全文获取类型
收费全文 | 11345篇 |
免费 | 549篇 |
国内免费 | 1篇 |
出版年
2021年 | 109篇 |
2020年 | 83篇 |
2019年 | 108篇 |
2018年 | 322篇 |
2017年 | 278篇 |
2016年 | 352篇 |
2015年 | 261篇 |
2014年 | 389篇 |
2013年 | 678篇 |
2012年 | 807篇 |
2011年 | 1028篇 |
2010年 | 595篇 |
2009年 | 264篇 |
2008年 | 581篇 |
2007年 | 521篇 |
2006年 | 506篇 |
2005年 | 364篇 |
2004年 | 304篇 |
2003年 | 309篇 |
2002年 | 242篇 |
2001年 | 156篇 |
2000年 | 235篇 |
1999年 | 176篇 |
1998年 | 141篇 |
1997年 | 83篇 |
1996年 | 94篇 |
1995年 | 92篇 |
1994年 | 102篇 |
1993年 | 91篇 |
1992年 | 89篇 |
1991年 | 98篇 |
1989年 | 66篇 |
1988年 | 83篇 |
1987年 | 73篇 |
1985年 | 99篇 |
1984年 | 84篇 |
1983年 | 84篇 |
1982年 | 88篇 |
1981年 | 92篇 |
1980年 | 92篇 |
1979年 | 80篇 |
1978年 | 82篇 |
1976年 | 71篇 |
1975年 | 79篇 |
1974年 | 93篇 |
1973年 | 66篇 |
1972年 | 75篇 |
1970年 | 62篇 |
1969年 | 70篇 |
1968年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
81.
Reversibility of the respiration-deficient locuspet23 and auxotrophic locuslys2 was followed in the standard (RAD1) and UV sensitive (rad1–2) strains ofSaccharomyces cerevisiae, both after identical doses of UV radiation and at identical survival. When comparing the reversibility after the treatment
with identical doses of UV radiation a much higher reversibility of both loci in strainrad1–2 could be detected. When comparing the reversibility of the loci in question at identical survival of both strains it could
be found that the reversibility of thepet23 locus is again much higher in strainrad1–2, whereas the reversibility of thelys2 locus is roughly identical in the two strains. Thus, the function of geneRAD1 in repair processes is apparently associated with the “error-free” repair, both at low and high doses of ultraviolet radiation. 相似文献
82.
Glucose inhibits the inducible synthesis of β-D-glucosidase inStreptomyces granaticolor. Neither cAMP nor cGMP influence the inhibitory effect of glucose. Glucose also inhibits the inducible synthesis of the cellobiose
uptake system but has no effect on its activity. This may be the mechanism underlying glucose inhibition of induction of β-D-glucosidase inS.granaticolor. 相似文献
83.
84.
M. Kučera 《Journal of invertebrate pathology》1984,43(2):190-196
Gel permeation, preparative isoelectric focusing, and affinity chromatography were used to purify three inhibitors of proteolytic activity from perchloric acid extracts of last instar Galleria mellonella larvae. Electrofocusing experiments revealed three isoinhibitors with different isoelectric points: inhibitor I-1 with p1 of pH 5.6, inhibitor I-2, pH 7.7, and inhibitor I-3 (of small inhibitory activity), pH 8.6. By affinity chromatography on trypsin-Sepharose 4B the I-1 was purified 9.7 ×, but 71.1% of inhibitory activity was lost. Molecular mass of the inhibitory complex was 12,600 Da. I-1 and I-2 are relatively stable to heat at several pHs with minor stability at pH 10. I-1 and I-2 inhibit serine proteases about 2.5 times as much as sulfhydryl proteases. In the same ratio protease P-1 and protease P-2 from Metarhizium anisopliae are inhibited. 相似文献
85.
86.
The contribution deals with the phytocenological analysis of theRondeletio correifoliae-Andropogonetum multinervosi, an endemic savanna association occuring on the Siguanea Hills (Sierra de la Siguanea) near the Colony Hotel. 相似文献
87.
88.
Lj. Vitale M. Renko B. Lenarčič V. Turk M. Pokorny 《Applied microbiology and biotechnology》1986,23(6):449-455
Summary A leucine aminopeptidase was purified to homogeneity fromStreptomyces rimosus culture filtrates, which are waste broth of oxytetracycline bioproduction process. Purification procedure includes ultrafiltration
and chromatography on CM-Sephadex, AH-Sepharose and FPLC Mono S column.
The enzyme is a monomer with molecular weight of 27,500 Daltons and pI of 7.3, stable in broad pH range and up to 70°C. It
is a metallo enzyme dependent on Ca2+ ions for its full activity. By its specificity it is a true aminopeptidase active on amino acid amide, arylamide, peptide
and ester bonds. The hydrolysing activity shows preference for leucine at the N-terminal position of substrates, also acts
on aromatic acids and methionine, but does not release glycine, proline, acidic amino acids orD-amino acid residues. 相似文献
89.
We developed a mathematical model and an algorithm for numerical treatment of a model of honeycomb construction in a beehive. The model contains essential features of the bee-bee and bee-wax interactions, and in a qualitative way captures the dynamics of parallel comb construction. The construction is represented by a set of dynamical coupled partial differential equations for the density of bees situated on the hive ceiling, and the quantity of wax distributed by the bees. A spectral algorithm is invented for treatment of these equations, based on a modified thin-sheet gain scheme and a fast Fourier transform technique.Work at City College supported in part by the Army Research Office and the Department of Energy 相似文献
90.
Agrobacterium radiobacter, strain B6 (a strain isolated in this laboratory, which limited the occurrence of damping-off of sugar beet and influenced growth of plants in hot-house and field experiments) was found to produce an acidic exopolysaccharide in a mineral medium with various carbon sources. Hydrolyzates of the polysaccharide contained glucose, galactose, glycerol, succinic acid and pyruvic acid, whose quantitative content varied according to the carbon source used. The polysaccharide isolated from the medium containing glucose exhibited the highest physiological activity. Seeds germinated best and sugar beet roots were found to grow most rapidly in a medium containing 0.2 % (W/W) of the polysaccharide. The roots exposed for 3 d in this medium grew 2.7-fold as compared with non-treated plants. Higher sumbers of microorganisms were detected on the surface of roots treated with the polysaccharide. Growth of roots was also stimulated when immersing the seeds (30 min) in a 0.2 –0.4 % solution of this polysaccharide. After a two-fold treatment the roots were less damaged by the fungusPythium ultimum. Plants from seeds treated with the polysaccharide grew in the field soil more rapidly than the non-treated plants but worse than after bacterization of the seeds byA. radiobacter B6 and were only partially protected against the damping-off of sugar beet. 相似文献