全文获取类型
收费全文 | 1691篇 |
免费 | 86篇 |
出版年
2022年 | 7篇 |
2020年 | 9篇 |
2019年 | 10篇 |
2018年 | 18篇 |
2017年 | 21篇 |
2016年 | 29篇 |
2015年 | 34篇 |
2014年 | 43篇 |
2013年 | 114篇 |
2012年 | 76篇 |
2011年 | 83篇 |
2010年 | 37篇 |
2009年 | 58篇 |
2008年 | 90篇 |
2007年 | 67篇 |
2006年 | 101篇 |
2005年 | 95篇 |
2004年 | 85篇 |
2003年 | 100篇 |
2002年 | 99篇 |
2001年 | 27篇 |
2000年 | 33篇 |
1999年 | 33篇 |
1998年 | 39篇 |
1997年 | 29篇 |
1996年 | 23篇 |
1995年 | 28篇 |
1994年 | 26篇 |
1993年 | 20篇 |
1992年 | 17篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 16篇 |
1985年 | 10篇 |
1984年 | 17篇 |
1983年 | 14篇 |
1982年 | 24篇 |
1981年 | 26篇 |
1980年 | 15篇 |
1979年 | 21篇 |
1978年 | 13篇 |
1977年 | 9篇 |
1976年 | 18篇 |
1975年 | 7篇 |
1974年 | 15篇 |
1973年 | 12篇 |
1972年 | 8篇 |
排序方式: 共有1777条查询结果,搜索用时 15 毫秒
1.
Yusuke Nakamura Michio Ogawa Takahiro Nishide Mitsuru Emi Goro Kosaki Seiichi Himeno Kenichi Matsubara 《Gene》1984,28(2):263-270
The nucleotide sequences of the cloned human salivary and pancreatic α-amylase cDNAs correspond to the continuous mRNA sequences of 1768 and 1566 nucleotides, respectively. These include all of the amino acid coding regions. Salivary cDNA contains 200 bp in the 5′-noncoding region and 32 in the 3′-noncoding region. Pancreatic cDNA contains 3 and 27 bp of 5′- and 3′-noncoding regions, respectively. The nucleotide sequence humology of the two cDNAs is 96% in the coding region, and the predicted amino acid sequences are 94% homologous.Comparison of the sequences of human α-amylase cDNAs with those previously obtained for mouse α-amylase genes (Hagenbuchle et al., 1980; Schibler et al., 1982) showed the possibility of gene conversion between the two genes of human α-amylase. 相似文献
2.
The activities of glutamic oxaloacetic transaminase and Ca++ ion-activated ATPase of muscle in the adult rats fed a protein-free diet for 8, 16 and 24 days were measured in order to clarify their metabolic responses with respect to reserve proteins. It was found that these enzyme activities, or presumably their enzyme proteins, decreased at the stage as early as the 8th day of protein depletion following the same pattern as seen in reserve proteins. Their responses, particularly those in unit activity, were somewhat different from each other. The metabolic significance of those responses was discussed in relation to protein nutrition. 相似文献
3.
4.
Feedbacks between nutrient cycling and vegetation predict plant species coexistence and invasion 总被引:5,自引:0,他引:5
To investigate the role of species‐specific litter decomposability in determining plant community structure, we constructed a theoretical model of the codevelopmental dynamics of soil and vegetation. This model incorporates feedback between vegetation and soil. Vegetation changes the nutrient conditions of soil by affecting mineralization processes; soil, in turn, has an impact on plant community structure. The model shows that species‐level traits (decomposability, reproductive and competitive abilities) determine whether litter feedback effects are positive or negative. The feedback determines community‐level properties, such as species composition and community stability against invasion. The model predicts that positive feedback may generate multiple alternative steady states of the plant community, which differ in species richness or community composition. In such cases, the realized state is determined by initial abundance of co‐occurring species. Further, the model shows that the importance of species‐level traits depends on environmental conditions such as system fertility. 相似文献
5.
The rate and period of DNA synthesis during meiotic prophasewere examined using lily microsporocytes. Meiocytes at the earlyleptotene stage were cultured for discrete periods in the presenceof inhibitors of DNA synthesis, deoxyadenosine and nalidixicacid. Deoxyadenosine, which arrests meiotic development at theearly zygotene stage, markedly suppressed DNA synthesis to 35%of control at 2 mM. Nalidixic acid simply reduced the rate ofDNA synthesis, resulting in prolongation of the synthetic period.The relevance of DNA synthesis to meiotic development is discussed. (Received January 12, 1987; Accepted May 7, 1987) 相似文献
6.
Characterization of Microtubule-Associated Protein 2 from Mouse Brain and Its Localization in the Cerebellar Cortex 总被引:3,自引:2,他引:1
Michio Niinobe Nobuaki Maeda Hidetoshi Ino Katsuhiko Mikoshiba 《Journal of neurochemistry》1988,51(4):1132-1139
Microtubule-associated protein (MAP) 2 was purified from the microtubule fraction of mouse brain by heat treatment and BioGel A-5m gel filtration. The purified preparation showed a single protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis using both a gradient gel (3.75-12.5%) and a low-percentage gel (5%), a finding indicating that MAP2B was absent under the conditions used. Amino acid analysis revealed that mouse MAP2 was an acidic protein with an isoelectric point (pI 4.5) and amino acid composition similar to those of porcine brain MAP2. Immunoblot analysis indicated that the antigens that reacted with MAP2 antiserum were present in large quantities in mouse brain. However, we also found a weak reaction in various tissues other than brain, and the major antigens involved were recognized to be common molecular species with the same molecular mass, 162 and 170 kilodaltons. Using antiserum against mouse brain MAP2, the developmental localization patterns of MAP2 in the mouse cerebellar cortex were studied by immunohistochemistry. MAP2 was mainly localized in the neuronal cells throughout development, with the expression in Purkinje cell dendrites being especially remarkable in the growth of arborization from postnatal day 3 to day 20. At the mature stage, the reaction was strong in the dendritic tree but very weak in the proximal dendrites and cell bodies. 相似文献
7.
Antipsychotics represent high affinity for sigma receptors and sigma-like drugs often have the psychotomimetic properties. Besides, the receptors are unevenly distributed in human brain. These findings suggest that sigma receptors might be involved in the pathophysiology of schizophrenia. Sigma receptors in rat and human brain were measured with [3H]-1, 3, di-o-tolylguanidine (DTG) and non-specific binding of [3H]DTG was determined in the presence of 10–5M haloperidol. Monovalent and divalent cations strongly inhibited [3H]DTG binding. Glutamate, aspartate and glycine also decreased the binding to human cerebral membranes. With post-mortem brain samples from 12 schizophrenics and 10 controls, sigma receptors were measured in 17 areas of cerebral cortex. Sigma receptors binding showed the regional differences in the cortex, but no significant differences between schizophrenics and controls were observed except the superior parietal cortex where the binding significantly increased in the schizophrenic group. These results suggest that sigma receptors in cerebral cortices might not be directly concerned with the pathophysiological role in schizophrenia.Dedicated to Dr. Morris Aprison. Received too late for publication in special issue. 相似文献
8.
The Sau3A DNA family consists of unique alphoid human repetitive DNA which is prone to be excised from the chromosomes and exhibits restriction fragment length polymorphism. We studied the chromosomal localization of the DNA by in situ hybridization using cultured normal human lymphocytes. Under standard hybridization conditions, the sequence hybridized with the centromeric regions of chromosomes 1, 2, 4, 11, 15, 17, 18, 19 and X, but under high stringency hybridization conditions, it hybridized with the centromeric regions of chromosomes 1, 17 and X, and particularly chromosome 11. Based on these results, we discuss the evolutionary relationship among the sequences of the Sau3A DNA family. 相似文献
9.
A Z-DNA binding protein isolated from D. radiodurans 总被引:2,自引:0,他引:2
S Kitayama O Matsumura S Masuda 《Biochemical and biophysical research communications》1985,130(3):1294-1300
A DNA binding protein isolated from D. radiodurans changes CD-spectrum of Z-form poly(dG-dC) X poly(dG-dC). We have found that a positive band at 268 nm is converted close to that of B-form in the presence of the protein. Concomitantly, a negative band at 295 nm shown by Z-form poly(dG-dC) X poly (dG-dC) was weakened by the protein but not by albumin. Such changes in the CD-spectra were not induced by the protein and by albumin when they were mixed with Z- or B-form poly(dG-me5dC) X poly(dG-me5dC) or with B-form poly(dG-dC) X poly(dG-dC). The protein formed a complex preferentially with Z-form poly(dG-dC) X poly(dG-dC). 相似文献
10.
An acidic α-D-mannosidase has been isolated from the culture filtrate of a wood-rotting Basidiomycete, Pycnoporus sanguineus and the molecular and enzymatic properties of the enzyme determined. The extracellular mannosidase was homogeneous on PAGE at pH 9.4. The Mr as determined by SDS-polyacrylamide disc gel electrophoresis was 64000, and the pI was pH 4.7 using electrofocusing. The purified enzyme had a pH optimum of 4.5 with Baker's yeast mannan and had no activity towards p-nitrophenyl-α-mannoside. The Km and kcat values for Manα1-2Man at pH 4.5 and 30° were 0.9 mM and 1.9 sec. the enzyme had no activity towards Manα1-3Manα1-2Man, and it cleaved specifically the 1,2-α-linked side chain of yeast α-mannan, producing free α-D-mannose. 相似文献