全文获取类型
收费全文 | 1751篇 |
免费 | 79篇 |
国内免费 | 1篇 |
出版年
2023年 | 20篇 |
2022年 | 22篇 |
2021年 | 68篇 |
2020年 | 47篇 |
2019年 | 46篇 |
2018年 | 64篇 |
2017年 | 61篇 |
2016年 | 70篇 |
2015年 | 100篇 |
2014年 | 96篇 |
2013年 | 155篇 |
2012年 | 124篇 |
2011年 | 124篇 |
2010年 | 86篇 |
2009年 | 59篇 |
2008年 | 94篇 |
2007年 | 85篇 |
2006年 | 87篇 |
2005年 | 73篇 |
2004年 | 72篇 |
2003年 | 51篇 |
2002年 | 43篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 14篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1962年 | 2篇 |
1958年 | 3篇 |
排序方式: 共有1831条查询结果,搜索用时 390 毫秒
191.
Aceto S Di Maro A Conforto B Siniscalco GG Parente A Delli Bovi P Gaudio L 《Biological chemistry》2005,386(4):307-317
Ribosome-inactivating proteins isolated from Phytolacca dioica L. leaves are rRNA-N-glycosidases, as well as adenine polynucleotide glycosylases. Here we report that some of them cleave supercoiled pBR322 dsDNA, generating relaxed and linear molecules. PD-L1, the glycosylated major form isolated from the winter leaves of adult P . dioica plants, produces both free 3'-OH and 5'-P termini randomly distributed along the DNA molecule, as suggested by labelling experiments with [alpha- 32P]dCTP and [gamma- 32 P]dATP. Moreover, when the reaction is carried out under low-salt conditions, cleavage is observed mainly at a specific site, located downstream of the ampicillin resistance gene (close to position 3200), ending with the deletion of a fragment of approximately 70 nucleotides. This cleavage pattern is similar to that obtained under the same conditions with mung bean nuclease, a single-strand endonuclease. Furthermore, pBR322 DNA treated with PD-L1 shows reduced transforming activity with E . coli HB101 competent cells in comparison to untreated control plasmid DNA. 相似文献
192.
Various chromosomal banding techniques were utilized on the catfish, Iheringichthys labrosus, taken from the Capivara Reservoir. C-banding regions were evidenced in telomeric regions of most of the chromosomes. The B microchromosome appeared totally heterochromatic. The restriction endonuclease AluI produced a banding pattern similar to C-banding in some chromosomes; the B microchromosome, when present, was not digested by this enzyme and remained stained. G-banding was conspicuous in almost all the chromosomes, with the centromeres showing negative G-banding. When the restriction endonuclease BamHI was used, most of the telomeres remained intact, while some centromeres were weakly digested. The B chromosome was also not digested by this enzyme. The first pair of chromosomes showed a pattern of longitudinal bands, both with G-banding and BamHI; this was more evident with G-banding. This banding pattern can be considered a chromosomal marker for this population of I. labrosus. 相似文献
193.
The reactions of the triangulo-cluster [Pt3(μ-CO)3(PtBu3)3] with activated olefins and alkynes have been examined under various conditions. At low temperature, cluster fragmentation occurs yielding the Pt(0) complexes [Pt(CO)(PtBu3)(olefin)] (olefin = maleic anhydride and maleimide), while di(tert-butyl)acetylenedicarboxilate reacts quantitatively giving the dinuclear Pt(0) complex [Pt2(CO)2(PtBu3)2(μ-η2:η2-tBuO2CCCCO2tBu)]. At higher temperature and in the presence of alkyne in large excess, the latter dimer converts quantitatively to the monomers [Pt(CO)(PtBu3)(alkyne)] (alkyne = CF3CCCF3 and tBuO2CCCCO2tBu). The stereochemistry of these complexes has been established by NMR and IR measurements. The structure of [Pt(CO)(PtBu3)(CF3CCCF3)] was confirmed by X-ray diffraction analysis. 相似文献
194.
The arsonium-substituted isocyanides, o-(I−+R3AsCH2)C6H4NC (AsR3=AsPh3, L1; AsMePh2, L2; AsMe2Ph, L3), were prepared by reaction of o-(chloromethyl)phenyl isocyanide, o-(CH2Cl)C6H4NC, with a slight molar stoichiometric amount of the arsine in the presence of a 3-fold excess of NaI in acetone at room temperature. The isocyanides L1-L3 coordinate to some Pt(II) complexes such as trans-[PtX{o-(I−+R3AsCH2)C6H4NC}(PPh3)2] [BF4] (AsR3=AsPh3, 1; AsMePh2, 2; AsMe2Ph, 3; X=Cl, I) and [PtX{o-(I−+R3AsCH2)C6H4NC}(Ph2PCHCHPPh2)] [BF4] (AsR3=AsMePh2, 4; X=Cl, I). Complexes 2-4 are converted in CH2Cl2 at room temperature in the presence of NEt3 to the corresponding indolidin-2-ylidene derivatives trans-[PtX{(AsR3)}(PPh3)2]BF4] (AsR3=AsPh3, 5; AsMePh2, 6; AsMe2Ph, 7) and [PtX{(AsMePh2)}(Ph2PCHCHPPh2)][BF4] (8). 相似文献
195.
Tringali C Papini N Fusi P Croci G Borsani G Preti A Tortora P Tettamanti G Venerando B Monti E 《The Journal of biological chemistry》2004,279(5):3169-3179
Recombinant human cytosolic sialidase (HsNEU2), expressed in Escherichia coli, was purified to homogeneity, and its substrate specificity was studied. HsNEU2 hydrolyzed 4-methylumbelliferyl alpha-NeuAc, alpha 2-->3 sialyllactose, glycoproteins (fetuin, alpha-acid glycoprotein, transferrin, and bovine submaxillary gland mucin), micellar gangliosides GD1a, GD1b, GT1b, and alpha 2-->3 paragloboside, and vesicular GM3. alpha 2-->6 sialyllactose, colominic acid, GM1 oligosaccharide, whereas micellar GM2 and GM1 were resistant. The optimal pH was 5.6, kinetics Michaelis-Menten type, V(max) varying from 250 IU/mg protein (GD1a) to 0.7 IU/mg protein (alpha(1)-acid glycoprotein), and K(m) in the millimolar range. HsNEU2 was activated by detergents (Triton X-100) only with gangliosidic substrates; the change of GM3 from vesicular to mixed micellar aggregation led to a 8.5-fold V(max) increase. HsNEU2 acted on gangliosides (GD1a, GM1, and GM2) at nanomolar concentrations. With these dispersions (studied in detailed on GM1), where monomers are bound to the tube wall or dilutedly associated (1:2000, mol/mol) to Triton X-100 micelles, the V(max) values were 25 and 72 microIU/mg protein, and K(m) was 10 and 15 x 10(-9) m, respectively. Remarkably, GM1 and GM2 were recognized only as monomers. HsNEU2 worked at pH 7.0 with an efficiency (compared with that at pH 5.6) ranging from 4% (on GD1a) to 64% (on alpha(1)-acid glycoprotein), from 7% (on GD1a) to 45% (on GM3) in the presence of Triton X-100, and from 30 to 40% on GM1 monomeric dispersion. These results show that HsNEU2 differentially recognizes the type of sialosyl linkage, the aglycone part of the substrate, and the supramolecular organization (monomer/micelle/vesicle) of gangliosides. The last ability might be relevant in sialidase interactions with gangliosides under physiological conditions. 相似文献
196.
Winter E Chiaradia LD de Cordova CA Nunes RJ Yunes RA Creczynski-Pasa TB 《Bioorganic & medicinal chemistry》2010,18(22):8026-8034
In this study, we investigated the effects of 24 chalcone derivatives from 2-naphthylacetophenone toward a lymphoblastic leukemia cell line (L1210). Three compounds, called R7, R13, and R15, presented concentration- and time-dependent cytotoxicity and induced cellular death by apoptosis via mitochondrial injury and oxidative stress. The effects of these compounds appear to occur through different mechanisms because R13 and R7 induced a greater disturbance of mitochondrial potential, and all compounds induced disturbances of cellular ATP content and increased caspase-3 activity before cellular death. These compounds also interfered with antioxidant enzymes activities and GSH content through different mechanisms. 相似文献
197.
Previous studies have shown that the amplitude of daily melatonin production in cultured ruin lizard pineal organs explanted in the summer is significantly higher than that from organs explanted in the winter. To test whether seasonal photoperiodic changes are decoded autonomously by the pineal gland, pineals explanted in summer were cultured in vitro and exposed to changes between winter and summer photoperiods. The changes in photoperiod duration did not affect the daily profiles of in vitro melatonin production. The discrepancy between the present in vitro results and those from lizards exposed to winter or summer photoperiods before pineal explantation supports the view that circadian information entering the pineal gland via its innervation is involved in determining seasonal changes of melatonin production in ruin lizards. We further examined whether a central component of the circadian system of ruin lizards, specifically the retinae of the lateral eyes, expresses similar seasonal changes in function as does the pineal gland. We did not find any difference between summer and autumn-winter in the effectiveness of either bilateral retinalectomy or optic nerve lesion-at the level of the optic chiasm-in altering circadian locomotor behavior in constant conditions. Both surgical procedures mostly induced a shortening of the free-running period of the locomotor rhythm of similar magnitude in all seasons. Thus, the retinae do not appear to participate in the seasonal reorganization of the circadian system in ruin lizards. 相似文献
198.
Fairweather D Frisancho-Kiss S Njoku DB Nyland JF Kaya Z Yusung SA Davis SE Frisancho JA Barrett MA Rose NR 《Journal of immunology (Baltimore, Md. : 1950)》2006,176(6):3516-3524
Complement and complement receptors (CR) play a central role in immune defense by initiating the rapid destruction of invading microorganisms, amplifying the innate and adaptive immune responses, and mediating solubilization and clearance of immune complexes. Defects in the expression of C or CR have been associated with loss of tolerance to self proteins and the development of immune complex-mediated autoimmune diseases such as systemic lupus erythematosus. In this study, we examined the role of CR on coxsackievirus B3 (CVB3)-induced myocarditis using mice deficient in CR1/2. We found that CR1/2 deficiency significantly increased acute CVB3 myocarditis and pericardial fibrosis resulting in early progression to dilated cardiomyopathy and heart failure. The increase in inflammation was not due to increased viral replication, which was not significantly altered in the hearts of CR1/2-deficient mice, but was associated with increased numbers of macrophages, IL-1beta levels, and immune complex deposition in the heart. The complement regulatory protein, CR1-related gene/protein Y (Crry), was increased on cardiac macrophage populations, while immature B220(low) B cells were increased in the spleen of CR1/2-deficient mice during acute CVB3-induced myocarditis. These results show that expression of CR1/2 is not necessary for effective clearance of CVB3 infection, but prevents immune-mediated damage to the heart. 相似文献
199.
Maria Bernardete Cordeiro de Sousa Silvana Lúcio Nogueira Moura Alexandre Augusto de Lara Menezes 《International journal of primatology》2006,27(1):263-272
Scent-marking behavior is associated with different behavioral contexts in callitrichids, including signalizing a territory, location of feeding resources, and social rank. In marmosets and tamarins it is also associated with intersexual communication. Though it appears very important for the daily routine of the individuals, very few researchers have investigated distribution through the 24-h cycle. In a preliminary report, we described a preferential incidence of this behavior 2 h before nocturnal rest in families of common marmosets. We expand the data using 8 family groups (28 subjects), 8 fathers, 6 mothers, 8 nonreproductive adults (4 sons and 4 daughters), and 6 juvenile (3 sons and 3 daughters) offspring that we kept in outdoor cages under natural environmental conditions. We recorded the frequency of anogenital scent marking for each group during the light phase, twice a wk, for 4 consecutive wks, from March 1998 to September 1999. Cosinor test detected 24- and 8-h variations in 89.3% and 85.7% of the subjects, respectively, regardless of sex or reproductive status. The 8-h component is a consequence of the 2 peaks for the behavior, at the beginning and end of the light phase. Daily distribution of scent marking is similar to that others described previously for motor activity in marmosets. The coincident rhythmical patterns for both behaviors seem to be associated with feeding behavior, as described for callitrichids in free-ranging conditions, involving an increase in foraging activities early in the morning and shortly before nocturnal rest. 相似文献
200.
In this work, an alternative to conventional preparation procedures for scanning electron microscopy (SEM) analysis of Cryptococcus neoformans was performed. The cells were fixed directly in the agar culture. This method is simpler than others already reported and the morphology of the cells was well preserved. 相似文献