singh A. K. Singh T. R. Sharma Aqbal Singh N. K. Singh 《Journal of plant biochemistry and biotechnology.》2007,16(2):75-82
Aroma is one of the most important quality traits of basmati rice (Oryza sativa L) that leads to high consumer acceptance. Earlier three significant QTLs for aroma, namely aro3-1, aro4-1 and aro8-1, have been mapped on rice chromosomes 3, 4 and 8, respectively, using a population of recombinant inbred lines (RILs) derived from a cross between Pusa 1121 (a basmati quality variety) and Pusa 1342 (a non-aromatic variety). For fine mapping of these QTLs, 184 F6 RILs were grown in the Kharif season of 2005 at New Delhi and Karnal, India. A total of 115 new SSR markers covering the three QTL intervals were designed and screened for parental polymorphism. Of these, 26 markers were polymorphic between parents, eight for the interval aro3-1, eight for the interval aro4-1 and ten for the interval aro8-1, thus enriching the density of SSR markers in these QTL intervals. Revised genetic maps were constructed by adding 23 of these new markers to the earlier map, by giving physical order of the markers in the pseudomolecules a preference. In the revised maps, the interval for QTL aro4-1 could not be improved further but QTL aro3-1 was narrowed down to an interval of 390 kbp from the earlier reported interval of 8.6 Mbp and similarly the QTL aro8-1 was narrowed down to a physical interval of 430 kbp. The numbers of candidate genes in the aro3-1 and aro8-1 intervals have now been reduced to 51 and 66, respectively. The badh2 gene on chromosome 8 was not associated with the aroma QTL on this chromosome. 相似文献
103.
Sondhi SM Jain S Dinodia M Shukla R Raghubir R 《Bioorganic & medicinal chemistry》2007,15(10):3334-3344
A number of pyrimidine derivatives (1-10) have been synthesized by condensation of 4-isothiocyanato-4-methylpentan-2-one with furfurylamine, histamine, 1-(3-aminopropyl)imidazole, 1-(3-aminopropyl)-2-pyrrolidinone, 2-aminobenzonitrile and 3-isothiocyanatobutanal with 1-(3-aminopropyl)-2-pyrrolidinone and 2-hydrazinopyridine under different reaction conditions. Various bispyrimidine derivatives (11-15) were obtained by condensation of 4-isothiocyanato-4-methylpentan-2-one with 2,4,8,10-tetraoxaspiro[5,5]undecane3,9-dipropamine (11'), 1,4-bis(3-aminopropyl)piperazine (13'), 3,5-diamino 1,2,4-triazole (15') and 3-isothiocyanatobutanal with 2,4,8,10-tetraoxaspiro[5,5]undecane 3,9-dipropamine, 1,4-bis(3-aminopropyl)piperazine. All these compounds were characterized by correct FT-IR, (1)H NMR, MS and elemental analysis. These compounds were screened for anti-inflammatory and analgesic activities. Anti-inflammatory activity of 3 is comparable while analgesic activity was found to be better than that of standard drug. 相似文献
104.
Wang ZZ Au P Chen T Shao Y Daheron LM Bai H Arzigian M Fukumura D Jain RK Scadden DT 《Nature biotechnology》2007,25(3):317-318
We describe the differentiation of human embryonic stem (hES) cells into endothelial cells using a scalable two-dimensional method that avoids an embryoid-body intermediate. After transplantation into severe combined immunodeficient (SCID) mice, the differentiated cells contributed to arborized blood vessels that integrated into the host circulatory system and served as blood conduits for 150 d. 相似文献
105.
Koenitzer JR Isbell TS Patel HD Benavides GA Dickinson DA Patel RP Darley-Usmar VM Lancaster JR Doeller JE Kraus DW 《American journal of physiology. Heart and circulatory physiology》2007,292(4):H1953-H1960
Hydrogen sulfide (H(2)S) has recently been shown to have a signaling role in vascular cells. Similar to nitric oxide (NO), H(2)S is enzymatically produced by amino acid metabolism and can cause posttranslational modification of proteins, particularly at thiol residues. Molecular targets for H(2)S include ATP-sensitive K(+) channels, and H(2)S may interact with NO and heme proteins such as cyclooxygenase. It is well known that the reactions of NO in the vasculature are O(2) dependent, but this has not been addressed in most studies designed to elucidate the role of H(2)S in vascular function. This is important, since H(2)S reactions can be dramatically altered by the high concentrations of O(2) used in cell culture and organ bath experiments. To test the hypothesis that the effects of H(2)S on the vasculature are O(2) dependent, we have measured real-time levels of H(2)S and O(2) in respirometry and vessel tension experiments, as well as the associated vascular responses. A novel polarographic H(2)S sensor developed in our laboratory was used to measure H(2)S levels. Here we report that, in rat aorta, H(2)S concentrations that mediate rapid contraction at high O(2) levels cause rapid relaxation at lower physiological O(2) levels. At high O(2), the vasoconstrictive effect of H(2)S suggests that it may not be H(2)S per se but, rather, a putative vasoactive oxidation product that mediates constriction. These data are interpreted in terms of the potential for H(2)S to modulate vascular tone in vivo. 相似文献
106.
107.
Mishra RK Yamagishi T Vasanthi D Ohtsuka C Kondo T 《Genesis (New York, N.Y. : 2000)》2007,45(9):570-576
Temporal colinearity in mouse HoxD is dependent on repressive activity of sequences within the 5' end of the complex. We show that a 5-kb DNA fragment from this region represses transgenes when combined in mouse as well as in Drosophila melanogaster. Moreover, repressive activity in Drosophila depends on some members of the Polycomb-group (PcG) genes, for example, extra sex combs. We also showed direct association of these factors with the repressive fragment, both in transgenic flies and in the context of the native mouse HoxD complex. These results suggest that the global repressive region of the HoxD complex functions in two very different species and that some PcG genes are involved in establishing the early repressive state of the HoxD complex, thus contributing to temporal colinearity. 相似文献
108.
109.
110.
Jian Yang Robert A. Spicer Teresa E. V. Spicer Nan Crystal Arens Frédéric M. B. Jacques Tao Su Elizabeth M. Kennedy Alexei B. Herman David C. Steart Gaurav Srivastava Rakesh C. Mehrotra Paul J. Valdes Naresh C. Mehrotra Zhe‐Kun Zhou Jiang‐Shan Lai 《Global Ecology and Biogeography》2015,24(10):1113-1125