全文获取类型
收费全文 | 4500篇 |
免费 | 452篇 |
国内免费 | 17篇 |
专业分类
4969篇 |
出版年
2022年 | 39篇 |
2021年 | 81篇 |
2020年 | 25篇 |
2019年 | 45篇 |
2018年 | 75篇 |
2017年 | 51篇 |
2016年 | 95篇 |
2015年 | 229篇 |
2014年 | 255篇 |
2013年 | 271篇 |
2012年 | 345篇 |
2011年 | 345篇 |
2010年 | 215篇 |
2009年 | 161篇 |
2008年 | 221篇 |
2007年 | 208篇 |
2006年 | 220篇 |
2005年 | 187篇 |
2004年 | 181篇 |
2003年 | 134篇 |
2002年 | 117篇 |
2001年 | 129篇 |
2000年 | 101篇 |
1999年 | 57篇 |
1998年 | 42篇 |
1997年 | 36篇 |
1996年 | 42篇 |
1995年 | 25篇 |
1994年 | 40篇 |
1993年 | 31篇 |
1992年 | 67篇 |
1991年 | 50篇 |
1990年 | 57篇 |
1989年 | 62篇 |
1988年 | 38篇 |
1987年 | 50篇 |
1986年 | 32篇 |
1985年 | 45篇 |
1984年 | 38篇 |
1983年 | 33篇 |
1982年 | 49篇 |
1980年 | 20篇 |
1979年 | 42篇 |
1978年 | 25篇 |
1977年 | 33篇 |
1976年 | 33篇 |
1975年 | 40篇 |
1974年 | 36篇 |
1973年 | 40篇 |
1971年 | 24篇 |
排序方式: 共有4969条查询结果,搜索用时 15 毫秒
91.
92.
93.
A P Reddy B L Hsu P S Reddy N Q Li K Thyagaraju C C Reddy M F Tam C P Tu 《Nucleic acids research》1988,16(12):5557-5568
We have characterized a cDNA pGPX1211 encoding rat glutathione peroxidase I. The selenocysteine in the protein corresponded to a TGA codon in the coding region of the cDNA, similar to earlier findings in mouse and human genes, and a gene encoding the formate dehydrogenase from E. coli, another selenoenzyme. The rat GSH peroxidase I has a calculated subunit molecular weight of 22,155 daltons and shares 95% and 86% sequence homology with the mouse and human subunits, respectively. The 3'-noncoding sequence (greater than 930 bp) in pGPX1211 is much longer than that of the human sequences. We found that glutathione peroxidase I mRNA, but not the polypeptide, was expressed under nutritional stress of selenium deficiency where no glutathione peroxidase I activity can be detected. The failure of detecting any apoprotein for the glutathione peroxidase I under selenium deficiency and results published from other laboratories supports the proposal that selenium may be incorporated into the glutathione peroxidase I co-translationally. 相似文献
94.
Digestion of fixed metaphase chromosomes by endonucleases (micrococcal nuclease and DNase II) under optimal digestion conditions followed by Giemsa staining produces sharp banding patterns identical to G-bands. In 3H-thymidine labeled, synchronized metaphase cells of the chinese hamster (CHO line), the band induction is accompanied by the removal of DNA. The single strand specific nuclease S1 and DNase I do not produce such banding patterns. 相似文献
95.
Analysis of unintegrated avian RNA tumor virus double-stranded DNA intermediates. 总被引:28,自引:60,他引:28 下载免费PDF全文
Previous studies by Guntaka et al. have shown that the unintegrated DNA intermediates of avian RNA tumor virus replication can be readily isolated from cultures of the quail tumor line QT-6 at 1 day after infection. The intermediates include double-stranded linear and covalently closed circular DNA species. Using the analysis procedure of Southern together with previously obtained information regarding the sites of action of certain restriction endonucleases on avian sarcoma virus DNA, we have further characterized the viral DNA intermediates. Evidence is presented that, relative to the RNA genome, most of the linear species possess a direct terminal sequence redundancy equivalent to 0.5 X 10(6) +/- 0.3 X 10(6) daltons of double-stranded DNA. Some of the circular forms also possess a sequence redundancy of 0.21 X 10(6) +/- 0.03 X 10(6) daltons. 相似文献
96.
Yi-Jiun Pan Tzu-Lung Lin Yen-Hua Chen Chun-Ru Hsu Pei-Fang Hsieh Meng-Chuan Wu Jin-Town Wang 《PloS one》2013,8(12)
Capsule is an important virulence factor in bacteria. A total of 78 capsular types have been identified in Klebsiella pneumoniae. However, there are limitations in current typing methods. We report here the development of a new genotyping method based on amplification of the variable regions of the wzc gene. Fragments corresponding to the variable region of wzc were amplified and sequenced from 76 documented capsular types of reference or clinical strains. The remaining two capsular types (reference strains K15 and K50) lacked amplifiable wzc genes and were proven to be acapsular. Strains with the same capsular type exhibited ≧94% DNA sequence identity across the variable region (CD1-VR2-CD2) of wzc. Strains with distinct K types exhibited <80% DNA sequence identity across this region, with the exception of three pairs of strains: K22/K37, K9/K45, and K52/K79. Strains K22 and K37 shared identical capsular polysaccharide synthesis (cps) genes except for one gene with a difference at a single base which resulted in frameshift mutation. The wzc sequences of K9 and K45 exhibited high DNA sequence similarity but possessed different genes in their cps clusters. K52 and K79 exhibited 89% wzc DNA sequence identity but were readily distinguished from each other at the DNA level; in contrast, strains with the same capsular type as K52 exhibited 100% wzc sequence identity. A total of 29 strains from patients with bacteremia were typed by the wzc system. wzc DNA sequences confirmed the documented capsular type for twenty-eight of these clinical isolates; the remaining strain likely represents a new capsular type. Thus, the wzc genotyping system is a simple and useful method for capsular typing of K. pneumoniae. 相似文献
97.
Heme oxygenase is involved in nitric oxide- and auxin-induced lateral root formation in rice 总被引:1,自引:0,他引:1
Lateral root (LR) development performs the essential tasks of providing water, nutrients, and physical support to plants. Therefore, understanding the regulation of LR development is of agronomic importance. In this study, we examined the effect of nitric oxide (NO), auxin, and hemin (Hm) on LR formation in rice. Treatment with Hm [a highly effective heme oxygenase (HO) inducer], sodium nitroprusside (SNP, an NO donor), or indole-3-butyric acid (IBA, a naturally occurring auxin) induced LR formation and HO activity. LR formation and HO activity induced by SNP and IBA but not Hm was reduced by the specific NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. As well, Hm, SNP, and IBA could induce OsHO1 mRNA expression. Zn protoporphyrin IX (the specific inhibitor of HO) and hemoglobin (the carbon monoxide/NO scavenger) reduced LR number and HO activity induced by Hm, SNP, and IBA. Our data suggest that HO is required for Hm-, auxin-, and NO-induced LR formation in rice. 相似文献
98.
David Wang Jeng Wei Kang Hsu Jin-Chi Jau Mei-Wen Lieu Tai-Jong Chao Hsing I. Chen 《Journal of biomedical science》1999,6(1):28-35
Endotoxin shock is characterized by systemic hypotension, hyporeactiveness to vasoconstrictors and acute lung edema. A nitric oxide synthase (NOS) inhibitor, NG-monomethyl-L-arginine (L-NMMA) has been shown to be effective in reversing acute lung injury. In the present study, we evaluated the effects of NOS blockade by different mechanisms on the endotoxin-induced changes. In anesthetized rats, lipopolysaccharide (LPS,Klebsiella pneumoniae) was administered intravenously in a dose of 10 mg/kg. LPS caused sustained systemic hypotension accompanied by an eightfold increase of exhaled NO during an observation period of 4 h. After the experiment, the lung weight was obtained and lung tissues were taken for the determination of mRNA expressions of inducible NOS (iNOS), interleukin-1 (IL-1) and tumor necrosis factor--(TNF-). Histological examination of the lungs was also performed. In the control group injected with saline solution, mRNA expressions of iNOS, IL-1 and TNF- were absent. Four hours after LPS, the mRNA expressions of iNOS and IL-1 were still significantly enhanced, but TNF- was not discernibly expressed. LPS also caused a twofold increase in lung weight. Pathological examination revealed endothelial damage and interstitial edema. Various NOS inhibitors were given 1 h after LPS administration. These agents included N-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg), a constitutive NOS and iNOS inhibitor; S,S-1,4-phenylene-bis-(1,2-ethanedinyl) bis-isothiourea dihydrobromide (1,4-PBIT, 10 mg/kg), a relatively specific iNOS inhibitor, and dexamethasone (3 mg/kg), an inhibitor of iNOS expression. These NOS inhibitors all effectively reversed the systemic hypotension, reduced the exhaled NO concentration and prevented acute lung injury. The LPS-induced mRNA expressions of iNOS and IL-1 were also significantly depressed by these NOS inhibitors. Our results suggest that NO production through the iNOS pathway is responsible for endotoxin-induced lung injury. Certain cytokines such as IL-1 are possibly involved. These changes are minimized by NOS inhibitors through different mechanisms. 相似文献
99.
Kuo YH Liang TW Liu KC Hsu YW Hsu HC Wang SL 《Marine biotechnology (New York, N.Y.)》2011,13(3):451-461
The antioxidant activity of the culture supernatant of Serratia ureilytica TKU013 with squid pen as the sole carbon/nitrogen source was assessed by three methods, and the phenolic contents were assayed.
The supernatant with the highest antioxidant activity was further purified by liquid–liquid partition, revealing the ethyl
acetate extract exhibited the strongest antioxidant activity and the highest total phenolic content. Eight fractions were
retrieved from silica gel column chromatography of this extract, designated F1–F8. F4 was found to possess the strong antioxidative
activity and the highest total phenolic content and also exhibited strong cytotoxic activities against two different tumoural
cell lines. A new compound (Serranticin) with antioxidant and antitumor activity was obtained from F4. The structure of Serranticin
is analogous to that of siderophores (hexacoordinated catecholamine), which are iron chelators. As such, Serranticin has the
potential for use as a deferration agent in various iron overload diseases. 相似文献
100.
Prolonged rapamycin treatment inhibits mTORC2 assembly and Akt/PKB 总被引:15,自引:0,他引:15
Sarbassov DD Ali SM Sengupta S Sheen JH Hsu PP Bagley AF Markhard AL Sabatini DM 《Molecular cell》2006,22(2):159-168
The drug rapamycin has important uses in oncology, cardiology, and transplantation medicine, but its clinically relevant molecular effects are not understood. When bound to FKBP12, rapamycin interacts with and inhibits the kinase activity of a multiprotein complex composed of mTOR, mLST8, and raptor (mTORC1). The distinct complex of mTOR, mLST8, and rictor (mTORC2) does not interact with FKBP12-rapamycin and is not thought to be rapamycin sensitive. mTORC2 phosphorylates and activates Akt/PKB, a key regulator of cell survival. Here we show that rapamycin inhibits the assembly of mTORC2 and that, in many cell types, prolonged rapamycin treatment reduces the levels of mTORC2 below those needed to maintain Akt/PKB signaling. The proapoptotic and antitumor effects of rapamycin are suppressed in cells expressing an Akt/PKB mutant that is rapamycin resistant. Our work describes an unforeseen mechanism of action for rapamycin that suggests it can be used to inhibit Akt/PKB in certain cell types. 相似文献