全文获取类型
收费全文 | 3337篇 |
免费 | 199篇 |
国内免费 | 5篇 |
出版年
2023年 | 6篇 |
2022年 | 16篇 |
2021年 | 49篇 |
2020年 | 21篇 |
2019年 | 26篇 |
2018年 | 45篇 |
2017年 | 27篇 |
2016年 | 54篇 |
2015年 | 120篇 |
2014年 | 153篇 |
2013年 | 202篇 |
2012年 | 239篇 |
2011年 | 230篇 |
2010年 | 152篇 |
2009年 | 155篇 |
2008年 | 219篇 |
2007年 | 240篇 |
2006年 | 222篇 |
2005年 | 255篇 |
2004年 | 217篇 |
2003年 | 184篇 |
2002年 | 189篇 |
2001年 | 28篇 |
2000年 | 21篇 |
1999年 | 41篇 |
1998年 | 52篇 |
1997年 | 32篇 |
1996年 | 35篇 |
1995年 | 33篇 |
1994年 | 39篇 |
1993年 | 23篇 |
1992年 | 17篇 |
1991年 | 23篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 19篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 17篇 |
1984年 | 18篇 |
1983年 | 10篇 |
1982年 | 7篇 |
1981年 | 22篇 |
1980年 | 8篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1961年 | 2篇 |
排序方式: 共有3541条查询结果,搜索用时 531 毫秒
21.
The physical characteristics of a mutant, R(M201-2), capable of conferring high and stable ampicillion resistance was analyzed. The R(M201-2) and its parent R-factor deoxyribonucleic acid (DNA) could be isolated as an extrachromosomal and covalently closed circular form. Their buoyant densities were both 1.712 g/cm(3), and their molecular weights were about 82 x 10(6) and 64 x 10(6), respectively, when measured by CsCl and sucrose density gradient analyses. The contour lengths by electron microscopy were 35.9 +/- 0.6 and 31.0 +/- 0.6 mum, respectively. By using the extracted R-factor DNA, the mutant and parent characters were transformable to another Escherichia coli strain. The mutant R factor showed an increased amount of DNA even after conjugal transfer to Proteus. An increase in the size of R-factor DNA was thus considered to be the cause of the high level of ampicillin resistance. 相似文献
22.
Summary Three non-chromosomal and two chromosomal genes which influence resistance to streptomycin are described. Each of the non-chromosomal factors,sr-500,sr-1500, andsd, exhibits uniparental inheritance, with all progeny receiving the factor when it is carried by the parent of mating-typeplus, and none when it is carried by the mating-typeminus parent. The streptomycin-dependence factor,sd, shows zygotic dominance when contributed by the mating-typeplus parent, but not when coming from the mating-typeminus parent, indicating that the uniparental transmission results from events occurring within the zygote early in maturation and well before meiosis. The chromosomal geneA interacts both with chromosomal and non-chromosomal genes at the biochemical level, but does not alter their patterns of inheritance.With 1 Figure in the TextThis paper is dedicated to ProfessorL. C. Dunn in gratitude to him as teacher and advisor, on the occasion of his retirement.This work was supported by grants from the U.S. Public Health Service and the National Science Foundation. The generosity and interest of ProfessorFrancis J. Ryan in providing laboratory space is gratefully acknowledged, as is the technical assistance of MissFran Yablonsky. 相似文献
23.
Kazutake Shimada Yoshihiro Komine Kuniko Mitamura 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1991,565(1-2)
The high-performance liquid chromatographic separation of bile acid pyrenacyl esters with cyclodextrin-containing mobile phase is presented. Compared with conventional methods, inclusion chromatography gives much more satisfactory separation of derivatized bile acids in a short time. The application of this method to the separation of glycine-conjugated bile acids in human bile is also described. 相似文献
24.
The ratio of the extracellular to the intracellular activityof carbonic anhydrase (CA) in cells of Chlorella ellipsoideaC-27, adapted to low levels of CO2 for 24 h (low-CO2 cells),was about one to one. Treatment of intact cells with PronaseP inactivated about one-half of the extracellular CA activitywithout affecting photosynthetic activity. The CA activity incell homogenates and in cell-wall ghosts liberated during celldivision was completely inactivated by the same treatment. Pretreatmentwith Glycosidase mix, Chitosanase and Macerozyme enhanced theinactivation of the CA activity in intact cells. These resultssuggest that extracellular CA is evenly distributed throughoutthe whole cell-wall region. The apparent K1/2 for dissolved inorganic carbon (DIC) in low-CO2cells doubled when extracellular CA was inactivated by treatmentwith Pronase P, but the K1/2 obtained was still one-half ofthat in high-CO2 cells. Photosynthetic 14CO2-fixation in low-CO2cells was enhanced by acetazolamide, whereas H14CO3-fixationwas suppressed. The results suggest that CO2 is a dominant substrateutilized by cells and that HCO3 is utilized after conversionto CO2. The present results show that both intracellular andextracellular CA contribute to the increase in affinity forDIC during photosynthesis in low-CO2 cells of Chlorella ellipsoideaC-27. (Received May 7, 1990; Accepted July 18, 1990) 相似文献
25.
Matsuda Yoshihiro; Uzaki Tomoya; Iwasawa Norio; Tanaka Takaharu; Saito Tatsuaki 《Plant & cell physiology》1990,31(5):717-720
A cell wall lytic enzyme (gamete wall-autolysin) from Chlamydomonasreinhardtii specifically cleaved several synthetic model peptides,-neo-endorphin, dynorphin (113), neurotensin and mastoparan,at the peptide bonds between consecutive hydrophobic amino-acidresidues. The cleavage was not significantly affected by high-saltconditions which are known to inhibit digestion of the cellwall. (Received December 14, 1989; Accepted April 5, 1990) 相似文献
26.
Takashi Kamaishi Tetsuo Hashimoto Yoshihiro Nakamura Fuminori Nakamura Shigenori Murata Norihiro Okada Ken-ichi Okamoto Makoto Shimizu Masami Hasegawa 《Journal of molecular evolution》1996,42(2):257-263
Partial regions of the mRNA encoding a major part of translation elongation factor 1 (EF-1) from a mitochondrion-lacking protozoan,Glugea plecoglossi, that belongs to microsporidians, were amplified by polymerase chain reaction (PCR) and their primary structures were analyzed. The deduced amino acid sequence was highly divergent from typical EF-1's of eukaryotes, although it clearly showed a eukaryotic feature when aligned with homologs of the three primary kingdoms. Maximum likelihood (ML) analyses on the basis of six different stochastic models of amino acid substitutions and a maximum parsimony (MP) analysis consistently suggest that among eukaryotic species being analyzed,G. plecoglossi is likely to represent the earliest offshoot of eukaryotes. Microsporidians might be the extremely ancient eukaryotes which have diverged before an occurrence of mitochondrial symbiosis.
Sequence availability: The nucleotide sequence data reported here appear in the GSDB, DDBJ, EMBL, and NCBI databases with the accession number D32139 相似文献
27.
Two Polypeptides Inducible by Low Levels of CO2 in Soluble Protein Fractions from Chlorella regularis Grown at Low or High pH 总被引:1,自引:0,他引:1
Previous studies suggested that certain protein(s) other thancarbonic anhydrase might play an important role in the facilitatedtransport of dissolved inorganic carbon (DIC) from the mediumto the site of CO2 fixation by ribulose-1,5-bisphosphate carboxylase/oxygenasein the unicellular green alga Chlorella regularis adapted tolow-CO2 (ordinary air) conditions [Shiraiwa et al. (1991) Jpn.J. Phycol. 39: 355; Satoh and Shiraiwa (1992) Research in Photosynthesis,Vol. III, p. 779]. The proteins that might be involved in thisfacilitated transport of DIC were investigated by pulse-labelingof induced proteins with 35S-sulfate during adaptation of cellsgrown under high-CO2 conditions to low CO2. Analysis by SDS-PAGErevealed that synthesis of two polypeptides, with molecularmasses of 98 and 24 kDa, respectively, was induced under low-CO2conditions. The 24-kDa polypeptide was induced at pH 5.5 butnot at pH 8.0, whereas the 98-kDa polypeptide was induced atboth pH 5.5 and pH 8.0. The possible role of these polypeptidesin the facilitated transport of DIC in Chlorella regularis isdiscussed. (Received October 30, 1995; Accepted February 26, 1996) 相似文献
28.
Yuriko Osakabe Kazuya Nanto Hiroko Kitamura Shinya Kawai Yuki Kondo Tomoyuki Fujii Keiji Takabe Yoshihiro Katayama Noriyuki Morohoshi 《Planta》1996,200(1):13-19
The polypeptide encoded by the partial fragment of cDNA of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5), PALcDNAl (Osakabe et al., 1995, Plant Sci. 105: 217–226), isolated from Populus kitakamiensis (P. sieboldii x P. grandidentata), was expressed in Escherichia coli cells. The polypeptide was purified and an antiserum raised against it. The antiserum recognized a protein of 77 kDa on nitrocellulose blots after sodium dodecyl sulfate-poly-acrylamide gel electrophoresis of total protein and the partially purified PAL protein from P. kitakamiensis. Moreover,the antiserum recognized a protein on the blot after non-denaturing polyacrylamide gel electrophoresis of P. kitakamiensis proteins and this protein had PAL activity. Furthermore, the antibody inhibited PAL activity of extracts from stem tissues. These results showed that the antiserum against the partial PAL peptide recognized only the PAL subunits in extracts of P. kitakamiensis. Immunolocalization studies of P. kitakamiensis tissues revealed that the PAL protein was specifically localized in the xylem and the phloem fibers and no immunogold signal was found in the epidermis, the cortex, the pith, or the cambium of either stems or leaves.Abbreviations IgG
immunoglobulin G
- IPTG
isopropylthio--d-galactoside
- PAL
phenylalanine ammonia-lyase
The authors thank Dr. Kunio Hata of Nippon Paper Industries Co., Ltd. (Japan) for supplying P. kitakamiensis. This work was supported in part by a grant-in-aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (No. 07406008). 相似文献
29.
30.
Ritsuko Katoh-Semba Reiji Semba Hiroyuki Kato† Masataka Ueno† Yoshihiro Arakawa† Kanefusa Kato‡ 《Journal of neurochemistry》1994,62(6):2141-2147
Abstract: Our previous studies showed that the concentration of the β subunit of nerve growth factor (β-NGF) in nervous tissues is higher in male than in female mice. To identify the brain regions that are affected by androgens, the amounts of β-NGF protein and its mRNAs were measured in male, female, and castrated male CD-1 mice and testicular feminization mice at 3–4 months of age. Among tissues examined, the hypophysis of males contained the highest average concentration of β-NGF protein. In most regions of the brain, individual levels were more variable in males than in females. However, after the castration, such variations in β-NGF levels disappeared. Average levels of β-NGF protein in males were higher in the cerebellum (eightfold higher), olfactory bulb (12-fold higher), hypothalamus (sixfold higher), and hypophysis (72-fold higher) than thope in corresponding regions of females. No significant differences were observed in levels of β-NGF protein in the hippocampus, cerebral cortex, striatum, septum, and brainstem. The castration of male mice caused a reduction in levels of β-NGF protein in the hypothalamus and hypophysis, but not in the cerebellum and olfactory bulb, to the femgle levels. The concentrations of β-NGF protein in testicular feminization mice were similar to those in female CD-1 mice in all regions. The concentrations of mRNA for β-NGF in the olfactory bulb and hypophysis from males were higher than those from females. By contrast, northern blots showed no remarkable differences in the amounts of brain-derived neurotrophic factor and neurotrophin-3 between the two sexes. Thus, in some regions of the brain, the production of β-NGF appears to be regulated by testosterone, but the regulatory mechanisms do not appear to be simple. Our present results indicate that the binding of testosterone to its receptor is an important step in the regulation of the level of β-NGF in these region. 相似文献