全文获取类型
收费全文 | 1526篇 |
免费 | 82篇 |
国内免费 | 2篇 |
专业分类
1610篇 |
出版年
2024年 | 4篇 |
2023年 | 19篇 |
2022年 | 42篇 |
2021年 | 74篇 |
2020年 | 37篇 |
2019年 | 40篇 |
2018年 | 75篇 |
2017年 | 47篇 |
2016年 | 58篇 |
2015年 | 76篇 |
2014年 | 100篇 |
2013年 | 90篇 |
2012年 | 101篇 |
2011年 | 75篇 |
2010年 | 52篇 |
2009年 | 56篇 |
2008年 | 78篇 |
2007年 | 78篇 |
2006年 | 55篇 |
2005年 | 50篇 |
2004年 | 59篇 |
2003年 | 44篇 |
2002年 | 29篇 |
2001年 | 23篇 |
2000年 | 32篇 |
1999年 | 17篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 16篇 |
1991年 | 15篇 |
1990年 | 16篇 |
1989年 | 18篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1977年 | 4篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1965年 | 2篇 |
排序方式: 共有1610条查询结果,搜索用时 15 毫秒
21.
Microbial mineralization of organic phosphate in soil 总被引:35,自引:0,他引:35
Summary Phosphate-dissolving microorganisms were isolated from non-rhizosphere and rhizosphere of plants. These isolates included
bacteria, fungi and actinomycetes. In broth cultures, Gram-negative short rod,Bacillus andStreptomyces species were found to be more active in solubilizing phosphate thanAspergillus, Penicillium, Proteus, Serratia, Pseudomonas andMicrococcus spp. The sterile soils mixed with isolated pure culture showed slower mineralization of organic phosphate than that of non-sterile
soil samples at all incubation periods. Maximum amount of phosphate mineralization by isolated microorganisms were obtained
at the 60th and the 75th day of incubation in sterile and non-sterile soils respectively. The mixed cultures were most effective
in mineralizing organic phosphate and individuallyBacillus sp. could be ranked next to mixed cultures. Species ofPseudomonas andMicrococcus were almost the same as that of the control under both sterile and non-sterile conditions. 相似文献
22.
Oxathiolanes and disulfonyl derivatives of steroids were tested for mutagenic activity in the Ames tester strains. The test compounds exhibited mutagenic activity without metabolic activation although metabolic activation markedly enhanced their activity. A significant decrease in the survival of the radiation-sensitive mutants recA, lexA and rer of E. coli was observed as compared to their wild-type counterpart in the presence of the test steroid. Structural features which appear to be crucial for the mutagenic activity in these steroidal drugs are: (i) an electron-donating group at position 3, and (ii) a bulky group anchored at the 5th and 6th positions. The test steroids appear to damage DNA which in turn initiates the SOS repair with the concomitant induction of mutation. 相似文献
23.
Genomic in situ hybridization to identify alien chromosomes and chromosome segments in wheat 总被引:15,自引:0,他引:15
T. Schwarzacher K. Anamthawat-Jónsson G. E. Harrison A. K. M. R. Islam J. Z. Jia I. P. King A. R. Leitch T. E. Miller S. M. Reader W. J. Rogers M. Shi J. S. Heslop-Harrison 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1992,84(7-8):778-786
Summary Genomic in situ hybridization was used to identify alien chromatin in chromosome spreads of wheat, Triticum aestivum L., lines incorporating chromosomes from Leymus multicaulis (Kar. and Kir.) Tzvelev and Thinopyrum bessarabicum (Savul. and Rayss) Löve, and chromosome arms from Hordeum chilense Roem. and Schult, H. vulgare L. and Secale cereale L. Total genomic DNA from the introgressed alien species was used as a probe, together with excess amounts of unlabelled blocking DNA from wheat, for DNA:DNA in-situ hybridization. The method labelled the alien chromatin yellow-green, while the wheat chromosomes showed only the orange-red fluorescence of the DNA counterstain. Nuclei were screened from seedling root-tips (including those from half-grains) and anther wall tissue. The genomic probing method identified alien chromosomes and chromosome arms and allowed counting in nuclei at all stages of the cell cycle, so complete metaphases were not needed. At prophase or interphase, two labelled domains were visible in most nuclei from disomic lines, while only one labelled domain was visible in monosomic lines. At metaphase, direct visualization of the morphology of the alien chromosome or chromosome segment was possible and allowed identification of the relationship of the alien chromatin to the wheat chromosomes. The genomic in-situ hybridization method is fast, sensitive, accurate and informative. Hence it is likely to be of great value for both cytogenetic analysis and in plant breeding programmes. 相似文献
24.
25.
Human Genetics - In a sample of Bengali Muslems from Dacca, haptoglobin, group-specific component, haemoglobin, adenosine deaminase, adenylate kinase, 6-phosphogluconate dehydrogenase,... 相似文献
26.
27.
The advent of long PCR (XL-PCR) has proven to be a major advance in PCR technology and is currently being utilised to investigate numerous biological systems. The analysis of mixed DNA populations is a particularly useful application for XL-PCR. For example, XL-PCR has been used to investigate the occurrence of heterogeneous mitochondrial DNA (mtDNA) rearrangement mutations. With XL-PCR it became possible to amplify the entire length of the mtDNA chromosome and detect any mtDNA deletion or insertion mutations based on a measurable change in overall sequence length. In the present communication, XL-PCR and conventional short-length PCR were used to amplify mitochondrial DNA sequences from several human vastus lateralis skeletal muscle samples. The experiments demonstrated that there was minimal preferential amplification of shorter DNA sequences with XL-PCR and was significantly less than the preferential amplification of shorter sequences observed with conventional PCR. Also, XL-PCR amplification of the complete mtDNA sequence from control DNA containing a single mtDNA template (leucocyte extracts) showed that the generation of PCR artefacts was not a predisposed failing of the system but was dependant on the standard rules that govern the set up and optimisation of any PCR reaction. In optimised systems, XL-PCR artefacts were not generated and a single PCR product was always recovered. 相似文献
28.
Organic amendments have received renewed attention to improve soil fertility for crop production. A randomized complete block split plot experiment was conducted to evaluate the dairy manure (DM) amendments of soil for corn (Zea mays L. cv. Monsanto 919) production under different tillage systems. Main plot treatments were no-till (NT), conventional tillage (CT), and deep tillage (DT), and subplot treatments were chemical fertilization (DM(0)), and DM at 10Mgha(-1)yr(-1) (DM(10)) and 20Mgha(-1)yr(-1) (DM(20)) with supplemental chemical fertilization. Results show that tillage and DM had significantly reduced bulk density (rho(b)) with greater porosity (f(t)) and hydraulic conductivity (K(fs)) than soils under NT and DM(0). Manuring was effective to improve soil physical properties in all tillage treatments. While manure significantly increased C sequestration, the N concentration was influenced by both tillage and manure with significant interaction. The CT significantly increased P as did the addition of manure. However, with manure, K was significantly increased in all tillage treatments. While tilled soils produced taller plants with higher grain yields, and water-use efficiency than NT soils, manuring, in contrast, increased corn harvest index. Manure exerted significant quadratic effect on corn biomass N and K uptake. The variable effects of tillage and dairy manuring on soil properties and corn growth are most probably related to "transitional period" in which soil ecosystems may have adjusting to a new equilibrium. 相似文献
29.
Cloning and molecular characterization of a cubilin-related serine proteinase from the hard tick Haemaphysalis longicornis 总被引:3,自引:0,他引:3
Miyoshi T Tsuji N Islam MK Kamio T Fujisaki K 《Insect biochemistry and molecular biology》2004,34(8):799-808
Serine proteinases are one of the largest proteolytic families of enzymes, and have diverse cellular activities in mammalian tissues. We report here the cloning and molecular characterization of a cDNA encoding the serine proteinase of the hard tick Haemaphysalis longicornis (HlSP). The HlSP cDNA is 1570 bp long and the deduced precursor protein consists of 464 amino acids with a predicted molecular mass of 50.4 kDa and a pI of 8.2. The preprotein, consisting of 443 amino acids, was predicted to include a complement C1r/C1s, Uegf, and bone morphogenic protein-1 domain, a low-density lipoprotein receptor class A domain, and a catalytic domain. HlSP sequence analysis showed high similarity to serine proteinases reported from arthropods and vertebrate animal species. Two-dimensional immunoblot analysis revealed endogenous HlSP in adult tick extracts at 50 kDa. Endogenous HlSP was also expressed in all lifecycle stages of H. longicornis. Immunohistochemical studies detected the endogenous enzyme in the midgut epithelial cells of an adult tick. The Escherichia coli-expressed recombinant HlSP was demonstrated to degrade bovine serum albumin and hydrolyze the substrate Bz-L-Arg-pNA at the rate of 30.2 micromol/min/mg protein. Further, HlSP expression was up-regulated during a blood-feeding process, indicating its involvement in the digestion of host blood components. 相似文献
30.