全文获取类型
收费全文 | 16833篇 |
免费 | 1098篇 |
国内免费 | 6篇 |
出版年
2023年 | 101篇 |
2022年 | 192篇 |
2021年 | 337篇 |
2020年 | 231篇 |
2019年 | 322篇 |
2018年 | 387篇 |
2017年 | 356篇 |
2016年 | 589篇 |
2015年 | 870篇 |
2014年 | 943篇 |
2013年 | 1190篇 |
2012年 | 1445篇 |
2011年 | 1325篇 |
2010年 | 810篇 |
2009年 | 750篇 |
2008年 | 1014篇 |
2007年 | 994篇 |
2006年 | 949篇 |
2005年 | 832篇 |
2004年 | 747篇 |
2003年 | 734篇 |
2002年 | 658篇 |
2001年 | 132篇 |
2000年 | 110篇 |
1999年 | 132篇 |
1998年 | 143篇 |
1997年 | 146篇 |
1996年 | 136篇 |
1995年 | 112篇 |
1994年 | 108篇 |
1993年 | 109篇 |
1992年 | 84篇 |
1991年 | 72篇 |
1990年 | 57篇 |
1989年 | 62篇 |
1988年 | 54篇 |
1987年 | 35篇 |
1986年 | 37篇 |
1985年 | 52篇 |
1984年 | 56篇 |
1983年 | 48篇 |
1982年 | 57篇 |
1981年 | 53篇 |
1980年 | 35篇 |
1979年 | 42篇 |
1978年 | 34篇 |
1977年 | 26篇 |
1975年 | 24篇 |
1974年 | 33篇 |
1973年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
Cartesio Favalli Teresa Jezzi Antonio Mastino Cristina Rinaldi-Garaci Carlo Riccardi Enrico Garaci 《Cancer immunology, immunotherapy : CII》1985,20(3):189-192
Summary A single injection of -interferon (-IFN) (30 000 units/mouse), a major biological modifier of natural killer (NK) cytolytic activity, strongly stimulated NK activity in normal mice, as expected, while the same treatment did not statistically alter the NK response in cyclophosphamide (CY)-suppressed animals.We investigated the possibility of thymosin 1 cooperating with -IFN in boosting NK activity in CY-suppressed animals.The results show that treatment with thymosin 1 (200 g/kg) for 4 days, followed by a single injection of -IFN 24 h before testing, strongly restored NK activity in CY-suppressed mice. Thymosin 1 was, moreover, able to accelerate the recovery rate of NK activity in bone marrow reconstituted murine chimeras.Taken together the data support the concept that the synergic effect between thymosin 1 and -IFN could be the result of effects on differentiation of the NK lineage at different levels. 相似文献
72.
Dr. Manuel Megias Miguel A. Caviedes Francisco Rodriguez-Quiñones Antonio J. Palomares Francisco Ruiz-Berraquero 《Current microbiology》1985,12(6):325-328
Rhizobium trifolii was highly resistant to the lethal effect ofN-methyl-N-nitro-N-nitrosoguanidine (MNNG), but it was sensitive to the mutagenic action of this chemical. A concentration of 500g/ml yields a survival of between 1% and 10%, which allows us to obtain a higher number of mutants than lower concentrations that yield higher survival rates. Lethal damage produced by nitrosoguanidine was repaired, and repair is inhibited by acriflavine. 相似文献
73.
Antonio Campos-Neto Fernanda W. M. Lima Arnaldo F. B. Andrade 《The Journal of eukaryotic microbiology》1985,32(1):84-88
A rapid and simple method for the purification of amastigotes of Trypanosoma cruzi from spleens of infected mice is described. A protein A-Scpharose 4B immunoadsorbent column bound with antisera to epimastigotes of T. cruzi was used to purify the tissue forms of this parasite. Host cells and debris are not retained, and parasites can be eluted in high yields and purity. Studies of surface glycoproteins and glycolipids of the purified amastigotes with 18 lectins of various specificities revealed the presence on the parasites of receptors for N-acetylglucosamine, N-acetylgalactosamine, D-galactose, and D-mannose binding lectins. 相似文献
74.
Mixing patterns in Amazon lakes 总被引:2,自引:2,他引:0
Jose G. Tundisi Bruce R. Forsberg Allan H. Devol Thomas M. Zaret Takako M. Tundisi Antonio Dos Santos Jorge S. Ribeiro Elsa R. Hardy 《Hydrobiologia》1984,108(1):3-15
The diel mixing patterns of two small floodplain lakes, Lago Jacaretinga in the Amazon drainage, and Lago Cristalino in the Rio Negro system, were investigated during both the high-water and low-water states of the Amazon River hydrograph. Measurements included temperature, oxygen, ammonia, phosphate, and chlorophyll. In both lakes thermal stratification developed during the day and was eroded at night. During the low-water period when the lakes were shallow, nocturnal circulation extended to the lake bottom, whereas when the lakes were deeper (greater than about 5 m), circulation did not reach the bottom and an anoxic hypolimnion developed. During the low-water period, percent of oxygen concentrations were relatively high but always less than saturation. Low oxygen concentrations were observed during the high-water period. At all times nocturnal mixing supplied a significant amount of oxygen to the lake ecosystems. Nighttime upward mixing of recycled nitrogen and phosphorus also appeared to be important nutrient sources for algal productivity. 相似文献
75.
Antonio Gomez Sanchez Manuel Mancera Francisco Rosado Manuel Rico 《Carbohydrate research》1984,134(1):75-82
3,4,5,6,7-Penta-O-acetyl-1,2-dideoxy-1-nitro-d-gluco-hept-1-enitol reacts with methyl acetoacetate in an unusual Michael reaction, giving the normal adduct (6), and a bicyclic derivative (9) that arises from quasi-dimerization of the former when a high concentration of the base is used. Acetylation of compound 9 gives the hydroxylamine O-acetate (10).From the reactions of 3,4,5,6,7-penta-O-acetyl-1,2-dideoxy-1-nitro-d-galacto-hept-1-enitol with ethyl and tert-butyl acetoacetate, the normal adducts (7 and 8) were isolated. The structures of compounds 6 to 10 were established on the basis of their spectral properties (u.v., i.r., mass, and 1H- and 13C-n.m.r.) 相似文献
76.
77.
78.
Polypeptide composition of rat sperm outer dense fibers. A simple procedure to isolate the fibrillar complex 总被引:6,自引:0,他引:6
Treatment of caput or cauda epididymal rat sperm with a low concentration (0.05%) of the cationic detergent cetyltrimethylammonium bromide and 30 mM 2-mercaptoethanol solubilized most of the sperm structures except for the sperm head and the outer dense fiber-connecting piece complex. The latter were purified, and about 10% of these complexes are formed by nine fibers attached to the connecting piece. Of these fibers, two are shorter than the other seven and presumably correspond to fibers 3 and 8 (Fawcett, D.W. (1975) Dev. Biol. 44, 394-436). Electron microscopy confirmed the purity of the isolated outer dense fibers and revealed their characteristic irregular cross-sectional shape. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate showed six major polypeptides (Mr = 87,000, 30,400, 26,000, 18,400, 13,000, and 11,500) with a high content of serine, aspartic and glutamic acids, proline, cysteine, leucine, and tyrosine. Furthermore, several lines of evidence indicate a close structural relationship between the components of 30,400 and 26,000 Da. The six major components of the fibers are phosphorylated at serine residues. These results indicate that the major components of rat sperm outer dense fibers are a unique family of phosphoproteins. 相似文献
79.
Sven Fischer Axel Vischer Vera Preac-Mursic Peter C. Weber 《Prostaglandins & other lipid mediators》1987,34(3)
In a 24 h kinetic study docosahexaenoic acid (DCHA, C22:6n-3) or eicosapentaenoic acid (EPA, C20:5n-3) were given in a single dose to healthy male volunteers. PGI3-M, the main urinary metabolite of prostaglandin I3 was below the detection limit in the control periods, but was excreted already in the first 4 h after ingestion of DCHA or EPA and decreased thereafter. Excretion of PGI2-M did not change significantly. In a second dietary trial DCHA and EPA were given cross-over to 7 healthy male volunteers for 6 days. PGI3-M was formed after DCHA and EPA in amounts of 35 and 20 % of PGI2-M and showed a considerable interindividual variation. The structure of PGI3-M was verified by independant biochemical synthesis. Our data indicate that dietary DCHA is retroconverted to EPA in man, which is quickly transformed - like dietary EPA itself - to prostaglandin I3. DCHA may therefore serve as a precursor fatty acid for EPA and its cyclooxygenated and lipoxygenated products. 相似文献
80.
Summary
Aspergillus sp strains from decaying lemons were tested for extracellular pectinase production, testing differently pretreated lemon peel as the carbon source instead of pectin. It was found that the production of extracellular polygalacturonase was about the same and that of pectinesterase substantially higher when unwashed fresh lemon peel was used instead of pectin. The culture filtrate obtained showed a clarifying capacity similar to that of a commercial pectinase preparation, but the vitamin C of the juice was less affected by the treatment. 相似文献