全文获取类型
收费全文 | 2892篇 |
免费 | 150篇 |
出版年
2023年 | 3篇 |
2022年 | 11篇 |
2021年 | 32篇 |
2020年 | 16篇 |
2019年 | 29篇 |
2018年 | 33篇 |
2017年 | 34篇 |
2016年 | 58篇 |
2015年 | 89篇 |
2014年 | 109篇 |
2013年 | 145篇 |
2012年 | 194篇 |
2011年 | 200篇 |
2010年 | 121篇 |
2009年 | 109篇 |
2008年 | 167篇 |
2007年 | 204篇 |
2006年 | 171篇 |
2005年 | 189篇 |
2004年 | 182篇 |
2003年 | 170篇 |
2002年 | 169篇 |
2001年 | 51篇 |
2000年 | 40篇 |
1999年 | 53篇 |
1998年 | 30篇 |
1997年 | 28篇 |
1996年 | 24篇 |
1995年 | 38篇 |
1994年 | 23篇 |
1993年 | 25篇 |
1992年 | 38篇 |
1991年 | 37篇 |
1990年 | 26篇 |
1989年 | 27篇 |
1988年 | 23篇 |
1987年 | 19篇 |
1986年 | 7篇 |
1985年 | 17篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1978年 | 5篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1973年 | 3篇 |
1968年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有3042条查询结果,搜索用时 15 毫秒
61.
A new synthesis of desmosterol was described using hyodeoxycholic acid (3,6-dihydroxy-5β-cholanic acid) as a starting material. Epidesmosterol (3-hydroxycholesta-5,24-diene) was also synthesized for the first time from the same starting material. 相似文献
62.
Dye-coupled electrode system for the rapid determination of cell populations in polluted water. 总被引:7,自引:1,他引:6
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We determined cell populations in polluted waters by using a fuel cell-type electrode. The electrode was constructed from a platinum anode, a silver peroxide cathode, and a membrane filter for retaining microorganisms. The principle of cell number determination is based on sensing a redox dye reduced by the microorganisms with the electrode. Sample solutions containing microorganisms were membrane filtered, and the resulting filter containing microbial cells was attached to the surface of a platinum anode. The electrode was immersed in phosphate buffer solution (0.05 M, pH 7) containing a redox dye (2,4-dichlorophenol-indophenol), and the current generated was measured. The response time of the electrode system was 10 to 20 min, and the current generated was proportional to cell populations above 10(4) cells/ml. 相似文献
63.
64.
V Ramaswami R C Haaseth T O Matsunaga V J Hruby D F O'Brien 《Biochimica et biophysica acta》1992,1109(2):195-202
The interaction of the delta-opioid receptor selective peptides, cyclic [D-Pen2, D-Pen5]-enkephalin [DPDPE] and its acyclic analog, DPDPE(SH)2, with neutral phospholipid bilayer membranes was examined by permeability and calorimetry measurements. The permeabilities were accomplished by entrapping either peptide inside of unilamellar liposomes (composed of a mixture of a molar ratio 65:25:10 phosphatidylcholine/phosphatidylethanolamine/cholesterol) then monitoring the peptide efflux through the bilayer. The initial permeability of DPDPE (first 12 h) averaged over four experiments was (0.91 +/- 0.47).10(-12) cm s-1. In contrast the average permeability of the acylic DPDPE(SH)2 was (4.26 +/- 0.23).10(-12) cm s-1. The effect of these peptides on the phase transition, Tm, of 1,2-dipalmitoylphosphatidylcholine (DPPC) bilayers was examined by high sensitivity differential scanning calorimetry. The Tm, the calorimetric enthalpy, and the van 't Hoff enthalpy of DPPC were not significantly altered by the presence of DPDPE, whereas the calorimetric data for DPPC with DPDPE(SH)2 showed a small, yet significant, increase (0.2 degrees C) in the Tm with a 30% decrease in the cooperative unit. Both the permeability and calorimetry data reveal a stronger peptide-membrane interaction in the case of the more flexible acyclic peptide. 相似文献
65.
L Fang R J Knapp T Matsunaga S J Weber T Davis V J Hruby H I Yamamura 《Life sciences》1992,51(20):PL189-PL193
Both [D-Ala2,Glu4]Deltorphin and [D-Ala2,4'-I-Phe3,Glu4]Deltorphin are highly selective ligands for delta, relative to mu, opioid receptors. Radiolabeled [D-Ala2, 4'-125I-Phe3,Glu4]Deltorphin ([125I]Deltorphin) was prepared with a specific activity of 2200 Ci/mmol from [D-Ala2, 4'-NH2-Phe3, Glu4]Deltorphin through a diazonium salt intermediate. The inhibition of [125I]Deltorphin binding to rat brain membranes by ligands selective for mu, delta, and kappa opioid receptors is consistent with binding by the radioligand to a single site having the properties of a delta opioid receptor. The results of these studies are in good agreement with those obtained by structurally different delta opioid receptor ligands. The similarity between the delta receptor site labeled by [125I]Deltorphin and those labeled by other delta receptor agonists, in contrast to differences seen by in vivo studies of their analgesic effects, is discussed. 相似文献
66.
Purification and properties of a lytic enzyme from the cell wall of Chlorella ellipsoidea C-87 总被引:1,自引:0,他引:1
Cell wall lytic activity was detected in the culture medium and cell wall of 1AM Chlorella ellipsoidea C-87. The enzymes of both fractions had their highest activity at pH 5. The lytic activity bound to the cell wall consisted of a polysaccharide releasing enzyme, an exo-type enzyme releasing disaccharide, and glucosidase; but only the polysaccharide releasing enzyme was solubilized by lithium chloride. A polysaccharide releasing enzyme with a molecular weight around 40 kDa was isolated from the culture medium. Hemicellulose is degraded by the polysaccharide releasing enzyme, and the rigid wall by the exo-type enzyme. 相似文献
67.
Kazuhiro Nakamura Yasuhiro Goto Naoko Yoshie Yoshio Inoue 《International journal of biological macromolecules》1992,14(6):321-325
It was found that an optically active copolyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), denoted as P(3HB-co-3HV), is synthesized by Alcaligenes eutrophus H16 from several amino acids under various fermentation conditions. The optimum condition for the biosynthesis from one amino acid, threonine, was investigated and its biosynthetic pathway was discussed on the basis of the relation between the fermentation condition and the co-monomer composition of the produced polyesters. 相似文献
68.
ATP-dependent Sr2+ transport was examined in vitro using basolateral membrane (BLM) vesicles isolated from rat renal cortex to clarify the discrimination
mechanisms between strontium (Sr) and calcium (Ca) in renal tubules during reabsorption. ATP-dependent Sr2+ uptake and Ca2+ uptake were observed in renal BLM vesicles and were inhibited by vanadate. Hill plots indicate similar kinetic behavior for
Ca2+ and Sr2+ uptake. The apparentK
m andV
max of ATP-dependent Sr2+ uptake were both higher than those for Ca2+ uptake. ATP-dependent Sr2+ uptake by BLM vesicles diminished in the presence of 0.1 μM Ca2+ and was more markedly inhibited by 1 μM Ca2+. Hill plots of Sr2+ uptake data with and without 0.1 μM Ca2+ showed that the cooperative behavior of Sr2+ uptake was not changed by Ca2+. In the presence of 0.1 μM Ca2+, the affinity of the transport system for Sr2+ and the velocity of Sr2+ uptake in the BLM were both decreased. However, the rate of Ca2+ uptake was not diminished by Sr2+ concentrations of <1.6 μM. These results suggest that Ca2+ is preferentially transported in the renal cortex BLM when Ca2+ and Sr2+ are present at the same time. 相似文献
69.
Koji Sode Masahiro Tatara Haruko Takeyama J. Grant Burgess Tadashi Matsunaga 《Applied microbiology and biotechnology》1992,37(3):369-373
Summary Versatility of gene transfer by transconjugation in marine cyanobacteria was demonstrated. In this study, seven different marine cyanobacteria were used as recipient cells. First, transconjugation was carried out using the mobilizable transposon (Tn5) carrying plasmid pSUP1021. Transconjugants were observed in all marine cyanobacteria tested. Second, the broad-host-range vector pKT230 (IncQ) was tested for transconjugation. pKT230 has been successfully transferred in a marine cyanobacterium Synechococcus sp. NKBG15041C, and replicated as an autonomous replicon without alteration in the restriction enzyme pattern. A maximum transfer efficiency of 5.2 × 10–4 transconjugants/recipient cell was observed, when mating was performed on agar plates containing low salinity (0.015 m NaCl) medium. This is the first study to demonstrate gene transfer in marine cyanobacteria via transconjugation.
Correspondence to: K. Sode 相似文献
70.
A convenient and nonradioactive method for DNA hybridization tests termed the "Universal probe system" has been developed. This method is based on the principle of sandwich hybridization. This system consists of two single-stranded DNA probes (a primary probe and a biotin-labeled secondary probe). The primary probe is prepared from a chimeric phage-plasmid vector containing the complementary sequence to a target gene. The secondary probe has a sequence complementary to the vector portion of the primary probe and is labeled with biotin via the transamination reaction. An advantage of this method is that the single-stranded primary probe can be prepared with ease by using the chimeric phage-plasmid vector system, thereby avoiding tedious labeling of individually different probes. As the primary probe is not modified with biotin and other labels, it conserves the sequence to be hybridized with a target. Accordingly, the primary probe containing a relatively short hybridizing region (ca. 50 bp) can efficiently hybridize with the target. In fact, the universal probe is sensitive enough to detect a single-copy human gene on Southern blots. 相似文献