全文获取类型
收费全文 | 174034篇 |
免费 | 7549篇 |
国内免费 | 3811篇 |
出版年
2023年 | 479篇 |
2022年 | 1175篇 |
2021年 | 2217篇 |
2020年 | 1513篇 |
2019年 | 1940篇 |
2018年 | 13591篇 |
2017年 | 11958篇 |
2016年 | 9903篇 |
2015年 | 4950篇 |
2014年 | 5320篇 |
2013年 | 5915篇 |
2012年 | 11035篇 |
2011年 | 18904篇 |
2010年 | 15743篇 |
2009年 | 11638篇 |
2008年 | 14424篇 |
2007年 | 15592篇 |
2006年 | 4444篇 |
2005年 | 4243篇 |
2004年 | 4546篇 |
2003年 | 4179篇 |
2002年 | 3505篇 |
2001年 | 2462篇 |
2000年 | 2130篇 |
1999年 | 1626篇 |
1998年 | 850篇 |
1997年 | 737篇 |
1996年 | 627篇 |
1995年 | 560篇 |
1994年 | 457篇 |
1993年 | 417篇 |
1992年 | 778篇 |
1991年 | 649篇 |
1990年 | 580篇 |
1989年 | 566篇 |
1988年 | 485篇 |
1987年 | 457篇 |
1986年 | 351篇 |
1985年 | 365篇 |
1984年 | 319篇 |
1983年 | 262篇 |
1982年 | 209篇 |
1981年 | 176篇 |
1979年 | 229篇 |
1978年 | 203篇 |
1977年 | 181篇 |
1976年 | 174篇 |
1974年 | 198篇 |
1972年 | 407篇 |
1971年 | 399篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
991.
Summary
Torulopsis bombicola (ATCC 22214) produced sophorose lipid to 80 g/l in batch culture containing 11% glucose and 10% soybean oil as carbon and energy sources. According to the carbon mass balance analysis, 13% and 37% of input carbon were channeled to cells and to products, respectively, and 50% of the total input carbon was channeled to CO2 gas in batch culture. In fed-batch culture with intermittent oil feeding, however, the carbon fractions incorporated into sophorose lipid and cells were 60% and 12%, respectively, and the carbon fraction evolved as CO2 gas was 30%. In conclusion, yield of sophorose lipid based on total input carbon substrates was increased from 0.37 g/g-substrate in batch culture to 0.6 g/ g-substrate by employing a fed-batch culture. 相似文献
992.
W.-J. Sun C. Lee H. A. George A. L. Powell M.E. Dahlgreir R. Greasham C.-H. Park 《Biotechnology letters》1993,15(8):809-814
Summary Acetate was inhibitory to the growth of early induced E. coli cells and their expression of fusion protein, transforming growth factor--Pseudomonas exotoxin 40 (TGF-PE40), but the inhibitory level was strain dependent For E. coli JM109 (pTAC-TGF57-PE40), 2 g/L of added acetate (3 g/L of total acetate in the medium) decreased TGFa-PE40 production by 38.0%. Acetate was less inhibitory to E. coli RR1, and RR1 was not affected by adding 2 g/L of acetate. However, 5 g/L of added acetate (6.7 g/L of total acetate in the medium) decreased TGF-PE40 production by 21.2%. These results indicate that higher acetate concentration was associated with inhibition of TGF-PE40 expression of E. coli JM109 during late induction. 相似文献
993.
Summary Two strains of osmophilic yeast which were isolated from honey-comb, produced good yields of erythritol as a main product. These strains were identified as Trichosporonoides sp., 150-5 and 331-1.From the fermentation studies with these strains using glucose and sucrose as substrate, strain 331-1 produced more erythritol as the sole polyhydric product,with trace quantities of glycerol, than strain 150-5. 相似文献
994.
Kyung Hoon Jung Jeong Hwan Kim Yeong Joong Jeon Jae Heung Lee 《Biotechnology letters》1993,15(1):65-70
Summary A novel two enzyme system of fructosyltransferase and glucose oxidase to enhance the content of the net fructo—oligosaccharide (FOS) fractions in the industrial production of FOS syrup from sucrose was devised. The net FOS content in the commercial FOS syrup has been limited only to 55–60 % due to the accumulation of glucose which acts as a feedback inhibitor of the fructosyltransferase. By supplementing glucose oxidase to the conventional FOS reaction system, we could convert the glucose to gluconic acid readily separable from neutral sugars by simple ion exchange operation in the next step. The simultaneous removal of glucose was proved effective in proceeding the reaction by fructosyltransferase further by relieving the product inhibition caused by glucose. By this way, we could raise the net FOS content as high as 90 %. 相似文献
995.
Almost every cell in the Drosophila pupal wing forms a single, distally pointing cuticular hair. The function of the frizzled (fz) gene is essential for the elaboration of the normal wing hair pattern. In the absence of fz function hairs develop, but they display an abnormal polarity. We have examined the developmental expression of the fi gene at the RNA level via in situ hybridization and at the protein level via Western blotting. We have found that fz is expressed in all regions of the epidermis before, during, and after the fz cold sensitive period. We have also found that fz function is not required for normal fi expression. We have further found that mutations in several other tissue polarity genes do not noticeably alter the expression or the modification state of the Fz protein. © 1994 Wiley-Liss, Inc. 相似文献
996.
Weng Naidong Jean W. Lee James D. Hulse 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1994,654(2)
An isocratic HPLC method was developed and validated for the quantitation of methocarbamol in human plasma. Methocarbamol and internal standard in 200 μl of human plasma were extracted with ethyl acetate, evaporated to dryness and reconstituted in water. Separation was achieved on a reversed-phase C18 column with a mobile phase of methanol—0.1 M potassium phosphate monobasic—water (35:10:55, v/v/v). The detection was by ultraviolet at 272 nm. Linearity was established at 1–100 μg/ml (r > 0.999). The limit of quantitation was designed as 1 μg/ml to suit pharmacokinetic studies. Inter-day precision and accuracy of the calibration standards were 1.0 to 3.6% coefficients of variance (C.V.) and −2.0 to +1.6% relative error (R.E.). Quality controls of 3, 20 and 70 μg/ml showed inter-day precision and accuracy of 2.5 to 3.6% C.V. and −0.9 to −0.4% R.E. Recovery of methocarbamol was 91.4–100.3% in five different lots of plasma. The method was shown to be applicable on different brands of C18 columns. 相似文献
997.
Arianna Lee Karen L. Clark Martin Fleischmann Markus Aebi Michael W. Clark 《Molecular genetics and genomics : MGG》1994,245(1):32-44
Prp20/Srm1, a homolog of the mammalian protein RCC1 in Saccharomyces cerevisiae, binds to double-stranded DNA (dsDNA) through a multicomponent complex in vitro. This dsDNA-binding capability of the Prp20 complex has been shown to be cell-cycle dependent; affinity for dsDNA is lost during DNA replication. By analyzing a number of temperature sensitive (ts) prp20 alleles produced in vivo and in vitro, as well as site-directed mutations in highly conserved positions in the imperfect repeats that make up the protein, we have determined a relationship between the residues at these positions, cell viability, and the dsDNA-binding abilities of the Prp20 complex. These data reveal that the essential residues for Prp20 function are located mainly in the second and the third repeats at the amino-terminus and the last two repeats, the seventh and eighth, at the carboxyl-terminus of Prp20. Carboxyl-terminal mutations in Prp20 differ from amino-terminal mutations in showing loss of dsDNA binding: their conditional lethal phenotype and the loss of dsDNA binding affinity are both suppressible by overproduction of Gsp1, a GTP-binding constituent of the Prp20 complex, homologous to the mammalian protein TC4/Ran. Although wild-type Prp20 does not bind to dsDNA on its own, two mutations in conserved residues were found that caused the isolated protein to bind dsDNA. These data imply that, in situ, the other components of the Prp20 complex regulate the conformation of Prp20 and thus its affinity for dsDNA. Gsp1 not only influences the dsDNA-binding ability of Prp20 but it also regulates other essential function(s) of the Prp20 complex. Overproduction of Gsp1 also suppresses the lethality of two conditional mutations in the penultimate carboxyl-terminal repeat of Prp20, even though these mutations do not eliminate the dsDNA binding activity of the Prp20 complex. Other site-directed mutants reveal that internal and carboxyl-terminal regions of Prp20 that lack homology to RCC1 are dispensable for dsDNA binding and growth. 相似文献
998.
999.
1000.