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991.
992.
The three-dimensional structure of the sodium salt of beijeran has been determined by X-ray fiber diffraction analysis. The acidic polysaccharide forms an extended twofold helix. Two chains are nestled tightly in a monoclinic unit cell of dimensions a=12.72, b=11.41, c (fiber axis)=24.62 A and gamma=123.7 degree in an antiparallel fashion. In the crystalline lattice, helices are stacked tightly to form a thick sheet along the vertical plane passing through the short diagonal of the basal net. Adjacent sheets associate via a network of sodium ions and water molecules embedded between them. The morphology of sodium beijeran in the solid state is consistent with its observed rheological properties. 相似文献
993.
Lee HG Zhu X Ghanbari HA Ogawa O Raina AK O'Neill MJ Perry G Smith MA 《Neuro-Signals》2002,11(5):282-292
Selective neurodegeneration is a prominent feature in Alzheimer's disease; however, the mechanism of neuronal death is still unclear. Nonetheless, the topographical distribution of different types of receptors is thought to contribute to the regional selective nature of neuronal degeneration. Specifically, since glutamatergic transmission is severely altered by the early degeneration of cortico-cortical connections and hippocampal projections in Alzheimer's disease, we suspect that glutamate receptors may play a new role in the pathophysiology of disease. Here we review the salient aspects of glutamate receptor expression in Alzheimer's disease and how their differential regulation can contribute to the selective neurodegeneration seen in the disease. Additionally, we assess the potential therapeutic value of glutamate receptors as a target for drug intervention in Alzheimer's disease. 相似文献
994.
Gamma-glutamyl transpeptidase (gamma-GTP) is a membrane-bound enzyme which is known to play a crucial role in active transport of amino acids across membrane barriers. We prepared a monoclonal antibody recognizing specifically rat gamma-GTP and investigated localization of the enzyme in the rat brain by immunohistochemistry with this antibody. The antigen was localized on the ependyma, epithelia of the choroid plexus and microvessels. More precise localization of gamma-GTP was examined with immuno-electron microscopy. The antigen was recognized on the microvilli and cilia of the ependymal cells, microvilli of the choroid epithelial cells and luminal membranes of the vascular endothelial cells. 相似文献
995.
Aminooxyacetic acid (AOA) inhibited photoperiodically inducedflowering in Pharbitis nil. The application of AOA to the plumulejust after an inductive period was the most effective in inhibitingflowering. A correlation between inhibition of flowering andinhibition of glutamic-oxalacetic transaminase activity wasobserved with fifteen aminooxy derivatives. (Received April 18, 1992; Accepted June 25, 1992) 相似文献
996.
Hiroshi Sakamoto Yasuyuki Shimohigashi Iori Maeda Takeru Nose Kin-ichi Nakashima Ichiro Nakamura Tomoshisa Ogawa Motonori Ohno Keiichi Kawano 《Journal of molecular recognition : JMR》1993,6(2):95-100
A complete series of configurationally isomers (L -L , L -D , D -L AND D -D ) of a dipeptide Leu-Phe benzyl ester have been synthesized and assayed for chymotrypsin. In the conformational analysis by 400 MMz 1H NMR, the L -D and D -L isomers, but not hte L -L and D -D isomers, showed fairly large up field shifts (0.2–0.4 ppm) of Leu-βCH2 and γCH proton signals, indicating the presence of shielding effects from the benzene ring. In addition to distinct signal splitting of Phe-βCH2, the NOE enhancement observed between Leu-δCH3 and Phe-phenyl groups revealed that these groups are in close proximity. These data indicated that L -D and D -L isomers from a hydrophobic core between side chains of adjacent Leu and Phe residues. When the dipeptides were examined for inhibition of chymotrypsin using Ac-Try-OEt as a substrate, the L -L isomer showed no inhibition, itself becoming a substrate. However, the other three isomers inhibited chymotrypsin in a competitive manner, and the D -L isomer was strongest with Ki of 2.2 × 10?5 M . It was found that the D -L isomer was only slowly hydrolysed but the L (or D )-D isomer was not. H-D -Phe-L -Leu-OBzl with the inverse sequence of H-D -Leu-L -Pre-OBzl inhibited chymotrypsin more strongly (Ki = 6.3 × 10?6 M ). Since the free acid analogue of the D -L isomer exhibited no inhibition, the benzyl ester moiety itself was thought to be involved in the enzyme inhibition. It is assumed that in the inhibitory conformation the ester-benzyl group fits the S1 site of chymotrypsin, while the side chain-side chain complexing hydrophobic core fits the S2 site. 相似文献
997.
Shigeki Ohshima Yasuji Ishimaru Mitsuo Honda Susumu Ohkawara Michio Ogawa 《Cell and tissue research》1993,273(2):363-370
A cell surface-associated adhesive factor (AF) separated from differentiated rat ascites hepatoma AH136B cells (forming cell islands in vivo) has been highly purified by chromatography. AF is assumed to mediate the cell-cell adhesion essential to island formation of the hepatoma cells. A substance, immunologically crossreactive with AF, is present in the ascites fluid or culture medium of the AH136B cells. Because the substance is almost identical to AF in molecular weight and aggregation-promoting activity, it has been concluded that AF is released into the ascites fluid where it is concentrated. Monoclonal antibodies have been raised against AF purified from ascites fluid of AH136B cells. We have obtained a monoclonal antibody, coded MoAF-6D6, that strongly abolishes the aggregation-promoting activity of AF. When AH136B cell islands are incubated in the presence of Fab fragments of MoAF-6D6, cell detachment from the islands is evident within 24 h. Cell islands following 36-h culture show a distinct dissociation and islands completely lose their organization 48 h after culture. The dissociating effect of MoAF-6D6 is neutralized by the addition of AF. These results suggest that AF plays a significant role in the maintenance of cell islands. 相似文献
998.
999.
Haruo Seto Satoshi Imai Takashi Tsuruoka Hiroshi Ogawa Atsuyuki Satoh Toru Sasaki Noboru Otake 《Biochemical and biophysical research communications》1983,111(3):1008-1014
During biosynthetic studies on bialaphos to reveal the formation mechanisms of carbon-phosphorous bonds in detail, three new metabolites containing a HPC bond structure were isolated from the fermentation broth of a mutant of SF-1293. Based on the spectroscopic analysis, the structures of these compounds have been determined as shown in Fig. 1. Transformation experiments of these metabolites to bialaphos suggested that the reduction of the phosphorous atom in phosphate will take place at an early biosynthetic stage. 相似文献
1000.
The brain concentration and distribution of β-endorphin immunoreactivity in the brain have been studied in intact and hypophysectomized rats. The results obtained with different methods for killing the animals and extracting β-endorphin are compared. Different methodologies of killing the rat and extracting the brain yield concentrations of β-endorphin which vary ten fold. Consistently the highest concentrations of β-endorphin have been found in the hypothalamus, midbrain and hindbrain. After hypophysectomy major reduction of β-endorphin concentration in the brain was observed. 相似文献