全文获取类型
收费全文 | 4230篇 |
免费 | 187篇 |
国内免费 | 98篇 |
出版年
2022年 | 42篇 |
2021年 | 68篇 |
2020年 | 27篇 |
2019年 | 37篇 |
2018年 | 477篇 |
2017年 | 365篇 |
2016年 | 194篇 |
2015年 | 143篇 |
2014年 | 137篇 |
2013年 | 200篇 |
2012年 | 212篇 |
2011年 | 177篇 |
2010年 | 119篇 |
2009年 | 114篇 |
2008年 | 210篇 |
2007年 | 109篇 |
2006年 | 100篇 |
2005年 | 106篇 |
2004年 | 76篇 |
2003年 | 66篇 |
2002年 | 70篇 |
2001年 | 75篇 |
2000年 | 42篇 |
1999年 | 90篇 |
1998年 | 23篇 |
1997年 | 32篇 |
1994年 | 21篇 |
1993年 | 28篇 |
1992年 | 78篇 |
1991年 | 90篇 |
1990年 | 58篇 |
1989年 | 78篇 |
1988年 | 59篇 |
1987年 | 46篇 |
1986年 | 54篇 |
1985年 | 54篇 |
1984年 | 37篇 |
1983年 | 25篇 |
1979年 | 32篇 |
1978年 | 20篇 |
1975年 | 51篇 |
1974年 | 44篇 |
1973年 | 37篇 |
1972年 | 34篇 |
1971年 | 39篇 |
1970年 | 35篇 |
1969年 | 25篇 |
1968年 | 27篇 |
1967年 | 23篇 |
1966年 | 21篇 |
排序方式: 共有4515条查询结果,搜索用时 15 毫秒
101.
Genomic structures of two major species in section Eusorghum (Sorghum), Sorghum bicolor and Sorghum halepense, and their phylogenetic relationships with a species in section Parasorghum, Sorghum versicolor, were studied by using cloned repetitive DNA sequences from the three species. Of the five repetitive DNA clones isolated from S. bicolor and S. halepense, four produced qualitatively similar hybridization patterns with detectable variations in copy numbers of some of the restriction fragments on the Southern blots of the two genomic DNAs. One clone was shown to be diagnostic for S. halepense. Molecular analysis at the DNA level indicates that S. bicolor and S. halepense have similar but not identical genomes, consonant with differences in karyotypes, meiotic chromosome behaviors, morphology, and physiology of the species. In addition to five repetitive clones isolated from S. bicolor and S. halepense, eight more sequences were cloned from S. versicolor. Nine clones were found to be specific for either S. bicolor and S. halepense or S. versicolor. The remaining four had a moderate to strong homology with sequences present in all Sorghum species studied. We speculate that the genome in the common ancestor of Sorghum has differentiated to give rise to genomes of at least three major chromosome sizes; large, medium, and small, as seen at present. Amplifications, eliminations, rearrangements, and new syntheses of repetitive sequences may have been involved in genome differentiation of these species. The results also suggest that the S. versicolor genome has strongly diverged from the genomes of the two species in section Eusorghum. 相似文献
102.
Co-localization of ecdysteroid receptors and c-fos-like protein in the brain of Manduca sexta larvae
Hans-Jürgen Bidmon Noelle Audrey Granger Walter Erich Stumpf 《Development genes and evolution》1991,200(3):149-155
Summary The presence of c-fos, a marker for cell activation, was investigated in cerebral neurons actively expressing ecdysteroid receptors during larval-pupal development in the tobacco hornworm, Manduca sexta. Colocalization was accomplished by ecdysteroid autoradiography using the tritiated high affinity 20-hydroxyecdysone agonist ponasterone A and immunocytochemistry with an antibody to a peptide sequence which is highly conserved in both human and murine c-fos. Immunoreactivity to a c-fos-like protein(s) was present in nuclei of many neurons of all the developmental stages examined. However, with the exception of the optic lobe, cells expressing nuclear ecdysteroid receptors were more immunoreactive than non-ecdysteroid-binding neurons. These data suggest that ecdysteroid-induced gene activation and translation may involve c-fos expression.
Offprint requests to: H.-J. Bidmon 相似文献
103.
Sanjay Awasthi Faiyaz Ahmad
Rashmi Sharma
Hassan Ahmad 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1992,584(2):167-173A chromatographic method for the specific determination of glutathione in malignant cell lines is described. The method is based on the ability of glutathione-S-transferase to specifically and quantitatively conjugate glutathione to 1-chloro-2,4-dinitrobenzene and chromatographic quantitation of the resultant conjugate, dinitrophenyl-S-glutathione, by reversed-phase liquid chromatography. The assay can be performed on 20 000 g supernatants of cell homogenates without acid extraction. 2-Mercaptoethanol, a sulfhydryl compound often used as a thiol-protective agent to preserve enzymatic activities of a number of enzymes, did not interfere with glutathione determination by this method. The dinitrophenyl-S-glutathione isolated from either standard glutathione samples or from cell homogenates was shown to be identical to authentic dinitrophenyl-S-glutathione using mass spectrometry. Recovery of glutathione in standard samples by the current method was identical to that determined using 5,5′-dithiobis(2-nitrobenzoic acid). Exogenous glutathione added to supernatants of cell homogenate in the presence or absence of 2-mercaptoethanol was also completely recovered. 相似文献
104.
Kenichiro Nakashima Mitsuyo Okamoto Kazunori Yoshida Naotaka Kuroda Shuzo Akiyama
Masatoshi Yamaguchi
《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1992,584(2):275-279A sensitive high-performance liquid chromatographic method using 3-bromomethyl-6,7-dimethoxy-1-methyl-2(1H)-quinoxalinone (Br-DMEQ) as a fluorescent labeling reagent is described for the determination of benzoylecgonine (BE) and ecgonine (EC). The Br-DMEQ derivatives of BE and EC were separated on a C18 column and detected at 455 nm with excitation at 370 nm. The detection limits of the proposed method were 18.7 fmol for BE and 12.5 pmol for EC at a signal-to-noise ratio of 3. Relative standard deviations of five replicate measurements were 1.94% (10 pmol) and 2.98% (50 pmol) for BE and 6.3% (250 pmol) and 5.62% (1.25 pmol) for EC. This method was applied to the determination of BE in human urine. BE was extracted from urine by solvent extraction with chloroform—isopropyl alcohol (9:1, v/v) solution. Levels of 2.5 · 10−8 M BE in urine (25 pmol/ml) could be determined. 相似文献
105.
E E Galyov A V Smirnov OYuKarlishev K I Volkovoy A I Denesyuk I V Nazimov K S Rubtsov V M Abramov S M Dalvadyanz V P Zav'yalov 《FEBS letters》1990,277(1-2):230-232
The plasmid-located gene caf1 encoding the capsular antigen fraction 1 (F1) of Yersinia pestis was cloned and sequenced. The gene codes for a 170 amino acid peptide with a deduced Mr of 17.6 kDa. The signal peptide sequence was highly homologous to the E. coli consensus signal sequence. The F1 was assumed to have beta-sheet structure for the most part. The region located between amino acids 100 and 150 was suggested to contain putative antigenic determinants and to stimulate T cells. 相似文献
106.
A Gololobov MYuPetrauskas R Pauliukonis V Koschke I L Borisov V Svedas 《Biochimica et biophysica acta》1990,1041(1):71-78
Alpha-chymotrypsin-catalyzed acyl transfer from Boc-L-MetONp, Ac-L-TyrOEt, Bz-L-TyrOMe, Mal-L-PheOMe to the C-protected amino acids (L-AlaNH2, L-LeuNH2, L-ArgOMe and beta-naphthylamides of L-Arg, L-Leu, L-Ala and L-Glu) has been studied. Modification of the carboxylic groups with beta-naphthylamide was shown to increase the reactivity of nucleophiles in these reactions by a factor of more than 100 in comparison with amides and esters of the same amino acids. This effect can be accounted for by the effective formation of the nucleophile-acylenzyme complex due to hydrophobic interactions of the beta-naphthylamide moiety with the corresponding subsite of alpha-chymotrypsin. The reaction kinetics follows the scheme involving hydrolysis of the nucleophile-acylenzyme intermediate. The contribution of this pathway depends on the structures of both the acyl-group donor and the added nucleophile. The competitive inhibition by amino acid beta-naphthylamides is also observed. The results obtained show that modification of the COOH-group of added nucleophiles by beta-naphthylamide strongly affects the reactivity of these compounds in the alpha-chymotrypsin-catalyzed peptide synthesis. 相似文献
107.
The effect of the electric field on the phase transition temperature (Tc) of acidic 1,2-dipalmitoyl-sn-glycero-3-phosphate (DPPA) and 1,2-dipalmitoyl-sn-glycero-3-thionphosphate (thion-DPPA) and zwitterion, i.e. 1,2-dipalmitoyl-rac-3-phosphocholine and 1,2-distearoyl-rac-glycero-3-phosphocholine (DPPC and DSPC), lipids has been investigated. The phase transition was detected using the jump-like increase effect in the conductance of the planar bilayer membrane. A voltage increase to 150 mV has been shown to increase the phase transition temperature in a bilayer lipid membrane (BLM) of phosphatidic acids (DPPA and thion-DPPA) by 8-12 degrees C while the transition temperature in the bilayer of zwitterion lipids (DPPC and DSPC) increases insignificantly. The increasing of Tt in BLM of acidic lipids is attributed to the voltage-induced changes in the molecule packing density. 相似文献
108.
A comparison of experimental and theoretical melting maps for replicative form of phi X174 DNA
下载免费PDF全文
![点击此处可从《Nucleic acids research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A previously elaborated technique for fixing a chosen partially melted state of DNA with glyoxal was used in a study of the melting process of the replicative form (RF III) of phi X174 DNA. Electron-microscopic maps corresponding to five points of the melting curve of RF III were obtained and compared with the theoretical melting maps obtained in (4) and (6). This comparison clearly shows that only rigorous calculations (4) and not the ones proposed by Azbel (6,7) correctly predict the course of RF III melting. 相似文献
109.
Pauline Yahr Deborah Commins J.Carey Jackson Audrey Newman 《Hormones and behavior》1982,16(3):304-322
This research studied the role of the medial preoptic area and adjacent cell populations in androgen control of scent marking and sexual behavior in male gerbils (Meriones unguiculatus). Experiment 1 replicated previous research showing that implants of testosterone propionate in or near the medial preoptic area reinstate marking behavior in castrates. Implant sites near the diagonal band of Broca or in the posterior part of the medial preoptic area, near the anterior hypothalamus, are more effective than other sites. Experiment 2 showed that medial preoptic area lesions permanently impair sexual behavior despite testosterone stimulation. Experiments 2–4 showed that lesions in or near the medial preoptic area can also disrupt scent marking; however, this behavior gradually recovered in many lesioned males, especially if they received testosterone. The data suggest that both scent marking and sexual behavior are controlled by androgens acting on cells in or near the medial preoptic area, but the cell populations involved in these two behaviors are probably not the same. 相似文献
110.