全文获取类型
收费全文 | 67390篇 |
免费 | 2409篇 |
国内免费 | 1228篇 |
专业分类
化学 | 33135篇 |
晶体学 | 1099篇 |
力学 | 3909篇 |
综合类 | 73篇 |
数学 | 5765篇 |
物理学 | 27046篇 |
出版年
2022年 | 834篇 |
2021年 | 819篇 |
2020年 | 790篇 |
2019年 | 745篇 |
2018年 | 857篇 |
2017年 | 782篇 |
2016年 | 1310篇 |
2015年 | 1046篇 |
2014年 | 1436篇 |
2013年 | 3124篇 |
2012年 | 3055篇 |
2011年 | 3801篇 |
2010年 | 2646篇 |
2009年 | 2682篇 |
2008年 | 3335篇 |
2007年 | 3042篇 |
2006年 | 2947篇 |
2005年 | 2535篇 |
2004年 | 2275篇 |
2003年 | 1989篇 |
2002年 | 1872篇 |
2001年 | 3181篇 |
2000年 | 2320篇 |
1999年 | 1734篇 |
1998年 | 1252篇 |
1997年 | 1218篇 |
1996年 | 1047篇 |
1995年 | 917篇 |
1994年 | 823篇 |
1993年 | 735篇 |
1992年 | 1033篇 |
1991年 | 1013篇 |
1990年 | 922篇 |
1989年 | 808篇 |
1988年 | 773篇 |
1987年 | 827篇 |
1986年 | 688篇 |
1985年 | 904篇 |
1984年 | 845篇 |
1983年 | 582篇 |
1982年 | 577篇 |
1981年 | 536篇 |
1980年 | 503篇 |
1979年 | 622篇 |
1978年 | 650篇 |
1977年 | 660篇 |
1976年 | 575篇 |
1975年 | 482篇 |
1974年 | 521篇 |
1973年 | 450篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
I. Ihsanullah Y. Iqbal T. N. Khattak 《Journal of Radioanalytical and Nuclear Chemistry》2005,266(2):361-366
Summary Date samples were irradiated with different doses using a gamma-irradiator. Levels of moisture, protein, fibre and fats were
determined on monthly basis for 5 months. Generally, the moisture contents of control date samples packed in white polythene
decreased from 14.1±1.1 to 9.7±0.8% over a 5-month period while the irradiated samples were in the range of 10.4-11.2%, however,
no proper pattern of change was observed. After 5-month storage, the protein level of irradiated samples was reduced to 1.00-1.30%,
while the percent fibre levels were found to be in the range of 2.40-2.48. Similarly, the fat level decreases from 1.06±0.12
to 0.68±0.06 for control date sample while after 5-month the decrease in fat content was 0.45±0.04%, 0.44±0.04%, 0.44±0.05%,
0.42±0.05% and 0.40±0.04% for samples irradiated with 20, 50, 100, 200 and 300 krads, respectively. 相似文献
992.
With the development of transgenic crops, regulations to label the genetically modified organisms (GMOs) and their derived products have been issued in many countries. Polymerase chain reaction (PCR) methods are thought to be reliable and useful techniques for qualitative and quantitative detection of GMOs. These methods are generally needed to amplify the transgene and compare the amplified results with that of a corresponding reference gene to get the reliable results. Specific primers were developed for the rapeseed (Brassica napus), high-mobility-group protein I/Y(HMG-I/Y) single-copy gene and PCR cycling conditions suitable for the use of this sequence as an endogenous reference gene in both qualitative and quantitative PCR assays. Both methods were assayed with 15 different rapeseed varieties, and identical amplified products were obtained with all of them. No amplification was observed when templates were the DNA samples from the other species of Brassica genus or other species, such as broccoli, stem mustard, cauliflower, Chinese cabbage, cabbage, sprouts, Arabidopsis thaliana, carrot, tobacco, soybean, mung bean, tomato, pepper, eggplant, plum, wheat, maize, barley, rice, lupine, and sunflower. This system was specific for rapeseed. Limits of detection and quantitation in qualitative and quantitative PCR systems were about 13 pg DNA (about 10 haploid genomes) and about 1.3 pg DNA (about 1 haploid genome), respectively. To further test the feasibility of this HMG-I/Y gene as an endogenous reference gene, samples containing transgenic rapeseed GT73 with the inserted glyphosate oxidoreductase (GOX) gene were quantitated. These demonstrated that the endogenous PCR detection systems were applicable to the qualitative and quantitative detection of transgenic rapeseed. 相似文献
993.
994.
研究了溴酚蓝(BPB)·亚甲蓝(MB)等色染料离子对萃取光度测定银、汞和铜的方法。首先将被测金属离子形成[Me(phen)3]BPB的二氯乙烷萃取液,用KCN解析并反萃入水相,而后加入和溴酚蓝等色的亚甲蓝溶液继续萃取。由于等色染料离子对和Me(CN)nBPB三元络合物同时进入二氯乙烷中而提高了灵敏度、测定Ag、Hg和Cu的摩尔吸光系数均在105L·mol(-1)·cm(-1)以上。 相似文献
995.
H Toyoda T Ikei Y Demachi T Toida T Imanari 《Chemical & pharmaceutical bulletin》1992,40(10):2882-2884
The N-linked oligosaccharides from human urinary trypsin inhibitor were purified and their structures were investigated by compositional analysis, the two-dimensional sugar map method and 500 MHz 1H-NMR. The results revealed that they were composed of disialosyl, monosialosyl and asialosyl oligosaccharides, which have the common biantennary core structure; Gal1-4GlcNAc1-2Man1-3(Gal1-4GlcNAc1-2Man1-6)M an1-4GlcNAc1-4GlcNAc. 相似文献
996.
Antianoxic action and active constituents of evodiae fructus 总被引:1,自引:0,他引:1
J Yamahara T Yamada T Kitani Y Naitoh H Fujimura 《Chemical & pharmaceutical bulletin》1989,37(7):1820-1822
In order to develop new drugs from natural products, constituents of natural medicines were examined for their effectiveness in the KCN-induced anoxia model in mice. Methanol extract from a Chinese medicine, evodia (fruits of Evodia rutaecarpa Benth. or E. officinalis Dode), had a significant effect in the KCN-induced anoxia model in mice and therefore the active constituents were further examined. The results indicated that the antianoxic action of evodia was found in the fraction containing evodiamine. Further analysis of the active constituent indicated that evodiamine and rutaecarpine, indole-alkaloids found in large amounts in the Chinese medicine evodia, were mainly responsible for the antianoxic action. 相似文献
997.
Tolis EJ Teberekidis VI Raptopoulou CP Terzis A Sigalas MP Deligiannakis Y Kabanos TA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(12):2698-2710
Two series of octahedral oxovanadium(IV) compounds, containing charged or neutral axial ligands, with the tetradentate amidate molecules Hcapca and H2capcah of the general formulae trans-[V(IV)OX(capca)]0/+ (where X = Cl- (1.CH2Cl2), SCN- (2), N3 (3), CH3COO- (4), PhCOO- (5), imidazole (6. CH3NO2), and eta-nBuNH2 (7)) and cis-[V(VI)OX(Hcapcah)]0/+ (where X = Cl- (8.0.5CH2Cl2), SCN (9), N3 (10.2CH3OH), and imidazole (11)), were synthesized and characterized by X-ray crystallography (1.CH3OH,8.CHCl3, 9.2CH3CN, 10.CH3CN and cis-[VO(imidazole)(Hcapcah)+) and continuous-wave electron paramagnetic resonance (cw EPR) spectroscopy. In addition to the synthesis, crystallographic and EPR studies, the optical, infrared and magnetic properties (room temperature) of these compounds are reported. Ab initio calculations were also carried out on compound 8 CHCl3 and revealed that this isomer is more stable than the trans isomer, in good agreement with the experimental data. The cw EPR studies of compounds 1-5, that is, the V(IV)O2+ species containing monoanionic axial ligands, revealed a novel phenomenon of the reduction of their A, components by about 10% relative to the N4 reference compounds ([V(IV)O-(imidazole)4]2+ and [V(IV)O(2,2-bipyridine)2]2+). In marked contrast, such a reduction is not observed in compounds 6. CH3NO2-11, which contain neutral axial ligands. Based on the spin-Hamiltonian formalism a theoretical explanation is put forward according to which the observed reduction of Az is due to a reduction of the electron - nuclear dipolar coupling (P). The present findings bear strong relevance to cw EPR studies of oxovanadium(IV) in vanadoproteins, V(IV)O2+-substituted proteins, and in V(IV)O2+ model compounds, since the hyperfine coupling constant, Az, has been extensively used as a benchmark for identification of equatorial-donor-atom sets in oxovanadium(IV) complexes. 相似文献
998.
Vlatakis G. Skarpelis G. Stratidaki I. Bouriotis V. Clonis Y. D. 《Applied biochemistry and biotechnology》1987,15(3):201-212
The resolution of restriction endonucleases from the same microorganism is conventionally achieved by lengthy fractionation
protocols. We now report effective single-step procedures that exploit dye-ligand chromatography for the resolution and purification
of restriction enzymes. After suitable initial screening, we demonstrated that resolution of two restriction activites can
be achieved in one chromatographic step, and further purification can subsequently be effected using selected dye-adsorbents.
Accordingly, we resolved in one step, Hpa I from Hpa II, Hind II from Hind III, and Sac I from Sac II. Furthermore, a three-step
Chromatographic procedure has been developed to purify EcoRV suitable for commercial exploitation, as judged by the “overdigestion”
and “cut-ligate-recut” quality control tests. 相似文献
999.
1000.