全文获取类型
收费全文 | 110694篇 |
免费 | 13264篇 |
国内免费 | 412篇 |
出版年
2018年 | 994篇 |
2017年 | 966篇 |
2016年 | 1260篇 |
2015年 | 1555篇 |
2014年 | 1946篇 |
2013年 | 2471篇 |
2012年 | 2869篇 |
2011年 | 2815篇 |
2010年 | 1895篇 |
2009年 | 1855篇 |
2008年 | 2366篇 |
2007年 | 2353篇 |
2006年 | 2349篇 |
2005年 | 2138篇 |
2004年 | 2078篇 |
2003年 | 2107篇 |
2002年 | 2082篇 |
2001年 | 9646篇 |
2000年 | 9513篇 |
1999年 | 7198篇 |
1998年 | 1615篇 |
1997年 | 1794篇 |
1996年 | 1580篇 |
1995年 | 1411篇 |
1994年 | 1308篇 |
1993年 | 1249篇 |
1992年 | 4795篇 |
1991年 | 4524篇 |
1990年 | 3999篇 |
1989年 | 4018篇 |
1988年 | 3617篇 |
1987年 | 3087篇 |
1986年 | 2781篇 |
1985年 | 2683篇 |
1984年 | 1975篇 |
1983年 | 1734篇 |
1982年 | 1230篇 |
1981年 | 984篇 |
1980年 | 916篇 |
1979年 | 1763篇 |
1978年 | 1361篇 |
1977年 | 1202篇 |
1976年 | 1030篇 |
1975年 | 1149篇 |
1974年 | 1168篇 |
1973年 | 1164篇 |
1972年 | 1034篇 |
1971年 | 955篇 |
1970年 | 823篇 |
1969年 | 744篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
851.
D Y Lee P E Johnson 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1989,190(2):211-216
Rats were fed diets containing either soy protein or casein and different levels of manganese, methionine, phytic acid, or arginine for 7 days and then fed test meals labeled with 2 microCi of 54Mn after an overnight fast. Retention of 54Mn in each rat was measured every other day for 21 days using a whole-body counter. Liver manganese was higher (P less than 0.0001) in soy protein-fed rats (8.8 micrograms/g) than in casein-fed rats (5.2 micrograms/g); manganese superoxide dismutase activity also was higher in soy protein-fed rats than in casein-fed rats (P less than 0.01). There was a significant interaction between manganese and protein which affected manganese absorption and biologic half-life of 54Mn. In a second experiment, rats fed soy protein-test meals retained more 54Mn (P less than 0.001) than casein-fed rats. Liver manganese (8.3 micrograms/g) in the soy protein group was also higher than that (5.7 micrograms/g) in the casein group (P less than 0.0001), but manganese superoxide dismutase activity was unaffected by protein. Supplementation with methionine increased 54Mn retention from both soy and casein diets (P less than 0.06); activity of manganese superoxide dismutase increased (P less than 0.05) but liver manganese did not change. The addition of arginine to casein diets had little effect on manganese bioavailability. Phytic acid affected neither manganese absorption nor biologic half-life in two experiments, but it depressed liver manganese in one experiment. These results suggest that neither arginine nor phytic acid was the component in soy protein which made manganese more available from soy protein diets than casein diets. 相似文献
852.
Brefeldin A inhibits oligosaccharide processing of glycoproteins in mouse hypothyroid pituitary tissue at several subcellular sites 总被引:2,自引:0,他引:2
V S Perkel Y Miura J A Magner 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1989,190(3):286-293
We have studied the effects of brefeldin A (BFA) and monensin on the processing of the oligosaccharides of thyrotropin (TSH), free alpha-subunits, and cellular glycoproteins of mouse pituitary tissue to clarify the subcellular sites of action of BFA. BFA was previously shown to inhibit the translocation of glycoproteins from the rough endoplasmic reticulum to the Golgi apparatus but action at other sites was possible. Pituitaries from hypothyroid mice were incubated with [35S]methionine, [3H]mannose, [3H]galactose, [3H]fucose, N-[3H]acetylmannosamine, or [35S]sulfate for 2 hr in the absence or presence of 5 micrograms of BFA/ml or 2 microM monensin. TSH and free alpha-subunits were immunoprecipitated from tissue lysates and analyzed by sodium dodecyl sulfate-gel electrophoresis. The tryptic glycopeptides of TSH were separated using high-performance liquid chromatography. Total glycoproteins in cell lysates were precipitated using trichloroacetic acid. Labeled oligosaccharides were released from the tryptic glycopeptides of TSH and cellular glycoproteins by endoglycosidase H and they were analyzed by paper chromatography. Compared with control incubations, BFA caused the intracellular accumulation of glycoproteins having less than expected amounts of Man9GlcNAc2 units, but with excess Man8GlcNAc2, Man7GlcNAc2, Man6GlcNAc2, and Man5GlcNAc2 units. There was a lesser accumulation of glucose-containing oligosaccharides, especially Glc1Man9GlcNAc2. Monensin also caused the accumulation of certain high mannose species, but the pattern differed from that seen for BFA, since Man9GlcNAc2 units were preserved and there was less excess of Man8GlcNAc2, Man7GlcNAc2, Man6GlcNAc2, and Man5GlcNAc2 units. BFA did not block the initial attachment of oligosaccharides at any of the three Asn-glycosylation sites of TSH, but caused the accumulation of Man5-8GlcNAc2 units at each site. Both monensin and BFA inhibited fucosylation, sulfation, and sialylation more markedly than mannose incorporation. Thus, in addition to its previously described action of inhibiting rough endoplasmic reticulum to Golgi transport, BFA appears to partially inhibit the glucose-trimming enzymes as well as some Golgi enzymes. 相似文献
853.
K. -Y. To C. -C. Chen Y. -K. Lai 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,78(1):81-86
Summary Streptomycin-resistant colonies were isolated from protoplast cultures of haploid Nicotiana plumbaginifolia based on their ability to green in medium containing 1 mg/ml streptomycin sulfate. The frequency of resistant colonies was 0.9×10–5 in nonmutagenized culture, and increased ten-fold following treatment of culture with 10 g/ml N-methyl-N-nitro-N-nitrosoguanidine. Of a total of 52 resistant clones isolated, 2 gave rise to haploid, 15 to diploid, and 3 to tetraploid plants upon transfer of calli to differentiation medium. Leaf-segment and protoplast assays showed that all diploid regenerates were resistant to streptomycin but sensitive to chloramphenicol, kanamycin, lincomycin, neomycin, and spectinomycin. Plants in most diploid clones were fertile and able to set seeds when self-fertilized and crossed reciprocally to wild-type plants. Inheritance of streptomycin resistance was studied in the diploid clones and, without exception, the resistance was transmitted maternally. Comparative studies of the ultrastructure of organelles and protein synthesis in isolated chloroplasts between wild-type and resistant clones in the presence of streptomycin suggest that streptomycin resistance is controlled by chloroplasts. 相似文献
854.
B. Wang W. Cheng Y. -N. Li D. -D. Li 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,77(4):581-586
Summary Certain physicochemical properties of rice mitochondrial DNA (mtDNA) were determined. Certain low-molecular-weight mtDNA bands were found in addition to the major mtDNA band. Rice mtDNA appeared in the electron microscope as a collection of linear molecules with heterogeneous length in the range of 1–156 kb. The major distribution area was 60–105 kb. A small fraction (less than 5%) of rice mtDNA was found in the form of a circular molecule. Some molecules had the appearance of being supercoiled. Replication fork structures were found in both circular and linear mtDNA molecules. In one rice species, Jin Nante, 15 different circular molecules were found. Rice mtDNA was digested with different restriction enzymes. The total molecular weight of rice mtDNA was calculated to be about 300 kb according to the data of restriction enzyme digestion and electron microscopy. 相似文献
855.
Preaxial polydactyly of the fore- and hindlimbs was found in Wistar-derived rats in 1978. Genetic analysis indicated that the polydactyly was due to the effects of an autosomal recessive gene (gene symbol; pd). Polydactylous homozygous rats had two or three pollices (six or seven digits) in the forelimbs and one to three preaxial extra digits (six to eight digits) in the hindlimbs. Skeletal examination revealed the presence of the extra carpal, metacarpal, and phalangeal bones that seemed to be complete or incomplete duplication of the navicular, greater multangular, first metacarpal, and phalanges of digit I in the forelimbs. In the hindlimbs, extra tarsal, metatarsal, and phalangeal bones were also observed preaxially. These extra elements seemed to be mirror-image duplications of the talus, navicular, second cuneiform, third cuneiform, cuboid, and metatarsals and phalanges of digits II-V with the absence of the first cuneiform, tibiale, first metatarsal, and phalanges of digit I. In addition, morphological changes were observed in the humerus, radius, and ulna in the forelimbs and femur, tibia, and fibula in the hindlimbs. Especially in the radius and tibia, thickening and bifurcation were found, indicating incomplete duplication of these bones. Based on these findings, the limb anomaly was classified as preaxial carpometacarpal/tarsometatarsal-type polydactyly with incomplete duplication of the radius and tibia. The mutant rats had other associated anomalies such as accessory spleens and cryptorchism. The males are sterile, whereas the females breed normally. 相似文献
856.
857.
The changes in monoamine levels of different brain regions following Japanese encephalitis virus (JEV) intraperitoneal inoculation were examined in experimentally JEV-infected mice. In addition, virus distribution was studied using infectivity assay and immuno-histochemistry of viral antigen. 1) The level of monoamines in brain tissues was not affected by 48 hours after viral inoculation, but marked effects were elicited at 96 hours after the inoculation. The cerebral concentration of 5-hydroxyindole-3-acetic acid (5 HIAA) was increased, while that of dopamine (DA) showed a decrease. Especially these alteration were observed in the cerebral cortex, but not in the cerebellum. 2) The viral growth in the brain was observed at 48 hours after the inoculation. The growth in the cerebellum, however, was found to be lower than those in other cerebral regions. 3) The viral antigen was detected in the cerebral cortex, hippocampus, mesencephalon and diencephalon in addition to the substantia nigra and striatum. From these results, it is presumed that clinical manifestation of JEV infection may involve the changes in the metabolism of neurotransmitter, especially those of DA and serotonin in the brain. 相似文献
858.
Sire JY 《Tissue & cell》1989,21(3):447-462
The elasmoid scales of the cichlid fish, Hemichromis bimaculatus, are localized within dermal pockets, the floors of which are separated from the stratum compactum by uninterrupted cellular sheets, the scale-pocket linings (SPL). TEM study of the fry skin shows that the SPL cells originate from the cell population constituting the dermal papilla of the scale. The upper-layer cells of the papilla, close to the epidermal-dermal junction, differentiate into scleroblasts that, subsequently, form the scale-bag, while the inner-layer cells, close to the stratum compactum, constitute a bi-layered sheet, the SPL. The SPL cells are joined one to another by numerous desmosomes and their cytoplasm is filled principally by microfilaments and free ribosomes. The SPL is also characterized by the presence of a basement membrane on its two faces. When a scale is experimentally pulled off, the scale-forming cells are removed with the dermis and the epidermis covering the free region of the scale, but the SPL is not damaged and epidermal fragments remain at the posterior edge of each scale-pocket. The epithelial cells migrate, from the epidermal fragments, on an extracellular matrix situated on the surface of the SPL, and the wound is closed from 3 to 6 h after scale removal. The scale-regenerating cells differentiate from the upper-layer cells of the SPL, initially in the central region of the scale-pocket where epithelial cells first contacted the SPL surface. Consequently, it is shown that scale-forming cells and scale-regenerating cells are derived from the same ontogenetic population, the dermal papilla. 相似文献
859.
O A Kovalenko N I Tarasova A G Ivannikova L N Voronkova T G Nikolaeva 《Tsitologiia》1989,31(4):447-452
The effect of picolinic acid (PA) on SPEV cell proliferation is found to be different from that on normal and virus transformed NRC cells, and on spontaneously transformed CHO cells. It is shown that SPEV cells are arrested by PA at the end of G1-phase and at the beginning of S-phase and probably in G2-phase of the cell cycle. Ferrous ions remove the G1/S block induced by PA to permit the cell transfer through S-phase. On the one hand, PA chelates ferrous ions from the cells, and on the other one it inhibits the replicative DNA synthesis. It can be suggested that PA may arrest the SPEV cell growth affecting the iron-depend stable radical formation which is introduced into the active centre of ribonucleotiDE reduCTase. This results in the lower enzyme activity. 相似文献
860.
The CD16+ lymphoblastic cell lines of crab-eating monkeys shared the U-5 antigen recognized by a monoclonal antibody. The CD16+U-5+ cell lines expressed high natural killer activity to K562 cells, whereas the CD16-U-5- control cell line had no significant natural killer activity. A possible involvement of the U-5 antigen in natural killer function was also suggested by reduction of the natural killer activity in peripheral blood mononuclear cells of Japanese monkeys after treatment with U-5 monoclonal antibody and complement. 相似文献