全文获取类型
收费全文 | 539473篇 |
免费 | 50706篇 |
国内免费 | 227篇 |
出版年
2018年 | 5132篇 |
2016年 | 8163篇 |
2015年 | 12288篇 |
2014年 | 13496篇 |
2013年 | 16985篇 |
2012年 | 17756篇 |
2011年 | 15939篇 |
2010年 | 11492篇 |
2009年 | 10512篇 |
2008年 | 13074篇 |
2007年 | 13731篇 |
2006年 | 12912篇 |
2005年 | 18066篇 |
2004年 | 16999篇 |
2003年 | 15034篇 |
2002年 | 12622篇 |
2001年 | 21791篇 |
2000年 | 21589篇 |
1999年 | 17624篇 |
1998年 | 5927篇 |
1997年 | 5984篇 |
1996年 | 5525篇 |
1995年 | 5343篇 |
1994年 | 5239篇 |
1993年 | 5203篇 |
1992年 | 15405篇 |
1991年 | 15116篇 |
1990年 | 14845篇 |
1989年 | 14413篇 |
1988年 | 13595篇 |
1987年 | 12987篇 |
1986年 | 11730篇 |
1985年 | 11951篇 |
1984年 | 9674篇 |
1983年 | 8336篇 |
1982年 | 6175篇 |
1981年 | 5450篇 |
1980年 | 5243篇 |
1979年 | 9531篇 |
1978年 | 7304篇 |
1977年 | 6650篇 |
1976年 | 6169篇 |
1975年 | 7071篇 |
1974年 | 7834篇 |
1973年 | 7858篇 |
1972年 | 7265篇 |
1971年 | 6767篇 |
1970年 | 5851篇 |
1969年 | 5682篇 |
1968年 | 5174篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
991.
The role of O6-methylguanine-DNA methyltransferase in cell survival, mutagenesis and carcinogenesis 总被引:13,自引:0,他引:13
D B Yarosh 《Mutation research》1985,145(1-2):1-16
992.
F F Smith J R Mertz I Krebs L L Tres C B Chae Z Zakeri J Engelhardt D Hoover M Tenniswood A L Kierszenbaum 《Molecular reproduction and development》1992,33(4):363-372
We have previously reported that a heterodimeric protein secreted by rat Sertoli cells is antigenically related to a protein associated with outer dense fibers of the sperm tail. Therefore, we have explored the possibility that Sertoli and spermatogenic cells express a similar gene encoding a homologous protein. A Sertoli cell heterodimeric protein cDNA probe recognizes specific mRNA in pachytene and round spermatids fractionated by centrifugal elutriation; however, this specific mRNA was less prominent than in cultured Sertoli cells. In agreement with these observations, in situ hybridization experiments show that Sertoli cells are predominantly engaged in active heterodimeric protein mRNA synthesis, while meiotic prophase spermatocytes and spermatids also show significant but less abundant specific mRNA. Immunoblotting experiments demonstrate that, while Sertoli cells synthesize a heterodimeric protein consisting of two disulfide-linked components with molecular masses of 45 and 35 kD, both primary spermatocytes and round spermatids synthesize single 30 kD monomers not associated by disulfide linkage but recognized by antisera to Sertoli cell heterodimeric protein. Immunoblotting and immunogold electron microscopic studies show that antisera to Sertoli cell heterodimeric protein recognize a protein associated with outer dense fibers. This immunoreactivity was abolished by a 5-min pronase treatment, without affecting the integrity of outer dense fibers. Results of this study and previous studies demonstrate that both Sertoli and spermatogenic cells express a similar gene and that an antigenically related product encoded by this gene becomes associated with outer dense fibers during their assembly at spermiogenesis. 相似文献
993.
A Jans E F Ippel P F Dijkstra J B Bijlsma 《Genetic counseling (Geneva, Switzerland)》1992,3(3):139-143
We report two sisters with mental retardation, coarse facial features, telecanthus, flat malar region, prominent lower lip, kyphoscoliosis, and tapering fingers. Although these patients' phenotypes showed considerable overlap with the Coffin-Lowry and the Atkin-Flaitz syndromes, their overall picture makes these diagnoses controversial. 相似文献
994.
M B Hallett 《Biochimica et biophysica acta》1985,847(1):15-19
The release of 9-aminoacridine loaded into neutrophil granules has been monitored using quantitative fluorescence microscopy of individual rat neutrophils. Within the granule, the fluorescence of the dye was substantially quenched, but release into the surrounding medium restored fluorescence. From kinetic analysis of the increase in fluorescence it was shown that secretion from a single neutrophil in response to a low concentration of chemotactic peptide occurred in 'bursts'. Each 'burst' of secretion was of equal size and kinetics, which were equal to the size and kinetics of the smallest evoked response possible. A significant time-lag of 5-10 s between the arrival of the stimulus at the cell and the onset of secretion was recorded. It was therefore concluded that secretion from neutrophils was the result of release of quantal amounts of dye following a delay period. 相似文献
995.
H. B. OSBORNE A. C. BAKKE J. YU 《Differentiation; research in biological diversity》1982,21(1-3):66-69
A murine erythroleukemic cell line, 745 A4-TG, deficient in hypoxanthine-guanine-phosphoribosyl transferase, can be induced with 3 mM hexamethylene bisacetamide to yield at least 50% of cells undergoing irreversible erythroid differentiation and finally losing capacity for cell divisions. The effects of such induced differentiation of 745 A4-TG on its ability to form viable and proliferating hybrids when fused with 3T3 1T22 fibroblasts were investigated. We found that when the induced 745 A4-TG cells were used, more continuously proliferating hybrids were obtained than could be accounted for by the residual uninduced cells which remained in these induced preparations. This suggests that some of the induced 745 A4-TG cells, when fused with 3T3 1T22 reverted from the induced phenotype of a limited capacity for cell proliferation to an uninduced state of continuous proliferation. This observation was further confirmed with the use of fully differentiated 745 A4-TG cells, which were obtained after selection with a bromodeoxyuridine suicide treatment to eliminate the uninduced and the partially differentiated cells in the preparations. When these selected, fully differentiated cells, as characterized by their lack of proliferation capacity and thymidine kinase activity, were fused with 3T3 1T22 (also deficient in thymidine kinase), it was found that not only were viable hybrid colonies obtained in a selection medium, which precluded the proliferation of either parental cells, but these hybrids continued to proliferate for more than two months in selection medium. These data thus confirmed that some fully differentiated erythroleukemic nucleus components in the hybrids were reactivated to regain capacity for cell proliferation and to dedifferentiate to synthesize thymidine kinase for survival in the selection medium. The lack of hemoglobin synthesis by these hybrids also indicates dedifferention of these murine erythroleukemic components in the hybrids. 相似文献
996.
R M Sweeting B A McKeown 《Comparative biochemistry and physiology. A, Comparative physiology》1987,88(1):147-151
1. Effects of growth hormone (GH) were examined on short-term aspects of seawater adaptation in coho salmon smolts. 2. Injection of somatostatin (SRIF) immediately prior to seawater entry suppressed plasma GH levels, but did not have any significant effects at 6 or 12 hr on hematocrits, plasma glucose or plasma Na+ levels. 3. Plasma GH levels increased 250% within 36 hr after seawater exposure. 4. Plasma glucose levels, in contrast, were significantly lower in the seawater fish after 36 hr post-exposure. 5. Plasma Na+ levels increased to 190 mEq/1 by 24 hr but subsequently returned to freshwater levels while hematocrits showed no significant changes over the 72 hr of exposure. 6. The significance of these results is discussed in terms of successful seawater adaptation in coho salmon. 相似文献
997.
998.
A 71-year-old female with a widespread double mycotic infection caused byC. Albicans andT. rubrum was discovered to be suffering from mycosis fungoides. Clinically she was found to have large, polycyclic erythematous plaques with scaly, slightly infiltrated borders, covering almost all areas of the glabrous skin, and also involving the scalp (with no hair penetration), the soles and palms, toe-webs, finger and toe nails; there was also perleche and oral thrush. Cultures yieldedC. albicans from most of the skin lesions, from the scalp, mouth, finger nails and urine and stool specimens, andT. rubrum from intermingled skin specimens, from the palms and soles and toe-nails. Blood culture was negative as were intracutaneous tests with fungal antigens and tuberculin. Histological examination confirmed the fungal invasion of the horny layer and at the same time revealed an underlying pathologic picture of mycosis fungoides, the lesions having been masked by the mycotic eruption. Intensive cytostatic and antifungal therapy led to a transient improvement but shortly thereafter there was a relapse of the fungal and lymphoproliferative manifestations and the patient died in septic shock.
Résumé Une femme, agée 71 ans, ayant une double infection mycosique due àC. albicans et auT. rubrum, a été décélée qu'elle souffrait aussi d'un mycosis fungoïde. Au point de vue clinique elle avait de larges plaques érythémato-squameuses, polycicliques, aux bords légèrement infiltrés, répandues sur une grande partie de la peau glabre, paumes et plantes inclus, et affectant aussi le cuir chevelu (sans pénétration des poils), les ongles des doigts et des orteils. Les cultures ont permis d'isoler leC. albicans à partir de la majorité des lésions de la peau et du cuir chevelu, des ongles des doigts, ainsi que de la bouche, de l'urine et des selles. On a trouvé aussiT. rubrum dans des lésions cutanées entremêlées aux precedentes, dans la région palmaire et plantaire et dans les ongles des orteils. Les testes intradermiques aux antigens fongiques et à tuberculine ont été négatifs, ainsi que les hémocultures. L'examen histologique a montré l'invasion de la couche cornée par les champignons et en même temps a découvert un tableau pathologique sous-jacent d'un mycosis fungoïde, ayant été masqué par l'éruption fongique. Un traitement intensif par des produits cytostatiques et antifongiques a mené à une amélioration temporaire, mais brièvement après on a assisté à une réchute rapide des manifestations lymphoprolifératives et fongiques et la malade a décédé à la suite d'un état septique.相似文献
999.
G N Kryzhanovski? N G Lutsenko V N Grafova E I Danilova V K Lutsenko 《Biulleten' eksperimental'no? biologii i meditsiny》1986,101(4):399-401
The ability of serotonin derivatives to stimulate cAMP accumulation in isolated nerve terminals and lumbar enlargement of the spinal cord of normal rats was compared. The effect of the compounds on the intensity of spinal pain syndrome was also assessed. It has been established that substitutes injected into NH2-group of serotonin in 5-OH position attenuate the ability to stimulate cAMP accumulation in synaptosomes, with the effect more pronounced with substitutes of larger volume. A certain correlation between the ability of serotonin derivatives to stimulate adenylate cyclase in vivo and in vitro, on the one hand, and their analgetic effect, on the other hand, is suggested. 相似文献
1000.
It was demonstrated that the nuclear matrix of rat liver possesses the protease activity. The specific activity of nuclear matrix proteases exceeds that of intact nuclei 7-fold. The optimum activity of nuclear matrix proteases is observed at pH 8-9. The protease activity of the nuclear matrix is inhibited by p-chloromercuribenzoate, N-ethylmaleimide, EDTA, phenylmethylsulfonyl fluoride. This suggests that thiol, serine and metalloproteases are associated with the nuclear matrix. 相似文献