全文获取类型
收费全文 | 31843篇 |
免费 | 2499篇 |
国内免费 | 9篇 |
出版年
2023年 | 216篇 |
2022年 | 444篇 |
2021年 | 832篇 |
2020年 | 563篇 |
2019年 | 743篇 |
2018年 | 930篇 |
2017年 | 802篇 |
2016年 | 1153篇 |
2015年 | 1537篇 |
2014年 | 1716篇 |
2013年 | 2072篇 |
2012年 | 2349篇 |
2011年 | 2223篇 |
2010年 | 1350篇 |
2009年 | 1255篇 |
2008年 | 1589篇 |
2007年 | 1588篇 |
2006年 | 1397篇 |
2005年 | 1275篇 |
2004年 | 1193篇 |
2003年 | 1064篇 |
2002年 | 990篇 |
2001年 | 576篇 |
2000年 | 562篇 |
1999年 | 495篇 |
1998年 | 270篇 |
1997年 | 243篇 |
1996年 | 237篇 |
1995年 | 201篇 |
1994年 | 197篇 |
1993年 | 187篇 |
1992年 | 301篇 |
1991年 | 259篇 |
1990年 | 224篇 |
1989年 | 224篇 |
1988年 | 216篇 |
1987年 | 208篇 |
1986年 | 195篇 |
1985年 | 166篇 |
1984年 | 180篇 |
1983年 | 122篇 |
1982年 | 129篇 |
1981年 | 103篇 |
1979年 | 134篇 |
1978年 | 107篇 |
1977年 | 105篇 |
1976年 | 100篇 |
1975年 | 133篇 |
1974年 | 97篇 |
1973年 | 115篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
S Ribeiro C S Alviano F C Silva-Filho E F da Silva J Angluster W de Souza 《Microbios》1989,57(231):121-129
The surface anionic groups of Entamoeba invadens were analysed by cell electrophoresis, by ultrastructural cytochemistry, and by identification of sialic acids using paper and gas-liquid chromatography. Binding of colloidal iron hydroxide (CIH) and of cationized ferritin (CF) particles at pH 1.8 and 7.2, respectively, was observed on the cell surface. E. invadens has a highly negative surface charge (-0.96 microns s-1 V-1 cm). Treatment of the cells with trypsin and neuraminidase significantly reduced the electrophoretic mobility by 24% and 40%, respectively. Treatment of the amoebae with neuraminidase also markedly decreased the binding of CIH to the cell surface. This finding suggests that sialic acid residues are the major anionogenic groups exposed on the surface of E. invadens. Paper and gas-liquid chromatography showed that N-acetylneuraminic acid was the only derivative characterized in E. invadens. 相似文献
102.
The effects of Cd on poly(γ-glutamylcysteinyl)glycine [(γEC)nG] biosynthesis and formation of (γEC)nG:Cd complexes were measured in two cell lines of Datura innoxia with differing Cd tolerance. In addition, RNA synthesis, protein synthesis, and GSH concentrations were measured during a 48 hour exposure to Cd. Exposure to 250 micromolar CdCl2 was toxic to the sensitive line, whereas the tolerant line survived and grew in its presence. Cd-sensitive cells synthesized the same amount of (γEC)nG as tolerant cells during an initial 24 hour exposure to 250 micromolar CdCl2. However, rates of (γEC)nG:Cd complex formation differed between the two cell lines with the sensitive cells forming complexes later than tolerant cells. In addition, the complexes formed by sensitive cells were of lower molecular weight than those of tolerant cells and did not bind all of the cellular Cd. Pulse-labeling of cells with l-[35S]cysteine resulted in equivalent rates of incorporation into the (γEC)nG of both cell lines during the initial 24 hours after Cd. Rates of protein and RNA synthesis were similar for both cell lines during the initial 8 hours after Cd but thereafter declined rapidly in sensitive cells. This was reflected by a decline in viability of sensitive cells. The GSH content of both cell lines declined rapidly upon exposure to Cd but was higher in sensitive cells throughout the experiment. These results show that the biosynthetic pathway for (γEC)nG synthesis in sensitive cells is operational and that relative overproduction of (γEC)nG is not the mechanism of Cd-tolerance in a Cd-tolerant cell line of D. innoxia. Rapid formation of (γEC)nG:Cd complexes that bind all of the cellular Cd within 24 hours appears to correlate with tolerance in these cells. 相似文献
103.
X. M. Shang H. T. Nguyen R. C. Jackson 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,77(1):84-94
Summary Heterochromatin differentiation, including band size, sites, and Giemsa staining intensity, was analyzed by the HKG (HCl-KOH-Giemsa) banding technique in the A genomes of 21 diploid (Triticum urartu, T. boeoticum and T. monococcum), 13 tetraploid (T. araraticum, T. timopheevi, T. dicoccoides and T. turgidum var. Dicoccon, Polonicum), and 7 cultivars of hexaploid (T. aestivum) wheats from different germplasm collections. Among wild and cultivated diploid taxa, heterochromatin was located mainly at centromeric regions, but the size and staining intensity were distinct and some accessions' genomes had interstitial and telomeric bands. Among wild and cultivated polyploid wheats, heterochromatin exhibited bifurcated differentiation. Heterochromatinization occurred in chromosomes 4At and 7At and in smaller amounts in 2At, 3At, 5At, and 6At within the genomes of the tetraploid Timopheevi group (T. araraticum, and T. timopheevi) and vice versa within those of the Emmer group (T. dicoccoides and T. turgidum). Similar divergence patterns occurred among chromosome 4Aa and 7Aa of cultivars of hexaploid wheat (T. aestivum). These dynamic processes could be related to geographic distribution and to natural and artifical selection. Comparison of the A genomes of diploid wheats with those of polyploid wheats shows that the A genomes in existing diploid wheats could not be the direct donors of those in polyploid wheats, but that the extant taxa of diploids and polyploids probably have a common origin and share a common A-genomelike ancestor.Contribution of the College of Agricultural Sciences, Texas Tech Univ. Journal No. T-4-233. 相似文献
104.
L. O. e Silva S. P. Singh M. A. Pastor-Corrales 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,78(5):619-624
Summary Inheritance of resistance to common bacterial blight in the trifoliate leaf, plant canopy, and pods was controlled by a single major gene. Additive followed by dominance effects were more important than epistatic interactions. Narrow-sense heritability values ranged from 0.18 to 0.87 for trifoliate leaf, from 0.26 to 0.76 for canopy, and from 0.11 to 0.36 for pods. Observed gains from selection for resistance were higher than expected gains. Implications of these results in breeding for resistance are discussed. 相似文献
105.
T L Machado L C Formiga R D Machado R R da Silva 《Memórias do Instituto Oswaldo Cruz》1989,84(2):241-243
The isolation of toxigenic Corynebacterium diphtheriae from sperm is reported. The organism was identified through the investigation of fluorescence under the UV light, the presence of pirazinecarboxilamidase enzyme (Pyz), in vitro and in vivo and virulence methods (single radial immunodiffusion, cell culture, guinea pig intradermic test). The strain was initially considered nontoxinogenic by single radial immunodiffusion, but its virulence was observed afterwards, when we applied the tests already mentioned. The strain could be considered a "Diphtheroid" without adequate specification. 相似文献
106.
107.
108.
Inhibition of Ca2+-induced cytosolic enzyme efflux from skeletal muscle by vitamin E and related compounds. 总被引:2,自引:2,他引:0
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
1. Efflux of an intracellular enzyme (creatine kinase) from normal rat skeletal muscles was induced by treatment with the Ca2+ ionophore A23187. Addition of alpha-tocopherol (230 microM) to the incubation medium was found to significantly diminish this efflux, and this effect was mimicked by alpha-tocopherol acetate, phytol and isophytol, but not by Trolox C (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid). 2. Analysis of muscle cation content has shown that these protective effects of alpha-tocopherol etc. are not due to an inhibition of the Ca2+ accumulating effects of the ionophore. 3. Non-enzymic lipid peroxidation of skeletal-muscle homogenates was found to be inhibited by alpha-tocopherol and Trolox C, partially inhibited by phytol and isophytol, but unaffected by alpha-tocopherol acetate. 4. The activity of lipoxygenase enzymes was partially inhibited by alpha-tocopherol, phytol and isophytol, but not by alpha-tocopherol acetate or Trolox C. 5. Prostaglandin E2 efflux from isolated skeletal muscles was stimulated by treatment with the Ca2+ ionophore, but this was unaffected by alpha-tocopherol treatment. 相似文献
109.
Development and validation of a sensitive immunohistochemical oestrogen receptor assay for use on archival breast cancer tissue 总被引:1,自引:0,他引:1
In a preliminary paper (Teasdale et al. 1987) comparing the oestrogen receptor (ER) content of breast cancers by the biochemical dextran coated charcoal (DCC) method and by two histochemical methods, peroxidase immunocytochemistry (ERICA) and immunogold-silver staining (IGSS), it was indicated that ERICA is more sensitive than DCC and that IGSS is as specific as ERICA but less sensitive. This paper describes the comparison of the above three assay methods with two other biochemical methods, iso-electric focusing (IEF) and an enzyme immuno-assay (EIA) on a larger number of cancers. All methods gave statistically comparable results except that IGSS remained less sensitive than the rest. Various modifications to IGSS showed that an immunogold streptavidin enhancement method (IG-SAM) produced sensitivity and specificity equal to that of ERICA. Since IGSS and its modifications are the only methods which can be used on archival paraffin-embedded cancers and IG-SAM gives results highly comparable to ERICA, retrospective studies can be performed on patients whose outcome and response to various treatments are known. Most recent studies have shown that ER positive results can be obtained from 10-year-old paraffin blocks. 相似文献
110.
C. E. Scanlon N. R. Chalmers M. A. O. Monteiro da Cruz 《International journal of primatology》1989,10(2):123-136
Three wild groups of common marmoset, Callithrix jacchus jacchus,in north-east Brazil, of approximately similar size, had home ranges between 2.5 and 6.5 ha. But their core areas were similar
in size between 1.0 and 1.5 ha, with a monthly area of heavy use between 1.1 and 1.6 ha. The groups were selective in the
use of their home ranges, even though they were small: they used some areas heavily and others lightly. The core areas had
higher densities of trees that produced gum exudates than did other parts of the home ranges. Our data suggest that a group
of marmosets in this habitat may require a minimum of about 50 gum trees in its home range at a minimum density of about 50
trees/ha. In addition, the animals require suitable trees in which to sleep. We suggest that patches of forest with these
desirable properties remain relatively fixed in size and location over the years and that individual animals are constantly
in flux between them. 相似文献