全文获取类型
收费全文 | 6835篇 |
免费 | 321篇 |
国内免费 | 159篇 |
出版年
2023年 | 59篇 |
2022年 | 87篇 |
2021年 | 98篇 |
2020年 | 106篇 |
2019年 | 170篇 |
2018年 | 184篇 |
2017年 | 123篇 |
2016年 | 126篇 |
2015年 | 158篇 |
2014年 | 361篇 |
2013年 | 450篇 |
2012年 | 245篇 |
2011年 | 354篇 |
2010年 | 279篇 |
2009年 | 399篇 |
2008年 | 365篇 |
2007年 | 386篇 |
2006年 | 306篇 |
2005年 | 357篇 |
2004年 | 248篇 |
2003年 | 249篇 |
2002年 | 221篇 |
2001年 | 123篇 |
2000年 | 120篇 |
1999年 | 124篇 |
1998年 | 135篇 |
1997年 | 97篇 |
1996年 | 85篇 |
1995年 | 104篇 |
1994年 | 90篇 |
1993年 | 76篇 |
1992年 | 90篇 |
1991年 | 55篇 |
1990年 | 52篇 |
1989年 | 51篇 |
1988年 | 51篇 |
1987年 | 46篇 |
1986年 | 29篇 |
1985年 | 55篇 |
1984年 | 114篇 |
1983年 | 78篇 |
1982年 | 60篇 |
1981年 | 65篇 |
1980年 | 67篇 |
1979年 | 62篇 |
1978年 | 34篇 |
1977年 | 29篇 |
1976年 | 26篇 |
1975年 | 19篇 |
1974年 | 20篇 |
排序方式: 共有7315条查询结果,搜索用时 15 毫秒
51.
52.
Alpha 1- and beta 2-adrenergic receptors co-expressed on cloned MDCK cells are distinct glycoproteins 总被引:2,自引:0,他引:2
K E Meier D R Sternfeld P A Insel 《Biochemical and biophysical research communications》1984,118(1):73-81
We have explored the molecular differences between alpha 1- and beta 2-adrenergic receptors that are co-expressed by a clonally-derived cell line, Madin-Darby canine kidney clone D (MDCK-D). MDCK-D membranes were pre-labeled with selective alpha 1- and beta-adrenergic radioligands and were then solubilized with the non-ionic detergent digitonin. Solubilized alpha 1- and beta 2-adrenergic receptors were retained by immobilized wheat germ agglutinin and were eluted following addition of N-acetyl-D-glucosamine or sialic acid. Both receptors were also retained by immobilized Limax flavus lectin, a sialic acid-binding lectin. Lectins that were specific for N-acetyl-D-glucosamine residues did not bind to these receptors. These results indicate that both alpha 1 and beta 2 receptors are sialylated glycoproteins. The solubilized alpha 1- and beta 2-adrenergic receptors migrated with different elution profiles from an Ultragel AcA 34 column. The apparent molecular sizes of the digitonin-receptor complexes were 68A for the alpha 1 receptor and 55A for the beta 2 receptor. These results show that alpha 1- and beta 2-adrenergic receptors can be present on the same cell as distinct sialic acid-containing glycoproteins. 相似文献
53.
Yohei Hashimoto Hiroyuki Ishizone Midori Moriyasu Kazuko Kawanishi Atsushi Kato Masaru Ogura 《Phytochemistry》1984,23(8):1807-1808
Three oleanane triterpenes were isolated from the roots of Periandra dulcis,and identified as 3β-hydroxy-25-al-olean-18-en-30-oic acid (periandric acid I), 3β-hydroxy-25-al-olean-12-en-30-oic acid (periandric acid II) and 3-oxo-25-hydroxy-olean-12-en-30-oic acid. The former two compounds (periandric acids I and II) were identical with the aglycones obtained by hydrolysis of periandrin I and II, respectively and the latter one was a new triterpene. 相似文献
54.
H. Ichikawa A. Hirai T. Katayama 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1986,72(3):353-358
Summary Relationships in a wide range of Oryza species (13 species) were analyzed using the large subunits (LS) of Fraction I protein (Rubisco) and the Bam HI restriction patterns of chloroplast DNA (ctDNA) as molecular markers. Four types of LS were detected by isoelectrofocusing with and without S-carboxymethylation. The close relation between AA and CCDD genome species was suggested by analyses of LS and ctDNA. Intraspecific variation in O. latifolia was detected at the levels of both LS and ctDNA. The LS of the BB, BBCC, and CC genomes and FF (O. brachyantha) were not distinguishable, although the native Rubisco of the latter was slightly different from those of the first three. It was also shown that O. australiensis, the only EE genome species, might have evolved differently than the other Oryza species. 相似文献
55.
The genomes of phage I3 and its host Mycobacterium smegmatis have been compared. From thermal melting studies the GC contents of DNA from mycobacteriophage I3 and its host M. smegmatis were found to be 66%. A new method, based only on the initial rates of reassociation, has been developed for calculating the DNA homology. Analysis of DNA reassociation kinetics suggested the presence of one equivalent of the phage I3 genome within the M. smegmatis genome. Southern analysis revealed the presence of almost all of the phage I3 specific sequences within the host genome. 相似文献
56.
E. B. Bröcker L. Suter B. M. Czarnetzki E. Macher 《Cancer immunology, immunotherapy : CII》1986,23(2):155-157
Summary Previously, we have provided evidence for a positive correlation between HLA-DR expression in primary melanoma and early metastasis [3, 4]. In the present study we investigated whether this relationship was modified by adjuvant BCG immunotherapy. The study comprised 107 patients with a stage I high-risk melanoma; 44 patients had been treated with BCG, whereas the remaining patients had not received any adjuvant therapy. There was no difference in disease-free survival between BCG-treated and untreated patients. Disease-free survival was significantly shorter in patients with high expression of HLA-DR antigens in the primary tumor.Subgrouping BCG-treated and control patients according to HLA-DR phenotype of the melanoma revealed a prolongation of disease-free survival in the subgroup of BCG-treated patients with no or low expression of HLA-DR antigens in the primary melanoma. BCG therapy apparently did not influence prognosis of patients with high expression of HLA-DR antigens in the tumor. 相似文献
57.
R Dante M Arnaud A Niveleau 《Biochemical and biophysical research communications》1983,114(1):214-221
The treatment of transformed rat cells with micromolar amounts of 5'deoxy 5'methyl thioadenosine induces rapid effects on the rate of methylation of DNA concomitantly with alterations of intracellular pools of S-adenosyl methionine and S-adenosyl homocysteine. Pulse chase labelling experiments indicate that 5'deoxy 5'methylthioadenosine does not inhibit the degradation of S-adenosyl homocysteine but inhibits the consumption of S-adenosyl methionine. In vitro transmethylation assays performed with heterologous DNA show that low doses of the thioethernucleoside do not significantly affect the DNA methyltransferase activity of cellular extracts. The biological role of 5'deoxy 5'methylthioadenosine, a natural molecule formed during the synthesis of polyamines is discussed. 相似文献
58.
Induction of 2',5' oligo(A) synthetase in tumor-bearing mice with encephalomyocarditis (EMC) virus or poly(I)poly(C) 总被引:1,自引:0,他引:1
Infection of 13 month-old C3H mice with EMC virus or inoculation with the interferon inducer poly(I)poly(C) results in elevated levels of the enzyme 2',5' oligo(A) synthetase only in animals with spontaneous tumors (breast cancer or hepatomas). High enzymatic activities are detected in homogenates from liver, spleen, plasma and neoplastic cells of the animals with breast carcinomas and only in the neoplastic liver cells of the animals with hepatomas. 相似文献
59.
The isolation of a brain peptide identical to the intestinal peptide PHI (peptide HI) is described. The peptide was isolated from porcine brain extract using a chemical assay method based on its C-terminal isoleucine amide structure. The complete amino acid sequence of the peptide was found to be: His-Ala-Asp-Gly-Val-Phe-Thr-Ser-Asp-Phe-Ser-Arg-Leu-Leu-Gly-Gln-Leu-Ser-Ala- Lys-Lys-Tyr-Leu-Glu-Ser-Leu-Ile-NH2. This sequence is identical to the intestinal peptide thus demonstrating PHI to be a brain-gut peptide. The role of PHI in the central nervous system as a neurotransmitter or neuromodulator is discussed. 相似文献
60.
Kiyoshi Nose Hiroshi Okamoto 《Biochemical and biophysical research communications》1983,111(2):383-389
A nick-translation reaction with DNA polymerase I (pol. I) was used to detect DNA breaks produced by chemical carcinogens. Normal human fibroblasts treated with N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) in various doses were permeabilized with lysolecithin, and were nick translated in the presence of [3H]dCTP and pol. I. The radioactivity incorporated increased with MNNG concentration, and was directly proportional to the poly(ADP-ribose) synthetase activity. Other DNA-damaging agents such as bleomycin or 4-nitroquinoline 1-oxide also caused the nick translation rate to increase. When MNNG-treated cells were cultured in fresh medium containing no MNNG, the increase in the rate of nick translation in permeable cells became less and this decrease was abolished by addition of aphidicolin or cytosine arabinoside. The nick translation method described here may be a useful means for estimating intrinsic DNA breaks in cells treated with carcinogens. 相似文献