全文获取类型
收费全文 | 1478篇 |
免费 | 68篇 |
国内免费 | 126篇 |
专业分类
1672篇 |
出版年
2024年 | 2篇 |
2023年 | 19篇 |
2022年 | 20篇 |
2021年 | 16篇 |
2020年 | 30篇 |
2019年 | 49篇 |
2018年 | 36篇 |
2017年 | 49篇 |
2016年 | 41篇 |
2015年 | 36篇 |
2014年 | 61篇 |
2013年 | 163篇 |
2012年 | 46篇 |
2011年 | 94篇 |
2010年 | 41篇 |
2009年 | 76篇 |
2008年 | 63篇 |
2007年 | 66篇 |
2006年 | 64篇 |
2005年 | 63篇 |
2004年 | 54篇 |
2003年 | 58篇 |
2002年 | 55篇 |
2001年 | 75篇 |
2000年 | 37篇 |
1999年 | 44篇 |
1998年 | 18篇 |
1997年 | 18篇 |
1996年 | 27篇 |
1995年 | 24篇 |
1994年 | 32篇 |
1993年 | 30篇 |
1992年 | 36篇 |
1991年 | 27篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 2篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 14篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有1672条查询结果,搜索用时 15 毫秒
71.
Social interest reflects the motivation to approach a conspecific for the assessment of social cues and is measured in rats by the amount of time spent investigating conspecifics. Virgin female rats show lower social interest towards unfamiliar juvenile conspecifics than virgin male rats. We hypothesized that the neuropeptide oxytocin (OT) may modulate sex differences in social interest because of the involvement of OT in pro-social behaviors. We determined whether there are sex differences in OT system parameters in the brain and whether these parameters would correlate with social interest. We also determined whether estrus phase or maternal experience would alter low social interest and whether this would correlate with changes in OT system parameters. Our results show that regardless of estrus phase, females have significantly lower OT receptor (OTR) binding densities than males in the majority of forebrain regions analyzed, including the nucleus accumbens, caudate putamen, lateral septum, bed nucleus of the stria terminalis, medial amygdala, and ventromedial hypothalamus. Interestingly, male social interest correlated positively with OTR binding densities in the medial amygdala, while female social interest correlated negatively with OTR binding densities in the central amygdala. Proestrus/estrus females showed similar social interest to non-estrus females despite increased OTR binding densities in several forebrain areas. Maternal experience had no immediate or long-lasting effects on social interest or OT brain parameters except for higher OTR binding in the medial amygdala in primiparous females. Together, these findings demonstrate that there are robust sex differences in OTR binding densities in multiple forebrain regions of rats and that OTR binding densities correlate with social interest in brain region- and sex-specific ways. 相似文献
72.
Alison Baker 《Molecular membrane biology》2013,30(1-2):1-2
The interactions of mouse thymocytes with unilamellar phospholipid vesicles comprised of dimyristyl lecithin (DML), dipalmitoyl lecithin (DPL), dioleoyl lecithin (DOL), and egg yolk lecithin (EYL) were examined in vitro.In cells treated with [3H]DML or [3H]DPL vesicles, electron microscope (EM) autoradiographic analysis showed most of the radioactive lipids to be confined to the cell surface. Transmission EM studies showed the presence of intact vesicles (DPL) and collapsed or ruptured vesicle fragments (DML) adsorbed to the surfaces of treated cells. In cells treated with DPL vesicles containing a watersoluble dye (6-carboxyfluorescein; 6-CF), most of the fluorescent vesicles were localized at the periphery of the treated cells. Furthermore, substantial fractions of the cell-associated DPL and DML could be released by a mild trypsinization without damaging the cells. These results suggest that the uptake of DML and DPL is primarily due to vesicle-cell adsorption. Such an adsorption process appears to be enhanced at or below the thermotropic-phase transition temperature of the vesicle lipid. Under certain conditions these adherent vesicles also formed patches or caps on the cell surface.In cells treated with DOL or EYL vesicles, transmission EM and EM autoradiography showed relatively little exogenous vesicle lipid located at the cell surface. Thymocytes incubated (37°C) with [14C] EYL vesicles containing a trapped marker, [3H]inulin, incor porated both isotopes at identical rates. In separate experiments it was found that this marker was located inside the treated cells. Thymocytes treated with DOL vesicles containing 6-CF exhibited a uniform and diffuse distribution of dye in the internal volume of the cells. Little cell-associated EYL or DOL could be released by trypsinization. Evidence against endocytosis of intact vesicles as a major pathway of vesicle uptake is also presented. These observations, coupled with the demonstration of vesicle-cell lipid exchange as a minor component of vesicle uptake suggest that incorporation of EYL and DOL vesicles by thymocytes is primarily by vesicle-cell fusion. 相似文献
73.
Tuhidul Islam Noor Shad Bibi Rami Reddy Vennapusa Marcelo Fernandez‐Lahore 《Journal of molecular recognition : JMR》2013,26(8):341-350
Peptide affinity tags have become efficient tools for the purification of recombinant proteins from biological mixtures. The most commonly used ligands in this type of affinity chromatography are immobilized metal ions, proteins, antibodies, and complementary peptides. However, the major bottlenecks of this technique are still related to the ligands, including their low stability, difficulties in immobilization, and leakage into the final products. A model approach is presented here to overcome these bottlenecks by utilizing macroporous ceramic fluorapatite (CFA) as the stationary phase in chromatography and the CFA‐specific short peptides as tags. The CFA chromatographic materials act as both the support matrix and the ligand. Peptides that bind with affinity to CFA were identified from a randomized phage display heptapeptide library. A total of five rounds of phage selection were performed. A common N‐terminal sequence was found in two selected peptides: F4‐2 (KPRSMLH) and F5‐4 (KPRSVSG). The peptide F5‐4, displayed by more than 40% of the phages analyzed in the fifth round of selection, was subjected to further studies. Selectivity of the peptide for the chemical composition and morphology of CFA was assured by the adsorption studies. The dissociation constant, obtained from the F5‐4/CFA adsorption isotherm, was in the micromolar range, and the maximum capacity was 39.4 nmol/mg. The chromatographic behavior of the peptides was characterized on a CFA stationary phase with different buffers. Preferential affinity and specific retention properties suggest the possible application of the phage‐derived peptides as a tag in CFA affinity chromatography for enhancing the selective recovery of proteins. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
74.
Ali Reza Harifi-Mood Fatemeh Hadavand-Mirzaie 《Chemical Speciation and Bioavailability》2013,25(1):8-14
Waste sugar beet pulp has been used as adsorbent for the removal of a hazardous cationic dye, Basic violet 16, from its aqueous solution. Adsorption of the dye was studied as function of time, pH of the solution, dosage of the adsorbent, sieve size of the particles, concentration of the dye, and temperature. The initial pH of the dye solution did not affect the chemistry of the dye molecule and the surface of beet pulp. Langmuir and Freundlich adsorption isotherms were successfully employed, and on the basis of these models, the thermodynamic parameters were evaluated. Adsorption of Basic violet 16 on beet pulp was found to be an exothermic reaction. Time contact studies showed that more than 80% adsorption of the dye is achieved in less than 1 h. Kinetics investigations confirmed both pseudo-first-order and pseudo-second-order behaviors; on the other hand, it shows that the intraparticle diffusion step is not the only rate-controlling step in all concentrations. 相似文献
75.
Nicholas T. Loux David S. Brown Claudia R. Chafin Jerry D. Allison Sayed M. Hassan 《Chemical Speciation and Bioavailability》2013,25(3):111-125
AbstractCoupled geochemical speciation/transport models are being developed to assess potential transport of metal contaminants in the subsurface environment. In a test of the geochemical speciation portion of the effort, MINTEQA2 model predictions are compared with laboratory data concerning the pH dependent partitioning behavior of eight cationic contaminants (Ba, Be, Cd, Cu, Ni, Pb, Tl and Zn) on a sandy aquifer material in an oxidized environment. MINTEQA2 contains provisions for describing potential attenuation due to both mineral phase precipitation processes and adsorption processes resulting from amorphous iron oxides in aquifer materials (MIT Diffuse Layer Model). In the comparison, several trends were discerned. (1) Adsorptive processes tend to better describe the pH-dependent partitioning behavior of transition metals (especially Pb, Zn and Ni). (2) Cd behavior is better described by precipitation as a cadmium carbonate phase. (3) Cu behavior is not reasonably described by the model. (4) Ba and Be comparisons are poor (although presumably their partitioning behavior results from adsorptive and/or pH sensitive solid solution processes). (5) unlike the other elements, the behavior of Tl is relatively insensitive to pH. 相似文献
76.
Celeste C. Ibarra‐Herrera Rami Reddy‐Vennapusa Marco Rito‐Palomares Marcelo Fernández‐Lahore 《Journal of molecular recognition : JMR》2013,26(12):618-626
Hydrophobic interaction chromatography (HIC) is an important tool in the industrial purification of proteins from various sources. The HIC separation behavior of individual (or model) proteins has been widely researched by others. On the contrary, this study focused on the fractionation ability of HIC when it is challenged with whole proteomes. The impact of the nature of three different proteomes, that is, yeast, soybean, and Chinese hamster ovary cells, on HIC separation was investigated. In doing so, chromatography fractions obtained under standardized conditions were evaluated in terms of their overall hydrophobicity—as measured by fluorescence dye binding. This technique allowed for the calculation of an average protein surface hydrophobicity (S0) for each fraction; a unique correlation between S0 and the observed chromatographic behavior was established in each case. Following a similar strategy, the effect of three different ligands (polypropylene glycol, phenyl, and butyl) and two adsorbent particle sizes (65 and 100 µm) on the chromatographic behavior of the yeast proteome was evaluated. As expected, the superficial hydrophobicity of the proteins eluted is correlated with the salt concentration of its corresponding elution step. The findings reveled how—and in which extent—the type of ligand and the size of the beads actually influenced the fractionation of the complex biological mixture. Summarizing, the approach presented here can be instrumental to the study of the performance of chromatography adsorbents under conditions close to industrial practice and to the development of downstream processing strategies. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
77.
《Bioscience, biotechnology, and biochemistry》2013,77(12):1945-1949
A thin porous silica membrane (average pore size of 3.3 mm) was prepared by the sol–gel method and used to separate the solute from supercritical carbon dioxide. The characteristics of solute permeation were investigated in respect of the adsorption properties of the solute, the desorption rate of the solute from the membrane being measured and the potential energy of solute near the silica surface being calculated by the molecular modeling technique. It was found that caffeine was strongly adsorbed to the surface and then slowly desorbed to form an adsorption layer, making the pores narrower and causing a molecular-sieving effect. Therefore, the rejection value was positive. On the other hand, the rejection value of n-octanoic acid, which was well adsorbed and rapidly desorbed, was negative. It is presumed that the molecules filled the pores due to their potential energy and were then forced to flow through the pores by the transmembrane pressure. 相似文献
78.
Satoshi Ōmura Haruo Tanaka Juichi Awaya Yoshitsugu Narimatsu Yaeko onda Toju Hata 《Bioscience, biotechnology, and biochemistry》2013,77(5):899-906
In the course of our examination for the alkaloid productivities of Streptomyces strains, Streptomyces sp. NA–15 was found to produce a new alkaloid, pyrindicin, in the culture medium. The strain NA–15 was found to be a variant of Streptomyces griseoflavus and was designated as S. griseoflavus var. pyr indie us nov. var.After the culture conditions for pyrindicin production were studied, pyrindicin was obtained as its hydrochloride (mp 145°C, decomp.) from the cultured broth. The compound was shown to possess weak antimicrobial and several pharmacological activities. The LD50 of the hydrochloride (ip, in mice) was 87 mg/kg. 相似文献
79.
William Kelly Jonathan Rubin Jennifer Scully Hari Kamaraju Piotr Wnukowski Ravinder Bhatia 《Biotechnology progress》2016,32(6):1520-1530
Within the last decade, fully disposable centrifuge technologies, fluidized‐bed centrifuges (FBC), have been introduced to the biologics industry. The FBC has found a niche in cell therapy where it is used to collect, concentrate, and then wash mammalian cell product while continuously discarding centrate. The goal of this research was to determine optimum FBC conditions for recovery of live cells, and to develop a mathematical model that can assist with process scaleup. Cell losses can occur during bed formation via flow channels within the bed. Experimental results with the kSep400 centrifuge indicate that, for a given volume processed: the bed height (a bed compactness indicator) is affected by RPM and flowrate, and dead cells are selectively removed during operation. To explain these results, two modeling approaches were used: (i) equating the centrifugal and inertial forces on the cells (i.e., a force balance model or FBM) and (ii) a two‐phase computational fluid dynamics (CFD) model to predict liquid flow patterns and cell retention in the bowl. Both models predicted bed height vs. time reasonably well, though the CFD model proved more accurate. The flow patterns predicted by CFD indicate a Coriolis‐driven flow that enhances uniformity of cells in the bed and may lead to cell losses in the outflow over time. The CFD‐predicted loss of viable cells and selective removal of the dead cells generally agreed with experimental trends, but did over‐predict dead cell loss by up to 3‐fold for some of the conditions. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1520–1530, 2016 相似文献
80.