全文获取类型
收费全文 | 6964篇 |
免费 | 386篇 |
国内免费 | 1288篇 |
出版年
2024年 | 49篇 |
2023年 | 159篇 |
2022年 | 204篇 |
2021年 | 230篇 |
2020年 | 215篇 |
2019年 | 287篇 |
2018年 | 312篇 |
2017年 | 203篇 |
2016年 | 157篇 |
2015年 | 170篇 |
2014年 | 442篇 |
2013年 | 511篇 |
2012年 | 300篇 |
2011年 | 409篇 |
2010年 | 334篇 |
2009年 | 356篇 |
2008年 | 356篇 |
2007年 | 449篇 |
2006年 | 336篇 |
2005年 | 274篇 |
2004年 | 186篇 |
2003年 | 201篇 |
2002年 | 165篇 |
2001年 | 136篇 |
2000年 | 121篇 |
1999年 | 93篇 |
1998年 | 73篇 |
1997年 | 70篇 |
1996年 | 76篇 |
1995年 | 64篇 |
1994年 | 52篇 |
1993年 | 43篇 |
1992年 | 46篇 |
1991年 | 76篇 |
1990年 | 33篇 |
1989年 | 40篇 |
1988年 | 31篇 |
1985年 | 76篇 |
1984年 | 149篇 |
1983年 | 124篇 |
1982年 | 148篇 |
1981年 | 104篇 |
1980年 | 134篇 |
1979年 | 132篇 |
1978年 | 99篇 |
1977年 | 104篇 |
1976年 | 71篇 |
1975年 | 50篇 |
1974年 | 54篇 |
1973年 | 44篇 |
排序方式: 共有8638条查询结果,搜索用时 31 毫秒
231.
A Ziegelhoffer M B Anand-Srivastava R L Khandelwal N S Dhalla 《Biochemical and biophysical research communications》1979,89(4):1073-1081
The sarcolemmal membrane obtained from rat heart by hypotonic shock-LiBr treatment method was found to incorporate 32P from [γ-32P] ATP in the absence and presence of cyclic AMP and protein kinase. The phosphorylated membrane showed an increase in Ca2+ ATPase and Mg2+ ATPase activities without any changes in Na+K+ ATPase activity. The observed increase in ATPase activity was found to be associated with an increase in Vmax value of the reaction whereas Ka value for was not altered. These results provide information concerning biochemical mechanism for increased calcium entry due to hormones which are known to elevate cyclic AMP levels in myocardium and produce a positive inotropic effect. 相似文献
232.
R Kobayashi M Tawata H Hidaka 《Biochemical and biophysical research communications》1979,88(3):1037-1045
Agents such as N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), and its derivatives, chlorpromazine and amitriptyline that interact with calcium-regulated modulator protein were found to inhibit not only Ca2+ dependent cyclic nucleotide phosphodiesterase but also Ca2+-Mg2+-ATPase of human erythrocyte ghosts. I50 values of modulator interacting agents for testis modulator-activated, brain modulator-activated and erythrocyte modulator-activated-ATPase are indistinguishable. However, I50 of W-7 for troponin C-activated-ATPase is lower than that for modulator-activated ATPase. The specificity of these agents toward modulator-related enzyme reaction is also shown by the negative effect on modulator-unrelated enzyme system such as erythrocyte ghost protein kinase and Mg2+-ATPase. These agents provide a useful tool for elucidating the physiological role of modulator. 相似文献
233.
Measurements of proton translocation in CF1-depleted, N, N′-dicyclohexylcarbodiimide-resealed broken chloroplasts were made under different light intensities. Kinetic analysis of the data shows that the outward leakage of accumulated protons through CF0 is still dependent on light intensity with a first-order rate constant equal to mR0, where R0 is the initial rate of proton uptake which normally increases with light intensity and m is a characteristic constant which is independent of proton gradient and light intensity. Measurements of proton translocation in these modified chloroplasts cross-linked with glutaraldehyde under illumination and in the dark respectively suggest that the light-dependent proton leakage through CF0 is regulated by conformation change in the membrane. It is proposed that the ovserved regulation of proton leakage through the CF1.CF0 complex in native chloroplasts is for optimizing the steady state synthesis of ATP under different light intensities. 相似文献
234.
235.
236.
237.
A procedure is described that enables use of the p-phenylphenol color reaction to determine acetaldehyde in the presence of formaldehyde. The sample is first treated with an acidic 2,4-pentanedione reagent, which selectively removes formaldehyde. The method is applicable to blochemical reactions using tissue preparations. 相似文献
238.
Nonallelic histone gene clusters of individual sea urchins (Lytechinus pictus): mapping of homologies in coding and spacer DNA 总被引:5,自引:0,他引:5
The linear arrangement and lengths of the spacers and coding regions in the two nonallelic histone gene variant clusters of L. pictus are remarkably homologous by R loop analysis and are similar in general topography to the histone gene repeat units of other sea urchins examined to date. No interventing sequences were detected. The coding regions of these two histone gene variants share considerable sequence homology; however, there are areas of nonhomology in every spacer region and the lengths of the nonhomologous spacers between the H2A and H1 genes are not the same for the two repeat unit classes (inter-gene heterogeneity). Combining length measurements obtained with both R loops and heteroduplexes suggests that the DNA sequences of the analogous leader regions for the two H1 mRNAs are nonhomologous. Similar observations were made for the H4 leader sequences, as well as the trailer region on H2B. S. purpuratus spacer DNA segments share little sequence homology with L. pictus; however, the analgous coding (and possibly flanking) regions have conserved their sequences. The various coding and spacer regions within a repeat unit do not share DNA sequences. Thus certain areas in the sea urchin histone gene repeat units have been highly conserved during evolution, while other areas have been allowed to undergo considerable sequence change not only between species but within a species. 相似文献
239.
Characterization of cross-reacting antigens on the Epstein-Barr virus envelope and plasma membranes of producer cells. 总被引:14,自引:0,他引:14
D A Thorley-Lawson 《Cell》1979,16(1):33-42
A rabbit antiserum has been prepared against the B95-8 transforming strain of EBV. The antiserum has a high virus neutralizing titer (approximately 1:1000) against both the marmoset B95-8 EBV and the human P3HR-1 EBV. The neutralizing antibodies may be absorbed completely with EBV producer cell lines, but not with nonproducer cell lines or producer cell lines treated with phosphonoacetic acid (PAA) so as to be nonproducer. After repeated absorption with PAA-treated B95-8, the serum remains reactive with the membranes of producer cell lines as judged by immunofluorescence or the 125I--Staphylococcal protein A radioimmunoassay. Thus the neutralizing antigens are expressed on the membranes of producer cell lines and may be purified from this source using the serum and 125I--Staph A binding as an assay. The ability of the serum to differentiate between producer and nonproducer cells by means of cell surface determinants has been exploited to achieve a separation of these two populations from the same culture. Immunoprecipitation by the protein A technique shows that the serum recognizes two polypeptides from producer cells of approximate molecular weights 150,000 and 75,000. 相似文献
240.
This paper describes a highly specific method for determining urinary 17-hydroxycorticosteroids, which has been developed by (i) changing the composition of the Porter-Silber reagent and (ii) removing contaminants interfering with the color reaction by addition of sodium bisulfite to β-glucuronidase-hydrolyzed urine before extraction with solvent. For a reference method the Norymberski-Riondel (J. K. Norymberski and A. Riondel 1970, Biochem. J. 120, 493–498) gas chromatography (glc) was used: Correlation coefficient between the present method and GLC = 0.988, deviation from the theoretical regression LINE = 6.8%, and coefficient of SIMILARITY = 0.56. These results are much better than those obtained by I. Ernest, B. Håkansson, J. Lehmann, and B. Sjögren (1964, Acta Endocrinol. 46, 552–562) for the original Porter-Silber method in comparison with the chromatographic measurement of grouped and individual steroids. 相似文献