全文获取类型
收费全文 | 8692篇 |
免费 | 630篇 |
国内免费 | 5篇 |
出版年
2023年 | 38篇 |
2022年 | 81篇 |
2021年 | 200篇 |
2020年 | 132篇 |
2019年 | 128篇 |
2018年 | 185篇 |
2017年 | 150篇 |
2016年 | 287篇 |
2015年 | 411篇 |
2014年 | 472篇 |
2013年 | 581篇 |
2012年 | 708篇 |
2011年 | 728篇 |
2010年 | 454篇 |
2009年 | 389篇 |
2008年 | 504篇 |
2007年 | 527篇 |
2006年 | 516篇 |
2005年 | 424篇 |
2004年 | 388篇 |
2003年 | 313篇 |
2002年 | 338篇 |
2001年 | 82篇 |
2000年 | 60篇 |
1999年 | 62篇 |
1998年 | 95篇 |
1997年 | 40篇 |
1996年 | 54篇 |
1995年 | 53篇 |
1994年 | 51篇 |
1993年 | 48篇 |
1992年 | 46篇 |
1991年 | 46篇 |
1990年 | 36篇 |
1989年 | 42篇 |
1988年 | 35篇 |
1987年 | 47篇 |
1986年 | 32篇 |
1985年 | 42篇 |
1984年 | 37篇 |
1983年 | 48篇 |
1982年 | 37篇 |
1981年 | 40篇 |
1980年 | 25篇 |
1979年 | 24篇 |
1978年 | 20篇 |
1977年 | 36篇 |
1976年 | 22篇 |
1975年 | 21篇 |
1973年 | 19篇 |
排序方式: 共有9327条查询结果,搜索用时 15 毫秒
81.
The Lys residues in the 75-residue Ca2+-binding protein calbindin D9k were reductively methylated with13C-enriched formaldehyde. The possible structural effects resulting from the chemical modification were critically investigated by comparing two-dimensional NMR spectra and the exchange rates of some of the amide protons of the native and the modified protein. Our results show that the protein retains its structure even though 10 Lys out of a total of 75 amino acid residues were modified. In the Ca2+- and apo-forms of the protein, the13C-methylated Lys residues can be detected with high sensitivity and resolution using two-dimensional (1H,13C)-heteronuclear multiple quantum coherence (HMQC) NMR spectroscopy. ThepKa values of the individual Lys residues in Ca2+-calbindin D9k and apo-calbindin D9k were obtained by combiningpH titration experiments and (1H,13C)-HMQC NMR spectroscopy. Each Lys residue in the Ca2+- and apo-forms of calbindin D9k has a uniquepKa value. The LyspKa values in the calcium protein range from 9.3 to 10.9, while those in the apo-protein vary between 9.7 and 10.7. Although apo-calbindin D9k has a very similar structure compared to Ca2+-calbindin D9k, the removal of two Ca2+ ions from the protein leads to an increase of thepKa values of the Lys residues. 相似文献
82.
Mariam Lebbadi Antonio Gálvez Eva Valdivia Manuel Martínez-Blueno Mercedes Maqueda 《Archives of microbiology》1994,162(1-2):98-102
Three antibiotic peptides with amoebolytic activity have been purified from culture supernatants of Bacillus licheniformis M-4 (amoebicins m4-A, m4-B, and m4-C). They were hydrophilic peptides consisting of six different amino acids (Asp, Glu, Ser, Thr, Pro, Tyr). Their molecular weights ranged from 3,000 to 3,200. Purified amoebicins were active against human pathogenic and non-pathogenic strains of Naegleria. They also showed a broad antifungal spectrum, but a narrow antibacterial activity.Abbreviations (TFA)
Trifluoroacetic acid 相似文献
83.
Tova Rahn Martin Ridderstrle Hans Tornqvist Vincent Manganiello Gudrun Fredrikson Per Belfrage Eva Degerman 《FEBS letters》1994,350(2-3):314-318
Incubation of rat adipocytes with wortmannin, a potent and selective phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor, completely blocked the antilipolytic action of insulin (IC50≈ 100 nM), the insulin-induced activation and phosphorylation of cGMP-inhibited cAMP phosphodiesterase (cGI-PDE) as well as the activation of the insulin-stimulated cGI-PDE kinase (IC50≈ 10–30 nM). No direct effects of the inhibitor on the insulin-stimulated cGI-PDE kinase, the cGI-PDE and the hormone-sensitive lipase were observed. These data suggest that activation of PI 3-kinase upstream of the insulin-stimulated cGI-PDE kinase in the antilipolytic insulin signalchain has an essential role for insulin-induced cGI-PDE activation/ phosphorylation and anti-lipolysis. 相似文献
84.
85.
A heat-shock promoter fusion to the Ac transposase gene drives inducible transposition of a Ds element during Arabidopsis embryo development 总被引:1,自引:0,他引:1
Lluis Balcells Eva Sundberg George Coupland 《The Plant journal : for cell and molecular biology》1994,5(5):755-764
A heat-shock promoter fusion to the Ac transposase gene (hs::TPase) was constructed and introduced into Arabidopsis. In five transformants containing the fusion the abundance of transposase mRNA increased approximately 120-fold on exposure to high temperatures. Hybrid plants containing hs::TPase and a Ds element inserted in a streptomycin resistance gene (Ds::SPT) were made and these plants were self-fertilized either after heat shocking at different stages in development or without exposure to high temperature. The progeny of these plants were sown on streptomycin-containing medium and the frequency with which variegated or streptomycin-resistant (strepR) seedlings occurred was used as an indication of the frequency of Ds excision. Very few of the progeny of plants not exposed to heat shock or of those heat shocked only during vegetative development were variegated or strepR. However, plants that were heat shocked after the appearance of flower buds and during seed development produced high frequencies (approaching 100%) of variegated, but very few strepR, progeny. Furthermore, when variegated seedlings were grown to maturity and self-fertilized without further exposure to heat shock then strepR seedlings often occurred at high frequency among their progeny. Southern analysis indicated that the majority of these strepR plants contained a transposed Ds at a new location. These data indicate that in response to heat shock Ds excision frequently occurs in embryonic cells which ultimately give rise to the gametes, as well as in cells of the developing cotyledons. The importance of an inducible transposon system for transposon tagging is discussed. 相似文献
86.
87.
Numerous studies have demonstrated that several diseases and stress conditions are associated with changes in the levels of zinc in the blood plasma and cellular elements. In this research the association between serum zinc concentrations and other hematic parameters of diagnostic interest has been evaluated. Quantitative determinations of zinc, total plasmatic proteins, albumin, hemoglobin and calculation of mean corpuscular volume were performed on blood samples from 58 males aged 20–61 years. Concentrations measured in our sample are comparable with reference values. Statistically significant correlation coefficients were found between age and albumin (r = - 0.562, P < 0.001), serum zinc and albumin (r = 0.328, P < 0.05), serum zinc and hemoglobin (r = 0.291, P < 0.05), and total plasmatic proteins and albumin (r = 0.463, P < 0.001). These correlation coefficients were significant even after adjustment for age effect. The determination of serum zinc concentration may be useful in the assessment of clinical scenarios. Particularly, it may provide additional information for the diagnosis of specific pathologies, such as hepatic malfunctions. It could also be useful in the identification of different stages of anemia. 相似文献
88.
Calvin cycle genes in Nitrobacter vulgaris T3 总被引:1,自引:0,他引:1
Maren Strecker Eva Sickinger Robert S. English Jessup M. Shively 《FEMS microbiology letters》1994,120(1-2):45-50
Abstract The genes encoding the Calvin cycle enzymes of Nitrobacter vulgaris T3 are found as two separate clusters on the chromosome. One cluster contains the genes for the large and small subunits of ribulose-1,5-biphosphate carboxylase/oxygenase (RuBisCO), glyceraldehyde-3-phosphate dehydrogenase, and one encoding a regulatory protein of the LysR family. The other cluster contains the genes for fructose-1,6-/sedoheptulose-1,7-bisphosphatase, phosphoribulokinase, and fructose-1,6-/sedoheptulose-1,7-biphosphate aldolase. With the exception of the LysR-like gene, the genes in each cluster are apparently transcribed in the same direction. The deduced amino acid sequence of both the large and small subunits of RuBisCO are most similar (84–86%) to those of Thiobacillus ferrooxidans and Chromatium vinosum . The deduced sequences of phosphoribulokinase and fructose/sedoheptulose bisphosphatase are 67–73 aand 44–46% similar to those reported for other autotrophic bacteria, respectively. 相似文献
89.
Summary We used in vitro growth inhibition assays to demonstrate that synthetic cecropin protein has potent activity against a range of plant pathogenic bacteria. We then prepared transgenic tobacco plants which express cecropin mRNA and protein. We have used Pseudomonas syringae pv tabaci infection of these transgenic tobacco as a model system to evaluate whether the plants which express cecropin protein also have increased tolerance to infection. We found no dramatic difference in disease response between plants which are expressing cecropin protein and control plants which were derived from the transformation with a binary vector which did not carry the gene encoding cecropin protein. 相似文献
90.
David J. Munroe Melanie Haas Eva Bric Tania Whitton Hiroyuki Aburatani Kent Hunter David Ward David E. Housman 《Genomics》1994,19(3)
A significant issue in the analysis of any genomic DNA segment is the generation of a unique set of short single-copy sequences that are representative of that region. In this report we describe a novel technique, IRE-bubble PCR, which was designed to amplify the human DNA content of somatic cell hybrids, YACs, cosmids, and λ phage and result in greater complexity and representation than standard inter-IRE, PCR. Here we demonstrate that IRE-bubble PCR is species specific and that it results in the generation of a product that is at least 10-fold more complex and representative than that produced by standard inter-IRE PCR. In addition, we have addressed the factors that contribute to the representation of the IRE-bubble PCR product and show how they may be used to further increase the complexity of this reaction. Finally, we have illustrated how the complexity and distribution of products generated by IRE-bubble PCR can be exploited and applied to FISH mapping and "chromosome painting" as well as to the generation of STSs targeted to specific chromosomal or subchromosomal regions. 相似文献