全文获取类型
收费全文 | 2494篇 |
免费 | 129篇 |
出版年
2023年 | 5篇 |
2022年 | 11篇 |
2021年 | 33篇 |
2020年 | 27篇 |
2019年 | 22篇 |
2018年 | 39篇 |
2017年 | 33篇 |
2016年 | 40篇 |
2015年 | 81篇 |
2014年 | 101篇 |
2013年 | 167篇 |
2012年 | 152篇 |
2011年 | 161篇 |
2010年 | 101篇 |
2009年 | 121篇 |
2008年 | 167篇 |
2007年 | 167篇 |
2006年 | 173篇 |
2005年 | 138篇 |
2004年 | 150篇 |
2003年 | 147篇 |
2002年 | 151篇 |
2001年 | 25篇 |
2000年 | 33篇 |
1999年 | 25篇 |
1998年 | 20篇 |
1997年 | 19篇 |
1996年 | 20篇 |
1995年 | 19篇 |
1994年 | 18篇 |
1993年 | 19篇 |
1992年 | 19篇 |
1991年 | 18篇 |
1990年 | 16篇 |
1989年 | 15篇 |
1988年 | 12篇 |
1987年 | 11篇 |
1986年 | 12篇 |
1985年 | 8篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 20篇 |
1979年 | 5篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有2623条查询结果,搜索用时 343 毫秒
31.
32.
Satoru Ohba Kiyoshi Kidouchi Toshiyuki Katoh 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1991,568(2)
A column-switching high-performance liquid chromatographic method, requiring no sample preparation apart from filtration, is described for quantification of urinary orotic acid, uracil and pseudouridine. The analyses were carried out using a reversed-phase octadecylsilane-bonded column for sample clean-up and a cation-exchange column for separation; 5–20 ]sml samples of urine were directly analysed, and more than 100 samples could be analysed consecutively. Each sample required only 30 min. Detection limits of these compounds were 5 pmol. Creatinine-related urinary uracil excretion was lowest in the newborn period (17.3 ± 14.4 μmol/g of creatinine). A patient with partial ornithine transcarbamylase deficiency and his mother usually excreted a high level of uracil during the period of normal orotic acid excretion and normal serum ammonia level. 相似文献
33.
The cephalosporinase of Citrobacter freundii GN346 is a class-C beta-lactamase comprising 361 amino acids. The substitution of the glutamic acid at position 219 in the enzyme by lysine was previously shown to broaden its substrate specificity to unfavorable substrates such as oxyimino cephalosporins [Tsukamoto, K., Ohno, R. & Sawai, T. (1990) J. Bacteriol. 172, 4348-4351]. To investigate the cause of this phenomenon, Glu219 was changed to glutamine, cysteine or tryptophan. All the resultant enzymes showed higher cefuroxime-hydrolytic activities than the wild type, the order of increasing cefuroxime-hydrolytic activity being as follows: Trp greater than Lys greater than Cys greater than Gln greater than Glu. The rate of hydrolysis of cefuroxime by the Trp219 enzyme was approximately 3 x 10(4) times that of the wild-type enzyme. The order of increasing cefuroxime hydrolysis was approximately proportional to the molecular volume of the amino acid substituted and independent of the ionic character of the amino acids. The cysteine residue at position 219 in the Cys219 enzyme allowed its complete reaction with an SH-blocking reagent, 4-chloromercuriphenylsulfonic acid. The modified enzyme with the bulkier residue showed a 45% higher cefuroxime-hydrolytic activity than the untreated enzyme. These results suggested that extension of the substrate spectrum may be attributed to alteration in the configuration of the enzyme around position 219. 相似文献
34.
T Suzuki H Sasano T Sawai J I Mason H Nagura 《The journal of histochemistry and cytochemistry》1992,40(7):903-908
Cytochrome P-45017 alpha catalyzes both 17 alpha-hydroxylation and 17,20-side-chain cleavage in steroidogenesis and lies at a key branch point in the pathways of steroid hormone biosynthesis. To obtain information on the precise localization of P-45017 alpha in swine testis, ovary, and adrenal, we undertook the simultaneous detection of P-45017 alpha mRNA and protein by combining immunohistochemistry with in situ hybridization. In situ hybridization was performed on 4% paraformaldehyde-fixed, paraffin-embedded sections by employing either a 39-base oligomer or a cDNA insert (1.7 KB) of porcine testis P-45017 alpha as DNA probe. Immunohistochemical study was performed by employing anti-P-45017 alpha. Hybridization signals were obtained in Leydig cells of the testis, theca interna of the ovarian follicle, and zona fasciculata reticularis cells of the adrenal cortex. Oligonucleotide probing yielded lower background signal than the cDNA probe. No specific signals were obtained in seminiferous tubules of the testis, medulla, and zona glomerulosa of the adrenal, and in membrana granulosa and interstitial cells of the ovary. Hybridization signals were obtained in the cells where immunoreactivity of the enzyme was observed by immunohistochemistry, except for some Leydig cells of the testis and theca interna cells of the ovary in which only immunoreactivity but not hybridization signal was observed. The present study provided detailed information about the precise cellular localization of P-45017 alpha expression at both the protein and mRNA levels in swine adrenal glands and gonads. This approach of simultaneous immunohistochemistry and in situ hybridization analysis of steroidogenic enzymes can be applied in the future to tissues exhibiting abnormal steroid metabolism and should contribute to a better understanding of steroidogenesis. 相似文献
35.
About half the activity level of DNA ligase I in cycling human lymphoblastoid cells (Raji and Akata) remained in the cells arrested at G1 by a 4-day treatment with 1.5% dimethyl sulfoxide (DMSO), and one-third the enzyme activity in actively growing promyelocytic leukemia cells HL-60 was detected in the terminally differentiated cells after DMSO-treatment. In contrast, DNA ligase I mRNA was negligible in the G1-arrested Raji and differentiated HL-60 cells. The steady-state mRNA level was increased 9 h after release from DMSO in the G1-arrested Raji cells and reached a maximum at 18 h. These results indicate that gene expression of human DNA ligase I, but not activity level of the enzyme, is closely correlated with activity of cell proliferation. 相似文献
36.
Hiroaki Sawai 《Journal of molecular evolution》1981,17(2):108-109
Summary Chemical polymerization of adenosine-5-phosphorimidazolide was conducted in the presence of oligouridylate templates. Oligo U with chain length more than eight served as a template and facilitated oligoadenylate formation. No template activity was observed when oligo U up to a hexamer was used. These results correlate with thermal transition temperatures of oligo U-pA complexes. 相似文献
37.
The activity of a neutral protease is increased in soluble fractions from the intestine of rats after a shift from a protein-free to a casein mash and an injection of triiodothyronine. The increased activity is prevented by the administration of cycloheximide. The time curve of the response of the protease activity in intestine is similar to that of liver DNA synthesis after a shift to 50% casein and triiodothyronine. 相似文献
38.
2,2,2-trichloroethyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranoside (9) was synthesized in 6 steps from the readily available 1,3,4,6-tetra-O-acetyl-2-deoxy-2-phthalimido-β-d-glucopyranose in 25% overall yield by employing the stannyl method for the regioselective activation of hydroxyl groups. Dibenzyl ether 9 was then glycosylated with appropriate glycosyl donors to afford lactosamine and chitobiose derivatives in good yield. 相似文献
39.
A lactosaminyl donor, 3,6-di-O-acetyl-2-deoxy-2-phthalimido-4-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-β-d- glucopyranosyl chloride, was synthesized in 10 steps, starting from 1,3,4,6-tetra-O-acetyl-2-deoxy-2-phthalimido-β-d-glucopyranose. Benzyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-d-glucopyranoside was prepared by regioselective benzylation at the primary hydroxyl group by the stannyl method, and was used as a key intermediate. 相似文献
40.