全文获取类型
收费全文 | 7256篇 |
免费 | 1297篇 |
国内免费 | 1370篇 |
专业分类
化学 | 6167篇 |
晶体学 | 139篇 |
力学 | 329篇 |
综合类 | 129篇 |
数学 | 810篇 |
物理学 | 2349篇 |
出版年
2024年 | 25篇 |
2023年 | 159篇 |
2022年 | 295篇 |
2021年 | 318篇 |
2020年 | 400篇 |
2019年 | 431篇 |
2018年 | 353篇 |
2017年 | 356篇 |
2016年 | 429篇 |
2015年 | 472篇 |
2014年 | 494篇 |
2013年 | 639篇 |
2012年 | 625篇 |
2011年 | 684篇 |
2010年 | 544篇 |
2009年 | 489篇 |
2008年 | 523篇 |
2007年 | 423篇 |
2006年 | 372篇 |
2005年 | 304篇 |
2004年 | 211篇 |
2003年 | 202篇 |
2002年 | 214篇 |
2001年 | 194篇 |
2000年 | 138篇 |
1999年 | 106篇 |
1998年 | 68篇 |
1997年 | 50篇 |
1996年 | 40篇 |
1995年 | 45篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 21篇 |
1991年 | 21篇 |
1990年 | 30篇 |
1989年 | 23篇 |
1988年 | 16篇 |
1987年 | 14篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1979年 | 6篇 |
1977年 | 7篇 |
1975年 | 9篇 |
1974年 | 8篇 |
1972年 | 11篇 |
1971年 | 6篇 |
1969年 | 5篇 |
排序方式: 共有9923条查询结果,搜索用时 734 毫秒
991.
本文综述了近年来含吡啶鎓阳离子受体在阴离子识别领域的研究进展。系统阐述了以吡啶鎓阳离子为主要识别位点的环状、非环状和互锁型阴离子受体的设计合成以及在阴离子识别领域的应用。 相似文献
992.
Hui-ming Mao Bing-guan Chen Wei-min Wang Ping Zhuang Ming Zong Zeng-guang Xu 《Microchemical Journal》2011,97(2):291-295
We developed a method for simultaneously determining l-citrulline and l-arginine levels in serum and tissue samples using RP-HPLC with ultraviolet (UV) detection. The serum was deproteinized by trichloroacetic acid and heat; the tissue was homogenized by trichloroacetic acid and deproteinized as the same as serum. Phenyl-isothiocyanate (PITC) solution was used as derivatization reagent and a gradient elution was carried out. The linearity for l-arginine and l-citrulline ranged from 0 to at least 1000 μmol/L. R2 values were above 0.9999 for both. LODs for l-arginine and l-citrulline were 0.0462 μmol/L and 0.0195 μmol/L, respectively, while LOQs were 0.530 μmol/L and 0.417 μmol/L, respectively. Intra- and inter-day CVs were less than 3.5% and 7.5% in serum, respectively. The average recovery was from 85.5% to 116.5% in serum. Intra-assay CVs were 3.8% and 10.3%, and inter-assay CVs were 13.7% and 10.7% for l-arginine and l-citrulline respectively in tissue. The average recovery was from 92.8% to 113.5% in tissue. This is a reliable and convenient analytical method which is suitable for most clinical laboratories. 相似文献
993.
A sensitive fluorescent assay was developed for the detection of DNA specifically for Staphylococcus aureus. A sandwich-type detection system was fabricated by first immobilizing biotinylated capture DNA on avidin-modified wells of microplates, then hybridizing the capture DNA with one end of the target DNA, and then recognizing the other end of the target DNA with a signal probe labeled with CdTe nanocrystals and gold nanoparticles (Au-NPs) at the 3′- and 5′-terminus, respectively. Hybridization was monitored by measuring the fluorescent intensity of the assembly. The experimental results demonstrated that the incorporation of Au-NPs in this detection system can significantly enhance the sensitivity and the selectivity because a single Au-NP can be loaded with hundreds of signal DNA probe strands modified with CdTe nanocrystals. Under the optimized conditions, a detection limit of 10 fmol of DNA per L can be achieved and at least 50 colony forming units of Staph. aureus per mL of sample can be detected. The method was assessed by analyzing real samples, and it was validated by comparing it to an official standard method. Figure
A sensitive fluorescent assay was developed for the detection of DNA specifically for Staphylococcus aureus, using nanogold linked CdTe nanocrystals as signal amplification labels 相似文献
994.
研究了以泡沫镍载NiCo2O4纳米线阵列为阴极催化剂的Al-H2O2半燃料电池的性能. 以无模板生长法制备了泡沫镍载NiCo2O4纳米线阵列阴极材料, SEM测定结果表明, NiCo2O4纳米线几乎垂直于泡沫镍载体表面生长. 以电压和功率密度-电流密度曲线研究了H2O2浓度、电解液流速和温度对电池性能的影响, 结果显示, 以铝片为阳极, 0.6 mol/L H2O2为氧化剂的电池的开路电压约为1.40 V; 在室温和57 ℃下, 电流密度为98和172 mA/cm2时, 最大功率密度分别达到79和120 mW/cm2. 在5000 s的测试时间内, 0.70 V的恒电流密度和75 mA/cm2 的恒电压值几乎为一常数, 这表明以泡沫镍载NiCo2O4纳米线阵列为催化剂电还原H2O2具有很好的活性、稳定性和传质性能. 相似文献
995.
996.
997.
998.
Song K Wang H Wang H Wang L Qiao M Wu S Liu T 《Applied biochemistry and biotechnology》2011,165(3-4):776-784
The in vitro suitable action distance between umbilical cord blood-derived hematopoietic stem/progenitor cells and its feeder cell, human adipose-derived stem cells, during their co-culture, was investigated through a novel transwell co-culture protocol, in which the distance between the two culture chambers where each cell type is growing can be adjusted from 10 to 450 μm. The total cell number was determined with a hemacytometer, and the cell morphology was observed under an inverted microscope each day. After 7 days of co-culture, the fold-expansion, surface antigen expression of CD34(+) and CFU-GM assay of the hematopoietic mononuclear cells (MNCs) were analyzed. The results showed that there was an optimal communication distance at around 350 μm between both types of stem cells during their in vitro co-culture. By using this distance, the UCB-MNCs and CD34(+) cells were expanded by 15.1?±?0.2 and 5.0?±?0.1-fold, respectively. It can therefore be concluded that the optimal action distance between stem cells and their supportive cells, when cultured together for 7 days, is of around 350 μm. 相似文献
999.
Wang D Jiang H Zong X Xu Q Ma Y Li G Li C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(4):1275-1282
Monoclinic BiVO(4) crystals with preferentially exposed (040) facets were hydrothermally synthesized by using a trace amount of TiCl(3) as the directing agent; this function was confirmed by X-ray diffraction patterns (XRD) and high-resolution transmission electron microscopy (HRTEM). The effects of the directing agent TiCl(3) and the pH values applied during synthesis have been studied, and the optimized BiVO(4) sample with highly exposed (040) facet could be obtained by using 1.2 at.% of TiCl(3) as the directing agent at a pH value of 2. Some complementary techniques were also applied to exclude the effects of the structural and physical property changes, such as surface area and hydrophilicity. The photocatalytic activity of oxygen evolution on BiVO(4) is found to be proportionally correlated with the exposed surfaces of the (040) facet. It is assumed that the active sites with a BiV(4) structure on the exposed (040) facet is assigned to be responsible for the high activity of O(2) evolution. 相似文献
1000.
Hu W Liu J Luo Q Han Y Wu K Lv S Xiong S Wang F 《Rapid communications in mass spectrometry : RCM》2011,25(10):1429-1436
Hydrogen/deuterium exchange mass spectrometry (H/DX MS) has become a powerful tool to investigate protein-protein and protein-ligand interactions, but it is still challenging to localize the interaction regions/sites of ligands with pepsin-resistant proteins such as lipocalins. β-Lactoglobulin (BLG), a member of the lipocalin family, can bind a variety of small hydrophobic molecules including retinols, retinoic acids, and long linear fatty acids. However, whether the binding site of linear molecules locates in the external groove or internal cavity of BLG is controversial. In this study we used H/DX MS combined with docking simulation to localize the interaction sites of a tested ligand, sodium dodecyl sulfate (SDS), binding to BLG. H/DX MS results indicated that SDS can bind to both the external and the internal sites in BLG. However, neither of the sites is saturated with SDS, allowing a dynamic ligand exchange to occur between the sites at equilibrium state. Docking studies revealed that SDS forms H-bonds with Lys69 in the internal site and Lys138 and Lys141 in the external site in BLG via the sulfate group, and interacts with the hydrophobic residues valine, leucine, isoleucine and methionine within both of the sites via its hydrocarbon tail, stabilizing the BLG-SDS complex. 相似文献