全文获取类型
收费全文 | 740259篇 |
免费 | 83131篇 |
国内免费 | 495篇 |
专业分类
823885篇 |
出版年
2016年 | 7714篇 |
2015年 | 10768篇 |
2014年 | 12570篇 |
2013年 | 18545篇 |
2012年 | 20579篇 |
2011年 | 20801篇 |
2010年 | 13885篇 |
2009年 | 13033篇 |
2008年 | 18732篇 |
2007年 | 19261篇 |
2006年 | 18415篇 |
2005年 | 17677篇 |
2004年 | 17429篇 |
2003年 | 16869篇 |
2002年 | 16591篇 |
2001年 | 33363篇 |
2000年 | 33948篇 |
1999年 | 27334篇 |
1998年 | 9470篇 |
1997年 | 9917篇 |
1996年 | 9362篇 |
1995年 | 8776篇 |
1994年 | 8794篇 |
1993年 | 8731篇 |
1992年 | 22547篇 |
1991年 | 21711篇 |
1990年 | 21430篇 |
1989年 | 21089篇 |
1988年 | 19625篇 |
1987年 | 18656篇 |
1986年 | 17540篇 |
1985年 | 17652篇 |
1984年 | 14467篇 |
1983年 | 12591篇 |
1982年 | 9765篇 |
1981年 | 8894篇 |
1980年 | 8405篇 |
1979年 | 14127篇 |
1978年 | 11163篇 |
1977年 | 10124篇 |
1976年 | 9667篇 |
1975年 | 10675篇 |
1974年 | 11470篇 |
1973年 | 11376篇 |
1972年 | 10467篇 |
1971年 | 9453篇 |
1970年 | 8214篇 |
1969年 | 7935篇 |
1968年 | 7234篇 |
1967年 | 6296篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
122.
Einhard Bezzel und H. -J. Fünfstück 《Journal of Ornithology》1995,136(3):294-296
In 1990 and 1994, two males of Golden Eagles were found with small lead particles in their stomachs. Both individuals died soon after they had been taken sitting on the soil in bad condition. There are some findings of dead eagles in the same area which showed no sign of having been injured. The two cases of presumed lead poisoning coincide with intense efforts to reduce the number of ChamoixRupicapra rupicapra by hunting. The bullets used contain a nucleus of lead and eagles were seen taking the entrails of the shot chamoix. 相似文献
123.
124.
Synaptonemal complexes and meiosis in myxomycetes 总被引:4,自引:0,他引:4
Synaptonemal complexes (SC) have been observed in spores 18–24 hr past cleavage in natural fruitings of Physarum cinereum, P. bogoriense, Hemitrichia stipitata, Tubifera ferruginosa, and Arcyria incarnata. Laboratory fruitings of Arcyria cinerea, Stemonitis herbatica, and a homothallic isolate of Physarum pusillum also have SC's present in spores during the same postcleavage period. The presence of these paired chromosomes of meiotic prophase in spores of species collected in nature and in a diversity of taxa suggests that the usual position of meiosis in Myxomycetes is inside the postcleavage spore. Criteria are proposed for evaluating the validity of the SC as an indicator of meiosis. 相似文献
125.
126.
Peanut (Arachis hypogaea) agglutinin (PNA) is extensively used as tumour marker as it strongly recognises the cancer specific T antigen (Galβ1→3GalNAc-), but not its sialylated version. However, an additional specificity towards Galβ1→4GlcNAc (LacNAc), which is not tumour specific, had been attributed to PNA. For correct interpretation of lectin histochemical results we examined PNA sugar specificity using naturally occurring or semi-synthetic glycoproteins, matrix-immobilised galactosides and lectin-binding tissue glycoproteins, rather than mono- or disaccharides as ligands. Dot-blots, transfer blots or polystyrene plate coatings of the soluble glycoconjugates were probed with horse-radish peroxidase (HRP) conjugates of PNA and other lectins of known specificity. Modifications of PNA-binding glycoproteins, including selective removal of O-linked oligosaccharides and treatment with glycosidases revealed that Galβ1→4GlcNAc (LacNAc) was ineffective while terminal α-linked galactose (TAG) as well as exposed T antigen (Galβ1→3 GalNAc-) was excellent as sugar moiety in glycoproteins for their recognition by PNA. When immobilised, melibiose was superior to lactose in PNA binding. Results were confirmed using TAG-specific human serum anti-α-galactoside antibody. 相似文献
127.
128.
Ramakrishna A. Bangaru Yatish K. Bansal A. R. M. Rao T. P. Gandhi 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2000,739(2)
A rapid, simple and sensitive reversed-phase high-performance liquid chromatographic (HPLC) method has been developed for the measurement of acyclovir concentrations in human plasma and its use in bioavailability studies is evaluated. Unchanged acyclovir has been quantified without the introduction of an internal standard using the present method. Human plasma proteins were selectively precipitated by the addition of 7% perchloric acid to spiked plasma samples or to the plasma samples obtained after acyclovir administration to human volunteers and the mixture was spun at 1000 g for 10 min. The supernatant was directly injected into a Novaflex C18 column and detected at 254 nm. The mobile phase consisted of octane sulfonic acid buffer (pH 2.5) and methanol (92:08). The limit of quantitation for acyclovir in plasma was 20 ng/ml, which enabled the determination of the area under the curve (AUC) more precisely, that is, it is much closer to its extrapolated value. The present method has been successfully applied to samples from bioavailability studies. 相似文献
129.
The cellular long-chain component patterns of 33 strains of Eubacterium lentum were determined by gas chromatography. Two main types of long-chain component patterns were distinguished. The first (26 strains) was characterized by saturated branched-chain fatty acids (br14:0, br15:0, br16:0 and br17:0). The second (7 strains) did not contain branched-chain fatty acids and was characterized by saturated straight-chain fatty acids (11:0, 12:0, 14:0 and 16:0). Both types contained fatty aldehydes and their respective dimethyl acetals (14ald and 14dma, 16ald and 16dma). br16dma was only found in the first type. The G + C content of the DNA (Tm) of the 33 strains varied between 63.7 and 69.1 mol %. Canonical correlation analysis distinguished three subtypes within the first main type. 相似文献
130.
A simple new procedure was described for producing a sequential series of overlapping clones for use in DNA sequencing. The technique used single-stranded M13 DNA and complementary DNA oligomers to form specific cleavage and ligation substrates. It was, therefore, independent of the sequence of the DNA cloned into the vector. Deletions of varying sizes were generated from one end of the insert through the 3' to 5' exonuclease activity of T4 DNA polymerase. The approximate size of the deletion and therefore the starting point for DNA sequencing could be estimated by electrophoresis of the subcloned phage DNA on a agarose gel. This greatly reduced the number of templates that must be sequenced to obtain a complete sequence. The entire procedure could be carried out in one tube in less than a day. The procedure was used to subclone and sequence the maize mitochondrial 18 S rDNA and 5' flanking region (2622 bases) in less than a week. Other applications of oligomers and single-stranded DNA in the construction of insertions, deletions, and cDNAs are discussed. 相似文献