全文获取类型
收费全文 | 1790篇 |
免费 | 77篇 |
国内免费 | 14篇 |
专业分类
1881篇 |
出版年
2024年 | 12篇 |
2023年 | 15篇 |
2022年 | 29篇 |
2021年 | 31篇 |
2020年 | 31篇 |
2019年 | 31篇 |
2018年 | 51篇 |
2017年 | 58篇 |
2016年 | 63篇 |
2015年 | 71篇 |
2014年 | 82篇 |
2013年 | 126篇 |
2012年 | 137篇 |
2011年 | 120篇 |
2010年 | 80篇 |
2009年 | 87篇 |
2008年 | 110篇 |
2007年 | 101篇 |
2006年 | 82篇 |
2005年 | 82篇 |
2004年 | 59篇 |
2003年 | 58篇 |
2002年 | 60篇 |
2001年 | 17篇 |
2000年 | 25篇 |
1999年 | 22篇 |
1998年 | 13篇 |
1997年 | 16篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 14篇 |
1993年 | 12篇 |
1992年 | 15篇 |
1991年 | 15篇 |
1990年 | 17篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1980年 | 5篇 |
1978年 | 4篇 |
1973年 | 5篇 |
1970年 | 3篇 |
1968年 | 3篇 |
1967年 | 3篇 |
1965年 | 4篇 |
排序方式: 共有1881条查询结果,搜索用时 15 毫秒
1.
Aqueous solutions of silver nitrate (10–100 g/plant) and cobalt chloride (125–500 g/plant), injected into the main stem of plants of the pistillate cv. 240 ofRicinus communis when the vegetative shoot apex was beginning to become reproductive, induced the formation of staminate (male) flowers with viable pollen in the normally strictly pistillate (female) terminal inflorescence, their number increasing with the dose of Ag+ and Co2+. No formation of bisexual flowers was noted. Female flowers pollinated with pollen from the induced male ones produced fruits and viable seeds. 相似文献
2.
Summary Adsorption isotherms for the adsorption of chromium onZoogloea ramigera are developed. The rates were affected by the pH and temperature of adsorption medium. The biomass ofZ. ramigera at pH 2.0 where the optimum pH for biosorption lies exhibited the highest chromium adsorptive uptake capacity. In general, higher adsorptive uptake was observed at 25°C than 35°C and 45°C. 相似文献
3.
R G Sa?futdinov 《Biulleten' eksperimental'no? biologii i meditsiny》1985,100(9):296-297
The electron-spin resonance (ESR) was applied to examine human plasma and red cell lipids. In the lipids, the signal of ESR of alpha-tocopherylquinone was recorded. The concentration of the latter in the lipids was found to be elevated in coronary heart disease. Intramuscular injection of 30% oily solution of alpha-tocopherylquinone in a dose of 2 ml two times a day over three days entailed an increase in the concentration of alpha-tocopherylquinone in plasma and red cell lipids. 相似文献
4.
Process development for biologics is expensive and lengthy, tools are needed to rapidly understand where the difficulties will lie, and, hence, rationally deploy resources. In this work we introduce and evaluate a methodology to determine the manufacturability of a protein candidate. The methodology determines protein impurities by mass spectrometry and separation difficulty from the product based on adsorption properties deduced from a single set of experiments. This information can aid early process strategy decisions to target hard to remove protein impurities (nearest neighbors) and allow the re-evaluation of conventional process synthesis. The methodology chosen gives consideration to the fact that at this point in early phase development, material, and established analytical methods are limiting. This study uses surface enhanced laser desorption ionization mass spectroscopy (SELDI-MS), for its rapid analysis and minimal sample requirement to measure product and contaminant adsorption properties. The technique is used to provide an array of hydrophobic and electrostatic conditions for protein adsorption. The adsorption pattern produced for each protein is analyzed and visualized via a star plot. Dendrograms then define nearest neighbor protein contaminants by quantifying differences in the adsorption pattern between the product and contaminants. By comparison to an existing process to manufacture a 28 kDa recombinant protein expressed in Escherichia coli, we confirm the method is capable of determining where the greatest separation difficulty lies and what separation methods should be considered. The technique identified that the nearest neighbor contaminants were product-related proteins (28.6 and 29.1 kDa/e). Thus demonstrating a capability to measure the relative difficulty of purifying early stage protein candidates where little is known about the separation properties of products and contaminants, or the process sequence for their production. 相似文献
5.
Alginate matrix tablet of diltiazem hydrochloride (DTZ), a water-soluble drug, was prepared using sodium alginate (SAL) and
calcium gluconate (CG) by the conventional wet granulation method for sustained release of the drug. The effect of formulation
variables like SAL/CG ratio, drug load, microenvironmental pH modulator, and processing variable like compression force on
the extent of drug release was examined. The tablets prepared with 1:2 w/w ratio of SAL/CG produced the most sustained release of the drug extending up to 13.5 h. Above and below this ratio, the drug
release was faster. The drug load and the hardness of the tablets produced minimal variation in drug release. The addition
of alkaline or acidic microenvironmental modulators did not extend the release; instead, these excipients produced somewhat
faster release of diltiazem. This study revealed that proper selection of SAL/CG ratio is important to produce alginate matrix
tablet by wet granulation method for sustained release of DTZ. 相似文献
6.
Kuwahara M Hanawa K Ohsawa K Kitagata R Ozaki H Sawai H 《Bioorganic & medicinal chemistry》2006,14(8):2518-2526
We synthesized modified 2'-deoxyuridine triphosphates bearing amino acids at the C5 position and investigated their substrate properties for KOD Dash DNA polymerase during polymerase chain reaction (PCR). PCR using C5-modified dUTP having an amino acyl group (arginyl, histidyl, lysyl, phenylalanyl, tryptophanyl, leucyl, prolyl, glutaminyl, seryl, O-benzyl seryl or threonyl group) gave the corresponding full-length PCR products in good yield. Although dUTP analogues bearing aspartyl, glutamyl or cysteinyl were found to be poor substrates for PCR catalyzed by KOD Dash DNA polymerase, optimization of the reaction conditions resulted in substantial generation of full-length product. In the case of reaction using dUTP analogue having a cysteinyl group, addition of a reducing agent improved the reaction yield. Thus, PCRs using KOD Dash DNA polymerase together with amino acyl dUTP provide convenient and efficient preparation of various modified DNA libraries with potential protein-like activities. 相似文献
7.
Introduction
Recent studies suggest that heat is associated with an increase in the number of ambulance calls and emergency department visits. We investigated the association between heat and daily number of emergency department visits at the University Hospital of Verona during the warm seasons 2011–2012 and we assessed the magnitude of the impact in terms of attributable events, focusing on the role of age and triage codification.Materials and methods
We used a Poisson model to analyse the association between daily number of visits and daily mean apparent temperature, accounting for air pollution level and seasonality. The analyses were stratified by age group and were performed both on the total number of emergency department visits and on the subsample of high-priority visits. Impact estimates were obtained only for this subsample, using a Monte Carlo approach to account for sampling variability. Number of attributable events and attributable community rate were calculated.Results
We found a positive and immediate association between event occurrence and mean apparent temperatures exceeding a threshold located around 28–29°C. The estimated percent change in the total number of visits per 1°C increase of exposure above the threshold was equal to 3.75 (90% CI: 3.01; 4.49). Focusing only on high-priority visits, the estimated percent change was larger and the greatest effect was among children. We estimated that apparent temperatures above the threshold were responsible for 1177 high-priority visits during the study period. Due to the record high temperatures observed in 2012 in Italy and in Europe, the impact in 2012 was much larger than in 2011, and consisted in 34 high-priority visits every 10000 children, 30 every 10000 people aged 15–64, and 38 every 10000 people aged 65 and over.Discussion
Our results indicate that heat affects not only the elderly, but also children and non-elderly adults, stressing the need for developing public health preparedness plans for the entire community. 相似文献8.
9.
Avraham Geier Rachel Beery Michal Haimsohn Rina Hemi Zvi Malik Avraham Karasik 《In vitro cellular & developmental biology. Animal》1994,30(12):867-874
Summary The ability of epidermal growth factor (EGF), insulinlike growth factor-1 (IGF-1), insulin, 12-O-tetradecanoylphorbol-13-acetate (TPA), and aurintricarboxylic acid (ATA) to protect the human breast cancer cell line MDA-231 from death induced by the anticancer drug adriamycin was investigated. Cell death was induced in the MDA-231 cells either by a short-time exposure to a high dose of adriamycin (2 μg · ml−1 · 1 h−1) and further culturing in the absence of the drug, or by continuous exposure to a low dose of adriamycin (0.3μg/ml). Cell death was evaluated after 48 h of incubation by several techniques (trypan blue dye exclusion, lactic dehydrogenase activity, cellular ATP content, transmission electron microscopy, and DNA fragmentation). EGF, TPA, and ATA, each at an optimal concentration of 20 ng/ml, 5 ng/ml, and 100μg/ml respectively, substantially enhanced survival of cells exposed either to a high or low dose of adriamycin. Neither IGF-1 nor insulin, each at concentrations of 20 ng/ml, had an effect on cell survival. The three survival factors enhanced protein synthesis in the untreated cells and attenuated the continuous decrease in protein synthesis in the adriamycin-treated cells. Moreover, the three survival factors protected the MDA-231 cells from death in the absence of protein synthesis (cycloheximide 30μg/ml). These results suggest that EGF, TPA, and ATA promote survival of adriamycin pretreated cells by at least two mechanisms: enhancement of protein synthesis and by a protein synthesis independent process, probably a posttranslational modification effect. 相似文献
10.
近年来有关细胞内信号传导的研究,着重体现在Ca2+信号传导途径及相应的蛋白质分子如蛋白激酶C(PKC)、钙调素(CaM)、钙调素激酶Ⅱ(CaMKⅡ),同时也对Ras途径中出现的Vav、Rap、Crk、C3G等蛋白质分子以及cAMP和NF-κB途径作了有益的补充与修改.细胞外信号分子通过以上4种途径及其相互通讯(cross-talk),激活了某些蛋白激酶,调控了基因转录及其他相关功能,其中磷酸化对蛋白激酶及转录因子活性的调节起到了非常重要的作用. 相似文献