全文获取类型
收费全文 | 4421篇 |
免费 | 284篇 |
国内免费 | 15篇 |
出版年
2023年 | 11篇 |
2022年 | 43篇 |
2021年 | 92篇 |
2020年 | 72篇 |
2019年 | 81篇 |
2018年 | 123篇 |
2017年 | 107篇 |
2016年 | 140篇 |
2015年 | 267篇 |
2014年 | 287篇 |
2013年 | 321篇 |
2012年 | 369篇 |
2011年 | 361篇 |
2010年 | 252篇 |
2009年 | 194篇 |
2008年 | 267篇 |
2007年 | 266篇 |
2006年 | 208篇 |
2005年 | 209篇 |
2004年 | 193篇 |
2003年 | 181篇 |
2002年 | 151篇 |
2001年 | 57篇 |
2000年 | 55篇 |
1999年 | 45篇 |
1998年 | 32篇 |
1997年 | 23篇 |
1996年 | 15篇 |
1995年 | 15篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 21篇 |
1989年 | 12篇 |
1988年 | 22篇 |
1987年 | 18篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1973年 | 8篇 |
1972年 | 11篇 |
1971年 | 9篇 |
1970年 | 9篇 |
排序方式: 共有4720条查询结果,搜索用时 46 毫秒
21.
Hyung Suk Kim Karen M. Lyons Eiichi Saitoh Edwin A. Azen Oliver Smithies Nobuyo Maeda 《Mammalian genome》1993,4(1):3-14
We present the nucleotide sequences of four members of the six-member human salivary prolinerich protein (PRP) gene family. The four genes are PRB1 and PRB2, which encode basic PRPs, and PRB3 and PRB4, which encode glycosylated PRPs. Each PRB gene is approximately 4.0 kb in length and contains four exons, the third of which is entirely composed of 63-bp tandem repeats and encodes the proline-rich portion of the protein products. Exon 3 contains different numbers of tandem repeats in the different PRB genes. Variation in the numbers of these repeats is also responsible for length variations in different alleles of the PRB genes. We have determined a probable evolutionary history of the human PRP gene family by comparing the nucleotide sequences of the six PRP genes. The present-day six PRP loci probably evolved from a single ancestral gene by four sequential gene duplications, leading to six genes that fall into three subsets, each consisting of two genes. During this evolutionary process, multiple rearrangements and gene conversion occurred mainly in the region from the 3 end of IVS2 and the 3 end of exon 3. 相似文献
22.
Specimens of basidiomes and/or rhizomorphs ofArmillaria mellea complex and basidiomes ofRhodophyllus abortivus, developing on the same decaying stumps or stems of forest trees, were collected in three forests in Hokkaido. Normal basidiomes
ofR. abortivus were found near to, but free from, the rhizomorphs and/or basidiomes ofArmillaria, while abnormal basidiomes, as carpophoroid forms, were developed on the rhizomorphs ofArmillaria. Of three mycoparasiticArmillaria isolates found withR. abortivus, one was identified asA. gallica and two asA. jezoensis. The isolates ofR. abortivus showed excellent mycelial growth and rhizomorph formation on PDA. However, on MDA, RMDA and BMDA, they showed poor aerial
mycelia growth and no rhizomorphs. In the contrapositional cultures, the growth ofA. gallica was completely inhibited byR. abortivus on PDA but only slightly inhibited on MDA and RMDA. On the other hand, mutual inhibition at a distance was observed on BMDA.
The mycelial growth and rhizomorph formation inA. jezoensis were severely inhibited by the colony ofR. abortivus on PDA, but only slightly inhibited on MDA. On RMDA and BMDA, the colonies of twoArmillaria species andR. abortivus showed mutual inhibition at a distance and apparent rhizomorph formation by bothArmillaria species. 相似文献
23.
Summary The direct, lipase-catalyzed esterifications of glycerol-3-phosphate in an organic solvent system and in a solvent free system were carried out. In a solvent free system only, LPA synthesis could be achieved within the acceptable reaction time. Open reaction system was preferable to closed reaction system for LPA synthesis. Yield of LPA isolated by silica gel column chromatography was 32.3%. 相似文献
24.
Prostaglandin H Synthetase-Mediated Metabolism of Dopamine: Implication for Parkinson's Disease 总被引:2,自引:1,他引:1
† Michael B. Mattammal ‡§Randy Strong †Vijaya M. Lakshmi ¶Hyung D. Chung #Alan H. Stephenson 《Journal of neurochemistry》1995,64(4):1645-1654
Abstract: Differences in prostaglandin H synthetase (PHS) activity in the substantia nigra of age- and post-mortem interval-matched parkinsonian, Alzheimer's, and normal control brain tissue were assessed. Prostaglandin E2 (PGE2 , an index of PHS activity) was higher in substantia nigra of parkinsonian brain tissue than Alzheimer's or control tissue. Incubation of substantia nigra slices with arachidonic acid (AA) increased PGE2 synthesis. Dopamine stimulated PHS synthesis of PGE2 . [3 H]Dopamine was activated by PHS to electrophilic intermediate(s) that covalently bound to DNA, microtubulin protein, bovine serum albumin, and sulfhydryl reagents. When AA was replaced by hydrogen peroxide, PHS/H2 O2 -supported binding proceeded at rates similar to those observed with PHS/AA. Indomethacin and aspirin inhibited AA-mediated cooxidation of dopamine but not H2 O2 -mediated metabolism. PHS-mediated metabolism of dopamine was not affected by monoamine oxidase inhibitors. Substrate requirements and effects of specific inhibitors suggest cooxidation of dopamine is mediated by the hydroperoxidase activity of PHS. 32 P-postlabeling was used to detect dopamine-DNA adducts. PHS/AA activation of dopamine in the presence of DNA resulted in the formation of five dopamine-DNA adducts, i.e., 23, 43, 114, 70, and 270 amol/µg DNA. DNA adduct formation was PHS, AA, and dopamine dependent. PHS catalyzed cooxidation of dopamine in dopaminergic neuronal degeneration is discussed. 相似文献
25.
Acetylcholinesterase (AChE) purified from mouse brain was reconstituted in liposomes of a different charge, and the properties of liposome-associated AChE were investigated. Relative to the Km value (38.5 M) of AChE bound to a neutral liposome, the value of AChE reconstituted in a negatively-charged liposome decreased to 23.3 M, whereas that of AChE in a positively-charged liposome increased to 90.9 M. Additionally, AChE bound to a positively-charged liposome expressed a wider range of optimum pH than the enzyme in a negatively-charged liposome. In a stability study, it was found that soluble AChE was unstable at pH 5.5 and 7.4, while it was relatively stable at pH 10. Noteworthy, the immobilization of AChE to liposome enhanced the stability of soluble enzyme at acidic and neutral pH. Moreover, in the stabilization of the enzyme, a neutral liposome was more effective than charged liposomes, of which a positively-charged liposome was more effective than a negatively-charged liposome at acidic pH. Based on these results, it is proposed that while the Km value and the pH dependence of AChE activity are affected by the charge of liposome, the stability of AChE is determined mainly by a hydrophobic binding to a phospholipid membrane.This work was supported in part by Agency for Defense Development. 相似文献
26.
Phosphorescence and optically detected zero field magnetic resonance ( ODMR ) spectra are reported for a bromine atom-containing polynucleotide, poly(dA- br5dU ). The triplet state luminescence of poly(dA- br5dU ) is dominated by the phosphorescence of the bromouracil base which possesses sub-millisecond triplet lifetimes. Characteristic multiple slow passage ODMR transitions, which are observed in both br5dUrd and poly(dA- br5dU ), are assigned to the triplet state of bromouracil. In addition, an abnormally-perturbed adenine triplet state, which is not apparent in the phosphorescence spectrum of poly(dA- br5dU ), is detected and identified by its slow passage ODMR and amplitude-modulated phosphorescence microwave double resonance spectra. It is proposed that the perturbed adenine is a minor component of the polynucleotide structure which is present in regions of altered stacking induced by the high polarizability of the Br atom. 相似文献
27.
常绿杜鹃亚属Subgenus Hymenanthes是由K.Koch(1872)根据Blume(1826)建立的Genus Hymenanthes改级组合而成。但长期以来人们一直沿用了Maximowicz(1870)所建立的、后由Koehne(1893)修订过的Subgenus Eurhododendron这一亚属名称,直到最近D.F.Chamberlain(1978,1979,1982)对该亚属的名称才作了正式订正。 相似文献
28.
The loach embryos differing in age by 0.5 tau0 (tau0--duration of the mitotic cycle during the synchronous cleavage divisions) were combined in pairs at the stage of 4--8 blastomeres to elucidate the role of intercellular relationships in the preservation of cell division synchrony during cleavage. Following the incubation during 3 tau0 the mean value of interval between mitotic phases in the pairs of combined embryos somewhat decreased but this phenomenon cannot be considered as the proof of cell division synchronization due to the intercellular relationships since it was observed to the same extent in all groups of chimaeric embryos irrespective of the degree of fusion as well as in the control embryos. 相似文献
29.
Glutamine release from hindlimb and uptake by kidney in the acutely acidotic rat. 总被引:5,自引:3,他引:2
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The arteriovenous difference (release) for glutamine across the hindlimb increases significantly during acute HCl-induced acidosis. This additional amount release by muscle tissue can account for the extra glutamine taken up by the kidney. 相似文献
30.
An agar-diffusion method for determination of oleandomycin and tetracycline low levels in solutions of the drug combination was developed. The medhod may be used for investigation of oletetrin absorption and distribution in humans and animals. It provides high accuracy in separate determination of oleandomycin and tetracycline activity in solutions of the drugs at a ratio of 1 : 2. The same test-culture, Bac. subtilis, variant L2 is used for the assay of tetracycline and oleandomycin activity. The only differences are in the values of pH and the buffer solution and the standards. 相似文献