全文获取类型
收费全文 | 116773篇 |
免费 | 13652篇 |
国内免费 | 416篇 |
专业分类
130841篇 |
出版年
2021年 | 804篇 |
2018年 | 1075篇 |
2017年 | 1021篇 |
2016年 | 1343篇 |
2015年 | 1715篇 |
2014年 | 2144篇 |
2013年 | 2912篇 |
2012年 | 3163篇 |
2011年 | 3105篇 |
2010年 | 2086篇 |
2009年 | 2035篇 |
2008年 | 2663篇 |
2007年 | 2676篇 |
2006年 | 2614篇 |
2005年 | 2435篇 |
2004年 | 2372篇 |
2003年 | 2397篇 |
2002年 | 2352篇 |
2001年 | 9776篇 |
2000年 | 9658篇 |
1999年 | 7355篇 |
1998年 | 1705篇 |
1997年 | 1859篇 |
1996年 | 1642篇 |
1995年 | 1468篇 |
1994年 | 1375篇 |
1993年 | 1327篇 |
1992年 | 4898篇 |
1991年 | 4605篇 |
1990年 | 4081篇 |
1989年 | 4102篇 |
1988年 | 3699篇 |
1987年 | 3178篇 |
1986年 | 2847篇 |
1985年 | 2766篇 |
1984年 | 2055篇 |
1983年 | 1795篇 |
1982年 | 1287篇 |
1981年 | 1035篇 |
1980年 | 957篇 |
1979年 | 1817篇 |
1978年 | 1388篇 |
1977年 | 1239篇 |
1976年 | 1059篇 |
1975年 | 1179篇 |
1974年 | 1211篇 |
1973年 | 1205篇 |
1972年 | 1068篇 |
1971年 | 985篇 |
1970年 | 870篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
The heterogeneity and differential expression of protein kinase C in nervous tissues 总被引:1,自引:0,他引:1
993.
Newly identified groups of genes in chloroplasts 总被引:9,自引:0,他引:9
994.
A. Birkenfeld Y. Ezra N. Ron D. Navot S. Granovsky J. G. Schenker I. S. Levij I. Vlodavsky 《In vitro cellular & developmental biology. Plant》1988,24(12):1188-1192
Summary The culturing of human endometrium in conventional plastic dishes and media is only partially successful, mainly because a
growth of a heterogeneous population of cells is achieved. Naturally produced extracellular matrix closely resembles the subepithelial
basement membrane and seems to affect both growth and differentiation of cells. These qualities of the extracellular matrix
(ECM) were applied for obtaining endometrial epithelial cultures. Endometrial tissue specimens were plated after slicing on
ECM-coated dishes and kept for up to 8 d. The growth of a confluent homogeneous tissue composed of polygonal epithelial-like
cells was demonstrated. To further characterize these cells, cultures were examined by scanning electron microscopy and transmission
electron microscopy. Scanning electron microscopy revealed flattened polygonal cells covered with microvilli, among which
ciliated cells were observed. By transmission electron microscopy the cells were seen as a monolayer, with some cells overlapping,
closely adherent to the matrix. Microvilli, as well as intracellular vacuoles and glycogen granules were observed. Cell type
specific cytoskeletal markers were demonstrated by antibodies to intermediate filament proteins (keratin and epithelial membrane
antigen). Taken together, the morphologic and immunohistochemical studies indicate that a selective growth of the epithelial
component of endometrial tissue was obtained after plating unprocessed endometrial tissue fragments on ECM-coated culture
dishes.
This work was supported by PHS grant no. CA 30289 to J.V. 相似文献
995.
Proteinases were excreted by strains of Bacillus subtilis during fermentation of African locust bean cotyledons. Those excreted by one strain were purified and characterized by ammonium sulphate precipitation, ion-exchange chromatography (IEC), gel filtration, inhibition tests and polyacrylamide gel electrophoresis (PAGE). Three proteinases and an esterase without proteolytic activity were identified. A serine proteinase which showed a high degree of hydrophobicity and a neutral proteinase were present. The third proteinase showed both proteolytic and esterolytic activities, and had multiple electrophoretic mobilities on polyacrylamide gel. 相似文献
996.
Sulfated cholecystokinin octapeptide (CCK-8) was administered either intraperitoneally or into the cerebral ventricle of fully conscious mice, and locomotor activity was quantified. CCK-8 administered by either route suppressed locomotor activity. Subcutaneously administered selective CCK-A receptor antagonist, L-364,718 (1 mg/kg), reversed the inhibitory effect of centrally as well as peripherally administered CCK-8, but the selective CCK-B receptor antagonist, L-365,260 (1 mg/kg), did not. These results demonstrate that centrally as well as peripherally administered CCK-8 suppresses locomotor activity in mice through an interaction with CCK-A, but not CCK-B, receptors. 相似文献
997.
R M Campbell Y Lee T F Mowles K W McIntyre M Ahmad A M Felix E P Heimer 《Peptides》1992,13(4):787-793
A series of novel hGRF(1-29)-NH2 analogs were synthesized and biotinylated. The immunological and biological activities of these analogs were then characterized. To distance the biotin moiety from the putative bioactive core, a C-terminal spacer arm consisting of -Gly-Gly-Cys-NH2 (-GGC) was added to hGRF(1-29)-NH2 (hGRF29) and analogs, with subsequent biotinylation performed at the cysteine residue. Neither addition of the C-terminal spacer arm nor biotinylation affected affinity of these analogs for GRF antibody. Relative to hGRF(1-44)-NH2 (hGRF44: potency = 1.0), the biotinylated analogs were equipotent in vitro to their nonbiotinylated, parent compounds: [desNH2Tyr1,D-Ala2,Ala15]hGRF29-GGC-(tpBiocyt in)-NH2 (4.7) = [Ala15]hGRF29-GGC-(tpBiocytin)-NH2 (3.9) greater than hGRF29-GGC-(tpBiocytin)-NH2 (0.8). Based upon cumulative GH release data in vivo (0-60 min postinjection), [desNH2Tyr1,D-Ala2,Ala15]hGRF29-GGC-(tpBiocyt in)-NH2, [Ala15]hGRF29-GGC-(tpBiocytin)-NH2, and hGRF29-GGC-(tpBiocytin)-NH2 displayed 8.6, 5.5, and 0.8 times, respectively, the potency of hGRF44. These in vivo potency values were not significantly different from the corresponding parent compounds (i.e., with or without the C-terminal spacer arm). In summary, biotinylated hGRF analogs have been developed that retain full immunoreactivity and potent bioactivity (in vitro and in vivo), thus permitting their use in GRF receptor isolation, ELISA, and histochemical procedures. 相似文献
998.
Previous studies have demonstrated that NMDA receptor antagonists and protein kinase C inhibitors induced marked memory impairment in rats, but that peripherally administered cerulein (CER) prevented these effects. In the present study, the effect of subcutaneously administered CER on amnesia induced by protein synthesis inhibitors was examined in passive and active avoidance responses and in the Morris water maze test. Intraperitoneal injection of the inhibitors produced marked memory impairment, but the effect was abolished by combined administration with CER. The effective dose of subcutaneously injected CER was, on a molar basis, three thousand- and six thousandfold less than the dose of anisomycin, and two hundred eighty- and three thousandfold less than the dose of puromycin in the passive and active avoidance response experiments, respectively. Similarly, in the Morris water maze test, behavioral disturbances produced by the protein synthesis inhibitors were abolished by CER. These results indicate the effectiveness of CER in preventing memory impairment induced by protein synthesis inhibitors. 相似文献
999.
F Petitet M Saffroy Y Torrens S Lavielle G Chassaing D Loeuillet J Glowinski J C Beaujouan 《Peptides》1992,13(2):383-388
The guinea pig ileum possesses NK-1 and NK-3 tachykinin receptors. As expected, [Pro9]SP and senktide, which are selective agonists of NK-1 and NK-3 receptors, respectively, were found to be highly potent in contracting the guinea pig ileum. Surprisingly, similar observations were made with septide, SP-O-CH3, [Apa9-10]SP, or [Pro9,10]SP although, in contrast to [Pro9]SP, these four peptides showed a low affinity for 3H-[Pro9]SP-specific NK-1 binding sites on membranes from the guinea pig ileum. They were also devoid of affinity for NK-2 and NK-3 binding sites. GR 71251, a compound which has been described as a NK-1 antagonist, was more potent in inhibiting the septide- than the [Pro9]SP-evoked contracting response. Altogether, these results suggest that septide, [Apa9-10]SP, and [Pro9,10]SP exert their high contracting activity in the guinea pig ileum by acting on a new subtype of tachykinin receptors. 相似文献
1000.
A 4 x 6 cm ulcerative mass in the antrum was found to consist of papillary adenocarcinoma in the surrounding wall and the small round cell neoplasm at its base. Immunohistochemical staining revealed that elements of the papillary adenocarcinoma were positive for carcinoembryonic antigen, epithelial membrane antigen, keratin, endocrine granule constituent, and CA19-9, while components of the small cell carcinoma were weakly positive only for neuron-specific enolase. In one portion of the small cell carcinoma, particularly large cells with pleomorphic nuclei which were intensely positive for desmin were detected. Electron microscopic examination revealed dense-cored granules and intercellular junctions in the small neoplastic cells and bundles of intermediate filaments in the desmin-positive large cells. These findings suggest that ultrastructural examination is vital in diagnosis of small cell carcinoma and they reveal the capability of this carcinoma toward multidirectional differentiation. 相似文献