全文获取类型
收费全文 | 2386篇 |
免费 | 44篇 |
国内免费 | 4篇 |
专业分类
化学 | 1884篇 |
晶体学 | 31篇 |
力学 | 43篇 |
数学 | 88篇 |
物理学 | 388篇 |
出版年
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 16篇 |
2019年 | 23篇 |
2018年 | 18篇 |
2017年 | 11篇 |
2016年 | 28篇 |
2015年 | 19篇 |
2014年 | 42篇 |
2013年 | 91篇 |
2012年 | 110篇 |
2011年 | 113篇 |
2010年 | 63篇 |
2009年 | 76篇 |
2008年 | 121篇 |
2007年 | 113篇 |
2006年 | 133篇 |
2005年 | 124篇 |
2004年 | 128篇 |
2003年 | 111篇 |
2002年 | 104篇 |
2001年 | 61篇 |
2000年 | 70篇 |
1999年 | 44篇 |
1998年 | 32篇 |
1997年 | 47篇 |
1996年 | 34篇 |
1995年 | 28篇 |
1994年 | 25篇 |
1993年 | 36篇 |
1992年 | 47篇 |
1991年 | 29篇 |
1990年 | 22篇 |
1989年 | 22篇 |
1988年 | 34篇 |
1987年 | 33篇 |
1986年 | 33篇 |
1985年 | 53篇 |
1984年 | 38篇 |
1983年 | 19篇 |
1982年 | 35篇 |
1981年 | 24篇 |
1980年 | 24篇 |
1979年 | 31篇 |
1978年 | 21篇 |
1977年 | 15篇 |
1976年 | 12篇 |
1975年 | 11篇 |
1974年 | 14篇 |
1973年 | 12篇 |
排序方式: 共有2434条查询结果,搜索用时 15 毫秒
51.
Summary The molecular-shape recognition of polycyclic aromatic hydrocarbons has been studied on various stationary phases in reversed-phase high-performance liquid chromatography. The examined stationary phases were phenyl-, diphenyl-, triphenyl- and benzyl-bonded silicas. The results of regression analysis inidcated that triphenylsilica is the best packing material to recognize the difference in the molecular-shape of structural isomers. This fact was confirmed by the separation of 4-ring isomers. 相似文献
52.
Zeolite T membranes were synthesized on tubular porous mullite tubes by hydrothermal synthesis. The membranes selectively permeated carbon dioxide from CO2/CH4 and CO2/N2 mixtures with high separation performances, which were due to combined effects of molecular sieving and competitive adsorption. 相似文献
53.
54.
A microanalytical method for the determination of traces of natural brassinosteroids as their dansylaminophenylboronates by liquid chromatography with fluorimetric detection is described. The boronates are easily prepared by the reaction of brassinosteroids with dansylaminophenylboronic acid (DABA), which was newly synthesized as a precolumn fluorogenic reagent for brassinosteroids. The potential of the method is demonstrated by the separation of a standard brassinosteroid mixture and the analysis of a biologically active fraction sample obtained from an extract of Zea mays L. pollen. The detection limit of the DABA derivative was found to be 25 pg for brassinolide, which is superior to that of the phenanthreneboronate derivative. 相似文献
55.
According to the traditional usage of the plant for antiinflammation and analgesia, Leucas aspera was tested for its prostaglandin (PG) inhibitory and antioxidant activities. The extract showed both activities, i.e., inhibition at 3 x 10(-4) g/ml against PGE(1)- and PGE(2)-induced contractions in guinea pig ileum and a 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging effect. The separation guided by the activities in these dual assay methods provided eight lignans and four flavonoids, LA-1- -12, among which LA-1- -7 and LA-10- -12 were identified as nectandrin B, meso-dihydroguaiaretic acid, macelignan, acacetin, apigenin 7-O-[6"-O-(p-coumaroyl)-beta-D-glucoside], chrysoeriol, apigenin, erythro-2-(4-allyl-2, 6-dimethoxyphenoxy)-1-(4-hydroxy-3-methoxyphenyl)propan-1-ol, myristargenol B, and machilin C, respectively. LA-8 was determined to be (-)-chicanine, the new antipode of the (+) compound, by spectroscopic methods including CD and ORD. Chiral-HPLC analysis of LA-9 showed that it was a mixture of two enantiomers, (7R, 8R)- and (7S, 8S)-licarin A. All of these components were first isolated from L. aspera. PG inhibition was observed in LA-1, LA-2, and LA-5, and antioxidant activity in LA-1- -3 and LA-8- -12. 相似文献
56.
K. Okamoto 《Accreditation and quality assurance》1997,2(3):157-158
The Japan Society for Analytical Chemistry has recently issued a river water-certified reference material (CRM) for use in
the ultratrace analysis of elements in fresh water. The river water CRM consists of a set of two (natural and spiked) 500-ml
samples. The natural water is certified for Pb, Cr, As, Cu, Fe, Mn, Zn, B and Al at their sub-μg/l levels, while the spiked
water is intended for use in the regulatory analysis of tap water and fresh water.
Key words River water · Trace element analysis · Regulatory analysis · Reference materials 相似文献
57.
The purpose of this study is to propose the application of a compression test to the determination of an optimal formulation for extrusion granulation. The electric current during extrusion was measured and the characteristics of the wet kneaded mass in the compression test were analyzed under various operating conditions, with different types of extruders and several formulations of kneaded mass. It was found that addition of a binder (HPC-L) to pharmaceutical powders lowered the load of a high-compressing type extruder, since the binder reduced the friction among the wet mass during extrusion. Also, the support stress was found to be proportional to the compression pressure without a binder, although an inflection point appeared on the support stress curve when a binder was present. This inflection point suggested large water retention of the wet kneaded mass, at which the medium of pressure was changed from a discontinuous solid powder to a continuous liquid, and large water retention contributed to the low friction of the wet mass. The friction of the wet kneaded mass and the aptitude of the formulation for extrusion were understood by using the compression test. The compression test is a very useful procedure at the first stage of a formulation study. 相似文献
58.
Yoshihisa Kurasawa Tomoyoshi Hosaka Yuko Matsumoto Aiko Ishikura Kazue Ikeda Atsushi Takada Ho Sik Kim Yoshihisa Okamoto 《Journal of heterocyclic chemistry》1994,31(6):1697-1700
The reaction of 7-chlorotetrazolo[1,5-α]quinoxaline 5-oxide 6a with acetic anhydride gave 7-chloro-5-(7-chlorotetrazolo[1,5-α]quinoxalin-4-yl)-4,5-dihydro-4-oxotetrazolo[1,5-α]quinoxaline 7a , while the reaction of 7-chloro-1,2,4-triazolo[4,3-α]quinoxaline 5-oxide 6b with acetic anhydride afforded 7-chloro-5-(7-chloro-1,2,4-triazolo[4,3-α]quinoxalin-4-yl)-4,5-dihydro-4-oxo-1,2,4-triazolo[4,3-α]quinoxaline 7b and 7-chloro-4,5-dihydro-4-oxo-1,2,4-triazolo[4,3-α]quinoxaline 8b . The reaction of compound 6a or 6b with acetic anhydride/acetic acid provided 7-chloro-4,5-dihydro-4-oxo-tetrazolo[1,5-α]quinoxaline 8a or compound 8b , respectively. 相似文献
59.
Iida K Hayakawa Y Okamoto H Danjo K Luenbergerb H 《Chemical & pharmaceutical bulletin》2003,51(12):1455-1457
The effect of the surface covering of lactose carrier particles on the dry powder inhalation properties of salbutamol sulfate was investigated. Lactose carrier surfaces were covered with sucrose tristearate (J-1803F) by a high-speed elliptical-rotor-type powder mixer (Theta-Composer). In the present study, drug/carrier powder mixtures were prepared consisting of micronized salbutamol sulfate and lactose carriers with various particle surface conditions prepared by surface covering. These powder mixtures were aerosolized by a Jethaler), and the in vitro inhalation properties of salbutamol sulfate were evaluated by a twin impinger. Compared with the powder mixed with uncovered lactose carrier, the in vitro inhalation properties of the powder mixture prepared using the surface covering lactose carrier were significantly different, showing that the in vitro inhalation properties of salbutamol sulfate were improved. In vitro inhalation properties increased with the percentage of J-1803F added. Using this surface covering system would thus be valuable for increasing the inhalation properties of dry powder inhalation with lactose carrier particles. 相似文献
60.
Influence of storage humidity on the in vitro inhalation properties of salbutamol sulfate dry powder with surface covered lactose carrier 总被引:1,自引:0,他引:1
Iida K Hayakawa Y Okamoto H Danjo K Luenberger H 《Chemical & pharmaceutical bulletin》2004,52(4):444-446
The influence of storage humidity on the in vitro inhalation properties of salbutamol sulfate dry powder with surface covered lactose carrier was investigated. In the present study, drug/carrier powder mixtures were prepared consisting of micronized salbutamol sulfate and lactose carriers with different particle surface conditions prepared by surface covering. Lactose carrier surfaces were covered with vegetable magnesium stearate (Mg-St-V) by a high-speed elliptical-rotor-type powder mixer (Theta-Composer). These powder mixtures were aerosolized by a Jethaler), and the in vitro inhalation properties of salbutamol sulfate were evaluated by a twin impinger. Compared with the powder mixed with uncovered lactose carrier, the in vitro inhalation properties of the powder mixture prepared using the surface covered lactose carrier were little decreased with increased in relative humidity (RH), showing that the in vitro inhalation properties of salbutamol sulfate were improved at high RH. Using this surface covering technique would thus be valuable for storage humidity of dry powder inhalation (DPI) with lactose carrier particles. 相似文献