全文获取类型
收费全文 | 7811篇 |
免费 | 1568篇 |
国内免费 | 1114篇 |
专业分类
化学 | 5738篇 |
晶体学 | 176篇 |
力学 | 531篇 |
综合类 | 135篇 |
数学 | 813篇 |
物理学 | 3100篇 |
出版年
2024年 | 12篇 |
2023年 | 177篇 |
2022年 | 250篇 |
2021年 | 322篇 |
2020年 | 461篇 |
2019年 | 399篇 |
2018年 | 329篇 |
2017年 | 326篇 |
2016年 | 492篇 |
2015年 | 526篇 |
2014年 | 573篇 |
2013年 | 740篇 |
2012年 | 782篇 |
2011年 | 784篇 |
2010年 | 558篇 |
2009年 | 477篇 |
2008年 | 491篇 |
2007年 | 434篇 |
2006年 | 358篇 |
2005年 | 338篇 |
2004年 | 268篇 |
2003年 | 212篇 |
2002年 | 215篇 |
2001年 | 180篇 |
2000年 | 122篇 |
1999年 | 95篇 |
1998年 | 63篇 |
1997年 | 46篇 |
1996年 | 44篇 |
1995年 | 23篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 31篇 |
1991年 | 24篇 |
1990年 | 29篇 |
1989年 | 18篇 |
1988年 | 20篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 15篇 |
1983年 | 21篇 |
1982年 | 13篇 |
1981年 | 19篇 |
1980年 | 16篇 |
1979年 | 17篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1974年 | 9篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 745 毫秒
81.
82.
83.
Chao Feng Zhang Li Fan Pin Yang 《中国化学快报》2007,18(1):97-98
Zinc may play a role as a co-factor in the pathogenesis of Alzheimer's disease(AD)through influencing the conformation and neurotoxicity of amyloidβ-protein(Aβ).Using the fluorescamine assay,we show for the first time that Zn~(2 )induced Aβ(10-21) aggregate in a concentration-dependent manner.These results indicate that Aβ(10-21)can be used as an in vitro model in Zn~(2 )- induced Aβaggregation and that the region 10-21 to be the minimal fragment of zinc-binding domain of full length Aβ(1-42). 相似文献
84.
Macroporous chitosan membranes were prepared by using NaCl particles porogen and genipin as cross-linking agent. For characterization and sorption behavior comparison, other genipin cross-linked chitosan membranes were prepared by either freeze drying or by using silica particles as porogen. The mean pore diameter, the porosity, the crystallinity index (CrI) as well as the effect of the drying procedures of these chitosan membranes were examined. NaCl reduced the CrI of the chitosan membrane. The oven drying (OD) procedure decreased the mean pore diameter, the porosity, and increased the CrI of the chitosan membranes when compared with the vacuum drying (VD) procedure. The heat treatment of chitosan membrane in aqueous NaOH to attract silica porogen increased the CrI of the membrane. Under the same conditions, the membranes prepared with NaCl had better sorption performance on RR 189 and Cu2+ than other membranes. The maximum sorption capacity (qe) reached 1836.17 mg RR 189/g chitosan and 151.98 mg Cu2+/g chitosan. The pore diameter (dpore) of the membranes was much larger than the diameter of the adsorbate molecules (dadsorbate), such that the ratio of dpore/dadsorbate had little influence on qe. The porosity and the amorphous extent of the membranes were almost the same on qe. When using tyrosinase catalyzing, the hydrocaffeic acid (HCA) grafted on the NaCl treated chitosan membrane was almost 10 times more than on chitosan beads. The chitosan membrane prepared with NaCl can be used as a good adsorbent with high loading capacity for implanting molecules (such as ligands, enzymes, etc.) on. 相似文献
85.
86.
Four para-dialkylaminophenyl (PDAAP1-PDAAP4) bearing carboxyl groups were studied for application to the dye-sensitized solar cells (DSC). It was found the short spacer CH2 between carboxyl and dialkylaminophenyl chromophore in PDAAP3 and PDAAP4 led to highly efficient monochromatic incident photon-to-current conversion efficiencies (IPCE), however the long alkyl group C4H9 attached on aniline moieties in PDAAP2 and PDAAP4 favored improvement of open-circuit photovoltage. Thus, the solar cell sensitized by PDAAP4, having both short carboxyl groups CH2COOH and long alkyl groups C4H9, exhibited the IPCE maximum of 73% at 670 nm and overall energy conversion efficiency η of 3.06%, representing the highest IPCE and η values so far in dialkylaminophenyl-based organic dye-sensitized semiconductor solar cells. Taking advantage of the highly efficient sensitizing ability of PDAAP4 in far-red region, the data of IPCE above 630 nm of the solar cells were improved greatly by cosensitization with both N3 and PDAAP4. The influences of the TiO2 film thickness and the concentration of 4-tert-butylpyridine (TBP) in electrolyte were also investigated. 相似文献
87.
Sesquiterpene Lactone Glycosides from Carpesium macrocephalum 总被引:1,自引:0,他引:1
Two new sesquiterpene lactone glycosides were isolated from the seeds of Carpesium meacrocephalum. Their structures were elucidated as 2α-O-β-D-glucopyranosy-5α,11αH-eudesma-4(15)-en-12,8β-olide and 2α-O-β-D-glucopyranosy-5αH-eudesma-4(15),11(13)-dien-12,8β-olide by spectral methods (HRMS,1D and 2D NMR). 相似文献
88.
采用固相反应与水热法相结合制得了钽酸盐光催化剂. 对其在紫外光区降解刚果红溶液的行为进行了研究. 实验结果表明, 其具有光催化活性. 相似文献
89.
A capillary electrophoresis (CE) method was developed for the separation of heparin oligosaccharides compatible to study the interactions between the oligosaccharides and granulocyte-colony stimulating factor (G-CSF). Unfractionated heparin was eliminitively degraded to heparin oligosaccharides by an endolytic heparinase. The degraded smaller oligosaccharides (M(r) < 1000) were baseline-separated by CE under a 50 mM phosphate buffer (pH 9.0) in 10 min. Standard heparin disaccharides and larger oligosaccharides (1000 < M(r) < 8000) were all separated under optimized separation conditions. Compared with standard heparin disaccharides, smaller oligosaccharides contained one nonsulfated, two monosulfated, and two disulfated disaccharides, but trisulfated disaccharides were not found. The smaller oligosaccharides were also identified and molecular mass was deduced by electrospray ionization-mass spectrometry (ESI-MS). Furthermore, interactions between G-CSF and the oligosaccharides were studied by using capillary zone electrophoresis (CZE) under the above separation conditions. It was found that larger oligosaccharides could interact with G-CSF while smaller oligosaccharides were not observed to bind to G-CSF under the experimental conditions. In conclusion, the purified heparinase could selectively degrade heparin into oligosaccharides and the interaction between G-CSF and heparin was correlated with the chain length of heparin. 相似文献
90.
建立了气相 质谱联用 (GC/MS)测定苯乙烯中阻聚剂对叔丁基邻苯二酚含量的方法。苯乙烯样品直接进样 ,通过毛细管柱 (HP 1,30m× 0 32mmi.d .× 0 2 5 μm)分离 ,由电子轰击 (EI)源于选择离子监测 (SIM)模式下进行检测。结果表明 ,对叔丁基邻苯二酚含量在 5mg/kg~ 5 0mg/kg时线性关系良好 (r2 =0 9987) ,回收率高 ;与美国材料测试标准ASTMD4 5 90中的分光光度测量法比较具有操作简捷、准确度高的特点。 相似文献